Patent Publication Number: US-2022213973-A1

Title: Piezoelectric valve and method of manufacturing the piezoelectric valve

Description:
TECHNICAL FIELD 
     The present disclosure relates to a piezoelectric valve in which the valve is opened/closed utilizing a displacement of a laminated piezoelectric element, and a method of manufacturing the piezoelectric valve. 
     BACKGROUND ART 
     A piezoelectric valve is conventionally known in which the valve is opened/closed utilizing a displacement of a laminated piezoelectric element to eject compressed gas (see Patent Literature 1). 
     The piezoelectric valve described in Patent Literature 1 utilizes properties of the laminated piezoelectric element having excellent high-speed response performance, and includes a displacement enlarging mechanism that enlarges a small displacement of the laminated piezoelectric element based on the principle of leverage. 
     In the piezoelectric valve, application of a voltage to the laminated piezoelectric element causes a displacement of the laminated piezoelectric element in an extending direction, the displacement is transmitted to a valving element via the displacement enlarging mechanism, and the valving element is immediately moved to open the valve. 
     Moreover, in the piezoelectric valve, cancellation of voltage application to the laminated piezoelectric element causes a return force associated with return of the laminated piezoelectric element to an original state, the return force is transmitted to the valving element via the displacement enlarging mechanism, and the valving element is immediately brought into contact with a valve seat to close the valve. 
     The laminated piezoelectric element has excellent features such as low consumption energy associated with the operation, suitability for high-speed operation, and compactness. 
     However, the laminated piezoelectric element has a piezoelectric ceramic layer, and is thus structurally fragile, which may cause broken pieces to be ejected together with compressed gas when the piezoelectric valve is used. 
     Moreover, the laminated piezoelectric element is vulnerable to a highly-humid environment. Thus, in a case of using the piezoelectric valve in a highly-humid environment, moisture may enter the laminated piezoelectric element to shorten the life of the piezoelectric valve. 
     Thus, the inventors of the present invention have proposed coating a surface of the laminated piezoelectric element with a polyolefin-based resin (see Patent Literature 2). 
     A piezoelectric valve described in Patent Literature 2 utilizes a laminated piezoelectric element coated with a polyolefin-based resin having properties of small Young&#39;s modulus and excellent flexibility and having properties of small moisture permeability and excellent water resistance. This prevents broken pieces of the laminated piezoelectric element from being ejected together with compressed gas when using the piezoelectric valve. Moreover, even in a case of usage in a highly-humid environment, moisture will not enter the laminated piezoelectric element to shorten the life. 
     Ejection of broken pieces of the laminated piezoelectric element is prevented by coating the surface of the laminated piezoelectric element thinly with a polyolefin-based resin. However, in order to prevent reduction in insulation resistance of the laminated piezoelectric element in a high-temperature, highly-humid environment, the surface of the laminated piezoelectric element needs to be coated with a polyolefin-based resin thickly to some extent. In that case, the movement of the laminated piezoelectric element may be interfered with to reduce the stroke or to cause a failure to perform a correct operation. 
     CITATION LIST 
     Patent Literature 
     
         
         [Patent Literature 1] Japanese Patent Laid-Open No. 2013-124695 
         [Patent Literature 2] Japanese Patent Laid-Open No. 2016-61412 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     Thus, the present disclosure has an object to provide a piezoelectric valve that can prevent broken pieces of a laminated piezoelectric element from being ejected together with compressed gas when in use, can prevent moisture from entering the laminated piezoelectric element to shorten the life even in a case of usage in a highly-humid environment, and can prevent the movement of the laminated piezoelectric element from being interfered with to reduce the stroke or to cause a failure to perform a correct operation, and to provide a method of manufacturing the piezoelectric valve. 
     Solution to Problem 
     In order to achieve the above object, the present disclosure is a piezoelectric valve in which the valve is opened/closed utilizing a displacement of a laminated piezoelectric element, including: a valve main body having a gas pressure chamber that receives compressed gas supplied externally; and an actuator having a valving element, the laminated piezoelectric element that generates a driving force required for operating the valving element as the displacement, and a displacement enlarging mechanism that enlarges the displacement of the laminated piezoelectric element to be acted on the valving element, the actuator being disposed in the valve main body, in which a surface of the laminated piezoelectric element is coated with silicone in a state in which the laminated piezoelectric element is integrated into the actuator. 
