AT2401 Engine and Vehicle Management System.pdf

Course : AU 2401 – Engine & Vehicle Management Systems

Faculty : A.J.D. Nanthakumar

UNIT – I

FUNDAMENTALS OF AUTOMOTIVE ELECTRONICS

Microprocessor architecture, open and closed loop control strategies, PID control, Look up tables,

introduction to modern control strategies like Fuzzy logic and adaptive control. Parameters to be

controlled in SI and CI engines and in the other parts of the automobile.

Microprocessor architecture – self study (already studied in IV sem)

Control system:

Control systems are systems that are used to regulate the operation of other systems. For this

discussion, the system being controlled is known as the system plant. The controlling system is called an

electronic controller. A control system should

1. Perform its function accurately.

2. Respond quickly

3. Be stable

4. Respond only to valid inputs (noise immunity)

Open-Loop Control

In the open-loop control system of the following figure, the command input is sent to the

electronic controller, which performs a control operation on the input to generate an intermediate

electrical signal (denoted i in Figure 2.22).This electrical signal is the input to the actuator which

generates a control input (denoted u in Figure) to the plant that, in turn, regulates the plant output to the

desired value. This type of control is called open-loop control because the output of the system is never

compared with the command input to see if they match. The operation of the plant is directly regulated

by the actuator (which might simply be an electric motor). The system output may also be affected by

external disturbances that are not an inherent part of the plant but are the result of the operating

environment. One of the principal drawbacks to the open-loop controller is its inability to compensate

for changes that might occur in the controller or the plant or for any disturbances.

Closed-Loop Control

It is the potential for change in an open-loop system that led to feedback, or closed-loop, control. In a

closed-loop control system a measurement of the output variable being controlled is obtained via a

sensor and fed back to the controller, as illustrated in the following figure.The measured value of the

controlled variable is compared with the desired value for that variable based on the reference input. An

error signal based on the difference between desired and actual values of the output signal is created, and

the controller generates an actuator signal u that tends to reduce the error to zero. In addition to reducing



this error to zero, feedback has other potential benefits in a control system. It can affect control system

performance by improving system stability and suppressing the effects of disturbances in the system.

Later chapters will include numerous examples of closed-loop control, such as idle speed control.

PID CONTROLLER:

A proportional–integral–derivative controller (PID controller) is a generic control loop feedback

mechanism (controller) widely used in industrial control systems – a PID is the most commonly used

feedback controller. A PID controller calculates an "error" value as the difference between a measured

process variable and a desired setpoint. The controller attempts to minimize the error by adjusting the

process control inputs.

The PID controller calculation (algorithm) involves three separate constant parameters, and is

accordingly sometimes called three-term control: the proportional, the integral and derivative values,

denoted P, I, and D. Heuristically, these values can be interpreted in terms of time: P depends on the

present error, I on the accumulation of past errors, and D is a prediction of future errors, based on

current rate of change. The weighted sum of these three actions is used to adjust the process via a control

element such as the position of a control valve or the power supply of a heating element.



In the absence of knowledge of the underlying process, a PID controller is the best controller. By tuning

the three parameters in the PID controller algorithm, the controller can provide control action designed

for specific process requirements. The response of the controller can be described in terms of the

responsiveness of the controller to an error, the degree to which the controller overshoots the setpoint

and the degree of system oscillation. Note that the use of the PID algorithm for control does not

guarantee optimal control of the system or system stability.

Some applications may require using only one or two actions to provide the appropriate system control.

This is achieved by setting the other parameters to zero. A PID controller will be called a PI, PD, P or I

controller in the absence of the respective control actions. PI controllers are fairly common, since

derivative action is sensitive to measurement noise, whereas the absence of an integral term may prevent

the system from reaching its target value due to the control action.

PID controller theory

The PID control scheme is named after its three correcting terms, whose sum constitutes the

manipulated variable (MV). The proportional, integral, and derivative terms are summed to calculate

the output of the PID controller. Defining u(t) as the controller output, the final form of the PID

algorithm is:

where

Kp: Proportional gain, a tuning parameter

Ki: Integral gain, a tuning parameter

Kd: Derivative gain, a tuning parameter

e: Error = SP − PV

t: Time or instantaneous time (the present)

Proportional term:

The proportional term makes a change to the output that is proportional to the current error value. The

proportional response can be adjusted by multiplying the error by a constant Kp, called the proportional

gain.

The proportional term is given by:

A high proportional gain results in a large change in the output for a given change in the error. If the

proportional gain is too high, the system can become unstable (see the section on loop tuning). In

contrast, a small gain results in a small output response to a large input error, and a less responsive

or less sensitive controller. If the proportional gain is too low, the control action may be too small

when responding to system disturbances. Tuning theory and industrial practice indicate that the

proportional term should contribute the bulk of the output change.



Droop

A pure proportional controller will not always settle at its target value, but may retain a steady-state

error. Specifically, drift in the absence of control, such as cooling of a furnace towards room

temperature, biases a pure proportional controller. If the drift is downwards, as in cooling, then the

bias will be below the set point, hence the term "droop".

Droop is proportional to process gain and inversely proportional to proportional gain. Specifically

the steady-state error is given by:

e = G / Kp

Droop is an inherent defect of purely proportional control. Droop may be mitigated by adding a

compensating bias term (setting the setpoint above the true desired value), or corrected by

adding an integral term.

Graph for proportional term

Integral term:

The contribution from the integral term is proportional to both the magnitude of the error and the

duration of the error. The integral in a PID controller is the sum of the instantaneous error over time and

gives the accumulated offset that should have been corrected previously. The accumulated error is then

multiplied by the integral gain (Ki) and added to the controller output.

The integral term is given by:

The integral term accelerates the movement of the process towards setpoint and eliminates the

residual steady-state error that occurs with a pure proportional controller. However, since the

integral term responds to accumulated errors from the past, it can cause the present value to

overshoot the setpoint value.



Graph for Integral term Graph for derivative term

Derivative term:

The derivative of the process error is calculated by determining the slope of the error over time and

multiplying this rate of change by the derivative gain Kd. The magnitude of the contribution of the

derivative term to the overall control action is termed the derivative gain, Kd.

The derivative term is given by:

The derivative term slows the rate of change of the controller output. Derivative control is used to

reduce the magnitude of the overshoot produced by the integral component and improve the

combined controller-process stability. However, the derivative term slows the transient response of

the controller. Also, differentiation of a signal amplifies noise and thus this term in the controller is

highly sensitive to noise in the error term, and can cause a process to become unstable if the noise

and the derivative gain are sufficiently large. Hence an approximation to a differentiator with a

limited bandwidth is more commonly used.

Lookup table: A lookup table is a data structure, usually an array or associative array, often used to replace a

runtime computation with a simpler array indexing operation. The savings in terms of processing time

can be significant, since retrieving a value from memory is often faster than undergoing an 'expensive'

computation or input/output operation.

The concept of table lookup is illustrated in Figure 4.25, in which a pair of variables, Vo and X,

are related by the graph depicted therein. Also shown in Figure 4.25 is a table listing certain specific

values for the relationship. The functional relationship between Vo and X might, for example, be the

output voltage of a nonlinear sensor Vo for measuring a quantity X. If the value for Vo is known, then

the corresponding value for X can theoretically be found using the graph or the tabulated values. In the

latter case, the nearest two tabulated values for Vo are located, and the corresponding values for X are



read from the table. Denoting V1and V2as the nearest values and X1, X2as the corresponding tabulated

values, the value for X corresponding to Vo is found by linear interpolation

A microcomputer can perform the same operation using tabulated values for the relationship between

Vo and X(i.e., Vo(X) in correct mathematical notation). This method is illustrated using a specific

example of the measurement of a variable X using a sensor output voltage, and variable X is assumed to

be that which is illustrated in Figure 4.24. A microcomputer is to obtain the value for X using a table

lookup operation. The portion of the microcomputer that is involved in the table lookup process is

illustrated in Figure 4.26. The relationship Vo(X) is stored in ROM for representative points along the

curve. These data are stored using Vo values as addresses, and corresponding values of X as data. For

example, consider a point (V1, X1). The data X1are stored at memory location V1in binary format. The

operation of the table lookup is as follows. The sensor S has output voltage Vo. The computer reads the

values of Vo(using an ADC to convert to digital format) through the I/O device. Then the MPU under

program control (program ROM) calculates the addresses for the two nearest values to Vo, which are

V1and V2(V1<Vo<V2). The computer, under program control, reads values X1and X2and then

calculates X using the preceding formula.

Fuzzy logic:

Humans have a remarkable capability to reason and make decisions in an environment of

uncertainty, imprecision, incompleteness of information, and partiality of knowledge, truth and class

membership. The principal objective of fuzzy logic is formalization/mechanization of this capability

Definition of fuzzy

Fuzzy – ―not clear, distinct, or precise; blurred‖

Definition of fuzzy logic

A form of knowledge representation suitable for notions that cannot be defined precisely,

but which depend upon their contexts.



Fuzzy Logic provides a more efficient and resourceful way to solve Control Systems.

Some Examples

Temperature Controller

Anti – Lock Break System ( ABS )

Anti Lock Breaking System:

Nonlinear and dynamic in nature

Inputs for Intel Fuzzy ABS are derived from

Brake

4 WD

Feedback

Wheel speed

Ignition

Outputs

Pulsewidth

Error lamp

The point of an ABS is to monitor the braking system on the vehicle and release the brakes just before

the wheels lock. A computer is involved in determining when the best time to do this is. Two main

factors that go into determining this are the speed of the car when the brakes are applied, and how fast

the brakes are depressed. Usually, the times you want the ABS to really work are when you're driving

fast and slam on the brakes. There is, of course, a margin for error. It is the job of the ABS to be "smart"

enough to never allow the error go past the point when the wheels will lock.

ADAPTIVE CONTROL: Adaptive control is the control method used by a controller which must adapt to a controlled

system with parameters which vary, or are initially uncertain. For example, as an aircraft flies, its mass

will slowly decrease as a result of fuel consumption; a control law is needed that adapts itself to such

changing conditions. Adaptive control is different from robust control in that it does not need a priori

information about the bounds on these uncertain or time-varying parameters; robust control guarantees

that if the changes are within given bounds the control law need not be changed, while adaptive control

is concerned with control law changes themselves.



Adaptive Cruise control:

Operation

The basic function of Adaptive Cruise Control relies on the conventional cruise-control system

(vehicle-speed controller), which maintains a desired speed specified by the driver. In addition, ACC

can adapt vehicle speed to changing traffic conditions by means of automatic acceleration, deceleration

or braking. This system thus maintains the vehicle's distance to the vehicle driving in front as a function

of road speed.

Distance sensor

The most important component in an ACC system is a sensor which measures the distance, the relative

speed and the relative position of the preceding vehicles. Maximum performance is achieved – even in

poor weather conditions – with a radar sensor.

The radar sensor (see Sensor types) operates at a frequency of ... 77 GHz which was specially allocated

for ACC. Three beams are emitted simultaneously for measurement purposes. The beams reflected by

the preceding vehicles are analyzed regarding their propagation time, Doppler shift and amplitude ratio,

and from these factors the distance, relative speed, and relative position are calculated (for details, refer

Sensor types).

Course setting

To ensure reliable ACC operation, no matter what the situation – e.g. also on curves/bends – it is

essential that the preceding vehicles are allocated to the correct lane(s). For this purpose, the information

from the ESP sensor system (yaw rate, steering-wheel angle, wheel speeds and lateral acceleration) is

evaluated with regard to the ACC-equipped vehicle's actual curve status. Further information on the

traffic flow is obtained from the radar signals.

Video imaging and navigation systems are also being considered for future assistance in defining the

courses taken by the vehicles.



Engine intervention

Speed control requires an electronic engine-power control system (ETC or EDC). Such a system enables

the vehicle to be accelerated to the desired speed or, if an obstacle appears, to be decelerated by means

of automatic throttle closing.

Active brake intervention

Experience has shown that deceleration by means of throttle closing is not sufficient for ACC operation.

Only the inclusion of brake intervention makes it possible for longer follow-on control operations with

ACC without the need for frequent driver interventions. ESP provides the possibility of braking without

driver intervention.

ACC permits only "soft" brake interventions. Emergency braking due to the sudden appearance of

obstacles (e.g. the slow-moving vehicle in front suddenly changing its lane) is therefore not possible.

Setting options

The driver inputs the desired speed and the desired time gap; values of 1 ... 2 s are offered for the latter.

Display elements

The driver must be provided with at least the following information:

indication of the desired speed,

indication of the switch-on status,

indication of the desired time gap selected by the driver,

indication of the follow-on mode, which informs the driver as to whether the system is

controlling the distance to a detected target object or not.

Aim of ACC

The aim of ACC is to relieve the driver of the stress associated with "mindless" driving tasks

such as maintaining speeds and driving behind other vehicles in heavy traffic. This system helps

to improve road safety as well as driver comfort.

System limits

Even with this form of driver support, the driver remains fully responsible for controlling the

vehicle. He/she continues to remain responsible for complex decisions relating to straight-ahead

driving and control of the vehicle – and obviously for steering as well. The alignment of the

functions to emphasize the comfort aspect for the driver, means that a clear boundary has been

defined between the tasks which are the responsibility of ACC and those which are the

responsibility of the driver. Safety functions such as emergency braking and forced spacing are



thus not featured in this system. These functions, together with selecting the desired speed and

the desired time gap, are the sole responsibility of the driver.

ACC does not yet permit control operations in urban environments. This system can only be

activated at speeds in excess of 30 km/h.

Expanding functions for operation in urban areas would require considerably higher performance

on the part of the sensors responsible for monitoring the environment. Such performance cannot

be achieved by the 76.5 GHz radar alone.

Layout of Adaptive Cruise Control:

Parameters to be controlled in SI, CI engines: The parameters are:

1. Fuel metering control

2. Ignition control

3. Ignition timing

4. Exhaust gas recirculation control

1. Fuel metering control:

The following figure illustrates the variation in the performance variables of torque(T) and brake power

(BSFC) as well as engine emissions with variations in the air/fuel ratio with fixed spark timing and a

constant engine speed. In this figure the exhaust gases are represented in brake-specific form. This is a

standard way to characterize exhaust gases whose absolute emission levels are proportional to power.

The definitions for the brake-specific emission rates are



One specific air/fuel ratio is highly significant in electronic fuel control systems, namely, the

stoichiometric mixture. The stoichiometric (i.e., chemically correct) mixture corresponds to an air and

fuel combination such that if combustion were perfect all of the hydrogen and carbon in the fuel would

be converted by the burning process to H2O and CO2. For gasoline the stoichiometric mixture ratio is

14.7:1.Stoichiometry is sufficiently important that the fuel and air mixture is often represented by a ratio

called the equivalence ratio, which is given the specific designation l(i.e., the Greek letter lambda). The

equivalence ratio is defined as follows:

A relatively low air/fuel ratio, below 14.7 (corresponding to l<1), is called a rich mixture; an air/fuel

ratio above 14.7 (corresponding to l>1) is called a lean mixture. Emission control is strongly affected by

air/fuel ratio, or by l. Note from the following figure that torque (T) reaches a maximum in the air/fuel

ratio range of 12 to 14. The exact air/fuel ratio for which torque is maximum depends on the engine

configuration, engine speed, and ignition timing. Also note that the CO and unburned hydrocarbons tend

to decrease sharply with increasing air/fuel ratios, as one might expect because there is relatively more

oxygen available for combustion with lean mixtures than with rich mixtures. Unfortunately for the

purposes of controlling exhaust emissions, the NOx exhaust concentration increases with increasing

air/fuel ratios. That is, there is no air/fuel ratio that simultaneously minimizes all regulated exhaust

gases.

2. Spark timing: Spark advance is the time before top dead center (TDC) when the spark is initiated. It is usually

expressed in number of degrees of crankshaft rotation relative to TDC. Figure 5.9 reveals the

influence of spark timing on brake-specific exhaust emissions with constant speed and constant

air/fuel ratio. Note that both NOx and HC generally increase with increased advance of spark

timing. BSFC and torque are also strongly influenced by timing. The following figure shows that

maximum torque occurs at a particular advanced timing denoted MBT. Operation at or near

MBT is desirable since this spark timing tends to optimize performance. This optimal spark

timing varies with RPM. As will be explained, engine control strategy involves regulating fuel



delivery at a stoichiometric mixture and varying ignition timing for optimized performance.

However, there is yet another variable to be controlled, which assists the engine control system

in meeting exhaust gas emission regulations.

EGR Control: Up to this point in the discussion, only the traditional calibration parameters of the engine

(air/fuel ratio and spark timing) have been considered. However, by adding another control variable, the

undesirable exhaust gas emission of NOx can be significantly reduced while maintaining a relatively

high level of torque. This new control variable, exhaust gas recirculation (EGR), consists of

recirculating a precisely controlled amount of exhaust gas into the intake. Figure 5.5 shows that exhaust

gas recirculation is a major subsystem of the overall control system. Its influence on emissions is shown

in Figures 5.10 and 5.11 as a function of the percentage of exhaust gas in the intake. Figure 5.10 shows

the dramatic reduction in NOx emission when plotted against air/fuel ratio, and Figure 5.11 shows the

effect on performance variables as the percentage of EGR is increased. Note that the emission rate of

NOx is most strongly influenced by EGR and decreases as the percentage of EGR increases. The HC

emission rate increases with increasing EGR; however, for relatively low EGR percentages, the HC rate

changes only slightly. The mechanism by which EGR affects NOx production is related to the peak

combustion temperature. Roughly speaking, the NOx generation rate increases with increasing peak

combustion temperature if all other variables remain fixed. Increasing EGR tends to lower this

temperature; therefore, it tends to lower NOx generation.



