Servovalve having two stages and a pilot stage adapted to such a servovalve

Abstract

A hydraulic servovalve having two stages and feedback members in which the movable power distribution member has clamp means for clamping the feedback member, while allowing a clamped portion of the feedback member at least one freedom of movement relative to the movable distribution member.

Claims

1. A two-stage hydraulic servovalve comprising: a power stage including a movable power distribution member; and a pilot stage comprising a torque motor having a rotor connected to a hydraulic fluid emitter or deflector, and a deformable feedback rod or blade operationally connected to the rotor and to the movable power distribution member in order to establish a mechanical connection between them, wherein the movable power distribution member has clamp means for clamping the feedback rod or blade, and the clamp means exerts a clamping force directly on the feedback rod or blade, and the clamp means are arranged to allow a clamped portion of the feedback rod or blade to move relative to the movable power distribution member at least along a direction extending transversely to a clamping force generated by the clamp means, and the clamp means are also arranged to allow a portion of the feedback rod or blade on which the clamping force is applied to slide relative to the movable power distribution member along a power stage main axis.

2. The servovalve according to claim 1, wherein the clamp means comprise at least one presser screw.

3. The servovalve according to claim 1, wherein the clamp means comprise two presser screws mounted in opposition.

4. The servovalve according to claim 1, wherein the clamp means comprise cantilevered-out metal rods having ends that clamp against the feedback rod or blade, thereby allowing the clamped portion of the feedback rod or blade to move under the effect of the metal rods bending.

5. The servovalve according to claim 1, wherein the movable power distribution member is substantially cylindrical and the clamp means are installed in a bore made in the movable power distribution member along an axis of revolution of said movable power distribution member.

6. The servovalve according to claim 1, wherein the power distribution member is slidable along the power stage main axis and where the clamping means applies the clamping force in a direction co-axial with the main axis.

7. The servovalve according to claim 1, wherein the power distribution member is slidable along the power stage main axis and where the clamping means comprises a presser screw that moves in a direction co-axial with the main axis so as to apply the clamping force in the direction co-axial with the main axis.

8. A two-stage hydraulic servovalve comprising: a power stage including a movable power distribution member movable in an axial direction of the power stage; and a pilot stage comprising a torque motor having a rotor connected to a hydraulic fluid emitter or deflector, and a deformable feedback rod or blade operationally connected to the rotor and to the movable power distribution member in order to establish a mechanical connection between them; wherein the movable power distribution member has a clamp that clamps the feedback rod or blade, while allowing a clamped portion of the feedback rod or blade to move relative to the movable power distribution member at least along a direction extending transversely to a clamping force generated by the clamp; and wherein the clamp applies the clamping force directly on the feedback rod or blade in the axial direction of the power stage, and the clamp means are also arranged to allow a portion of the feedback rod or blade on which the clamping force is applied to slide relative to the movable power distribution member in the axial direction of the power stage.

9. The servovalve according to claim 8, the clamp is a presser screw that moves in the axial direction of the power stage.

10. The servovalve according to claim 9, wherein the presser screw includes a cantilevered rod with a free end directly abutting and clamping the feedback rod or blade.

11. The servovalve according to claim 8, wherein the clamp comprises a rod with a free end directly abutting and clamping the feedback rod or blade.

12. The servovalve according to claim 8, wherein the clamp comprises two presser screws, each presser screw moves in the axial direction of the power stage but in opposite directions to one another, each presser screw comprising a rod with a free end directly engaged to and clamping the feedback rod or blade with opposing forces.

13. A two-stage hydraulic servovalve comprising: a power stage including a movable power distribution member movable along a power stage main axis; and a pilot stage comprising a torque motor having a rotor connected to a hydraulic fluid emitter or deflector, and an elongated deformable feedback member operationally connected to the rotor and to the movable power distribution member in order to establish a mechanical connection between them; wherein the movable power distribution member has two opposing rod members that clamp one end portion of the elongated deformable feedback member, wherein the clamped end portion of the elongated deformable feedback member can move relative to the movable power distribution member at least along a direction extending transversely to a clamping force generated by the opposing rod members; and wherein the opposing rod members apply the clamping force in a direction co-axial with or parallel to the power stage main axis.

