Wheel hub drive

A wheel hub drive including a wheel hub and a drive means for selectively driving said wheel hub, said drive means including a housing, a drive motor, a hollow output shaft operatively connected to said drive motor and having a first end located within said wheel hub, a planetary gear train including an input-end sun wheel rotated by said hollow output shaft, an output element fixed to said wheel hub, releasable connection means located at said first end of said hollow output shaft for selectively connecting and disconnecting said wheel hub and said hollow output shaft, an axially movable means for moving said releasable connection means, and means actuated by pressurized hydraulic fluid and by a spring force for moving said releasable connection means axially to connect and disconnect said releasable connection means to control rotation of said wheel hub by said drive means for said wheel hub, said means for moving said releasable connection means axially being an axial rod having a first end adjacent to said first end of said hollow output shaft and a second end, a piston having a first face fixed to said second end of said axial rod and a second face, spring means in contact with said first face of said piston to urge said piston in a first axial direction to connect said releasable connection means and means to supply a pressurized hydraulic fluid to said second face of said piston to move said piston against the force of said spring means in a second axial direction to disconnect said releasable connection means.