UNIT- II SENSORS: Inductive, Hall Effect, hot wire, thermistor, piezo electric, piezoresistive, based sensors. Throttle position,

air mass flow, crank shaft position, cam position, engine and wheel speed, steering position, tire pressure, brake

pressure, steering torque, fuel level, crash, exhaust oxygen level (two step and linear lambda), knock, engine

temperature, manifold temperature and pressure sensors.

Inductive sensor:

An inductive sensor is an electronic proximity sensor, which detects metallic objects without

touching them. The sensor consists of an induction loop. Electric current generates a magnetic field,

which collapses generating a current that falls asymptotically toward zero from its initial level when the

input electricity ceases. The inductance of the loop changes according to the material inside it and since

metals are much more effective inductors than other materials the presence of metal increases the

current flowing through the loop. This change can be detected by sensing circuitry, which can signal to

some other device whenever metal is detected. Magnetic reluctance sensor is an inductive sensor.

Magnetic reluctance sensor: - To measure crankshaft angular position:

In electronic engine control it is often desirable to measure the angular position of the engine

relative to a specific point in the cycle. For such measurement it is normally necessary to measure the

position of the camshaft. The measurement of engine position via crankshaft and camshaft position

sensors (as well as its use in timing fuel delivery and ignition) is described in Chapter 7. Normally it is

sufficient to measure camshaft position at a fixed point. Such a sample of camshaft position is readily

achieved by a magnetic sensor similar to that described above for the crankshaft position measurement.

This sensor detects a reference point on the angular position of the camshaft that defines a beginning to a

complete engine cycle (e.g., power stroke for all cylinders). Once this reference point has been detected,

crankshaft position measurements (as described above) provide sufficient information for timing fuel

injection pulses and ignition.

Magnetic Reluctance position sensor: This sensor is of the magnetic reluctance type and is based on the concept of a magnetic circuit.

A magnetic circuit is a closed path through a magnetic material (e.g., iron, cobalt, nickel, or synthetic

magnetic material called ferrite). In the case of the sensor in the following figure, the magnetic circuit is

the closed path through the magnet material and across the gap between the pole pieces. The magnetic

field in a magnetic circuit is described by a pair of field quantities that can be compared to the voltage

and current of an ordinary electric circuit. One of these quantities is called the magnetic field intensity. It



exerts a force similar to the voltage of a battery. The response of the magnetic circuit to the magnetic

field intensity is described by the second quantity, which is called magnetic flux. A line of constant

magnetic flux is a closed path through the magnetic material. The magnetic flux is similar to the current

that flows when a resistor is connected across a battery to form a closed electrical circuit. As we shall

see, the voltage generated by the reluctance sensor is deter-mined by the strength of this magnetic flux.

The strength of the magnetic flux is, in turn, determined by the reluctance of the magnetic circuit.

Reluctance is to a magnetic circuit what resistance is to an electrical circuit. The path for the magnetic

flux of the reluctance sensor is illustrated in the figure below. The reluctance of a magnetic circuit is

inversely proportional to the magnetic permeability of the material along the path. The magnetic

permeability of steel is a few thousand times larger than air; therefore, the reluctance of steel is much

lower than air. Note that when one of the tabs of the steel disk is located between the pole pieces of the

magnet, a large part of the gap between the pole pieces is filled by the steel. Since the steel has a lower

reluctance than air, the ―flow‖ of magnetic flux increases to a relatively large value. On the other hand,

when a tab is not between the magnet pole pieces, the gap is filled by air only. This creates a high-

reluctance circuit for which the magnetic flux is relatively small. Thus, the magnitude of the magnetic

flux that ―flows‖ through the magnetic circuit depends on the position of the tab, which, in turn, depends

on the crankshaft angular position. The magnetic flux is least when none of the tabs is near the magnet

pole pieces. As a tab begins to pass through the gap, the magnetic flux increases. It reaches a maximum

when the tab is exactly between the pole pieces, and then decreases as the tab passes out of the pole

piece region. In most control systems, the position of maximum magnetic flux has a fixed relationship to

TDC for one of the cylinders.

The change in magnetic flux induces a voltage, Vo, in the sensing coil that is proportional to the

rate of change of the magnetic flux. Since the magnetic flux must be changing to induce a voltage in the

sensing coil, its output voltage is zero whenever the engine is not running, regardless of the position of

the crankshaft. This is a serious disadvantage for this type of sensor because the engine timing cannot be

set statically. As shown in Figure 6.8, the coil voltage, Vo, begins to increase from zero as a tab begins

to pass between the pole pieces, reaches a maximum, and then falls to zero when the tab is exactly

between the pole pieces). (Note that although the value of magnetic flux is maximum at this point, the

rate of change of magnetic flux is zero; therefore, the induced voltage in the sensing coil is zero.) Then it

increases with the opposite polarity, reaches a maximum, and falls to zero as the tab passes out of the

gap between the pole pieces. The coil voltage waveform shown in Figure occurs each time one of the

cylinders reaches TDC on its power stroke.



Hall Effect position sensor:

The Hall Effect:

The Hall element is a small, thin, flat slab of semiconductor material. When a current, I, is

passed through this slab by means of an external circuit as shown in Figure, a voltage is developed

across the slab perpendicular to the direction of current flow and perpendicular to the direction of

magnetic flux. This voltage is proportional to both the current and magnetic flux density that flows

through the slab. This effect—the generation of a voltage that is dependent on a magnetic field—is

called the Hall Effect. In Figure 6.11b, the current, I, is represented by electrons, e, which have negative

charge, flowing from left to right. The magnetic flux flows along the legs of the magnet as indicated and

is generally perpendicular to the face of the semiconductor Hall element. Whenever an electron moves

through a magnetic field, a force (called the Lorentz force) that is proportional to the electron velocity

and the strength of the magnetic flux is exerted on the electron. The direction of this force is

perpendicular to the direction in which the electron is moving. In Figure, the Lorentz force direction is

such that the electrons are deflected toward the lower sense electrode. Thus, this electrode is more

negative than the upper electrode and a voltage exists between the electrodes, having the polarity shown

in Figure 6.11b.As the strength of the magnetic flux density increases, more of the electrons are

deflected downward. If the current, I, is held constant, then the voltage, Vo, is proportional to the

strength of the magnetic flux density, which, in turn, is determined by the position of the tabs. This

voltage tends to be relatively weak so it is amplified, as shown in Figure

The voltage waveform Vo that is produced by the Hall element in the position sensor is illustrated in the

below Figure. Since Vo is proportional to the magnetic flux density, it reaches maximum when any of

the tabs is symmetrically located between the magnet pole pieces (corresponding to TDC of a cylinder).

If the disk is driven by the camshaft, then the disk must have as many tabs as the engine has cylinders.

Therefore, the disk shown would be for a 4-cylinder engine.



Temperature sensor – Engine temperature: Coolant Sensor

A typical coolant sensor, shown in Figure 6.16, consists of a thermistor mounted in a housing

that is designed to be inserted in the coolant stream. This housing is typically threaded with pipe threads

that seal the assembly against coolant leakage. A thermistor is made of semiconductor material whose

resistance varies inversely with temperature. For example, at -40°C a typical coolant sensor has a

resistance of 100,000 ohms. The resistance decreases to about 70,000 ohms at 130°C.The sensor is

typically connected in an electrical circuit like that shown in Figure 6.17, in which the coolant

temperature sensor resistance is denoted RT. This resistance is connected to a reference voltage through

a fixed resistance R. The sensor output voltage, VT, is given by the following equation: The sensor

output voltage varies inversely with temperature; that is, the output voltage decreases as the temperature

increases.

Throttle position (angle) sensor: - variable resistance type:

Another variable that must be measured for electronic engine control is the throttle plate angular

position. As explained in Chapter 1, the throttle plate is linked mechanically to the accelerator pedal.

When the driver depresses the accelerator pedal, this linkage causes the throttle plate angle to increase,

allowing more air to enter the engine and thereby increasing engine power. Measurement of the

instantaneous throttle angle is important for control purposes. Most throttle angle sensors are essentially

potentiometers. A potentiometer consists of a resistor with a movable contact, as illustrated in the below

figure. A section of resistance material is placed in an arc around the pivot axis for the movable contact.

One end of the resistor is connected to ground, the other to a fixed voltage V(e.g., 5 volts). The voltage

at the contact point of the movable contact is proportional to the angle (a) from the ground contact to the

movable contact. Thus, where v(a) is the voltage at the contact point, k is a constant, and a is the angle

of the contact point from the ground connection. This potentiometer can be used to measure any angular

rotation. In particular, it is well suited for measuring throttle angle. The only disadvantage to the

potentiometer for automotive applications is its analog output. For digital engine control, the voltage

v(a) must be converted to digital format using an analog-to-digital converter.



Knock sensor: Engine Knock sensor is based on Piezo electric effect. Piezoelectricity is the charge which

accumulates in certain solid materials (notably crystals, certain ceramics, and biological matter such as

bone, DNA and various proteins) in response to applied mechanical stress. The word piezoelectricity

means electricity resulting from pressure.

A knock sensor that is commonly used in engine control systems utilizes the piezoelectric

generator effect, i.e. the sensing element produces a small electric charge when it is compressed and

then relaxed. Materials such as quartz and some ceramics like PZT (a mixture of platinum, zirconium

and titanium) are effective in piezoelectric applications. In the application shown, the knock sensor is

located on the engine block. This is the best position to detect vibrations arising from combustion knock

in any of the four cylinders. Because combustion knock is most likely to occur close to TDC in any

cylinder, the control program held in the ECM memory enables the processor to use any knock signal

generated to alter the ignition timing by an amount that is sufficient to eliminate the knock. When knock

has ceased the ECM will advance the ignition, in steps, back to its normal setting. The mechanism by

which vibrations arising from knock are converted to electricity is illustrated in Figure below. The

sensor is accurately designed and the center bolt that pre-tensions the piezo electric crystal is accurately

torqued. The steel washer that makes up the seismic mass has very precise dimensions. When

combustion knock occurs, the resulting mechanical vibrations are transmitted by the seismic mass, to the

piezo electric crystal. The ‗squeezing up‘ and relaxing of the crystal in response to this action, produces

a small electrical signal that oscillates at the same frequency as the knock sensor element. The electrical

signal is conducted away from the crystal by wires that are secured to suitable points on the crystal.

The tuning of the sensor is critical because it must be able to distinguish between knock from

combustion and other knocks that may arise from the engine mechanism. This is achieved because

combustion knock produces vibrations that fall within a known range of frequencies.



Mass Air Flow sensor:

A mass air flow sensor is used to find out the mass of air entering a fuel-injected internal

combustion engine. The air mass information is necessary for the engine control unit (ECU) to balance

and deliver the correct fuel mass to the engine. Air changes its density as it expands and contracts with

temperature and pressure. In automotive applications, air density varies with the ambient temperature,

altitude and use of forced induction and this is an ideal application for a mass sensor. (See stoichiometry

and ideal gas law.)

There are two common types of mass airflow sensors in use on automotive engines. These are the vane

meter and the hot wire. Neither design employs technology that measures air mass directly. However,

with an additional sensor or two, the engine's air mass flow rate can be accurately determined. Both

approaches are used almost exclusively on electronic fuel injection (EFI) engines. Both sensor designs

output a 0.0–5.0 volt or a pulse-width modulation (PWM) signal that is proportional to the air mass flow

rate, and both sensors have an intake air temperature (IAT) sensor incorporated into their housings.

When a MAF is used in conjunction with an oxygen sensor, the engine's air/fuel ratio can be controlled

very accurately. The MAF sensor provides the open-loop controller predicted air flow information (the

measured air flow) to the ECU, and the oxygen sensor provides closed-loop feedback in order to make

minor corrections to the predicted air mass

Vane meter sensor (VAF sensor)

The VAF sensor measures the air flow into the engine with a spring-loaded air flap/door attached to a

variable resistor (potentiometer). The vane moves in proportion to the airflow, and a voltage is generated

in proportion to the distance the vane moves, or the movement of the vane directly regulates the amount

of fuel injected, as in the K-Jetronic system.

Many VAF sensors have an air-fuel adjustment screw, which opens or closes a small air passage on the

side of the VAF sensor. This screw controls the air-fuel mixture by letting a metered amount of air flow

past the air flap, thereby, leaning or richening the mixture. By turning the screw clockwise the mixture is

enriched and counterclockwise the mixture is leaned.

The vane moves because of the drag force of the air flow against it, it does not measure volume or mass

directly. The drag force depends on air density (air density in turn depends on air temperature), air

velocity and the shape of the vane, see drag equation. Some VAF sensors include an additional intake air

temperature sensor (IAT sensor) to allow the engines ECU to calculate the airs density, and the fuel

delivery accordingly.

The vane meter approach has some drawbacks:

it restricts airflow which limits engine output

its moving electrical or mechanical contacts can wear

finding a suitable mounting location within a confined engine compartment is problematic

the vane has to be oriented with respect to gravity.



Hot wire sensor (MAF)

A hot wire mass airflow sensor determines the mass of air flowing into the engine‘s air intake system.

The theory of operation of the hot wire mass airflow sensor is similar to that of the hot wire anemometer

(which determines air velocity). The General Motors division (GM) was the first car company to use the

hot wire sensor. This is achieved by heating a wire with an electric current that is suspended in the

engine‘s air stream, like a toaster wire. The wire's electrical resistance increases as the wire‘s

temperature increases, which limits electrical current flowing through the circuit. When air flows past

the wire, the wire cools, decreasing its resistance, which in turn allows more current to flow through the

circuit. As more current flows, the wire‘s temperature increases until the resistance reaches equilibrium

again. The amount of current required to maintain the wire‘s temperature is directly proportional to the

mass of air flowing past the wire. The integrated electronic circuit converts the measurement of current

into a voltage signal which is sent to the ECU.

If air density increases due to pressure increase or temperature drop, but the air volume remains

constant, the denser air will remove more heat from the wire indicating a higher mass airflow. Unlike

the vane meter's paddle sensing element, the hot wire responds directly to air density. This sensor's

capabilities are well suited to support the gasoline combustion process which fundamentally responds to

air mass, not air volume.

This sensor sometimes employs a mixture screw, but this screw is fully electronic and uses a variable

resistor (potentiometer) instead of an air bypass screw. The screw needs more turns to achieve the

desired results. A hot wire burn-off cleaning circuit is employed on some of these sensors. A burn-off

relay applies a high current through the platinum hot wire after the vehicle is turned off for a second or

so, thereby burning or vaporizing any contaminants that have stuck to the platinum hot wire element.

The hot film MAF sensor works somewhat similar to the hot wire MAF sensor, but instead it usually

outputs a frequency signal. This sensor uses a hot film-grid instead of a hot wire. It is commonly found

in late 80‘s early 90‘s fuel injected vehicles. The output frequency is directly proportional to the amount

of air entering the engine. So as air flow increases so does frequency. These sensors tend to cause

intermittent problems due to internal electrical failures. The use of an oscilloscope is strongly

recommended to check the output frequency of these sensors. Frequency distortion is also common

when the sensor starts to fail. Many technicians in the field use a tap test with very conclusive results.

Not all HFM systems output a frequency. In some cases, this sensor works by outputting a regular

varying voltage signal.

Some of the benefits of a hot-wire MAF compared to the older style vane meter are:

responds very quickly to changes in air flow

low airflow restriction

smaller overall package

less sensitive to mounting location and orientation

no moving parts improve its durability

less expensive

separate temperature and pressure sensors are not required (to determine air mass)



There are some drawbacks:

dirt and oil can contaminate the hot-wire deteriorating its accuracy

installation requires a laminar flow across the hot-wire

The MAF sensor used in cars is a variation of a classic air flow sensor that was known as a hot

wire anemometer and was used, for example, to measure wind velocity for weather forecasting. In the

MAF, the hot-wire, or sensing, element is replaced by a hot-film structure mounted on a substrate. On

the air inlet side is mounted a honeycomb flow straightener that ―smooths‖ the air flow (causing

nominally laminar air flow over the film element). At the lower portion of the structure is the signal

processing circuitry. The film element is electrically heated to a constant temperature above that of the

inlet air. The latter air temperature is sensed using a solid-state temperature sensor (explained later in

this chapter). The hot-film element is incorporated in a Wheatstone bridge circuit (Figure below). The

power supply for the bridge circuit comes from an amplifier. The Wheatstone bridge consists of three

fixed resistors R1, R2, and R3anda hot-film element having resistance RHW. With no air flow the

resistors R1, R2, and R3are chosen such that voltage va and vb are equal (i.e., the bridge is said to be

balanced). As air flows across the hot film, heat is carried away from the film by the moving air. The

amount of heat carried away varies in proportion to the mass flow rate of the air. The heat lost by the

film to the air tends to cause the resistance of the film to vary, which unbalances the bridge circuit,

thereby producing an input voltage to the amplifier. The output of the amplifier is connected to the

bridge circuit and provides the power for this circuit. The amplified voltage changes the resistance in

such a way as to maintain a fixed hot-film temperature relative to the inlet temperature. The amplifier

output voltage vc varies with MAF and serves as a measure of Rm. Typically the conversion of MAF to

voltage is slightly nonlinear, as indicated by the calibration curve depicted in Figure below. Fortunately,

a modern digital engine controller can convert the analog bridge output voltage directly to mass air flow

by simple computation.



