The present invention relates to a downhole driving unit (11) for insertion into a well, comprising a driving unit housing (51), a hydraulic motor (23) comprising a hydraulic motor housing (93), a wheel assembly (90) comprising a stationary part (91) and a rotational part (92), the stationary part being connected with the driving unit housing and being rotatably connected with the rotational part, the stationary part and the rotational part constituting the hydraulic motor housing, the rotational part comprising a wheel ring (99) closed from one end, wherein the wheel assembly comprises a spring member (113) assembling the hydraulic motor housing. The present invention also relates to a downhole system comprising the driving unit according to the invention and an operational tool connected with the driving unit for being moved forward in a well or borehole as well as to a use of the driving unit according to the invention in a well or borehole for moving itself and/or an operational tool forward in a well or borehole.