Improvements relating to leadscrew mechanisms

摘要

914,165. Screw-and-nut gearing. FAIREY CO. Ltd. Dec. 7, 1959 [Sept. 8, 1958], No. 28792/58. Class 80 (3). [Also in Group XXXIV] In a lead-screw mechanism which comprises two co-operating screw-threaded members, the co-operating surface of one of the two members is provided with at least three recesses or groups of recesses distributed circumferentially around the axis of rotation of the lead-screw, each recess or group of recesses having a fluid connection to a source of pressurized fluid whereby a continuous flow of fluid can be maintained from each recess through a clearance gap between cooperating parts of the nut and lead-screw to a low-pressure outlet, the arrangement being such that changes in the position of the leadscrew relative to the nut in a radial direction result in pressure changes in the clearance gaps in a sense which will tend to restore the lead-screw to a central position in the nut. The flanks of the thread formation of the nut 11 are formed with recesses 13, 14, or alternatively helical recesses distributed along the length of the thread, pressurized oil being fed to the recesses of each flank through a separate restrictor or restrictors 17. The oil flows through the clearance between the flanks of the co-operating threads of the screw and nut to the relatively large clearance passage 26 between the root of the nut thread and the crest of the lead-screw thread. In a modification, Fig. 5, the flanks of a rectangular thread are formed with recesses 35, 36 and the root surface of the nut thread is also formed with recesses 40 connected to a separate pressurized system to counteract radial forces, the low-pressure outlet being formed by the large clearance 43 between the root and crest of the nut and screw thread, respectively. The lead-screw may be supported at one or each end by a multiple ring thrust bearing 50, the annular flanks 58, 59 of the stationary rings 54-57 having recesses connected to a pressurized oil system. In an application where the axis of the screw is vertical and supporting a heavy load, the restrictor values may be selected so that in the mean flank clearance position a pressure differential exists to support the static load without imposing any limitation on the upward drive thrust.