Patent Publication Number: US-2023145967-A1

Title: Servovalve having a linear actuator and mechanical feedback

Description:
FIELD OF THE INVENTION 
     The invention relates to the field of hydraulic servovalves, and more particularly to servovalves having a pilot stage including a linear actuator. 
     BACKGROUND OF THE INVENTION 
     A conventional servovalve is constituted by a pilot stage that controls a movable power-directing member of a power stage. The function of the power stage is to deliver a pressure or a flow rate that is proportional to an instruction applied to the pilot stage. 
     The pilot stage comprises two hydraulic elements, namely a hydraulic emitter (a nozzle or an ejector) and a hydraulic receiver (a flapper, a deflector, or a stationary receiver), such that modifying their relative position gives rise to pressure differences that are used for finely controlling movement of a movable power-directing member of the power stage of the servovalve. The movable power-directing member slides in a cylindrical sleeve located in the body of the servovalve. In general, the position of the hydraulic emitter or receiver is controlled by a torque motor that moves one of the hydraulic elements of the pilot stage facing the other. Movement of the movable power-directing member in its sleeve then establishes communication between a set of openings and drilled channels that are arranged to deliver a pressure or a flow rate that is proportional to the movement of said movable power-directing member. The mechanical directing member is connected to a mechanical feedback rod that is rigidly secured to that one of the hydraulic emitter and receiver that is movable. 
     There exist servovalves in which the hydraulic emitter or receiver is moved by a linear actuator. A position sensor measures the position of the power member and controls the linear actuator via power electronics serving to provide electronic feedback in a manner similar to the feedback provided mechanically by the feedback rod in a servovalve. Such electronics are expensive and have an unfavorable impact on the size, the weight, and the reliability of a servovalve. 
     OBJECT OF THE INVENTION 
     An object of the invention is to improve the reliability of a servovalve. 
     SUMMARY OF THE INVENTION 
     To this end, there is provided a servovalve having a pilot stage comprising a hydraulic element for ejecting a jet of fluid and a hydraulic element for receiving the jet of fluid, the hydraulic elements 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 of the servovalve, one of the two elements being mounted in a fixed position on a body of the servovalve and the other one of the elements being mounted at the movable end of a support that is connected to the body of the servovalve, the pilot stage including a linear actuator comprising a main pusher arranged to exert a force selectively on the support tending to modify the relative position of the hydraulic elements, the pilot stage also including a lever provided with a force transfer interface comprising an application, first point for applying an output force on the lever and a transmission, second point for transmitting the output force from the lever towards the support, the lever also being connected at a connection, third point to the power-directing member, the application, first point and the transmission, second point being situated on opposite sides of a first plane extending parallel to an output direction of the main pusher and perpendicularly to a neutral axis of the lever. 
     This results in a servovalve that is provided with a position feedback device that enables a linear actuator to be used without having recourse to a movement sensor for sensing the movement of the power-directing member. Having feedback that is entirely mechanical greatly improves the reliability of the servovalve of the invention. 
     Advantageously, the connection interface is arranged in such a manner that the connection at the application, first point or at the transmission, second point is a point connection or a ball joint connection or a linear connection or a pivot connection. 
     The vibration behavior of the servovalve is improved when the force transfer interface includes a cam and indeed when the cam is arranged to provide a pivot connection at the transmission, second point and/or when the support is connected to the body of the servovalve by a fixed connection. 
     In a particular embodiment, the force transfer interface includes both a first portion extending in a first direction intersecting the neutral axis of the lever and also a second portion extending in a second direction intersecting the second direction and/or the force transfer interface includes both a third portion extending in a third direction intersecting the neutral axis of the lever and also a fourth portion extending in a fourth direction intersecting the third direction. 
     Also advantageously, the transmission, second point acts on an auxiliary pusher that comes into contact with the rod in order to push it. 
     The fixed-position hydraulic element may be a fluid receiver and the hydraulic element carried by the rod is a fluid ejector, or else the fixed-position hydraulic element may be a fluid ejector and the movable element a fluid receiver. 
     In a preferred embodiment, the linear actuator comprises a piezoelectric actuator. 