     In the present disclosure, preferably, the surface of the laminated piezoelectric element is coated with silicone filled between a pair of projecting pieces positioned on both sides of the laminated piezoelectric element along a longitudinal direction of the laminated piezoelectric element with gaps between the pair of projecting pieces. 
     In the present disclosure, preferably, the piezoelectric valve further includes a plate disposed in the valve main body, the actuator being fixed to the plate and disposed in the valve main body together with the plate, in which the pair of projecting pieces are provided on a surface of the plate, the pair of projecting pieces being positioned on both the sides of the laminated piezoelectric element along the longitudinal direction of the laminated piezoelectric element with gaps between the pair of projecting pieces when the actuator is fixed to the plate, and the surface of the laminated piezoelectric element is coated with the silicone filled between the pair of projecting pieces in a state in which the actuator is fixed to the plate. 
     Herein, in the present disclosure, silicone means a low-viscosity silicone rubber, and preferably a silicone rubber having a viscosity of more than or equal to 0.01 Pa·s and less than or equal to 10.0 Pa·s, and more preferably, a silicone rubber having a viscosity of 2.5 Pa·s can be used. 
     Moreover, considering workability, a one-component room temperature curing silicone rubber is preferably used. For example, a low-viscosity silicone rubber “KE-3475 (product name)” manufactured by Shin-Etsu Chemical Co., Ltd. or the like is preferably used. 
     In the present disclosure, preferably, the displacement enlarging mechanism is formed of a metallic material, and an interconnection line for supplying power to the laminated piezoelectric element is molded in a plate formed of a resin material, and an electrode of the interconnection line exposed from the plate is coated with an insulation material in a state in which the electrode is connected to a lead line of the laminated piezoelectric element. 
     In the present disclosure, preferably, the displacement enlarging mechanism is formed of a metallic material, and a lead line of the laminated piezoelectric element is arranged on an insulating film bonded to a surface of the displacement enlarging mechanism. 
     Moreover, in order to achieve the above object, the present disclosure is a method of manufacturing a piezoelectric valve in which the valve is opened/closed utilizing a displacement of a laminated piezoelectric element, the piezoelectric valve including a valve main body having a gas pressure chamber that receives compressed gas supplied externally, and an actuator having a valving element, the laminated piezoelectric element that generates a driving force required for operating the valving element as the displacement, and a displacement enlarging mechanism that enlarges the displacement of the laminated piezoelectric element to be acted on the valving element, the actuator being disposed in the valve main body. The method includes supplying silicone onto a surface of the laminated piezoelectric element integrated into the actuator to coat the surface of the laminated piezoelectric element with the silicone. 
     In the present disclosure, preferably, the silicone is supplied onto the surface of the laminated piezoelectric element integrated into the actuator to coat the surface of the laminated piezoelectric element with the silicone filled between a pair of projecting pieces positioned on both sides of the laminated piezoelectric element along a longitudinal direction of the laminated piezoelectric element with gaps between the pair of projecting pieces. 
     In the present disclosure, preferably, the piezoelectric valve further includes a plate disposed in the valve main body, the actuator being fixed to the plate and disposed in the valve main body together with the plate, the pair of projecting pieces are provided on a surface of the plate, the pair of projecting pieces being positioned on both the sides of the laminated piezoelectric element along the longitudinal direction of the laminated piezoelectric element with gaps between the pair of projecting pieces when the actuator is fixed to the plate, and after the laminated piezoelectric element is integrated into the actuator and the actuator is fixed to the plate, the silicone is supplied onto the surface of the laminated piezoelectric element to coat the surface of the laminated piezoelectric element with the silicone filled between the pair of projecting pieces. 
     Advantageous Effects of Invention 
     In the piezoelectric valve of the present disclosure, the surface of the laminated piezoelectric element is coated with silicone having properties excellent in water resistance and water proofness. This can prevent broken pieces of the laminated piezoelectric element from being ejected together with compressed gas when in use, and can prevent moisture from entering the laminated piezoelectric element to shorten the life even in a case of usage in a highly-humid environment. 
