Hydraulic Control Unit
| ITEM | DESCRIPTION |
|---|---|
| 1 | Anti-lock Brake System (ABS) control module |
| 2 | Rear right brake caliper outlet port |
| 3 | Front left brake caliper outlet port |
| 4 | Front right brake caliper outlet port |
| 5 | Rear left brake caliper outlet port |
| 6 | Primary circuit inlet port |
| 7 | Secondary circuit inlet port |
| 8 | Hydraulic Control Unit (HCU) |
The Hydraulic Control Unit (HCU) is located on the rear left side of the engine compartment. The HCU is an integral component with the Anti-lock Brake System (ABS) control module. The HCU is a 4 channel unit that modulates the supply of hydraulic pressure to the brakes under the control of the ABS control module.
The primary and secondary outlet ports of the brake master cylinder are connected via 8 mm (0.315 in) diameter brake pipes to the primary and secondary circuits of the HCU. The primary circuit in the HCU provides 2 separate outlet ports to the front right and rear left brake calipers. The secondary circuit in the HCU provides 2 separate outlet ports to the front left and rear right brake calipers.
Each of the HCU circuits contains the following components to control the supply of hydraulic pressure to the brakes:
- A normally open, solenoid-operated pilot valve, to enable active braking.
- A normally closed, solenoid-operated priming valve, to connect the brake fluid reservoir to the dual circuit return pump during active braking.
- A dual circuit return pump, driven by an electric motor, to generate hydraulic pressure for active braking.
- Normally open, solenoid-operated inlet valves and normally closed, solenoid-operated outlet valves, to modulate the hydraulic pressure in the individual brake calipers.
- An accumulator and a relief valve, to allow the fast release of pressure from the brakes.
- Filters to protect the internal components from contamination.
The HCU incorporates 3 brake operating modes as follows:
- Normal braking/Electronic Brake Force Distribution (EBD)
- ABS braking
- Active braking.
Details of these operating modes are given in the Anti-Lock Control - Traction Control Service Information. For additional information, refer to: Anti-Lock Control - Traction Control .