-
8/9/2019 06abs and Asr
1/5
The Control of Anti-Lock Braking System (ABS) and Anti-Skid
Reduce System (ASR)
in the Diesel-Powered Cars Based on the TMS320F243 DSP
Branislav Lojko, Peter Fuchs
Department of Radio and Electronics, Faculty of Electrical
Engineering and Information
Technology, Slovak University of Technology, Ilkoviova 3, 812 19
BratislavaE-mail: [email protected], [email protected]
Abstract
This paper presents a design of combined safety system
(ABS&ASR) designed for
using in the diesel-powered cars. There is an introduction to
problem, description a physical
terms of function, available information about this systems and
design of block structure. The
core of system is designed following of DSP controller
TMS320F243, high performance
product of Texas Instruments. In article is described
four-channel version ABS&ASR with
engine intervention and brake intervention.
1. The physical terms of a tire on the roadAt the moving vehicle
are affected weight force, air resistance and voluble resistance
of
tire above all. The force actuating for tire is consist of
o circumferential force, which is descended from driving
mechanism,
o side force, which is descended from vehicle control,
o normal force, which is descended from vehicle weight.
The forces efficiency depends from road status, tire status and
atmospheric conditions. The
transferred force intensity between road and tire at
accelerating or decelerating are determined
by the friction forces. A car safety systems (ABS&ASR) are
seeked maximum uses
instantaneous value of the friction forces, which is determined
by the adhesive force [1], [2].
The more is friction force FT, the more can be driving force of
motor F and the more will be
car accelerating. If value of friction force will be decreased
come about wheel skid. In this
case, ABS&ASR system must decrease of motor driving force to
the FT level and if some
wheel is skiding, it must be slowed. The most important
parameter procesed in ABS&ASR
systems is slip. The slip is non-dimensional parameter
designated . This parameter determine
of skid rate at the roll moving in braking time
(1)
or in accelerating time
(2)
where vF [m.s-1] is a car speed and vU [m.s
-1] is a circumferential speed of wheel.
The dependence of the adhesion coefficient on the braking slip
value is in Fig. 1. The value of
adhesion coefficient HF rising from zero slip very sheer and
achieve maximum value
approximately between 10% till 40% braking slip. The rising part
of this curve called stabile
sphere, falling part called astabile sphere. The car safety
systems seek keep slip value in the
interval from 0 to 20%.
2. Systems description
ABS refers to a number of devices designed to avoid wheellock
during hard and panic
braking conditions. These systems have gained world attention
only in the past fifteen years,but even the simplest system
provides huge gains over electro-mechanical systems. Four
1=
= F
U
F
FU
v
v
v
vv
F
U
F
UF
v
v
v
vv=
= 1
-
8/9/2019 06abs and Asr
2/5
Fig. 1: The dependence of the adhesion coefficient on the
braking slip value
wheel systems provide more security with both steerability and
stability, and are second only
to engine control in electronic content. ABS systems are
designed around system hydraulics,
sensors and control electronics. These systems are dependent on
each other and the different
system components are interchangeable with minor changes in the
controller software [3].
Anti-Locksystems are low cost with one wheel sensor on the
differential, one control circuit
and a system controller or primarily light truck and front wheel
drive passenger cars. This
improves stability and only affects the rear wheels.
Anti-Skidsystems provide the next level by adding control to all
wheels and includesthree
wheel sensors, three control ircuits and the system controller.
This system provides bothsteerability and stability during heavy
braking, meaning that a driver can maintain full
control of the vehicle.
Advanced Anti-Skidsystem is upgrade of the previous system and
requires four wheel speed
sensors, four control circuits, and a high performance control
system. This system provides
greatly increased control decreased stopping distances, split
surface control (dissimilar road
surfaces), and automatic parameter adjustment (to match weather
changes). Presently, this
system is used only on very high performance vehicles.
3. Traction Control
To control wheel slip during acceleration on slippery surfaces,
the control system
must balance the torque at the driven wheels and the friction
from the road and tire surfaces.
Two of the most popular methods for controlling torque are
engine intervention and brake
intervention. These techniques apply the brakes intermittently,
where wheel slip has been
determined, to absorb excess engine torque. Engine intervention
techniques provide some
means of controlling torque by either fuel or spark timing
adjustments. In the diesel-powered
cars is engine intervention provided of power control rod of
motor inject pump.
4. System hydraulics
The hydraulic system in the vehicle is augmented by the addition
of special hydraulic
solenoid switches which allows the control unit to modulate the
brake pressure on each of the
controlled wheels. The number of wheels controlled depends on
the configuration selected bythe manufacturer. Typically, an
Anti-Lock system has one control circuit which acts on both
a b
HF
=4
TS
0 50 100 (%)
1,0
0,5
BA
-
8/9/2019 06abs and Asr
3/5
of the rear wheels, while an Anti-Skid system has three control
circuits; one for the two rear
wheels and one for each of the two front wheels. These hydraulic
switches allow the brake
pressure to be increased, decreased, or held constant during ABS
control of the circuit. In the
non-operating mode the switches are in the pressure increase
position which under normal
driving conditions equates to flow through position. Control
circuits are either one three
position switch or two two-position switches, again depending on
the manufacturer. Recently,a great deal of attention has been given
to the use of Pulse Width Modulated (PWM) pumps
which act as pressure boosters on each of the control lines.
