JP2018206801A - Laminated piezoelectric element and injector including the same, and fuel injection system - Google Patents

Abstract

To provide a laminated piezoelectric element that can reduce the generation of cracks in portions other than scheduled breaking layers and an injector including the same, and a fuel injection system.SOLUTION: A laminated piezoelectric element of the present disclosure comprises: a plurality of lamination units 3 that each have piezoelectric layers 1 and internal electrode layers 2 laminated alternately; and scheduled breaking layers 4 that are each arranged between the lamination unit 3 and lamination unit 3 adjacent to each other. In each of the lamination units 3, a first piezoelectric layer 11 that is the first piezoelectric layer 1 counted from the scheduled breaking layer 4 is thinner than a second piezoelectric layer 12 that is the second piezoelectric layer 1 counted from the scheduled breaking layer 4.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to a laminated piezoelectric element used as a piezoelectric driving element (piezoelectric actuator), a pressure sensor element, a piezoelectric circuit element, and the like, an injection apparatus including the same, and a fuel injection system.

  A multilayer piezoelectric element having a plurality of laminated units in which a plurality of piezoelectric layers and internal electrode layers are alternately laminated, and having a predetermined rupture layer disposed between adjacent laminated units Is known (see Patent Document 1). Here, the planned fracture layer is a layer that is easier to break than the surrounding layers. Such a multilayer piezoelectric element is intended to reduce the stress and cracks applied to other parts by generating cracks in the planned fracture layer, and to maintain the performance over a long period of time.

JP 2006-518934 Gazette

  In recent years, there is a demand for driving at higher displacement and higher frequency, and there is a demand for a multilayer piezoelectric element that can be used stably for a long time even in such driving.

  However, in the drive as described above, when all the piezoelectric layers in the active region are formed with the same thickness, for example, the stress applied to the end portion of the internal electrode layer in the vicinity of the planned fracture layer increases, There was a risk that cracks would occur at sites other than the fractured layer.

  The present disclosure has been made in view of the above circumstances, and an object thereof is to provide a multilayer piezoelectric element capable of suppressing the occurrence of cracks in a portion other than a planned fracture layer, an injection device including the same, and a fuel injection system. To do.

  The multilayer piezoelectric element of the present disclosure includes a plurality of multilayer units in which piezoelectric layers and internal electrode layers are alternately stacked, and includes a predetermined fracture layer disposed between adjacent multilayer units. In each of the stacked units, the first piezoelectric layer that is the first piezoelectric layer counted from the planned fracture layer is the second piezoelectric layer that is the second piezoelectric layer counted from the planned fracture layer. It is characterized by being thinner than the body layer.

  An injection device of the present disclosure includes a container having an injection hole and the multilayer piezoelectric element having the above-described configuration, and the injection hole is opened and closed by driving the multilayer piezoelectric element.

  A fuel injection system according to the present disclosure includes a common rail that stores high-pressure fuel, an injection device configured as described above that injects the high-pressure fuel stored in the common rail, a pressure pump that supplies the high-pressure fuel to the common rail, and the injection And an injection control unit for supplying a drive signal to the apparatus.

According to the multilayer piezoelectric element of the present disclosure, it is possible to suppress the occurrence of cracks in portions other than the planned fracture layer and to have excellent long-term reliability.

  Further, according to the injection device and the fuel injection system of the present disclosure, since the multilayer piezoelectric element having excellent long-term reliability is provided, it is possible to realize accurate and stable driving over a long period of time.

It is a schematic perspective view which shows an example of embodiment of a lamination type piezoelectric element. It is a schematic sectional drawing of the laminated body shown in FIG. It is a schematic perspective view which shows the other example of embodiment of a lamination type piezoelectric element. It is a schematic sectional drawing of the laminated body shown in FIG. It is a schematic sectional drawing of the other example of the laminated body shown in FIG. It is a schematic sectional drawing which shows an example of an injection apparatus. It is the schematic which shows an example of a fuel-injection system.

