#
ABS HU PART CONSTRUCTION/OPERATION

BME041343750T12

## Construction

• The ABS HU mainly consists of the inlet/outlet solenoid valves, reservoir and pump.

### Hydraulic circuit diagram

1 | Inlet solenoid valve
2 | Outlet solenoid valve
3 | Reservoir
4 | ABS pump
5 | ABS motor
6 | Master cylinder
7 | Front brake caliper
8 | Rear brake caliper
9 | Check valve

### Main component parts

  Solenoid valve
  • The solenoid valves control the fluid pressure at individual brake calipers in accordance with the signal received from the ABS CM.
  • There are eight solenoid valves in total and in each wheel two solenoid valves (one for retaining pressure and one for reducing pressure) are used. There are four valves for the front wheels, and the left and right wheels are controlled separately. There are four valves used to control the rear wheels simultaneously.
  Reservoir
  • The reservoirs temporarily store the hydraulic pressure which flows from the brake caliper through the outlet solenoid valve during pressure reduction.
  Pump
  • The pump returns brake fluid from the reservoir to the master cylinder.

## Operation

• The ABS HU/CM controls ABS by calculating wheel slip from ABS wheel-speed sensor signals, and adjusting the brake pressure.

| Inlet solenoid valve | Outlet solenoid valve | ABS motor
--- | --- | --- | ---
Normal brake and pressure increase | Off (open) | Off (close) | Stopped
Pressure retention | On (close) | Off (close) | Stopped
Pressure reduction | On (close) | On (open) | Operating

1 | Normal brake and pressure increase
2 | Master cylinder
3 | ABS motor
4 | ABS pump
5 | Reservoir
6 | Off (open)
7 | Off (close)
8 | Inlet solenoid valve
9 | Outlet solenoid valve
10 | Brake caliper
11 | Pressure reduction
12 | On (close)
13 | On (open)
14 | Pressure retention