Pressure detection device, piezoelectric module, and method for manufacturing piezoelectric module

Abstract

To suppress variations in pressure detection caused by static electricity generated inside a pressure detection device.SOLUTION: A pressure detection device 1 includes: a piezoelectric element 41; a front-end electrode member 42 disposed on the front-end side in the axial direction of the piezoelectric element 41; a rear-end electrode member 44 disposed on the rear-end side in the axial direction of the piezoelectric element 41; and an insulating tube 50 for accommodating at least one of the front-end electrode member 42, the piezoelectric element 41, and the rear-end electrode member 44 arranged along the axial direction, the inner peripheral surface of the insulating tube 50 being in contact with the outer peripheral surface of at least one of the front-end electrode member 42, the piezoelectric element 41, and the rear-end electrode member 44. The device further includes a pressing member 49 for accommodating the front-end electrode member 42, the piezoelectric element 41, the rear-end electrode member 44, and the insulating tube 50 therein, and is electrically connected to the front-end electrode member 42. A conductive layer having conductivity is formed on an outer peripheral surface of the insulating tube 50.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a pressure detection device, a piezoelectric module, and a method for manufacturing a piezoelectric module. [Background technology]

[0002] A pressure detection device that detects the pressure of a fluid from an internal combustion engine is known (for example, see Patent Document 1). The result of detection by the pressure detection device is output as a pressure waveform. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-056119 Summary of the Invention [Problem to be solved by the invention]

[0004] Among the pressure waveforms output from pressure detection devices, there are some that exhibit momentary deviations from the waveform's baseline (the line connecting the points indicating zero pressure) due to the structure of the pressure detection device, and these deviations continue without returning to the original waveform baseline. This deviation in the pressure waveform's baseline is also known as "step deviation," and can result in inaccurate pressure detection. One cause of step deviation is static electricity generated by friction between insulating and conductive components inside the pressure detection device, or friction between insulating components. For this reason, there is a need for technology to suppress changes in pressure detection caused by static electricity generated inside the pressure detection device.

[0005] An object of the present invention is to suppress changes in pressure detection caused by static electricity generated inside a pressure detection device. [Means for solving the problem]

[0006] The pressure detection device of the present invention, which achieves the above-mentioned object, comprises a piezoelectric element that outputs an electrical signal corresponding to pressure applied in the axial direction from one end to the other end, a first electrode member that is conductive and arranged on the one end side of the piezoelectric element, a second electrode member that is conductive and arranged on the other end side of the piezoelectric element, a cylindrical, insulating insulating tube that houses at least one of the first electrode member, the piezoelectric element, or the second electrode member that are arranged along the axial direction and whose inner circumferential surface is in contact with the outer circumferential surface of at least one of the first electrode member, the piezoelectric element, or the second electrode member, and a cylindrical, conductive pressure member that houses the first electrode member, the piezoelectric element, the second electrode member, and the insulating tube and is electrically connected to the first electrode member, and is characterized in that a conductive layer that is conductive is formed on the outer circumferential surface of the insulating tube. Here, the insulating tube may be characterized by having heat shrinkability. The conductive layer may also be a conductive tube that is cylindrical and conductive, houses at least one of the first electrode member, the piezoelectric element, the second electrode member, or the insulating tube that are aligned along the axial direction, and whose inner surface contacts the outer surfaces of the insulating tubes. The conductive layer may be made of a fluororesin containing a conductive material. In addition, the pressure detection device of the present invention, which achieves the above-mentioned object, is a pressure detection device comprising: a piezoelectric element that outputs an electrical signal corresponding to pressure applied in an axial direction from one end side to the other end side; a first electrode member that is conductive and arranged on the one end side of the piezoelectric element; a second electrode member that is conductive and arranged on the other end side of the piezoelectric element; a rod-shaped, conductive conductive member to which the second electrode member is electrically connected; a cylindrical, insulating holding member that holds the other end side of the conductive member by accommodating the other end side of the conductive member inside; and a cylindrical, conductive support member that accommodates the one end side of the holding member inside and is accommodated inside a pressure member whose one end side is conductive, and is characterized in that a conductive conductive layer is formed on the outer surface of the holding member. Here, the support member may be characterized in that it accommodates the one end side of the holding member therein, thereby supporting the holding member either constantly or temporarily. Furthermore, the pressure detection device of the present invention, which achieves the above-mentioned object, comprises a piezoelectric element that outputs an electrical signal corresponding to pressure applied in an axial direction from one end side to the other end side, a first electrode member that is conductive and arranged on the one end side of the piezoelectric element, a second electrode member that is conductive and arranged on the other end side of the piezoelectric element, a cylindrical, conductive pressure member that houses the first electrode member, the piezoelectric element, and the second electrode member and is electrically connected to the first electrode member, an annular, insulating insulating member that is arranged on the outer periphery of the pressure member, and a cylindrical, conductive housing that houses the pressure member and the insulating member, and is a pressure detection device characterized in that a conductive layer that is conductive is formed on the outer periphery or inner periphery of the insulating member. Furthermore, the piezoelectric module of the present invention, which achieves the above-mentioned object, is a piezoelectric module comprising: a piezoelectric element that outputs an electrical signal corresponding to pressure applied in the axial direction from one end to the other end; a first electrode member that is conductive and arranged on the one end side of the piezoelectric element; a second electrode member that is conductive and arranged on the other end side of the piezoelectric element; and an insulating tube that is cylindrical and insulating, houses the first electrode member, the piezoelectric element, and the second electrode member that are lined up along the axial direction, and whose inner surface is in contact with the outer surfaces of the first electrode member, the piezoelectric element, and the second electrode member, and is characterized in that a conductive layer that is conductive is formed on the outer surface of the insulating tube. Here, the insulating tube may be characterized by having heat shrinkability. Furthermore, a method for manufacturing a piezoelectric module according to the present invention, which achieves the above-mentioned object, includes an arrangement step of arranging a piezoelectric element that outputs an electrical signal corresponding to pressure applied in an axial direction from one end to the other end, a conductive first electrode member, and a conductive second electrode member along the axial direction in the order of the first electrode member, the piezoelectric element, and the second electrode member; a first tube installation step of installing a cylindrical insulating tube that is insulating and heat-shrinkable so that both openings of the insulating tube are aligned along the axial direction and the inner circumferential surface of the insulating tube faces the outer circumferential surfaces of the first electrode member, the piezoelectric element, and the second electrode member; a second tube installation step of installing a cylindrical conductive conductive tube so that both openings of the conductive tube are aligned along the axial direction and the inner circumferential surface of the conductive tube faces the outer circumferential surface of the insulating tube; and a heat shrinking step of heating the insulating tube and the conductive tube to shrink them toward their inner circumferential surfaces. Here, the heat shrinking step may be characterized in that after the insulating tube is heated and shrunk, the conductive tube is heated and shrunk. The heat shrinking step may be characterized in that the insulating tube and the conductive tube are simultaneously heated and shrunk. [Effects of the Invention]

[0007] According to the present invention, it is possible to suppress changes in pressure detection caused by static electricity generated inside the pressure detection device. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a side view of a pressure detection device according to an embodiment of the present invention; [Figure 2] 2 is a cross-sectional view showing a schematic configuration of the pressure detection device of FIG. 1 attached to an internal combustion engine. [Figure 3] FIG. 2 is a cross-sectional view of the pressure detection device of FIG. 1 (a cross-sectional view taken along III-III in FIG. 1). [Figure 4] 2 is an enlarged cross-sectional view of a portion of the end portion on the tip side in the axial direction of the pressure detection device of FIG. 1. FIG. [Figure 5] 2A to 2D are diagrams showing an example of a configuration for suppressing changes in pressure detection caused by static electricity generated inside the pressure detection device of FIG. 1. [Figure 6] 10 is a flowchart showing an example of a method for forming a conductive layer on the outer peripheral surface of an insulating tube on the outside in the radial direction. [Figure 7] 10 is a graph showing a specific example of a deviation (step deviation) in a pressure waveform output from a pressure detected by a conventional pressure detection device. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. [Configuration of pressure detection device] Fig. 1 is a side view of a pressure detection device 1 according to this embodiment. Fig. 2 is a cross-sectional view showing a schematic configuration of the pressure detection device 1 of Fig. 1 attached to an internal combustion engine 10. Fig. 3 is a cross-sectional view of the pressure detection device 1 of Fig. 1 (a cross-sectional view taken along III-III in Fig. 1). Fig. 4 is an enlarged cross-sectional view of a portion of the end portion on the axial tip side of the pressure detection device 1 of Fig. 1.

