The brake assist system consists of the following:
The hydraulic brake boost system uses fluid from the power steering pump (8) through the hydraulic boost inlet hose (3) and to the brake booster assembly (4). In addition to supplying the brake system with fluid for increased apply, the power steering pump is also connected to the power steering gear (6) and cooler (7).
The steering pump (8) is a continuous flow device supplying approximately 3 GPM at 1000 RPM, at the pump shaft. The fluid flows through the booster spool valve, then the return hose (5), and then to the steering gear (6). Pressure is produced by applying the brake pedal, resulting in the spool valve being actuated, internal to the hydraulic brake booster. The spool valve produces a marginal restriction that causes pressure in the booster (4) to rise and forces the power piston and therefore the output rod forward to generate force and motion at the master cylinder (1). The brake corners are actuated by the fluid impulse generated by the master cylinder (1). Internal blow by, or pressure relief, is directed to the low pressure return hose (2) back to the power steering pump (8).
Brake system input force is multiplied by the brake pedal and transferred by the pedal pushrod to the hydraulic brake master cylinder. Effort required to apply the brake system is reduced by the vacuum brake booster.
Incorporated into the vacuum brake booster, is an electric solenoid actuator. This actuator can be used to apply the brake booster and thus the master cylinder as commanded by the electronic brake control module (EBCM). During stability events, the EBCM can command the solenoid actuator in the brake booster to apply the booster. This quickly provides a large volume of pressurized brake fluid to the brake pressure modulator valve (BPMV). The BPMV will then control the flow of fluid to the brake corners to obtain the appropriate response for the vehicle.
