Servovalve for regulating the flow or pressure of a fluid

Abstract

The invention relates to a servovalve for regulating the flow or pressure of a fluid, comprising: a control stage comprising at least one permanent magnet, at least one coil and an armature (13) configured to be able to be driven in rotation around an axial direction; a power stage comprising a filler plate (23) and a drum (22) mounted rotatably in said filler plate (23); a slender mechanical transmission shaft (31) extending along said axial direction and having a first end (31a) connected to said armature (13) and an opposite end (31b) connected to said drum (22); characterized in that said control stage further comprises a slender torsionally flexible tube (32) extending along the axial direction (8) around said slender transmission shaft (31) and having a first end (32a) secured with said armature (13), shrunk onto said first end (31a) of said transmission shaft (31), and an opposite end (32b) clamped by a tube support (33) extending as far as said filler plate (23), so as to form a flexible mobile assembly that limits the frictional forces between said drum (22) and said filler plate (23) of the servovalve.

Claims

1. A servovalve for regulating the flow or pressure of a fluid, comprising: a control stage comprising at least one permanent magnet, at least one coil and an armature configured to be able to be driven in rotation about a direction, called the axial direction, if at least one coil is supplied with an electric current, said rotation of said armature being proportional to said supplied electric current, a power stage comprising a filler plate and a drum mounted rotatably in said filler plate and said drum comprising fluid circulation channels arranged so as to be able to be placed in fluid communication according to the position of the drum with respect to the filler plate to deliver a fluid to at a flow rate or pressure depending on the rotation of said drum relative to the filler plate, a mechanical transmission shaft extending along said axial direction and having a first end connected to said armature and an opposite end connected to said drum so as to be able to mechanically transmit a control torque delivered by said armature to said drum along a torque transmission axis, wherein said control stage further comprises a torsionally flexible tube extending along the axial direction around said transmission shaft and having a first end secured with said armature, shrunk onto said first end of said transmission shaft, and an opposite end clamped by a tube support extending as far as said filler plate, so as to form a flexible mobile assembly that limits the frictional forces between said drum and said filler plate of the servovalve.

2. The servovalve according to claim 1, wherein said end of said mechanical transmission shaft secured to said drum is connected to said drum by means of a torque transmission plate secured to said drum, extending perpendicularly to said axial direction and having rigidity in said torque transmission axis and flexibility in the other directions.

3. The regulating servovalve according to claim 2, wherein that said drum and said torque transmission plate are formed in one piece.

4. The regulating servovalve according to claim 2 wherein said torque transmission plate is rigid in the axial direction and flexible in all other directions.

5. The regulating servovalve according to claim 1 wherein that said tube support is made of carbide.

6. The regulating servovalve according to claim 1 wherein said torsionally flexible tube has a length and a diameter whose ratio is greater than or equal to 8.

Description

5. LIST OF FIGURES

(1) Further aims, features and advantages of the invention will become apparent upon reading the following description, which is provided solely by way of non-restrictive example, and which refers to the appended figures, in which:

(2) FIG. 1 is a schematic perspective view of a servovalve according to another embodiment of the invention,

(3) FIG. 2 is a schematic view of the servovalve of FIG. 1 in which elements are not shown so as in particular to show the torque transmission plate,

(4) FIG. 3 is a schematic view in longitudinal section of the servovalve of FIG. 1,

(5) FIG. 4 is a schematic view in longitudinal section of an upper detail of FIG. 3 illustrating the connections between the armature, the torsionally flexible tube and the transmission shaft of the servovalve,

(6) FIG. 5 is a schematic view in longitudinal section of a lower detail of FIG. 3 illustrating the connections between the transmission shaft, the drum and the tube support of the servovalve

6. DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

(7) For the sake of illustration and clarity, the scales and proportions are not strictly adhered to in the figures. Throughout the detailed description that follows in reference to the figures, unless otherwise indicated, each element of the servovalve is described as it is arranged when the servovalve is oriented such that said axial direction along which the torsionally flexible tube extends is vertical. This arrangement is shown in FIG. 1.

(8) In addition, identical, similar or analogous elements are denoted using the same reference signs throughout the figures. The longitudinal direction corresponds to the axial direction that is the main direction of the torsionally flexible tube.