[0010] In the description of the embodiment of the present invention, in FIG. 1, the side toward the left in the figure is referred to as the "front end side" of the pressure detection device 1, and the side toward the right in the figure is referred to as the "rear end side" of the pressure detection device 1. The axial direction along the center line of the pressure detection device 1 is referred to as the "axial direction." The direction indicating the diameter of the pressure detection device 1 is referred to as the "radial direction." When referring to the radial direction, the direction toward the center line of the pressure detection device 1, indicated by the dashed dotted line in FIG. 1, etc., is referred to as the "inner side," and the direction away from the center line is referred to as the "outer side." In the present embodiment, the "front end side" corresponds to the "one end side," and the "rear end side" corresponds to the "other end side."

[0011] The pressure detecting device 1 according to this embodiment is a device that detects the pressure (combustion pressure) inside a combustion chamber C in an internal combustion engine 10. When the pressure detecting device 1 detects the pressure inside the combustion chamber C, a control device (not shown) controls the operation of the internal combustion engine 10 based on the detected pressure. The pressure detecting device 1 and the control device (not shown) are electrically connected via a connection cable 90.

[0012] The pressure detection device 1 has a housing section 30 that is cylindrical overall and exposed to the outside, a detection mechanism section 40 that includes various mechanisms for detecting pressure and is almost entirely housed inside the housing section 30 with a portion exposed to the outside, a seal section 70 attached to the outer peripheral surface of the housing section 30, and a buffer member 80 attached to the end of the housing section 30 on the axial tip side.

[0013] Here, we will explain the configuration of the internal combustion engine 10, the pressure of which is to be detected by the pressure detection device 1. As shown in Fig. 2, the internal combustion engine 10 has a cylinder block 11 with a cylinder formed therein, a piston 12 that reciprocates within the cylinder, and a cylinder head 13 that is fastened to the cylinder block 11 and forms a combustion chamber C together with the piston 12, etc. The cylinder block 11, piston 12, and cylinder head 13 are made of a conductive metal material such as cast iron or aluminum.

[0014] The cylinder head 13 is provided with a communication hole 130 that communicates between the combustion chamber C and the outside. A step portion 13a and a step portion 13b that is located closer to the combustion chamber C than the step portion 13a are formed in the middle of the communication hole 130. The communication hole 130 is made up of a small diameter portion 131 that is located closer to the combustion chamber C than the step portion 13b and has a smaller inner diameter, a medium diameter portion 132 that is located outside the step portion 13b (upper side in FIG. 2) and closer to the combustion chamber C than the step portion 13a and has a larger inner diameter than the small diameter portion 131, and a large diameter portion 133 that is located outside the step portion 13b and has a larger inner diameter than the medium diameter portion 132.

[0015] The pressure detecting device 1 is inserted into the communication hole 130 of the cylinder head 13 from the axial tip end side and fixed therein. This positions the pressure detecting device 1 relative to the internal combustion engine 10. Specifically, the pressure detecting device 1 is attached to the internal combustion engine 10 so that the axial tip end side faces the combustion chamber C (lower side in FIG. 2) and the axial rear end side faces the outside (upper side in FIG. 2).

[0016] (Configuration of the housing) 1, the housing unit 30 includes a tip external housing 31, a diaphragm head 32 attached to the axial tip side of the tip external housing 31, an intermediate external housing 33 attached to the axial rear end side of the tip external housing 31, and a rear external housing 34 attached to the axial rear end side of the intermediate external housing 33. Also, as shown in Fig. 4, the housing unit 30 further includes a first internal housing 35 attached to the radial inside of the tip external housing 31 and to the axial rear end side of the diaphragm head 32, and a second internal housing 36 attached to the radial inside of the tip external housing 31 and to the axial rear end side of the first internal housing 35.

[0017] [External housing for tip] The distal end external housing 31 constituting the housing unit 30 is a hollow, cylindrical member. The distal end external housing 31 is made of a metal material such as stainless steel that is electrically conductive and highly heat-resistant and acid-resistant. Examples of such metal materials include SUS630, known as a precipitation-hardened stainless steel, and SUH660, known as an austenitic heat-resistant steel (heat-resistant alloy). However, other metals or alloys (stainless steels, heat-resistant steels, or heat-resistant alloys) can also be used as long as they satisfy the required properties.

[0018] The outer diameter of the portion of the tip external housing 31 that is inserted into the communication hole 130 of the cylinder head 13 roughly matches the inner diameter of the medium-diameter portion 132 of the communication hole 130, and a protruding portion 311 having an outer diameter larger than the inner diameter of the medium-diameter portion 132 of the communication hole 130 is provided on the axial rear end side. When the pressure detection device 1 is attached to the cylinder head 13, a seat surface 312, which is the surface on the axial tip side of the protruding portion 311, abuts against a stepped portion 13a in the communication hole 130 via the first seal member 71. In addition, the buffer member 80 of the pressure detection device 1 abuts against a stepped portion 13b in the communication hole 130.

[0019] Although not shown, a male thread is provided on the outer peripheral surface of the axially outer side of the tip external housing 31. Furthermore, a female thread that can be threadably engaged with the male thread is provided on the inner peripheral surface of the medium diameter portion 132 of the communication hole 130 of the cylinder head 13. A step portion 13b of the communication hole 130 is formed on the combustion chamber C side of the portion of the communication hole 130 where the female thread is formed.

[0020] [Diaphragm head] The diaphragm head 32 constituting the housing 30 is a member having an overall disk shape. The diaphragm head 32 is provided so as to close the opening on the axial tip side of the tip external housing 31, and abuts against a part of the axial tip side of the tip external housing 31. The boundary between the diaphragm head 32 and the tip external housing 31 is laser welded around the entire outer periphery. The diaphragm head 32 functions as a spring by displacing in response to an external force. The diaphragm head 32 displaces so as to vibrate in response to the pressure of the combustion gas (an example of a fluid) generated in the combustion chamber C.

[0021] The diaphragm head 32 is made of a metal material such as stainless steel that is electrically conductive and highly heat-resistant and acid-resistant. Examples of such metal materials include SUS630, which is known as a precipitation-hardened stainless steel, and SUH660, which is known as an austenitic heat-resistant steel (heat-resistant alloy). However, other metals or alloys (such as various stainless steels, heat-resistant steels, or heat-resistant alloys) can be used as long as they satisfy the required characteristics. In this example, the diaphragm head 32 is made of the same material (e.g., SUS630) as the tip external housing 31.

[0022] [Intermediate external housing] The intermediate external housing 33 constituting the housing unit 30 is a hollow, cylindrical member. The intermediate external housing 33 is made of a metal material, such as stainless steel, that is electrically conductive and highly heat- and acid-resistant. An example of such a metal material is SUS430LX, a known ferritic stainless steel. However, other metals or alloys (stainless steels, heat-resistant steels, or heat-resistant alloys) may be used as long as they satisfy the required characteristics. In this example, the intermediate external housing 33 is made of a different material (e.g., SUS430LX) from the distal external housing 31. The distal end of the intermediate external housing 33 in the axial direction is fitted into the proximal end of the distal external housing 31 in the axial direction. The boundary between the intermediate external housing 33 and the distal external housing 31 is laser-welded around the entire outer periphery.

[0023] [Rear end external housing] The rear end external housing 34 constituting the housing unit 30 is a hollow, cylindrical member. The rear end external housing 34 is made of a metal material, such as stainless steel, that is electrically conductive and highly heat-resistant and acid-resistant. An example of such a metal material is SUS430LX, a known ferritic stainless steel. However, other metals or alloys (such as stainless steels, heat-resistant steels, or heat-resistant alloys) can be used as long as they satisfy the required characteristics. In this example, the rear end external housing 34 is made of the same material (e.g., SUS430LX) as the intermediate external housing 33. The axial leading end of the rear end external housing 34 is fitted into the axial rear end of the intermediate external housing 33. The boundary between the rear end external housing 34 and the intermediate external housing 33 is laser-welded around the entire outer periphery.

[0024] [First internal housing] The first internal housing 35 constituting the housing unit 30 is a hollow, cylindrical member also called a "front housing." The first internal housing 35 is made of a metal material such as stainless steel that is electrically conductive and has high heat resistance and acid resistance.

[0025] The first inner casing 35 has a first front cylindrical portion 351 located at the most forward end in the axial direction, and a first rear cylindrical portion 352 located at the rear end of the first front cylindrical portion 351 in the axial direction. In the first inner casing 35, the outer diameter of the first rear cylindrical portion 352 is larger than that of the first front cylindrical portion 351. The through hole provided inside the first inner casing 35 has an inner diameter that increases stepwise from the forward end to the rear end in the axial direction. The forward end of the first rear cylindrical portion 352 of the first inner casing 35 abuts against the rear end of the diaphragm head 32 in the axial direction. The boundary between the first inner casing 35 and the diaphragm head 32 is laser welded around the entire outer periphery.