     Other characteristics and advantages of the invention appear on reading the following description of particular, nonlimiting embodiments of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a diagrammatic side view of an servovalve in a first embodiment of the invention; 
         FIG.  2    is a diagrammatic side view of a lever in a first embodiment of the invention; 
         FIG.  3    is a diagrammatic view of the  FIG.  1    servovalve in a first transient state; 
         FIG.  4    is a diagrammatic view of the  FIG.  1    servovalve in a second transient state; 
         FIG.  5    is a diagrammatic view of the  FIG.  1    servovalve in a third transient state; 
         FIG.  6    is a diagrammatic view of the  FIG.  1    servovalve in a fourth transient state; 
         FIG.  7    is a diagrammatic view of the  FIG.  1    servovalve in a fifth transient state; 
         FIG.  8    is a diagrammatic side view of a lever in a second embodiment of the invention; 
         FIG.  9    is a diagrammatic face view of the  FIG.  8    lever placed in situation; 
         FIG.  10    is a diagrammatic plan view of the  FIG.  9    lever; 
         FIG.  11    is a diagrammatic detail view of a lever in a third embodiment of the invention; 
         FIG.  12    is a diagrammatic detail view of the  FIG.  10    lever in a first state; 
         FIG.  13    is a diagrammatic detail view of the  FIG.  10    lever in a second state; and 
         FIG.  14    is a diagrammatic detail view of a lever in a fourth embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to  FIGS.  1  and  2   , the invention is illustrated in this example in application to a servovalve for regulating air flow rate, the servovalve having two stages, one of which is a pilot stage. Naturally, the invention is not limited to this application, and can be used in other types of servovalve. 
     The servovalve, given overall reference  100 , comprises a body  1  having a power-directing member  2  mounted therein to slide in leaktight manner in a cylindrical housing  3  so as to form the power-directing stage. The power-directing member  2  is movable between two extreme positions and it is shaped so as to define leaktight chambers C 1 , C 2 , C 3 , and C 4  in the housing  3  such that in the extreme positions of the power-directing member  2  relative to a center (or neutral) position, they put the following into communication:
         either a feed port P with a first utilization port U 1 , and a return port R with a second utilization port U 2 ; or else   the feed port P with the second utilization port U 2 , and the return port R with the first utilization port U 1 .       

     The sliding of the power-directing member  2  in the housing  3  is controlled by means of pilot chambers  4  and  5 , which are fed with fluid under pressure by a pressure distribution member, in this example, specifically a stationary receiver  6 . The receiver  6  comprises a receptacle  9  with two orifices  7  and  8 . The orifices  7  and  8  are in fluid flow communication with respective ones of the pilot chambers  4  and  5 , via ducts  10  and  11 . The receptacle  9  is connected to the return R by a duct  12 . 
     The pilot stage  20  of the servovalve  100  includes a rod  21  pivotally mounted at its first end  22  to the body  1 . The rod  21  has a second end  23  that is free and that has a fluid ejector  30  mounted thereon so as to face the receiver  6 . A pressure spring  24  is mounted to act between the body  1  and a portion  25  of the rod  21  so as to exert a return force on the rod  21  causing it to pivot about the first end  22  in a direction that is counterclockwise as shown in  FIG.  1   . The rod  21  includes an internal duct  31  for delivering fluid to the fluid ejector  30 . The internal duct  31  is in fluid flow connection with the feed port P of the servovalve  100  via a duct  32  formed in the body  1 . 
     The pilot stage  20  includes a piezoelectric linear actuator  40  having a main pusher  41  for selectively applying a force on the rod  21 . 
     The pilot stage also includes a lever  50  placed between the main pusher  41  and a first end  61  of an auxiliary pusher  60  that is 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 . 
     At its first end  51 , the lever  50  is provided with a force transfer interface  52 . The force transfer interface  52  comprises a first ceramic hemisphere  53  having a first center  53 . 1  and projecting from the first face  54  of the lever  50 . A second ceramic hemisphere  55  having a second center  55 . 1  projects from the second face  56  of the lever  50 , opposite from the first face  54 . The first and second hemispheres  53  and  55  are located in such a manner that when the first and second centers  53 . 1  and  55 . 1  are projected orthogonally onto the neutral axis  57  of the lever  50  their respective first and second orthogonal projections  53 . 1  and  57 . 2  are spaced apart by a nonzero distance d 53 - 55 . 
     The second end  58  of the lever  50  includes a tungsten carbide bead  59  that is received in a notch  13  in the power-directing member  2 . 
     Thus, an output force Fs of the main pusher  41  is applied on a first point  70  of the first hemisphere  53 . The output force Fs is then transmitted via a second point  71  of the second hemisphere  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  so as to move the fluid ejector  30  towards the first orifice  7 . In corresponding manner, withdrawal of the main pusher  41  causes the fluid ejector  30  to move 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 actuator exerts a force on the rod  21  that tends to move the fluid ejector  30  mounted on the end  23  of the rod  21  where it faces the receiver  6 . 
