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, which 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.
| ITEM | DESCRIPTION |
|---|---|
| 1 | Caliper piston |
| 2 | Thrust nut |
| 3 | Spindle |
| 4 | Spindle thread |
| 5 | Flat surface |
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. The fluid flows around the nut during mechanical operation by the Electric Park Brake (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 and disconnects the power supply when it equates to a clamp load of 18.7 kN being applied by the thrust nut.
When the EPB is released, the electric motor turns the spindle for approximately 800 milliseconds to retract the thrust nut and release the pressure on the caliper piston.