     Moreover, in the piezoelectric valve of the present disclosure, the surface of the laminated piezoelectric element is coated with silicone having properties whose elasticity and compressibility are greater than those of a conventional polyolefin-based resin. This can prevent the movement of the laminated piezoelectric element from being interfered with to reduce the stroke or to cause a failure to perform a correct operation even in a case where the surface of the laminated piezoelectric element is coated with silicone thickly to some extent in order to prevent reduction in insulation resistance of the laminated piezoelectric element in a high-temperature, highly-humid environment. 
     In the piezoelectric valve of the present disclosure, the entire circumferential surface of the laminated piezoelectric element can be easily coated with silicone since the surface of the laminated piezoelectric element is coated with silicone filled between the pair of projecting pieces positioned on both sides of the laminated piezoelectric element along the longitudinal direction of the laminated piezoelectric element with gaps between the pair of projecting pieces. 
     In the piezoelectric valve of the present disclosure, the entire circumferential surface of the laminated piezoelectric element can be easily coated with silicone since the piezoelectric valve further includes a plate disposed in the valve main body, the actuator being fixed to the plate and disposed in the valve main body together with the plate, and the pair of projecting pieces are provided on the surface of the plate, the pair of projecting pieces being positioned on both the sides of the laminated piezoelectric element along the longitudinal direction of the laminated piezoelectric element with gaps between the pair of projecting pieces element when the actuator is fixed to the plate, and the surface of the laminated piezoelectric element is coated with the silicone filled between the pair of projecting pieces in a state in which the actuator is fixed to the plate. 
     In the method of manufacturing a piezoelectric valve of the present disclosure, silicone is supplied onto the surface of the laminated piezoelectric element integrated into the actuator to coat the surface of the laminated piezoelectric element with the silicone. This prevents an assembling failure when integrating the laminated piezoelectric element into the actuator from occurring even in a case where silicone spreads out and adheres to a place other than the surface of the laminated piezoelectric element. 
     In the method of manufacturing a piezoelectric valve of the present disclosure, the entire circumferential surface of the laminated piezoelectric element can be easily coated with silicone since silicone is supplied onto the surface of the laminated piezoelectric element integrated into the actuator to coat the surface of the laminated piezoelectric element with the silicone filled between the pair of projecting pieces positioned on both the sides of the laminated piezoelectric element along the longitudinal direction of the laminated piezoelectric element with gaps between the pair of projecting pieces. 
     In the method of manufacturing a piezoelectric valve of the present disclosure, an assembling failure when fixing the actuator into which the laminated piezoelectric element has been integrated to the plate does not occur even in a case where silicone spreads out and adheres to a place other than the surface of the laminated piezoelectric element since the piezoelectric valve further includes a plate disposed in the valve main body, the actuator being fixed to the plate and disposed in the valve main body together with the plate, the pair of projecting pieces are provided on the surface of the plate, the pair of projecting pieces being positioned on both the sides of the laminated piezoelectric element along the longitudinal direction of the laminated piezoelectric element with gaps between the pair of projecting pieces when the actuator is fixed to the plate, and after the laminated piezoelectric element is integrated into the actuator and the actuator is fixed to the plate, the silicone is supplied onto the surface of the laminated piezoelectric element to coat the surface of the laminated piezoelectric element with the silicone filled between the pair of projecting pieces. 
     Moreover, in the method of manufacturing a piezoelectric valve of the present disclosure, the pair of projecting pieces positioned on both the sides of the laminated piezoelectric element along the longitudinal direction of the laminated piezoelectric element with gaps between the pair of projecting pieces when the actuator is fixed to the plate are provided on the surface of the plate. This enables the entire circumferential surface of the laminated piezoelectric element to be easily coated with silicone filled between the pair of projecting pieces. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a sectional view of a laminated piezoelectric element. 
         FIG. 2  is a perspective view of a piezoelectric valve. 
         FIG. 3  is an assembly exploded view of the piezoelectric valve. 
