Hydraulic Control Assembly - Antilock Brakes: Description and Operation

Modulator Unit
The modulator unit consists of the inlet solenoid valve, outlet solenoid valve, VSA Normally Open (NO) solenoid valve, VSA Normally Closed (NC) solenoid valve, reservoir, pump, pump motor, and the damping chamber.
The modulator controls the caliper fluid pressure directly. It is a circulating-type modulator because the brake fluid circulates through the caliper, the reservoir, and the master cylinder.
The hydraulic control has three modes: pressure intensifying, pressure retaining, and pressure reducing.
The hydraulic circuit is an independent four channel type, one channel for each wheel.