Crank knob arrangement on a crank arm

摘要

The axially movable arrangement of a crank knob on a crank arm, the crank knob being held under prestress in the rest position in a first limit position closely adjacent to the crank arm. The crank knob has an intermediate piece mounted on the crank arm in such a way as to be rotatable about the axis of rotation of the knob and has a grip which can be moved relative to the intermediate piece about the axis of rotation of the knob between two stops. The grip and the intermediate piece are in engagement via a controlling cam situated on one part and via a bearing surface situated on the other part and resting against the controlling cam under the effect of the prestress. On both sides of an apex, the controlling cam has two portions sloping in opposite directions. The grip and the intermediate piece are connected to one another by a clutch which can be released by a torque which is greater than the torque to be applied to the grip in order, by rotating the grip relative to the intermediate piece and overcoming the prestress, to move the bearing surface over one of the sloping portions until the grip comes up against the intermediate piece and hence to move the grip into a second limit position remote from the crank arm. The clutch can be designed as a slipping clutch which is held in engagement by the clamping element which serves to produce the prestress.