         FIG. 4  is an explanatory view of an actuator. 
         FIG. 5  is an explanatory view in a state in which the actuator is fixed to a valve seat plate. 
         FIG. 6  is a sectional view of the piezoelectric valve, which is an explanatory view in a state in which the valve seat plate is disposed in a valve main body. 
         FIG. 7  is a plan view of an actuator included in a piezoelectric valve according to an embodiment of the present disclosure. 
         FIG. 8  is a plan view in a state in which the actuator is fixed to a valve seat plate included in the piezoelectric valve according to an embodiment of the present disclosure. 
         FIG. 9  is a cross-sectional view taken along A-A in  FIG. 8 . 
         FIG. 10  is a graph showing an ejection pressure property of air ejected from the piezoelectric valve according to an embodiment of the present disclosure. 
     
    
    
     DESCRIPTION OF EMBODIMENT 
     An embodiment of the present disclosure will be described with reference to the drawings. 
       FIG. 1  shows a cross-sectional view of a representative example of a laminated piezoelectric element (hereinafter referred to as a “piezoelectric element”). 
     A piezoelectric element  1  shown in  FIG. 1  has a laminate  4  obtained by alternately laminating piezoelectric ceramic layers  2  and inner electrode layers  3 . The inner electrode layers  3  are exposed at side surfaces of the laminate  4 . The exploded side surfaces of the respective inner electrode layers  3  are coated with an insulation layer  5  in every other layer. The laminate  4  further has an external electrode  6  that covers the insulation layer  5  and conducts with the inner electrode layers  3  that are not coated with the insulation layer  5 . 
       FIG. 2  shows a perspective view of an example of a piezoelectric valve.  FIG. 3  shows an assembly exploded view of the piezoelectric valve in  FIG. 2 .  FIG. 4  shows an explanatory view of an actuator.  FIG. 5  shows an explanatory view in a state in which the actuator is fixed to a valve seat plate.  FIG. 6  shows a sectional view of the piezoelectric valve, which is an explanatory view in a state in which the valve seat plate is disposed in a valve main body. 
     A piezoelectric valve  10  shown in  FIG. 2  to  FIG. 6  includes a valve main body  20 , a valve seat plate  25  disposed in the valve main body  20  and fixed to the valve main body  20 , and actuators  30  fixed to both surfaces of the valve seat plate  25  with screws. 
     The valve main body  20  is a case whose front surface is openable, and includes therein a gas pressure chamber to be supplied with compressed gas from an external compressed gas supply source (not shown). 
     Moreover, a connector part  50  is provided on the front surface of the valve main body  20 . A gas inlet  51  for taking in compressed gas into the valve main body  20  and a gas outlet  52  for discharging compressed gas are open in the front surface of the connector part  50 . 
     An interconnection line substrate  55  for supplying power to the piezoelectric element  32  is disposed between the valve main body  20  and the connector part  50 . An interconnection line connector  29  for supplying power to the piezoelectric element  32  via the interconnection line substrate  55  is disposed on one side end of the connector part  50  and at a lateral position of the valve main body  20 . 
     The valve seat plate  25  includes attachment portions for the actuators  30  on both of the surfaces, and has a valve seat  26  with which a valving element  31  which will be described later of the actuator  30  is to be brought into contact. Moreover, a lid member  28  for closing the opening of the case is attached to the front surface of the valve seat plate  25 . A gas discharge path that communicates from a valve seat plane of the valve seat  26  to the outlet  52  that is open in the front surface of the connector part  50  is formed in the lid member  28 . Furthermore, a gas inlet path that communicates from the inlet  51  that is open in the front surface of the connector part  50  into the valve main body  20  is formed in the lid member  28 . 
     The valve seat plate  25  is molded with a synthetic resin material, for example, and interconnection lines from the interconnection line substrate  55  to the piezoelectric element  32  are molded. 
     Moreover, electrodes  58  of interconnection lines to be connected to the lead lines  57  of the piezoelectric element  32  as will be described later using  FIG. 8  are exposed at a rear position of the valve seat plate  25 . 