14. The two-stage hydraulic servovalve according to claim 13, wherein at least one of the opposing rod members is adjustable via a presser screw that presses on at least one of the opposing rod members.

15. The two-stage hydraulic servovalve according to claim 13, wherein the rod members are configured to flex in combination with flexure of the elongated deformable feedback member.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Reference is made to the accompanying drawings, in which:

(2) FIG. 1 is a section view on a plane normal to the movement axis of the movable power distribution member of a servovalve of the invention;

(3) FIG. 2 is a section view on a plane marked by a broken line A-A in FIG. 1;

(4) FIG. 3 is a view analogous to that of FIG. 2, showing the power stage during a movement of the movable power distribution member of the servovalve; and

(5) FIG. 4 is a fragmentary perspective view of the feedback member during a movement of the movable power distribution member of the servovalve.

DETAILED DESCRIPTION OF AT LEAST ONE EMBODIMENT OF THE INVENTION

(6) With reference to FIGS. 1 and 2, the servovalve given overall reference 1 comprises a pilot stage 100 and a power stage 200. The pilot stage 100 has a torque motor comprising TM a stator 2 and a rotor 3. The stator 2 has a stage surrounding the rotor 3, which turns about the axis Z. The rotor 3 has two main elements: a magnetic flapper 19 subjected to the magnetic field developed by the stator 2 and movable relative to the body of the servovalve 1; and a column 20 secured to the magnetic flapper 19 and extending along the axis Z, projecting from the stator and penetrating into the inside of the servovalve body.

(7) The column 20 carries a fluid ejector 4 that faces a stationary receiver 5. The column 20 is fed with fluid and the fluid ejector 4 sends a jet of hydraulic fluid towards the stationary receiver 5 along an angular orientation that is a function of the movement of the rotor 3. The column 20 is coupled to a resilient return member (not shown) urging it towards an equilibrium position in which the ejector 4 is substantially facing the center of the receiver 5.

(8) The power stage 200 comprises a cylinder 10 fastened in leaktight manner to the frame of the servovalve 1. This cylinder has an axial bore 12 machined along its center and having a spool 7 slidably mounted therein. The cylinder 10 has drilled channels and slots communicating with a hydraulic power feed port P, outlet ports U1 and U2, and a return port R of the servovalve. The cylinder 10 is pierced by a second bore 13 that is radial and passes through its middle. Two plugs 21 screwed onto the body of the servovalve 1 at opposite ends of the cylinder 10 participate in holding the cylinder in the body of the servovalve 1 and provide sealing between the bore 12 and the outside.

(9) The receiver 5 is in fluid flow connection with pilot chambers 9 situated at opposite ends of the spool 7; as a result an angular movement of the ejector 4 facing the receiver 5 gives rise to a pressure difference in the pilot chambers 9, thereby imparting a movement force on the spool 7.

(10) The spool 7 is cylindrical in shape and pierced by two bores comprising an axial first bore 14 and a radial second bore 15 made substantially through its middle.

(11) A feedback blade 6 mechanically connected to the spool 7 and secured to the column 20 passes through the radial bore 13 in the cylinder 10 and the radial bore 15 in the spool 7 so that one end of the feedback blade 6 extends inside the axial bore 12 of the spool 7.

(12) In this example, the feedback blade 6 is substantially triangular in shape and has a base 23 that is connected to a bushing 11 that is shrink-fitted on the column 20. The tip of the blade 6 forms an end 22 that extends through the radial bores 13 and 15 of the cylinder 10 and of the spool 7.