Hotwire MAF sensor installation diagram Hotwire MAF sensor wiring diagram

Camshaft position sensor:

In electronic engine control it is often desirable to measure the angular position of the engine

relative to a specific point in the cycle. For such measurement it is normally necessary to measure the

position of the camshaft. Normally it is sufficient to measure camshaft position at a fixed point. Such a

sample of camshaft position is readily achieved by a magnetic sensor similar to that described above for

the crankshaft position measurement. This sensor detects a reference point on the angular position of the

camshaft that defines a beginning to a complete engine cycle (e.g., power stroke for all cylinders). Once

this reference point has been detected, crankshaft position measurements (as described above) provide

sufficient information for timing fuel injection pulses and ignition. In one scheme a variable-reluctance

sensor is located near a ferromagnetic disk on the camshaft. This disk has a notch cut (or it can have a

protruding tab), as shown in Figure below. The disk provides a low-reluctance path (yielding high

magnetic flux) except when the notch aligns with the sensor axis. When-ever the notch aligns with the

sensor axis; the reluctance of this magnetic path is increased because the permeability of air in the notch

is very much lower than the permeability of the disk. This relatively high reluctance through the notch

causes the magnetic flux to decrease and produces a change in sensor output voltage.

As the camshaft rotates, the notch passes under the sensor once for every two crankshaft

revolutions. The magnetic flux abruptly decreases, then increases as the notch passes the sensor. This

generates a voltage pulse that can be used in electronic control systems for timing purposes.



Wheel speed sensor: This sensor is based on magnetic reluctance effect discussed in the first topic. Each speed sensor

usually has a toothed wheel, like a gear, that rotates at the same speed as the vehicle wheel or axle.

Mounted close to, but not touching this toothed wheel, is a permanent magnet wrapped with a coil of

wire, called the pick-up coil (see illustration). As each tooth rotates past the permanent magnet, it causes

the magnetic field to concentrate and increase slightly. This, in turn, induces a small pulse of current in

the coil of wire. The numbers of pulses per second are directly proportional to the speed of the wheel.

The faster the wheel turns, the faster the teeth pass the magnet and the higher the pulse rate.

The toothed wheel or gear in the speed sensor is made of soft iron, usually cast. Iron is chosen

because of its high magnetic permeability and low magnetic reluctance. Magnetic reluctance is roughly

equivalent to electrical resistance, and sometimes the toothed wheel is called the reluctor. The function

of the toothed wheel is to allow the permanent magnet's field to easily pass through each tooth to cause a

momentary concentration of field strength which induces a current in the pick-up coil. The pick-up coil

has a permanent magnet in the core, wrapped with a coil of copper wire.

Tire Pressure sensor:

A block diagram of a hypothetical system is shown in the left Figure below. In this scheme, a tire

pressure sensor continually measures the tire pressure. The signal from the sensor mounted on the

rolling tire is coupled by a link to the electronic signal processor. Whenever the pressure drops below a

critical limit, a warning signal is sent to a display on the instrument panel to indicate which tire has the

low pressure. To connect a tire sensor with signal processor we can use a small radio transmitter

mounted on the tire. By using modern solid-state electronic technology, a low-power transmitter is

mounted in the tire valves. The transmitter sends a signal to a receiver in the car body. The distance

from the transmitter to the receiver is a few feet, so only very low power is required.

Low tire pressure allows the spring-loaded switch to close, thereby switching on the micro

transmitter. The receiver, which is directly powered by the car battery, receives the transmitted signal

and passes it to the signal processor, also directly powered by the car battery. The signal processor then



activates a warning lamp for the driver, and it remains on until the driver resets the warning system by

operating a switch on the instrument panel. One reason for using a signal processing unit is the relatively

short life of the transmitter battery. The transmitter will remain on until the low-pressure condition is

corrected or until the battery runs down.

Fuel Level sensor:

Several fuel quantity sensor configurations are available. The following figure illustrates the type

of sensor to be described, which is a potentiometer connected via mechanical linkage to a float.

Normally, the sensor is mounted so that the float remains laterally near the center of the tank for all fuel

levels. A constant current passes through the sensor potentiometer, since it is connected directly across

the regulated voltage source. The potentiometer is used as a voltage divider so that the voltage at the

wiper arm is related to the float position, which is determined by fuel level. The sensor output voltage is

not directly proportional to fuel quantity in gallons because of the complex shape of the fuel tank. The

computer memory contains the functional relationship between sensor voltage (in binary number

equivalent) and fuel quantity for the particular fuel tank used on the vehicle.

Crash sensor:

In a frontal collision equivalent to hitting a solid barrier at nine miles per hour (14.48 kilometers

per hour), the crash sensors located in the front of the car detect the sudden deceleration and send an

electrical signal activating an initiator. The crash sensor can take a number of forms; these can be

described as mechanical or electronic. The mechanical system, as shown in the figure, works by a spring

holding a roller in a set position until an impact above a predetermined limit, provides enough force to

overcome the spring and the roller moves, triggering a micro switch.



Mechanical Crash Sensor Location of crash sensor

The switch is normally open with a resistor in parallel to allow the system to be monitored. Two

switches similar to this may be used to ensure the bag is deployed only in the case of sufficient frontal

impact. Note that the airbag is not deployed in the event of a roll over. The other main type of crash

sensor can be described as an accelerometer. This will sense deceleration, which is negative

acceleration.

Optical Crankshaft Position Sensor

In a sufficiently clean environment a shaft position can also be sensed using optical techniques.

Figure illustrates such a system. Again, as with the magnetic system, a disk is directly coupled to the

crankshaft. This time, the disk has holes in it that correspond to the number of tabs on the disks of the

magnetic systems. Mounted on each side of the disk are fiber-optic light pipes. The hole in the disk

allows transmission of light through the light pipes from the light-emitting diode (LED) source to the

phototransistor used as a light sensor. Light would not be transmitted from source to sensor when there

is no hole because the solid disk blocks the light. As shown in Figure, the pulse of light is detected by

the phototransistor and coupled to an amplifier to obtain a satisfactory signal level. The output pulse

level can very easily be standard transistor logic levels of +2.4V for the high level and +0.8V for the low

level. Used as pulses, the signals provide time-referenced pulses that can be signal processed easily with

digital integrated circuits. One of the problems with optical sensors is that they must be protected from

dirt and oil; otherwise, they will not work properly. They have the advantages that they can sense

position without the engine running and that the pulse amplitude is constant with variation in speed.

The same sensor can also be used for measuring wheel speed or crankshaft speed. The number of

electrical pulses per second from the sensor represents the speed per second.



Conclusion:

Steering angle sensor, Steering torque sensor: Self study

S. No. Working principle Sensor application

1 Inductive type Magnetic

Reluctance)

Crankshaft position, Camshaft position,

Wheel speed, Engine speed

2 Hall effect Crankshaft position, Camshaft position

3 Thermistor Engine temperature(coolant), Manifold

temperature

4 Piezo electric / Piezo resistive Engine Knock sensor

5 Hot wire Mass Air Flow sensor

6 Variable resistance (Rheostat) Fuel level sensor

7 Optical type Speed, Angular position



UNIT- III SI ENGINE MANAGEMENT Three way catalytic converter, conversion efficiency versus lambda. Layout and working of SI

engine management systems like Bosch L-Jetronic and LH-Jetronic. Group and sequential injection

techniques. Working of the fuel system components. Cold start and warm up phases, idle speed control,

acceleration and full load enrichment, deceleration fuel cutoff. Fuel control maps, open loop control of

fuel injection and closed loop lambda control. Electronic ignition systems and spark timing control.

Closed loop control of knock.

Three way catalytic converter: A catalytic converter configuration that is extremely important for modern emission control

systems is called the three-way catalyst (TWC). It uses a specific catalyst formulation containing

platinum, palladium, and rhodium to reduce NOx and oxidize HC and CO all at the same time. It is

called three-way because it simultaneously reduces the concentration of all three major undesirable

exhaust gases by about 90% if used optimally. The conversion efficiency of the TWC for the three

exhaust gases depends mostly on the air/fuel ratio. Unfortunately, the air/fuel ratio for which NOx

conversion efficiency is highest corresponds to very low conversion efficiency for HC and CO and vice

versa. However, as shown in Figure 5.14, there is a very narrow range of air/fuel ratio (called the

window) in which an acceptable compromise exists between NOx and HC/CO conversion efficiencies.

The conversion efficiencies within this window are sufficiently high to meet the very stringent EPA

requirements established so far.

Note that this window is only about 0.1 air/fuel ratio wide (±0.05air/fuel ratio) and is centered at

stoichiometry. (Recall that stoichiometry is the air/fuel ratio that would result in complete oxidation of

all carbon and hydrogen in the fuel if burning in the cylinder were perfect; for gasoline, stoichiometry

corresponds to an air/fuel ratio of 14.7.) This ratio and the concept of stoichiometry is extremely

important in an electronic fuel controller. In fact, the primary function of most modern electronic fuel

control systems is to maintain average air/fuel ratio at stoichiometry. The operation of the three-way

catalytic converter is adversely affected by lead. Thus, in automobiles using any catalyst, it is necessary

to use lead-free fuel. Controlling the average air/fuel ratio to the tolerances of the TWC window (for

100,000 miles) requires accurate measurement of mass air flow rate and precise fuel delivery and is the

primary function of the electronic engine control system. A modern electronic fuel control system can

meet these precise fuel requirements. In addition, it can maintain the necessary tolerances for

government regulations for over 100,000 miles.



L Jetronic system:

Initially Bosch introduced D jetronic system. Here the "D" stands for druck-German for pressure

– because the calculation of the quantity of fuel to be injected was based on manifold pressure. The main

disadvantage of this type is was the mechanical triggering contacts. Many of the shortcomings of the D-

Jetronic system were answered in the L-Jetronic, introduced in 1974. L-Jetronic established the principle

of calculating the fuel quantity required and thus the pulse time of the injectors on the basis of airflow,

rather than manifold pressure as on the D-Jetronic. This fundamental difference is reflected in the

designation – the "L" stands for luft, the German word for air.

L Jetronic system Layout

Air flow sensor: The air flow sensor is a box through which all of the intake air has to pass. Within the box is a

spring loaded vane or flap, hinged at the top, which is deflected from the down (closed) position by the

momentum of the air passing through the sensor. Attached to the vane's hinge is a potentiometer –a

variable resistor, like a radio volume control. Movement of the vane causes an electrical contact in the

potentiometer to wipe around a ring- shaped surface that is wound with a resistance wire, so that the

total resistance of the potentiometer depends on the position of the wiper, and thus of the vane. By

measuring this resistance value, the ECU is thus able to "know" the position of the vane and thus the rate

of air flow through the meter.

Idle air bypass: To permit a degree of manual adjustment of idle mixture strength (mainly to allow adjustment of

idle speed), a small amount of air is allowed to bypass around the measuring section of the airflow meter

through a separate small passage way. This extra idle air is thus unmetered; the ECU is "unaware" of it.

The amount of air that is bypassed in this way can be adjusted by a small needle valve arranged at the



end of the bypass passage nearest the engine. Turning this screw in makes the opening smaller, reducing

bypass airflow and so richening the mixture.

Other sensors: There is an engine temperature sensor the output of which is used by the ECU to enrich the

mixture during cold starts and during warm-up. Also like the early D-Jetronic, there is a throttle position

sensor that reports just closed (idle) throttle and full throttle. This information is used by the ECU to

provide mixture strength corrections for those two operating conditions.

Mechanical components: An electrically driven roller type rotary pump draws fuel from the tank. The L- Jetronic's pump

is equipped with a check valve that keeps the fuel lines full and pressurized even when the engine is

stopped. This permits quicker restarts, and helps to prevent vapor lock. The pump also has a relief valve

at its intake end, which returns fuel to the tank if the internal pressure rises too high. The regulator is

schematically at the far end of the fuel rail, maintaining pressure within the rail for the injectors, and

bleeding excess fuel back to the tank. It maintains either 36 psi or 44 psi fuel pressure.

ECU working: L- Jetronic systems use the firing of the ignition system as a trigger signal. In a four-cylinder,

four-stroke engine, there will be a spark plug firing twice per engine revolution. Thus, the ECU

(electronic control unit) receives two triggering pulses per revolution. Then a basic pulse time is

generated, on the basis of engine speed and air mass flow. The rpm is known from the frequency of the

pulses arriving from the frequency divider; the air mass flow is known from the position of the vane in

the air flow meter. When the throttle is opened suddenly, the rapid increase in air flow through the

sensor causes the vane to overshoot momentarily. Because the ECU is using the vane position as a

measure of air flow, this exaggerated movement of the vane influences the ECU to briefly increase the

pulse time, thereby providing the enrichment needed. For cold starting, L-Jetronic uses a cold start

valve, in conjunction with a thermo-time switch. This cold-cold start circuit, which operates only as long

as the starter is cranking, is quite independent of the ECU.

Auxiliary air by pass:

It is provided for supplying more air while cold starting the engine in idling condition. This

bypass amounts to a small rotary disc valve; depending on the position of the disc, more or less air (or

none) is allowed to bleed around the nearly closed throttle. The position of the disc, in turn, is governed

by a bimetallic coil. When the coil is warm, the valve is completely closed; when very cold, it is fully

open; at intermediate temperatures, it adopts a position somewhere in between. A smooth and gradual

transition from open to close as the engine warms up is assured by the profiling of the valve disc and the

calibration of the bimetallic coil and of a return spring that pulls the valve to the closed position.

Engine warm up:

Once a cold engine has fired, the ECU immediately cuts back on the wholesale enrichment that

has been provided for starting. A much richer than nominally stoichiometric mixture is still needed,

however, until the engine is fully warmed up, so instead of two to three times normal pulse time (plus

whatever has been added through the cold start valve),the enrichment drops to,say,1-1/2times the "basic"

pulse time. The ECU gradually tapers off the "post-start" and warm up enrichment.

Idle / Coasting:

There is a micro switch that signals two important conditions, closed throttle and wide open

throttle. The signal from this switch tells the ECU to provide slight enrichment for idle/coasting

condition.



LH Jetronic system:

Disadvantage of L Jetronic system:

The ECU has to take data from two sensors: Mass Air flow sensor and Air temperature sensor.

Moreover Mass air flow sensor used is of Mechanical vane type which is prone to mechanical errors and

also requires more calculations. Hence a light, compact, simple, all electronic sensor with no moving

parts that directly measures air mass, with no need for calculations relating volume flow, temperature

and density, a hot wire mass air flow sensor is used. H stands for heiss, the German word for hot.

Hot Wire Sensor:

The sensing element is a very fine wire of platinum alloy, just 0.7millimeters (less than 0.003

inches) in diameter, strung across the interior of a housing through which all the incoming air stream has

to pass. The wire is heated by an electric current, but cooled by the passing air stream. An electrical

circuit adjusts the current passing through the wire so as to maintain it at a temperature that is

consistently 180°F above that of the entering air. Thus, if the air temperature is 80°F, the wire will be

running at 260°F; if the air is at 30°F, the wire temperature will be at 210°. The current required to

maintain this equilibrium is a measure of the mass of air passing the wire, and is used as the principal

signal to the ECU as to air quantity.

LH Jetronic Layout: Hot wire assembly with circuit:

All other components of LH jetronic is same as that of L Jetronic except a very few. The main

disadvantage of LH Jetronic is that if its surface becomes contaminated, the rate of heat flow out of it

will be reduced, in which case it would send the ECU a false signal.

Note:

The students can write the same content as that of L Jetronic and replace Vane type of air flow

sensor by hot wire air flow sensor.



Fuel Injection modes: Multi-point fuel injection injects fuel into the intake ports just upstream of each cylinder's intake

valve, rather than at a central point within an intake manifold. There are three types of MPFI (or just

MPI) systems.

1. Sequential injection:

Injection is timed to coincide with each cylinder's intake stroke. It‘s the most widely used

technique now-a-days. The injectors are usually opened individually in sequence (to match the engine

firing order). All the required fuel is therefore delivered in one ‗opening‘ of the injector

2. Batched (group injection): Fuel is injected to the cylinders in groups, without precise synchronization to any particular

cylinder's intake stroke.

3. Simultaneous injection:

Fuel is injected at the same time to all the cylinders.

Fuel system components and working: The main components required for a simple multi-point injection system is given below. An

electronic petrol injection system effectively consists of two sub-systems: an electrical/electronic system

and a fuel delivery system.

Electrical/electronic system:

1. Injectors– electrically operated fuel valves that, when open, allow petrol to flow into the engine.

2. ECU– the computer that calculates the required amount of petrol and then opens the injectors for the

appropriate amount of time.

3. Sensors– provide the necessary information to the ECU to enable it to calculate the fuel required for

different operating conditions.

Fuel system 1. Fuel pump– moves the fuel from the fuel tank to the injectors; the pump provides an excess of fuel,

which results in pressure being developed in the fuel system.

2. Fuel filter– filters the fuel to remove dirt particles that could damage the system components or block

the injectors.

3. Fuel pressure regulator and fuel rail– the regulator controls the pressure of the fuel; the fuel rail acts

as the distribution pipe to pass fuel to the injectors.

Layout of simple electronic fuel injection system:



Injectors and fuel rail: Petrol injectors used on electronic injection systems are fuel valves that open and close to control

fuel delivery. The injectors are solenoids with a needle valve attached to the solenoid armature, so that,

when current flows in the solenoid winding, the magnetic field moves the armature, which in turn moves

the needle valve off its seating and allows the fuel to flow through the nozzle. The injector solenoid

valve is connected to a fuel supply rail, or in some cases is located within the fuel rail. The fuel within

the rail is regulated at a predetermined pressure, which is altered to suit operating conditions. However,

the quantity of fuel delivered is largely controlled by opening the injectors for differing lengths of time.

Fuel is fed to the injector under pressure (typically around 3bar); because the fuel is under pressure,

when it flows out through the injector nozzle a spray of finely atomized fuel is formed that is able to mix

easily with the air.

Fuel rail components:

ECU: The ECU controls the fuel injectors in response to the information received from the sensors. An

ECU contains a programmed memory, which, in an injection ECU, contains data on how much fuel

should be injected under different operating conditions. When information is received from the sensors,

the ECU refers to the programmed data and switches on the fuel injectors so that they deliver the

required amount of petrol.

