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Modern Automotive Engines – Trends & Technologies
1.1 Introduction
The advent of Automotive Electronics has brought a new dimension to the field of
automotive research. The prime motive of this involves making an Automobile more fuel
efficient without compromising with performance and also Eco friendly. Modern IC Engines
are not an exception in this respect. Some of the trends observed in Engine designs are
Engine Design trends: The location of various parasitic loads has been changed like
engines with Over Head camshaft arrangement. Some of the parasitic loads have been
made independent of engine like Steering Assist Hydraulic pump. Even combining
Alternator and Starter motor (ISG) is a new development. Unorthodox IC Engines
like Wankel engine, Air engine and Grail engine have also paved new opportunities
for research.
Material trends: Previous IC engines were manufactured by casting or forging of
ferrous metals. But the need to improve power to weight ratio has made way for use
of aluminium alloys for cylinder blocks, cylinder heads and intake manifolds are
made of magnesium. Parts such as engine covers, intake manifolds, and oil pans are
being manufactured by powder metallurgy by using plastic or composite materials
which are less dense and reduce engine noise and vibration.
Ignition & Fuel Supply trends: Distributor less ignition system are replaced by coil-
on-plug or direct ignition system. In this ignition system ignition coil sits directly
above each spark plug. Modern IC Engines have ECU’s capable of monitoring
exhaust gases by the help of oxygen sensors and control the air fuel mixture
accordingly by electronic actuators.
1.2 Technology in Modern IC Engines
The various new technologies introduced in IC Engines are explained here
o Drive by Wire Throttle System: This system eliminates the mechanical linkage
between Accelerator pedal and Throttle. A accelerator pedal module based on Hall
effect sensor or a rotary potentiometer detects the driver input and through ECU sends
signal to electric motor (BLDC) to adjust the throttle position accordingly. TPS is also
included in the control loop for a closed loop operation. A major advantage of this
system is that it can be integrated with ESP, ACC and TC since throttle position can
be controlled irrespective of driver input. In case of failure of the system ‘limp home
mode’ will be activated setting the throttle in a fixed position to maintain uniform
vehicle speed.
o Variable valve timing (VVT): Traditional Valve mechanism use fixed valve timing
which is a compromise between low and high Engine speed. A typical VVT engine is
capable of varying Valve timing & lift of valve according to engine speed. The engine
has 2 camshafts for operating intake valves and operating exhaust valves. Each
camshaft has two lobes per cylinder for high and low rpm, with two intake valves and
exhaust valves. Each set of two valves are controlled by one rocker arm which has a
slipper follower mounted to the rocker arm with a spring .The Engine speed sensor,
the ECM, oil pressure switch forms a closed loop which pushes a sliding pin under the
slipper follower on each rocker arm to switch to the high lobe causing high lift and
longer duration at high rpm. VVT improves Engine fuel efficiency, Torque and
Engine responsiveness.
o Common Rail Direct Injection (CRDI): The fuel is supplied directly to a common
rail from where it is injected directly onto the pistons which ensures the onset of the
combustion in the whole fuel mixture at the same time. CRDI provides highly
accurate and uniform distribution of air/fuel ratio at all engine operating condition and
better engine response
o Multi point Fuel Injection (MPFI): In this system each cylinder has number
of injectors to supply fuel in the cylinders as compared to one injector located
centrally to supply fuel in case of single point injection system. MPFI with direct
injection provides allows higher compression ratios and more efficient fuel intake,
which deliver higher performance with lower fuel consumption.
o Integrated Starter/Generator (ISG): In this system the Starter motor also acts as a
alternator and stores energy in the battery when the engine is running. At idling
condition the ECM signals the engine to stop and start as required and the alternator
drives the engine to start. Regenerative braking can also be implemented in this
system for higher fuel efficiency without effecting driver comfort.
o Cylinder deactivation: This system enables the ECM to cut off fuel supply to some
cylinders (Normally in 6-8 cylinder engines) at low load condition to reduce the fuel
consumption. This system is not suitable for 3-4 cylinder engines because it may
greatly reduce the engine performance. The ECM signals the VVTi to close the intake
and exhaust valve creating an air spring in the combustion chamber and hence no load
is supported by the cylinder.
