Electrical actuation mechanism suitable for a disc brake assembly

An apparatus comprising:

• a motor for imparting rotary motion;
• a shaft;
• a conversion gear assembly operatively connecting said motor to said shaft, said conversion gear assembly converting rotary motion of said motor to axial motion of said shaft;
• a piston;
• and
• a seal sealingly engaged with said shaft and said piston, said shaft, said piston, and said seal defining a fluid chamber capable of containing a constant volume of fluid, thereby coupling said piston to said shaft so that said piston can move relative to said shaft
• where said shaft further defines an opening providing communication through said shaft into said chamber, said apparatus further including a valve for selectively preventing fluid from escaping said fluid chamber through said opening.

A disc brake assembly comprising:

• a rotor adapted to be connected to a vehicle wheel for rotation therewith;
• a caliper including an inboard leg, an outboard leg, and an intermediate bridge portion;
• an electrical actuation mechanism secured to said inboard leg of said caliper, said electrical actuation mechanism including a housing, an electrical motor disposed in said housing, and a spindle disposed in said housing and operatively coupled to said motor by a conversion gear assembly which is effective to convert rotary motion generated by said motor into axial movement of said spindle;
• a sensor for sensing the rotation of said motor;
• a clutch mechanism adapted to couple and uncouple said motor from said spindle by movement to, respectively, an engaged position and a disengaged position;
• and
• a spring wrap brake for preventing movement of said spindle when said motor is not engaged, said spring wrap brake is movable between an engaged, position, wherein movement of said spindle is prevented, and a disengaged position, wherein movement of said spindle is permitted, said spring wrap brake operatively coupled to said motor through said clutch for movement to said disengaged position by rotating motion of said motor when said clutch is engaged.