Antilock Brakes / Traction Control Systems: Description and Operation

PURPOSE

The Anti-Lock Brake System (ABS) consists of electronic and hydraulic components. It allows for control of braking force so that locking of the wheels can be avoided. The ABS:
1) Improves proper tracking performance through steering wheel operation.
2) Eases obstacle avoidance through steering wheel operation.
3) Improves vehicle stability.

OPERATION

^ When the vehicle speed is less than 10 km/h (6 MPH) this system does not work.
^ The Anti-Lock Brake System (ABS) has a self-test function. The system turns on the ABS warning lamp for one second each time the ignition switch is turned ON. After the engine is started, the ABS warning lamp turns off. The system performs a test the first time the vehicle reaches 6 km/h (4 MPH). A mechanical noise may be heard as the ABS performs this self-test. This is a normal part of the self-test feature. If a malfunction is found during this check, the ABS warning lamp will stay on.
^ While driving, a mechanical noise may be heard during ABS operation. This is a normal condition.





ABS HYDRAULIC CIRCUIT

Part 1 of 2:

SYSTEM COMPONENTS





Sensor
The sensor unit consists of a gear-shaped sensor rotor and a sensor element. The element contains a bar magnet around which a coil is wound. The sensor is installed on the back side of the brake rotor. Sine-wave current is generated by the sensor as the wheel rotates. The frequency and voltage increase(s) as the rotating speed increases.





Control Unit
The control unit computes the wheel rotating speed by the signal current sent from the sensor. Then it supplies a DC current to the actuator solenoid valve. It also controls ON-OFF operation of the valve relay and pump relay. If any electrical malfunction should be detected in the system, the control unit causes the warning lamp to light up. In this condition, the ABS will be deactivated by the control unit, and the vehicle's braking system reverts to normal operation.