     The first point  70  corresponds to an application, first point  70  for application of the output force. The second point  71  corresponds to a second point  71  for transmitting the output force. The bead  59  constitutes a third point  73  for connection with the power-directing member  2 . 
     As can be seen in  FIG.  1   , the first point  70  for application of the output force Fs from the main pusher  41  on the lever  50  and the second point  71  for transmitting the output force Fs from the lever  50  to the rod  21  are situated on opposite sides of a first plane P 1  lying parallel to an output direction Oy of the main pusher  41  and perpendicularly to the neutral axis  57  of the lever  50 . 
     In operation, and as shown in  FIG.  1   , when a voltage Ue is applied to the terminals of the actuator  40  that corresponds to half a nominal utilization voltage Un, then the main pusher  41  of the actuator  40  is at half-stroke. The servovalve  100  is in its equilibrium state and of the ejector  30  ejects a jet of fluid towards the receptacle  9 . No pressure difference is created between the pilot chambers  4  and  5 , and the power directing member  2  remains in its neutral position, with the utilization ports U 1  and U 2  being isolated from the feed port P. 
     When an input voltage Ue is applied to the terminals of the actuator  40  that corresponds to the nominal utilization voltage Un, then the voltage Ue causes the main pusher  41  to be extended to 100% of its stroke, and by acting on the first point  70 , this causes the lever  50  to pivot about the third point  73  (in a counterclockwise direction as shown in  FIG.  3   ), thereby moving the second point  71  and causing the auxiliary pusher  60  to shift in translation against the force of the spring  24 . The ejector  30  is then to be found facing the orifice  7  and it ejects a jet of fluid towards the orifice  7  ( FIG.  3   ). The pressure difference thus created between the pilot chambers  4  and  5  causes the power-directing member  2  to move in its housing  3  to the right as shown in  FIGS.  1  and  3    (increasing the volume of the pilot chamber  4 ). The utilization port U 1  is then put into fluid flow communication with the feed port P ( FIG.  4   ). While the power-directing member  2  is moving, the third point  73  shifts in translation to the right (as shown in  FIG.  4   ), thereby causing the lever  50  to pivot about the third point  73 . This shift in translation causes the second contact point  71  to move towards the right (as shown in  FIG.  4   ), thereby reducing the force transmitted by the second point  71  of the lever  50  to the auxiliary pusher  60  ( FIG.  4   ) and causing the rod  21  to return to its initial position ( FIG.  5   ). The servovalve then returns to its equilibrium state. 
     The illustrations of  FIGS.  4  and  5    show stages in the movements of the lever  50  and of the auxiliary pusher  60  and they show the second point  71  of the lever  50  moving away from the first end  61  for the purposes of clarity. On reading the description, the person skilled in the art understands that the pivoting movement of the lever  50  about the third point  73  and the movement of the auxiliary pusher  60  to the left as shown in  FIGS.  4  and  5   ) take place simultaneously. 
     When a zero input voltage Ue is applied to the terminals of the actuator  40 , then the voltage Ue causes the main pusher  41  to be retracted, and by action of the spring  24 , this causes the lever  50  to pivot R 1  about the third point  73  (in a clockwise direction as shown in  FIG.  6   ), thereby moving the second point  71  and causing the auxiliary pusher  60  to shift in translation to the right (as shown in  FIG.  6   ). The ejector  30  is then to be found facing the orifice  8  and it ejects a jet of fluid towards the orifice  8  ( FIG.  6   ). The pressure difference thus created between the pilot chambers  4  and  5  causes the power-directing member  2  to move in its housing  3  to the left as shown in  FIGS.  1  and  6    (increasing the volume of the pilot chamber  5 ). The utilization port U 2  is then put into fluid flow communication with the feed port P ( FIG.  7   ). While the power-directing member  2  is moving, the third point  73  shifts in translation to the left (as shown in  FIG.  7   ), thereby causing the lever  50  to pivot about the first point  70 . This shift in translation causes the second contact point  71  to move towards the left (as shown in  FIG.  7   ), thereby causing the auxiliary pusher  60  to shift towards the left (as shown in  FIG.  7   ) and causing the rod  21  to return to its initial position ( FIG.  7   ). 
