Assembly of gear and rotating shaft, and assembly method therefor

An assembly of a gear and rotating shaft, comprising:

• the gear, the rotating shaft, and a first side and a second side with respect to an axial direction thereof,
• the gear having teeth on an outer peripheral surface thereof, and a center hole having an inner peripheral surface penetrating in the axial direction through a center portion thereof, the inner peripheral surface of the center hole comprising a cylindrical surface;
• and
• the rotating shaft assembled with the rotating shaft inserted into the center hole from a second side of the center hole toward a first side of the center hole with respect to the axial direction with an end portion on a first side of the rotating shaft leading towards the first side of the assembly with respect to the axial direction,
• wherein the rotating shaft includes a serrated shaft portion having a male serration portion on an outer peripheral surface thereof and press-fitted into the center hole with an interference fit against the cylindrical surface of the inner peripheral surface of the center hole, and a guide shaft portion provided adjacent to the serrated shaft portion on the first side of the rotating shaft with respect to the axial direction and having an outer diameter capable of being internally fitted in the center hole with a clearance fit such that a minute gap exists between the inner peripheral surface of the center hole and an outer peripheral surface of at least a portion of the guide shaft portion in an assembled state of the assembly, and
• wherein the center hole has a first chamfered portion at an end portion of the inner peripheral surface of the center hole on the second side of the center hole with respect to the axial direction, and a second chamfered portion at a portion of the inner peripheral surface adjacent to the first chamfered portion, the second chamfered portion having a smaller chamfer angle than the first chamfered portion.