Safety Systems
2.1 Introduction:
At the time of launch of first affordable road car in the year 1909 Ford Model
T [1] people were fascinated about this indigenous locomotive which can carry people
from one place to another with minimum human effort. With top speed of just 40 to
45kmph [1] safety of the passengers were least of the concerns. But as the industrial
age has emerged and flourished in both developed and developing countries car
design and driver attitude has changed greatly. According to WHO September 2012
reports about 1.3 million people die each year on roads worldwide. Road traffic
injuries are the leading cause of death among young people, aged between 15 and 29
[2] which is a very disturbing fact. Over 90% of the deaths on the roads occur in low-
income and middle-income countries, which have only 48% of the world’s registered
vehicles [2] which includes India. Even with these alarming figures common
commuters are more aware of traffic congestion then road fatalities, so it is the duty of
the car designers to prioritise safety of cars over speed, acceleration and aesthetics.
Modern car safety systems are widely branched into active and passive safety
system. The prime motive of these systems is to assist the driver to avoid any
impending danger to passengers as well as pedestrians in driving condition or in a
worst case scenario damp the effects of an accident to the passengers. Various active
and passive systems installed in modern cars are explained here.
Passive Safety System:
In occurrence of a collision the vehicle deformation occurs within 0.1-0.2
seconds but braking maneuver will take few seconds [3]. Hence the occupants will
subjected to very thrust in the direction of motion and in case of absence of any
restraints the occupants will be subjected to injury due to vehicle interior trims.
Primary objective of a passive safety system is to safe guard the occupant by a
combination of restraint and by collision damping to the passenger cabin. Based on
these two methods following safety measures are implemented in modern cars.
o Vehicle Structure: This category mainly deals with the crashworthiness of the
vehicle body. In case of frontal, rear or side impact the vehicle body is designed to
absorb the crash energy by deforming with minimal deformation of the passenger
cabin. This is realised by understanding the various crash scenarios and vehicle
behaviour in these crash scenarios.
Figure 2.1 [4]
From Figure 1 it can be understood that the two vehicles with different front hood
length have to absorb same energy, because of this the SUV becomes much stiffer
then the Sedan and hence passenger in SUV is injured more in this case. Both the
front and the rear of the car act as a crumple zone and hence are made less stiff to
absorb crash energy. To inhibit the effects of side impact modern cars have side doors
with beam, cells, padding and other energy absorbing medium. Modern vehicles are
also provided with safety cages which are built around the passenger cabin to provide
protection in case of vehicle roll over.
o Restraint System: Modern automobiles are fitted with occupant restraint systems,
like seat belt with pre-tensioner and airbags to reduce passenger injuries and fatalities
at the occurrence of a crash. Seat belts are the primary restraint systems whereas air
bag is supplementary to the seat belt. Type of seat belt also greatly affects the
occupant safety because insufficient restraint might still be dangerous. The various
seat belt restraints are shown in the figure 2.
Figure 2.2 Left to Right Lap Strap, 3 point, Belt in seat, Five point Harness [5]
Three point Harness is best restraint for passenger cars since they support both torso
and shoulder region. They are easy to detach. Seat belt pre tensioner arrests the slack
of the seat belt in case of sudden deceleration which pulls the occupant firmly on the
seat when crash occurs. Air bags have three basic functions which are slowing the
driver deceleration by deflating at a controlled rate, preventing the driver and
passenger head from colliding with the internal trims and supplementing the seat belt
constrain to reduce occupant chest compression. Airbag operates by detecting crash
with the help of accelerometer sensors, and calculating the severity of the crash and
deploying the airbag if necessary.
Active Safety System
As the name suggests this safety system is a drive assistance system controlled
by various electro mechanical devices to prevent accidents either by cautioning the
driver or by overriding driver command. The various Active safety systems include
ABS, TCS, ESP, TPMS, ACC and Parking Assist.
