GB693837A - Improvements in or relating to screw and nut mechanisms - Google Patents

Abstract

693,837. Screw-and-nut gearing. BISHOP, R., JOHNSTON, R. H., and WHITLOCK, G. B. R. Oct. 1, 1951 [Aug. 8, 1950], No. 19744/50. Classes 80 (i) and 80 (iii). [ Also in Group XXXI] A screw-and-nut mechanism applicable to a jack or a steering gear comprises a screw having a triple start thread of partcircular or V section, and a nut having three coplanar balls held in an annular cage which constitutes the driving or driven member, the balls being held in their respective threads by freely rotatable bearing races which are adjustable for wear. In a steering gear, Fig. 1, wherein a nut member is mounted at the top of a steering column 12 through resilient elements 13, a non-rotatable screw 1 is axially moved by rotation of a cage 11 secured to the steering wheel and having three coplanar apertures in each of which is mounted a ball 9. The balls are held in their respective threads by two spaced annuli 7, 7a rotatably mounted by ball bearings 5 in adjustably interthreaded portions 3a, 3b of the nut member. The screw 1 extends throughout the column 12, projects through a bearing 14 and bellows 17 at the lower end, and carries a pin 16 engaging a slot in a rocker arm, Fig. 4 (not shown). Alternatively. Fig. 3 (not shown), the bearing 14 is omitted and the pin 16 is directly pivoted to a rocker arm, lateral movement of the screw 1 being accommodated by the elements 13. In a modification, Fig. 5, a driving cage 11 has two axially spaced series of apertures 10, 10a, receiving balls having separate outer races and a common inner race element 23. In a further modification, Figs. 6-8 (not shown), wherein a nut member similar to that of Fig. 1 is mounted at the lower end of a steering column, i.e. adjacent the rocker arm housing, and is rotated by a cage extending the length of the column, a pin on the axially moved screw engages an open-ended slot in the rocker arm and carries a roller running in a groove in the inner face of the rocker arm housing. In a construction wherein the screw is rotatable and forms the driving member, the threaded part thereof is contained in the rocker arm housing and is engaged by three balls 9, Fig. 10, running on ball bearings 35 and held in a cage 11 adjustably secured, Fig. 11 (hot shown), to the nut. The nut has a projection 37 carrying a pin and roller engaging the rocker arm, and an enlargement 40 engaging a guide rod 42. Alternatively the enlargement and guide rod may be dispensed with and the pin be extended to carry a roller engaging a groove in a cover plate 25a. This groove may be rectilinear or shaped to give a controlled rotation of the nut. A construction of combined nut and cage is shown having two series of balls 9 similar to the two series shown in Fig. 5. In a steering mechanism not employing a rocker arm, a screw 1, Fig. 14, is axially displaced transversely of the vehicle and, is universally jointed at its ends to arms on the road wheels. The cage 11 is rotated by the steering shaft 62 through gearing 61, 63, rotation of the screw 1 being prevented by a ball 52 which engages a groove 53 therein. It is stated that in all modifications it is possible to employ a screw having a single-start thread, the balls 9 being then axially as well as angularly spaced and each being provided with a set of races and ball bearings.