Trailer coupling with a sensor assembly and a rotating reciprocating rod

The tow coupling (10a) has a coupling unit (11a) which has a ball carrier (13) and a coupling ball (15a) for rotatable supporting of a coupling receiver (18) of a trailer hitch ball coupling (16) of a roll trailer (17). A rotary driving device (31a) is provided with a rotary drive body (30a) that is projected from the ball upper surface (23) in a contact position.