o Tire Pressure Management System (TPMS): Tire is the most crucial part any
automobile in all the aspects imaginable. The contact patch defined by the tyre on the
ground can define vehicle handling & stability, Fuel economy, Acceleration, Top
Speed and many more. Many times Tire is the most neglected part by any automobile
owner. Tire pressure defines the geometry of the contact patch, roll resistance and
cornering stiffness. TPMS continuously monitors the pressure in individual tires and
notifies the driver in case of under inflation or sudden drop in tire pressure. TPMS
consists of Tire pressure sensor, Control Module, radio frequency transmitter and
receiver. The pressure sensor is mounted on the tire rim hence each sensor is fitted
with independent batteries having a low discharge rate. Tire pressure is detected at
intervals of time and transmitted to the receiver by low frequency radio signal. The
signal from receiver is then amplified, conditioned, converted from analog to digital
and rendered to the control module. The control module detects any pressure drop and
notifies the drive through Warning lamp.
o Adaptive Cruise Control (ACC): ACC is intended to reduce driver fatigue while on
long drives on highways where any mishandling will lead to fatality. It allows a driver
to set a desired speed similar to ordinary cruise control but if a vehicle immediately
ahead of the equipped vehicle is moving at a slower speed, then throttle and braking
of the host vehicle is controlled to match the speed of the slower vehicle as per the
driver defined gap. The defined speed is automatically re attained when the roadway
ahead is unobstructed, either due to slower vehicle ahead leaving the lane or the driver
of the host vehicle changing to a clear lane. The current ACC Systems monitor the
road ahead using either radar or Lidar (laser radar).The operating modes of an ACC is
shown in figure 2.3.
Figure 2.3 Various modes of ACC operation [Refer 7]
o Antilock Braking System (ABS): This system is primarily addressing the problem of
wheel locking due to sudden application of brakes under driver panic. A wheel under
locked condition may lead to under steer or over steer and finally lead to fatalities.
Major components of an ABS include Brake Module, Wheel Speed Sensor and
Hydraulic Modulator with solenoid valves and Brake assembly. ABS control module
analyses wheel speed sensors data and detects any wheel approaching lock condition.
It signals the hydraulic modulator to release the brake pressure momentarily on the
locked wheel using solenoid assembly. The control strategy for ABS is shown in
figure 2.4.
Figure 2.4 ABS Control Strategy [Refer 8]
2.2 Active Safety System-Passive Safety System, A comparison
Active Safety System
o Technology: The technology used in Active safety system is highly advanced
compared to passive safety system. The control algorithms have to deal with a lot of
variables and either affected by driver attitude, vehicle stability or the road
environment. The sensors used in Active safety range from Wheel speed sensors
(ABS & TCS), Yaw rate sensors (ESP), Proximity sensors (Parking Assistance) &
Radar (ACC).
o Application: Active safety system has a wide range of application ranging from
Passenger cars, Performance cars, Trailer trucks etc. But it is noticed that certain road
legal race cars have option to turn off ABS & TCS for fast cornering and other
manuevers. High speed Trucks used for goods transport have high vulnerability for
roll over. ESP’s with body roll mitigation is used for this purpose.
o Cost: Due to a large range of sensor and high performance control module make
active safety comparatively expensive compared to its counterpart but operation of
this safety system provides larger duty cycle since it avoids damage to the car and
hence to system itself, but if any part requires servicing then the expense will be high.
o Viability: Installation of Active safety system in Indian cars is in a very basic stage.
Although ABS, TCS & Parking Assist is a usual feature in many new Indian brands
the high end safety systems like ESP & ACC are yet to be launched in any affordable
cars. ACC especially is not suitable in Indian Highways due to the lack of driving
discipline
Passive Safety System
o Technology: The control strategies for passive safety systems like air bag, seat belt
pretension, head restraint system is very straight forward. Hence variables to be
considered are less. Sensors used are mainly to detect crash hence are mainly
accelerometers mounted at various locations in the car. The response time of Passive
safety systems has to be very high and hence actuation of these safety systems is
mainly done by explosive techniques.
o Application: Passive safety systems find application in almost all kind of
locomotives whether road vehicle or air vehicles. Passive safety is an integral part of
any automobile even with or without active safety systems. The Vehicle structure
itself is a passive safety device hence all vehicles are designed to provide passive
safety as a minimum safety measure.
o Cost: Passive safety systems are less compared to active safety systems due to less
components & simple operation. But the passive safety systems have very low duty
cycle because they are designed for one operation and then have to be replaced. Since
Passive safety system does not avoid accidents it is completely dependent on driver
behaviour on expense of passive safety system.
o Viability: Although Passive safety is a necessity in all cars it has a limitation of
triggering time as for air bag and seat belt. If the vehicle speed is very high the
triggering time wouldn’t be sufficient to safeguard the passengers. For mid-sized
family cars used in India for city commutation Airbag and seat belt pretension is a
very viable choice. Since most of the cars used in India are compact in design Vehicle
structure absorption of crash energy is very less hence restraint system is a very good
safety measure.
