Valve control device

The invention relates to a device for displacing a moving part along a longitudinal axis relative to a housing, said device being symmetrical about a plane extending longitudinally relative to the moving part, the device comprising two structures that are secured to said moving part and elements of active material comprising at least two blocks extending between inside walls of each structure, with the elongation directions of the blocks being antisymmetrical about an axis substantially perpendicular to the displacement axis of the moving part, wherein the structures are flexible and suitable for displacing the moving part by deforming as a function of the elongation of the blocks.

GENERAL TECHNICAL FIELD

The present invention relates to devices for controlling hydraulic valves or slides, in particular in hydraulic circuits, e.g. in the aviation or automotive fields.

More precisely, the invention relates specifically to devices for controlling hydraulic circuit valves enabling the valve to move progressively, and providing greater safety in use over a wide range of temperatures.

STATE OF THE ART

Devices for controlling valves in hydraulic circuits are already known in the state of the art.

Such control devices are used in numerous systems, for example in brake servo-control systems, or in flight control actuators in the field of aviation.

Certain devices in the state of the art are intended to adjust the hydraulic flow rate of the circuit to a desired level.

In general, hydraulic flow rate is controlled by moving a needle disposed in an orifice, the position of the needle in the orifice and the displacement thereof serving to regulate the flow rate of the liquid.

The control systems most commonly in use at present are electromagnetic. They are large in volume and they consume a large amount of energy.

Certain valve control systems make use of piezo-electric actuators for moving the needle.

However, those devices do not give full satisfaction.

The needle is moved along the elongation axis of the piezoelectric material. In that type of configuration, a change in the volume of the piezoelectric material as a function of temperature leads to instability in the position of the needle when the temperature varies over a large range. Furthermore, most systems including such a piezoelectric device present displacement of the operating zero position that is greater than the operating range.

SUMMARY OF THE INVENTION

The invention seeks to mitigate those drawbacks.

An object of the invention is to propose a device which presents great stability over a large range of temperatures, typically −55° C. to +80° C.

Another object of the invention is to propose a system enabling valves to be actuated with a force that is typically equal to 50 newtons (N), over a displacement amplitude that is typically of ±0.5 millimeters (mm).

Finally, an object of the invention is to propose a valve control device that is compact.

To this end, the invention provides a device for displacing a moving part along a longitudinal axis relative to a housing, said device being symmetrical about a plane extending longitudinally relative to the moving part, the device comprising two structures that are secured to said moving part and elements of active material comprising at least two blocks extending between inside walls of each structure, with the elongation directions of the blocks being antisymmetrical about an axis substantially perpendicular to the displacement axis of the moving part, wherein the structures are flexible and suitable for displacing the moving part by deforming as a function of the elongation of the blocks.

The invention advantageously further comprises the following characteristics taken singly or in any technically feasible combination:each structure comprises a plate extending substantially parallel to the displacement axis of the moving part and oblique pushers integral with the plate, at least one pair of pushers being secured to the moving part at their ends via at least one junction block;each structure includes portions of narrow section between the plate and the oblique pushers, and between the oblique pushers and the junction blocks connected to the moving part, these portions of narrow section being suitable for imparting flexibility to each structure;each structure comprises a plate extending substantially parallel to the displacement axis of the moving part and oblique pushers fitted to said plate, at least one pair of pushers being secured to the moving part at their ends via at least one junction block, the connection between the plate and the pushers and/or the connection between the pushers and the junction block being a resilient hinge without play constituted by at least one connecting blade;the device includes means suitable for prestressing the displacement means between the plates;the pushers are geometrically antisymmetrical relative to a plane perpendicular to the plates;one junction block is connected to the moving part and the other junction block is fixed relative to the housing external to the structures, the fixed block being secured to a rod coming into abutment against a screw for adjusting the displacement zero position of the moving part;the pushers are geometrically symmetrical about a plane perpendicular to the plates;both junction blocks are connected to the moving part;the device includes at least one diaphragm on either side of the junction blocks, the diaphragms being flexible along the displacement axis of the moving part and stiff transversely relative thereto;the diaphragms are suitable for providing sealing between the moving part and the housing;the housing is filled with a counterpressure liquid;at least one diaphragm includes bellows;the device includes at least one expansion chamber for the filler liquid; andeach expansion chamber includes a cutout constituting a portion of the wall of the housing, said cutout being connected to the housing by bellows;

DETAILED DESCRIPTION

FIG. 1is a diagram of a possible embodiment of a valve control device1comprising an outer housing2in which there is disposed a rod3extending along a substantially longitudinal axis of the housing2.

