The main function of the traction control system is to prevent wheel spin and regain the traction on the tyres. For example if you are driving the vehicle at the excessive speed the wheels could may result in spinning on particullarly soft, slippery, or gravel road surfaces. During these type of conditions of the road the traction control system is operational to reduce engine torque and also reduce the traction between the tyres of the driving wheels and the road surface. Traction control system also assists in the steering therefore if the vehicle is accelarating on the curve the driver may understeer to compensate and may also intend to slacken off the accelerator. Traction control with a steering sensor can be used to reduce traction automatically and improve driving safety.
The arrangement of Traction Control Unit
The ABS/TCS hydraulic modulator is the same as the ABS except there is an extra valve added.The ECU holds up all the electronic programs in the vehicle therefore it receives inputs from the front and rear wheel sensors as well as from the engine's power control modulator (PCM) and then the output signals are send to the ABS/TCS mudulator and then to the engine's PCM.The PCM then receives signals from acceleration pedal and also from other sources and for the traction control system it sends signal to the engine's fuel and ignition system.
The Operation of the Traction Control Unit
Its operation is to reduce engine torque and to reduce traction between tyres and the road and it also uses ABS to prevent the car from wheel spin while braking.
Three ways in which the engine torque is decreased:
- By reducing or cutting off fuel from the injectors.
- By retarding the ignition.
- By closing the throttle valve
An ABS has a extra program that is for the traction control and also there is additional valves in the modulator. The ABS / TCS sends the TCS signal to the PCM illustrating it to reduce the engine torque during the soft, slippery and gravel road surface conditions. The engine ECU then takes the control and reduces the fuel from the injectors, retards the ignition and closes the throttle valve. The traction control unit is active over time but it enables it to do its fuction when it is neccesary therfore when the wheel starts to spin and looses traction on the tyres and the light will flash at the dash board when it is in operation. Depending on the manufacturer some of the cars have got the "on" and "off" switch for the traction control in the vehicle.
Traction Control and the ABS
The ABS operates in the conjunction with the traction control unit. In the ABS the hydraulic modulator is using the internal hydraulic pump to boost therefore it reduces the pressure of the master cylinder whereas the traction control unit uses the hydraulic pressure from the pump without the driver applying the brakes. In this there are priming and switching valves which is operated by the ECU, opened and closed to control th brake fluidflowing to and from the master cylinder.
Electronic Throttle Control For TCS
The device which can be used with the traction control is the "drive by wire" and the "electronic throttle control". When the accelerator pedal is connected to an electronic sensor which signals the "TP" to the engine ECU then it operates the servo motor which is fitted to the throttle valve. During the normal braking when the traction control is not working then the signals are passing through the engine ECU and servo motor opens the throttle in acception to accelerate pedal movement. When the traction control is in use then the engine ECU receieves signals from the antilock braking system / traction control ECU and adjusts the opening of the throttle valve.
The functions of the Traction Control
- Traction Control ECU - receives the information from various sources and signals the engine control module to reduce engine output when this is required.
- Engine ECU - it operates the vacuum and vent solemoid valves to control vacuum at the vaccuum actuator.
- ABS ECU - it converts wheel speed sensor signals and sends information to the traction control ECU.
- Transaxle ECU - it sends signals from the automatic transmission to the traction control ECU.
- Steering wheel sensor - its sends a steering wheel angle signal to the traction control ECU.
- Accelerator position sensor - detects accelerator movement and sends signals to the traction control ECU.
- Stop lamp switch - it sends the signal to thr traction control ECU when the brake pedal is pushed.
- Vacuum actuator - which opens or closes the throttle valve to reduce engine torque.
- Vacuum tank - it provides vacuum to operate the vacuum actuator.
- Vacuum solenoid valves - it regulates vacuum by opening o closing passages between the vacuum tank and the vaccum actuator.
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