[0026] [Second internal housing] The second inner housing 36 constituting the housing unit 30 is a hollow, cylindrical member. The second inner housing 36 is made of a metal material such as stainless steel that is electrically conductive and has high heat resistance and acid resistance.

[0027] The second inner casing 36 has a second front end tubular portion 361 located at the most front end side in the axial direction, and a second rear end tubular portion 362 located at the rear end side in the axial direction of the second front end tubular portion 361. In the second inner casing 36, the second rear end tubular portion 362 has a larger outer diameter than the second front end tubular portion 361. In addition, the through hole provided inside the first inner casing 35 has a substantially constant inner diameter.

[0028] The axial leading end of the second inner casing 36, i.e., the axial leading end of the second inner casing 361, is accommodated inside the first rear end casing 352 of the first inner casing 35. The axial leading end of the second inner casing 36 abuts against the axial rear end surface of the second insulating member 52, which will be described later. At this time, the axial rear end side of the second front end casing 361 and the second rear end casing 362 are exposed further rearward from the axial rear end of the first inner casing 35. The boundary between the second inner casing 36 and the first inner casing 35 is laser welded around the entire outer periphery.

[0029] (Configuration of the detection mechanism) The detection mechanism 40 includes a piezoelectric element 41, a front electrode member 42 as a first electrode member, a front insulating member 43, a rear electrode member 44 as a second electrode member, a rear insulating member 45, a first coil spring 46, a conductive member 47, a holding member 48, a pressure member 49, and an insulating tube 50. The detection mechanism 40 also includes a first insulating member 51, a second insulating member 52, a support member 53, a second coil spring 54, a first housing member 55, a second housing member 56, a circuit-containing member 57, a connecting member 58, a blocking member 59, and a third insulating member 60.

[0030] [Piezoelectric element] The piezoelectric element 41 constituting the detection mechanism 40 is a cylindrical member as a whole. The piezoelectric element 41 includes a piezoelectric body that exhibits the piezoelectric action of the piezoelectric longitudinal effect. The piezoelectric element 41 is disposed radially inside the distal external housing 31 (and the first internal housing 35). Here, the piezoelectric longitudinal effect refers to the generation of electric charges on the surface of the piezoelectric body in the charge generation axis direction when an external force is applied to a stress application axis in the same direction as the charge generation axis of the piezoelectric body. Therefore, in this example, signals (charge signals) due to the generated electric charges are output from the distal and proximal surfaces of the piezoelectric element 41 in the axial direction in response to changes in pressure along the axial direction.

[0031] Next, we will explain an example of using the piezoelectric shear effect in the piezoelectric element 41. The piezoelectric shear effect refers to the generation of electric charges on the surface of the piezoelectric element in the direction of the charge generation axis when an external force is applied along a stress application axis perpendicular to the charge generation axis of the piezoelectric element. The piezoelectric element 41 may be configured by stacking multiple thin piezoelectric elements. By stacking these elements in this way, the electric charges generated in the piezoelectric elements can be efficiently collected, increasing the sensitivity of the sensor. Examples of piezoelectric elements that can be used in the piezoelectric element 41 include langasite-based crystals (langasite, langatate, langanite, LTGA), quartz, gallium phosphate, etc., which have both the piezoelectric shear effect and the piezoelectric shear effect.

[0032] [Tip electrode member] The tip electrode member 42, which constitutes the detection mechanism 40, is a cylindrical component also known as an "insulating base." The tip electrode member 42 is made of a metal material, such as stainless steel, that is electrically conductive and highly heat-resistant. The tip electrode member 42 is disposed radially inside the tip external housing 31 and at the axial tip end of the piezoelectric element 41, so that the axial rear end surface of the tip electrode member 42 contacts the axial tip end surface of the piezoelectric element 41. In this example, the axial tip end surface, rear end surface, and outer peripheral surface of the tip electrode member 42 are not gold-plated, leaving the bare metal of the tip electrode material exposed. The outer diameter of the tip electrode member 42 is larger than that of the piezoelectric element 41.

[0033] [Tip insulating member] The tip insulating member 43 constituting the detection mechanism 40 is a cylindrical member as a whole. The tip insulating member 43 is made of a ceramic material such as alumina or zirconia, which has insulating properties and high heat resistance. The tip insulating member 43 is disposed radially inside the tip external housing 31 and on the axial tip side of the tip electrode member 42, so that the axial rear end surface of the tip insulating member 43 contacts the axial tip side surface of the tip electrode member 42. Meanwhile, the axial tip side surface of the tip insulating member 43 contacts the axial rear end surface of the diaphragm head 32. The outer diameter of the tip insulating member 43 is smaller than the outer diameter of the tip electrode member 42.

[0034] [Rear end electrode member] The rear electrode member 44, which constitutes the detection mechanism 40, is a cylindrical member overall. The rear electrode member 44 is made of a metal material, such as stainless steel, that is electrically conductive and highly heat-resistant. The rear electrode member 44 is disposed radially inside the distal external housing 31 and toward the axial rear end of the piezoelectric element 41, such that the axial front surface of the rear electrode member 44 contacts the axial rear surface of the piezoelectric element 41. In this example, the axial rear surface and outer circumferential surface of the rear electrode member 44 are gold-plated. In contrast, the axial front surface of the rear electrode member 44, i.e., the surface that contacts the axial rear end of the piezoelectric element 41, is not gold-plated, leaving the bare metal of the metal material constituting the rear electrode member 44 exposed. The outer diameter of the rear electrode member 44 is larger than the outer diameter of the piezoelectric element 41.

[0035] [Rear end insulating member] The rear-end insulating member 45, which constitutes the detection mechanism 40, is a hollow member having an annular (cylindrical) shape as a whole. The rear-end insulating member 45 is made of a ceramic material such as alumina or zirconia, which has insulating properties and high heat resistance. The rear-end insulating member 45 is disposed radially inside the front-end external housing 31 and on the axial rear-end side of the rear-end electrode member 44, so that the axial front-end surface of the rear-end insulating member 45 comes into contact with the axial rear-end surface of the rear-end electrode member 44. The outer diameter of the rear-end insulating member 45 is larger than the outer diameter of the piezoelectric element 41.

[0036] [First coil spring] The first coil spring 46 constituting the detection mechanism 40 is a generally helical member that expands and contracts in the axial direction. The first coil spring 46 is made of a conductive metal material such as brass, and its surface is gold-plated. The first coil spring 46 is disposed radially inside the front external housing 31. More specifically, the axial front side of the first coil spring 46 is disposed inside a through-hole provided in the rear-end insulating member 45, and its front side contacts the axial rear-end surface of the rear-end electrode member 44. Meanwhile, the axial rear side of the first coil spring 46 protrudes toward the axial rear end of the rear-end insulating member 45. The outer diameter of the first coil spring 46 is smaller than the inner diameter of the through-hole provided in the rear-end insulating member 45.

[0037] [Conductive member] The conductive member 47 constituting the detection mechanism 40 is a rod-shaped member also known as a "lead wire." The conductive member 47 is disposed radially inside the distal external housing 31. The conductive member 47 is made of a conductive metal material such as brass, and its surface is gold-plated. The conductive member 47 includes a distal rod-shaped portion 471 located at the distal end, an intermediate rod-shaped portion 472 located at the axial rear end of the distal rod-shaped portion 471, and a rear rod-shaped portion 473 located at the axial rear end of the intermediate rod-shaped portion 472. The outer diameters of the conductive member 47 increase in the order of the distal rod-shaped portion 471, the intermediate rod-shaped portion 472, and the rear rod-shaped portion 473.

[0038] [Holding member] The holding member 48 constituting the detection mechanism 40 is a hollow, cylindrical member. The holding member 48 is made of an insulating synthetic resin material such as PPS (Polyphenylene Sulfide) or PPT (Polypropylene Terephthalate). The holding member 48 has a leading end portion 481 (also called the "amplifier housing front") located at the axially most distal end, an intermediate portion 482 located at the axially rearward end of the leading end portion, and a rear end portion 483 located at the axially rearward end of the intermediate portion. The outer diameters of the holding member 48 increase in the order of leading end portion 481, intermediate portion 482, and rear end portion 483. The holding member 48 is disposed across the radially inner side of the leading end external housing 31 and the radially inner side of the intermediate external housing 33. The conducting member 47 is housed and held within the holding member 48. The boundary between the conductive member 47 and the holding member 48 is tightly joined by insert molding.

