Hydraulic Control Assembly - Antilock Brakes: Description and Operation

ABS Modulator





The ABS modulator consists of inlet solenoid valves, outlet solenoid valves, reservoir, pump, and the pump motor. The modulator reduces the caliper fluid pressure directly. It is a circulating-type modulator because the brake fluid circulates through the caliper, reservoir, and the master cylinder. The hydraulic control has three modes: normal braking, pressure retaining, and pressure reducing. The hydraulic circuit is an independent four channel type, one channel for each wheel.

Normal braking mode
Inlet valve open, outlet valve closed
Master cylinder fluid is pumped out to the caliper.

Pressure retaining mode
Inlet valve closed, outlet valve closed
Caliper fluid is retained by the inlet valve and outlet valve.

Pressure reducing mode
Inlet valve closed, outlet valve open
Caliper fluid flows through the outlet valve to the reservoir.
When in pressure reducing mode, the pump motor is ON.
The reservoir fluid is pumped out by the pump, through the damping chamber, to the master cylinder.
When stopping ABS operation, the pump motor is OFF.