GB1132889A - Screw and nut mechanism - Google Patents

Abstract

1,132,889. Screw-and-nut gearing; disc brakes. ROTAX Ltd. 11 July, 1966, No. 31020/66. Headings F2E and F2Q. In a recirculating ball type screw-and-nut mechanism (Fig. 1, not shown) having an efficiency greater than 50%, one member of which is driven from an input shaft 19 through a worm 18 and wormwheel 12, also with an efficiency greater than 50%, to move a load applied to one of the members, on removal of the driving effort on the shaft 19 the axial thrust thereon due to the load on the screw-and-nut gearing actuates a braking device associated with the shaft 19 to prevent rotation of the gearing. The shaft 19 runs in thrust bearings 25 housed in rotatable collars 24 connected to the shaft 19 by one-way clutches 27. Fixed annular friction pads 26 are engageable by the outer end faces of the collars 24 for braking. When the shaft 19 is driven in one direction, the axial thrust on the worm 18 will cause one collar 24 to engage its pad 26, so that the collar remains stationary, the associated one-way clutch allowing rotation of the shaft. On removal of the drive, the thrust on the worm remains in the same direction, but the shaft 19 will be urged to rotate in the opposite sense by the load, the one-way clutch engaging to prevent such reverse rotation. To allow the load to move in the return direction, the shaft 19 must be driven to overcome the friction torque due to the collar 24 and pad 26. The second collar/pad assembly is effective for a load in the opposite direction. The worm-wheel 12 may be secured between two nut members (16), rotatable but axially located, with the screw (14) axially movable (Fig. 1, not shown), or alternatively the wormwheel may drive the screw, and the nut member be connected to the load.