SERVO VALVE WITH LINEAR ACTUATOR AND MECHANICAL FEEDBACK

Description

FIELD OF THE INVENTION

[0001] The invention relates to the field of hydraulic servovalves and more particularly to servovalves with a pilot stage comprising a linear actuator. BACKGROUND OF THE INVENTION

[0002] A conventional servovalve consists of a pilot stage controlling a moving power distribution element of a power stage. The function of the power stage is to deliver a pressure or flow rate proportional to an instruction transmitted to the pilot stage.

[0003] The control stage comprises two hydraulic elements, namely a hydraulic transmitter (nozzle or ejector) and a hydraulic receiver (vane, deflector or fixed receiver) whose modification of their relative position generates pressure differentials which are used to finely move a mobile power distribution member of the power stage of the servovalve. This mobile power distribution member slides in a cylindrical sleeve located in the body of the servovalve. Generally, the position of the hydraulic transmitter or receiver is controlled by a torque motor which moves one of the hydraulic elements of the control stage opposite the other. The movement of the mobile power distribution member in its sleeve then connects a set of drilled channels and ports whose arrangement makes it possible to deliver a pressure or a flow rate, proportional to the movement of said mobile power distribution member.A mechanical feedback rod rigidly secured to that of the hydraulic transmitter or receiver which is movable is connected to the mechanical distribution member. The servovalves described in document FR2046759 and document FR1511251 are examples of servovalves at the control stage known in the state of the art.

[0004] There are servovalves in which the movement of the hydraulic transmitter or receiver is caused by a linear actuator. A position sensor measures the position of the power element and controls the linear actuator via dedicated power electronics to provide electronic feedback in a similar way to that provided mechanically by the feedback rod in the case of a servovalve. Such electronics are expensive and adversely impact the size, weight and reliability of a servovalve. SUBJECT OF THE INVENTION

[0005] The object of the invention is to improve the reliability of a servovalve. SUMMARY OF THE INVENTION

[0006] For this purpose, a servo valve with a pilot stage is provided according to independent claim 1.

[0007] This results in a servovalve equipped with a position feedback device that allows the use of a linear actuator without the need for a displacement sensor of the power distribution member. The fully mechanical feedback greatly improves the reliability of the servovalve according to the invention.

[0008] Advantageously, the force transfer interface is arranged so that the connection at the first point of application or the second point of transmission is a point connection or a ball joint connection or a linear connection or a pivot connection.

[0009] The vibration behavior of the servovalve is improved when the force transfer interface includes a cam or when the cam is arranged to provide a pivot connection at the second transmission point and / or when the support is connected to the body of the servovalve by a recess.

[0010] According to a particular embodiment, the force transfer interface comprises a first portion extending in a first direction intersecting the neutral fiber of the lever and a second portion extending in a second direction intersecting the first direction and / or the force transfer interface also comprises a third portion extending in a third direction intersecting the neutral fiber of the lever and a fourth portion extending in a fourth direction intersecting the third direction.

[0011] Advantageously also, the second transmission point acts on an auxiliary pusher which comes into contact with the rod to push it.

[0012] The fixed hydraulic element may be a fluid receiver and the hydraulic element carried by the rod is a fluid ejector or the fixed hydraulic element may be a fluid ejector and the movable element a fluid receiver. According to a preferred embodiment, the linear actuator comprises a piezoelectric actuator.