The housing2may be of any shape, but it is preferably in the form of a rectangular parallelepiped.

The rod3is movable in translation along the longitudinal axis of the housing2. At least one of its ends is connected to a valve in a hydraulic circuit. Double-headed arrows visible inFIG. 1represent displacement of the rod3relative to the housing2.

Sealing is provided between the housing2and the rod3by means4suitable for securing the rod3and the housing2together in such a manner as to guarantee leak-tightness while nevertheless ensuring that the rod3can be displaced relative to the housing2. By way of example, the sealing means comprise a diaphragm4closely surrounding the rod3and also connected to the housing2. The diaphragm4is flexible and allows the rod3to be displaced longitudinally in the housing2.

When the valve is opened or closed to a greater or lesser extent, fluid flows around the housing2, for example.

Means for actuating the rod3are contained within the housing2.

FIG. 2is a diagram of a first possible embodiment of means for actuating the rod3. The actuator means are symmetrical about a plane30containing the longitudinal axis of the rod3. Consequently, this figure shows only the top half of the actuator means, above the plane30. The entire system is shown in longitudinal section inFIG. 3.FIGS. 4aand4bshow a portion of the actuator system in a perspective view.

With reference toFIGS. 2 to 4b, the actuator means comprise means5for causing the rod3to slide longitudinally. By way of example, the means5comprise a part that is substantially in the form of a thick plate5constituting a rectangular parallelepiped and pierced by a hole surrounding the rod3.

The rod3may equally well be circular or square in section.

The means5are fixed relative to the housing2and are fixed to its inside walls. By way of example, the part5is fixed relative to the inside wall of the housing2via one of its sides that are parallel to the axis of the rod3.

Means for displacing the rod3enable it to be caused to slide in the means5.

In the diagram ofFIG. 2, the displacement means comprise means6for deforming a structure7secured to the rod3. Naturally, the device1has two structures7on opposite sides of the plane30.

InFIG. 2, the top structure7is substantially in the form of a bridge surrounding the central portion of the rod3, the ends of the rod3projecting from the structure7and the housing2in order to actuate valves.

The structure7comprises a top plate10extending in a rest position substantially parallel to and spaced apart from the axes of the rod3and the part5. The top plate10is substantially in the form of a rectangular parallelepiped extending substantially parallel to the top surface of the part5. For greater clarity, this top plate10is not shown inFIGS. 4aand4b.

The structure7also has lateral pushers9made integrally with the top plate10and extending obliquely towards the rod3. The ends13of the pushers9are secured to the rod3and form connection blocks, for example.FIGS. 4aand4bshow two possible embodiments of the pushers9. InFIG. 4a, the right section of the pushers tapers going from the plate10towards the blocks13. InFIG. 4b, the right section of the pushers9is constant and square in shape. Other embodiments are also possible. For example, the dimensions of the plate10and of the pushers9along an axis perpendicular toFIGS. 2 and 3can be the same. Dimensioning depends on the section of the rod3.

The structure7has portions8of narrow section at the junctions between the top plate10and the oblique pushers9, and also at the junctions between the oblique pushers9and the blocks13. The portions of narrow section8thus form locations in the part7that are highly flexible, thereby forming hinge type means.

The deformation means6deform the structure7which in turn moves the rod3in the means5.

With reference toFIG. 2, the means6comprise blocks of active materials6aand6bconnected firstly to the outside surface of the means5and secondly to the inside face of the top plate10of the structure7. The blocks6aand6bmay equally well be circularly symmetrical in radial section or they may be square. Their ends bear against two plane surfaces. The first plane surface is the bottom wall of the top plate10. The second plane surface is the top wall of the means5.

Prestress means11enable the deformation means6to be prestressed against the parts5and7. For example, the prestress means comprise a threaded rod11co-operating with a nut12and a washer14. The nut12presses the washer14against the outside face of the top plate10in order to prestress the parts7,6, and5against one another.

The active materials6aand6bmay be of the electrostrictive, magnetostrictive, or piezoelectric type. They are advantageously made of piezoelectric materials.

There follows a description of the mechanism for deforming the structure7and displacing the rod3.

The elongation axis of the active materials6aand6bis normal to the axes of the rod3and the hollow part5. Similarly, the elongation axis of the active materials6aand6bis normal to the top plate10of the structure7.

