Piezo-hydraulic device for multiplying force from a piezoelectric element

Abstract

The invention relates to a piezo-hydraulic device (100) comprising at least one hydraulic circuit containing a pressurized fluid (1, 2) such as a liquid, a first piston (10) having a working surface subjected to the pressure of the fluid in the hydraulic circuit, the first piston (10) being connected to at least one piezoelectric element (40) such that the position of the first piston (10) varies according to a mechanical deformation of the piezoelectric element (1), at least one second piston (20) having a working surface subjected to the pressure of the fluid in the hydraulic circuit, the working surface of the first piston (10) being strictly greater than the working surface of the second piston (20) so as to transmit a multiplied force to move a moving mass (50). (Fig. 7)

Description

Title of the invention: piezohydraulic device for multiplying a force from a piezoelectric element Technical field of the invention

[0001] The invention relates, in general, to the technical field of piezoelectric devices, in particular piezoelectric actuators, or even piezoelectric sensors.

[0002] The invention relates more specifically to a piezoelectric device, actuator and / or sensor, allowing a multiplication of a force between the mechanical deformation of a piezoelectric element and the displacement of a mass.

[0003] Such a piezoelectric device can in particular be used as a dynamic actuator to ensure vibration control, in particular to balance shafts of rotating machines requiring very high levels of force. State of the prior art

[0004] Piezoelectricity is the property that certain materials have of becoming electrically polarized under the action of mechanical stress and conversely of deforming when an electric field is applied to them. The first is called the direct piezoelectric effect, the second the inverse piezoelectric effect. More generally, the direct effect can be used to make sensors (pressure sensors, etc.) while the inverse effect makes it possible to make precision actuators (piezoelectrically controlled injectors in automobiles, etc.).

[0005] The sensitivity of a piezoelectric element is characterized by the displacement obtained under a given voltage. Since the displacements generated are very small, numerous mechanical amplification configurations have been developed in order to increase the stroke of the actuators without excessively affecting the forces they are capable of providing. A majority of the configurations used involve flexible joints, obtained by electroerosion machining, making it possible to achieve very low material thicknesses. These joints allow rotations with limited travel but are without play, which is essential for this type of application where each micron has a significant impact on the precision of the device. This is, for example, the case of the vibration damping solutions developed by the company PYTHEAS Technology, or also the solutions developed by the company CEDRAT Technologies (Amplified Piezoelectric Actuators, AP A®).These solutions use the elliptical shape of a shell to both prestress the piezoelectric material, but also amplify the displacements in the minor axis of the ellipse.

[0006] These existing devices generally use gearing mechanisms allowing relatively low amplification, for example by a factor of between 2 and 20. Such amplified actuators thus generally have strokes of between 0.1 and 1 mm. The displacements, and consequently the accelerations, provided by this type of transducer therefore remain low, which requires the use of large seismic masses to achieve significant force levels at low frequencies to balance vibratory systems requiring very high force levels.

[0007] As a result, the compromise between compactness, mass, forces developed and energy consumption remains unfavorable for high-power electrodynamic actuators. Statement of the invention

[0008] The invention aims to remedy all or part of the drawbacks of the state of the art by proposing in particular a solution allowing an improved multiplication of the forces developed for an acceptable or even reduced energy consumption, the compactness of which is improved and the useful seismic mass of which can be reduced.

[0009] To do this, according to one aspect of the invention, a piezohydraulic device is proposed comprising at least one hydraulic circuit comprising a pressurized fluid such as a liquid, a first piston having a useful surface subjected to the pressure of the fluid of the hydraulic circuit, the first piston being connected to at least one piezoelectric element so that the position of the first piston varies as a function of a mechanical deformation of the piezoelectric element, at least one second piston having a useful surface subjected to the pressure of the fluid of the hydraulic circuit, the useful surface of the first piston being strictly greater than the useful surface of the second piston so as to transmit a multiplied force to move a mobile mass.

[0010] Thanks to such a combination of characteristics, the piezo-hydraulic device implements a hydraulic reduction which allows significantly greater amplifications than those obtained by other mechanical means, this with great compactness and therefore reduced size. By application of Pascal's principle, the hydraulic reduction results from the use of at least two pistons of different useful sections or surfaces immersed in the same incompressible fluid volume, housed here in the hydraulic circuit. The reduction ratio is then the ratio of the useful sections or surfaces of the first and second pistons.