2.3 Electronic Stability Program (ESP):
ESP is an active safety system which detects any changes of the vehicle
behaviour from the driver input and controls the braking system on individual tires to
improve vehicle stability and handling to avoid accidents. ESP acts as a controlling
member which picks data from various sensors and guides the ABS to avoid
accidents.
Under steer and Over Steer: This phenomenon occurs due to the stable yaw
moment of the vehicle when cornering due to a combination of panic driving
and wheel locking. Both the phenomenons are observed in the figure 2.5.
Figure 2.5 [Refer 9]
Under steer occurs when Front wheel of the vehicle locks up and the driver steering is
not transferred to the vehicle and hence the vehicle continues to propagate in the
direction before the wheel locked up and finally comes to halt. Oversteer occurs when
Rear wheel locks up and the vehicle stability completely depends on the mercy of
driver input. Any average driver under these conditions panics and erratically steers
the vehicle and lead to fatalities. An ESP collects data from Wheel speed sensor and
yaw rate sensor to detect whether the vehicle is in the verge of understeer or oversteer
and directs the ABS release the break pressure on particular tire of maintain pure
rolling moment between road and wheel.
Configuration of an ESP: The basic control algorithm of an ESP is shown in
figure 2.6.
Figure 2.6 [Refer 6]
According to the algorithm the basic components required for this control system are
1. Steering Angular speed Sensor
2. Wheel Speed Sensor
3. Yaw rate Sensor (Accelerometer)
4. ABS
5. EBCM
Process: The ESP control module continuously monitors the data from all the
sensors and matches it with reference models hard coded in its memory. Data
regarding Vehicle Speed, Steering Angle Input and Vehicle Yaw is enough to
determine the Vehicle stability. The decision is made in the control module
whether to override driver input and with the aid of ABS selective braking is
applied. Some EPS with Active steering can control even the steering system
to avoid understeer or oversteer. Figure 2.7 shows the layout of a complete
ESP with all its subsystem installation location.
Figure 2.8 Layout of ESP in Mercedes Benz E class [Refer 6]
o Steering Angular Speed/Angle Sensor: These sensors are mounted on the steering
column below the Air bag Module and can detect both steering angle and angular
velocity. Most steering angle sensors have multi turn capability and hence steering
angle can be used to predict the car wheel angle by including wheel slip, steering
linkage friction and backlash compensation in the control algorithm. Most popular
Steering Angle sensors are of optical type or Hall Effect sensors.
Figure 2.7 [Refer 10]
Figure 2.7 shows a Steering Angle Sensor by Methode Electronics, which uses optical
technology and has multi-turn capability with a resolution of 0.10o and accuracy of ± 1.5o. Its
single output can be CAN, LIN or PWM [10].
o Yaw rate Sensor (Accelerometer): A yaw rate sensor measure the lateral
acceleration of the vehicle (Yaw moment). They are basically gyroscopic devices
based on MEMS technology and are installed in the passenger cabin. Figure 2.8
shows a yaw rate sensor based on MEMS technology with CAN interface. It has a
minimum resolution of ± 0.2o/s and sensitivity of 18mV/o/s.
Figure2.8 [Refer 11]
o Wheel Speed Sensors: The speed sensor shown in Figure 2.8 is a Variable
reluctance sensor consisting of a toothed wheel and a inductive sensor. The output
signal of this sensor is analog in nature but because of its simple construction and
since direction of rotation is not necessary to determine this type of sensor is most
popular for detecting Wheel speed.
