Antilock Brakes / Traction Control Systems: Description and Operation

ANTI-LOCK OPERATION

Fig. 1 Hydraulic Assembly:

The Anti-Lock Braking 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 diagonally split, hydraulic power assist system. During heavy braking, however, each wheel's braking pressure is modulated according to its speed. To maintain vehicle stability, both rear wheels receive the same signal.

There are four major components, in this ABS system that act in unison to control brake operation.

During Anti-Lock Braking, brake pressures are modulated by cycling electric valves. The cycling of these valves can be heard as a series of popping or ticking noises. In addition, the cycling may be felt as a pulsation in the brake pedal, although no pedal movement will be noticed. If Anti-Lock operation occurs during hard braking. Some pulsation may be felt in the vehicle body due to fore and aft movement of the vehicles suspension as brake pressures are modulated.

Although ABS operation is available at virtually all vehicle speeds. It will automatically turn off at speeds below 3 to 5 mph. Therefore wheel lock-up may be perceived at the very end of an Anti-Lock stop and should be considered normal.