This form ofcontrol is not only
more accurate but avoids many of the traditional problems
associated with relatively slow
switching solenoids. PWM control will be the next hydraulic
system advancement for ABS,
both in performance and in cost.
5. System elektronics sensors
Several different parameters must be checked during normal
driving as well as during
ABS braking. Possibly, the most important input(s) is that of
the speed sensor. In the form of
a reluctance sensor, it reads the passing teeth on a gear on the
wheel hub. The sensor outputs a
sinusoidal wave form which must be changed to a digital wave
proportional to wheel speed.In addition, there are several on/off
(digital) inputs which tell the processing unit if the brake
pedal has been depressed, if brake fluid is insufficient, and if
the parking brake is on.
Fig. 2: ABS&ASR block structure
6. Processing
Processing unit reads the speed sensors to determine both wheel
and vehicle speed,
and if an ABS event is occurring, and ABS control functions need
to be performed. This can
include eight solenoids with feed lock loops, continuous self
and system diagnosis, service
interface, and a display of system status. The substantial
control requirements of an advancedABS system requires a very high
performance controller.
Speed Sensor
of left back
wheel
Speed Sensor
of right back
wheel
Speed Sensor
of left front
wheel
Speed Sensor
of right front
wheel
SPU
Signal Processing Unit
(atenuators, limiters, filters, comparators, convertors to the
TTL level)
Extern
SEEPROM -
fault memory
TMS320F243
(#2)
system diagnostic
TMS320F243
(#1)
main processor
SPI
CAN bus
124 ohm 124 ohm
Others internal systems
e.g. on-board computer
DECU
Diesel Engine Control Unit
SCU
Solenoidos Control Unit
Power-Control Rod of
Inject Pump
-
8/9/2019 06abs and Asr
4/5
7. Key design challenges
1. Provide a system that allows for a large number of wheel
speed samples independently for
all four wheels within the allotted ABS cycle time of
approximately 5 ms. Wheel acceleration
and deceleration calculations in realtime require fast multiply
and divide instruction cycle
times to optimize the system response times.
2. Maximum fault tolerance and on-board diagnostics for sensor,
actuator and internalelectronic faults.
3. Integration. In order to reduce size for mounting in very
space limited locations, integration
must be optimized. This must be accomplished without a major
impact on system cost.
4. Underhood operation. All components used in next generation
ABS&ASR systems must be
capable of operation at ambient temperatures ranging from 40C to
+125C.
8. Design of the ABS&ASR block structure
The real ABS&ASR system is consist of five level. At the
first level, a physical
parameters needed to the system function are scaned by means of
wheel speed reluctance
sensor (WSRS). At the second level, scaned signals are
processing by means of atenuators,
limiters (overvoltage impulse limiting), low pass filters and at
last are signals processing inthe zero detector, which is generated
of TTL compatible impulse with constant width. At the
third level, mathematical processing of measured periods of the
impulses is execute. There are
used adaptive algorithm usually. The fourth level provides power
isolation of actuators and
last level executing action intervention into the brake system
and motor power management.
The specific level in this hierarchy is zero level software.
This concept is presented on the
fig. 2. We are applied TMS320F243, high performance digital
signal processor, at the position
of mathematical processing after account required facilities.
This DSP provides control and
communication with peripheral equipment via SCI, SPI and CAN bus
(external SEEPROM-
fault memory, on board computer and test PC).
The diesel engine control unit (DECU) is based on the PIC16F84
controller and it is receives
movement commands from a host (main processor), compares them to
the actual position,
calculates the desired motor drive level and then pulses a full
H-bridge [4]. In this way it
serves as a remote intelligent positioner, driving the load
until it has reached the commanded
position. It is used to control proportional D.C. actuator.
Because of the 5-wire serial
interface, the DECU can be installed near its power supply and
load. Since the DECU is
running its own closed-loop PID algorithm, the host central
processor needs only to send
position commands and is therefore free to service the main
application software.
Acknowledgement
This work was supported by the Ministry of Education of the
Slovak Republic under
grant VTP 102 Digital Processing of Audio, Video and Biomedical
Signals.
Reference
[1] Lojko, B.-Fuchs, P.: The Control of ASR System in a Car
Based on the TMS320F243
DSP. Diploma Thesis, Dept. of Radio&Electronics, FEI SUT,
Bratislava 2002
(in slovak)
[2] Rika, A.-Petrs, Z.: Anti-Lock Systems ABS-BOSCH. Robert
Bosch
odbytov s.r.o., Praha 1998 (in czech)
[3] National Semiconductor Inc.: Adaptive Braking Systems (ABS).
Arlington 1995
[4] Microchip Technology Inc.: Microchip Technical Library
CD-ROM, First Edition 2000.
Arizona 1999
-
8/9/2019 06abs and Asr
5/5
