4. Back-up Brake Function: 4 Wheel Back-up / ESC Hydraulic Brake Boost
Describes brake circuit in case of Hydraulic Power Unit (HPU) failure.
As shown in the diagram, all valves are not active in the HPU. Because NO VALVE3 is not operating, the simulator chamber pressure is not generated when the brake pedal is engaged as the brake field of the simulator chamber is linked to the reservoir tank. However, when the simulator rod begins to move as the brake pedal is engaged, the boosting chamber rod is mechanically pushed. This generates pressure in the master cylinder. This pressure is transferred to the ESC, which then controls the wheels in pressurized mode to achieve braking. The ESC therefore controls braking if the HPU fails.
| AHB System | NO VALVE 1 | NO VALVE 2 | NO VALVE 3 | NC VALVE 1 | NC VALVE 2 | Motor |
|---|---|---|---|---|---|---|
| Mode | OFF(opened) | OFF(opened) | OFF(opened) | OFF(closed) | OFF(closed) | OFF |