Patent ID: 7213693

Claim:
A rotational transfer mechanism including: a hollow-cylindrical rotary output shaft having an inner peripheral surface serving as a torque transfer cylindrical surface; a rotary input shaft positioned radially inside said hollow-cylindrical rotary output shaft to be rotatable relative to said hollow-cylindrical rotary output shaft; a circumferentially-uneven-width-space forming portion which includes at least one cam surface, and is formed on said rotary input shaft to form at least one accommodation space between said rotary input shaft and said torque transfer cylindrical surface, said accommodation space having different radial widths at different circumferential positions; and at least one torque transfer member installed in said accommodation space, said torque transfer member being movable in said accommodation space in a circumferential direction to wedge between said cam surface and said torque transfer cylindrical surface to cause said rotary input shaft and said hollow-cylindrical rotary output shaft to become integral with each other in said circumferential direction when said rotary input shaft rotates relative to said hollow-cylindrical rotary output shaft, wherein said torque transfer member is circular in cross section along a plane orthogonal to a rotational axis of said rotary input shaft and said hollow-cylindrical rotary output shaft, wherein the shape of a cross section of said cam surface along a plane orthogonal to said rotational axis is defined by a straight line which passes through said rotational axis and an axis of said torque transfer member which is in contact with said cam surface; an imaginary circle having the same cross sectional shape as said torque transfer member on said straight line at a point thereon where an axis of said imaginary circle and said axis of said torque transfer member are symmetrical with respect to said rotational axis; a cam-surface defining circle which inscribes both said imaginary circle and said torque transfer member; and a circular arc which forms a part of said cam-surface defining circle as said cam surface.