[0011] According to one embodiment, the hydraulic circuit may comprise a hydraulic chamber, or even preferably be made up of a hydraulic chamber. Such a characteristic makes it possible to improve the compactness of the piezo-hydraulic device by simplifying the hydraulic circuit to a simple hydraulic chamber.

[0012] According to one embodiment, the piezoelectric element is made of a piezoelectric material. The piezoelectric material is for example based on lead zirconate titanoates (PZT), preferably made entirely of lead zirconate titanoates.

[0013] The gear ratio can be easily increased for a given piezoelectric element by using a first large piston actuated by said piezoelectric element. A gear ratio strictly greater than 20, preferably greater than or equal to 100, more preferably greater than or equal to 400, will preferably be chosen.

[0014] According to one embodiment, the first piston forms a double-acting piston, the first piston comprising two opposite faces, each of the two faces having a useful surface subjected to the pressure of a fluid contained in separate associated hydraulic chambers.

[0015] According to one embodiment, the piezohydraulic device comprises a third piston, the second piston being subjected to the pressure of the fluid contained in a first of the two hydraulic chambers, the third piston being subjected to the pressure of the fluid contained in a second of the two hydraulic chambers, opposite the first with respect to the first piston, the second and third pistons preferably being movable along parallel axes, more preferably coaxial. Such a configuration makes it possible, for example, to use a push-pull effect, also called "push-pull" in Anglo-Saxon jargon, so as to make it possible to reverse the roles of the motor system and the moving mass.

[0016] According to one embodiment, the second and third pistons are integral with each other, preferably so as to form an external envelope of the piezohydraulic device. In other words, the second and third pistons are fixed relative to an external envelope of the piezohydraulic device. This external envelope preferably delimits a closed enclosure, in which the mobile mass is housed in its interior space.

[0017] According to one embodiment, the moving mass is integral with the second piston.

[0018] According to one embodiment, the moving mass forms a hydraulic casing delimiting the first and second hydraulic chambers. In this configuration, where the hydraulic casing is housed in the interior space delimited by the external casing, most of the mass is used as seismic mass and the system can be used more easily in different positions. In addition, the seismic mass benefits from better guidance thanks to the second and third pistons.

[0019] According to one embodiment, the mobile mass is immersed in a hydraulic fluid, preferably a dielectric hydraulic fluid, contained in an interior space of the external envelope of the piezo-hydraulic device, said external envelope of the piezo-hydraulic device preferably forming a Faraday cage.

[0020] The use of a dielectric fluid presents in particular an advantage with regard to the electrical supply of the piezoelectric elements.

[0021] The fact that the system is entirely bathed in a hydraulic fluid, in particular the moving mass delimiting the first and second hydraulic chambers, including in particular the piezoelectric element(s) and the first, second and third pistons, is advantageous in that the fluid provides thermal inertia at the same time as a means of cooling the system if necessary. Furthermore, the characteristic according to which the external casing of the piezohydraulic device forms at least in part, in particular constitutes, a Faraday cage makes it possible to limit the impact of the electromagnetic compatibility of the piezohydraulic device.

[0022] According to one embodiment, the piezo-hydraulic device comprises means for controlling the pressure of the pressurized fluid of the hydraulic circuit(s) allowing fluid communication between the hydraulic circuit(s) and at least one regulation chamber, the pressure control means comprising for example at least one valve.

[0023] Indeed, a technical problem that must be solved is that of the sealing of the hydraulic system and mainly the sealing at the level of the small piston(s), that is to say the second and / or third piston, which are the smallest compared to the first piston connected to the piezoelectric element. These pistons are in motion relative to the hydraulic casing. One way of solving this problem is to use high-precision machining techniques associated with high-hardness surface treatments. However, such machining is particularly expensive.

[0024] Another solution is to take into account a leak at the connection and a filling system such as the regulation chamber, in the depression phases, controlled for example by at least one valve forming a control means. In a particular configuration, a sealed bellows makes it possible to delimit a regulation chamber and thus contain liquid before its suction into the cavity formed by the associated chamber in the depression phases.

