GB1467932A - Position-responsive hydraulic cylinder - Google Patents

Abstract

1467932 Fluid-pressure servomotor systems DEERE & CO 15 May 1975 [15 May 1974] 20671/75 Heading G3P A hydraulic actuator, e.g. for positioning a tractor-drawn plough, comprises a piston 24 slidable within a cylinder 12 under the control of a valve 38 operated by a position selector (63), Fig. 1 (not shown), a screw-type feedback mechanism 100 being connected between piston-rod 16 and control valve 38 so as to restore the latter to a neutral position when the piston has moved to a position corresponding to that set by the selector. Valve 38 comprises a landed sleeve 51 axially slidable within a fixed bore 37 to control fluid-flow from an inlet port 42 to one or other of ports 40, 44 communicating respectively via passages 48, 46 with chambers 26, 28 on opposite sides of piston 24. Sleeve 51 also controls flow from the chambers to exhaust passage 36. Axial movement of sleeve 51 is limited by abutment surfaces 98, 98A. A further sleeve 52 is disposed within sleeves 51 and connected thereto by an arrangement 49 comprising a spring 90 held between washers 92, 92A retained by rings 94, 94A and 96, 96A. One end of sleeve 52 is threaded within a nut 76 externally slotted to receive two lugs on a bifurcated arm 68. The latter is fixed to a pivot shaft (66) Figs. 1, 4 (not shown) carrying a crank (64) connected via a cable (62) to the operator lever (58) of the position selector (63). Should lever (58) be moved to an excessive position, the spring arrangement 49 permits inner sleeve 52 to move relative to sleeve 51 after the latter has engaged abutment surfaces 98, 98A. Feedback mechanism 100 comprises an axially fixed screw 104 engaged by pins 106 on piston-rod 16 such that movement of the latter causes the screw to rotate within bearing 102. The screw has an extension 108 slidably passing through an oblong aperture 82 in the end of sleeve 52. Thus rotation of screw 104 is transmitted to sleeve 52 which, by virtue of its threaded engagement within non-rotatable nut 76, is caused to move axially together with outer sleeve 51 until valve 38 has been restored to its neutral position. A free-float valve 110 places both actuator chambers 26, 28 in communication with exhaust when operator lever (58) is moved into a minimum rod extension position. A scale (23) indicates the degree of rod extension. In a modification Fig. 6 (not shown) inner sleeve 51 and connecting spring 90 are not provided.