  Hereinafter, an example of an embodiment of a multilayer piezoelectric element will be described with reference to the drawings.

  FIG. 1 is a schematic perspective view showing an example of an embodiment of a multilayer piezoelectric element, and FIG. 2 is a schematic cross-sectional view of the multilayer body shown in FIG.

  A laminated piezoelectric element 10 shown in FIGS. 1 and 2 has a laminated body 30 including a plurality of laminated units 3 in which piezoelectric layers 1 and internal electrode layers 2 are alternately laminated.

  In the multilayer unit 3, internal electrode layers 2 (first internal electrode layers 21 and second internal electrode layers 22) are alternately stacked via piezoelectric layers 1. The stacked unit 3 includes an active region where the first internal electrode layer 21 and the second internal electrode layer 22 overlap each other when viewed from the stacking direction, and the first internal electrode layer 21 and the second internal electrode viewed from the stacking direction. An inactive region that does not overlap with the electrode layer 22 is provided. Here, the active region is a portion that expands or contracts in the stacking direction during driving. The inactive region is a portion that does not stretch or shrink in the stacking direction during driving or is difficult to drive.

  The laminated body 30 has a portion in which a plurality of laminated units 3 are laminated, and has a portion in which only the piezoelectric layer 1 is laminated at both ends in the lamination direction of the portion in which the plurality of laminated units 3 are laminated. doing. The portions where only the piezoelectric layers 1 positioned at both ends in the stacking direction are stacked are also inactive regions that do not stretch or contract in the stacking direction during driving.

  The laminated body 30 is formed in, for example, a rectangular column shape (a rectangular parallelepiped shape) having a length of 0.5 to 10 mm, a width of 0.5 to 10 mm, and a height of 1 to 100 mm. The shape of the laminated body 30 may be a hexagonal column shape, an octagonal column shape, a cylindrical shape, or the like.

The piezoelectric layer 1 is made of a ceramic having piezoelectric characteristics. As such a ceramic, for example, a perovskite oxide made of lead zirconate titanate (PbZrO ₃ —PbTiO ₃ ), lithium niobate (LiNbO ₃ ), lithium tantalate (LiTaO ₃ ), or the like can be used. The thickness of the piezoelectric layer 1 is, for example, 3 to 250 μm.

The internal electrode layer 2 is formed by simultaneous firing with the ceramic forming the piezoelectric layer 1. The internal electrode layer 2 includes a first internal electrode layer 21 and a second internal electrode layer 22, and is alternately stacked with the piezoelectric layer 1 to sandwich the piezoelectric layer 1 from above and below. For example, by alternately arranging the first internal electrode layer 21 as a positive electrode and the second internal electrode layer 22 as a negative electrode or a ground electrode, a driving voltage is applied to the piezoelectric layer 1 sandwiched therebetween. . As such a material, for example, a conductor mainly composed of a silver-palladium alloy that can be fired at a low temperature, or a conductor containing copper, platinum, or the like can be used. The thickness of the 1st internal electrode layer 21 and the 2nd internal electrode layer 22 shall be 0.1-5 micrometers, for example.

  In the example shown in the figure, the first internal electrode layer 21 and the second internal electrode layer 22 are alternately drawn out to a pair of opposing side surfaces of the multilayer unit 3 (laminate 30), and the multilayer unit 3 (laminate) 30) and electrically connected to a pair of external electrodes 5 to be described later. Note that the end surfaces of both the first internal electrode layer 21 and the second internal electrode layer 22 may be exposed at the other pair of side surfaces facing each other of the multilayer unit 3 (laminated body 30). Both end surfaces of the electrode layer 21 and the second internal electrode layer 22 may be located on the inner side away from the side surface without being exposed.