[0025] According to one embodiment, the pressure control means are configured to control a fluid communication between each of the first and second hydraulic chambers with a common regulation chamber, the regulation being contained in the interior space of the outer casing of the piezohydraulic device, between the moving mass and said outer casing. In such a configuration, where the system is immersed in the hydraulic fluid, the space delimited in the outer casing of the piezohydraulic device, between walls of said outer casing and the hydraulic casing, forms a regulation chamber surrounding the hydraulic casing. The fluid can also be maintained in equilibrium with atmospheric pressure if necessary.

[0026] In addition to the aforementioned advantages, such a piezo-hydraulic device according to the invention makes it possible, with a single actuator, to envisage the active control of several phenomena simultaneously: for example, dynamic balancing of the crankshaft for a 3-cylinder engine. Such a piezo-hydraulic device also has a low level of complexity and uses relatively economical materials. It also makes it possible to reduce the mass and improve the efficiency of vibration reduction devices, such as those for example fitted to an engine.

[0027] According to another aspect of the invention, it relates to a vehicle, for example a motor vehicle, comprising at least one piezo-hydraulic device as described above.

[0028] According to one embodiment, the vehicle comprises a plurality of piezo-hydraulic devices as described above and supports for an engine on a fixed structure of the vehicle, the engine supports each being equipped with at least one of the piezo-hydraulic devices so as to reduce the dynamic forces applied to the fixed structure of the vehicle. The piezo-hydraulic devices each being configured to locally reduce the dynamic forces applied to the fixed structure of the vehicle, all while having a reduced mass and size and being able to generate sufficiently large forces due to the hydraulic reduction, such an application is particularly advantageous.

[0029] According to one embodiment, the vehicle is an electric vehicle, the engine of the vehicle being an electric motor. brief description of the figures

[0030] Other characteristics and advantages of the invention will emerge on reading the description which follows, with reference to the appended figures, which illustrate:

[0031] [Fig.l]: a schematic view of a piezohydraulic device according to one embodiment;

[0032] [Fig.2]: a schematic view of a piezohydraulic device according to another mode of realization;

[0033] [Fig.3]: a schematic view of a piezo-hydraulic device according to another mode of realization;

[0034] [Fig.4]: a schematic view of a piezo-hydraulic device according to another embodiment;

[0035] [Fig.5]: a schematic view of a piezohydraulic device according to another embodiment;

[0036] [Fig.6]: a schematic view of a piezohydraulic device according to another embodiment;

[0037] [Fig.3]: a schematic view of a piezohydraulic device according to another embodiment.

[0038] For clarity, identical or similar elements are identified by identical reference signs throughout the figures. DETAILED description of an embodiment

[0039] [Fig.l] ([Fig.l]) illustrates a schematic view of a piezohydraulic device 100 according to one embodiment. In particular, the piezohydraulic device 100 comprises a hydraulic circuit 101 here constituting a hydraulic chamber 101' to simplify the structure. The hydraulic chamber 101' is filled with a fluid 1 under pressure such as a liquid, preferably an incompressible liquid. An incompressible fluid is considered to be a fluid whose volume is considered to be constant, regardless of the pressure to which it is subjected. Since any fluid is in reality sensitive to pressure, it will be considered approximately in practice that the effects of compression can be ignored for fluids characterized by a Mach number below 0.3.

[0040] The piezohydraulic device 100 comprises a first piston 10 having a useful surface 11 and extending into the hydraulic chamber 101' so that the useful surface 11 is subjected to the pressure of the fluid 1 contained in the hydraulic chamber 101'. The first piston 10 slides relative to the hydraulic chamber 101', the walls which delimit it of which guide said first piston 10 in translation. The walls delimiting the hydraulic chamber 101' form a hydraulic casing 60. The first piston 10 is connected to at least one piezoelectric element 40 made here of a piezoelectric material. The piezoelectric material is here made of lead zirconate titanoates ("PZT").

[0041] The piezo-hydraulic device 100 thus uses the piezoelectric effect: by applying an electrical voltage to the piezoelectric material, a mechanical deformation of said piezoelectric material is generated. The first piston 10 is connected to the piezoelectric element 40 so that the position of the first piston 10 varies as a function of a mechanical deformation of the piezoelectric element 40 at least axially along a main reference displacement axis A40. The piezoelectric element 40 therefore provides an actuator function for the piezo-hydraulic device 100. In the embodiment of [Fig.l] ([Fig.l]), the first piston 10 is constituted by the piezoelectric element 40 itself, said piezoelectric element 40 being immersed in the fluid 1 contained in the hydraulic chamber ior.

