Component Functional Description - Hydraulic Control Unit (HCU) Assembly

The HCU Assembly internal components are slightly different depending on the brake system. The functionality of applying the brakes is also different. During an Anti-lock braking, traction control or stability control event, the functionality of the systems is relatively the same.

• NON-eBOOSTER SYSTEMS:  The HCU on this system incorporates a Master Cylinder Pressure (MCP) Sensor, motor/actuator, hydraulic circuit pressure sensors, Inlet Valves and Outlet Valves. The Brake Pedal Position Sensor is external, but hard-wired to the BSCM. The BSCM in this system is capable of operating the motor/actuator inside the HCU to apply the brakes during an autonomous braking event. The vehicle operator can directly brake the vehicle by pressing on the Brake Pedal.

• eBOOSTER SYSTEMS:  The HCU on this system incorporates a Brake Pedal Simulator Pressure Sensor, two Brake Pedal Position (BPP) Sensors, motor/actuator, hydraulic circuit pressure sensors, Inlet Valves and Outlet Valves. The BSCM in this system operates the motor/actuator to apply the brakes during both vehicle operator input and autonomous braking events. During normal operation there is no direct link between the Brake Pedal and the hydraulic circuits to the calipers. However, if the BSCM is not able to monitor the Brake Pedal travel or pressure due to a fault in the system, a bypass valve is opened in the chamber which allows a direct connection between the hydraulic pressure in the chamber and the hydraulic circuits to the calipers.

The Inlet Valves allow the fluid and hydraulic pressure to the calipers in each hydraulic circuit. The Outlet Valves are used to relieve the pressure in each circuit. There are two pressure sensors located in each hydraulic circuit that allow the BSCM to monitor the pressure in the system for each circuit.