[0013] Other characteristics and advantages of the invention will emerge from reading the following description of particular non-limiting embodiments of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] There figure 1 is a schematic view of the servovalve according to a first embodiment of the invention; the figure 2 is a schematic view of a lever according to a first embodiment of the invention; the figure 3 is a schematic view of the servovalve of the figure 1 in a first transitional state; the figure 4 is a schematic view of the servovalve of the figure 1 in a second transient state; the figure 5 is a schematic view of the servovalve of the figure 1 in a third transitional state. figure 6 is a schematic view of the servovalve of the figure 1 in a fourth transitional state; the figure 7 is a schematic view of the servovalve of the figure 1 in a fifth transitional state; the figure 8 is a schematic detail view of a lever according to a second embodiment of the invention; the figure 9 is a schematic front view of the lever of the figure 8 placed in situation; the figure 10 is a schematic top view of the lever of the figure 9 ; there figure 11 is a schematic detail view of a lever according to a third embodiment of the invention; the figure 12 is a detailed schematic view of the lever of the figure 10 in a first state; the figure 13 is a detailed schematic view of the lever of the figure 10 in a second state; the figure 14 is a schematic detail view of a lever according to a fourth embodiment of the invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] In reference to the figures 1 And 2 , the invention is illustrated here in application to a two-stage barometric flow control servovalve including a pilot stage. Of course, the invention is not limited to this application, and can be used for other types of servovalves.

[0016] The servovalve, generally designated 100, comprises a body 1 in which a power distribution member 2 is mounted to slide in a sealed manner in a cylindrical housing 3, forming the distribution stage. The power distribution member 2 is movable between two extreme positions and is shaped to delimit in the housing 3 sealed chambers C1, C2, C3, C4 to communicate respectively, depending on the extreme position of the power distribution member 2 relative to a centered position (or neutral position): either a supply port P with a first use port U1, and a return port R with a second use port U2, or the supply port P with the second use port U2, and the return port R with the first use port U1.

[0017] The sliding of the power distribution member 2 in the housing 3 is controlled by means of control chambers 4, 5 which are supplied with pressurized fluid by a pressure distribution member, in this case a fixed receiver 6. The receiver 6 comprises two orifices 7 and 8 and a receptacle 9. The orifices 7 and 8 are respectively placed in fluid communication, via conduits 10 and 11, with the control chambers 4 and 5. The receptacle 9 is connected to the return R by a conduit 12.

[0018] The control stage 20 of the servovalve 100 comprises a rod 21 rotatably mounted at its first end 22 on the body 1. The rod 21 comprises a second free end 23 on which is mounted a fluid ejector 30 which comes opposite the receiver 6. A pressure spring 24 mounted to bear between the body 1 and a portion 25 of the rod 21 exerts a return force on the rod 21 to cause it to rotate around the first end 22 in an anticlockwise direction according to the representation of the figure 1 The rod 21 comprises an internal conduit 31 for supplying fluid to the fluid ejector 30. This internal conduit 31 is fluidically connected to the supply port P of the servovalve 100 by a conduit 32 drilled in the body 1.

[0019] The control stage 20 comprises a piezoelectric linear actuator 40 which comprises a main pusher 41 for selectively exerting a force on the rod 21.

[0020] The control stage also comprises a lever 50 placed between the main pusher 41 and a first end 61 of an auxiliary pusher 60 slidably mounted on the body 1. The second end 62 of the auxiliary pusher 60 comes into contact with the portion 25 of the rod 21.

[0021] The lever 50 is provided at its first end 51 with a force transfer interface 52. The force transfer interface 52 comprises a first ceramic hemisphere 53 with a first center 53.1 and which projects from the first face 54 of the lever 50. A second ceramic hemisphere 55 with a second center 55.1 projects from the second face 56 of the lever 50 opposite the first face 54. The first hemisphere 53 and the second hemisphere 55 are located so that the first orthogonal projection 57.1 of the first center 53.1 on a neutral fiber 57 of the lever 50 and the second orthogonal projection 57.2 of the second center on a neutral fiber 57 of the lever 50 are separated by a non-zero distance d53-55.

[0022] The second end 58 of the lever 50 comprises a tungsten carbide ball 59 which is received in a groove 13 of the power distribution member 2.