[0042] The piezohydraulic device 100 further comprises a second piston 20 having a useful surface 21 subjected to the pressure of the same fluid 1 of the hydraulic circuit 101, namely of the same hydraulic chamber 101'. The second piston 20 slides relative to the hydraulic chamber 101', the walls which delimit it of which guide said second piston 20 in translation. Preferably, the second piston 20 slides relative to the same hydraulic chamber 101' on a side opposite the first piston 10 relative to the hydraulic chamber 101'. The hydraulic casing 60 therefore guides the first and second pistons 10, 20 so that they are each movable in translation along an axis A1 and A2, respectively. The translation axes A1 and A2 of the first and second pistons 10, 20 are here parallel, and even coaxial, and also parallel and coaxial to the displacement axis A40 of the piezoelectric element 40.

[0043] The second piston 20 therefore comprises a rod sliding relative to the hydraulic chamber 101', a proximal end of which is wetted in the liquid 1 contained in the hydraulic chamber 101', the proximal end carrying the useful surface 21, and a distal end, opposite the proximal end, secured to a mobile mass 50, here located outside the hydraulic casing 60.Thus, during operation of the piezo-hydraulic device 100, as an actuator for example, the application of an electrical voltage to the piezoelectric material 40 causes a mechanical deformation of said piezoelectric material at least along its axis A40, which causes the position of the first piston 10 to vary in translation relative to the hydraulic chamber 101' along its axis A1, which consequently causes the internal pressure of the liquid in the hydraulic chamber 101' to vary, the liquid 1 transmitting the entire variation in pressure produced to the second piston 20 which also translates along its translation axis A2.

[0044] In the context of the invention, the useful surface of the first piston 10 is chosen to be strictly greater than the useful surface of the second piston 20 so as to transmit a multiplied force to move a mobile mass 50. Thus, the fluid 1 makes it possible to multiply a pressing force which is exerted on it by the first piston 10 by transmitting it to the second piston 20. The piezo-hydraulic device 100 implements a hydraulic multiplication which allows amplifications significantly greater than those obtained by other mechanical means. The hydraulic multiplication results from the use of the first and second pistons 10, 20, of different sections immersed in the same incompressible fluid volume 1 contained in the hydraulic chamber 101'. The multiplication ratio is then the ratio of the useful sections or surfaces of the two pistons, namely the first and second pistons 10, 20. In [Fig.l] ([Fig.l]), the gear ratio obtained is of the order of 10. The pressure in the hydraulic fluid is the force exerted divided by the section of the small piston.

[0045] The reduction ratio can be further increased for a given quantity of piezoelectric material by using a first large piston 10 actuated by the piezoelectric element 40 as illustrated in [Fig.2] ([Fig.2]) where the reduction ratio obtained is of the order of 400.

[0046] The piezohydraulic device 100 of [Fig.2] ([Fig.2]) differs essentially from that of [Fig.l] ([Fig.l]) in that the first piston 10 is distinct from the piezoelectric element 40, the first piston 10 forming a mechanical interface between the incompressible fluid 1 contained in the hydraulic chamber 101' on one side, and the piezoelectric element 40 on another side opposite and attached to the first piston 10 so that the mechanical deformation of the piezoelectric element 40 in one direction or the other causes the displacement of the first piston 10 in one direction or the other respectively, by sliding relative to the hydraulic chamber 101'.

[0047] More precisely, the first piston 10 is slidably mounted in the hydraulic chamber 101' of complementary shape, guided by the hydraulic casing 60. The first piston 10 has two opposite faces 12, 13, one 12 of the two faces being in direct contact with the fluid 1 contained in the hydraulic chamber 101' and subjected to the pressure of the fluid 1 contained in the hydraulic chamber 101', the other of the two walls 13, opposite the wall 12, being integral with the piezoelectric element 40.

[0048] The hydraulic casing 60 of the piezohydraulic device 100 delimits an interior space inside which the first piston slides, sealingly separating two spaces, a first space containing the fluid 1 and a second space housing the piezoelectric element 40, the piezoelectric element 40 being arranged between, preferably interposed between (see [Fig.2] ([Fig.2])), a wall of the hydraulic casing 60 and the wall 13 of the first piston 10. In this embodiment, the central axis A40 of the piezoelectric element 40 corresponding to its main displacement axis and the sliding axes A1, A2 of the first and second pistons 10, 20 are also parallel and coaxial.

