Description And Operation-Braking Systems
GENERAL NON-eBOOSTER BRAKING SYSTEM OPERATION: The Integrated Control Unit (ICU) consists of the Brake System Control Module (BSCM) and Hydraulic Control Unit (HCU). The BSCM monitors the signal from the Brake Pedal Position (BPP) Sensor mounted on the Brake Pedal assembly and Master Cylinder Pressure (MCP) Sensor signal, mounted inside the HCU to detect when the Brake Pedal is applied. The BSCM also monitors the pressure sensors in each hydraulic circuit to calculate the Brake Torque signal. The calculation is based on the sum of pressure applied to the caliper in each hydraulic circuit. These signals are broadcast on the CAN bus. When the BSCM receives an autonomous brake input it controls a motor/actuator inside the Hydraulic Assembly to apply hydraulic pressure to the calipers to brake the vehicle.
GENERAL eBOOSTER BRAKING SYSTEM OPERATION: The Electronic Booster (eBooster) system consists of the Brake System Control Module (BSCM) and Hydraulic Control Unit (HCU). The system does not use a conventional Master Cylinder mounted on the booster. During normal operation there is no direct link between the Brake Pedal and the hydraulic circuits to the calipers. To maintain normal Brake Pedal feel, when the Brake Pedal is pressed it creates hydraulic pressure in a fluid filled chamber inside the HCU. The pressure acts on a cap and spring inside the chamber allowing the pedal to get firm. This system uses a Brake Pedal Simulator Pressure Sensor in place of the MCP Sensor and two unique Brake Pedal Position (BPP) Sensors to monitor for an operator braking input. The BSCM monitors these and other inputs, and controls a motor/actuator inside the HCU to apply hydraulic pressure to the calipers during an operator braking input or autonomous braking event.
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.
WHEEL SPEED SENSOR OPERATION: Wheel Speed Sensors (WSS) are used to monitor vehicle speed and wheel slip conditions. The Wheel Speed Sensors are hard-wired to the Brake System Control Module. The BSCM broadcasts the WSS signals on the CAN bus. The BSCM performs circuit fault diagnostics for the WSS sensors and wiring. The BSCM and PCM perform rationality checks against the outputs from the sensors. This is described in detail in the DIAGNOSTIC OVERVIEW information below. The WSS signals are also compared to the Steering Wheel Angle and Dynamic Sensors. Comparing these signals together can determine when the vehicle is in a turning event or if there is a fault in one of the WSS signals.
ANTI-LOCK BRAKING EVENT: During a braking event, the BSCM monitors the WSS signals to detect a wheel lock condition due to a skid event. If a wheel is determined to be locked, the BSCM cycles the Outlet Valve. Cycling the valve off/on relieves and applies the pressure to the wheel to correct the condition. The pressure will be regulated until the wheel lock condition is no longer present.
TRACTION CONTROL AND ELECTRONIC STABILITY CONTROL (ESC): If a wheel spin condition is detected during driving, and the brakes are not being applied, the BSCM will cycle the Inlet Valve in the system, applying braking to the wheel to correct the wheel slip condition. The system monitors the steering wheel angle, yaw rate and lateral acceleration (Dynamic Sensor) and Wheel Speed Sensors to determine an over/under steer condition. The BSCM will open the appropriate Inlet Valves, applying braking to counteract the condition.