1
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Rear wheel speed sensor
2
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Hydraulic control unit (HCU)
3
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Front wheel speed sensor
The anti-lock control consists of a conventional brake system with diagonally split dual-circuits, a hydraulic control unit , wheel sensors and sensor rings. The anti-lock control incorporates electronic brake force distribution and low speed anti-wheelspin control.
The hydraulic control unit consists of:
- hydraulic actuator
- brake pressure pump
- module
- wheel speed sensors
The wheel speed signals required for the anti-lock control – anti-wheelspin control are supplied by four wheel sensors. The signals are compared with the physical limiting values stored within the module.
If the wheel speed of one or more of the wheels approaches the locking limit during braking, the corresponding solenoid valves are activated by the module to create a brake pressure drop that releases the appropriate brakes.
If the wheel speed now exceeds the locking limit, the brake pressure is switched on by the module. The brake pressure pump rapidly increases the pressure to the relevant brakes to equal the brake pressure applied by the brake pedal. The solenoid valves are deactivated during the pressure build-up phase.
This procedure can be repeated several times per second depending on the condition of the road surface and the duration of the braking procedure. This is known as the control frequency.
Anti-lock control does not come into effect at road speeds of less than 5 km/h (3 mph).
The electronic brake force distribution system limits the slip of the rear wheels before the anti-lock control comes into effect. The system is able to optimise the brake distribution, by comparing the slip of the front and rear wheels, for maximum driver control regardless of the vehicle loading. The system also eliminates the need for a load apportioning valve, as it automatically compensates for all conditions of vehicle loading.
The anti-wheelspin control is designed to prevent wheelspin in such conditions as driving on wet or icy roads.
The system is integrated with the anti-lock control. Both systems use the same wheel speed sensors, hydraulic actuator and module. The anti-wheelspin control system does require additional valves to be incorporated into the hydraulic actuator anti-wheelspin control can only be fitted in conjunction with anti-lock control.
The system operates by transferring torque from the spinning wheel to the wheel with the most traction. This is achieved by applying the relevant brake using the hydraulic control unit.
The system is active at road speeds up to 50 km/h (30 mph).
The warning indicator will illuminate for approximately three seconds after key-on and then extinguish if no faults are present in the system.
If the system should develop a fault the warning indicator will illuminate continuously. Only when the fault has been rectified will the warning indicator revert to normal operation.