[0049] [Fig. 3] ([Fig. 3]) illustrates a diagram of a piezohydraulic device 100 according to another embodiment. This embodiment differs essentially from the previous ones in that it comprises two second pistons, called second piston 20 and third piston 30, each subjected to the pressure of a fluid 1, 2, in one of the associated separate hydraulic chambers 101', 102'. In such a configuration, the second piston 20 is subjected to the pressure of the fluid 1 contained in a first 101' of two hydraulic chambers 101', 102' and the third piston 30 is subjected to the pressure of the fluid 2 contained in a second 102' of the two chambers hydraulics 101', 102', opposite the first 101' with respect to the first piston 10. The two hydraulic chambers 101', 102' are delimited externally by a hydraulic casing 60 having an interior space. The same hydraulic casing 60 formed in one piece delimits an interior space housing the two hydraulic chambers 101', 102'. Indeed, the interior space of the hydraulic casing 60 is crossed by the first piston 10 so that the first piston 10 divides the interior space of the hydraulic casing 60 into two sub-spaces, sealed with respect to each other, each of the two sub-spaces forming one of the two hydraulic chambers 101', 102'.

[0050] In this embodiment, the first piston 10 forms a double-acting piston. The first piston 10 comprises two opposite faces 12, 13, each of the two faces 12, 13 having a useful surface 11', 11" subjected to the pressure of a fluid 1, 2 contained in one and the other of the two separate hydraulic chambers 101', 102' associated. In this way the first piston 10 can work in both directions along its sliding axis AL

[0051] The first piston 10 has transversely on its periphery relative to its sliding axis A1, a peripheral edge arranged between two internal supports of the hydraulic casing 60. The peripheral edge of the first piston 10 is interposed between two piezoelectric elements 40, each of the piezoelectric elements 40 being themselves interposed between, on the one hand, a portion of one of the two faces 12, 13 of the first piston 10 located at the level of said edge and, on the other hand, one of the two associated supports of the hydraulic casing 60. In this way, the piezoelectric elements 40 allow, under the effect of a voltage, the first piston 10 to be moved along its axis A1, in one direction or the other.

[0052] The hydraulic casing 60 delimiting the first and second hydraulic chambers 101', 102' here constitutes the mobile mass allowing it to be moved. Indeed, the hydraulic casing 60 is housed in an interior space 105' of an external casing 105 of the piezohydraulic device 100. The external casing 105 delimits a closed enclosure. The second and third pistons 20, 30 are integral with this external casing 105 so that they are fixed relative to each other. In this way, the outer casing 105 forms a closed housing powered by electrical wires (not shown) which pass through the outer casing 105 to be connected to the piezoelectric elements 40. When the piezoelectric elements 40 are energized, the first piston 10 is moved in one direction or the other along a displacement axis A1, this depending on the difference in voltage applied to the different piezoelectric elements 40.The movement of the first piston 10 has the effect of translating the mobile mass 50 relative to the external casing 105, which is guided by the second and third pistons 20, 30 whose axes of movement A2, A3 are parallel, and coaxial, to the axis of movement of the first piston AL. When the piezohydraulic device 100 is in equilibrium, the hydraulic casing 60, also the moving mass 50 here, is centered in the interior space 105' of the outer casing 105 so that a space is delimited between the walls delimiting the outer casing 105 and the hydraulic casing 60. The piezohydraulic device 100 is configured so that the space between these elements is sufficient so that the movement of the hydraulic casing 60 constituting the moving mass 50 does not come into contact against the walls of the outer casing 105 during its use. This interior space 105' between the hydraulic casing 60 and the walls delimiting the casing 105 is here filled with air, but it could be filled with another gas.

[0053] The piezohydraulic device 100 has a symmetry with respect to a reference plane P, orthogonal to the axis of movement of the first piston 10. This plane of symmetry corresponds to the plane of symmetry of the first piston 10. In particular, the casing 105, the hydraulic casing 60, i.e. also the mobile mass 50, and the first piston 10 are symmetrical with respect to the reference plane P. The third piston 30 corresponds to a symmetry of the second piston with respect to this reference plane P.