     The actuator  30  includes the valving element  31  made of rubber, preferably smooth rubber, a piezoelectric element  32  that generates a driving force required for operating the valving element  31  as a displacement, and a displacement enlarging mechanism  33  that enlarges the displacement of the piezoelectric element  32  to be acted on the valving element  31 , as shown in  FIG. 4 . 
     The piezoelectric element shown in  FIG. 1  can be used for the piezoelectric element  32 . Alternatively, a resin-coated piezoelectric element whose entire circumferential surface including the side surfaces at which the inner electrode layers  3  are exposed is coated thinly with epoxy resin can also be used for the piezoelectric element  32 . 
     The displacement enlarging mechanism  33  has a displacement enlarging section  34  that enlarges a displacement of the piezoelectric element  32 , and a displacement transmitting section  35  that transmits the displacement of the piezoelectric element  32  to the displacement enlarging section  34 . The displacement enlarging mechanism  33  is arranged symmetrically with respect to an axial line in an operating direction of the valving element  31 , herein, a straight line (hereinafter referred to as a “center line”) connecting the valving element  31  and a longitudinal axial line of the piezoelectric element  32 . 
     The displacement transmitting section  35  has a U-shaped base substrate  36  to which one end of the piezoelectric element  32  is connected, and a cap member  37  to which the other end of the piezoelectric element  32  is connected. Since the piezoelectric element  32  is disposed in a space of the U-shaped base substrate  36 , the displacement enlarging mechanism  33  has an arrangement symmetric about the longitudinal axial line of the piezoelectric element  32 . 
     Herein, the piezoelectric element  32  is incorporated into the space of the U-shaped base substrate  36  and between the bottom of the U-shaped base substrate  36  and the cap member  37 . By plastically deforming the bottom of the U-shape base substrate  36 , the piezoelectric element  32  has one end joined to the bottom of the U-shape base substrate  36  and the other end joined to the cap member  37 . 
     The displacement enlarging section  34  is composed of first and second displacement enlarging sections  34   a ,  34   b  arranged symmetrically with respect to the center line. 
     The first displacement enlarging section  34   a  has first and second hinges  39 ,  40 , a first arm  41 , and a first plate spring  42 . One end of the first hinge  39  is integrated with one side leading end of the U-shaped base substrate  36 , and one end of the second hinge  40  is integrated with the cap member  37 . One end of the first plate spring  42  is joined to an outer leading end portion of the first arm  41 , and one side end portion of the valving element  31  is joined to the other end of the first plate spring  42 . 
     On the other hand, the second displacement enlarging section  34   b  has third and fourth hinges  43 ,  44 , a second arm  45 , and a second plate spring  46 . One end of the third hinge  43  is integrated with the other-side leading end of the U-shaped base substrate  36 , and one end of the fourth hinge  44  is integrated with the cap member  37 . One end of the second plate spring  46  is joined to an outer leading end portion of the second arm  45 , and the other side end portion of the valving element  31  is joined to the other end of the second plate spring  46 . 
     Herein, the displacement enlarging mechanism  33  can be formed integrally by punching a metallic material such as a stainless material including an invar material, for example. 
     In the above-described actuator  30 , the piezoelectric element  32  is elongated when applying a current to the piezoelectric element  32  in a valve-closed state. A displacement associated with the elongation of the piezoelectric element  32  is enlarged in accordance with the principle of leverage in the displacement enlarging mechanism  33  using the first and third hinges  39 ,  43  as a fulcrum, the second and fourth hinges  40 ,  44  as a point of effort, and the outer leading end portions of the first and second arms  41 ,  45  as a point of load to greatly displace the outer leading end portions of the first and second arms  41 ,  45 . 
     Then, the displacement of the outer leading end portions of the first and second arms  41 ,  45  moves the valving element  31  away from the valve seat  26  via the first and second plate springs  42 ,  46  to open the gas discharge path. 
     On the other hand, when current application to the piezoelectric element  32  is stopped in the above-described actuator  30 , the piezoelectric element  32  contracts, and the contraction causes the valving element  31  to be seated on the valve seat  26  via the displacement enlarging mechanism  33  to close the gas discharge path. 
