Modulator Unit

The modulator unit consists of the inlet solenoid valve, the outlet solenoid valve, the VSA NO (normally open) solenoid valve, the VSA NC (normally closed) solenoid valve, the reservoir, the pump, and the pump motor.

The hydraulic control has three modes of ABS action; pressure intensifying, pressure retaining, and pressure reducing. Pressure intensifying mode (VSA) is a combination of the TCS, VSA, and brake assist action.

The hydraulic circuit is an independent four channel type, one channel for each wheel.

Fig 1: Modulator Unit Circuit Diagram

Courtesy of AMERICAN HONDA MOTOR CO., INC.

Mode

VSA NO Valve

VSA NC Valve

Inlet Solenoid Valve

Outlet Solenoid Valve

Brake Fluid

Pressure intensifying mode

open

closed

open

closed

Master cylinder fluid is pumped out to the caliper.

Pressure retaining mode

open

closed

Caliper fluid is retained by the inlet and outlet valves.

Pressure reducing mode

open

closed

open

Caliper fluid flows through the outlet valve to the reservoir.
The motor pumps the reservoir fluid through the damping chamber to the master cylinder⁽¹⁾.

Pressure intensifying mode (VSA)

closed

open

closed

Master cylinder fluid is pumped out by pump with motor through VSA NC valve to the caliper.
Caliper fluid pressure exceeds master cylinder pressure.

⁽¹⁾	The motor will keep running until the operation of the anti-lock brake control is finished with the first pressure reducing mode.