Hydraulic Unit

The hydraulic unit is mounted below the master cylinder on the frame rail. Its components consist of:

^ Valve block with six solenoid valves

^ Motor with dual circuit return pump

^ Motor speed sensor





Valve Block

Six two-way electric solenoid valves are mounted in the valve block. There are three inlet and three outlet solenoid valves. Each front brake circuit has one inlet and one outlet valve. The third inlet and outlet valves control the regulation of the rear brake circuit.

In terms of the hydraulic circuitry, the inlet valves are between the brake master cylinder and the brake calipers, and the outlet valves are between the brake calipers and the master cylinder reservoir (via a return line).

The inlet valves are normally open valves, and the outlet valves are normally closed.





Return Pump

The return pump is a dual-piston pump, with one piston supplying the front brake circuits and the other piston supplying the rear brake circuit. The purpose of the pump is to ensure a sufficient volume and pressure supply of brake fluid during ABS regulation. When the pump is switched ON, brake fluid is drawn from the reservoir and pumped into the pressure circuits.

The pump does not run continuously during ABS regulation, but is swftched ON and OFF by the control unit as required. The signal from the motor speed sensor confirms pump operation to the control unit.





Pedal Sensor Operation

To prevent excessive travel of the brake pedal during ABS regulation, brake fluid is pumped back into the pressure circuits by the return pump.

During ABS regulation, the control unit monitors the brake pedal travel sensor and detects any changes in its signal.

As the pedal moves down during ABS regulation, the signal from the sensor changes, and the control unit switches ON the return pump, pumping brake fluid into the pressure circuits and moving the pedal back. When the pedal travel sensor reaches its original position (at the start of ABS regulation), the control unit switches OFF the return pump. This cycling of the return pump continues until ABS regulation ceases.