Patent ID: 6851535

Claim:
A tuning method for the exciting current-transmission torque characteristic of a power transmission apparatus, wherein the power transmission apparatus comprises: an outer rotary member having a groove; an inner rotary member, which is arranged to rotate relative to the outer rotary member; a friction clutch located between the inner and outer rotary members; an electromagnetic drive apparatus for driving the friction clutch when receiving an exciting current, wherein the electromagnetic drive apparatus includes an electromagnet that is energized by the exciting current and an armature, the electromagnet and the armature being located on opposite sides of the friction clutch; and a yoke, which supports the electromagnet, wherein part of the yoke and the electromagnet are located in the groove, and wherein a first clearance and a second clearance are formed between the yoke and inner surfaces of the groove, wherein there is a first distance between the yoke and the groove at the first clearance and a second distance between the yoke and the groove at the second clearance, the tuning method comprising: changing the first distance while maintaining the second distance constant.