[0039] [Pressure member] The pressure member 49 constituting the detection mechanism 40 is a hollow, cylindrical member also referred to as an "inner housing." The pressure member 49 is made of a metal material such as stainless steel that is electrically conductive and highly heat-resistant. The pressure member 49 is disposed radially inside the tip external housing 31, straddling the radial insides of the first internal housing 35 and the second internal housing 36.

[0040] The pressure applying member 49 has a first cylindrical portion 491 located at the axially most distal end, a second cylindrical portion 492 located at the axially rearward end of the first cylindrical portion 491, a third cylindrical portion 493 located at the axially rearward end of the second cylindrical portion 492, and a fourth cylindrical portion 494 located at the axially rearward end of the third cylindrical portion 493. In the pressure applying member 49, the second cylindrical portion 492 has a larger outer diameter than the first cylindrical portion 491. The third cylindrical portion 493 also has a larger outer diameter than the second cylindrical portion 492. The fourth cylindrical portion 494 has a smaller outer diameter than the third cylindrical portion 493. In this example, the outer diameters of the second cylindrical portion 492 and the fourth cylindrical portion 494 are set to be approximately the same. The inner diameter of the through hole provided inside the pressure applying member 49 increases stepwise from the axially distal end to the axially rearward end.

[0041] The pressure member 49 accommodates a piezoelectric element 41, a leading electrode member 42, a trailing electrode member 44, a trailing insulating member 45, a first coil spring 46, and the like within a through hole. The axial leading surface of the leading electrode member 42 is in contact with the pressure member 49. A leading insulating member 43 is disposed in the opening of the through hole in the pressure member 49 on the leading end side in the axial direction. The inner diameter of the through hole in the pressure member 49 is larger than the outer diameters of the piezoelectric element 41, the leading electrode member 42, the trailing electrode member 44, and the trailing insulating member 45. The inner diameter of the opening of the through hole in the pressure member 49 on the leading end side in the axial direction is larger than the outer diameter of the leading insulating member 43.

[0042] [Insulating tube] The insulating tube 50, which constitutes the detection mechanism 40, is a hollow, cylindrical member also known as an "element ring" with openings at both axial ends. The insulating tube 50 is made of an insulating material. The insulating tube 50 accommodates and secures the following components (from the axial tip end) within its radially inner space while maintaining contact with each other: the leading electrode member 42, the piezoelectric element 41, the trailing electrode member 44, and the trailing insulating member 45. In the following description, the leading electrode member 42, the piezoelectric element 41, the trailing electrode member 44, and the trailing insulating member 45, together with the insulating tube 50, may be collectively referred to as the "piezoelectric module 400."

[0043] The material for the insulating tube 50 may be selected from various insulating materials, whether organic or inorganic. However, from the perspective of facilitating the manufacture of the piezoelectric module 400, it is preferable to use a heat-shrinkable organic material (e.g., a synthetic resin material), i.e., a heat-shrinkable tube. Among the various synthetic resin materials, it is preferable to use a fluororesin material, which has superior heat resistance, insulating properties, and high-frequency characteristics compared to polyamides (e.g., various nylons). Among the fluororesin materials, PTFE (polytetrafluoroethylene) and PFA (perfluoroalkoxyalkane), which have excellent thermal stability with a continuous use temperature of 260°C, can be used.

[0044] Furthermore, when the ambient temperature of the piezoelectric module 400 is 200°C or lower, it is desirable to use FEP (tetrafluoroethylene-hexafluoropropylene copolymer) as the material for the insulating tube 50, as it has a lower continuous use temperature than PTFE or PFA but is easy to form into a hot melt shape.

[0045] Furthermore, PEI (polyetherimide), which has excellent insulating properties and heat resistance, or PEEK (polyetheretherketone), which has excellent heat resistance, insulating properties, and toughness, may be used as the material for forming the insulating tube 50. In the following description, the insulating tube 50 will be described as being formed of a heat-shrinkable tube made of FEP.

[0046] The insulating tube 50 is disposed radially inside the tip external housing 31 and radially inside the pressure member 49. A gap is formed between the insulating tube 50 and the pressure member 49. The insulating tube 50 accommodates the axial rear end of the tip electrode member 42, the piezoelectric element 41, the rear electrode member 44, and the axial front end of the rear insulating member 45. In other words, the axial front end of the tip electrode member 42 protrudes further toward the front than the axial front end of the insulating tube 50, and the axial rear end of the rear insulating member 45 protrudes further toward the rear than the axial rear end of the insulating tube 50. In this embodiment, the insulating tube 50 accommodates the tip electrode member 42, the piezoelectric element 41, and the rear electrode member 44, but this is not limiting. The insulating tube 50 may accommodate at least one of the tip electrode member 42, the piezoelectric element 41, and the rear electrode member 44.

[0047] The outer diameter of the insulating tube 50 is smaller than the inner diameter of the through hole provided in the pressure member 49, but larger than the inner diameter of an opening provided on the axially leading end side of this through hole. The inner diameter of the insulating tube 50 is also approximately equal to the outer diameters of the piezoelectric element 41, leading electrode member 42, trailing electrode member 44, and trailing insulating member 45. Details of the piezoelectric module 400 including the insulating tube 50 will be described later.

[0048] [First insulating member] The first insulating member 51 constituting the detection mechanism 40 is a generally annular member also referred to as an "insulating pipe." The first insulating member 51 is made of a ceramic material such as alumina, which has insulating properties and high heat resistance. The first insulating member 51 is disposed radially inside the tip outer housing 31, radially inside the first inner housing 35, and on the outer periphery of the pressure member 49. The surface of the first insulating member 51 on the tip end side in the axial direction contacts the first inner housing 35, and the surface of the first insulating member 51 on the rear end side in the axial direction contacts the pressure member 49. The outer diameter of the first insulating member 51 is larger than the outer diameter of the third cylindrical portion 493 of the pressure member 49.

[0049] [Second insulating member] The second insulating member 52 constituting the detection mechanism 40, like the first insulating member 51, is a ring-shaped member also known as an "insulating pipe." The second insulating member 52 is made of a ceramic material, such as alumina or zirconia, which has insulating properties and high heat resistance. The second insulating member 52 is disposed radially inside the distal outer housing 31, radially inside the first inner housing 35, and on the outer periphery of the pressure member 49. The second insulating member 52 is disposed axially on the rear end side of the first insulating member 51. The axial distal end surface of the second insulating member 52 contacts the pressure member 49, and the axial rear end surface of the second insulating member 52 contacts the second distal cylindrical portion 361 of the second inner housing 36. The outer diameter of the second insulating member 52 is larger than the outer diameter of the third cylindrical portion 493 of the pressure member 49. In this embodiment, the second insulating member 52 has the same dimensions as the first insulating member 51.

[0050] [Support member] The support member 53, which constitutes the detection mechanism 40, is a hollow, cylindrical member also referred to as an "inner body." The support member 53 is made of a metal material, such as stainless steel, that is electrically conductive and highly heat-resistant. The support member 53 is located radially inside the front external housing 31, with its axial front end positioned radially inside the pressure member 49. However, the axial rear end of the support member 53 protrudes further rearward than the axial rear end of the pressure member 49. The axial front surface of the support member 53 contacts the rear surface of the rear insulating member 45. The boundary between the support member 53 and the pressure member 49 is laser-welded around the entire outer periphery. The axial rear end of the first coil spring 46 and the axial front ends of the conductive member 47 and the holding member 48 are housed within the support member 53. The outer diameter of the support member 53 is slightly smaller than the inner diameter of the through-hole provided in the pressure member 49. The inner diameter of the through hole provided in the support member 53 is slightly larger than the outer diameter of the end portion of the holding member 48 on the tip side in the axial direction.

[0051] [Second coil spring] The second coil spring 54 constituting the detection mechanism 40 is a member having a helical shape as a whole, and is adapted to expand and contract in the axial direction. The second coil spring 54 is made of a metal material such as phosphor bronze, which has electrical conductivity and high heat resistance, and its surface is gold-plated. In this example, the second coil spring 54 is made of the same material (e.g., phosphor bronze) as the first coil spring.

[0052] The second coil spring 54 is disposed radially inside the tip external housing 31. More specifically, the axial tip side of the second coil spring 54 is disposed radially outside of the axial rear end side and outer peripheral surface of the support member 53, and the tip portion 541 is configured to contact the axial rear end side surface of the fourth cylindrical portion 494 of the pressure member 49. The conduction member 47, the holding member 48, the support member 53, and the axial tip side of the first accommodating member 55 are disposed radially inside the second coil spring 54. The outer diameter of the second coil spring 54 is smaller than the inner diameter of the tip external housing 31. The inner diameter of the second coil spring 54 is larger than the outer diameter of the support member 53.

