Anti-lock Brake Systems (ABS)

Originally developed for aircraft, ABS works by limiting the pressure to any wheel which decelerates too rapidly. This allows maximum stopping force to be applied without brake lockup. In operation, the wheelspeed sensors at each wheel send electronic pulse signals to the control unit. If wheel lockup (rapid deceleration) is detected during brake application, the computer signals the valve unit to limit the hydraulic pressure to the wheel cylinder. This is accomplished by diverting some of the fluid into a small reservoir, which is pumped out when the brakes are not being applied. The anti-lock brake system usually tests itself every time the vehicle is started and every time the brakes are applied. The system evaluates its own signals. If a defect is detected, the system then turns off, leaving normal braking unaffected.