The brake pressure is controlled during ABS operation by means of four pairs of solenoid valves, one inlet valve and one outlet valve per wheel brake, in the hydraulic unit.
The valve relay provides the positive supply for the solenoid valve as of ignition lock position 2.
The solenoid valves are switched by the ABS/ASC control unit applying ground.
Depending on the driving situation which is determined by the wheel speed signals, the following operating statuses can be represented by activation of the solenoid valves:
Operating status |
Solenoid valve / status |
|---|---|
Pressure build-up |
Inlet valve open (no power applied) |
|
Outlet valve closed (no power applied) |
Pressure retention |
Inlet valve closed (power applied) |
|
Outlet valve closed (no power applied) |
Pressure reduction |
Inlet valve closed (power applied) |
|
Outlet valve opened (power applied) |
The front wheels are controlled individually and the rear wheels jointly.
The solenoid valves can be switched 5 to 12 times per second during controlled braking.
The ABS/ASC pump is activated by the ABS/ASC control unit during ABS operation.
No power is applied to the input and output valves for the front wheel brakes during ASC operation. The ASC changeover valve is closed (power applied) and the ASC intake valve is open (power applied). The input and output valves for the rear wheel brakes are opened or closed depending on the control situation.
The ABS/ASC pump is activated by the ABS/ASC control unit during ABS operation.