[0023] Thus an output force Fs of the main pusher 41 is applied to a first point 70 of the first half-sphere 53. The output force Fs is then transmitted by a second point 71 of the second half-sphere 55 to the first end 61 of the auxiliary pusher 60. The second end 62 of the auxiliary pusher 60 then acts on the rod 21 against the force of the spring 24 to move the fluid ejector 30 towards the first orifice 7. A withdrawal of the main pusher 41 causes, in a homologous manner, the movement of the fluid ejector 30 towards the second orifice 8 under the effect of the spring 24. Thus, depending on the voltage applied to the terminals of the actuator 40, the latter exerts a force on the rod 21 which tends to move the fluid ejector 30 mounted on the end 23 of the rod 21 opposite the receiver 6.

[0024] The first point 70 corresponds to a first point 70 of application of the output force. The second point 71 corresponds to a second point 71 of application of transmission of the output force. The ball 59 constitutes a third connection point 73 with the power distribution member 2.

[0025] As visible in figure 1 , the first point 70 of application of the output force Fs of the main pusher 41 on the lever 50 and the second point 71 of transmission of the output force Fs from the lever 50 to the rod 21 are located on either side of a first plane P1 extending parallel to a direction Oy of output of the main pusher 41 and perpendicular to the neutral fiber 57 of the lever 50.

[0026] In operation, and as shown in figure 1 , when applying a voltage Ue corresponding to half of a nominal operating voltage Un to the terminals of the actuator 40, the main pusher 41 of the actuator 40 is at mid-stroke. The servovalve 100 is in its equilibrium state and the ejector 30 ejects a jet of fluid towards the receptacle 9. No pressure differential is created between the pilot chambers 4 and 5 and the power distribution member 2 remains in the neutral position, the operating ports U1 and U2 are isolated from the power supply port P.

[0027] When an input voltage Ue corresponding to the nominal operating voltage Un is applied to the terminals of the actuator 40, this voltage Ue causes the main pusher 41 to exit at 100% of its travel which, by acting on the first point 70, causes the lever 50 to rotate around the third point 73 (in an anticlockwise direction according to the representation of the figure 3 ) and induces a displacement of the second point 71 which causes a translation of the auxiliary pusher 60 against the force of the spring 24. The ejector 30 then finds itself facing the orifice 7 and ejects a jet of fluid towards the orifice 7 ( figure 3 ). The pressure differential thus created between the control chambers 4 and 5 causes the power distribution member 2 to move in its housing 3 to the right according to the representation of figures 1 And 3 (increase in the volume of the pilot chamber 4). The use port U1 is then put into fluid communication with the supply port P ( figure 4 ). During the movement of the power distribution member 2, the third point 73 translates to the right (according to the representation of the figure 4 ) which causes the lever 50 to pivot around the third point 73. This translation causes the second point of contact 71 to move to the right (according to the representation of the fi-gure 4 ), which reduces the force transmitted by the second point 71 of the lever 50 to the auxiliary pusher 60 ( figure 4 ) and causes the rod 21 to return to its initial position ( figure 5 ). The servovalve then returns to its equilibrium state.

[0028] The representations of the figures 4 And 5 break down the movement of the lever 50 and the auxiliary pusher 60 and represent a distance from the second point 71 of the lever 50 and the first end 61 for the sake of clarity. The person skilled in the art will understand from reading the description that the rotational movement of the lever 50 around the third point 73 and the movement of the auxiliary pusher 60 to the left according to the representation of the figures 4 And 5 are simultaneous.

[0029] When a zero input voltage Ue is applied to the terminals of the actuator 40, this voltage Ue causes a retraction of the main pusher 41 which, under the effect of the spring 24, causes a rotation R1 of the lever 50 around the third point 73 (in a clockwise direction according to the representation of the figure 6 ) and induces a displacement of the second point 71 which causes a translation of the auxiliary pusher 60 to the right (according to the representation of the figure 6 ). The ejector 30 then faces the orifice 8 and ejects a jet of fluid towards the orifice 8 ( figure 6 ). The pressure differential thus created between the control chambers 4 and 5 causes the power distribution member 2 to move in its housing 3 to the left according to the representation of figures 1 And 6 (increase in the volume of the pilot chamber 5). The use port U2 is then put into fluid communication with the supply port P ( figure 7 ). During the movement of the power distribution member 2, the third point 73 translates to the left (according to the representation of the figure 7 ) which causes the lever 50 to pivot around the first point 70. This translation causes the second point 71 to move to the left (according to the representation of the figure 7 ), which causes the auxiliary pusher 60 to move to the left (according to the representation of the figure 7 ) and a return of the rod 21 to its initial position ( figure 7 ).