ECU processes in an injection system:



Injector timing: The injectors are typically opened just prior to the inlet valve opening. All the required fuel is

therefore delivered in one ‗opening‘ of the injector. In occasions where a very large quantity of fuel is

required, for example during full load acceleration, where the injectors can be opened twice for every

operating cycle (half the fuel quantity is delivered at each opening). ECU uses separate sensors to

identify one of the cylinders, for example cylinder number 1; the ECU then uses this signal as a master

reference and operates the injectors in sequence at the appropriate times.

Injector timing diagram:

Injection duration:

When the ECU has calculated the quantity of fuel to be delivered (effectively by noting the

information from the sensors and then referring to the programmed fuel map within the memory), it will

then switch on the injectors for an appropriate length of time (the injection duration). The duration will

vary with the system‘s design and operating conditions, such as engine load, engine speed, temperature,

etc., but typical values are between 1.5ms and15 ms.

Sensors used: Mass Air flow sensor:

Some systems use an air ‗mass‘ sensor, others use different sensors such as manifold absolute

pressure sensors (MAP sensors), which measure the manifold depression; in this case, the ECU uses the

MAP sensor information along with engine speed, air temperature and other information to establish the

basic fuel requirements.

Coolant temperature sensor:

The engine coolant temperature information enables the ECU to alter the fuel quantity (thus

altering the air fuel ratio) so that, when the engine is cold, an excess of fuel (a rich mixture) can be

provided.

Air temperature sensor:

The air temperature sensor information helps in calculating the air mass, because air density

changes with temperature. Many air temperature sensors are incorporated within the airflow sensors.

Throttle position sensor:

It uses a potentiometer or variable resistor instead of switches. With a potentiometer based

sensor, it is possible to send a varying voltage analogue signal to the ECU; the signal indicates all

throttle opening angles and the ECU can also calculate the rate at which the throttle is being opened and

closed. The ECU is therefore able to alter the fuelling to suit the minor and major changes in throttle

position (load changes).



Fuel system:

Fuel pump:

The fuel pump moves the fuel from the fuel tank through to the injectors. The pump must

provide sufficient fuel for the engine to operate at full load: it delivers typically between 1 and 2litres of

fuel each minute (depending on engine size).The fuel pumps on most systems operate at full rateall the

time: there is no variation in the amount of fuel delivered by the pump, irrespective of engine speed and

load. However, at low engine speeds and loads only a small amount of fuel is used, so the excess fuel

flows back to the fuel tank. With most modern systems the fuel pump is located in the fuel tank. The

main pump is driven by an electric motor, which turns a pumping element. A number of different types

of pumping element have been used: positive displacement type and flow type. One disadvantage of

positive displacement types is that pulses are produced by the pumping action, which can cause noise

and vibration in the fuel system. Flow type pumps provide much quieter operation and are therefore

more widely used.

Fuel pressure regulator:

A high volume of fuel delivered by the pump flows to the injectors and, with only a small

amount of fuel able to escape through the injectors, this continuous flow of fuel causes the system to

build up pressure. Although excess fuel is allowed to return to the tank, a regulator valve is used (to

control the pressure in the system. In theory therefore, the fuel is always held in the system at a constant

pressure.

Fuel filter: The fuel filter is located in the fuel circuit after the fuel pump. The filter usually consists of a fine

paper element and a strainer, which can retain any larger particles. Filters are often constructed in such a

way that fuel should flow in one direction only; markings are usually provided to indicate the fuel flow.

Incorrect fitment can result in collapse of the paper element.

Fuel control maps:

A three-dimensional map provides the ECU with the necessary references for the required

quantity of fuel. The map shown in Figure gives references for fuelling based on engine load and engine

speed; the fuelling references (vertical scale) are air fuel ratios, which are expressed as lambda (λ)

values. In theory, the amount of fuel injected is matched to the mass of air injected so that the

stoichiometric air fuel ratio is provided. However, minor variations in air fuel ratio are necessary for

different operating conditions, so the ECU controls the injector opening time to suit the various

conditions as listed below:

1. Light load conditions– The injection duration is long enough to provide the quantity of fuel needed to

give the theoretical stoichiometric ratio. Minor increases or decreases in air mass (air drawn into the

engine) will result in minor changes in injection duration.

2. Acceleration and high load– The ECU will increase the injection duration so that the fuel quantity

increases to match the increase in air mass. However, under heavy load and acceleration, a slight excess

of petrol is usually required (a rich mixture), so the injection duration increases to slightly more than

would be required to achieve the ideal stoichiometric ratio.

3. Cold running– When the engine is cold, the cold surfaces of the intake port and combustion chamber

can cause slight condensation of the fuel and prevent complete mixing of the fuel vapour and air. The

injection duration is therefore increased slightly to provide a rich mixture, thus ensuring that sufficient

fuel is available to mix with the air.

4. Idle– When the engine is idling, the air fuel ratio on modern engines is controlled at around

stoichiometric or lambda 1. It was, however, normal on older engines for a slightly rich mixture to be

provided, which helped the engine to develop sufficient power and to run smoothly.

5. Deceleration– During deceleration, no power is required from the engine so fuel injection can be

completely cut off. Depending on engine speed and whether the throttle is partially or completely



closed(indicated by the throttle position sensor), the fuel injectors can be completely switched off, or the

injection duration reduced, so that very little fuel is injected.

Fuel control map for a typical engine

Digital engine control: - Control modes for fuel control:

Digital engine control system - Layout



The engine control system is responsible for controlling fuel and ignition for all possible engine

operating conditions. However, there are a number of distinct categories of engine operation, each of

which corresponds to a separate and distinct operating mode for the engine control system. The

differences between these operating modes are sufficiently great that different software is used for each.

The control system must determine the operating mode from the existing sensor data and call the

particular corresponding software routine. For a typical engine there are seven different engine operating

modes that affect fuel control: engine crank, engine warm-up, open-loop control, closed-loop control,

hard acceleration, deceleration, and idle. The program for mode control logic determines the engine

operating mode from sensor data and timers.

When the ignition key is switched on initially, the mode control logic automatically selects an

engine start control scheme that provides the low air/fuel ratio required for starting the engine. Once the

engine RPM rises above the cranking value, the controller identifies the ―engine started‖ mode and

passes control to the program for the engine warm-up mode. This operating mode keeps the air/fuel ratio

low to prevent engine stall during cool weather until the engine coolant temperature rises above some

minimum value. The instantaneous air/fuel is a function of coolant temperature. The particular value for

the minimum coolant temperature is specific to any given engine and, in particular, to the fuel metering

system. (Alternatively, the low air/fuel ratio may be maintained for a fixed time interval following start,

depending on start-up engine temperature.)

When the coolant temperature rises sufficiently, the mode control logic directs the system to

operate in the open-loop control mode until the EGO sensor warms up enough to provide accurate

readings. This condition is detected by monitoring the EGO sensor‘s output for voltage readings above a

certain minimum rich air/fuel mixture voltage set point. When the sensor has indicated rich at least once

and after the engine has been in open loop for a specific time, the control mode selection logic selects

the closed-loop mode for the system. (Note: other criteria may also be used.) The engine remains in the

closed-loop mode until either the EGO sensor cools or fails to read a rich mixture for a certain length of

time or a hard acceleration or deceleration occurs. If the sensor cools, the control mode logic selects the

open-loop mode again.

During hard acceleration or heavy engine load, the control mode selection logic chooses a

scheme that provides a rich air/fuel mixture for the duration of the acceleration or heavy load. This

scheme provides maximum torque but relatively poor emissions control and poor fuel economy

regulation as compared with a stoichiometric air/fuel ratio. After the need for enrichment has passed,

control is returned to either open-loop or closed-loop mode, depending on the control mode logic

selection conditions that exist at that time.

During periods of deceleration, the air/fuel ratio is increased to reduce emissions of HC and CO

due to unburned excess fuel. When idle conditions are present, control mode logic passes system control

to the idle speed control mode. In this mode, the engine speed is controlled to reduce engine roughness

and stalling that might occur because the idle load has changed due to air conditioner compressor

operation, alternator operation, or gear shift positioning from park/neutral to drive, although

stoichiometric mixture is used if the engine is warm.

Engine Crank:

While the engine is being cranked, the fuel control system must provide an intake air/fuel ratio of

anywhere from 2:1 to 12:1, depending on engine temperature. The correct air/fuel ratio (i.e., [A/F]d) is

selected from a ROM lookup table as a function of coolant temperature. Low temperatures affect the

ability of the fuel metering system to atomize or mix the incoming air and fuel. At low temperatures, the

fuel tends to form into large droplets in the air, which do not burn as efficiently as tiny droplets. The

larger fuel droplets tend to increase the apparent air/fuel ratio, because the amount of usable fuel (on the

surface of the droplets) in the air is reduced; therefore, the fuel metering system must provide a

decreased air/fuel ratio to provide the engine with amore combustible air/fuel mixture. During engine



crank the primary issue is to achieve engine start as rapidly as possible. Once the engine is started the

controller switches to an engine warm-up mode.

Engine warm up:

While the engine is warming up, an enriched air/fuel ratio is still needed to keep it running

smoothly, but the required air/fuel ratio changes as the temperature increases. Therefore, the fuel control

system stays in the open-loop mode, but the air/fuel ratio commands continue to be altered due to the

temperature changes. The emphasis in this control mode is on rapid and smooth engine warm-up. Fuel

economy and emission control are still a secondary concern. Essentially, the measured coolant

temperature (CT) is converted to an address for the lookup table. This address is supplied to the ROM

table via the system address bus (A/B). The data stored at this address in the ROM are the desired

air/fuel ratio (A/F)d for that temperature. These data are sent to the controller via the system data bus

(D/B).There is always the possibility of a coolant temperature failure. Such a failure could result in

excessively rich or lean mixtures, which can seriously degrade the performance of both the engine and

the three-way catalytic converter (3wcc). One scheme that can circumvent a temperature sensor failure

involves having a time function to limit the duration of the engine warm-up mode. The nominal time to

warm the engine from cold soak at various temperatures is known. The controller is configured to switch

from engine warm-up mode to an open-loop (warmed-up engine) mode after a sufficient time by means

of an internal timer. It is worthwhile at this point to explain how the quantity of fuel to be injected is

determined. This method is implemented in essentially all operating modes and is described here as a

generic method, even though each engine control scheme may vary somewhat from the following. The

quantity of fuel to be injected during the intake stroke of any given cylinder (which we call F) is

determined by the mass of air (A) drawn into that cylinder (i.e., the air charge) during that intake stroke.

That quantity of fuel is given by the air charge divided by the desired air/fuel ratio:

F = A / (A/F)d The quantity of air drawn into the cylinder, A, is computed from the mass airflow

rate and the RPM. The mass air flow rate (MAF) will be given in kg/sec. If the engine speed in

revolutions/minute is RPM, then the number of revolutions/second (which we call r) is r = (RPM/60),

Then, the mass air flow is distributed approximately uniformly to half the cylinders during each

revolution. If the number of cylinders is N then the air charge (mass) in each cylinder during one

revolution is A = MAF / [r(N/2)]. In this case, the mass of fuel delivered to each cylinder is

F = MAF / [r(N/2)(A/F)d]. This computation is carried out by the controller continuously so that the fuel

quantity can be varied quickly to accommodate rapid changes in engine operating condition. The fuel

injector pulse duration T corresponding to this fuel quantity is computed using the known fuel injector

delivery rate Rf: T = F/Rf. This pulse width is known as the base pulse width. The actual pulse width

used is modified from this according to the mode of operation at any time, as will presently be

explained.

Open loop control:

For a warmed-up engine, the controller will operate in an open loop if the closed-loop mode is

not available for any reason. For example, the engine may be warmed sufficiently but the EGO sensor

may not provide a usable signal. In any event, as soon as possible it is important to have a stoichiometric

mixture to minimize exhaust emissions. The base pulse width Tb is computed as described above, except

that the desired air/fuel ratio (A/F)d is 14.7.

An alternate method of computing mass airflow rate is the speed-density method. is based on

measurements of manifold absolute pressure (MAP), RPM, and intake air temperature Ti. The air

density da is computed from MAP and Ti, and the volume flow rate Rv of combined air and EGR is

computed from RPM and volumetric efficiency, the latter being a function of MAP and RPM. The

volume rate for air is found by subtracting the EGR volume flow rate from the combined air and EGR.



Finally, the mass air flow rate is computed as the product of the volume flow rate for air and the intake

air density. The speed-density method can be implemented either by computation in the engine control

computer or via lookup tables. Mass Air flow is given by

Closed loop control: The closed-loop mode can only be activated when the EGO (or HEGO)sensor is sufficiently

warmed. The output voltage of the sensor is high (approximately 1 volt) when the exhaust oxygen

concentration is low (i.e., for a rich mixture relative to stoichiometry). The EGO sensor voltage is low

(approximately 0.1 volt) whenever the exhaust oxygen concentration. The time-average EGO sensor

output voltage provides the feedback signal for fuel control in the closed-loop mode. The engine

controller continuously adjusts the pulse duration for varying operating conditions and for operating

parameters. A representative algorithm for fuel injector pulse duration for a given injector during the nth

computation cycle, T(n), is given by

Tb(n) is the base pulse width as determined from measurements of mass air flow rate and the desired

air/fuel ratio and CL(n) is the closed-loop correction factor. Once the computation of the closed-loop

correction factor is completed, the value is stored in a specific memory location (RAM) in the controller.

At the appropriate time for fuel injector activation (during the intake stroke), the instantaneous closed-



loop correction factor is read from its location in RAM and an actual pulse of the corrected duration is

generated by the engine control.

Acceleration enrichment:

During periods of heavy engine load such as during hard acceleration, fuel control is adjusted to

provide an enriched air/fuel ratio to maximize engine torque and neglect fuel economy and emissions.

This condition of enrichment is permitted within the regulations of the EPA as it is only a temporary

condition. It is well recognized that hard acceleration is occasionally required for maneuvering in certain

situations and is, in fact, related at times to safety. The computer detects this condition by reading the

throttle angle sensor voltage. High throttle angle corresponds to heavy engine load and is an indication

that heavy acceleration is called for by the driver. In some vehicles a switch is provided to detect wide

open throttle. The fuel system controller responds by increasing the pulse duration of the fuel injector

signal for the duration of the heavy load. This enrichment enables the engine to operate with a torque

greater than that allowed when emissions and fuel economy are controlled. Enrichment of the air/fuel

ratio to about 12:1 is sometimes used.

Deceleration leaning:

During periods of light engine load and high RPM such as during coasting or hard deceleration,

the engine operates with a very lean air/fuel ratio to reduce excess emissions of HC and CO.

Deceleration is indicated by a sudden decrease in throttle angle or by closure of a switch when the

throttle is closed (depending on the particular vehicle configuration). When these conditions are detected

by the control computer, it computes a decrease in the pulse duration of the fuel injector signal. The fuel

may even be turned off completely for very heavy deceleration.

Idle speed control:

The goal is to allow the engine to idle at as low an RPM as possible, yet keep the engine from

running rough and stalling when power-consuming accessories, such as air conditioning compressors

and alternators, turn on. The control mode selection logic switches to idle speed control when the

throttle angle reaches its zero (completely closed) position and engine RPM falls below a minimum

value, and when the vehicle is stationary. Idle speed is controlled by using an electronically controlled

throttle bypass valve (Figure7.7a) that allows air to flow around the throttle plate and produces the same

effect as if the throttle had been slightly opened. There are various schemes for operating a valve to

introduce bypass air for idle control. One relatively common method for controlling the idle speed

bypass air uses a special type of motor called a stepper motor. A stepper motor moves in fixed angular

increments when activated by pulses on its two sets of windings (i.e., open or close). Such a motor can

be operated in either direction by supplying pulses in the proper phase to the windings. This is

advantageous for idle speed control since the controller can very precisely position the idle bypass valve

by sending the proper number of pulses of the correct phasing. The engine control computer can know

precisely the position of the valve in a number of ways. In one way the computer can send sufficient

pulses to completely close the valve when the ignition is first switched on. Then it can send open pulses

(phased to open the valve) to a specified (known) position.



Conclusion:

Engine crank: 1. Engine RPM at cranking speed.

2. Engine coolant at low temperature.

3. Air/fuel ratio low.

4. Spark retarded.

5. EGR off.

6. Secondary air to exhaust manifold.

7. Fuel economy not closely controlled.

8. Emissions not closely controlled.

Engine warm up: 1. Engine RPM at cranking speed.

2. Engine coolant at low temperature.

3. Air/fuel ratio low.

4. Spark retarded.

5. EGR off.

6. Secondary air to exhaust manifold.

7. Fuel economy not closely controlled.

8. Emissions not closely controlled.

Open loop control:

1. Engine RPM at command of driver.

2. Engine temperature above warm-up

threshold.

3. Air/fuel ratio controlled by an open-

loop system to 14.7.

4. EGO sensor temperature less than

minimum threshold.

5. Spark timing set by controller.

6. EGR controlled.

7. Secondary air to catalytic converter.

8. Fuel economy controlled

Closed loop control: 1. Engine RPM at command of driver.

2. Engine temperature in normal range

(above warm-up threshold).

3. Average air/fuel ratio controlled to

14.7, ±0.05.

4. EGO sensor‘s temperature above

minimum threshold detected by a sensor

output voltage I indicating a rich

mixture of air and fuel for a minimum

amount of time.

5. System returns to open loop if EGO

sensor cools below minimum threshold

or fails to indicate rich mixture for given

length of time.

6. EGR controlled.

7. Secondary air to catalytic converter.

8. Fuel economy tightly controlled.

9. Emissions tightly controlled.

Hard acceleration: 1. Driver asking for sharp increase in

RPM or in engine power, demanding

maximum torque.