InFIG. 2, arrows22show the elongation directions of the active materials6aand6bduring a first stage of applying an electrical voltage.

The arrows22thus show that during the first stage, the active material6aelongates positively, whereas during the same stage, the active material6bdoes not elongate or is subjected to negative elongation.

This difference in elongation causes the top plate10to pivot in the direction indicated by arrows21. This pivoting is made possible by the flexibility of the structure7due to the hinges8.

The pivoting of the top plate10gives rise in turn to displacement of the oblique pushers9.

Since the ends13of the oblique pushers9are secured to the rod3, positive elongation of the material6acauses the rod3to move in the direction indicated by arrow20.

This actuates displacement of a valve in a hydraulic circuit located at the end of the rod3.

It will readily be understood that it is possible to reverse the direction in which voltage is applied to the active materials6aand6b. It is then possible to obtain positive elongation of the material6band negative elongation of the material6a. It will be understood that the top plate then pivots in the direction opposite to arrows21, and that the rod3moves in the direction opposite to that given by arrow20.

The displacement of the valve at the end of the rod3will therefore be reversed relative to the first voltage-application stage and hydraulic flow will thus be modulated.

Displacement of the rod3is easily modulated by the elongation amplitude of the materials6aand6b, thus enabling the hydraulic flow rate in the circuit to be modulated accurately.

Advantageously, the active materials6aand6band the voltages applied in the various stages enable the rod3to move over a stroke having an amplitude of ±0.5 mm.

Advantageously, the force exerted at the end of the rod3is equal to 50 N.

The fact that the active materials6aand6belongate in antisymmetrical directions relative to a longitudinal axis31of the rod11makes it possible to obtain automatic compensation of the neutral or equilibrium position. This compensation takes place regardless of temperature.

For zero applied voltage, the rod3naturally returns to a stable central position. Thus, this system provides good stability for the neutral position.

The deformable structure7enables the elongation of the active materials6aand6bto be amplified greatly.

The housing2is placed inside a hydraulic circuit. The static pressure of the liquid surrounding the housing2may therefore be very high. Consequently, the operation of the diaphragm4might be affected if there is nothing inside the housing2to counteract said pressure.

Thus, in order to counter the large static pressure of the liquid surrounding the housing2,FIG. 3shows that in a variant of the embodiment shown inFIG. 2, the inside of the housing2is advantageously filled with a counterpressure liquid18, this liquid being non-aggressive for the means for actuating the rod3.

When the inside of the housing2is filled with a liquid18, and in order to accommodate the very large thermal expansion of the filling liquid18relative to the walls of the housing2,FIG. 3shows that bellows15are provided at at least one diaphragm4in order to enable the filler liquid to expand.

In a variant, at least one expansion chamber is provided for the filler liquid18. By way of example, the expansion chamber comprises a cutout17in a portion of the wall of the housing2, this cutout being connected to the housing2by a bellows16. Thermal expansion of the filler liquid18is thus accommodated by moving the part17.

The bellows15of the diaphragms14are optionally associated with one or more expansion chambers.

Preferred Embodiment

FIG. 5is a diagram of a second possible embodiment of the means for actuating the rod3.

In this figure, elements similar to those ofFIGS. 2 to 4bare given identical numerical references.

As for the first embodiment, the actuator means are symmetrical about the plane30containing the longitudinal axis of the rod3.

However, in the second embodiment, the actuator rod3is no longer placed inside an outer housing2, and the housing2no longer has internal sliding means. One of the ends of the rod3is situated on the left of the device shown inFIG. 5.

As shown inFIG. 5, the displacement means comprises means6for deforming two structures7extending on opposite sides of the plane30and perpendicularly to the plates10of the structures7, i.e. substantially parallel to a prestress element11as described in greater detail below.

The means6comprise at least two blocks of active material6aand6b. Each block6aor6bmay comprise a pair of blocks stacked one on the other.

The active materials6aand6bmay be of the electrostrictive, magnetostrictive, or piezoelectric type. They are advantageously made of piezoelectric materials. The blocks6aand6bare biased in the direction of the major dimension.

Each structure7has a top plate10which, in the rest position, extends substantially parallel to and at a distance from the plane30. Each structure7also has lateral pushers9made integrally with the top plate10and extending obliquely towards the plane30.

The pushers9may alternatively be separate pieces fitted to the plates10via one or more flexible metal blades, or by blades made of a material other than metal, the blades serving to provide resilient links between the pushers9and the associated plates10.