       FIG. 7  shows a plan view of the actuator included in the piezoelectric valve according to an embodiment of the present disclosure. 
     In the actuator shown in  FIG. 7 , the surface of the piezoelectric element  32 , that is, at least the side surfaces of the piezoelectric element  32  at which the inner electrode layers are exposed are coated with a silicone  8  in a state in which the piezoelectric element  32  is integrated. 
     In the piezoelectric valve according to an embodiment of the present disclosure, for example, a piezoelectric element  32  of the type shown in  FIG. 1  whose surface is coated with the silicone  8  can be integrally incorporated into the actuator  30 . 
     Moreover, in the piezoelectric valve according to an embodiment of the present disclosure, the silicone  8  can also be supplied onto the surface of the piezoelectric element  32  in the state in which the piezoelectric element  32  is integrated into the actuator  30  with a dispenser, brush, or the like to coat the surface of the piezoelectric element  32  with the silicone  8 . 
     The piezoelectric valve according to an embodiment of the present disclosure eliminates the concern of an occurrence of assembling failure when integrating the piezoelectric element  32  into the actuator  30  even in a case where the silicone  8  spreads out and adheres to a place other than the surface of the piezoelectric element  32  since the silicone  8  is supplied onto the surface of the piezoelectric element  32  in the state in which the piezoelectric element  32  is integrated into the actuator  30  to coat the surface of the piezoelectric element  32  with the silicone  8 . 
     The surface of the piezoelectric element  32  is coated with the silicone  8  in the state in which the piezoelectric element  32  is integrated into the actuator  30 , and the piezoelectric valve according to an embodiment of the present disclosure can be assembled by fixing the actuator  30  to the valve seat plate. 
     Herein, it is sufficient that at least the side surfaces of the piezoelectric element  32  at which the inner electrode layers are exposed be coated with the silicone  8 , and preferably, it is sufficient that all the side surfaces (the entire circumferential surface) including the side surfaces at which the inner electrode layers are exposed be coated with the silicone  8 . 
     Moreover, in a case of using a resin-coated piezoelectric element whose entire circumferential surface is coated thinly with epoxy resin for the piezoelectric element  32 , it is preferable to coat the entire circumferential surface with the silicone  8 . 
       FIG. 8  shows a plan view in a state in which the actuator is fixed to the valve seat plate included in the piezoelectric valve according to an embodiment of the present disclosure.  FIG. 9  shows a cross-sectional view taken along A-A in  FIG. 8 . 
     In the piezoelectric valve according to an embodiment of the present disclosure, a pair of projecting pieces  27  are provided at attachment portions of the actuator  30  on the surface of the valve seat plate  25 . The pair of projecting pieces  27  are positioned between the piezoelectric element  32  and the displacement transmitting section  35  and on both sides along the longitudinal direction (elongating/contracting direction) of the piezoelectric element  32  with gaps between the pair of projecting pieces  27  when the actuator  30  is fixed with screws. 
     Moreover, as shown in  FIG. 9 , the pair of projecting pieces  27  are formed to be higher than the height of the surface of the piezoelectric element  32  of the actuator  30  fixed to the valve seat plate  25 . 
     The piezoelectric valve according to an embodiment of the present disclosure is the actuator  30  shown in  FIG. 7 , and the entire circumferential surface of the piezoelectric element  32  can be coated with the silicone  8  filled between the pair of projecting pieces  27  by supplying the silicone  8  onto the surface of the piezoelectric element  32  after fixing the piezoelectric element  32  whose side surfaces at which the inner electrode layers are exposed have been coated with the silicone  8  to the valve seat plate  25 . 
     Moreover, in the piezoelectric valve according to an embodiment of the present disclosure, the entire circumferential surface of the piezoelectric element  32  can also be coated with the silicone  8  filled between the pair of projecting pieces  27  by integrating the piezoelectric element  32  whose surface has not been coated with the silicone  8  into the actuator  30 , fixing the actuator  30  to the valve seat plate  25 , and then supplying the silicone  8  onto the surface of the piezoelectric element  32 . 