Figure 2.8 A disc brake unit with wheel speed sensor [Refer 11]
o Anti-Lock Braking System (ABS): As explained before ABS controls the wheel
locking by intermittent application of break pressure at high vehicle deceleration. The
complete layout of ABS in a car is shown in figure 2.9. The hydraulic brake pressure
modulator consists of hydraulic pump, isolation valves, dump valves
Figure 2.9, Representation of typical ABS system in a car [Refer 13]
o Electronic Brake Control Module (EBCM): The EBCM controls the solenoid
valves in the hydraulic modulator and pressure regulator valves to distribute pressure
among the brake callipers. It has a diagnostic tool interface to detect failure. The
EBCM contains two parts
1. System Relay: The system relay is energized only when car ignition is on. It
supplies battery voltage to the solenoid valves and pump motor
2. Solenoids: The solenoids are commanded by the EBCM to operate valves in the
hydraulic modulator.
Air bag System
3.1 Airbag as a safety system:
Accidents while driving a vehicle is inevitable whether it’s the driver’s mistake or
impended by the environment. It is very difficult to tackle all the scenarios of a n accident
with control system, the only thing possible is provide safety to the passenger even if the car
meets an accident. Role of an airbag system is to make this possible. In any accident scenario
two types of collision occurs
1. Primary collision: Collision between the vehicle exterior and the obstacle.
2. Secondary collision: Collision between the passenger and vehicle interior.
Airbag deals with the secondary collision. According to law of conservation of energy
“Energy can neither be created nor destroyed but can be transferred from one form to
another”. Hence when a collision occurs kinetic energy of the vehicle is transformed into heat
energy and vehicle deformation. And this transformation results within milliseconds and
hence the passenger in the vehicle is capable of shielding this kind of rapid retardation.
Airbag acts as an air pillow, protecting the fragile human body from colliding the hard trim
surfaces. From the figure 3.1 it can be understood that the absence of the airbag would have
led the drivers head to collide the steering wheel and cause injury. So the airbag is installed
for two purposes
1. Slow the retardation of the human body as a supplement to the seat belt system.
2. Protecting the human body from colliding the vehicle trims.
Figure 3.1 Deployment of a driver airbag [Refer 14]
3.2Requirements of an Airbag System
An air bag system is only effective when deployment is timed correctly, and this is
possible only when all the components are functioning properly. The various components of
an airbag system are shown in the figure 3.2.The sensors detect the crash and send the report
to the ECU. The ECU does the decision making whether to deploy the airbag or not
depending on the severity of the crash. The inflator deploys the nylon bag by a chemical
reaction. The bag is fully inflated before the occupant makes contact with the bag without
inflicting unnecessary forces on the occupant. This principle is applicable for both frontal and
side impact. The critical requirements of an air bag system is explained here.
Figure 3.2 Components of an airbag system [Refer 3]
1. Sensor Location: The location of the crash sensors is very important in registering
the crash whether it’s frontal or side impact. The frontal crash sensors are mounted
beneath the front bumpers and side and curtain airbags are mounted in the door panels
as shown in the figure 3.3 & 3.4.
Figure 3.3 Front Sensor Location [Refer 15]
Figure 3.4 Side Impact Sensor Location [Refer 15]
2. Time: Time for airbag deployment is the most crucial requirement of any air bag
system. The deployment time for a frontal crash is 50 milliseconds and for side
impact is 15 milliseconds [14]. Deploying earlier to this stipulated time will not
cushion the driver properly since the air bag is made of nylon material which deflates
rapidly. Deploying after the stipulated time will be of no use.
3. Crash Sensors: The present day sensors are electro-mechanical units, capable of
measuring crash-induced motion (such as accelerations, velocities or displacements)
of the points on the vehicle structure to which they are attached.
Front: Usually front crash sensors are accelerometers based on MEMS
technology. They are located either behind front bumpers or below passenger
seats. Some crash sensors are located both below the passenger seat and in the
front hood to detect even small area crashes. In some vehicle the sensing and
control unit both the sensors and control unit are integrated into a single
enclosure called sensing and diagnostic unit.
Side: Sensors for side airbags generally are accelerometers that measure the
lateral acceleration of the attached structure. These sensors may be integrated
with the front sensors as part of sensing and diagnostic unit or located in the
side pillar or in its vicinity.
Rollover: The roll over sensor is a Yaw rate sensor based on MEMS
technology. This sensor detects any unusual swaying of the vehicle and helps
the ECU in deciding whether to deploy curtain airbags in case of imminent
rollover possibility. These sensors are normally very small in size and can be
included as part of sensing and diagnostic unit.