[0054] Such a symmetrical configuration of the piezo-hydraulic device 100 with respect to such a plane of symmetry P and using a first double-acting piston 10 makes it possible to benefit from a push-pull effect, also called "push-pull", so as to make it possible to reverse the roles of the motor system and the seismic moving mass 50 while making the system closed. In this configuration, the majority of the mass is used as seismic mass and the piezo-hydraulic device 100 can be used more easily in different positions when it is integrated for example in a system to be balanced. In addition, the seismic mass 50 benefits from better guidance.

[0055] A technical problem that could be encountered is that of the sealing of the hydraulic system, that is to say the hydraulic circuits 101, 102, in particular the hydraulic chambers 101', 102'. Indeed, depending on the pressures involved, the sealing at the level of the small piston(s) which is in movement relative to the hydraulic casing 60, that is to say the second and third pistons 20, 30. One way of solving this problem is to use high-precision machining techniques associated with high-hardness surface treatments.

[0056] Another possible solution is to provide the piezo-hydraulic device 100 with means 110 for controlling the pressure of the fluid 1, 2 of the hydraulic circuit(s) 101, 102 allowing fluid communication between the hydraulic circuit(s) 101, 102 and at least one regulation chamber 103.

[0057] An exemplary embodiment is illustrated in [Fig.4] ([Fig.4]) which differs from the embodiment illustrated in [Fig.3] ([Fig.3]) essentially in that the piezohydraulic device 100 comprises a sealed bellows in the interior space 105' between the hydraulic casing 60 and the walls delimiting the envelope 105 located at the sliding connection of each of the second and third pistons 20, 30. These two bellows are filled with the same fluid 1, 2 as that of the associated hydraulic chamber 101', 102'. The interior spaces of these bellows form regulation chambers 103. Furthermore, the pressure control means 110 comprise a valve 111 placed in a connection channel located between each regulation chamber 103 and associated hydraulic chamber 101', 102'.

[0058] An alternative embodiment is also illustrated in [Fig.5] ([Fig.5]). This embodiment of [Fig.5] ([Fig.5]) differs essentially from that of [Fig.4] ([Fig.4]) in that the hydraulic casing 60 forming the moving mass 50 is immersed in a fluid 3. In other words, the interior space 105' between the hydraulic casing 60 and the walls delimiting the casing 105 is here filled with the fluid 3 forming a regulation chamber 103, and no longer with a gas. Such a configuration makes it possible to avoid the use of bellows.

[0059] The pressure control means 110 make it possible to control a fluid communication between each of the first and second hydraulic chambers 101', 102' with the regulation chamber 103 which is common to each of the hydraulic chambers 101', 102'. Thus, the hydraulic casing 60 is immersed in the hydraulic fluid 3, maintained in equilibrium with atmospheric pressure if necessary.

[0060] A hydraulic fluid 3 contained in the interior space 105' of the external casing 105 will preferably be chosen, which is dielectric. Preferably, the fluids 1, 2, 3 are made up of a fluid of the same nature. The external casing 105 of the piezohydraulic device 100 may also be configured so that it forms a Faraday cage in order to limit the impact of the electromagnetic compatibility of the piezohydraulic device 100.

[0061] [Fig.6] [([Fig.6]]) illustrates a diagram of a piezohydraulic device 100 according to another embodiment. This embodiment differs essentially from that of [Fig.2] [([Fig.2]]) in that the piezoelectric element 40 is also embedded in a fluid. The first piston 10 forms a mechanical interface between the incompressible fluid 1 contained in the hydraulic chamber 101' on one side, and the piezoelectric element 40 on another side opposite and interposed between said first piston 10 and a wall of the hydraulic casing 60. The mechanical deformation of the piezoelectric element 40 in one direction or the other causes the displacement of the first piston 10 in one direction or the other respectively, by sliding relative to the hydraulic chamber 101'.

[0062] The second piston 20 slides relative to the same hydraulic chamber 101', preferably on the same side as the first piston 10 relative to the hydraulic chamber 101'. The second piston 20 is guided in translation at the same time by one of the walls of the hydraulic casing 60 and by the first piston 10 itself. The first and second pistons 10, 20 are each movable in translation along an axis A1 and A2, respectively, the translation axes A1 and A2 of the first and second pistons 10, 20 being coaxial.