2. Engine temperature in normal range.

3. Air/fuel ratio rich mixture.

4. EGO not in loop.

5. EGR off.

6. Secondary air to intake.

7. Relatively poor fuel economy.

8. Relatively poor emissions control.

Deceleration and idle:

1. RPM decreasing rapidly due to driver

command or else held constant at idle.

2. Engine temperature in normal range.

3. Air/fuel ratio lean mixture.

4. Special mode in deceleration to

reduce emissions.

5. Special mode in idle to keep RPM

constant at idle as load varies due to air

conditioner, automatic transmission

engagement, etc.

6. EGR on.

7. Secondary air to intake.

8. Good fuel economy during

deceleration.

9. Poor fuel economy during idle, but

fuel consumption kept to minimum

possible.



Electronic Ignition systems: Disadvantages of mechanical (conventional) ignition systems:

1. The contact breaker mechanism wears (causing incorrect ignition timing and low ignition

coil output).

2. at higher engine speeds, there is insufficient time(ignition dwell time) for the ignition coil

to build up a strong magnetic field thus reducing ignition coil output

3. there is arcing at the contact breaker contact faces(causing reduced ignition coil output)

4. ignition timing control is inaccurate, which restricts the potential for engines to operate

close to their limits of efficiency

5. at high engine speeds, contact breakers are not able to open and close quickly and

accurately

6. weaker fuel mixtures can be more easily ignited with larger spark plug gaps but this

requires more energy to be produced by the ignition coil

The engine performance is strongly influenced by the spark timing relative to the engine position

during the compression stroke. The spark advance (relative to TDC) is determined in the electronic

engine control based on a number of measurements made by sensors and varies with engine position,

intake manifold pressure, RPM, and temperature. In conventional engines, the voltage pulse to fire the

spark plug in any given cylinder was routed from the coil to the relevant spark plug via a rotary switch

called a distributor. In modern engines, the distributor has been replaced with multiple coils, with each

coil dedicated to one (or sometimes two) cylinder(s). Electronic ignition can be implemented as part of

an integrated system or as a stand-alone ignition system.

Based on measurements from the sensors for engine position, mass air flow or manifold

pressure, and RPM, the electronic controller computes the correct spark advance for each cylinder. At

the appropriate time the controller sends a trigger signal to the driver circuits, thereby initiating spark.

Before the spark occurs, the driver circuit sends a relatively large current through the primary (P) of the

coil. When the spark is to occur, a trigger pulse is sent to the driver circuit for the coil associated with

the appropriate spark plug. This trigger causes the driver circuit to interrupt the current in the primary. A

very high voltage is induced at this time in the secondary (S) of the coil. This high voltage is applied to

the spark plugs, causing them to fire. In those cases for which a coil is associated with two cylinders,

one of the two cylinders will be in this compression stroke. Combustion will occur in this cylinder,

resulting in power delivery during its power stroke. The other cylinder will be in its exhaust stroke and

the spark will have no effect. Most engines have an even number of cylinders and there will be a

separate driver circuit and coil for each pair of cylinders. An ignition system such as this is often called a

distributorless ignition system (DIS) because the multiple coil packs and drivers are a modern

replacement for the (now essentially obsolete) distributor.

Electronic Ignition system (Distributorless)



Spark timing control:

The variables that influence the optimum spark timing at any operating condition include RPM,

manifold pressure (or mass air flow), barometric pressure, and coolant temperature. The correct ignition

timing for each value of these variables is stored in a ROM lookup table. For example, the variation of

spark advance (SA) with RPM for a representative engine is shown in the following Spark Advance

(SA) vs. RPM graph.

Spark Advance (SA) vs. Engine RPM

The engine control system obtains readings from the various sensors and generates an address to

the lookup table (ROM). After reading the data from the lookup tables, the control system computes the

correct spark advance. An output signal is generated at the appropriate time to activate the spark. The

following figure represents the electronic ignition implemented in a stand-alone ignition module. This

solid-state module receives the correct spark advance data and generates electrical signals that operate

the coil driver circuitry. These signals are produced in response to timing inputs coming from crankshaft

and camshaft signals (POS/RPM).



The coil driver circuits generate the primary current in windings P1andP2of the coil packs depicted in the

above figure. These primary currents build up during the so-called dwell period before the spark is to

occur. At the correct time the driver circuits interrupt the primary currents via a solid-state switch. This

interruption of the primary current causes the magnetic field in the coil pack to drop rapidly, inducing a

very high voltage (20,000–40,000 volts) that causes a spark. In the example depicted in the above figure,

a pair of coil packs, each firing two spark plugs, is shown. Such a configuration would be appropriate

for a 4-cylinder engine. Normally there would be one coil pack for each pair of cylinders. The ignition

system described above is known as a distributorless ignition system (DIS) since it uses no distributor.

There are a number of older car models on the road that utilize a distributor.

In a typical electronic ignition control system, the total spark advance, SA (in degrees before

TDC), is made up of several components that are added together

SA = SAS + SAP + SAT

The first component, SAS, is the basic spark advance, which is a tabulated function of RPM and

MAP. The control system reads RPM and MAP, and calculates the address in ROM of the SAS that

corresponds to these values. Typically, the advance of RPM from idle to about 1200 RPM is relatively

slow. Then, from about 1200 to about 2300 RPM the increase in RPM is relatively quick. Beyond 2300

RPM, the increase in RPM is again relatively slow. Each engine configuration has its own spark

advance characteristic, which is normally a compromise between a number of conflicting factors.

The second component, SAP, is the contribution to spark advance due to manifold pressure. This

value is obtained from ROM lookup tables. Generally speaking, the SA is reduced as pressure increases.

The final component, SAT, is the contribution to spark advance due to temperature. Temperature effects

on spark advance are relatively complex, including such effects as cold cranking, cold start, warm-up,

and fully warmed-up conditions.

Closed loop control of knock:

Closed-loop control of ignition timing is desirable from the standpoint of improving engine

performance and maintaining that performance in spite of system changes. One scheme for closed-loop

ignition timing is based on the improvement in performance that is achieved by advancing the ignition

timing relative to TDC. For a given RPM and manifold pressure, the variation in torque with spark

advance is as depicted in the following figure. One can see that advancing the spark relative to TDC

increases the torque until a point is reached at which best torque is produced. This spark advance is

known as mean best torque, or MBT.

Torque vs. Spark advance:

When the spark is advanced too far, an abnormal combustion phenomenon occurs that is known

as knocking which is a result of a portion of the air–fuel mixture auto igniting, as opposed to being

normally ignited by the advancing flame front that occurs in normal combustion following spark

ignition. Roughly speaking, the amplitude of knock is proportional to the fraction of the total air and fuel

mixture that auto ignites. It is characterized by an abnormally rapid rise in cylinder pressure during



combustion, followed by very rapid oscillations in cylinder pressure. The frequency of these oscillations

is specific to a given engine configuration and is typically in the range of a few kilohertz.

One control strategy for spark advance under closed-loop control is to advance the spark timing

until the knock level becomes unacceptable. At this point, the control system reduces the spark advance

(retarded spark) until acceptable levels of knock are achieved. Of course, a spark advance control

scheme based on limiting the levels of knocking requires a knock sensor. The following figure is a

diagram of the instrumentation for measuring knock intensity. Output voltage VE of the knock sensor is

proportional to the acoustical energy in the engine block at the sensor mounting point. This voltage is

sent to a narrow band pass filter that is tuned to the knock frequency. The filter output voltage VF is

proportional to the amplitude of the knock oscillations, and is thus a ―knock signal.‖ The envelope

voltage of these oscillations, Vd, is obtained with a detector circuit. This voltage is sent to the controller,

where it is compared with a level corresponding to the knock intensity threshold. Whenever the knock

level is less than the threshold, the spark is advanced. Whenever it exceeds the threshold, the spark is

retarded.

Instrumentation and Waveforms for Closed-Loop Ignition Control

An electronic gate that examines the knock sensor output at the time for which the knock amplitude is

largest (i.e., shortly after TDC). The gate is, in essence, an electronic switch that is normally open, but is

closed for a short interval (from0 to T) following TDC. It is during this interval that the knock signal is

largest in relationship to engine noise. The probability of successfully detecting the knock signal is

greatest during this interval. Similarly, the possibility of mistaking engine noise for true knock signal is

smallest during this interval. The final stage in the knock-measuring instrumentation is integration with

respect to time; this can be accomplished using an operational amplifier. The electronic gate actually

controls switches S1and S2. The output voltage VK at the end of the gate interval T is given by

dttVRV

T

dCK 0

/1

This voltage increases sharply (negative), reaching a maximum amplitude at the end of the gate interval,

as shown in the above figure, provided that knock occurs. However, if there is no knock, VK remains

near zero. The level of knock intensity is indicated by voltage VK(T) at the end of the gate interval. The

spark control system compares this voltage with a threshold voltage (using an analog comparator) to

determine whether knock has or has not occurred (as shown in knock level detector circuit). The



comparator output voltage is binary valued, depending on the relative amplitude of VK(T) and the

threshold voltage. Whenever VK(T) is less than the threshold voltage, the comparator output is low,

indicating no knock. Whenever VK(T) is greater than the threshold value, the comparator output is high,

indicating knock. Although this scheme for knock detection has shown a constant threshold, there are

some production applications that have a variable threshold. The threshold in such cases increases with

RPM because the competing noises in the engine increase with RPM.

Knock level detector circuit

Spark advance correction methods:

There are generally two classes of correction that are used: fast correction and slow correction. In

the fast correction scheme, the spark advance is decreased for the next engine cycle by a fixed amount

(typically from 5°to 10°) whenever knock is detected. Then the spark advance is advanced in one-degree

increments every 5 to 20 crankshaft revolutions. In the slow correction scheme, spark advance is

decreased by one (or more) degree each time knock is detected, until no knocking is detected. The spark

advance proceeds in one-degree increments after many engine cycles.



UNIT IV: CI ENGINE MANAGEMENT

Fuel injection system parameters affecting combustion, noise and emissions in CI engines. Pilot,

main, advanced post injection and retarded post injection. Electronically controlled Unit Injection

system. Layout of the common rail fuel injection system. Working of components like fuel injector, fuel

pump, rail pressure limiter, flow limiter, EGR valves

Fuel Injection system: It meters the fuel delivery according to engine requirements, it generates the high injection

pressure required for fuel atomization, for air-fuel mixing and for combustion and it contributes to the

fuel distribution in the combustion system-hence it significantly affects engine performance, emissions

and noise.

Parameters affecting combustion:

1. Ignition Delay:

Ignition delay is an important variable in diesel combustion because it has a strong correlation to

the amount of fuel that is burned in the premixed combustion phase. Longer ignition delays

allow more fuel to be injected and prepared for combustion. When ignition finally occurs, it

involves more fuel and produces a violent auto ignition, sometimes called diesel knock. In

addition to being a source of undesirable noise, high levels of premixed combustion contribute to

high nitric oxide (NO) levels in the exhaust.

2. Cetane Number:

3. Compression ratio:



4. Fuel Injection droplet size:

5. Intake temperature:

6. Engine speed:

7. Injection advance:

Noise in CI engines:

The rapid consumption of most of the fuel injected during the ignition delay period in the pre-

mixed burn release heat very rapidly, and the cylinder pressure rises almost instantaneously. This

imparts a large and steep-fronted force pulse to the structure which excites most of the mechanical

resonances and causes the surfaces of the engine to vibrate20. Acoustic radiation from the vibrating

surfaces completes the transmission to the ear. The sound generated by traditional diesel combustion has

a characteristic 'knock'; however the structure responds in the same way to mechanical impacts as the

pistons move in their bores and in the timing drive. Subjectively the noise sounds very similar to

combustion knock if it has a mechanical origin. The first option to reduce combustion noise is to reduce

the ignition delay and hence the quantity of fuel that contributes to the premixed burn. Increasing the

compression ratio, heating the intake air, turbo charging or supercharging, fumigating and reducing heat

transfer into the piston and cylinder head may be deployed to this end.

Emissions in CI engines: Self study: - Already studied in Engines paper



Electronically controlled Unit injection system:

Unit injector: An unit injector occupies lower space and has greater structural rigidity, thereby this type of

injectors can allow much higher injection pressures upto 203 MN/m2 resulting in rapid injection of the

fuel and also to spray it as a finer mist over a larger area through smaller holes in the nozzle. Hence, it

becomes possible to meet stricter emission limits, reduce noise levels and improve fuel consumption.

Construction: In a conventional system, a separately mounted multi-element pump provides the injection

pressure and regulation of fuel quantity for the fuel injectors. In a unit injection system each cylinder-

head-mounted unit injector combines the functions of metering, timing and high-pressure fuel injection.

These functions are performed by the movement of a plunger actually in the unit injector, via a push-rod

and rocker mechanism from the engine camshaft. Each engine cylinder is therefore provided with a self-

contained injection pump-and-nozzle unit, which receives fuel at relatively low pressure from a common

supply system.

Unit injector system – Layout:

In order to vary and control the quantity of fuel that is metered for injection, so that it is correctly related

to engine speed and load, the unit injector system super-imposes a governor and throttle control on the

engine-driven fuel transfer pump that supplies fuel to the unit injectors. Hence, the quantity of fuel that

is metered into them is subject to two variables, namely fuel pressure and metering time.

Disadvantages & Advantages of unit

injection system:

The unit injector system has generally

involved the expensive complication of

additional push-rods with lower and upper

rockers to actuate the injectors from the

engine camshaft, although more recent

versions may benefit from the simplification

of an overhead camshaft and single rocker

actuation of the injectors.

However, the system has the

advantages of eliminating the necessity for

high-pressure fuel pipe-lines between the

pump and injectors and of combining all

metering and injection functions. Other

advantages generally claimed are those of

enabling a wide range of engine speeds to be

attained with quick throttle response and low

idling speeds, and minimum maintenance

requirements.



Electronically controlled unit injection system:

It employs solenoid actuated spill control valves in the high pressure injection circuit. It will be

seen that various sensors provide the electronic control unit (ECU) with the necessary information on

engine operation, this relating to accelerator pedal position, engine speed, camshaft position, air intake

manifold temperature and pressure, and coolant temperature. The information received is then

continuously compared with optimum values stored in the memory of the ECU. As a result the latter can

issue command signals to the solenoid actuated spill control valves of the unit injectors, so that their

nozzles can deliver fuel to the cylinders according to engine requirements. The unit injectors are

supplied with fuel from a low pressure pump and are mounted above the combustion chambers in the

cylinder head, which is furnished with integral passages for the fuel feed and spill functions.

Each unit injector is of the piston type with a spring-returned pumping plunger. It operates

through a fixed stroke and receives its motion from the engine camshaft via an interposed rocker and

tappet assembly. The optimum timing and the fuel quantity required for each individual injection,

corresponding respectively to start of injection and governing in a conventional system, is determined by

the commencement and duration of a command signal from the ECU, which is computed just prior to

injection and then transmitted to the stator of the solenoid actuated spill control valve. This has the

effect of activating the solenoid armature to close the spill control valve, so that as the pumping plunger

continues its down-ward stroke the opening pressure of the injector nozzle valve is rapidly overcome

and fuel is sprayed into the cylinder. When the ECU command signal deactivates the solenoid armature

and allows the spill control valve to regain its open position there is a collapse in pressure and the

injection terminates as the nozzle valve closes in the usual manner. The basic operating sequence of the

unit injector is best visualized with a series of plunger displacement diagrams (operating sequence

diagrams).

Electronic unit injection system – Layout:

Note:

The student can draw the above diagram as a simple block diagram indicating all the components

in the exam. No need for 3D diagram as shown above.



Operating sequence of electronic unit injector:

Common Rail fuel injection system:

The essential difference between this type of fuel injection system and older conventional

systems is that in the common rail system the two functions of pressure generation and injection control

are separately performed. In other words, the high-pressure pump that charges the common rail plays no

part in the metering and timing of the injection process, the opening and closing of solenoid or more

recently piezo activated injectors being solely controlled from the electronic control unit (ECU) of the

engine management system.

A common rail fuel injection system basically comprises the following components:

2. A common rail that takes the form of a manifold-like tube, which is usually mounted at

cylinder head level and connected via short piping runs to the fuel injectors. It acts as a

constant pressure hydraulic accumulator, and is equipped at one end with a pressure

limiting valve and towards the other end with a pressure sensor.

3. A high-pressure plunger pump, which delivers fuel oil through an end connection to the

common rail and its associated piping. It serves only to maintain a constant pressure in

the common rail, since all metering and timing functions for the fuel injection are

performed separately at the fuel injectors themselves.



4. A feed pump, which transfers fuel oil from the supply tank to the high-pressure pump.

These two pumps are typically combined into one unit to provide a compact installation.

5. A protective filter unit, which acts in series with the sup-ply tank and the feed pump.

6. The cylinder head fuel injectors, which are activated by fast-response solenoid or piezo

valves and connected hydraulically to the common rail and electrically to the ECU of the

engine management system.

7. An electronic control unit (ECU), which serves the two-fold purpose of controlling the

pressure of fuel oil in the common rail through the pressure sensor and limiting valve;

and signaling the opening and closing of the solenoid or piezo activated fuel injectors to

perform the injection process. It can also provide an interface with other vehicle systems.

Common rail fuel injection system – Layout:

Fuel pressure system: - Fuel pump, Rail pressure limiter, Flow limiter

The fuel pressure is produced by means of a low-pressure pump that supplies fuel from

the fuel tank via a fuel filter to a high-pressure pump. The ECU controls the operation of the low

pressure pump. The pump location and design is very similar to that used in a petrol fuel injection

system. The high-pressure pump, normally driven at half crankshaft speed by the camshaft, generates

the high fuel pressure which is stored in the common fuel rail, hence the name ‗common rail diesel‘. The

ECU varies the pressure produced by the high-pressure pump up to a maximum pressure of

1350barusing electrically operated solenoid valves within the pump assembly. The ECU varies the fuel

pressure according to engine operating conditions, so the fuel pressure is not directly related to engine

speed. The diesel fuel lubricates the internal cams and plungers of the high-pressure pump.

