Drive mechanism for a bicycle transmission assist mechanism
A drive mechanism for a bicycle transmission assist mechanism includes a crank arm having a drive member. The drive member includes a first abutment facing a forward rotational direction of the crank arm and a non-concave sloped surface facing a rearward rotational direction of the crank arm.
1. A drive mechanism for a bicycle transmission assist mechanism comprising:
a crank arm having a crank axle mounting hole around a rotational axis;
a drive member supported coaxial with the rotational axis and including:
a first abutment facing a forward rotational direction of the crank arm; and
a first sloped surface extending from a radially outer portion of the abutment and facing a rearward rotational direction of the crank arm;
wherein the drive member is not structured to couple sprockets to the crank arm; and
wherein an outer peripheral surface of the drive member at a location of intersection with a radially inner portion of the first abutment extends at a substantially constant radius of curvature for more than 20°.
2. The drive mechanism according to claim 1 wherein the drive member further comprises:
a second abutment facing a forward rotational direction of the crank arm; and
a second sloped surface extending from a radially outer portion of the abutment and facing a rearward rotational direction of the crank arm; and
wherein the outer peripheral surface of the drive member at a location of intersection with a radially inner portion of the second abutment extends at a substantially constant radius of curvature for more than 20°.
3. A drive mechanism for a bicycle transmission assist mechanism comprising:
a bicycle crank arm having a crank axle mounting boss including a crank axle mounting hole and a rotational axis, wherein the crank axle mounting boss protrudes axially;
a drive member disposed at the crank axle mounting boss and including:
an outer peripheral surface;
wherein an abutment is disposed on the outer peripheral surface and faces a forward rotational direction of the crank arm;
wherein the abutment rotates around the rotational axis at a substantially constant radius; and
wherein the outer peripheral surface at a location of intersection with a radially inner portion of the abutment extends convex for at least 20°; and
wherein the drive member is not structured to couple sprockets to the crank arm.