Electric parking brake having a gearing with a torque limiting device

A vehicle disc brake assembly having a hydraulically actuated service brake and an electrically actuated parking brake, wherein the vehicle disc brake assembly comprises:

• a brake disc;
• a first brake piston having a first inner portion;
• a first spindle nut rotationally restrained in the first brake piston and having a first outer portion, wherein the first outer portion is configured to clamp against the first inner portion to produce a first clamp force when the first spindle is rotated and the first clamp force engages the first brake piston against the brake disc;
• a second brake piston having a second inner portion;
• a second spindle nut rotationally restrained in the second brake piston and having a second outer portion, wherein the second outer portion is configured to clamp against the second inner portion to produce a second clamp force when the second spindle is rotated and the second clamp force engages the second brake piston against the brake disc;
• an electric motor configured to produce a torque to actuate and apply the parking brake;
• a first torque limiting device configured to, during an application of the parking brake, fully transmit a first portion of the torque to the first spindle when a first threshold value exceeds the first clamp force and not fully transmit the first portion of the torque to the first spindle when the first clamp force exceeds the first threshold value;
• and
• a second torque limiting device configured to, during the application of the parking brake, fully transmit a second portion of the torque to the second spindle when a second threshold value exceeds the second clamp force and not fully transmit the second portion of the torque to the second spindle when the second clamp force exceeds the second threshold value, wherein each of the first and second torque limiting devices comprises:
• a first gear;
• a drive plate;
• a shaft extending from the drive plate through the first gear and being rotatable with the respective spindle;
• pockets in an end face of at least one of the first gear and the drive plate;
• force transmitting members;
• and
• a spring member producing a spring force on the drive plate, wherein, during the application of the parking brake, the spring force
• holds the force transmitting members compressed in the pockets to transmit a force between the first gear and the drive plate when the spring force exceeds a portion of a clamp force and
• does not hold the force transmitting members in the pockets, and the force is not transmitted between the first gear and the drive plate, when the portion of the clamp force exceeds the spring force;
• wherein for each of the first and second torque limiting devices the shaft is rotatably connected to the respective spindle and moves axially relative to the spindle in response to the spring force.