[0030] A servovalve 100 is then obtained provided with a position feedback device which allows the use of a linear actuator without recourse to a displacement sensor of the power distribution member 2. The entirely mechanical feedback greatly improves the reliability of the servovalve according to the invention. The first point 70 and the second point 71 are always located on either side of the first plane P1 regardless of the position of the power distribution member 2 in its housing.

[0031] Elements identical or similar to those previously described will bear the same numerical reference in the following description of the second, third and fourth embodiments of the invention.

[0032] According to a second embodiment shown in figure 8 à 10 , the force transfer interface 52 comprises a cam 80. The cam 80 is here a center disc O 80 provided in its lower left quarter (according to the representation of the figures 8 And 9 ) of a first bore 81. The cam 80 is received in a groove 82 opening onto the end 61 of the auxiliary pusher 60. An axis 83 is engaged in a second bore 84 of the auxiliary pusher 60 and passes through the first bore 81 to produce a pivot connection 83.1 at the second connection point 71. The first connection point 70 is provided by the right quadrants (according to the representation of the figure 9 ) and the second connection point 71 is provided by the pivot connection 83.1.

[0033] According to a third embodiment shown in figures 11 à 13 , the interface 52 is made of steel and comprises a first portion 90 extending in a first direction O90 intersecting the neutral fiber 57 of the lever 50 and a second portion 91 extending in a second direction O91 intersecting the first direction O90. The first portion 90 has a smaller section than the section of the second portion 91 and forms a first inflection point 92 allowing rotation of the second portion 91 relative to the first portion 90. Symmetrically with respect to a plane P57 comprising the neutral fiber 57, the interface 52 comprises a third portion 93 extending in a third direction O93 intersecting the neutral fiber 57 of the lever 50 and a fourth portion 94 extending in a fourth direction O94 intersecting the third direction O93.The third portion 93 has a smaller section than the section of the fourth portion 94 and forms a second inflection point 95 allowing rotation of the fourth portion 94 relative to the third portion 93.

[0034] The first inflection point 92 and the second inflection point 95 correspond respectively to the first connection point 70 and to the second connection point 71. The figures 12 And 13 represent two states of the interface 52 and the lever 50 subject to the movements of the main pusher 41 and the auxiliary pusher 60.

[0035] According to a fourth embodiment of the invention shown in figure 14 , the lever 50 acts directly on the rod 21 to push it.

[0036] The first point 70 is a first point of application of the output force Fs of the actuator 40. The second point 71 is a second point of transmission of the output force Fs of the actuator 40.

[0037] The invention is of course not limited to what has just been described, but encompasses any variant falling within the scope defined by the claims.

