ABS

Description

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:
- Ensures proper tracking performance through steering wheel operation.
- Enables obstacles to be avoided through steering wheel operation.
- Ensures vehicle stability by preventing flat spins.

OPERATION
- When the vehicle speed is less than 10 km/h (6 MPH) this system does not work.
- The ABS has self-test capabilities. The system turns on the ABS warning lamp for 1 second after turning the ignition switch ON. The system performs another test the first time the vehicle reaches 6 km/h (4 MPH). A mechanical noise may be heard as the ABS performs a 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 come on.
- During ABS operation, a mechanical noise may be heard. This is a normal condition.

Fail Safe
If trouble occurs in the ABS, the ABS warning lamp in the combination meter comes on. At the same time, the vehicle stops the ABS control and braking becomes the same as that of a vehicle without ABS.





Hydraulic Circuit





System Components

Control Unit





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

ABS Actuator and Electric Unit (Control Unit)
The ABS actuator and electric unit (control unit) contains:
- An electric motor and pump
- Two relays
- Eight solenoid valves, each inlet and outlet for
- LH front
- RH front
- LH rear
- RH rear
- ABS control unit

These components control the hydraulic circuit that increases, holds or decreases hydraulic pressure to all or individual wheels. The ABS actuator and electric unit (control unit) cannot be disassembled and must be replaced as an assembly.








ABS ACTUATOR OPERATION

Wheel Sensors





The front wheel sensors consist of a gear-shaped sensor rotor and a sensor element. The element contains a magnet around which a coil is wound. The front wheel sensors are installed on the front of the wheel knuckles. As the wheel rotates, the sensor generates a square-wave signal. The frequency increases as the wheel speed increases.





The rear wheel sensors consist of wheel hubs with a series of internal magnets and a sensor element. The rear wheel sensors are installed on the inner side of the wheel knuckles. As the wheel rotates, the sensor generates a square-wave signal. The frequency increases as the wheel speed increases.