The fuel pressure produced by the high pressure pump is monitored by the ECU using a

fuel pressure sensor situated in the common rail, so the fuel is always at the correct pressure to suit the

engine operating conditions. The fuel passes from the fuel rail to the injectors in metal fuel pipes. These

pipes are approximately equal in length and manufactured without excessively sharp bends which may

restrict fuel flow. Note that if any of the fuel pipes are disconnected during service or repair they should

be renewed. The pipes are made from steel which deforms to the common rail high pressure pump

connections when tightened, ensuring a fuel-tight seal. The common rail acts as an accumulator or

reservoir of fuel in which pressure fluctuations in the high-pressure system due to the pumping action

and injection are dampened. The fuel rail is also fitted with a fuel pressure regulator, if the fuel pressure

becomes abnormally high; the excess pressure is vented through the pressure-limiting valve to the fuel



tank. The fuel pressure-limiting valve on early generation common rail fuel systems was mechanical.

With later systems, the ECU controls the fuel rail pressure with an electrically operated solenoid valve.

Note that the ECU monitors the fuel pressure in the fuel rail and controls the pressure with a solenoid

valve on the side of the high-pressure pump.

Fuel Injection system:

The ECU controls the injectors in much the same way as in petrol fuel injection. The common

rail fuel system uses many of the sensors that provide information for an electronically controlled

distributor pump diesel fuel system; these include, engine speed sensor fitted to the crankshaft, camshaft

position sensor, accelerator pedal position sensor, MAP sensor, engine coolant and intake air

temperature sensor and air mass sensor. These sensors are used to monitor engine-operating conditions.

The accelerator sensor tells the ECU whether the driver wishes to accelerate, decelerate or allow the

engine to idle while stationary. The ECU uses the sensor information to calculate the desired fuel

pressure, injection volume and duration that produces optimum engine power and torque to meet driver

needs. The fuel pressure within the common rail is constant during injection and therefore the volume of

fuel injected is also constant during the injector-opening period. The precise volume of fuel can be

delivered during the injector-opening period. The injectors are connected to the fuel rail with short,

high-pressure metal fuel pipes. The EDC ECU determines the injector opening period (injector duration)

from sensor information and provides a control signal to the injector accordingly. The high fuel pressure

exerts a great force at the injector needle valve, so a very high voltage and current is required to initially

open the injector. The injector driver control module provides the necessary high voltage control signal

to the injector. The module may be located within the ECU or in some cases fitted as a separate unit.

The ECU uses the engine speed sensor to provide the timing control for each injector, and additional

information is required to synchronize each injector with the cylinder cycle. A cylinder recognition

sensor monitors the camshaft position, which provides the ECU with the information necessary to

control the phasing of the injectors. The injectors are situated in the cylinder head and spray fuel into the

swirling air within the combustion chamber, which is normally integrated into the crown of the piston.

Injector: If current is switched off to the solenoid circuit, the injector needle valve is closed which

prevents pressurized fuel leaving the injector nozzle. The high pressure fuel is applied to the needle

valve at the lower section of the injector and also to a control chamber which is located on top of the

injector needle valve within the top section of the injector. The force of the solenoid spring and the

needle valve spring is higher than the fuel pressure applied and therefore the needle valve remains

closed.

The ECU determines the injection period during which the injector opens and injects a volume of

fuel into the combustion chamber. The ECU provides the injector with a control signal that energizes the

injector solenoid. The solenoid valve lifts, allowing the fuel pressure to escape from the control chamber

into the chamber above. The fuel passing to the chamber returns to the tank via the fuel return system.

The initial current required to lift the solenoid is high due to the force of the spring. Once open, a

smaller current is required to maintain the solenoid position, and the ECU applies this ‗holding current‘.

An orifice restriction prevents the high-pressure fuel from rapidly re-entering the control chamber, as the

control chamber pressure is lower than the fuel pressure applied to the needle valve. Due to the

difference in fuel pressure between the control chamber and the fuel pressure at the needle valve, the

valve lifts from the seat and fuel is expelled through the injector nozzle into the combustion chamber.

The pressure of the injected fuel is equal to the pressure in the fuel rail. The high fuel pressure together

with the design of the injector nozzle allows excellent atomization of the fuel injected, which promotes

good mixing of the air and fuel within the combustion chamber. Thoroughly mixing the air and fuel

reduces the HC and soot emissions.

To end the injection of fuel, the ECU switches off the current flow through the injector solenoid

circuit, allowing the solenoid plunger and valve to return to its seat. The closing of the solenoid valve

allows the control chamber to refill will high-pressure fuel from the fuel rail. The high fuel pressure in



the control chamber, together with the force of the needle valve spring, exerts a greater force than that of

the high fuel pressure at the base of the needle valve; the needle valve returns to its seat and injection

ceases.

Common rail injector: closed position Open position

1. Fuel return

2. Electrical connection

3. Triggering element (solenoid)

4. Fuel inlet from rail – high pressure

5. Valve bell

6. Bleed orifice

7. Feed orifice

8. Valve control chamber

9. Valve control plunger

10. Feed passage to nozzle

11. Nozzle needle



Pilot injection:

Earlier types of diesel fuel system inject all of the fuel during one injector opening period

for one cylinder cycle. There is a short period between the start of injection and the start of

ignition. When the fuel ignites, the cylinder pressure rapidly increases which pushes the piston

down the cylinder. The sharp rise in cylinder pressure is heard and referred to as diesel knock.

The common rail fuel system normally injects fuel in two injection stages. These stages are often

referred to as pilot injection and main injection. A small volume of fuel is injected before the

piston reaches TDC. The small volume of fuel (typically1–4mm3) conditions the cylinder before

the main volume of fuel is injected. The pilot injection raises the cylinder pressure slightly due to

the combustion of the fuel and therefore the heat within the cylinder also rises. If the pilot

injection occurs too early in the compression stroke, the fuel will adhere to the cold cylinder

walls and crown of the piston, increasing hydrocarbons (HC) and soot in the exhaust gases.

Main injection:

The time delay between the point at which the fuel is injected and ignited is reduced due

to the pilot injection providing a slightly higher cylinder temperature and pressure. The rate at

which the combustion pressure increases is slower resulting in a reduction of combustion noise,

lower fuel consumption and lower emission levels. The length of time that the injector is opened

(injector duration) together with the pressure at which the fuel is injected dictates the volume of

fuel delivered to the cylinder. It should be noted that a rise in fuel pressure is used to increase the

volume of fuel delivered to a cylinder and not an increase in the injection duration. At high

engine speeds, insufficient time exists between the stages of injection and it is not possible to

provide pilot injection. The ECU combines both pilot and main stages of injection and uses a

single injector-opening period to inject the volume of fuel required. The ECU monitors any

imbalance between the torque generated between cylinders. After each injection period, the

power stroke occurs which increases the speed of the crankshaft. The ECU monitors the

acceleration speed of the crankshaft using the engine speed sensor signal. If all cylinders are

producing an equal amount of power, the acceleration of the crankshaft between each cylinder

power stroke should also be equal. Engine wear will affect the power produced by each cylinder,

so the ECU has been given the ability to alter the fuel volume and injection timing to each

cylinder to equalize the power produced at low engine speeds. Unequal power between cylinders

is very apparent at idle, and the ECU stabilizes engine speed ensuring a smooth engine idle.

Post injection: To reduce emissions, air fuel ratio is increased to higher values resulting in fuel dilution

inside the engines. As fuel dilution occurs, some of the fuel is not properly burnt and gets

converted into soot. Incorporation of diesel particulate filters is necessary to trap soot. To avoid

filter plugging, however, the accumulated soot needs to be burned off-a plugged filter will cause

high backpressure and operational issues. To avoid this, a regeneration scheme in which fuel is

introduced late in combustion (post injection) to create an exothermic reaction downstream in the

filter, which burns off the soot. The resulting ash from regeneration of the filter can collect for

hundreds of thousands of miles.



UNIT- V VEHICLE MANAGEMENT SYSTEMS ABS system, its need, layout and working. Electronic control of suspension – Damping control, Electric

power steering, Supplementary Restraint System of air bag system – crash sensor, seat belt tightening.

Cruise control. Vehicle security systems- alarms, vehicle tracking system. On board diagnostics.

Collision avoidance Radar warning system.

ABS system: - Self study (already studied in Automotive Chassis)

Electronic control of suspension: The control system for a typical electronic suspension system is depicted in the block diagram of

Figure. The control system configuration in Figure is generic and not necessarily representative of the

system for any production car. This system includes sensors for measuring vehicle speed; steering input

(i.e., angular deflection of steered wheels); relative displacement of the wheel assembly and car

body/chassis; lateral acceleration; and yaw rate. The outputs are electrical signals to the shock

absorber/strut actuators and to the motor/compressor that pressurizes the pneumatic springs (if

applicable).The actuators can be solenoid-operated (switched) orifices or motor-driven variable orifices

or electromagnets for RH fluid-type variable viscosity struts.

The control system typically is in the form of a microcontroller or microprocessor-based digital

controller. The inputs from each sensor are sampled, converted to digital format, and stored in memory.

The body acceleration measurement can be used to evaluate ride quality. The controller does this by

computing a weighted average of the spectrum of the acceleration. The relative body/wheel motion can

be used to estimate tire normal force, and damping is then adjusted to try to optimize this normal force.

The yaw rate sensor provides data which in relationship to vehicle speed and steering input

measurements can be used to evaluate cornering performance. In certain vehicles, these measurements

combine in an algorithm that is used to activate the electro hydraulic brakes.

Damping control:

Under program control in accordance with the control strategy, the electronic control system

generates output electrical signals to the various actuators. The variable damping actuators vary either

the oil passage orifice or the RH fluid viscosity independently at each wheel to obtain the desired

damping for that wheel. There are many possible control strategies and many of these are actually used

in production vehicles. For the purposes of this book, it is perhaps most beneficial to present a

representative control strategy that typifies features of a number of actual production systems.

The important inputs to the vehicle suspension control system come from road roughness

induced forces and inertial forces (due, for example, to cornering or maneuvering), steering inputs, and

vehicle speed. In our hypothetical simplified control strategy these inputs are considered separately.

When driving along a nominally straight road with small steering inputs, the road input is dominant. In

this case, the control is based on the spectral con-tent (frequency region) of the relative motion. The

controller (under program control) calculates the spectrum of the relative velocity of the sprung and

unsprung mass at each wheel (from the corresponding sensor‘s data). Whenever the weighted amplitude

of the spectrum near the peak frequencies exceeds at threshold, damping is increased, yielding a firmer

ride and improved handling. Otherwise, damping is kept low (soft suspension).

If in addition the vehicle is equipped with an accelerometer (usually located in the car body near

the center of gravity) and with motor-driven variable-aperture shock absorbers, then an additional

control strategy is possible. In this latter control strategy, the shock absorber apertures are adjusted to

minimize sprung mass acceleration in the 2 to 8Hz frequency region, thereby providing optimum ride

control. However, at all times, the damping is adjusted to control unsprung mass motion to maintain

wheel normal force variation at acceptably low levels for safety reasons. Whenever a relatively large

steering input is sensed (sometimes in conjunction with yaw rate measurement), such as during a

cornering maneuver, then the control strategy switches to the smaller aperture, yielding a ―stiffer‖



suspension and improved handling. In particular, the combination of cornering on a relatively rough

road calls for damping that optimizes tire normal force, thereby maximizing cornering forces.

Electronic suspension control – layout:

Adjustable shock absorber Force versus Relative Velocity of a

Solenoid-Switched Aperture Shock

Absorber

Electronic steering control: The steering effort required of the driver to overcome restoring torque generally decreases with

vehicle speed and increases with steering angle. Traditionally, the steering effort required by the driver

has been reduced by incorporating a hydraulic power steering system in the vehicle. Whenever there is a

steering input from the driver, hydraulic pressure from an engine-driven pump is applied to a hydraulic

cylinder that boosts the steering effort of the driver. Typically, the effort available from the pump

increases with engine speed (i.e., with vehicle speed), whereas the required effort decreases. It would be



desirable to reduce steering boost as vehicle speed increases. Such a feature is incorporated into a power

steering system featuring electronic controls. An electronically controlled power steering system adjusts

steering boost adaptively to driving conditions. Using electronic control of power steering, the available

boost is reduced by controlling a pressure relief valve on the power steering pump.

An alternative power steering scheme utilizes a special electric motor to provide the boost

required instead of the hydraulic boost. Electric boost power steering has several advantages over

traditional hydraulic power steering. Electronic control of electric boost systems is straightforward and

can be accomplished without any energy conversion from electrical power to mechanical actuation.

Moreover, electronic control offers very sophisticated adaptive control in which the system can adapt to

the driving environment.

An example of an electronically controlled steering system that has had commercial production

is for four-wheel steering systems (4WS). In the 4WS-equipped vehicles, the front wheels are directly

linked mechanically to the steering wheel, as in traditional vehicles. There is a power steering boost for

the front wheels as in a standard two-wheel steering system. The rear wheels are steered under the

control of a microcontroller via an actuator. Figure 8.23 is an illustration of the 4WS configuration. In

this illustration, the front wheels are steered to a steering angle δf by the driver‘s steering wheel input. A

sensor (S) measures the steering angle and another sensor (U) gives the vehicle speed. The

microcontroller (C) determines the desired rear steering angle δr under program control as a function of

speed and front steering angle. The details of the control strategy are proprietary and not available for

this book. However, it is within the scope of this book to describe a representative example control

strategy as follows. For speeds below 10mph, the rear steering angle is in the opposite direction to the

front steering angle. This control strategy has the effect of decreasing the car‘s turning radius by as

much as 30% from the value it has for front wheel steering only. Consequently, the maneuvering ability

of the car at low speeds is enhanced (e.g., for parking).At intermediate speeds (e.g., 11mph <U

<30mph), the steering might be front wheel only. At higher speeds (including highway cruise), the front

and rear wheels are steered in the same direction. At least one automaker has an interesting strategy for

higher speeds (e.g., at highway cruise speed). In this strategy, the rear wheels turn in the opposite

direction to the front wheels for a very short period (on the order of one second) and then turn in the

same direction as the front wheels. This strategy has a beneficial effect on maneuvers such as lane

changes on the highway. Figure illustrates the lane change for front wheel steering and for this latter

4WS strategy, in which the same front steering angle was used. Notice that the 4WS strategy yields a

lane change in a shorter distance and avoids the overshoot common in a standard-steering vehicle.

Turning the wheels in the same direction at cruising speeds has another benefit for a vehicle towing a

trailer. When front and rear wheels turn in the same direction, the angle between the car and trailer axes

is less than it is for front wheel steering only. The reduction in this angle means that the lateral force

applied to the rear wheels by the trailer in curves is less than that for front wheel only steering. This

lateral force reduction improves the stability of the car or truck/trailer combination relative to front

steering only.



AIRBAGS

An air bag slows the passenger's speed to zero with little or no damage. The constraints that it

has to work within are huge. The air bag has the space between the passenger and the steering wheel or

dash board and a fraction of a second to work with. Even that tiny amount of space and time is valuable,

if the system can slow the passenger evenly rather than forcing an abrupt halt to his/her motion.

Operation of the system

The sequence of events in the case of a frontal impact at about 35 km/h, as shown in figure below is as

follows.

1. The driver is in the normal seating position prior to impact. About 15 ms after the impact, the vehicle

is strongly decelerated and the threshold for triggering the airbag is reached. The igniter ignites the fuel

tablets in the inflater.

2. After about 30 ms the airbag unfolds and the driver will have moved forwards as the vehicle‘s

crumple zones collapse. The seat-belt will have locked or been tensioned depending on the system.

3. At 40 ms after impact the airbag will be fully inflated and the driver‘s momentum will be absorbed by

the airbag.

4. About 120 ms after impact the driver will be moved back into the seat and the airbag will have almost

deflated through the side vents, allowing driver visibility.

The main components of a basic airbag system are as follows.

Driver and passenger airbags.

Warning light.

Passenger seat switches.

Pyrotechnic inflater.

Igniter.

Crash sensor(s).

Electronic control unit.



There are three parts to an air bag that help to accomplish this feature.

1. The bag itself is made of a thin, nylon fabric with a coating on the inside. Prior to inflation it is

folded under suitable padding, into the steering wheel or dashboard or, more recently, the seat or

door. The driver‘s air has a volume of about 60 litres and the passenger airbag about 160 litres.

2. The sensor is the device that tells the bag to inflate. Inflation happens when there is a collision

force equal to running into a brick wall at 10 to 15 miles per hour (16 to 24 km per hour). A

mechanical switch is flipped when there is a mass shift that closes an electrical contact, telling

the sensors that a crash has occurred. The sensors receive information from an accelerometer

built into a microchip.

3. The air bag's inflation system (igniter and inflater) reacts sodium azide (NaN3) with potassium

nitrate (KNO3) to produce nitrogen gas. Hot blasts of the nitrogen inflate the air bag.

4. A warning light is used as part of the system monitoring circuit. This gives an indication of a

potential malfunction and is an important part of the circuit. Some manufacturers use two bulbs

for added reliability.

The pyrotechnic inflater and the igniter can be considered together. The inflater in the case of the driver

is located in the centre of the steering wheel. It contains a number of fuel tablets in a combustion

chamber. The igniter consists of charged capacitors, which produce the ignition spark. The fuel tablets

burn very rapidly and produce a given quantity of nitrogen gas at a given pressure.

