Brakes, Anti-Lock

When the brake pedal (2455) is applied, the anti-lock electronic control module (2C018) senses the drop in rear wheel speed. If the rate of deceleration is too great, indicating that wheel lockup is going to occur, the anti-lock electronic control module activates the RABS valve, causing the isolation valve to close. With the isolation valve closed, the rear wheel cylinders (2261) are isolated from the brake master cylinder (2140) and the rear brake pressure cannot increase. If the rate of deceleration is still too great, the anti-lock electronic control module will energize the dump solenoid with a series of rapid pulses to bleed off rear wheel cylinder fluid into an accumulator built into the RABS valve. This will reduce the rear wheel cylinder pressure and allow the rear wheels (1007) to spin back up to vehicle speed. Continuing under anti-lock electronic control module control, the dump and isolation solenoids will be pulsed in a manner that will keep the rear wheels rotating while still maintaining high levels of deceleration during braking.

At the end of the stop, when the operator releases the brake pedal, the isolation valve de-energizes and any fluid in the accumulator is returned to the brake master cylinder. Normal brake operation is resumed.