Brake and/or Accelerator Pedals - Operation
OPERATION
WITHOUT 5.7L HEV
The brake pedal is attached to the booster push rod. When the pedal is depressed, the primary booster push rod will move the booster secondary rod. The booster secondary rod will then depress the master cylinder piston, and the brakes will apply.
WITH 5.7L HEV
NOTE: The brake pedal assembly and it's components are serviced as an assembly only. The master cylinder may be replaced separately or as a unit with the active brake booster.
The brake pedal is attached to the booster primary push rod which is not directly connected to the booster secondary push rod. Instead, there is a pedal simulator assembly (2) which consists of a pedal simulator cut off solenoid (3) and a pedal simulator (4 ) which creates normal pedal feel during braking maneuvers. When there is a brake pedal application the pedal simulator creates pressure against the pedal while the transmission motors actually slow the vehicle, and in turn charge the 300V batteries. This is called regenerative braking.
When the brake pedal is depressed with a specific predetermined force/rate the booster will assist with normal brakes without the booster push rod connecting.
Under an emergency stop or a system fault the pedal simulator cut off solenoid will deactivate the simulator and allow the booster push rod to connect directly to the pedal. Under this condition the brake pedal will have slightly longer travel to allow direct contact with the booster push rod. For more information on regenerative braking Brakes - Operation.
Below is a brief explanation of the components of the brake pedal assembly that is unique to the 5.7L HEV:
- BRAKE PEDAL ASSEMBLYThe brake pedal assembly consists of the pedal bracket and all components as described below.
- BRAKE PEDAL ANGLE (BPA) SENSORThe BPA sensor has two signal circuits to the ABS module to accurately monitor the brake demand. One signal circuit increases voltage and the other signal circuit decreases voltage when the brakes are applied.
- BRAKE PEDAL SIMULATORThe brake pedal simulator consists of linkage that compresses a coil spring and rubber bumper (internally) to absorb the brake pedal input without mechanically pressing the brake master cylinder push rod. This process preserves brake pedal feel and allows regenerative braking.
- BRAKE PEDAL SIMULATOR CUT OFF SOLENOID (WITH PRESSURE SENSOR)The brake pedal simulator cut off solenoid is used to engage or disengage the pedal feel simulator and is controlled by the ABS module. Internal to the cut off solenoid are two small hydraulic chambers with spring loaded diaphragms that have an electronic solenoid in the fluid passage between the chambers that closes when activated. When energized the brake pedal feel simulator operates and when not energized the brake pedal feel simulator is deactivated. If voltage is lost to the cut off solenoid it defaults to deactivated and normal vacuum assisted braking remains. If the brake pedal feel simulator is deactivated the brake pedal travel will increase. The pressure sensor which is part of the brake pedal simulator cut off solenoid has a variable signal to the ABS module to determine how hard the brake pedal is being depressed.