Functional Enhancement of an Electric Parking Brake by “Sensorless” Motor Angle Measurement

Electric parking brakes are typically equipped with voltage and current sensors for control and safety purposes. Sensors for rotational or translational degrees of freedom of the actuator are not included for cost reasons. By usage of “sensorless” methods, these values can be measured or estimated through the already available electrical signals and hence contribute to a functional enhancement of the system without additional hardware costs. A new method is introduced for robust detection of an oscillation in the electrical motor signals of the electric parking brake whose frequency is proportional to the rotational speed. Hence, the motor can be used as an incremental encoder which allows for precise positioning of the leadscrew nut and in certain situations accordingly the brake piston. By this additional information about the system enhanced functions can be implemented. As examples a procedure for estimating the pad wear as well as control methods for a more accurate setting of the clamping force and clearance are presented.