system can build, hold or reduce pressure at each wheel of the vehicle. This is determined by the signals generated by the wheel speed sensors (WSS) at each wheel and received at the Controller-Anti-Lock Brake (CAB).

MAJOR ABS COMPONENTS

The following is a list of major system components. Details of all components can be found later in this section.

HYDRAULIC ASSEMBLY

The Hydraulic Assembly (Fig. 1) provides the function of an integral master cylinder and hydraulic booster assembly, and contains the wheel circuit valves used for brake pressure modulation.

WHEEL SPEED SENSORS

A Wheel Speed Sensor (Fig. 2) is located at each wheel to transmit wheel speed information to the Controller Anti-Lock Brake (CAB).

CONTROLLER-ANTI-LOCK BRAKE (CAB)

The (CAB) (Fig. 3) is a small control computer that receives wheel speed information, controls Anti-Lock operation and monitors system operation.

Fig. 2 Wheel Speed Sensor

PUMP/MOTOR ASSEMBLY

The Pump/Motor Assembly (Fig. 4) is an electrically driven pump. It takes low pressure brake fluid from the hydraulic assembly reservoir and pressur-

Fig. 3 (CAB) Controller Anti-Lock Brake Module

Fig. 4 ABS Pump/Motor Assembly

izes it for storage in the accumulators for power assist and Anti-Lock braking.

ANTI-LOCK OPERATION AND PERFORMANCE

NORMAL BRAKING SYSTEM FUNCTION

Under normal braking conditions, the ABS System functions much the same as a standard brake system with a diagonally split master cylinder. The primary difference is that power assist is provided by hydraulic power assist instead of the conventional vacuum assist.

If a wheel locking tendency is noticed during a brake application, the system will enter Anti-Lock mode. During Anti-Lock braking, hydraulic pressure in the four wheel circuits is modulated to prevent any wheel from locking. Each wheel has a set of electrical solenoid valves and a hydraulic line to provide modulation, although for vehicle stability, both rear wheel valves receive the same electrical signal. The system can build, hold or reduce pressure at each wheel. Depending on the signals generated by the wheel speed sensors (WSS) at each wheel and received at the Controller-Anti-Lock Brake (CAB).

The ABS system represents the current state-of-the- art in vehicle braking systems and offers the driver increased safety and control during braking. This is accomplished by a sophisticated system of electrical and hydraulic components. That differ from conventional vacuum boosted hydraulic actuation systems. Because, there are several performance characteristics that may at first seem different but should be considered normal. These characteristics are discussed below. More technical details are discussed further in this section.

PEDAL FEEL

The ABS System uses hydraulic power assist for both normal power assisted braking and to provide a source of high pressure hydraulic fluid during AntiLock Braking. In general, pedal feel will be similar to that of a conventional vacuum boosted brake system. If during an Anti-Lock stop additional force is applied to the brake pedal, or the brake pedal is released and reapplied rapidly. The driver may notice a very hard pedal feel. This is due to normal isolation of the master cylinder during A.B.S. operation as wheel brake pressure is fed from the hydraulic booster.

ANTI-LOCK 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.

TIRE NOISE & MARKS

Although the ABS system prevents complete wheel lock-up, some wheel slip is desired to achieve opti-