Pressure Limit Valve

Based upon wheel speed input signals, RWAL ECM controls hydraulic brake pressure to both rear wheels. Under normal conditions, RWAL system functions like a conventional brake system.

Normal wheel speed-to-acceleration/deceleration braking is programmed into RWAL ECM memory. If the difference between optimum braking rear wheel speed and actual braking rear wheel speed exceeds programmed limits, RWAL system will enter anti-lock mode.

During anti-lock mode, pressure in the rear wheel hydraulic circuit is modulated by the ECM through the pressure limit valve. This prevents rear wheel lock, while providing maximum stopping and directional stability. Pressure limit valve is located under the master cylinder and actually consists of 2 valves: a dump valve that releases pressure into an accumulator and an isolation valve that maintains rear wheel hydraulic pressure.

During anti-lock operation, a series of rapid pulsations (caused by the fluctuating position of the pressure limit valve) will be felt at the brake pedal. These pulsations, in conjunction with possible tire "chirping" (on dry pavement), are considered normal during anti-lock operation and will cease when normal braking is resumed or vehicle comes to a complete stop.