[0063] The first piston 10 comprises two opposite faces 12, 13, one 12 of the two faces being in direct contact with the fluid 1 contained in the hydraulic chamber 101' and subjected to the pressure of the fluid 1 contained in the hydraulic chamber 101', the other 13 of the two walls, opposite the wall 12, being integral with the piezoelectric element 40 and also immersed in a fluid, in communication or not with the fluid 1 of the hydraulic chamber 101'. Indeed, the hydraulic casing 60 delimits an interior space inside which the first piston 10 slides by separating two spaces, a first space containing the fluid 1 and a second space housing the piezoelectric element 40 immersed in the fluid, the piezoelectric element 40 being arranged between, preferably interposed between, one of the walls of the hydraulic casing 60 and the wall 13 of the first piston 10.This second space filled with fluid forms a regulation chamber 103 to take into account the connection between the second piston 20 relative to the first piston 10 which it passes through.

[0064] A flexible and elastic membrane 106 equips a portion of an external wall of the piezo-hydraulic device 100, in particular here a portion of the wall of the hydraulic casing 60. The membrane 106 forms an interface between the regulation chamber 103 and the exterior of the piezo-hydraulic device 100, namely the hydraulic casing 60. Such a flexible membrane 106 makes it possible to maintain an equilibrium with atmospheric pressure.

[0065] [Fig.7] ([Fig.7]) illustrates a diagram of a piezohydraulic device 100 according to another embodiment. This embodiment is comparable to that of [Fig.5] ([Fig.5]) to which has been added a membrane 106 as described above, namely flexible and elastic equipping a portion of an external wall of the piezohydraulic device 100, in particular here a portion of the external casing 105, the membrane 106 forming an interface between the regulation chamber 103 delimited between the casing 105 and the exterior of the hydraulic casing 60.

[0066] Whatever the embodiment, the membrane 106 can be removable to ensure emptying of the regulation chamber 103, in the external casing 105 or in the hydraulic casing 60.

[0067] In practice, it is possible to design, thanks to the invention, a piezo-hydraulic device 100 having a very high gear ratio. In general, the piezo-hydraulic device 100 is configured so that the gear ratio between the first piston 10 and at least the second piston 20, and preferably also with the third piston 30, is strictly greater than 20, preferably greater than or equal to 100, more preferably greater than or equal to 400.

[0068] When the piezo-hydraulic device 100 is used to actuate the movement of the mobile mass 50 from an electrical voltage delivered to the piezoelectric element, the piezo-hydraulic device 100 then forms an actuator, the advantage of which here is to be able to transmit significant forces from a minimal movement of the first piston or actuator piston. The second and third pistons 20, 30 are mass drive pistons actuated by the first actuator piston 10. Preferably, the first piston connected to the at least one piezoelectric element is unique, in order to simplify the structure.

[0069] When the piezohydraulic device 100 is used to create an electrical voltage from a displacement of the moving mass, the piezohydraulic device 100 then forms a sensor. Thanks to the gear ratio, it is possible to guarantee particularly fine displacement measurements.

[0070] A possible application is for example in the field of dynamic balancing of a crankshaft of an automobile engine. For example, for vibration reduction applications of a 200 kg internal combustion engine using two piezo-hydraulic actuators 100, each piezo-hydraulic device 100 or piezo-hydraulic actuator 100 must be capable of applying forces capable of generating displacements of the engine of the order of 100 pm at a frequency of 20 Hz. The necessary force is of the order of 150 N. By using a gear ratio of 100 this result can be obtained with a mobile mass 50 of a mass of 1 kg undergoing displacements of 10 mm. In the case where a first piston 10 with a diameter of 4 mm is used, the pressure inside the device would be 120 bars, which constitutes a usual order of magnitude for a hydraulic device.

[0071] The piezohydraulic device 100 according to the invention makes it possible to create sensors and actuators of great compactness and consequently of very reduced mass and size. In particular, this compactness is possible thanks to the principle of hydraulic reduction. Such advantages are particularly interesting in the field of electric vehicles in particular where weight and electrical consumption are omnipresent problems and in constant search of performances.