The air bag system ignites the solid propellant, which burns extremely rapidly to create a large volume

of gas to inflate the bag. The bag then literally bursts from its storage site at up to 200 mph (322 kph) --

faster than the blink of an eye! This gas is forced into the airbag through a filter and the bag inflates

breaking through the padding in the wheel centre. A second later, the gas quickly dissipates through tiny

holes in the bag, thus deflating the bag so you can move. After deployment, a small amount of sodium

hydroxide will be present in the airbag and vehicle interior. Personal protection equipment must be used

when removing the old system and cleaning the vehicle interior.

Even though the whole process happens in only one-twenty-fifth of a second, the additional time is

enough to help prevent serious injury. The powdery substance released from the air bag, by the way, is

regular cornstarch or talcum powder, which is used by the air bag manufacturers to keep the bags pliable

and lubricated while they're in storage.

If a failure is detected in any part of the circuit then the ECU operates a warning light.

The crash sensor can take a number of forms; these can be described as mechanical or electronic. The

mechanical system, as shown in the figure, works by a spring holding a roller in a set position until an

impact above a predetermined limit, provides enough force to overcome the spring and the roller moves,

triggering a micro switch.



Mechanical Crash Sensor

The switch is normally open with a resistor in parallel to allow the system to be monitored. Two

switches similar to this may be used to ensure the bag is deployed only in the case of sufficient frontal

impact. Note that the airbag is not deployed in the event of a roll over.

The other main type of crash sensor can be described as an accelerometer. This will sense deceleration,

which is negative acceleration.

Airbags working on the same techniques to those described previously are being used to protect against

side impacts. In some cases bags are stowed in the door pillars or the edge of the roof.

Air Bag Inflation



Air Bag Air Bag Inflation Device

SEAT BELT TIGHTENING SYSTEM [The Pre-tensioner]

Taking the ‗slack‘ out of a seat-belt in the event of an impact is a good contribution to vehicle passenger

safety. The decision to take this action is the same as for the airbag inflation. The two main types of

tensioners are:

Spring tension.

Pyrotechnic.

The mechanism used by one type of seat-belt tensioner is shown in figure below. When the explosive

charge is fired, the cable pulls a lever on the seat-belt reel, which in turn tightens the belt. The unit must

be replaced once deployed. This feature is sometimes described as anti-submarining.The idea of a Pre-

tensioner is to tighten up any slack in the belt webbing in the event of a crash. Whereas the conventional

locking mechanism in a retractor keeps the belt from extending any farther, the Pre-tensioner actually

pulls in on the belt. This force helps move the passenger into the optimum crash position in his or her

seat. Pre-tensioners normally work together with conventional locking mechanisms, not in place of

them.

There are a number of different Pre-tensioner systems on the market. Some Pre-tensioners pull the entire

retractor mechanism backward and some rotate the spool itself. Generally, Pre-tensioners are wired to

the same central control processor that activates the car's air bags. The processor monitors mechanical or

electronic motion sensors that respond to the sudden deceleration of an impact. When an impact is

detected, the processor activates the Pre-tensioner and then the air bag.

Some Pre-tensioners are built around electric motors or solenoids, but the most popular designs today

use pyrotechnics to pull in the belt webbing. The diagram below shows a representative model.

The central element in this Pre-tensioner is a chamber of combustible gas. Inside the chamber, there is a

smaller chamber with explosive igniter material. This smaller chamber is outfitted with two electrodes,

which are wired to the central processor.



When the processor detects a collision, it immediately applies an electrical current across the electrodes.

The spark from the electrodes ignites the igniter material, which combusts to ignite the gas in the

chamber. The burning gas generates a great deal of outward pressure. The pressure pushes on a piston

resting in the chamber, driving it upward at high speed.

A rack gear is fastened to one side of the piston. When the piston shoots up, the rack gear engages a gear

connected to the retractor spool mechanism. The speeding rack rotates the spool forcefully, winding up

any slack belt webbing.

Load Limiters

In severe crashes, when a car collides with an obstacle at extremely high speed, a seatbelt can inflict

serious damage. As a passenger's inertial speed increases, it takes a greater force to bring the passenger

to a stop. In other words, the faster you're going on impact, the harder the seatbelt will push on you.

Some seatbelt systems use load limiters to minimize belt-inflicted injury. The basic idea of a load limiter

is to release a little more excess belt webbing when a great deal of force is applied to the belt. The

simplest load limiter is a fold sewn into the belt webbing. The stitches holding the fold in place are

designed to break when a certain amount of force is applied to the belt. When the stitches come apart,

the webbing unfolds, allowing the belt to extend a little bit more.

More advanced load limiters rely on a torsion bar in the retractor mechanism. A torsion bar is just a

length of metal material that will twist when enough force is applied to it. In a load limiter, the torsion

bar is secured to the locking mechanism on one end and the rotating spool on the other. In a less severe

accident, the torsion bar will hold its shape, and the spool will lock along with the locking mechanism.

But when a great deal of force is applied to the webbing (and therefore the spool), the torsion bar will

twist slightly. This allows the webbing to extend a little bit farther.

Over the years, seatbelts have proven to be far and away the most important safety device in cars and

trucks. They are by no means infallible, however, and car safety engineers see a lot of room for

improvement in today's design. In the future, cars will be outfitted with better belts, better air bags and,

most likely, completely new safety technology. Of course, the government will still have to address the

biggest problem with safety devices -- getting people to use them.



Case Study: Toyota automatic seat belt tensioner

In the event of an impact, gas is discharged from the horizontal cylinder on the right, into the chamber

above the plunger, which it forces downwards. Dragging the pre-tensioner cable with it, the plunger thus

pre-tensions the seat belt for the duration of the impact, after which the tension is progressively released

as the gas escapes through the clearances round the cable and plunger.

Cruise control system:

Cruise control is a system that automatically controls the speed of a motor vehicle. The system

takes over the throttle of the car to maintain a steady speed as set by the driver. In the case of a cruise

control, the variable being regulated is the vehicle speed. The driver manually sets the car speed at the

desired value via the accelerator pedal. Upon reaching the desired speed the driver activates a

momentary contact switch that sets that speed as the command input to the control system. From that

point on, the cruise control system maintains the desired speed automatically by operating the throttle

via a throttle actuator. Under normal driving circumstances, the total drag forces acting on the vehicle

are such that a net positive traction force (from the power train) is required to maintain a constant

vehicle speed. Most systems do not allow the use of the cruise control below a certain speed (normally

around 25 mph). The vehicle will maintain the desired speed by pulling the throttle cable with a

solenoid, a vacuum driven servomechanism, or by using the electronic systems built into the vehicle

(fully electronic) if it uses a 'drive-by-wire' system.

All cruise control systems must be capable of being turned off both explicitly and automatically

when the driver depresses the brake and often also the clutch. Cruise control often includes a memory

feature to resume the set speed after braking and a coast feature to reduce the set speed without braking.



When the cruise control is engaged, the throttle can still be used to accelerate the car, but once the pedal

is released the car will then slow down until it reaches the previously set speed.

The configuration for a typical automotive cruise control is shown in Figure. The momentary

contact (pushbutton) switch that sets the command speed is denoted S1in Figure. Also shown in this

figure is a disable switch that completely disengages the cruise control system from the power supply

such that throttle control reverts back to the accelerator pedal. This switch is denoted S2in Figure and is

a safety feature. In an actual cruise control system the disable function can be activated in a variety of

ways, including the master power switch for the cruise control system, and a brake pedal–activated

switch that disables the cruise control any time that the brake pedal is moved from its rest position. The

throttle actuator opens and closes the throttle in response to the error between the desired and actual

speed. Whenever the actual speed is less than the desired speed the throttle opening is increased by the

actuator, which increases vehicle speed until the error is zero, at which point the throttle opening

remains fixed until either a disturbance occurs or the driver calls for a new desired speed.

Cruise control configuration

Digital cruise control:

The operation of the cruise control system can be further understood by examining the vehicle speed

sensor and the actuator in detail. Figure a is a sketch of a sensor suitable for vehicle speed measurement.

In a typical vehicle speed measurement system, the vehicle speed information is mechanically coupled

to the speed sensor by a flexible cable coming from the driveshaft, which rotates at an angular speed



proportional to vehicle speed. A speed sensor driven by this cable generates a pulsed electrical signal

(Figure b) that is processed by the computer to obtain a digital measurement of speed. A speed sensor

can be implemented magnetically or optically.

Fig a Fig b

Throttle actuator:

The throttle actuator is an electromechanical device that, in response to an electrical input from

the controller, moves the throttle through some appropriate mechanical linkage. Two relatively common

throttle actuators operate either from manifold vacuum or with a stepper motor. The throttle opening is

either increased or decreased by the stepper motor in response to the sequences of pulses sent to the two

windings depending on the relative phase of the two sets of pulses. The throttle actuator that is operated

by manifold vacuum through a solenoid valve is similar to that used for the EGR valve described in

Chapter 7and further explained later in this chapter. During cruise control operation the throttle position

is set automatically by the throttle actuator in response to the actuator signal generated in the control

system. This type of manifold-vacuum-operated actuator is illustrated in Figure. A pneumatic piston

arrangement is driven from the intake manifold vacuum. The piston-connecting rod assembly is attached

to the throttle lever. There is also a spring attached to the lever. If there is no force applied by the piston,

the spring pulls the throttle closed. When an actuator input signal energizes the electromagnet in the

control solenoid, the pressure control valve is pulled down and changes the actuator cylinder pressure by

providing a path to manifold pressure. Manifold pressure is lower than atmospheric pressure, so the

actuator cylinder pressure quickly drops, causing the piston to pull against the throttle lever to open the

throttle.

The force exerted by the piston is varied by changing the average pressure in the cylinder

chamber. This is done by rapidly switching the pressure control valve between the outside air port,

which provides atmospheric pressure, and the manifold pressure port, the pressure of which is lower

than atmospheric pressure. In one implementation of a throttle actuator, the actuator control signal Vc is

a variable-duty-cycle type of signal like that discussed for the fuel injector actuator. A high Vc signal

energizes the electromagnet; a low Vc signal deenergizes the electromagnet. Switching back and forth

between the two pressure sources causes the average pressure in the chamber to be somewhere between

the low manifold pressure and outside atmospheric pressure. This average pressure and, consequently,

the piston force are proportional to the duty cycle of the valve control signal Vc. The duty cycle is in

turn proportional to the control signal d(explained above) that is computed from the sampled error signal

en. This type of duty-cycle-controlled throttle actuator is ideally suited for use in digital control systems.

If used in an analog control system, the analog control signal must first be converted to a duty-cycle

control signal. The same frequency response considerations apply to the throttle actuator as to the speed



sensor. In fact, with both in the closed-loop control system, each contributes tothe total system phase

shift and gain.

Stepper Motor actuator:

An illustrative example of driver circuitry for a stepper motor actuator is shown in Figure. The

basic idea for this circuitry is to continuously drive the stepper motor to advance or retard the throttle in

accordance with the control signal that is stored in memory. Just as the controller periodically updates

the actuator control signal, the stepper motor driver electronics continually adjusts the throttle by an

amount determined by the actuator signal. This signal is, in effect, a signed number (i.e., a positive or

negative numerical value). A sign bit indicates the direction of the throttle movement (advance or

retard). The numerical value determines the amount of advance or retard. The magnitude of the actuator

signal (in binary format) is loaded into a parallel load serial down-count binary counter. The direction of

movement is in the form of the sign bit (SB of Figure 8.9). The stepper motor is activated by a pair of

quadrature phase signals (i.e., signals that are a quarter of a cycle out of phase) coming from a pair of

oscillators. To advance the throttle, phase A signal is applied to coil 1 and phase B to coil 2. To retard

the throttle these phases are each switched to the opposite coil. The amount of movement in either

direction is determined by the number of cycles of A and B, one step for each cycle. The number of

cycles of these two phases is controlled by a logical signal (Zin Figure 8.9). This logical signal is

switched high, enabling a pair of AND gates (from the set A1, A2, A3, A4). The length of time that it is

switched high determines the number of cycles and corresponds to the number of steps of the motor.

The logical variable Z corresponds to the contents of the binary counter being zero. As long as Z is not

zero, a pair of AND gates (A1 and A3, or A2and A4) are enabled, permitting phase A and phase B

signals to be sent to the stepper motor. The pair of gates enabled is determined by the sign bit. When the

sign bit is high, A1 and A3 are enabled and the stepper motor advances the throttle as long as Zis not

zero. Similarly, when the sign bit is low, A2 and A4are enabled and the stepper motor retards the

throttle. To control the number of steps, the controller loads a binary value into the binary counter. With

the contents not zero the appropriate pair of AND gates is enabled. When loaded with data, the binary

counter counts down at the frequency of a clock (CKin Figure 8.9). When the countdown reaches zero,

the gates are disabled and the stepper motor stops moving. The time required to count down to zero is

determined by the numerical value loaded into the binary counter. By loading signed binary numbers



into the binary counter, the cruise controller regulates the amount and direction of movement of the

stepper motor and thereby the corresponding movement of the throttle.

Vehicle security systems – Anti theft systems:

Anti-theft systems are designed to raise the difficulty of theft to an infeasible (but not necessarily

impossible) level. The kind of system implemented often depends on the acceptable threshold for theft.

Under normal circumstances, theft is prevented simply through the application and social acceptance of

property law. Ownership is often indicated by means of visual marking (license plates, name tags).

When clear owner identification is not possible and when there is a lack of social observance, people

may be inclined to take possession of items to their own benefit at the expense of the original owner.

Motive and opportunity are two enabling factors for theft. Given that motives for theft are varied and

complex and are generally speaking not within the control of the victim, most methods of theft

prevention rely on reducing opportunities for theft.

Three main types of intruder alarm are used in modern passenger cars are:

Switch operated on all entry points.

Battery voltage sensed.

Volumetric sensing.

Three main ways to disable the vehicle, in case of intrusion are:

Ignition circuit cut off.

Starter circuit cut off.

Engine ECU code lock.



Disabling the stolen item

Items with specific functionality can often be disabled to prevent the use of the item if it should be

stolen. The anti-theft system can require disabling on every use, or enabling when the item needs to be

secured. Disabling the anti-theft system is usually done by requiring identification of the owner at some

stage of use. Identification can occur through physical or other means (physical keys, numerical codes,

complex passwords, biometric identification). A passive immobilizer makes car theft almost impossible

because the vehicle cannot be started without a computer chip that is found within the ignition key.

Movement inhibitors (immobilizer) as anti theft system:

Movement inhibitors may be mechanical or automatic electronic system. Mechanically at least one

locking member that can be inserted into at least one inhibitor to prevent at least one wheel from turning

by utilizing a long steel bar that hooks and locks onto the steering wheel or by preventing inadvertent

movement of a motor vehicle gear shift selector brake interlock mechanism, between a non-drive "park"

or "neutral" position, and a "drive" position. Steering columns lock inhibitor for fixed and adjustable

steering columns preferably without a shifting function. Shield type devices are available to adjust to fit

most steering wheels, one-, two-, and three-spoke.

Passive anti-theft systems (PATS), like Ford's patented ‗SecuriLock T’ systems; protect against theft by

requiring a specially coded ignition key. The vehicle starts and operates only with the key that matches

the sensor in the vehicle, thwarting attempts to hot-wire the ignition. An indicator lamp shows the

system is working.

Stolen Car Tracking Devices

Tracking devices can be built-in to an unknown part of the vehicle‘s chassis. This can be activated in the

event of the car being stolen, allowing the police to trace the vehicle. The ‗Tracker‘ unit is a radio

transponder. When the vehicle is reported stolen the police are informed and the ‗Tracker‘ unit is

activated. The unit then broadcasts a unique reply code, which can be detected and decoded by police

tracking computers, which are fitted in police cars, helicopters and fixed land sites. The police then track

the vehicle, taking appropriate action.

Passive anti-theft system (PATS)

This system is a vehicle immobilizer developed by Ford. It is activated directly through the ignition

switch by means of an electronic code stored in a special key. Each key has a transponder that stores the

code, which does not require a battery. The key code is read by the receiver (which is part of the ignition

switch) when the key is turned from position 0 to 1 or 2 (usually marked as I or II). If the code matches

the one stored in the module, then it allows the engine to start. These systems operate independently of

the alarm.

Electronic Keys (aka immobilizers): Some car manufacturers have pre-installed electronic

immobilizing systems that allow the vehicle to operate only with a correctly coded key. The RFID chip



in the key fob contains a select set of codes designed to work with a given car. These codes are rolling

40-bit strings: With each use, the code changes slightly, creating about 1 trillion possible combinations

in total. When you push the unlock button, the key-fob sends a 40-bit code, along with an instruction to

unlock the car doors. If the synced-up receiver gets the 40-bit code it is expecting, the vehicle performs

the instruction. If not, the car does not respond.

A second antitheft use of RFID is for remote vehicle immobilizers. These tiny chips, embedded inside

the plastic head of the ignition keys, are used with more than 150 million vehicles today. Improper use

prevents the car's fuel pump from operating correctly. Unless the driver has the correct key chip

installed, the car will run out of fuel a few blocks from the attempted theft. (That's why valet keys don't

have the chips installed; valets need to drive the car only short distances.)

Benefits: These interrupt your car's ignition systems when an incorrect key or no

key at all is used to start the car. Systems are easy to use and reliable.

Drawbacks: Because they're invisible to thieves, inexperienced criminals will tear apart your

steering column before discovering this disabling feature. Unfortunately, your steering column

will need replacement and you probably won't be able to start your car.

Electronic Tracking Devices: An electronic transmitter hidden in the vehicle which emits a signal that

is picked up by the police or a monitoring station. Alpine's Mobile Mayday, Force‘s Tracker, Ford's

Rescu, GM's OnStar, LoJack, BlackJax, and PageTrack2 from Motorola start at $300, plus any monthly

subscription charges. There are a variety of services offered by each company, such as mapping services

and vehicle-location if your car is stolen.