     This results in a servovalve  100  that is provided with a position feedback device that enables a linear actuator to be used without having recourse to a movement sensor for sensing the movement of the power-directing member  2 . Having feedback that is entirely mechanical greatly improves the reliability of the servovalve of the invention. The first point  70  and the second connection point  71  are always situated on opposite sides of the first plane P 1  regardless of the position of the power-directing member  2  in its housing. 
     Elements identical or analogous to those described above are given same numerical references in the description below of the second, third and fourth embodiments. 
     In a second embodiment as shown in  FIG.  8  to  10   , the force transfer interface  52  includes a cam  80 . In this example, the cam  80  is a disk of center O 80  provided in its bottom left quarter (as shown in  FIGS.  8  and  9   ) with a first bore  81 . The cam  80  is received in a slot  82  formed in the end  61  of the auxiliary pusher  60 . A pin  83  is engaged in a second bore  84  of the auxiliary pusher  60  and passes through the first bore  81  in order to provide a pivot connection  83 . 1  at the second connection point  71 . The first connection point  70  is provided by the right-hand quadrants (as shown in  FIG.  9   ), and the second connection point  71  is provided by the pivot connection  83 . 1 . 
     In a third embodiment as shown in  FIGS.  11  to  13   , the interface  52  is made of steel and includes both a first portion  90  extending in a first direction O 90  intersecting the neutral axis  57  of the lever  50  and also a second portion  91  extending in a second direction O 91  intersecting the first direction O 90 . The section of the first portion  90  is smaller than the section of the second portion  91  and it provides a first flexing point  92  allowing the second portion  91  to pivot relative to the first portion  90 . In symmetrical manner about a plane P 57  containing the neutral axis  57 , the interface  52  includes both a third portion  93  extending in a third direction O 93  intersecting the neutral axis  57  of the lever  50  and a fourth portion  94  extending in a fourth direction O 94  intersecting the third direction O 93 . The section of the third portion  93  is smaller than the section of the fourth portion  94  and it provides a second flexing point  95  allowing the fourth portion  94  to pivot relative to the third portion  93 . 
     The first and second flexing points  92  and  95  correspond respectively to the first and second connection points  70  and  71 .  FIGS.  12  and  13    show two states of the interface  52  and of the lever  50  when they are subjected to movements of the main pusher  41  and of the auxiliary pusher  60 . 
     In a fourth embodiment of the invention, as shown in  FIG.  14   , the lever  50  acts directly on the rod  21  in order to push it. 
     The first point  70  is a first point for application of the output force Fs of the actuator  40 . The second point  71  is a second point for transmitting the output force Fs from the actuator  40 . 
     The invention is naturally not limited to the above description, but covers any variant coming within the ambit defined by the claims. 
     In particular:
         although above the connections at the first and second points are, in this example, point connections provided by a sphere contacting a plane, the invention applies equally to other ways of providing a point connection or connections of other types, such as a ball joint, a linear connection, or a pivot connection;   although above the first end of the rod is pivotally mounted on the body, the invention applies equally to other types of connection between the rod and the body of the servovalve, e.g. such as a fixed connection or a torsion column attached to a welded frame machined in the body of the servovalve, or indeed pressed into the body of the servovalve;   although above the rod has an internal duct for delivering fluid to the fluid ejector, the invention applies equally to other types of fluid feed, e.g. such as feed via a flexible hose or via an external duct attached to the rod;   although above the actuator is a piezoelectric actuator, the invention applies equally to other types of linear actuator, e.g. such as an electrical, pneumatic, or hydraulic jack;   although above the stationary hydraulic element is a fluid receiver and the element mounted at the end of the rod is a fluid emitter, the invention applies equally to a fluid emitter in a stationary position on a body of the servovalve associated with a fluid receiver mounted at the end of the rod, e.g. a receiver such as a deflector or a flapper;   although above the pilot stage includes a rod on which a fluid ejector is mounted, the invention applies to other types of support, e.g. such as a blade;   although above the pilot stage includes a spring acting on the rod, the invention applies equally to other position return means, e.g. such as a hydraulic spring or the rod having an end that is fixed. Furthermore, the invention can operate without means for restoring the position of the support, e.g. such as when a second piezoelectric actuator is positioned facing the first end on the other side of the rod, with control of the second actuator being paired with control of the first actuator;   although above the transfer interface is positioned at a first end of the lever, the invention applies equally to a transfer interface situated at a distance from the end of the lever; and   although above the second end of the rod has a tungsten carbide bead that is received in a notch of the power-directing member, the invention applies to other connection means for providing a third connection point, e.g. such as a ball joint, or a pivot.