US3025867A - Hydraulic servo-distributor with very small leakage - Google Patents

Description

March 20, 1962 R. LUClEN 3,025,867

HYDRAULIC SERVO-DISTRIBUTOR WITH VERY SMALL LEAKAGE Filed March 24, 1959 3 Sheets-Sheet 1 March 20, 1962 R. LUCIEN 3,025,867

HYDRAULIC SERVO-DISTRIBUTOR WITH VERY SMALL LEAKAGE Filed March 24, 1959 3 Sheets-Sheet 2 R. LUCIEN 3,025,867

' HYDRAULIC SERVO-DISTRIBUTOR WITH VERY SMALL LEAKAGE March 20, 1962 3 Sheets-Sheet 3 Filed March 24, 1959 F'IGA- FIGS I I l 3,025,867 HYDRAULHC SERVO DISTRIBUTOR WITH VERY SMALL LEAKAGE Ren Lucien, Nenilly-sur-Seine, France, assignor to Recherches Etudes Production KER, Paris, France, a

corporation of France Filed Mar. 24, 1959, Ser. No. 801,583 (Ilaims priority, application France Mar. 26, 1958 4 Qlaims. (Cl. 137-82) The present invention relates to hydraulic servo-distributors, and more particularly to hydraulic distributors consisting of two stages, the first stage being a distributor supplying the second stage, the second stage being a servomotor controlled by the first stage and actuating a slidevalve which supplies utilization units.

It is an object of the present invention to provide a servo-distributor having good performance from the servomechanical point of view and having very small internal leakage.

The said servo-distributor of the invention comprises two stages. The first stage comprises a motor of the type known as a torque-motor which moves a shutter, thus uncovering one or the other of a pair of jets or small nozzles, one being connected to an intake of fluid under pressure, the other to the return of fluid t a collector tank. A shutter chamber is thus placed under a variable pressure and the said pressure acts upon one face, which forms a piston, of a distribution slide-valve of the second stage. A second face of the said slidevalve also forms a piston and is subjected to supply pressure. The slide-valve is balanced when the hydrodynamic reactions on the two pistons are equal. Furthermore, the shutter is returned to its mean position by an elastic means such as, for example, a spring, but the distal extremity of this spring is fixed to the slide-valve, the arrangement of the spring being such that any displacement of the slide-valve tends, through the action of the said spring, to reduce the movement of the shutter which has caused the said displacement of the slide-valve. The force applied by this spring on the slide-valve is so small, as compared with the hydrodynamic forces applied on this slide-valve that it may be disregarded as a first approximation. As a consequence thereof, the slide-valve only recovers its balance if the pressure in the shutter chamber is restored to its initial valve. This can only take place if the shutter has returned to its initial position with respect to the jets or nozzles; that is, if the electrodynamic effort applied by the torque-motor to the shutter is exactly compensated by the effort applied by the spring to the shutter, this effort being proportional to the elongation of the spring, that is to say to the displacement of the slide-valve. Thus, the displacement of the slidevalve is proportional to the control current of the torquemotor without any displacement of the shutter.

The invention will be described below, reference being made to the accompanying drawing, given by way of example andnot by way of implied limitation, in which:

FIG. 1 is a diagrammatical illustration of the principle of the servo-distributor of the invention.

FIGS. 2 and 3 are respectively sections in plan and in elevation, of one construction of the servo-distributor of the invention.

FIGS. 4 and 5 are similar sections of another construction.

The principle of the invention will be more clearly explained below, reference being made to FIG. 1 in which the main units are illustrated diagrammatically, without any limitation being implied. In FIG. 1, the slide-valve T is provided with a piston q having a surface s subjected to the supply pressure P, and also with a piston Q having a surface S subjected to the pressure p in the chamber fifififi? Patented Mar. 20, 1962 containing the shutter chamber 0. This shutter 0 uncovers, in the course of its displacement, either the nozzle Gp fed under the pressure P, or the nozzle Gb for the return to the collector-tank B. The shutter is returned by two springs, Rf having a fixed point, and Rm attached to the slide-valve (the presence of the second spring does not essentially modify the operation, as described in connection with a single spring as will be explained below). The slide-valve T will be in equilibrium if pS:Ps; that is, if the shutter O has returned to its mean position (covering the two nozzles Gp and Gb) after setting up the pressure p in the shutter chamber. Following this, if the torque-motor applies a force F to the shutter 0, this latter will first be displaced in one direction or the other, for example, towards the left in the figure, thus uncovering the nozzle Gp. Since there is no flow of fluid out of the shutter chamber, the pressure in the shutter chamber instantaneously changes to the valve P and the slide-valve T is forced towards the right. This movement of the slide-valve T towards the right continues as long as the pressure in the shutter chamber does not return to the initial value p, on account of the condition of equilibrium pS=Ps. This is only possible if the shutter has returned to its initial position. For this position, the actions of the springs R and Rm counteract the electro-dynamic force F. Furthermore, for this condition to prevail the spring Rf must have returned to its initial length. Therefore, the extension of the spring Rm is proportional to the force F, that is to say to the displacement of the slide-valve T.