     In the piezoelectric valve according to an embodiment of the present disclosure, the pair of projecting pieces  27  positioned on both the sides of the piezoelectric element  32  along the longitudinal direction of the piezoelectric element  32  with gaps between the pair of projecting pieces  27  when the actuator  30  is fixed to the valve seat plate  25  are provided on the surface of the valve seat plate  25 . This enables the entire circumferential surface to be easily coated with the silicone  8  filled between the pair of projecting pieces  27 . 
     Note that the piezoelectric valve according to an embodiment of the present disclosure eliminates the concern of an occurrence of an assembling failure when fixing the actuator  32  to the valve seat plate  25  even in a case where the silicone  8  spreads out and adheres to a place other than the surface of the piezoelectric element  32  by integrating the piezoelectric element  32  whose surface has not been coated with the silicone  8  into the actuator  30 , fixing the actuator  30  to the valve seat plate  25 , and then supplying the silicone  8  onto the surface of the piezoelectric element  32  to coat the entire circumferential surface of the piezoelectric element  32  with the silicone  8  filled between the pair of projecting pieces  27 . 
     Herein, in the present disclosure, the silicone  8  indicates a low-viscosity silicone rubber, and preferably a silicone rubber having a viscosity of more than or equal to 0.01 Pa·s and less than or equal to 10.0 Pa·s, and more preferably, a silicone rubber having a viscosity of 2.5 Pa·s can be used. 
     Moreover, considering workability, a one-component room temperature curing silicone rubber is preferably used, and for example, a low-viscosity silicone rubber “KE-3475 (product name)” manufactured by Shin-Etsu Chemical Co., Ltd. or the like is preferably used. 
     In  FIG. 8 , the electrodes  58  of interconnection lines molded for supplying power to the piezoelectric element  32  are exposed at a rear position of the valve seat plate  25 , and are connected to the lead lines  57  of the piezoelectric element  32  by soldering. The electrodes  58  of the interconnection lines are coated with an insulation material not shown in a state in which the electrodes  58  is connected to the lead lines  57 . An insulation resin material such as silicone, for example, can be used as the insulation material. 
     Moreover, as shown in  FIG. 8 , the actuator  30  has an insulating film  62  bonded at a rear position on the surface of the displacement transmitting section  35  in the displacement enlarging mechanism  33 . 
     In  FIG. 8 , the interconnection lines from the interconnection line substrate  55  to the piezoelectric element  32  are molded in the valve seat plate  25  to which the actuator  30  is attached. The lead lines  57  of the piezoelectric element  32  are arranged on the insulating film  62  so as to be prevented from being in contact with the metallic material constituting the displacement enlarging mechanism  33  of the actuator  30 . The lead lines  57  of the piezoelectric element  32  are connected, by soldering, to the electrodes  58  of the interconnection lines exposed at the rear position of the valve seat plate  25 . 
     Herein, a low moisture-permeable film, for example, can be used as the insulating film  62 . 
     In the present disclosure, the low moisture-permeable film refers to a resin film made of a material having a moisture permeability of less than or equal to 0.5 g/m 2 ·24 hr in 1-mm thickness in an environment at a temperature of 40° C. and a relative humidity of 95%. 
     A resin film made of a low moisture-permeable material such as, for example, a polyolefin-based resin film of polyethylene, polypropylene, polyethylene terephthalate, or the like can be used as the low moisture-permeable film. Alternatively, a resin film subjected to moisture permeability reducing treatment such as being coated with a moisture permeability reducing agent such as fluorine can also be used as the low moisture-permeable film. 
     The piezoelectric valve according to an embodiment of the present disclosure described above is provided with the pair of projecting pieces  27  on the surface of the valve seat plate  25 . In a case of directly attaching the actuator  20  to the valve main body  20 , a pair of projecting pieces can also be provided on an inner wall surface of the valve main body. In that case, by fixing the actuator to the valve main body, and then supplying the silicone  8  onto the surface of the piezoelectric element, the entire circumferential surface of the piezoelectric element  32  can be coated with the silicone  8  filled between the pair of projecting pieces  27 . 
