7. Hydraulic unit

The hydraulic unit essentially consists of fast switching electromagnetic valves and a return pump.

Regardless of the pressure in the brake master cylinder, the hydraulic unit can change the fluid pressure to the wheel brake cylinders (holding or reducing pressure). Increasing the pressure above that of the brake master cylinder is not possible, however.

The ABS 5.3 hydraulic unit has three hydraulic outputs (3-channel system) and six electromagnetic valves (three inlet and three outlet valves). 

The ABS / TC 5.3 hydraulic unit has four hydraulic outputs (4-channel system) and ten electromagnetic valves (four inlet valves / four outlet valves, one switch-over valve and one intake valve). 

The intake and switch-over valves are required so that the return pump can perform two tasks:

I. Return flow to the brake master cylinder (pressure reduction) for ABS control.

II. Supply (pressure increase) to the right or left rear-wheel brake cylinder for TC control (ABD control).

In the case of ABS control at the rear axle, the solenoid valves for both rear wheels are actuated in parallel (joint control as in Solo ABS control (3-channel system)).