  In addition, the multilayer piezoelectric element 10 includes a predetermined fracture layer 4 disposed between the adjacent multilayer units 3. Here, the planned fracture layer 4 is a layer for relieving the stress generated in each multilayer unit 3 by driving the multilayer piezoelectric element 10. Examples of the planned fracture layer 4 include a porous metal layer that does not function as an internal electrode layer, and a metal layer that is cracked in advance.

  Further, as described above, the external electrode 5 is provided on each of the pair of side surfaces to which one of the end surfaces of the first internal electrode layer 21 and the second internal electrode layer 22 reaches, and the extracted first electrode The internal electrode layer 21 or the second internal electrode layer 22 is electrically connected. The external electrode 5 can be produced by baking a conductive paste containing a metal such as Ag or Cu. Here, when the external electrode 5 is viewed in a cross section perpendicular to the side surface of the multilayer body 30, the thickness of the external electrode 5 is set to, for example, 5 to 70 μm. Although not shown, a lead member is joined to the end of the external electrode 5, and an electrical connection with an external circuit is made through the lead member.

  Note that a covering material may be provided on the side surfaces where both end surfaces of the first internal electrode layer 21 and the second internal electrode layer 22 are exposed or both end surfaces are not exposed, if necessary. The covering material is made of, for example, a silicone resin, an epoxy resin, a nylon resin, or the like, and may be composed of not only a single layer but also a plurality of layers. This covering material has an effect of suppressing migration and discharge.

  As shown in FIG. 2, in each laminated unit 3, the first piezoelectric layer 11 that is the first piezoelectric layer counted from the planned fracture layer 4 is the second piezoelectric layer counted from the planned fracture layer 4. It is thinner than the second piezoelectric layer 12 which is a piezoelectric layer.

  As the piezoelectric layer 1 becomes thicker, the stress generated in the piezoelectric layer 1 becomes weaker. Here, if the stress for breaking the planned fracture layer 4 is the sum of the stresses generated in each piezoelectric layer 1 in the multilayer unit 3, the second piezoelectric layer 12 (2 counted from the planned fracture layer) is assumed. The stress generated in the first piezoelectric layer 1 (the first piezoelectric layer 1 counted from the planned fracture layer) adjacent to the planned fracture layer 4 due to the weakening of the stress generated in the first piezoelectric layer 1) The ratio of becomes stronger and becomes dominant. As a result, the stress generated in the vicinity of the planned fracture layer 4 is likely to concentrate on the planned fracture layer 4, and the planned fracture layer 4 is more reliably fractured, such as the internal electrode layer 2 in the vicinity of the planned fracture layer 4. It can suppress that a crack generate | occur | produces in parts other than the scheduled fracture | rupture layer 4. FIG. Therefore, the long-term reliability of the multilayer piezoelectric element 10 is improved.

  The thickness of the first piezoelectric layer 11 is set to, for example, 40 to 95% of the thickness of the second piezoelectric layer 12.

  Here, in each laminated unit 3, as shown in FIGS. 1 and 2, the third piezoelectric layer 13, which is the third piezoelectric layer 1 counted from the planned fracture layer 4, is the second piezoelectric layer 12. 3 and 4, the third piezoelectric layer 13, which is the third piezoelectric layer 1 counted from the planned fracture layer 4, is formed as the first piezoelectric layer. The body layer 11 may be the same as or thicker than the body layer 11 and thinner than the second piezoelectric layer 12.

  According to this configuration, the stress generated in the third piezoelectric layer 13 is weaker than the stress generated in the first piezoelectric layer 11 in the multilayer unit 3. The ratio of the stress generated in the layer 11 becomes stronger and dominant. As a result, the stress generated in the vicinity of the planned fracture layer 4 is more likely to be concentrated in the planned fracture layer 4, and the planned fracture layer 4 is more reliably broken and cracked in the internal electrode layer 2 in the vicinity of the planned fracture layer 4. Can be prevented from occurring. Therefore, the long-term reliability of the multilayer piezoelectric element 10 is improved. From the viewpoint of maintaining the basic performance (desired amount of displacement) of the multilayer piezoelectric element 10, as shown in FIGS. 3 and 4, it is the third piezoelectric layer 1 counted from the planned fracture layer 4. The third piezoelectric layer 13 may be configured to be the same as or thicker than the first piezoelectric layer 11 and thinner than the second piezoelectric layer 12.