The pushers9are geometrically antisymmetrical about a longitudinal plane30containing the axis of the prestressed means11, the plane31being perpendicular to the plane ofFIG. 5and to the plate10. Thus, starting from the plates10, the pushers extend towards the rod3, from right to left for the device as shown inFIG. 5.

As in the first embodiment, the prestress means preferably comprise a threaded rod11co-operating with a nut12and a washer14. The nut12presses the washer14against the outside face of the top plate10so as to prestress the parts7and6against each other. Compressing the blocks6aand6bavoids them suffering damage. However, the prestress means are sufficiently flexible to avoid impeding movement of the plates10.

The structures7which are symmetrical relative to each other are secured to each other by blocks13situated at one end of each pusher9.

The pushers9are secured to each other so as to form junction blocks13.

Because of the symmetry about the plane30and the antisymmetry about the plane31, each pair of pushers9forms an angle that opens out in the same direction, to the right inFIG. 5, but which may be of value that differs depending on torque, as described below.

Each structure7has portions8of narrow section at the junctions between the top plate10and the oblique pushers9and between the oblique pushers9and the blocks13. The portions8of narrow section thus form locations of great flexibility in the structure7, thereby forming hinge type means.

When the pushers9are fitted to the plate10, the hinge8is formed by a link blade between the pusher9and the plate10.

It is also possible to provide for the pushers9to be connected to the junction blocks13via at least one respective flexible blade made of metal, or made of a material other than metal, the blade providing the resilient connection between each pusher9and the corresponding blocks13.

It can thus be understood that the flexible blades perform the same function as the portions of narrow section in the pushers9, forming resilient hinges without play, that give flexibility to each structure7.

The connection blocks13are both connected to link means leading to other mechanical parts that pass through diaphragms4situated to the right and to the left of the structures7.

The block13ais movable longitudinally in the plane30and is connected to a connection rod55which passes through the diaphragm4a. The rod55is itself connected to the valve control rod3.

The block13bis fixed relative to the housing2while the device is in use. It is connected to a rod56situated on the axis of the rod55and on the axis of the rod3in the plane30. The rod56passes through the diaphragm4b.

At its end remote from the block13b, the rod56has a head57. The head57comes into abutment against the end of the threaded shank58of a screw60. The head59of the screw60is situated outside the housing2. The screw60enables the displacement zero of the rod3to be set. This zero setting of the displacement of the rod is performed by moving the structures7in translation parallel to the plane30. The structures7float relative to the housing2but they are connected to the inside of the housing2via the diaphragms4which allow the structures7to move parallel to the plane30.

It will be understood that once the zero position has been set, the block13bis fixed relative to the housing2. The screw60is stationary relative to the housing because of a tapped portion, and also the rod56and the head57, both of which are secured to the blocks13b, come into abutment against the end of the screw60.

The diaphragms4are flexible along the displacement axis of the rod3and stiff transversely relative thereto. The structures7therefore do not move in any transverse direction.

The diaphragm4athus enables the rod55to move, and consequently enables the rod3to move. The diaphragm4aand the diaphragm4benable the structures7to be moved in translation in order to set the zero position of the system.

FIGS. 6aand6bare diagrams showing possible embodiments for the diaphragms4of the invention. It can be seen in these figures that the diaphragms4do not necessarily provide the device with sealing.

Sealing can be provided elsewhere by other devices outside the housing2.

In addition, sealing is not necessary in all applications of the device of the invention.

The mechanism whereby the structure7deforms and the rod3is displaced in a device constituting the second embodiment of the invention is described below with reference toFIG. 5and with reference toFIGS. 7ato7c.

FIG. 5shows that the elongation axes of the active materials6aand6bare normal to the axes of the rod3and of the plates10of the structures7.

FIGS. 7ato7cthus show three different extension states for the blocks6aand6b, and consequently three different states for the rod3.

FIG. 7ashows the initial state or rest position of the device. The blocks6aand6bare not powered electrically. Both plates10are therefore parallel to each other and to the plane30.

The rod3is therefore in its zero position, and it is recalled that this position can set by acting on the screw60which enables the structures7to be moved in translation due to the longitudinal flexibility of the diaphragms4aand4b.

The initial angle made between the pushers9of the two structures7is marked α0. The initial distance between the blocks13aand13bis identified by lines70.

FIG. 7bshows that applying electric fields of equal magnitude and opposite sign to the two groups of blocks6aand6bcauses the plates10to tilt. The two plates10remain symmetrical relative to each other about the plane30.

