Wheel driving device for pedal propelled cycle

A wheel driving device for a pedal propelled cycle which includes left and right mounts spaced apart from each other in an axial direction, a wheel body disposed between and rotatable relative to the left and right mounts about an axis, and left and right cranks provided respectively with left and right pedals for driving the wheel body to rotate about the axis, said wheel driving device comprising:

• an axle including
• left and right mounted portions opposite to each other in the axial direction, said left and right mounted portions being adapted to be rotatably mounted on and to extend outboard to the left and right mounts, respectively, and terminating at left and right ends, respectively, said left and right ends being adapted to couple with the left and right cranks, respectively, and to be driven to rotate synchronously by a drive force acting on one of the left and right pedals,
• left and right annular race segments opposite to each other in the axial direction and inboard to said left and right mounted portions, respectively, and
• abutting and engaging segments opposite to each other in the axial direction and inboard to said left and right annular race segments, respectively, said engaging segment having an externally threaded surface;
• a hub shell having first and second lateral ends which are disposed opposite to each other in the axial direction, and an inner peripheral wall surface which extends in the axial direction to communicate said first and second lateral ends and which is disposed to be spaced apart from said abutting and engaging segments in radial directions relative to the axis to confine a surrounding accommodation space, said inner peripheral wall surface including first and second wall portions respectively proximate to said first and second lateral ends, and an intermediate wall portion interposed between said first and second wall portions, said first wall portion having a first friction wall surface;
• left and right antifriction bearings respectively disposed between said second lateral end and said left annular race segment, and between said first lateral end and said right annular race segment, such that said intermediate wall portion and said first wall portion are disposed to surround and to be rotatable relative to said abutting segment and said engaging segments, respectively, and such that said first friction wall surface confronts said engaging segment in a radial direction relative to the axis;
• a coupling socket disposed in said surrounding accommodation space, and movable relative to said intermediate wall portion in the axial direction, said coupling socket including
• an engaging end having a second friction wall surface which confronts said first friction wall surface, and an internally threaded portion which is disposed opposite to said second friction wall surface radially and which is movable in the axial direction between a fully engaged position, where said externally threaded surface is in a full threaded engagement with said internally threaded portion as a result of a clockwise rotation of one of said left and right ends of said axle, which corresponds to a forward movement of the wheel body, such that said second friction wall surface is frictionally engaged with said first friction wall surface to transmit the drive force through said engaging segment to said hub shell, thereby rotating the wheel body, and a partially engaged position, where said externally threaded surface is in a partial threaded engagement with said internally threaded portion as a result of a screwing-out movement of said internally threaded portion relative to said externally threaded surface, such that said second friction wall surface is disengaged from said first friction wall surface to place the wheel body in a freewheeling state, and
• a coupling end disposed opposite to said engaging end in the axial direction, and extending towards said second lateral end;
• and
• a coil spring disposed around said abutting segment to bias said second friction wall surface to move towards said first friction wall surface such that when the clockwise rotation of said one of said left and right ends of said axle is terminated suddenly by arresting turning movement of a corresponding one of the left and right pedals while the forward movement of the wheel body continues as a result of inertia, said internally threaded portion rotates relative to said externally threaded surface in a screwing-out movement against biasing action of said coil spring so as to be disposed in the partially engaged position, thereby placing the wheel body in the freewheeling state.