  In this case, the thickness of the third piezoelectric layer 13 is set to, for example, 100 to 250% of the thickness of the first piezoelectric layer 11, and is 40 to 98% of the thickness of the second piezoelectric layer 12, for example. The thickness is set.

  As shown in FIG. 5, in each stacked unit 3, all the piezoelectric layers 1 except for the first piezoelectric layer 11 and the second piezoelectric layer 12 have the thickness of the first piezoelectric layer 11. All the piezoelectric layers 1 except for the first piezoelectric layer 11 and the second piezoelectric layer 12 are the same or thicker, and the thickness decreases as the distance from the first piezoelectric layer 11 increases. Also good.

  According to this configuration, the stress applied to each piezoelectric layer 1 in the multilayer unit 3 can be moderately sloped, so that the stress applied to the first piezoelectric layer 11 is suppressed and more than necessary. It can suppress that the fracture | rupture layer 4 fractures | ruptures and a crack progresses in an inactive area | region.

  Further, as shown in FIGS. 2, 4 and 5, when the thickness of all the piezoelectric layers 1 is seen in the laminated unit 3 arranged between the planned fracture layer 4 and the planned fracture layer 4, It may be vertically symmetrical.

  According to this configuration, since the same stress is applied to the upper and lower first piezoelectric layers 11 in the multilayer unit 3, the degree of fracture for each planned fracture layer 4 is made uniform, and the long-term reliability of the multilayer piezoelectric element 10 is confirmed. More improved.

  Next, a method for manufacturing the multilayer piezoelectric element of this embodiment will be described.

First, a ceramic green sheet to be the piezoelectric layer 1 is produced. Specifically, a ceramic slurry is prepared by mixing a calcined powder of piezoelectric ceramic, a binder made of an organic polymer such as acrylic or butyral, and a plasticizer. And a ceramic green sheet is produced using this ceramic slurry by using tape molding methods, such as a doctor blade method and a calender roll method. As the piezoelectric ceramic, any material having piezoelectric characteristics may be used. For example, a perovskite oxide made of lead zirconate titanate (PbZrO ₃ —PbTiO ₃ ) can be used. As the plasticizer, dibutyl phthalate (DBP), dioctyl phthalate (DOP), or the like can be used.

  Next, a conductive paste to be the internal electrode layer 2 is produced. Specifically, for example, a conductive paste is prepared by adding and mixing a binder and a plasticizer to a metal powder of a silver-palladium alloy. This conductive paste is applied on the ceramic green sheet in the pattern of the internal electrode layer 2 using a screen printing method. Furthermore, after laminating a plurality of ceramic green sheets printed with this conductive paste and performing a binder removal treatment at a predetermined temperature, firing at a temperature of 900 to 1200 ° C., using a surface grinder or the like It is produced by grinding so as to obtain a shape.

  Here, in order to set the thickness of the fired piezoelectric layer 1 to the configuration of the above-described embodiment, the laminated body 30 may be created by preparing and laminating ceramic green sheets having different thicknesses.

  In addition, the laminated body 30 is not limited to what is produced by said manufacturing method, What kind of thing will be sufficient if the laminated body 30 formed by laminating | stacking the piezoelectric material layer 1 and the internal electrode layer 2 in multiple numbers is producible? It may be produced by a manufacturing method.