Tilting of the plates10has the consequence of changing the angles between the pushers9.

The pair of pushers9connected to the block13aforms an angle α1while the pair of pushers9connected to the block13bforms an angle α2. The angles between the pairs of pushers vary with opposite signs, i.e. if α1decreases, then α2increases, and vice versa, and the amount of variation in each of the angles α1and α2is different.

Since the block13bis fixed relative to the housing2, varying the angles between the pushers has the consequence of varying the distance between the blocks13aand13b. It can thus be seen that the block13ais advanced from its initial position as identified by the line70. The rod3is therefore displaced to the left inFIG. 7b. It is recalled that displacement of the block13ais due to the plates10tilting under drive from the blocks6aand6b.

InFIG. 5, arrows22show the direction in which the active materials6aand6blengthen when voltage is applied differently during another stage, which stage is also shown inFIG. 7c. This power supply is opposite to that shown inFIG. 7b. The plates10therefore tilt in the opposite direction and the block13ais moved to the right inFIG. 7c.

The displacement distance of the block13aas a function of the applied voltage can be evaluated approximately by a geometrical relationship between the three angles α0, α1, and α2. It is also influenced by the elastic deformations that arise in the structure when an external force is applied.

The rod3is movable in translation along the longitudinal axis of the housing2. At least one of its ends is connected to a valve in a hydraulic circuit. This makes it possible, for example, to adjust the pressure, or the flow rate of a hydraulic fluid by moving the rod.

By way of example, the device may be used in brake servo-controls or in actuators for flight controls.

Advantageously, the active materials6aand6b, and the voltages applied during the various stages enable the rod3to move through a stroke having an amplitude of ±0.5 mm.

Advantageously, the force generated by the system and exerted at the end of the rod3is equal to or greater than 50 N.

As for the first embodiment, the fact that the directions in which the active materials6aand6blengthen are antisymmetrical relative to the longitudinal axis31of the rod11makes it possible to obtain automatic compensation of the neutral or equilibrium position. This compensation takes place regardless of temperature.

When zero voltage is applied, the rod3returns naturally to a stable central position. Thus, the system provides good stability for the neutral position.

The deformable structure7enables the elongations of the active materials6aand6bto be amplified greatly.

In addition, in the second embodiment, the inclination of one of the pairs of pushers9is reversed relative to that of the first embodiment.

Furthermore, the displacements of the blocks13aand13bare decoupled because the rod3no longer passes through the center of the structures7and the blocks13aand13bare no longer both connected to the rod3.

These two characteristics present two main advantages.

Firstly, the deformations at the ends are accumulative so that the resulting displacement is greater.

Secondly, the internal forces of the device are smaller.

In addition, the fact that zero position is simple to adjust by means of a screw acting on the displacement means via tapping in the housing constitutes another advantage compared with the first embodiment of the device.

The second embodiment is more compact and has a smaller number of interfaces in series with the active materials, thereby minimizing losses in the stiffness of interfaces. This increases the precision with which the rod3can be moved.

It is also possible to increase the section of the active materials, thus making it possible to increase the stiffness of the device.

The second embodiment may naturally include a counterpressure liquid and expansion bellows as in the first embodiment.

The first embodiment may also have connection blades instead of portions of narrow section in the pushers9. It is thus possible to continue having a resilient hinge without play giving flexibility to each structure7.

The device of the invention has numerous advantages.

The means enabling the structure7to deform comprise only the portions8of narrow section. There are no joints. Consequently, there is no wear of parts nor is there any appearance of play as a result of use. Good accuracy in displacement is thus obtained, as is a long lifetime.

The active materials6aand6bare in the form of a solid block which enables the assembly as a whole to be made very rigid, and also enables a large force to be delivered by the rod3.

The valve actuator device thus delivers a large amount of energy for a system that is compact.

The size of the system as represented by double-headed32is advantageously 50 mm. The size of the device in directions normal to the plane30is likewise 50 mm, the portion symmetrical to that shown inFIG. 2complying within these dimensions. Size is even smaller for the second embodiment.

It will be understood fromFIG. 3that the device has at least four blocks of active material. This redundancy in active material blocks serves further to provide safety in the event of a block of active material not functioning correctly. The system can continue to function even in the event of one of its blocks breaking down.

Advantageously, the ceramics of the active materials are multi-layer materials. They thus make it possible to apply low voltages.