#
ABS (ABS/TCS) HU PART CONSTRUCTION/OPERATION

id041300202100

## Construction

• The ABS (ABS/TCS) HU mainly consists of the pressure-retention/pressure-reduction solenoid valves, pump motor (pump) and reservoir.

### Function Of Main Component Parts

Part name | Function
--- | ---
Pressure-retention solenoid valve | • Adjusts the fluid pressure in each brake system according to ABS (ABS/TCS) CM signals.
Pressure-reduction solenoid valve | • Adjusts the fluid pressure in each brake system according to ABS (ABS/TCS) CM signals.
Reservoir | • Temporarily stores the brake fluid from the caliper piston to ensure smooth pressure reduction.
Pump | • Returns brake fluid stored in the reservoir back to the master cylinder.
Pump motor | • Operates the pump according to ABS (ABS/TCS) CM signals.

### Hydraulic Circuit Diagram

.

1 | Master cylinder
2 | Pressure-retention solenoid valve
3 | Pressure-reduction solenoid valve
4 | Pump
5 | Pump motor
6 | Reservoir
7 | Caliper piston

## Operation

### Normal braking or pressure increase mode

  • During normal braking or pressure increase mode the inlet and outlet solenoid valves are not energized: the inlet solenoid valve is open and the outlet solenoid valve is closed. Brake fluid pressure from the master cylinder flows through the inlet solenoid valve and is transmitted to the caliper piston. At this time, the pump motor does not operate. (Description for single front wheel only)

Solenoid valve operation table

Inlet solenoid valve | Outlet solenoid valve | Pump motor, pump
--- | --- | ---
OFF (open) | OFF (closed) | Stopped

1 | Master cylinder
2 | Pressure-retention solenoid valve
3 | Pressure-reduction solenoid valve
4 | Pump
5 | Pump motor
6 | Reservoir

### Pressure reduction mode

  • During pressure reduction mode, when the wheels may possibly lock-up due to emergency braking or similar, the inlet solenoid valve closes and the outlet solenoid valve opens. The brake fluid being applied to the caliper piston flows out through the outlet solenoid valve into the reserve tank, thereby decreasing pressure. During this operation, the pump motor operates, returning the brake fluid stored in the reserve tank to the master cylinder. (Description for single front wheel only)

Solenoid valve operation table

Inlet solenoid valve | Outlet solenoid valve | Pump motor, pump
--- | --- | ---
ON (closed) | ON (open) | Operating

1 | Master cylinder
2 | Pressure-retention solenoid valve
3 | Pressure-reduction solenoid valve
4 | Pump
5 | Pump motor
6 | Reservoir

### Pressure maintain mode

  • During pressure maintain mode, both the inlet and outlet solenoid valves are closed. The path for the brake fluid being applied to the caliper piston is blocked and brake fluid pressure is maintained. (Description for single front wheel only)

Solenoid valve operation table

Inlet solenoid valve | Outlet solenoid valve | Pump motor, pump
--- | --- | ---
ON (closed) | OFF (closed) | Stopped

1 | Master cylinder
2 | Pressure-retention solenoid valve
3 | Pressure-reduction solenoid valve
4 | Pump
5 | Pump motor
6 | Reservoir