  Next, the external electrode 5 is formed. Specifically, a conductive paste containing a metal such as Ag or Cu is used. This is baked on a region where one end face of the first internal electrode layer 21 and the second internal electrode layer 22 on the side surface of the multilayer body 30 is drawn, and the external electrode 5 having a thickness of, for example, 5 to 70 μm is formed. Form. It can be formed by controlling to a predetermined thickness or width by screen printing or dispensing. For example, a silver glass-containing conductive paste prepared by adding a binder, a plasticizer, and a solvent to a mixture of conductive particles mainly containing silver and glass is used. And after printing with the pattern of the external electrode 5 on the side surface of the laminated body 30 by a screen printing method and making it dry, a baking process is performed at the temperature of 650-750 degreeC.

  Next, a coating material is formed if necessary. Specifically, for example, a resin such as epoxy, silicone, or nylon is used, and the thickness is controlled to a predetermined thickness by printing or dispensing.

  Thereafter, a DC electric field of 0.1 to 3 kV / mm is applied to the external electrode 5 to polarize the piezoelectric layer 1 constituting the multilayer body 30, thereby completing the multilayer piezoelectric element 10.

  Next, an example of the injection device of the present embodiment will be described.

  FIG. 6 is a schematic cross-sectional view showing an example of the injection device of the present embodiment. As shown in FIG. 6, in the injection device 19 of this example, the multilayer piezoelectric element 10 of the above example is accommodated in a storage container 23 as a container having an injection hole 21 at one end.

  A needle valve 25 that can open and close the injection hole 21 is provided in the storage container 23. A fluid passage 27 is disposed in the injection hole 21 so as to be able to communicate with the movement of the needle valve 25. The fluid passage 27 is connected to an external fluid supply source, and fluid is constantly supplied to the fluid passage 27 at a high pressure. Therefore, when the needle valve 25 opens the injection hole 21, the fluid supplied to the fluid passage 27 is discharged from the injection hole 21 to the outside or an adjacent container, for example, a fuel chamber (not shown) of the internal combustion engine. It is configured.

  The upper end of the needle valve 25 has a large inner diameter, and is a piston 31 that can slide with a cylinder 29 formed in the storage container 23. In the storage container 23, the multilayer piezoelectric element 10 of the above-described example is stored in contact with the piston 31.

In such an injection device 19, the injection hole 21 is opened and closed by driving the multilayer piezoelectric element 10. Specifically, when the laminated piezoelectric element 10 is extended by applying a voltage, the piston 31 is pressed, the needle valve 25 closes the fluid passage 27 leading to the injection hole 21, and the supply of fluid is stopped. When the voltage application is stopped, the laminated piezoelectric element 10 contracts, the disc spring 33 pushes back the piston 31, the fluid passage 27 is opened, and the injection hole 21 communicates with the fluid passage 27. Fluid injection is performed.

  The fluid passage 27 may be opened by applying a voltage to the multilayer piezoelectric element 10 and the fluid passage 27 may be closed by stopping the application of the voltage.

  Further, the laminated piezoelectric element 10 does not necessarily have to be inside the storage container 23, and is configured such that a pressure for controlling the ejection of fluid is applied to the inside of the storage container 23 by driving the laminated piezoelectric element 10. Just do it. In the injection device 19 of the present example, the fluid includes various liquids and gases such as conductive paste in addition to fuel, ink, and the like. By using the ejection device 19 of this example, the flow rate and ejection timing of the fluid can be stably controlled over a long period of time.

  Further, if the injection device 19 of the present example employing the laminated piezoelectric element 10 of the above example is used for an internal combustion engine, the fuel can be accurately supplied to the combustion chamber of the internal combustion engine such as an engine over a longer period than the conventional injection device. Can be injected well.

  Next, an example of the fuel injection system of this embodiment will be described.

  FIG. 7 is a schematic view showing an example of the fuel injection system of the present embodiment. As shown in FIG. 7, the fuel injection system 35 of this example includes a common rail 37 that stores high-pressure fuel as a high-pressure fluid, and a plurality of injection devices 19 of the above-described examples that inject the high-pressure fluid stored in the common rail 37. A pressure pump 39 for supplying a high-pressure fluid to the common rail 37 and an injection control unit 41 for supplying a drive signal to the injection device 19 are provided.

