VSA System Description - Components
VSA Modulator
The VSA 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, the pressure sensor, and the pump motor. The hydraulic control has four modes; pressure intensifying, pressure retaining, pressure reducing, and pressure intensifying mode.

Mode
VSA NO
Solenoid
Valve
VSA NC
Solenoid
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
closed
closed
Caliper fluid is retained by the inlet and outlet solenoid valves.
Pressure reducing mode
open
closed
closed
open
Caliper fluid flows through the outlet solenoid valve to the reservoir.
Pressure intensifying mode (VSA)
closed (current control )
open
open
closed
Master cylinder fluid is pumped out by the pump through the VSA NC solenoid valve to the caliper.
Caliper fluid pressure exceeds master cylinder pressure.
The VSA modulator unit controls amount of intensified fluid pressure to respond to each mode through current control of VSA NO solenoid valve.
Wheel Speed Sensor
The VSA system uses 4 wheel speed sensors to monitor individual wheel speed. The wheel speed sensor is a semiconductor, Hall effect sensor, and detects the magnetic field of a magnetic encoder installed on the inner sealing surface of each hub and wheel bearing assembly. The frequency of the sensor output signal is proportional to the speed of the wheel and this signal information is sent to the VSA control unit.