[0053] [First storage member] The first housing member 55 constituting the detection mechanism 40 is a hollow, cylindrical member. The first housing member 55 is made of a conductive metal material such as brass or stainless steel, and its surface is gold-plated. The first housing member 55 is disposed radially inside the tip external housing 31.

[0054] [Second storage member] The second housing member 56 constituting the detection mechanism 40 is a hollow, cylindrical member. Similar to the first housing member 55, the second housing member 56 is made of a conductive metal material such as brass or stainless steel, and its surface is gold-plated. The second housing member 56 is disposed across the radially inner side of the tip external housing 31 and the radially inner side of the intermediate external housing 33.

[0055] [Circuit-embedded components] As shown in FIG. 3, the circuit-containing member 57 constituting the detection mechanism 40 includes a circuit board 571 that performs various processes using electronic circuits on the electrical signal generated by the weak charge output by the piezoelectric element 41 (see FIG. 4), and a sealing portion 572 that houses the circuit board 571 and seals the circuit board 571. The circuit board 571 includes a processing circuit (not shown) that includes an integration circuit that time-integrates the electrical signal generated by the charge output by the piezoelectric element 41, and an amplifier circuit that outputs the output from the integration circuit as a voltage. The circuit-containing member 57 is located radially inside the intermediate external housing 33, and almost the entire area thereof, except for a portion on the rear end side in the axial direction, is disposed radially inside the second housing member 56. In particular, the entire area of ​​the circuit board 571 is disposed radially inside the second housing member 56.

[0056] The axial tip of the circuit-containing member 57 is fitted into a recess provided on the axial rear end of the holding member 48. A metal plate (electrode terminal) provided on the axial tip of the circuit-containing member 57 is connected to the axial rear end of the conductive member 47. A metal plate (electrode terminal) provided on the outer peripheral surface of the circuit-containing member 57 is in contact with the inner peripheral surface of the second accommodating member 56.

[0057] [Connecting member] The connection member 58 constituting the detection mechanism 40 is a columnar member as a whole. The connection member 58 includes a base material made of an insulating synthetic resin material such as PPS or PPT, and wiring and terminals made of a conductive metal material such as copper. The connection member 58 is disposed across the radially inner side of the intermediate external casing 33 and the radially inner side of the rear-end external casing 34. The portion (outer peripheral surface) of the connection member 58 that faces the intermediate external casing 33 or the rear-end external casing 34 is made of a synthetic resin material, and no metal material is exposed in this portion.

[0058] The axial rear end of the circuit-containing member 57 faces the axial front end of the connection member 58, and a metal plate (electrode terminal) provided on the circuit-containing member 57 is fitted into a terminal provided on the connection member 58. Furthermore, the conductor portions exposed on the axial front end side of the power line 91, signal line 92, and ground line 93 constituting the connection cable 90 are inserted into the axial rear end of the connection member 58. The power line 91, signal line 92, and ground line 93 will be described in detail later. The intermediate external housing 33 and the connection member 58 are integrated by press-fitting (tight fit).

[0059] [Closure member] The blocking member 59 constituting the detection mechanism 40 is a columnar member as a whole. However, the blocking member 59 has three through holes formed along the axial direction. The blocking member 59 is made of an insulating rubber material. The axial leading end of the blocking member 59 is disposed radially inside the rear external housing 34, and the axial trailing end protrudes further toward the rear end of the rear external housing 34. The axial leading end of the blocking member 59 faces the axial rear end of the connecting member 58. The above-mentioned power line 91, signal line 92, and ground line 93 are inserted into the three through holes formed in the blocking member 59. The rear external housing 34 and the blocking member 59 are integrated by press-fitting (tight fit).

[0060] [Third insulating member] The third insulating member 60 constituting the detection mechanism 40 is a hollow member having an overall cylindrical shape. However, the third insulating member 60 has a structure in which a cylindrical portion provided at the axial tip end side and an annular portion provided at the axial rear end side are integrated together. The third insulating member 60 is made of an insulating synthetic resin material such as PPS. The third insulating member 60 is disposed across the radial inside of the tip external housing 31 and the radial inside of the intermediate external housing 33.

[0061] (Configuration of seal part) As shown in FIG. 1, the seal portion 70 includes a first seal member 71 located relatively closer to the leading end in the axial direction, and a second seal member 72 located relatively closer to the rear end in the axial direction.

[0062] [First sealing member] The first seal member 71 constituting the seal unit 70 is an annular member as a whole, and in this example, is a square ring with a substantially square cross section as shown in FIG. 3. The first seal member 71 is made of a copper material with a tin-plated surface, which has high heat resistance and acid resistance. The first seal member 71 is attached to the outer peripheral surface of the tip outer housing 31 constituting the housing unit 30.

[0063] More specifically, the first seal member 71 is attached to the outer peripheral surface of the tip external housing 31 so as to contact the seat surface 312 of the protruding portion 311. Since the seat surface 312 is the surface on the axial tip side of the protruding portion 311, when the pressure detecting device 1 is attached to the cylinder head 13 with the first seal member 71 attached, the seat surface 312 faces the step portion 13a of the communication hole 130 via the first seal member 71.

[0064] [Second sealing member] The second seal member 72 constituting the seal unit 70 is an overall annular member, and in this example is constituted by an O-ring with a circular cross section as shown in Fig. 3. The second seal member 72 is made of a synthetic rubber material such as fluororubber, which has high mechanical recovery. The second seal member 72 is attached to the outer peripheral surface of the rear-end external housing 34 constituting the housing unit 30.

[0065] The second seal member 72 serves as a sealing member that prevents water and the like from entering from the outside of the internal combustion engine 10, and also serves as a vibration-damping member that prevents the pressure detection device 1 from vibrating due to vibrations in the installation environment or when the internal combustion engine 10 is in operation, and from colliding with the inner wall of the communication hole 130 in the cylinder head 13. For this reason, among materials with high mechanical resilience, a fluororubber material is particularly suitable for the second seal member 72, as it has high heat resistance in resilience and a long life for its vibration suppression function.

[0066] (Structure of buffer material) The buffer member 80 is a member having a cylindrical shape as a whole, and is disposed at the end portion on the leading end side in the axial direction of the pressure sensing device 1. The buffer member 80 is formed with a through hole 801 that allows combustion gas generated in the combustion chamber C to pass through. In this embodiment, the diaphragm head 32 and the buffer member 80 are integrated by laser welding the entire circumference of the outer circumferential surface to the boundary portion while the buffer member 80 is abutted against the diaphragm head 32. When the pressure sensing device 1 is attached to the cylinder head 13, the buffer member 80 abuts against a step portion 13b in the communication hole 130 of the cylinder head 13.

[0067] [Connection cable configuration] The connection cable 90 includes a twisted power line 91, a signal line 92, and a ground line 93, and a covering (not shown) that encases these wires. The power line 91, the signal line 92, and the ground line 93 each have a conductor made of tin-plated annealed copper twisted wire and an insulating portion made of polyethylene (cross-linked polyethylene) or the like, whose cross-linked structure is reinforced using an electron beam or the like, that covers and insulates the conductors. The covering portion is made of an insulating rubber or resin material. The connection cable 90 may also be provided with a shield to shield the power line 91, the signal line 92, and the ground line 93, if necessary.

[0068] [Procedure for installing a pressure detection device on an internal combustion engine] 2, the procedure for attaching the pressure detecting device 1 having the above-described configuration to the internal combustion engine 10 will be described. First, from the outside of the internal combustion engine 10, the pressure detecting device 1 is placed so that the end portion (buffer member 80) on the axial tip side faces the communication hole 130 provided in the cylinder head 13 of the internal combustion engine 10. Subsequently, the pressure detecting device 1 is inserted toward the inside of the communication hole 130.

[0069] Next, the pressure detection device 1 is rotated clockwise relative to the cylinder head 13 of the internal combustion engine 10 in the axial direction. This operation is preferably performed using a torque wrench. As a result, the female thread provided on the inner circumferential surface of the communication hole 130 in the cylinder head 13 and the male thread provided on the outer circumferential surface of the tip external casing 31 of the pressure detection device 1 become threaded together, and the pressure detection device 1 is screwed into the cylinder head 13. As a result, the buffer member 80 provided at the end on the tip side in the axial direction of the pressure detection device 1 moves toward the combustion chamber C provided in the internal combustion engine 10.

