GB816773A - Improvements in or relating to electro-hydraulic valves - Google Patents

Abstract

816,773. Fluid-pressure servomotor-control systems; valves. HEALY, D. V. Aug. 2, 1955, No. 22207/55. Class 135. An electro-hydraulic control valve comprising a pair of spaced fluid discharge nozzles having pressure chambers connected through restricted passageways with a common source of pressure fluid, includes a resiliently mounted armature having first surface portions adjacent said nozzles which may be moved simultaneously in the same direction relative to said nozzles or in opposite directions relative thereto and electromagnetic means separate from the nozzles co-operating with further surface portions of the armature, so that the first surface portions are normally equidistant from their respective nozzles but on application of an electrical signal to the electromagnetic means, one of these portions moves towards and the other away from its adjacent nozzle. To control a relay valve 19, Fig. 1, controlling the supply and exhaust of pressure fluid to a double-acting servomotor 10, the valve comprises a pair of nozzles 37 disposed adjacent the ends of a low hysteresis armature 39 passing through a solenoid coil 42 to which electric signals may be transmitted through leads 60. The armature is resiliently supported on plate springs 63 slotted at their upper ends so that the ends of the armature may be adjusted with respect to the nozzles by means of screws 68. Permanent magnets 45, 46, Fig. 3, are secured to U-shaped polepieces 43, 44, partly enclosing the coil 42, so that the ends of one polepiece are north seeking and the ends of the other polepiece south seeking, and the strength of the magnetic field is such that in co-operation with the springs 63, the armature floats freely in the air-gap between the polepieces. To prevent magnetic particles clogging the nozzles and entering a casing 40 to which operating liquid is initially admitted, each nozzle is shrouded by a sleeve 50, so that the liquid after being discharged from a nozzle passes, in the main, between the nozzle and its sleeve. The liquid then passes through ducts 51, 52 and a restriction 58 to a drain outlet 16 which also serves as the drain outlet for the relay valve 19 and the servomotor 10. Operating liquid supplied under pressure is admitted to the control and relay valves through an inlet 15 and goes through a strainer 32 into a duct 33 having restrictions 34 to the nozzle chambers and also after passing the restrictions 34 through restrictions 57 to act on the opposite ends of the valve piston 18 of the relay valve. The control and relay valves are initially adjusted so that the discharge pressure at each nozzle is the same with the valve piston 18 in its neutral position with its positive lapped lands covering annular recesses 20, 21, 22. On an electrical signal being transmitted to the coil 42, the armature is magnetized and in conjunction with the polepieces and in accordance with the direction of the signal, one end of the armature moves towards one nozzle and the other end away from the other nozzle to unbalance the nozzle discharge pressures and hence the pressures acting on the opposite ends of the valve piston 18. In a modification, the sleeves 50 are replaced by caps surrounding the nozzles and closed at their upper ends. The caps being urged into engagement with the armature by springs. In another modification, caps 81, Fig. 8, are secured to the nozzles and plungers 82 carried by the armature slidably pass through holes in the closed ends of the caps. In both these modifications, all the operating liquid is returned to drain whence it becomes necessary to provide a recess 78, Fig. 6, in the casing 40 connected by a duct 79 to the drain ducts 51, 52. Any magnetic particles in the liquid passing to the casing 40 to maintain the required pressure therein then adhere to the lower polepiece at a position where least interference to the proper functioning of the valve is likely to occur. Should either of the nozzles become choked, the pressure at the effected nozzle will increase to dislodge the offending particles. In Fig. 6, the centralizing springs of Fig. 1 are omitted and the valve piston is reduced in diameter at its two ends. The reduced diameter ends 86 of equal area being subjected to servomotor cylinder pressure so that the valve piston after moving from its neutral position to operate the servomotor, is urged towards its neutral position by the pressure on the pressure side of the servomotor piston. Specifications 816,774 and 816,775 are referred to.