(13) In the invention, the end 22 of the feedback blade 6 is clamped by clamp means 8 secured to the spool 7. In this example, the clamp means 8 comprise presser screws 16 screwed into the spool 7 in tapped lengths thereof that are coaxial with the bore 12. The presser screws 16 push against clamp members 17 that are slidably mounted in the axial bore 12 and that carry metal rods 18, which rods are cantilevered out to clamp against the end 22 of the feedback blade 6.

(14) The feedback blade 6 is clamped by screwing the presser screws 16 so that they exert a force on the clamp members 17, which in turn transmit this force to the rods 18. The ends of the rods 18 clamp against the feedback blade 6, thereby providing a connection between it and the spool 7.

(15) Assembly operations preferably comprise the following succession of steps: mounting the spool 7 in the cylinder 10 that is already held in place in the servovalve body 1; mounting the pilot stage 100 on the servovalve body 1, the feedback blade 6 being inserted through the bores 13 and 15; putting the clamp members 17 into place together with the presser screws 16 in the bore 14; tightening the presser screws 16 onto the end 22 of the feedback blade 6; and installing and tightening the plugs 21.

(16) There follows an explanation of the operation of the assembly. In response to a request from a user, an instruction in the form of an electric current is sent to the stator 2 of the torque motor TM. This instruction causes the rotor 3 to move angularly about the axis Z. The twisting force exerted by the torque motor on the column 20 via the rotor 3 modifies the relative position of the ejector 4 and the stationary receiver 5, leading to a pressure difference between the chambers 9 situated at opposite ends of the spool 7. The spool then moves by an amount that its substantially proportional to the electrical instruction received by the torque motor. The movement of the spool 7 in the cylinder 10 then puts a set of drilled channels and slots into communication, which channels and slots are arranged in such a manner as to deliver a pressure or a flow rate proportional to the movement of said power distribution member 7. The base 23 of the feedback blade 6 held firmly by the column 20 is then subjected to an angular movement in one direction while its clamped end is subjected to a movement of the spool 7 in an opposite direction, as shown in FIG. 4. The feedback blade 6 then exerts a resilient return force performing a servocontrol function between the spool 7 and the rotor 3 (via the column 20) by generating a torque on the rotor 3 that is subtracted from the control action.

(17) The movement of the clamped end 22 of the feedback blade 6 along the travel axis of the spool 7 (which is parallel to the clamping force) subjects the feedback blade 6 to a bending force, and thus causes the clamped end to move in a direction normal to said axis, and also, in the example shown, causes said end to move angularly, as represented by arrows in FIG. 4. This movement is made possible by the flexibility of the clamp means 8 resulting from the flexibility of the metal rods 18, without any additional stresses being transmitted to the movable power distribution member.

(18) Thus, the relative movement of the spool 7 and of the feedback blade 6 takes place without friction between these parts, thereby reducing their wear.

(19) Naturally, the invention is not limited to the embodiments described but covers any variant coming within the ambit of the invention as defined by the claims.

(20) In particular: the clamp means 8 of the feedback member 6 may have a single presser screw 16, e.g. clamping the feedback member against a stationary portion; the flexibility of the clamp means of the above-described feedback member may be provided by deformable members such as, for example: springs; polymer elements or elements based on latex; a hydraulic damper; or indeed Belleville washers; the feedback member 6 may be connected to the rotor via the column 20 or by a mechanical connection with the ejector or the nozzle of the pilot stage; although the bushing 11 connecting the feedback member to the column 20 is shrink-fitted thereon, the invention also applies to other fastening means such as welding or keying; although the movable power member described is a spool 7, the invention also applies to a servovalve having other types of movable power member such as rotary valves, for example; although the feedback member in this example is a feedback blade 6, the invention also applies to a servovalve fitted with other types of feedback member such as feedback rods, for example; and finally although the hydraulic emitter in the example is connected to the rotor of the motor via a column, the invention is naturally not limited to this configuration, and it applies to other types of servovalve in which the position of the hydraulic emitter relative to the receiver is determined for example by an eccentric or indeed by a connecting rod connected to the movable portion of the motor.