Hydraulic Circuits and Valve Operation

GENERAL INFORMATION
Through the following operation descriptions the function of the various hydraulic control valves in the ABS 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 ABS braking.

For explanation purposes, all wheel speed sensors except the right front are sending the same wheel speed information. The following diagrams show only the right front wheel in a antilock braking condition.

NORMAL BRAKING HYDRAULIC CIRCUIT AND SOLENOID VALVE FUNCTION

Normal Braking Hydraulic Circuit:

This condition is the normal operation of the vehicles base brake hydraulic system. The hydraulic system circuit diagram shows a situation where no wheel spin or slip is occurring relative to the speed of the vehicle. The driver is applying the brake pedal to build pressure in the brake hydraulic system to apply the brakes and stop the vehicle.

TEVES MARK 20 ABS CIRCUIT AND SOLENOID VALVE FUNCTION

ABS Mode Hydraulic Circuit:

This hydraulic circuit diagram shows the vehicle in the ABS braking mode. This hydraulic circuit shows a situation where one wheel is slipping because the driver is attempting to stop the vehicle at a faster rate than the surface the vehicle's tires are on will allow. The normally open and normally closed valves modulate the brake hydraulic pressure as required. The pump/motor is switched on so that the brake fluid from the low pressure accumulators is returned to the master cylinder circuits. The brake fluid will then be routed to either the master cylinder or the wheel brake depending on the position of the normally open valve.

TEVES MARK 20 SECONDARY ABS CIRCUIT AND SOLENOID VALVE FUNCTION

ABS Mode Secondary Hydraulic Circuit:

This hydraulic circuit diagram shows the vehicle in the ABS braking mode. This hydraulic circuit shows a situation where one wheel is slipping because the driver is attempting to stop the vehicle at a faster rate than the surface the vehicle's tires are on will allow. The normally open and normally closed valves modulate the brake hydraulic pressure as required. The pump/motor is switched on so that the brake fluid from the low pressure accumulators is returned to the master cylinder circuits. The brake fluid will then be routed to either the master cylinder or the wheel brake depending on the position of the normally open valve. A volume of 1.2 cc's of brake fluid is taken in by the lip seal saver to protect the lip seals on the piston of the master cylinder.