Circumferential rigidity of both axial end portions of each coupling-side convex portion is lower than circumferential rigidity of an axially intermediate portion of each coupling-side convex portion. The drive-side concave-convex portion is engaged with a half portion on the other axial side of the coupling-side concave-convex portion. The driven-side concave-convex portion is engaged with a half portion on one axial side of the coupling-side concave-convex portion.

A driving-side transmission portion of an output shaft of an electric motor and a driven-side transmission portion of a worm shaft are coupled to each other via a torque transmission joint including an elastic member and a coupling such that the torque can be transmitted. One axial end portion of a coupling-side concave-convex portion of the coupling is engaged with a first driving-side concave-convex portion of the driving-side transmission portion with a gap in the circumferential direction, and the other axial end portion thereof is engaged with a first driven-side concave-convex portion of the driven-side transmission portion with a gap in the circumferential direction. The elastic member is provided between an axial center portion of the coupling-side concave-convex portion, and a second driving-side concave-convex portion of the driving-side transmission portion and a second driven-side concave-convex portion of the driven-side transmission portion such that the torque can be transmitted respectively.

A connection system includes two connecting elements each having a respective connecting flange on which a plurality of coupling elements are arranged along a peripheral direction and which has a substantially round external profile; and a coupling belt, on which a plurality of opposing coupling elements are arranged which are configured to form a positive-locking connection with the coupling elements of the two connecting elements for the mutual rotation-proof fixing of the two connecting elements.

An adaptor is disclosed for connecting a generator to a prime mover. The adaptor comprises two separable parts. By providing an adaptor comprising two separable parts, it may be possible for one part to be removed in order to allow access to moving parts which would otherwise be inaccessible. This may simplify the process of servicing moving parts such as a coupling or bearings, without requiring the generator and the prime mover to be moved apart. A coupling with a radially removable elastomeric component is also disclosed.