(9) The servovalve shown in the figures comprises a control stage 10 and a power stage 20.

(10) The control stage 10 is housed in a casing 17, shown transparently in FIG. 1 to reveal the parts of the servovalve housed in the casing 17. This control stage 10 comprises two permanent magnets 11, two coils 12 and an armature 13 configured to be able to be driven in rotation around an axial direction 8, if the coils 12 are supplied with an electric current.

(11) The angular displacement of the armature 13 is proportional to the supply current of the coils 12. In the figures, the supply circuit of the coils is not shown for the sake of clarity.

(12) The permanent magnets 11 can for example be magnets made of an alloy of samarium and cobalt. Of course, other magnets can be used without calling the principle of the invention into question.

(13) The power stage 20 comprises a filler plate 23 and a drum 22 mounted rotatably in the filler plate 23 and each comprising fluid circulation channels, arranged so as to be able to be placed in fluid communication according to the position of the drum with respect to the filler plate to deliver a fluid to connection ports at a flow rate or pressure proportional to the rotation of the drum 22 relative to the filler plate 23.

(14) The servovalve also comprises a slender mechanical transmission shaft 31 extending along the axial direction 8. This shaft has a first end 31a connected to the armature and an opposite end 31b connected to the drum 22 so as to be able to mechanically transmit a control torque delivered by the armature 13 to the drum 22. This transmission shaft is for example made of tungsten carbide in order to limit the differential angular displacement between the armature and the drum. The torsionally flexible stiffness of such a shaft will be at least 30% stiffer in torsion than that of the torsionally flexible tube 32 described below.

(15) The end 31b of the transmission shaft 31 is connected to the drum 22 by means of a torque transmission plate 24.

(16) This torque transmission plate 24 has a rigidity in the axial direction and a flexibility in the other directions.

(17) According to the embodiment of the figures, the torque transmission plate 24 has a thickness of 0.3 mm, a torsionally flexible rigidity of 200 Nm/rad in the functional (torque transmission) direction and a flexibility in the directions perpendicular to the torsion tube axis of 1000 N/rad.

(18) The servovalve also comprises a slender torsionally flexible tube 32 that extends along the axial direction 8 around the transmission shaft 31. This torsionally flexible tube 32 has a first end 32a secured with the armature 13 that is shrunk onto the first end 31a of the transmission shaft 31. The torsionally flexible tube 32 also comprises an opposite end 32b clamped by a tube support 33 that extends to the filler plate 23 and that allows the mobile assembly to be fitted on the filler plate.

(19) FIG. 4 is a detailed schematic view of the shrinking of the torsionally flexible tube 32 on the transmission shaft 31. The connection between the armature 13 and the torsionally flexible tube 32 is also obtained by shrinking the tube on the armature 13. This shrinking is obtained by a tight fit of the torsionally flexible tube 32 in a bore formed in the armature 13. The transmission torque is obtained in a conventional manner by the conjunction of the effects due to friction and clamping in the contact zone between the two parts. In other words, this view provides a detailed illustration of the upper portion of FIG. 3.

(20) FIG. 5 is a detailed schematic view of the connection between the transmission shaft 31, the drum 22 and the tube support 33 at the lower end of the transmission shaft 31. In other words, this view provides a detailed illustration of the lower portion of FIG. 3.

(21) According to one embodiment of the figures, the torsionally flexible tube 32 has a ratio between the length and the outer diameter of the tube of 8. The tube is for example made of a material of the copper beryllium type.

(22) The flexibility of the torsionally flexible tube is for example 900N/rad in the axes transverse to the axis of the torsion tube. Its stiffness in the axis of torsion is for example 14 Nm/rad.

(23) In general, the component parts of the servovalve are chosen so that the ratio between the torque produced by the torque motor and the friction torque is greater than 50.

(24) Thus, a servovalve according to the invention makes it possible to form a mobile assembly that limits the frictional forces between the drum and the filler plate of the servovalve.

(25) Of course, the materials and numerical values given by way of example are not limiting and a servovalve according to the invention can have other embodiments which make it possible to address the technical problem underlying the invention, which is to reduce friction and present a limited hysteresis meeting the need for a servo loop despite a limited number of parts.