In order that the operation of the servo-distributor should remain properly symmetrical when the force F changes direction and in view of the condition of equilibrium pS=Ps, it is preferable, without being indispensable, to insure that the pressure p in the shutter chamber 0 is one-half the supply pressure P. This may be obtained by providing the piston Q with a surface S which is twice the surface s of the piston q. Under these conditions, at the commencement of the movement of the shutter 0 towards the left, the slide-valve T is subjected to a force towards the right equal to P(Ss) :Ps. The effects of friction on the slide-valve T are negligible as compared with this hydro-dynamic force Ps. The total output of the nozzle Gp during a displacement d of the slide-valve T is Sd corresponding to the increased volume Sd of the chamber bounded by S. Under the pressure P/2. The time required for this displacement is thus extremely small. Finally it is not necessary in this case to provide for a substantial continuous leakage at the first stage and it is possible to shut off the two nozzles almost entirely when at equilibrium without affecting the response of the servo-distributor. The resulting leakage is very many times less than the degree of leakage normally necessary for a standard first stage.

Experience shows that it is preferable to provide the slide-valve T with two springs which return it to its mean position. Since the force of the springs remains small compared with the hydrodynamic forces Ps which actuate the slide-valve, their effect, when the slide-valve T is not in its mean position, is only to produce a very small movement of the shutter O with respect to the mean position necessary to produce the very small difierence of the pressure p which counterbalances the said force of the springs on the surface S of the piston Q. These return springs have a double advantage. In the first place, the slide-valve, their effect, when the slide-valve T is not its mean position when the pressure increases, thus avoiding unnecessary jerks which are liable to be detrimental. In the second place, in the course of operation, the springs in question confer a certain static quality on the servodistributor which is favorable to the proper working of the device and prevents abrupt oscillations of the slide valve T which are liable to occur, for example, if the torque-motor receives successive and contradictory orders.

An embodiment of the invention will be described below with reference to FIGS. 2 and 3 which are given as examples of construction without any limitation being implied. The members already described also appear on these two figures with the same references. The torquemotor (FIG. 2) comprises a magnetic circuit ll, excited by two coils 2 and 2a, polarized by two permanent magnets, only one of these being visible at 3 (the other being placed above the plane of the figure). Sealing joints which may be seen in FIG. 2 on each side of a magnetic member 24 insure a fluid-tight chamber for the coils 2 and 2a which facilitates the passage of the wires of these coils and permits the utilization of a hydraulic fluid which is incompatible with the electrical insulators and enables the coils to be impregnated with any liquid, compound, varnish, or the like.

A further advantage of the fluid-tight wall 24 is to reduce the volume of the chamber housing the shutter O, and this has a beneficial effect on the quality of response of the servo-distributor since the said shutter chamber constitutes a dead space for the variations of the pressure p.

The electro-magnetic circuit is interrupted by an air-gap in which is housed the magnetic plate member 4 of the shutter two screws 5 and 6 acting on two springs 7 and 8 of non-magnetic metal enable the position of the plate 4 to be accurately adjusted. A membrane or diaphragm 9 prevents the fluid from flowing in the vicinity of the magnetic circuits, which fluid would tend to collect ferrous dust. The balance of pressures on the two sides of the diaphragm 9 is provided by means of a small channel with a filter 10. The shutter O is mounted on two spring blades 11 and 12 rigidly fixed to the end plate 13. The electro-magnetic attraction of the shutter 0 towards the plate member 4 causes the shutter to rotate about its own axis by means of the elastic deformation of the blades llll and 12, the rotation taking place about an imaginary axis located approximately at the intersection of the planes of the blades 11 and 12. The shutter O is subjected to the action of the spring R which is adjustable by means of the screw 14, and to the action of the spring Rm; these two springs are positioned under compression. The shutter 0 works in association with two nozzles, one nozzle Gp being connected to the ad mission conduit 15 for a fluid under pressure, the other nozzle Gb being connected to the conduit 16 for evacuation to the collector-tank. Each nozzle is adjusted when fitted so as to insure the exact correspondence of position of the edge of the shutter and the edge of the nozzle. By this means, a system is produced which avoids any delay on opening and entails, moreover, only very slight leakage.

On the other hand, the mounting of the shutter O on the two blades 11 and 12 forms a unit having very substantial transverse rigidity. As a result of this, the degree of play can be extremely small without risk of material contact between the shutter and nozzle. This play may, for example, be obtained by close grinding of the seatings followed by polishing or electrolytic treatment. The reduction of play to an absolute minimum further contributes to the reduction of leakage. The absence of friction also assists in increasing the sensitivity of the system.