[0070] Furthermore, as the pressure detection device 1 is screwed in in this manner, the buffer member 80 of the pressure detection device 1 abuts against the stepped portion 13b in the communication hole 130 of the cylinder head 13 of the internal combustion engine 10. Furthermore, the seat surface 312 of the protruding portion 311 of the tip external housing 31 of the pressure detection device 1 abuts against the stepped portion 13a in the communication hole 130 via the first seal member 71. As a result, the pressure detection device 1 basically cannot be screwed in any further, but by tightening it further using a torque wrench, a predetermined axial force (fastening axial force) is applied to the pressure detection device 1 and the cylinder head 13 in the axial direction.

[0071] In the pressure sensing device 1 according to this embodiment, the first seal member 71 is made of a material that is more elastic than the buffer member 80, and therefore the first seal member 71 is deformed when the step portion 13a in the communication hole 130 abuts against the pressure sensing device 1. Therefore, the position of the pressure sensing device 1 relative to the communication hole 130 of the cylinder head 13 of the internal combustion engine 10 is determined by the abutment between the step portion 13b in the communication hole 130 and the buffer member 80 of the pressure sensing device 1. With the above, the attachment of the pressure sensing device 1 to the internal combustion engine 10, in other words, the fastening of the pressure sensing device 1 to the cylinder head 13, is completed.

[0072] [Pressure detection operation by pressure detection device] Next, a description will be given of the pressure detection operation of the pressure detection device 1. When the internal combustion engine 10 is operating, the pressure (combustion pressure) of the combustion gas generated in the combustion chamber C is applied to the diaphragm head 32 via the buffer member 80. The buffer member 80 receives the combustion gas, and reduces the temperature of the combustion gas as it passes through the through-holes 801, and supplies the cooled combustion gas to the diaphragm head 32.

[0073] Pressure applied to the diaphragm head 32 is transmitted to the tip electrode member 42 via the tip insulating member 43. The pressure transmitted to the tip electrode member 42 acts on the piezoelectric element 41 sandwiched between the tip electrode member 42 and the rear electrode member 44, and an electric charge corresponding to the received pressure is generated in the piezoelectric element 41. The electric charge generated in the piezoelectric element 41 is supplied as an electric charge signal from the tip electrode member 42 or the rear electrode member 44 to the circuit board 571 via conductive members such as the conductive member 47 or the second coil spring 54. The electric charge signal supplied to the circuit board 571 is subjected to various processes in a processing circuit (not shown) mounted on the circuit board 571 and becomes an output signal. The output signal output from the circuit board 571 is then transmitted to a control device (not shown) via the wiring and terminals of the connection member 58 and the connection cable 90.

[0074] For example, in a pressure sensing device 1 installed in a combustion chamber C of an internal combustion engine 10, the application of combustion pressure compresses the piezoelectric element 41, and a negative charge corresponding to the applied pressure is generated in the piezoelectric element 41. Then, during the release process in which the piezoelectric element 41 is released from compression, a positive charge is generated. At this time, the absolute values ​​of the negative charge during the compression process and the positive charge during the release process match, and the integrated value of the charge in the integration circuit of the circuit board 571 during one cycle of the compression process and the release process becomes zero, and the output from the amplifier circuit of the circuit board 571 also becomes zero, resulting in a good charge balance.

[0075] [Configuration for suppressing changes in pressure detection] 5(A) to 5(D) are diagrams showing an example of a configuration for suppressing changes in pressure detection due to static electricity generated inside the pressure detection device 1 of FIG. 1. FIG. 5(A) shows an enlarged view of the dashed-line area 500 shown in FIG. 4. FIG. 5(B) shows an enlarged view of the dashed-line area 600 shown in FIG. 4. FIG. 5(C) shows an enlarged view of the dashed-line area 700 in FIG. 4. FIG. 5(D) shows an enlarged view of the dashed-line area 800 in FIG. 4.

[0076] Vibrations and heat generated inside the pressure detection device 1 can cause contact and friction between components constituting the pressure detection device 1, which in turn generates static electricity. This static electricity can then cause a "step shift" in the pressure waveform. Specifically, friction (including contact) between components constituting the pressure detection device 1 generates frictional charges on the surfaces of the components. This charge can then enter the conduction path of the charge generated by the piezoelectric element and affect the integral value of the integrating circuit configured on the circuit board 571. For example, if negative frictional charges enter the conduction path of the charge in the pressure detection device 1, the absolute value of the "charge during the compression process of the piezoelectric element 41 plus the frictional charge" in the output of the integrating circuit can exceed the absolute value of the positive charge during the compression and release of the piezoelectric element 41. In this case, the charge balance becomes poor, which can cause the "step shift" described above. Such charge imbalance is often caused by contact or friction at the boundary between an insulating and a conductive member, or by contact or friction at the boundary between insulating members. A specific method implemented in the pressure detection device 1 for suppressing changes in pressure detection due to static electricity generated inside the pressure detection device 1 will be described below with reference to FIGS. 5(A) to 5(D).

[0077] 5(A) shows a configuration in which a conductive layer 501 is formed on the outer peripheral surface of an insulating tube 50 as an example of a configuration for suppressing changes in pressure detection due to static electricity generated inside the pressure detection device 1. As shown in FIG. 5(A), a conductive thin-film conductive layer 501 is formed on the outer peripheral surface of the insulating tube 50 on the radially outer side, which fixes the rear end electrode member 44. Furthermore, a pressure member 49 is disposed radially outward of the conductive layer 501 via a gap 901. Furthermore, a first inner housing 35 is disposed radially outward of the pressure member 49 via a gap 902. The conductive layer 501 is made of a material such as a fluororesin blended with a conductive material such as carbon black or titanium oxide.

[0078] The method for forming the conductive layer 501 on the outer peripheral surface of the insulating tube 50 is not particularly limited. For example, the conductive layer 501 may be formed by closely contacting a conductive tube, which is a thin, heat-shrinkable tube having electrical conductivity, to the outer peripheral surface of the insulating tube 50. In this case, the thickness of the insulating tube 50 or the conductive tube is not particularly limited. For example, a conductive tube having a thickness of 0.03 mm (millimeters) before heat shrinkage and a thickness of 0.034 mm (millimeters) after heat shrinkage may be disposed on the outer peripheral surface of an insulating tube 50 having a thickness of 0.05 mm (millimeters) before heat shrinkage and a thickness of 0.056 mm (millimeters) after heat shrinkage. Alternatively, for example, a paint for forming the conductive layer 501 may be applied to the outer peripheral surface of the insulating tube 50. A specific example of a method for disposing a conductive tube that will become the conductive layer 501 on the outer peripheral surface of the insulating tube 50 will be described later with reference to FIG. 6 .

[0079] 5(A), static electricity generated by temporary contact or friction between the insulating tube 50 and the pressure member 49 disposed radially outward can be released to the pressure member 49 side via the conductive layer 501. As a result, changes in pressure detection caused by static electricity generated inside the pressure detection device 1 are suppressed.

[0080] 5(B) shows a configuration in which a conductive layer 484 is formed on the outer peripheral surface of the holding member 48 as an example of a configuration for suppressing changes in pressure detection due to static electricity generated inside the pressure detection device 1. As shown in FIG. 5(B), a conductive thin film conductive layer 484 is formed on the outer peripheral surface of the radially outer side of the holding member 48 that houses the conductive member 47. In addition, a support member 53 is disposed radially outward of the conductive layer 484. The conductive layer 484 is made of a fluororesin or the like blended with a conductive material such as carbon black or titanium oxide.

[0081] 5(B), static electricity generated by temporary contact or friction between the holding member 48 and the support member 53 disposed radially outward can be released to the support member 53 side via the conductive layer 484. As a result, changes in pressure detection caused by static electricity generated inside the pressure detection device 1 are suppressed.

[0082] FIG. 5C shows an example of a configuration for suppressing pressure detection variations due to static electricity generated inside the pressure detection device 1, in which a conductive layer 431 is formed on the outer peripheral surface of the tip insulating member 43. As shown in FIG. 5C, a conductive thin-film conductive layer 431 is formed on the outer peripheral surface of the tip insulating member 43 in the radial direction. The conductive layer 431 is made of a fluororesin or the like blended with a conductive material such as carbon black or titanium oxide. The conductive layer 431 has a shorter axial length than the tip insulating member 43. Specifically, the tip insulating member 43 is exposed further forward than the axial end of the conductive layer 431, and further rearward than the axial end of the conductive layer 431. This prevents the conductive layer 431 from being formed on the outer peripheral surfaces of both axial ends of the tip insulating member 43, thereby suppressing short-circuiting between the ground of the element and the ground of the housing. Furthermore, a pressure member 49 is disposed radially outward of the conductive layer 431, with a gap 903 interposed therebetween.

