Antilock Brakes / Traction Control Systems: Description and Operation
Fig. 3 System Components & Locations.:
1990-93
1994-95
The Anti-Lock Brake System (ABS) prevents the wheels from locking up when braking, regardless of the surface conditions. This allows the car to stop in a shorter distance, and allows the driver to maintain directional control of the vehicle during heavy braking.
During normal braking conditions, the ABS operates like a conventional system. During heavy braking, however, each wheels braking pressure is modulated according to its speed. To maintain vehicle stability, both rear wheels receive the same signal. There are four major components, Fig. 3, in the ABS which act in unison to control brake operation.
Traction control System (TCS)
If a driver accelerates hard on a snowy or otherwise slippery road, the driving wheels will start to spin, the degree of acceleration will decrease and the vehicle's stability will be reduced. With the TCS, all this is replaced with a stable feeling of safety - a car that is easier to drive thanks to the added functionality of TCS.
The TCS uses engine throttle control as well as an advanced system for individual control of the rear left and right brakes. It simply puts an appropriate amount of brake force on the spinning wheel, thus forcing the spin to end. On top of this, there is also Rear Viscous LSD, which neutralizes wheel spin occurring on uneven surfaces or when accelerating while turning. One doesn't need to mention the importance of the stability this renders to the driving wheels.
If both rear wheels should spin at the same time, the system prevents further torque from being applied by the engine by closing the throttle.
As a result of the TCS - the combination of Rear Viscous LSD and TCS - new levels of cornering performance and traction are achieved. This, combined with improved control of the driving wheels, is a vital factor in relieving the driver of stress - while the driver retains firm control of the car.
This system consists of the following components: 1) Wheel sensors 2) TCS control unit 3) Throttle control module (T.C.M.) 4) Throttle motor 5) TCS actuator 6) SLIP indicator 7) TCS OFF indicator.
1. Wheel speed sensors
These are positioned on all four wheels where they measure the individual speed of each wheel.
2. TCS control unit
On the basis of input signals from the wheel sensors and other sources, this control unit evaluates factors such as wheel slip and road and driving conditions. After evaluation, it sends control signals to the TCS actuator and the throttle control module. This is the heart of this optimal traction control system. This control unit possesses both self-diagnosis and fail-safe functions. When an abnormality is detected, the system releases its control over the throttle and brakes and returns everything to normal. In addition, this unit possesses an ABS function.
3. Throttle control module (T.C.M.)
This module receives the signal from the TCS control unit, whereupon it immediately alerts the throttle motor, which in turn optimally controls the degree of opening of the secondary throttle.
Here, again, a fail-safe device will operate if something is found to be out of the ordinary. In such a case, the TCS control unit is alerted and control of the throttle function is immediately released.
4. Throttle motor
The secondary throttle, positioned upstream of the throttle, the latter being controlled by the driver, opens and shuts in accordance with the throttle control module (T.C.M.) signals, thereby regulating engine drive torque.
5. TCS actuator
According to the signal from the TCS control unit, the degree of wheel spin is optimally controlled by increasing, holding or decreasing the individual brake fluid pressure of the left and right rear brakes.
6. SLIP indicator
This indicator will light when the TCS system is operating, thus alerting the driver to the fact that the road surface is slippery and informing the driver of when the vehicle is nearing its limits of stability.
7. TCS OFF indicator
When the TCS cancel switch is turned ON, this indicator will light and the TCS will not operate. In addition, when an abnormality is detected, this system will enter fall-safe. At this time, the SLIP Indicator and the TCS OFF Indicator will light, and/or the ABS warning lamp will light.