[0072] An advantageous application of such piezohydraulic devices 100 consists in integrating them into engine mounts of electric vehicles. Thus, by equipping each of the engine mounts with one or more piezohydraulic devices 100 according to the invention, these can reduce the dynamic forces applied to the bodywork and generated by the electric motor. Indeed, these dynamic forces have as their main origin the electromagnetic interactions within the motor or the meshes of the different reduction stages and are generally of a harmonic nature.

[0073] Naturally, the invention is described in the above by way of example. It is understood that those skilled in the art are able to carry out different variant embodiments of the invention without departing from the scope of the invention.

[0074] It is emphasized that all features, as they emerge for a person skilled in the art from the present description, the drawings and the attached claims, even if concretely they have only been described in relation to other determined features, both individually and in any combinations, can be combined with other features or groups of features disclosed herein, provided that this has not been expressly excluded or that technical circumstances make such combinations impossible or meaningless.

Claims

Claims

1. Piezohydraulic device (100) comprising at least one hydraulic circuit (101, 102) comprising a fluid (1, 2) under pressure such as a liquid, a first piston (10) having a useful surface (11) subjected to the pressure of the fluid of the hydraulic circuit, the first piston (10) being connected to at least one piezoelectric element (40) so that the position of the first piston (10) varies as a function of a mechanical deformation of the piezoelectric element (1), at least one second piston (20) having a useful surface (21) subjected to the pressure of the fluid of the hydraulic circuit (101, 102), the useful surface of the first piston (10) being strictly greater than the useful surface of the second piston (20) so as to transmit a multiplied force to move a mobile mass (50), the first piston (10) forming a double-acting piston, the first piston (10) having two opposite faces (12, 13), each of the two faces (12, 13) having a useful surface (11',11”) subjected to the pressure of a fluid (1, 2) contained in separate associated hydraulic chambers (101', 102'), and comprising a third piston (30), the second piston (20) being subjected to the pressure of the fluid (1) contained in a first (101') of the two hydraulic chambers (101', 102'), the third piston (30) being subjected to the pressure of the fluid (2) contained in a second (102') of the two hydraulic chambers (101', 102'), opposite the first (101') with respect to the first piston (10), the second and third pistons (20; 30) preferably being movable along parallel axes, more preferably coaxial (A2, A3).,

2. Piezohydraulic device (100) according to claim 1, characterized in that the hydraulic circuit (101, 102) comprises a hydraulic chamber (101', 102'), preferably consists of a hydraulic chamber (101', 102').

3. Piezo-hydraulic device (100) according to one of the preceding claims, characterized in that the second and third pistons (20, 30) are integral with each other, preferably so as to form an external casing (105) of the piezo-hydraulic device (100).

4. Piezohydraulic device (100) according to one of the preceding claims, characterized in that the moving mass (50) forms a hydraulic casing (60) delimiting the first and second hydraulic chambers (101', 102').

5. Piezo-hydraulic device (100) according to claim 4 and 3, characterized in that the mobile mass (50) is immersed in a hydraulic fluid (3), preferably a dielectric hydraulic fluid, contained in an interior space (105') of the external casing (105) of the piezo-hydraulic device (100), said external casing (105) of the piezo-hydraulic device (100) preferably forming a Faraday cage.

6. Piezo-hydraulic device (100) according to any one of the preceding claims, characterized in that it comprises means (110) for controlling the pressure of the fluid (1, 2) under pressure of the hydraulic circuit(s) (101, 102) allowing fluid communication between the hydraulic circuit(s) (101, 102) and at least one regulation chamber (103), the pressure control means (110) comprising for example at least one valve (111).

7. Piezo-hydraulic device (100) according to claim 6 depending at least on claim 5, characterized in that the pressure control means (110) are configured to control a fluid communication between each of the first and second hydraulic chambers (101', 102') with a common regulation chamber (103), the regulation chamber (103) being contained in the interior space (105') of the external casing (105) of the piezo-hydraulic device (100), between the mobile mass (50) and said external casing (105).

8. Vehicle, for example a motor vehicle, characterized in that it comprises at least one piezo-hydraulic device (100) according to any one of the preceding claims, the vehicle preferably comprising supports for an engine on a fixed structure of the vehicle, preferably an electric motor, the supports for the engine each being equipped with at least one of the piezo-hydraulic devices so as to reduce the dynamic forces applied to the fixed structure of the vehicle.

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