  The injection control unit 41 controls the amount and timing of high-pressure fluid injection based on external information or an external signal. For example, if the fuel injection system 35 of this example is used for engine fuel injection, the amount and timing of fuel injection can be controlled while sensing the state of the combustion chamber of the engine with a sensor or the like. The pressure pump 39 serves to supply fluid fuel from the fuel tank 43 to the common rail 37 at a high pressure. For example, in the case of an engine fuel injection system 35, fluid fuel is fed into the common rail 37 at a high pressure of 1000 to 2000 atmospheres (about 101 MPa to about 203 MPa), preferably 1500 to 1700 atmospheres (about 152 MPa to about 172 MPa). In the common rail 37, the high-pressure fuel sent from the pressure pump 39 is stored and sent to the injection device 19 as appropriate. As described above, the ejection device 19 ejects a certain fluid from the ejection holes 21 to the outside or an adjacent container. For example, when the target for injecting and supplying fuel is an engine, high-pressure fuel is injected from the injection hole 21 into the combustion chamber of the engine in the form of a mist.

  According to the fuel injection system 35 of this example, desired injection of high-pressure fuel can be stably performed over a long period of time.

DESCRIPTION OF SYMBOLS 10 ... Stack type piezoelectric element 1 ... Piezoelectric layer 11 ... 1st piezoelectric layer 12 ... 2nd piezoelectric layer 13 ... 3rd piezoelectric layer 2 ... Inside Electrode layer 21... First internal electrode layer 22... Second internal electrode layer 30. Laminated body 3. Laminated unit 4. -Injection device 21 ... Injection hole 23 ... Storage container 25 ... Needle valve 27 ... Fluid passage 29 ... Cylinder 31 ... Piston 33 ... Belleville spring 35 ... Fuel injection system 37 ... Common rail 39 ... Pressure pump 41 ... Injection control unit 43 ... Fuel tank

Claims (6)

A plurality of laminated units in which piezoelectric layers and internal electrode layers are alternately laminated, and a predetermined fracture layer disposed between adjacent laminated units and laminated units,
In each of the stacked units, the first piezoelectric layer that is the first piezoelectric layer counted from the planned fracture layer is the second piezoelectric body that is the second piezoelectric layer counted from the planned fracture layer. A laminated piezoelectric element characterized by being thinner than a layer.   In each of the stacked units, the third piezoelectric layer, which is the third piezoelectric layer counted from the predetermined fracture layer, is equal to or thicker than the thickness of the first piezoelectric layer, and The multilayer piezoelectric element according to claim 1, wherein the multilayer piezoelectric element is thinner than the second piezoelectric layer.   In each of the stacked units, all the piezoelectric layers except the first piezoelectric layer and the second piezoelectric layer are equal to or thicker than the thickness of the first piezoelectric layer, and 2. The thickness of all of the piezoelectric layers except the first piezoelectric layer and the second piezoelectric layer is reduced as the distance from the first piezoelectric layer is increased. The multilayer piezoelectric element according to claim 2.   The laminated unit disposed between the planned fracture layer and the planned fracture layer is vertically symmetric when the thickness of all the piezoelectric layers is viewed. The multilayer piezoelectric element according to claim 3.   A container having an injection hole and the multilayer piezoelectric element according to any one of claims 1 to 4 are provided, and the injection hole is opened and closed by driving the multilayer piezoelectric element. Injection device.   6. A common rail that stores high-pressure fuel, an injection device according to claim 5 that injects the high-pressure fuel stored in the common rail, a pressure pump that supplies the high-pressure fuel to the common rail, and a drive signal to the injection device A fuel injection system comprising: an injection control unit.

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