Ball nut and screw assemby with enhanced radial load capacity

A ball nut and screw assembly comprising a screw having an external helical groove defining groove portions separated by helical land portions, a nut received on said screw, said nut having an internal helical groove defining groove portions separated by helical land portions and co-operating with said external helical groove to define a first helical raceway between said nut and screw having an axial lead, a train of first balls received in said first helical raceway, said first helical raceway being adapted to contact said first balls only along opposite generally radially extending sides thereof, said first balls being operable in said first helical raceway to effect relative translation of said nut and screw on relative rotation thereof wherein essentially all axial loading of said nut and screw is through said first balls, a radial load bearing raceway configuration on said nut and screw cooperatively defining a second helical raceway between said nut and screw having substantially the same axial lead as said first raceway and which is helically interwoven with said first raceway, a train of second balls received in said second helical raceway and rolling therealong on relative rotation of said nut and screw without transmitting drive therebetween, and said second helical raceway and said second balls being adapted to be in continuous contact in a radial lashless relationship so as to react essentially all radial loading of said nut.