Patent GB-591589-A (GB)
Title: Improvements in or relating to servo-motors
IPC: F15B13/14
Filed: 1944-09-14
Abstract: 591,589. Fluid-pressure servomotorcontrol systems. DAVY & UNITED ENGINEERING CO., Ltd. (United Engineering & Foundry Co.). Sept. 14, 1944, No. 17609. [Class 135] A fluid-pressure servomotor comprises an oscillatable driven member adapted to be connected to a load, a housing, driving means in the housing connected to said driven member and having an opening therein, said means being oscillatable in the housing and dividing it into a pair of expansible and contractible chambers adapted to receive fluid under pressure, and manually operable fluid control means mounted in said opening in the driving means for movement in a helical path therein to control the delivery of pressure fluid to said chambers and thereby produce a pressure differential in the chambers for moving the driving means selectively in either direction, the relation of the driving means to the control means being such that the farther the latter is moved relative to the driving means, the greater is said pressure differential, and said control means being so formed that its said relative movement is resisted by the fluid pressure whereby increased manual effort is required to actuate the control means where a greater fluid pressure differential is required for moving a greater. load connected to said driven member. In an embodiment, an operating handle 27 is secured to the end of a piston valve 26 and is adjustably counterweighted at 30. Rotation of the handle causes the valve to move in a helical path in the axial direction due to the interengagement of threads 42 on the valve and on a rotary sleeve 4, the latter being secured to a lever 10 connected to the device to be operated. The sleeve rotates in a casing comprising flanged members 1, 2 and a cylindrical member 3, the casing housing a fixed semi-circular block 5 and a block-like vane 9 connected to the sleeve 4 so that the latter and the lever 10 rotate with the vane. Pressure fluid enters by the port 12 and, in the central position of the valve, flows equally past the valve faces .39, 40 to both sides of the vane 9 and also past valve faces 37, 38 to exhaust passages in the block 5. When the valve is moved axially, one set of passages will be throttled and the other correspondingly opened, and the differential pressure that will thus be applied to the vane will cause the latter to move and carry round with it the sleeve 4 and lever 10. Owing to the different sizes of the faces of the valve, differential pressures will be applied thereto by the pressure fluid, and the resultant pressure will oppose the original movement to give " feel to the operator. Movement of the sleeve will re-centre the valve through the action of the interengaging threads 42. If the device actuated by the servomotor offers but little resistance to movement, the friction between the two sets of threads 42 will not be overcome and the movement of handle 27 will actuate the lever 10 directly. As shown, the pressure fluid is supplied by a constant volume pump, but, in a modification for use with a constant pressure pump, the valve lands slide inside the seatings provided on the sleeve 4, and, in the central position, flow to and from the vane is cut off. The handle 27 may be pivoted to the base of the casing and be connected by a link to the plate 28 carried on the end of the valve.