     In the piezoelectric valve of the present disclosure, the surface of the piezoelectric element is coated with silicone having properties excellent in water resistance and water proofness. This can prevent broken pieces of the piezoelectric element from being ejected together with compressed gas when in use, and can prevent moisture from entering the piezoelectric element to shorten the life even in a case of usage in a highly-humid environment. 
     Moreover, in the piezoelectric valve of the present disclosure, the surface of the piezoelectric element is coated with silicone having properties whose elasticity and compressibility are greater than those of a conventional polyolefin-based resin. This can prevent the movement of the piezoelectric element from being interfered with to reduce the stroke or to cause a failure to perform a correct operation even in a case of coating the surface of the piezoelectric element with silicone thickly to some extent in order to prevent reduction in insulation resistance of the piezoelectric element in a high-temperature, highly-humid environment. 
       FIG. 10  shows a graph indicating an ejection pressure property of air ejected from the piezoelectric valve, which is a graph in which a case where the surface of the piezoelectric element is coated with silicone and a case where the surface of the piezoelectric element is not coated with silicone are compared. Note that a coating thickness in the case where the surface of the piezoelectric element is coated with silicone is about 150 μm, and reduction in insulation resistance in a high-temperature, highly-humid environment can be prevented. 
     Experiments were conducted based on the method described in [Example] in Japanese Patent Laid-Open No. 2017-160973. Experimental conditions were as follows: 
     (1) Supply pressure of compressed air: 0.15 MPa (a gauge pressure value at an atmospheric pressure) 
     (2) Driving voltage: 72V 
     (3) Set flow rate of compressed air: 39 L/min 
     (4) Input signal: first pre-pulse time t 1 =0.098 ms
         First down-time t 2 =0.08 ms   Second pre-pulse time t 3 =0.6 ms   Second down-time t 4 =0.03 ms   Main pulse time t 5 =0.192 ms       

     (Energizing time of piezoelectric element: 1 ms) 
     (5) Detection position of air ejection pressure: 2 mm from leading end of gas discharge path 
     In  FIG. 10 , the broken line indicates a result of a piezoelectric valve in which the surface of the piezoelectric element is coated with silicone. Moreover, the solid line indicates a result of a piezoelectric valve in which the surface of the piezoelectric element is not coated with silicone. 
     Comparing them, they substantially agree in air ejection pressure property, and in the piezoelectric valve according to an embodiment of the present disclosure, it was confirmed that the movement of the piezoelectric element was not interfered with even in a case of coating the surface of the piezoelectric element with silicone thickly to some extent in order to prevent reduction in insulation resistance of the piezoelectric element in a high-temperature, highly-humid environment. 
     The present disclosure is not limited to the above-described embodiment, and can obviously be modified as appropriate in configuration within the range of the disclosure. 
     INDUSTRIAL APPLICABILITY 
     The piezoelectric valve of the present disclosure is extremely useful since it is possible to prevent broken pieces of the laminated piezoelectric element from being ejected together with compressed gas when in use, prevent moisture from entering the laminated piezoelectric element to shorten the life even in a case of usage in a highly-humid environment, and prevent the movement of the laminated piezoelectric element from being interfered with to reduce the stroke or to cause a failure to perform a correct operation. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1  laminated piezoelectric element 
               2  ceramic layer 
               3  inner electrode layer 
               4  laminate 
               5  insulation layer 
               6  external electrode 
               7  lead line 
               8  silicone 
               10  piezoelectric valve 
               20  valve main body 
               25  valve seat plate 
               26  valve seat 
               27  projecting piece 
               28  lid member 
               29  interconnection line connector 
               30  actuator 
               31  valving element 
               32  laminated piezoelectric element 
               33  displacement enlarging mechanism 
               34  displacement enlarging section 
               35  displacement transmitting section 
               36  base substrate 
               37  cap member 
               39  first hinge 
               40  second hinge 
               41  first arm 
               42  first plate spring 
               43  third hinge 
               44  fourth hinge 
               45  second arm 
               46  second plate spring 
               50  connector part 
               51  gas inlet 
               52  gas outlet 
               55  interconnection line substrate 
               57  lead line 
               58  electrode 
               62  insulating film