Benefits: Very effective in helping authorities recover vehicles before they can be

stripped or chopped up.

Drawbacks: In addition to the high initial cost, a subscription charge ($15-$40) must be paid

each month.

Flashing LED warning lights: Warning lights typically identify a vehicle whose alarm system has been

armed. At a quick glance, the thief doesn't know that the warning light is bogus and may go on to

another vehicle rather than take a risk.

Benefits: An inexpensive way to bluff a car thief.

Drawbacks: None

Hood locks: A hood lock will keep a thief from getting to your car's battery to cut the power going to

the alarm.

Benefits: Prevents thieves from gaining access to your vehicle's engine

compartment.

Drawbacks: None - Usually standard equipment on vehicles made in the past 20 years.



Keyless entry: Increases your personal safety by enabling you to enter and exit your vehicle without

fumbling with your keys. Keyless entry enables you to lock & unlock your vehicle without using your

keys, thereby increasing the chances that you will lock it. It's also handy when you've got your hands

full and need to open your car doors or trunk. Keyless entry comes as standard equipment on many

makes and models and can be retrofitted to any vehicle that has electric door locks.

Benefits: Enables you to lock & unlock your vehicle & truck without using your

keys. Increases your personal safety by enabling you to enter and exit your vehicle without

fumbling with your keys. Also eliminates problems caused by frozen lock cylinders.

Drawbacks: None

Passive keyless entry systems1 mean the driver doesn‘t even need to press a button to unlock the

vehicle! The electronic key is simply carried in a pocket, on a belt clip or in a bag. The controllers in the

doors communicate with the key using radio frequency (RF). This action determines if the correct key is

present and, if it is, the doors are unlocked. This communication event is triggered by lifting the door

handle, or in some cases the vehicle will even unlock as the key holder approaches it.

Figure given below shows a block diagram of a typical system incorporating a ‗smart‘ ignition key

which allows several functions to be controlled. Besides its primary function of door lock control, each

driver could have their own personalized key that would program several vehicle functions for that

person such as seat position and mirror setting. Clever car thieves who captured the transmitted key

codes of upmarket vehicles using data recording equipment and then used them to gain access have been

thwarted by the development of rolling code generators that allow a unique code to be generated every

time the RKE system is activated. Full immobilization includes shutting off the vehicle‘s fuel pump, fuel

injectors, ignition, and starter while locking the transmission and steering, and causing the horn to sound

and lights to flash. Additionally, the vehicle‘s cell phone could broadcast its position via a Global

Position Satellite receiver to police authorities.



Kill Switches: Kill switches prevent the flow of electricity or fuel to the engine until the switch is

activated. Starter disablers are also growing in popularity.

Benefits: It's a hidden switch that needs to be flipped on for the car to start. For their

effectiveness as a security device, kill switches are for the most part inexpensive and easy to

install.

Drawbacks: A risk is that the driver may accidentally engage them while driving. Improperly

installed switches can damage the electrical systems on new cars and have the additional

drawback of voiding your new-car warranty.

Steering Column Armored Collars: Collars prevent thieves from breaking into the steering column to

hot-wire the vehicle. Some are installed permanently and others must be installed manually each time

the driver leaves the vehicle.

Benefits: The collar provides an excellent line of defense for older vehicles, which

can be easily stolen by breaking open the steering wheel column.

Drawbacks: Manual collars must be removed whenever you go for a drive.

Steering Wheel Lock: A long metal bar with a lock that fits on the steering wheel and is designed to

prevent the steering wheel from being turned. The locks are visible from outside the car and prevent the

wheel from being turned more than a few degrees. A variation on the steering wheel lock is the J-bar or

grip lock, an adjustable steel bar rod that hooks under the brake and locks to the steering wheel.

Benefits: Inexpensive way to keep would-be thieves away. Especially good device

to use when layering protection.

Drawbacks: Only effective against amateurs and kids looking to joyride. A professional can

cut through your steering wheel in a couple of seconds, making steering-wheel locks and most J-

bars useless.

Theft-Deterrent Decals: Typical decals identify the vehicle is protected by either an alarm system or

national theft prevention company. At a quick glance, the thief may not know that the warning sticker is

bogus and may go on to another vehicle rather than take a risk.

Benefits: Inexpensive way to bluff a car thief.

Drawbacks: Ignored by professional thieves who recognize bogus stickers

Tire Locks: Similar to the circular steel "boots" used by many larger city police departments, tire locks

make the car nearly impossible to move. The tire locks are also effective in deterring would-be thieves.

Benefits: Greatly hampers thieves who are looking to make a quick getaway. Not

only is the tire lock a strong visual deterrent, but it also provides a formidable challenge for

would-be car thieves.



Drawbacks: Bulky and time consuming to install and remove, must be installed manually each

time the driver leaves the vehicle. Accumulates dirt from the tires, very inconvenient to use in

bad weather.

Window Etching: Etching the vehicle identification number onto the window as well as other parts of

the car discourages thieves from taking the vehicle and also aids in recovering the vehicle if it is stolen.

Benefits: Chop-shop rings thrive on vehicles with easily removable VINs or none

etched on at all. By etching the VIN on important parts of the vehicle, you make your vehicle

less attractive to stolen parts resellers.

Drawbacks: Unless you make the etchings extremely obvious (which will severely hurt your

vehicle's resale value) it won't deter most professional thieves, as they may not have the time to

check for etchings before they steal your vehicle.

Pagers: Pagers will let you know when your alarm has been set off. 2-way systems allow you to send

commands to and get feedback from your vehicle.

Benefits: Pagers let you know when your alarm has been set off.

Drawbacks: Encourages confrontation with car thieves, which is not generally a good idea.

Car Alarms: The typical car alarm is equipped with motion sensors, impact sensors and a loud siren or

series of tones in the 120-decibel range.

Benefits: The best alarms arm themselves automatically when you leave the vehicle

and include an automatic kill switch. The best models flash the headlights and honk the horn in

addition to sounding a siren.

Drawbacks: After years of false alarms, people have stopped paying attention to alarms. There

is no statistical evidence that they reduce auto theft.

Security Alarm

A separate switch or IR transmitter can be used to set an alarm system. Often, they are set automatically

when the doors are locked.

The requirements of this particular alarm system are:

It must activate when a door is opened.

The ignition to be disabled.

The existing horn is used as the warning.

Once triggered, the horn must continue even when the door is closed.

It must reset after 15 seconds.



Simple alarm circuit

When a door is opened, the switches make an earth connection. This will be used to trigger the relay,

which in turn will operate the horn. The delay must be built in using a capacitor, which will keep the

relay energized even after the door closes, for a further 15 seconds. An external key switch is to be used

to arm and disarm whilst isolating the ignition supply. A capacitor will discharge to about 66% of its full

value in CR seconds. (If the supply voltage is 12V, the capacitor discharges to 8V in CR seconds.)

This system can be operated by remote control or using the key in a door lock. When first activated, the

system checks that the doors and tailgate are closed by monitoring the appropriate switches. If all is in

order, the anti-theft system is then activated after a 20-second delay. The function indicator LED flashes

rapidly during this time and then slowly once the system is fully active. The alarm can be triggered in a

number of ways:

Opening a door, the tailgate or the bonnet/hood.

Removal of the radio connector loop.

Switching on the ignition.

Movement inside the vehicle.

If the alarm is triggered the horn operates for 30 seconds and the hazard lights for 5 minutes. This stops

if the remote key or door key is used to unlock the vehicle.



Most security alarm systems can be considered as two pieces, with a separate control unit and siren;

most will have the control unit in the passenger compartment and the siren under the bonnet.

Most systems now come with two infrared remote ‗keys‘ that use small button-type batteries and have

an LED that shows when the signal is being sent. They operate with one vehicle only. Intrusion sensors

such as car movement and volumetric sensing can be adjusted for sensitivity. shows a block diagram of

a complex alarm system.

The system can be considered as a series of inputs and outputs.

Inputs

Ignition supply.

Engine crank signal.

Volumetric sensor.

Bonnet switch.

Trembler switch.

IR/RF remote (Figure 16.27).

Doors switches.

Control switch.

Outputs

Volumetric transmitter.

System LED.

Horn or siren.

Hazard lights.

Ignition immobilizer.

Loop circuit.

Electric windows, sun-roof and door locks.

Central Locking System

When the key is turned in the driver‘s door lock, all the other doors on the vehicle should also lock.

Motors or solenoids in each door achieve this. If the system can only be operated from the driver‘s door

key, then an actuator is not required in this door. If the system can be operated from either front door or

by remote control, then all the doors need an actuator. Vehicles with sophisticated alarm systems often

lock all the doors as the alarm is set.



Door lock circuit Motor Reverse circuit

The main control unit contains two change-over relays (as shown in the above figure), which are

actuated by either the door lock switch or, if fitted, the remote infrared key. The motors for each door

lock are simply wired in parallel and all operate at the same time. Infrared central door locking is

controlled by a small hand-held transmitter and an infrared sensor receiver unit as well as a decoder in

the main control unit. When the infrared key is operated by pressing a small switch, a complex code is

transmitted. The number of codes used is well in excess of 50,000. The infrared sensor picks up this

code and sends it in an electrical form to the main control unit. If the received code is correct, the relays

are triggered and the door locks are either locked or unlocked.

Door lock Actuator Remote key and Transmitter

If an incorrect code is received on three consecutive occasions when attempting to unlock the doors,

then the infrared system will switch itself off until the door is opened by the key. This will also reset the

system and allow the correct code to operate the locks again. This technique prevents a scanning type

transmitter unit from being used to open the doors.



ONBOARD DIAGNOSTIC SYSTEM [OBD] – Self Diagnosis system

Self-diagnosis is the capacity of a vehicle system (or more precisely the system ECU) to detect

system operating faults, and provide an indication that a specific fault exists. Self-diagnosis was initially

fitted to fuel and ignition systems, but it has become increasingly fitted to most vehicle systems with

electronic control.

Self-diagnosis was introduced to overcome anumber of potential problems.

1. One aim of self-diagnosis is to overcome the problems of working and diagnosing faults associated

with ‗new technology‘. This is especially important as each new vehicle system is introduced. Repair

technicians need to be able to identify faults relatively quickly and easily.

2. Fast and accurate diagnosis should help to reduce warranty costs, while retaining customer loyalty

and satisfaction.

3. The self-diagnosis system can be used during vehicle assembly to ensure that each vehicle leaves the

assembly plant without detectable faults.

4. Importantly, modern engine management systems and emission control systems are fitted to vehicles

to ensure that emission levels remain low and within legislated limits. Many faults that would result in

unacceptable emissions can remain undetected by the driver. With a self-diagnostic system, it is possible

to provide a warning to the driver or the workshop technician, along with an indication of what the fault

is.

5. Modern vehicle systems rely on complex software programs within the ECU as well as electrical and

electronic systems. In a high percentage of cases, technicians are not familiar with these ‗new‘

technologies. Self-diagnostic systems are designed to support technicians on unfamiliar aspects of anew

motor vehicle.

Fault codes, Blink codes and fault related messages:

Once the ECU has recognized that a fault exists on a vehicle system, it is able to implement

other functions. The following list covers the common functions performed by the ECU when a fault is

recognised.1The ECU can illuminate a dashboard warning light to indicate to the driver that a fault

exists.2A system failure, such as a sensor fault, could cause the engine to run poorly and generate high

emissions. Under these conditions, the ECU might be able to control the engine management system so

that it operates in a ‗limp home‘ or ‗fail safe‘ mode. When the ECU implements limp home operation, it

normally substitutes a preset value for the failed sensor, which should ensure reasonable

engineoperation.3The ECU can provide some form of coded output (fault code) which is accessed or

retrieved by a ‗fault code reader‘ or through other means such as a ‗blink code‘ transmitted via the

dashboard warning light or via an LED based test tool. A fault code usually consists of a number (or

series of numbers), although some systems provide a series of letters or even a short message. As

explained later in this section, some standardization has been adopted across all vehicles for fault code



systems, whereby specific faults are allocated a dedicated code number. This standardization generally

only applies to emissions related faults, but inevitably embraces the engine management system.

Methods of retrieving fault codes:

As mentioned above, fault codes can be retrieved from the vehicle ECU using a fault code reader

which, when connected to the ECU, displays a code number related to the fault. Many systems, however

(especially older on- systems and engine management systems), provide what is often referred to as a

‗blink code‘. A blink code can be output by the ECU to the dashboard warning light, and the number of

flashes on the warning light corresponds to the relevant code number. Some systems use an LED light

(often located on the ECU) or codes might be accessed by connecting a separate LED tester (or a volt or

dwell meter). When a fault code number has been retrieved, the technician refers to the appropriate

information source to look up the code number and establish the nature of the fault. Most code readers

indicate the messages within the code reader software. To access a blink code, it is normally necessary

to perform a set procedure which effectively ‗instructs‘ the ECU to output the code. The procedure may

involve linking two terminals on a connector plug or other similar procedures which will then cause the

ECU to output the code. When a code reader is connected to the appropriate connector plug, it

communicates with the vehicle ECU, and by following the instructions supplied with the code reader (or

the instructions on the code reader screen display), the technician can make the code reader transmit an

instruction to the ECU which causes the ECU to output the codes. The instruction from the code reader

may take the form of a password; when the instruction or password is sent to the ECU, the ECU

provides the coded output, thus allowing the code reader to display the code number. Although some

inexpensive code readers effectively act as a means of accessing the simple blink code (i.e. they simply

provide a code number), most elaborate readers also display a message which details the nature of the

fault associated with the displayed code. When a blink code is read via a warning light or LED, it is

normal practice to count the number of times the light flashes. When more than one code exists,

different systems will use slightly different methods of separating the different codes. There are different

methods of displaying a code number. For instance, code 12 could simply be displayed by 12 flashes,

but alternatively could be displayed by providing one flash a pause, then two flashes. The example in

Figure 3.82 shows how two codes might be displayed (i.e. code 12 and then code 23). A brief pause is

provided between the ‗tens and units‘ as is the case between the 1 and the 2 of code 12, and between the

2 and the 1 of code 23. However, a longer pause (in this case 2 seconds) is provided between the two

different codes, as is the case between codes for 12and 23.Some inexpensive code readers simply

provide a flashing LED; the flashes are counted in the same way as a normal blink code. Most code

readers provide a display screen that indicates the code as a number. A code reader might provide a

relevant message in addition to the code number.



Collision avoidance Radar warning system:

An on-board low-power radar system can be used as a sensor for an electronic collision

avoidance system to provide warning of a potential collision with an object lying in the path of the

vehicle. As early as 1976, at least one experimental system was developed that could accurately detect

objects up to distances of about 100 yards. This system gave very few false alarms in actual highway

tests. For an anti collision warning application, the radar antenna should be mounted on the front of the

car and should project a relatively narrow beam forward. Ideally, the antenna for such a system should

be in as flat a package as possible, and should project a beam that has a width of about 2°to

3°horizontally and about 4°to 5°vertically. Large objects such as signs can reflect the radar beam,

particularly on curves, and trigger a false alarm. If the beam is scanned horizontally for a few degrees,

say 2.5°either side of center, false alarms from roadside objects can be reduced. In order to test whether

a detected object is in the same lane as the radar-equipped car traveling around a curve, the radius of the

curve must be measured. This can be estimated closely from the front wheel steering angle for an

unbanked curve. Given the scanning angle of the radar beam and the curve radius, a computer can

quickly perform the calculations to determine whether or not a reflecting object is in the same lane as the

protected car. For the collision warning system, better results can be obtained if the radar transmitter is

operated in a pulsed mode rather than in a continuous-wave mode. In this mode, the transmitter is

switched on for a very short time, then it is switched off. During the off time, the receiver is set to

receive a reflected signal. If a reflecting object is in the path of the transmitted microwave pulse, a

corresponding pulse will be reflected to the receiver. The round trip time, t, from transmitter to object

and back to receiver is proportional to the range, R, to the object, as illustrated in Figure and expressed

in the following equation:

t = (2R/c)

Where c is the speed of light (186,000 miles per second). The radar system has the capability of

accurately measuring this time to determine the range to the object.

It is possible to measure the vehicle speed, V, by measuring the Doppler frequency shift of the pulsed

signal reflected by the ground. (The Doppler frequency shift is proportional to the speed of the moving

object. The Doppler shift is what causes the pitch of the whistle of a moving train to change as it

passes.) This reflection can be discriminated from the object reflection because the ground reflection is

at a low angle and a short, fixed range. The reflection from an object will have a pulse shape that is very

nearly identical to that of the transmitted pulse. As noted, the radar system can detect this object

reflection and find R to determine the distance from the vehicle to the object. In addition, the relative

speed of closure between the car and the object can be calculated by adding the vehicle speed, V, from

the ground reflected pulses and the speed of the object, S, which can be determined from the change in

range of the object‘s reflection pulses. A block diagram of an experimental collision warning system is

shown in Figure 11.12. In this system, the range, R, to the object and the closing speed, V+S, are

measured. The computer can perform a number of calculations on these data. For example, the computer

can calculate the time to collision, T. Whenever this time is less than a preset value, a visual and audible

warning is generated. The system could also be programmed to release the throttle and apply the brakes,

if automatic control were desired. If the object is traveling at the same speed as the radar-equipped car

and in the same direction, S=-V, and T is infinite. That is, a collision would never occur. If the object is

stationary, S=0 and the time to collision is: T = (R/V), If the object is another moving car approaching



the radar-equipped car head-on, the closing speed is the sum of the two car speeds. In this case, the time

to closure is T = R / (V+S)

Range to Object:

Collision avoidance radar warning system - Layout

Documents

AT2401 Engine and Vehicle Management System.pdf