ABS Hydraulic Circuits and Valve Operation

GENERAL INFORMATION
Through the following operation descriptions and diagrams. The function of the various hydraulic control valves in the ABS system will be described. The fluid control valves mentioned below, control the flow of pressurized brake fluid to the wheel brakes during the different modes of Antilock braking. The following hydraulic circuit drawings are only a representation of the actual hydraulic circuits. Note that only the valves for the right front wheel brake are shown actuated for the various modes.

Brake Released - Hydraulic Control Teves Mark IV-G ABS:

BRAKES RELEASED
When the brake pedal is in its fully released position, all pressures in the brake hydraulic system are equalized and are at atmospheric pressure.

ABS Baseline Brakes - Hydraulic Control Teves Mark IV-G:

BASE BRAKE SYSTEM
The Baseline Brake System is a diagonal split brake system. In a diagonal split brake system the master cylinder primary circuit supplies pressure to the right front and left rear wheel brakes. The master cylinder secondary circuit supplies pressure to the left front and right rear wheel brakes.

Pressure Hold - Hydraulic Control Teves Mark IV-G ABS:

PRESSURE HOLD
During an ABS stop, if a wheel speed sensor indicates a wheel locking tendency. The normally open inlet valve is cycled closed by the CAB. This will prevent any additional pressure from being applied to the wheel brake.

Pressure Decay - Hydraulic Control Teves Mark IV-G ABS:

PRESSURE DECAY
If the wheel locking tendency continues, the Controller Antilock Brakes CAB releases the pressure by opening the normally closed outlet valve. With the outlet valve open, fluid is stored in the accumulators.

Pressure Build - Hydraulic Control Teves Mark IV-G ABS:

PRESSURE BUILD
Once the locking wheel begins to accelerate the CAB closes the outlet valve and opens the inlet valve in order to rebuild the wheel brake pressure. The pressure is reapplied from the master cylinder and the accumulators which may cause the brake pedal to drop.