Electric Park Brake Actuators

Courtesy of JAGUAR LAND ROVER NORTH AMERICA, LLC

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 worm gear drive.

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. The linear motion applies a 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 drawn by the electric motor. The supply is disconnected when the current equates to 18.5 kN being applied to the thrust nut.

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