Spindle and Thrust Nut
| 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 around the nut during mechanical operation by the parking brake system and hydraulic operation by the brake pedal or ABS module.
Operation of each EPB actuator is controlled by the EPB module via two hardwired connections with the electric motor. The EPB module changes the polarity of the connections to change the direction of drive of the motor.
In each EPB actuator, when the parking brake is applied the electric motor turns the spindle to press the thrust nut against the caliper piston and apply the brake. The EPB module measures the current draw of the electric motor and disconnects the power supply when it equates to a clamp load of 11.40 to 16.5 kN being applied by the thrust nut.
When the parking brake 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.