[0038] Especially, although here the connections at the first point and the second point are, here, point connections made by contact of a sphere on a plane, the invention also applies to other ways of making a point connection or other types of connection such as a ball joint connection, a linear connection or a pivot connection; although here the rod is rotatably mounted at its first end on the body, the invention also applies to other types of connections of the rod on the body of the servovalve, such as for example a recess or a torsion column attached to a welded frame, machined in the body of the servovalve, or even fitted on the body of the servovalve; although here the rod comprises an internal conduit for supplying fluid to the fluid ejector, the invention also applies to other types of fluid supply such as for example a supply by hose or by an external conduit attached to the rod;although here the actuator is a piezoelectric actuator, the invention also applies to other types of linear actuators such as for example an electric, pneumatic or hydraulic cylinder; although here the fixed hydraulic element is a fluid receiver and the element mounted at the end of the rod is a fluid emitter, the invention also applies to a fluid emitter fixed on a body of the servovalve and to a fluid receiver, such as for example a deflector or a vane, mounted at the end of the rod; although here the control stage comprises a rod on which a fluid ejector is mounted, the invention applies to other types of support such as for example a blade;although here the control stage comprises a spring pressing on the rod, the invention also applies to other means of returning to position, such as for example a recess of the rod or a hydraulic spring. The invention is moreover operational without means of returning the support to position, such as for example when a second piezoelectric actuator is positioned opposite the first on the other side of the rod and its control is matched to that of the first; although here the transfer interface is positioned at a first end of the lever, the invention also applies to a transfer interface located at a distance from one end of the lever;although here the second end of the rod comprises a tungsten carbide ball which is received in a groove of the power distribution member, the invention applies to other connecting means for producing a third connecting point such as for example a ball joint, a pivot. although here the transfer interface is positioned at a first end of the lever, the invention also applies to a transfer interface located at a distance from one end of the lever; although here the second end of the rod comprises a tungsten carbide ball which is received in a groove of the power distribution member, the invention applies to other connecting means for producing a third connecting point such as for example a ball joint, a pivot.;

Claims

1. A servovalve (100) having a pilot stage (20) comprising a hydraulic element (30) for ejecting a jet of fluid and a hydraulic element (6) for receiving the jet of fluid, the hydraulic elements (30, 6) being movable relative to each other so as to modify their relative position and thus generate a pressure difference usable for moving a power-directing member (2) of the servovalve (100), one of the two elements (6) being mounted in a fixed position on a body (1) of the servovalve (100) and the other one of the elements (30) being mounted at the movable end (23) of a support (21) that is connected to the body (1) of the servovalve (100), the pilot stage (20) including a lever (50) provided with a force transfer interface (52) comprising an application, first point (70) for applying an output force (Fs) on the lever (50) and a transmission, second point (71) for transmitting the output force (Fs) from the lever (50) towards the support (21), the lever (50) also being connected at a connection, third point (73) to the power-directing member (2), the pilot stage (20) also comprising a linear actuator (40) including a main pusher (41) arranged to exert selectively the output force (Fs), so that an effort is exerted on the support (21) tending to modify the relative position of the hydraulic elements (30, 6), the application, first point (70) and the transmission, second point (71) being situated on opposite sides of a first plane (P1) extending parallel to an output direction (Oy) of the main pusher (41) and perpendicularly to a neutral axis (57) of the lever (50).

2. A servovalve (100) according to claim 1, wherein the connection interface (52) is arranged in such a manner that the connection at the application, first point (70) or at the transmission, second point (71) is a point connection or a ball joint connection or a linear connection or a pivot connection.

3. A servovalve (100) according to claim 1, wherein the force transfer interface (52) includes a cam (80).

4. A servovalve (100) according to claim 3, wherein the cam (80) is arranged to provide a pivot connection at the transmission, second point (71).

5. A servovalve (100) according to claim 1, wherein the force transfer interface (52) includes both a first portion (90) extending in a first direction (O90) intersecting the neutral axis (57) of the lever (50) and also a second portion (91) extending in a second direction (O91) intersecting the first direction (O90).

6. A servovalve (100) according to claim 5, wherein the force transfer interface (52) includes both a third portion (93) extending in a third direction (O93) intersecting the neutral axis (57) of the lever (50) and also a fourth portion (94) extending in a fourth direction (O94) intersecting the third direction (O93).

7. A servovalve (100) according to any preceding claim, wherein the transmission, second point acts on an auxiliary pusher (60) that comes into contact with the support (21) in order to push it.

8. A servovalve (100) according to claim 1, wherein the fixed-position hydraulic element is a fluid receiver (6) and the hydraulic element carried by the support (21) is a fluid ejector (30).

9. A servovalve (100) according to claim 1, wherein the support (21) is connected to the body of the servovalve by a fixed connection.

10. A servovalve (100) according to any preceding claim, wherein the linear actuator comprises a piezoelectric actuator (40).