The nozzle which does not eject fluid is mostly covered, thus reducing its leakage. Finally the small degree of transverse hydraulic reactions with respect to the substantial rigidity of the suspension of the shutter in the transverse direction prevents the leakage from increasing as a result of transverse deformation.

The slide-valve T is subjected to the action of two return springs 17 and 18 positioned under compression; the piston Q of the slide-valve T is subjected to the pressure in the shutter chamber 0. The piston Q of the slidevalve T the surface of which is one-half the surface of the piston Q, is subjected to the supply pressure through the channel 19. The slide-valve T is provided with grooves 2G and 21, co-operating with grooves and openings 22 and 23 placed in communication with the utilization members (not shown).

A further form of construction of the servo-distributor avoids use of the diaphragm and replaces it by a hollow member rigidly fixed mechanically to the shutter and moveable with said shutter, in approximately fluid-tight relationship with respect to the shutter chamber, with which hollow member communicates, on the one hand, a channel which is thus permanently coupled to the said hollow member and, on the other hand, the nozzle or nozzles when they are uncovered by the shutter. This hollow member is preferably tubular.

The advantages of this form of construction include the absence of the diaphragm which is a fragile member and is apt to cause undesirable mechanical reactions and, in consequence, the free choice of the axis of rotation of the shutter. The two suspension blades may be mounted in parallel in such manner as to obtain a movement of translation of the shutter compared with the nozzles. These two blades may be also mounted in such manner that their planes intersect in the vicinity of the center of gravity of the moving equipment in such manner as to improve its behavior under substantial vibration and at very high rates of acceleration.

Another additional advantage of this form of construction is to facilitate the draining of the apparatus which may be carried out without the precautions needed for handling the diaphragm. A final advantage is that the hollow member may be mounted with a play of a few microns with respect to the walls of the shutter chamber and, while this does not insure fluid-tightness during slow variations of pressure, adequate fluid-tightness is insured under rapid variations of pressure, thus producing a substantial reduction of the volume of oil under variable pressure and improvement in the time constant owing to the reduction of elasticity.

The servo-distributor in accordance with this further method of construction will be described below, reference being made to FIGS. 4 and 5, given by way of example and not by way of implied limitation.

The references being the same as those previously given, the torque-motor essentially comprises a polarized electro-magnetic circuit 1 (FIG. 4) excited by two coils 2 and 2a, acting upon the magnetic plate 4 of the shutter O mounted on two flexible blades 11 and 12 rigidly fixed to the terminal plate 13. On the shutter O is fixed a tube 25 into the interior of which open, on the one hand, the nozzles Gp and Gb (when they are uncovered by shutter O) and, on the other hand, the orifice 29 of a channel 27 issuing at 28 into the chamber 30 of the slide-valve T, which thus applies the pressure p to face Q of the slide-valve T. The supply pressure P is applied through the channel system 15, 19 to a face q of the slide-valve T in the chamber 31. The pressure in the chamber of shutter O at the exterior of the tube 25 acts upon the left-hand end face of the slide-valve T, but this effect is annulled by the application of the same pressure in the chamber 32 through the channel 33. Finally the chamber 34 located between the chambers 31 and 32, is connected to the collector-tank through the channel 35 so as to permit of the gradation of the sections between the chambers 31 and 32.

What I claim is:

1. Control apparatus for use with a source of pressure fluid comprising means having spaced parallel faces and defining in said faces substantially co-axially aligned openings, a shutter extending between said openings and being adapted for movement transverse to the axis thereof between said faces, said shutter being further adapted upon said movement to uncover progressively one of the openings selectively, at least one flat blade parallel to said axis and supporting said shutter in cantilever manner, said blade being flexible transverse to said axis and resisting deformation parallel to said axis whereby said shutter is accurately guided between said faces, coaxially aligned springs on opposite sides of the shutter and in engagement therewith, said springs defining an axis transverse to the first said axis, said means defining a chamber bounded in part by said faces, access to the chamber being provided by said openings, a diflerential piston coaxially aligned with said springs and engaged by one of the same, said piston being operatively coupled at one end to said chamber, and means for directing pressure fluid from said source against the other end of the piston and to one of said openings whereby the piston is adapted for being displaced, the other of said openings being a discharge opening leading from said chamber, and means to efiect a displacement of said shutter under the guidance of said blade whereby displacement of said shutter is controlled.

10 means for adjusting the other of said springs.

References Cited in the file of this patent UNITED STATES PATENTS 15 2,146,176 Donaldson Feb. 7, 1939 2,790,427 Carson Apr. 30, 1957 2,896,588 Hayner et al July 28, 1959

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