The Control of Anti-Lock Braking System (ABS) and Anti-Skid Reduce System (ASR) in the Diesel-Powered Cars Based on the TMS320F243 DSP

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 El

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, Ilkovičova 3, 812 19 Bratislava

E-mail: lojko@kre.elf.stuba.sk, fuchs@elf.stuba.sk

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 road

At 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 λ 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 µHF 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

F

U

v

v v

v

v

λ

F

U F

U

F

v

v v

v

v

−

=

−

λ

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-Lock systems 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-Skid systems provide the next level by adding control to all wheels and includes–three

wheel sensors, three control ircuits and the system controller This system provides both steerability and stability during heavy braking, meaning that a driver can maintain full control of the vehicle

Advanced Anti-Skid system 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 by the manufacturer Typically, an Anti-Lock system has one control circuit which acts on both

a b

µHF α=4°

µTS

0 50 100 λ(%)

µ

1,0

0,5

B

A

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 advanced ABS 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

Others internal systems e.g on-board computer

DECU Diesel Engine Control Unit

SCU Solenoidos Control Unit

Power-Control Rod of Inject Pump

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 internal electronic 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 –40°C to +125°C

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 in the 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] Růžička, A.-Petrás, Z.: Anti-Lock Systems ABS-BOSCH Robert Bosch

odbytová 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