Occupant Classification Sensor: These sensors are basically pressure sensors
mounted on the brackets connecting the seat rail and seat frame. These sensors
in conjunction with the occupant classification system detect whether the
occupant is adult, infant or absent. The figure 3.5 shows the location of
occupant classification sensor and its load v/s voltage curve.
Figure 3.5 [Refer 15]
4. Control Unit: When a crash occurs, data from sensors are sent to the control unit
where they are compared against the stored algorithms. If the control unit determines
that a deployment condition has been met, a signal is sent to the igniter module and
combustion of the propellants is initiated. Figure 3.6 shows the control system for
front collision airbag system. Here the ECM and the sensor can be a single unit called
sensing and diagnostic unit.
Figure 3.6 System diagram for airbag frontal collision system [Refer 15]
The control unit has to consider following variables before signalling the inflator to
deploy the air bag
1. Checking the severity of the crash, whether deployment of air bag necessary
or restraint system is enough for the task.
2. Check Occupant availability from the occupant classification system, and also
check whether the occupant is adult or infant.
3. Check for the seat belt switch for diver , driver has locked the seat belt or not
4. Decide which of the Airbags to deploy, whether it’s a front impact, side
impact or roll over.
5. Decide the deployment time depending on the retardation and also type of
impact since deployment time for side impact is less compared to frontal or
roll over impact.
5. Airbag: Airbags depending the position and purpose are classified into following
types
1. Driver Airbag
2. Passenger Airbag
3. Knee Air bag
4. Side Air bag
5. Curtain Airbag
Airbag is usually made of neoprene coated nylon material because of its softness,
high thermal resistance and flexibility. Folding of this is very crucial for on time
deployment of the air bag. L type folding is the most used folding type, because in
this the air pressure builds up in the top layer of air bag first and then spreads over the
air bag , which is very helpful in providing cushioning effect. The figure 3.7 shows
the various components in a air bag module. The figure 3.8 shows the different air
bags and their position in a car.
Figuren3.8, Various air bags in a car [Refer 15]
Airbags are provided with internal tethers (spring like elements) so that they
follow the profile of the passenger face, head or knee structure so that the
occupant does not feel any rebound effect from the air bag.
6. Inflator Module: The inflator module has three components, a detonator, Sodium
Azide (NAN3) capsules and enclosure. Figure 3.9 shows a inflator module.
Figure 3.9, [Refer 16]
Detonator is a heat sensitive filament that is supplied with electric current. It energises the
filament and heats it so that the sodium azide capsubles get ignited causing a detonation
effect. Sodium azide is a solid propellant with a very high gas generation ratio. Since it is a
solid propellant managing the propellant is easy. After combustion the major by-products
include Nitrogen gas & sodium hydroxide. This is commonly known as Lye, which is a
caustic compound. The quantities produced are very small and present a very small risk of
burns. The white powder residue seen after inflation is common corn starch, used as a
lubricant for expansion of the airbag.
7. Diagnostic Unit: A diagnostic unit in the Airbag control is very necessary since
airbag deployment is a very critical operation and any failed components will make
the air bag deployment fail. The diagnostic unit enables the inflator unit and sensors
when vehicle is turned on, performs a self-check.It constantly monitors airbag
readiness and indicates malfunctioning through an indicator on dashboard. It also
usually acts as autonomous battery storing electricity to activate airbag in the event
that a crash damages the battery link or the battery itself.
Reference
3. Ching-Yao Chan, "Automotive restraint systems", in Access Science @ McGraw-Hill,
http://www.accessscience.com, DOI 10.1036/1097-8542.YB061730
4. Jim Hopton, Manager Safety & Simulation MIRA Ltd “Future of Automotive Safety -
Integrating Safety in Design”
5. “Types of Seat belts”, www.sjtsa.org/TYPES%20OF%20SEAT%20BELTS.pdf
6. Electronic Stability Program & Trailer Stability Program
www.jacet.org/jacet50books/04.pdf
7. “Intelligent Vehicle Technology and Trends”, Richard Bishop.
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9. http://topalwaysdown.files.wordpress.com/2011/04/understeer.jpg
10. Multi-turn Steering Angle Sensor,
http://www.methode.com/Documents/TechnicalLibrary/Multiturn_Steering_Angle_Sensor_f
or_Automotive_Applications_Data_Sheet.pdf
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