[0083] 5(C), static electricity generated by temporary contact or friction between the tip insulating member 43 and the pressure member 49 disposed radially outward can be released to the pressure member 49 side via the conductive layer 431. As a result, changes in pressure detection caused by static electricity generated inside the pressure detection device 1 are suppressed.

[0084] FIG. 5(D) shows an example of a configuration for suppressing changes in pressure detection due to static electricity generated inside the pressure detection device 1, in which conductive layers 521 and 522 are formed on the outer and inner peripheral surfaces of the second insulating member 52. As shown in FIG. 5(D), a conductive thin-film conductive layer 521 is formed on the outer peripheral surface of the second insulating member 52 in the radial direction. A conductive thin-film conductive layer 522 is formed on the inner peripheral surface of the second insulating member 52 in the radial direction. The first inner housing 35 is disposed radially outside the conductive layer 521. The pressure member 49 is disposed radially inside the conductive layer 522. The conductive layers 521 and 522 are made of a material such as a fluororesin blended with a conductive material such as carbon black or titanium oxide.

[0085] Although not shown, the first insulating member 51 (see FIG. 4 ) also has a conductive layer formed on its outer and inner peripheral surfaces, similar to the second insulating member 52 described above. That is, a thin conductive layer having electrical conductivity is formed on each of the outer peripheral surface and the inner peripheral surface of the first insulating member 51 in the radial direction. The first inner housing 35 is disposed further outside the conductive layer formed on the outer peripheral surface of the first insulating member 51 in the radial direction. The pressure member 49 is disposed further inside the conductive layer formed on the inner peripheral surface of the first insulating member 51 in the radial direction. The conductive layers formed on the outer and inner peripheral surfaces of the first insulating member 51 are also made of a fluororesin or the like blended with a conductive material such as carbon black or titanium oxide.

[0086] 5(D), the pressure detection device 1 can dissipate static electricity generated by temporary contact or friction between the second insulating member 52 and the first inner housing 35 to the first inner housing 35 via the conductive layer 521. Furthermore, static electricity generated by temporary contact or friction between the second insulating member 52 and the pressure member 49 can dissipate to the pressure member 49 via the conductive layer 522. Furthermore, static electricity generated by temporary contact or friction between the first insulating member 51 and the first inner housing 35 can dissipate to the first inner housing 35 via a conductive layer (not shown). Furthermore, static electricity generated by temporary contact or friction between the first insulating member 51 and the pressure member 49 can dissipate to the pressure member 49 via a conductive layer (not shown). As a result, changes in pressure detection due to static electricity generated inside the pressure detection device 1 can be suppressed. In this embodiment, the conductive layers 521 and 522 are formed on the outer and inner peripheral surfaces of the second insulating member 52, respectively, but this is not limiting. A conductive layer may be formed on at least one of the outer circumferential surface or the inner circumferential surface of the second insulating member 52. Similarly, the first insulating member 51 may be configured such that a conductive layer is formed on at least one of the outer circumferential surface or the inner circumferential surface.

[0087] [Example of a method for forming a conductive layer on the outside of an insulating layer] Fig. 6 is a flowchart showing an example of a method for forming conductive layer 501 on the outer peripheral surface on the radially outer side of insulating tube 50. In the example of Fig. 6, insulating tube 50 and conductive tube (conductive layer 501) are assumed to be heat-shrinkable tubes that shrink when heated. When forming the conductive layer 501 on the outer peripheral surface of the insulating tube 50 in the radial direction, first, as an arrangement process (step 101), the piezoelectric element 41, the tip electrode member 42, the rear electrode member 44, and the rear insulating member 45 are arranged in the axial direction in the order of the tip electrode member 42, the piezoelectric element 41, the rear electrode member 44, and the rear insulating member 45.

[0088] Next, in the first tube installation process (step 102), the insulating tube 50 is installed so that both openings of the insulating tube 50 are aligned along the axial direction and the inner surface of the insulating tube 50 faces the outer surfaces of the front electrode member 42, the piezoelectric element 41, the rear electrode member 44, and the rear insulating member 45.

[0089] Next, in the second tube installation process (step 103), a conductive tube, which is an example of the conductive layer 501, is installed so that both openings are aligned along the axial direction and the inner surface of the conductive tube faces the outer surface of the insulating tube 50.

[0090] Finally, in the heat shrinking step (step 104), the insulating tube 50 and the conductive tube (conductive layer 501) are heated to shrink them in the radial direction. This allows the insulating tube 50 to be tightly attached to the outer circumferential surfaces of the front electrode member 42, the piezoelectric element 41, the rear electrode member 44, and the rear insulating member 45, and also allows the conductive tube (conductive layer 501) to be tightly attached to the outer circumferential surface of the insulating tube 50.

[0091] Here, in the heat shrinking step, one of the following two methods is selected: a method in which the insulating tube 50 is heated to shrink it, and then the conductive tube (conductive layer 501) is heated to shrink it (hereinafter referred to as the "two-stage heat shrinking method"), or a method in which the insulating tube 50 and the conductive tube (conductive layer 501) are heated to shrink it simultaneously (hereinafter referred to as the "batch heat shrinking method"). This completes the piezoelectric module 400, in which the conductive layer 501 is formed on the outer peripheral surface of the insulating tube 50.

[0092] When the two-stage heat shrinking method is selected, the insulating tube 50 is heated and shrunk, and then the conductive tube (conductive layer 501) is heated and shrunk. This allows the insulating tube 50 and the conductive tube (conductive layer 501) to be heated separately, making it possible to heat them for a heating time and at a heating temperature that matches the heat shrinkage rate of each heat-shrinkable tube. In contrast, when the all-at-once heat shrinking method is selected, the insulating tube 50 and the conductive tube (conductive layer 501) are heated and shrunk simultaneously. This allows the insulating tube 50 and the conductive tube (conductive layer 501) to be heated and shrunk at the same time, making it possible to shorten the time required for the heat shrinking process.

[0093] As a specific example of a method for forming a conductive layer on the outside of an insulating layer, the configuration shown in Figure 5(A) above, i.e., a method for realizing a configuration in which a conductive layer 501 is formed on the outer surface of the insulating tube 50, has been described. However, the configurations shown in Figures 5(B) to 5(D) can also be realized by undergoing steps similar to the second tube installation step and heat shrinking step in Figure 6.

[0094] 5(B), when the conductive layer 484 is formed on the outer peripheral surface of the holding member 48, before the holding member 48 is disposed radially inside the support member 53, the conductive tube (conductive layer 484) is placed so that both openings of the conductive tube (conductive layer 484) are aligned in the axial direction and the inner peripheral surface of the conductive tube (conductive layer 484) faces the outer peripheral surface of the holding member 48. The conductive tube (conductive layer 484) is then heated to shrink it in the radial direction and adhere it to the outer peripheral surface of the holding member 48. This allows the conductive tube (conductive layer 484) to be formed on the outer peripheral surface of the holding member 48.

[0095] 5(C), when the conductive layer 431 is formed on the outer peripheral surface of the tip insulating member 43, before the tip insulating member 43 is placed in the opening on the axial tip side of the through-hole provided in the pressing member 49, the conductive tube (conductive layer 431) is placed so that both openings of the conductive tube (conductive layer 431) are aligned in the axial direction and the inner peripheral surface of the conductive tube (conductive layer 431) faces the outer peripheral surface of the tip insulating member 43. The conductive tube (conductive layer 431) is then heated to shrink in the radial direction and adhere to the outer peripheral surface of the tip insulating member 43. This allows the conductive tube (conductive layer 431) to be formed on the outer peripheral surface of the tip insulating member 43.

[0096] 5(D), when the conductive layer 521 is formed on the outer peripheral surface of the second insulating member 52, before the second insulating member 52 is disposed radially inside the first inner casing 35, the conductive tube (conductive layer 521) is placed so that both openings of the conductive tube (conductive layer 521) are aligned in the axial direction and the inner peripheral surface of the conductive tube (conductive layer 521) faces the outer peripheral surface of the second insulating member 52. The conductive tube (conductive layer 521) is then heated to shrink it in the radial direction and adhere it to the outer peripheral surface of the second insulating member 52. This allows the conductive tube (conductive layer 521) to be formed on the outer peripheral surface of the second insulating member 52.

[0097] Here, as shown in Figure 5 (D), examples of a method for forming the conductive layer 521 on the inner surface of the second insulating member 52 include a method of applying paint to the inner surface of the second insulating member 52 to form the conductive layer 521.

