Electrically operated parking brake apparatus

A parking brake apparatus, comprising:

• an electric motor;
• a screw mechanism including a screw-threaded shaft adapted to be rotationally driven by said electric motor, and a nut member meshing with said screw-threaded shaft, said nut member being movable along said screw-threaded shaft by the rotation of said screw-threaded shaft;
• a transmission member connected to said nut member for transmitting a brake operating force to a wheel brake;
• and
• a rotation preventing unit for confining said screw-threaded shaft to a stationary portion of a vehicle body thereby preventing rotation of said screw-threaded shaft so as to hold said brake operating force by fixing a position of said nut member relative to said screw-threaded shaft,
• wherein the rotation preventing unit is an electromagnetic brake comprising:
• a core fixed to a stationary portion side of said vehicle body;
• a coil accommodated in said core to surround said screw-threaded shaft;
• a rotor fixed to an outer periphery of said screw-threaded shaft;
• a plate opposing to a back side of said rotor, said plate being movable in a longitudinal direction of said screw-threaded shaft;
• an armature disposed between said stationary portion side of said vehicle body and a front side of said rotor to be movable in the longitudinal direction of said screw-threaded shaft;
• a first coil spring disposed between said stationary portion side of said vehicle body and said armature;
• and
• a second coil spring disposed between said armature and said plate, a biasing force of said first coil spring being set to be stronger than a biasing force of said second coil spring.