DESCRIPTION
Rear Wheel Antilock (RWAL) brake system. The RWAL brake system is designed to prevent rear wheel lock-up under heavy braking conditions on virtually all types of road surfaces. RWAL braking is desirable because a vehicle which is stopped without locking the wheels will retain directional stability. This allows the driver to retain greater control of the vehicle during braking.
The RWAL components include
- RWAL Valve
- Antilock Brake Module (ABM)
- Rear Wheel Speed Sensor (WSS)
OPERATION
When the brakes are applied, hydraulic fluid is routed from the master cylinder's secondary circuit, to the RWAL valve. From there hydraulic fluid is routed to the rear brake wheel cylinders. The Controller Antilock Brake monitors rear wheel speed through the rear wheel speed sensor. If a wheel is about to lock-up, the ABM signals the RWAL valve. The RWAL valve modulates the hydraulic brake pressure to the rear wheels to prevent wheel lock-up.
The G-sensor is located inside the ABS controller. The sensor is not a separate serviceable part from the controller.
The HCU consists of a valve body, pump motor, low pressure accumulators, inlet valves, outlet valves and noise attenuators.
Accumulators in the valve body store extra fluid released to the system for ABS mode operation. The pump provides the fluid volume needed and is operated by a DC type motor. The motor is controlled by the ABM.
The valves modulate brake pressure during antilock braking and are controlled by the ABM.
The HCU provides three channel ABS or four channel With Traction Control pressure control to the front and rear brakes. One channel controls the rear wheel brakes in tandem ABS . The two remaining channels control the front wheel brakes individually.
During antilock braking, the solenoid valves are opened and closed as needed.
During normal braking, the HCU solenoid valves and pump are not activated. The master cylinder and power booster operate the same as a vehicle without an ABS brake system.
Note. The three modes mentioned below do occur but not necessarily in the order listed every time.
During antilock braking, solenoid valve pressure modulation occurs in three stages, pressure increase, pressure hold, and pressure decrease. The valves are all contained in the valve body portion of the HCU.