ANTI-LOCK BRAKING SYSTEM — Purpose / Operation

• Excessive braking in any condition (Dry or wet) will adversely affect the normal turning of the vehicle's wheels and they may lock up. • When the front wheels are locked, a vehicle cannot be controlled by the steering system. • When the rear wheels are locked, the vehicle may become unstable. The A.B.S., by the use of electronic and hydraulic components, allows for control of braking force so that locking of the wheels can be avoided in the circumstances described above. The A.B.S.: 1. Ensures proper tracking performance through steering wheel operation. 2. Enables obstacles to be avoided through steering wheel operation. 3. Ensures vehicle stability by preventing spins.

The A.B.S. is controlled by an electronic control unit (E.C.U.), which receives signals from wheel speed sensors. The hydraulic circuit is controlled by an actuator containing an electric motor, pump, accumulator and 4 solenoid valve pairs (one pair per wheel). The E.C.U. directs the actuator to increase, hold or decrease hydraulic pressure to all or individual wheels. The E.C.U. receives information regarding wheel speed from sensors, mounted one per wheel. When excessive braking force causes a wheel to lock, the E.C.U. sends a current to the actuator to release the locked wheel. As the wheel unlocks, it can be steered. The E.C.U. senses wheel speed is increasing and re-applies hydraulic pressure. The wheel locks again, is released, steered, braked, and so on. This continuous locking and unlocking of the wheels allows for rapid speed reduction and the vehicle to be steered in the correct manner. The hydraulic pressure can also be "held" constant by a current sent from the E.C.U. to the actuator. The rear wheels also utilize the load-sensing valve to further prevent wheel locking, especially under minimum vehicle load conditions. The system only operates at speeds above 6 mph (10 km/h). The E.C.U. also has a self-diagnosis facility. Therefore, if a fault occurs on an A.B.S. component, the E.C.U. records the fault and returns the system to normal hydraulic operation.