Electric Park Brake Actuators
| ITEM | DESCRIPTION |
|---|---|
| 1 | Electrical connector |
| 2 | Output shaft |
| 3 | Motor |
The Electric Park Brake (EPB) actuators are electro-mechanical positioning units attached to the calipers of the rear brakes. Each actuator incorporates a reversible electric motor driving an output shaft via a drive belt and planetary gear cluster.
The output shaft of the EPB actuator is engaged in the splined end of a spindle. The output shaft is inside the caliper piston and screwed into a thrust nut. Operation of the electric motor turns the spindle and produces linear movement of the thrust nut, to apply a target clamp load to the brake pads.
Two flat surfaces on the inside of the caliper piston prevent the thrust nut from turning with the spindle. Scallops around the circumference of the thrust nut allow the free flow of hydraulic fluid around the nut. This occurs during mechanical operation by the EPB system and hydraulic operation by the brake pedal or Anti-lock Brake System (ABS) control module.
Operation of each EPB actuator is controlled by the ABS control module via two hardwired connections with the electric motor. The ABS control module changes the polarity of the connections to change the direction of drive of the motor.
When the EPB is applied the electric motor turns the spindle to press the thrust nut against the caliper piston and apply the brake. The ABS control module measures the current draw of the electric motor. When the current equates to 18.5kN being applied to the thrust nut, the power supply is disconnected.
When the EPB is released, the electric motor turns the spindle to retract the thrust nut and release the pressure on the caliper piston. The electric motor operates for approximately 800 milliseconds
ANTI-LOCK BRAKE SYSTEM CONTROL MODULE
| ITEM | DESCRIPTION |
|---|---|
| 1 | Rear right brake outlet port |
| 2 | Front left brake outlet port |
| 3 | Front right brake outlet port |
| 4 | Rear left brake outlet port |
| 5 | Primary circuit inlet port |
| 6 | Secondary circuit inlet port |
| 7 | Hydraulic control unit |
| 8 | Electrical connector |
| 9 | Control module |
The Anti-lock Brake System (ABS) control module controls the two Electric Park Brake (EPB) actuators separately. A longitudinal motion sensor is integrated into the Restraints Control Module (RCM). The RCM communicates with ABS control module on the High Speed (HS) Controller Area Network (CAN) chassis systems bus. The longitudinal motion sensor allows the ABS control module to determine the longitudinal attitude of the vehicle and to monitor the deceleration of the vehicle.
Four hardwired connections with the EPB switch give the ABS control module the EPB apply and EPB release inputs. The EPB is integrated into ABS control module and the wheel speed sensors are also hard wired. Inputs from other components are received on the FlexRay circuit as follows:
- Accelerator Pedal Position (APP) sensor, from the Powertrain Control Module (PCM)
- Stop lamp switch, from the PCM
- Gear position, from the Transmission Control Module (TCM)
The ABS control module outputs status and fault signals on the FlexRay circuit and the HS CAN bus. These outputs operate the warning indicators and advise other systems if there is a fault with the EPB system.