Anti-Lock Brake System: Description
The Anti-Lock Brake System (ABS) eliminates wheel lock by modulating hydraulic pressure applied to the brake calipers. The system is assisted by the power hydraulic system.
Modulation of hydraulic pressure is achieved by a modulator containing 3 solenoid actuated valves, one valve in each hydraulic line to the front calipers and one in a common hydraulic line to the rear calipers. Each valve is controlled by the Electronic Control Unit (ECU). See Fig 1.
The ECU actuates the valve solenoids from inputs generated by speed sensors made of variable reluctance coils. Each wheel sensor is located close to an exciter disc attached to each wheel hub. Individual wheel deceleration rate is thus calculated and the perssure applied to the calipers is cycled through the control sequence and optimum brake efficiency is achieved.