[0098] [Example of step misalignment] FIG. 7 is a graph showing a specific example of deviation (step deviation) of a pressure waveform output from a pressure detected by a conventional pressure detection device. FIG. 7 shows a graph in which the pressure detected by a conventional pressure detection device is output as a pressure waveform. The graph in FIG. 7 has "time" on the horizontal axis and "pressure" on the vertical axis, and a "step shift" occurs in the area indicated by the dashed line. This occurs because negative frictional charges are mixed into the input path of the integrating circuit, causing the reference line for judging the measured pressure value to temporarily shift to the negative side. In contrast, the pressure detection device 1 configured as shown in FIGS. 1 to 6 described above takes measures such as those shown in FIGS. 5(A) to 5(D), thereby suppressing changes in pressure detection due to static electricity generated inside the pressure detection device 1. As a result, the "step shift" shown in the graph in FIG. 7 is suppressed.

[0099] In summary, the pressure detection device 1 to which the present invention is applied is sufficient if it has the following configuration, and can take on a variety of different embodiments. That is, the pressure detection device 1 to which the present invention is applied comprises a piezoelectric element 41 that outputs an electrical signal corresponding to pressure applied in the axial direction from the axial tip side, which is one end side, to the axial rear end side, which is the other end side; a leading electrode member 42 that is conductive and serves as a first electrode member arranged on the axial tip side of the piezoelectric element 41; a rear electrode member 44 that is conductive and serves as a second electrode member arranged on the axial rear end side of the piezoelectric element 41; an insulating tube 50 that is cylindrical and insulating, and houses at least one of the leading electrode member 42, the piezoelectric element 41, and the rear electrode member 44 that are lined up along the axial direction, with its inner circumferential surface in contact with the outer circumferential surface of at least one of the leading electrode member 42, the piezoelectric element 41, and the rear electrode member 44; and a pressure member 49 that is cylindrical and conductive, and houses the leading electrode member 42, the piezoelectric element 41, the rear electrode member 44, and the insulating tube 50 inside, and is electrically connected to the leading electrode member 42, and a conductive layer 501 that is conductive is formed on the outer circumferential surface of the insulating tube 50.

[0100] As a result, the conductive layer 501 having conductivity is formed on the outer peripheral surface of the insulating tube 50 having insulating properties, so that static electricity generated by temporary contact or friction between the insulating tube 50 and the pressure member 49 can be released to the pressure member 49 side via the conductive layer 501. As a result, changes in pressure detection caused by static electricity generated inside the pressure detection device 1 can be suppressed.

[0101] Here, the insulating tube 50 may be characterized by having heat shrinkability. As a result, by thermally shrinking the insulating tube 50 that houses at least one of the leading electrode member 42, the piezoelectric element 41, and the trailing electrode member 44 inside, the members placed inside the insulating tube 50 can be reliably insulated by the insulating tube 50. Furthermore, when multiple members are housed inside the insulating tube 50, the members housed inside can also be reliably positioned.

[0102] Here, the conductive layer 501 may be characterized as being a conductive tube that is cylindrical, conductive, and heat-shrinkable, and that houses at least one of the leading electrode member 42, the piezoelectric element 41, the trailing electrode member 44, and the insulating tube 50 arranged along the axial direction, and whose inner surface contacts the outer surface of each of the insulating tubes 50. As a result, the conductive layer 501 is composed of a conductive tube whose inner surface is in contact with the outer surface of the insulating tube 50. As a result, the conductive tube before heat shrinking can be placed radially outside the insulating tube 50 that houses at least one of the front electrode member 42, the piezoelectric element 41, and the rear electrode member 44, and then heat-shrunk, thereby easily forming the conductive layer 501 on the outer surface of the insulating tube 50.

[0103] The conductive layer 501 may be characterized by being made of a fluororesin containing a conductive material. As a result, since the conductive layer 501 is made of a fluororesin containing a conductive material, the heat resistance and releasability of the conductive layer 501 can be improved.

[0104] Furthermore, the pressure detection device 1 to which the present invention is applied comprises a piezoelectric element 41 that outputs an electrical signal corresponding to pressure applied in the axial direction from the axial tip side to the rear end side, a conductive tip electrode member 42 that is electrically conductive and arranged on the axial tip side of the piezoelectric element 41, a conductive rear electrode member 44 that is electrically conductive and arranged on the axial rear end side of the piezoelectric element 41, a rod-shaped, conductive conductive member 47 to which the rear end electrode member 44 is electrically connected, a cylindrical, insulating holding member 48 that holds the conductive member 47 by accommodating the axial tip side of the holding member 48 therein, and a cylindrical, conductive support member 53 that is accommodated inside a pressure member 49 that accommodates the axial tip side of the holding member 48 therein and whose axial tip side is conductive, and is a pressure detection device characterized in that a conductive conductive layer 484 is formed on the outer surface of the holding member 48.

[0105] As a result, conductive layer 484 having conductivity is formed on the outer peripheral surface of insulating holding member 48, so static electricity generated by temporary contact or friction between holding member 48 and support member 53 can be released to the support member 53 side via conductive layer 484. As a result, changes in pressure detection caused by static electricity generated inside pressure detection device 1 can be suppressed.

[0106] Here, the support member 53 may be characterized in that it accommodates the axial tip side of the holding member 48 therein, thereby supporting the holding member 48 either constantly or temporarily. This allows static electricity generated by temporary contact or friction between the holding member 48 and the support member 53 to escape to the support member 53 side via the conductive layer 484. As a result, changes in pressure detection caused by static electricity generated inside the pressure detection device 1 can be suppressed.

[0107] The pressure detection device 1 to which the present invention is applied includes a piezoelectric element 41 that outputs an electrical signal corresponding to pressure applied in the axial direction from the front end side to the rear end side in the axial direction, a front electrode member 42 that is conductive and arranged on the front end side of the piezoelectric element 41 in the axial direction, a rear electrode member 44 that is conductive and arranged on the rear end side of the piezoelectric element 41 in the axial direction, a cylindrical and conductive pressure member 49 that houses the front electrode member 42, the piezoelectric element 41, and the rear electrode member 44 inside and is electrically connected to the front electrode member 42, and an annular and This pressure detection device is characterized by having a first insulating member 51 and a second insulating member 52 that are insulating members that are arranged on the outer periphery of a pressure member 49, and a first inner housing 35 that is cylindrical and conductive and serves as a housing that houses the pressure member 49, the first insulating member 51, and the second insulating member 52, and in which conductive conductive layers (for example, conductive layers 521 and 522 formed on the outer periphery of the second insulating member 52) are formed on the outer or inner surfaces of each of the first insulating member 51 and the second insulating member 52.

[0108] As a result, the conductive layer 521, which is conductive, is formed on the outer peripheral surface of the insulating second insulating member 52, so that static electricity generated by temporary contact or friction between the second insulating member 52 and the first inner housing 35 can be dissipated to the first inner housing 35 via the conductive layer 521. Furthermore, the conductive layer 522 is formed on the inner peripheral surface of the second insulating member 52, so that static electricity generated by temporary contact or friction between the second insulating member 52 and the pressure member 49 can be dissipated to the pressure member 49 via the conductive layer 522. Furthermore, static electricity generated by temporary contact or friction between the first insulating member 51 and the first inner housing 35 can be dissipated to the first inner housing 35 via the conductive layer (not shown). Furthermore, static electricity generated by temporary contact or friction between the first insulating member 51 and the pressure member 49 can be dissipated to the pressure member 49 via the conductive layer (not shown). As a result, changes in pressure detection due to static electricity generated inside the pressure detection device 1 can be suppressed.

[0109] Furthermore, a piezoelectric module 400 to which the present invention is applicable is a piezoelectric module characterized in that it comprises a piezoelectric element 41 that outputs an electrical signal corresponding to pressure applied in the axial direction from the tip end to the rear end in the axial direction, a conductive tip electrode member 42 that is arranged on the tip end side of the piezoelectric element 41 in the axial direction, a conductive rear electrode member 44 that is arranged on the rear end side of the piezoelectric element 41 in the axial direction, and an insulating tube 50 that is cylindrical and insulating, and houses the tip electrode member 42, piezoelectric element 41, and rear electrode member 44 that are lined up along the axial direction, with its inner surface in contact with the outer surfaces of the tip electrode member 42, piezoelectric element 41, and rear electrode member 44, and a conductive conductive layer 501 that is formed on the outer surface of the insulating tube 50.

[0110] Here, the insulating tube 50 may be characterized by having heat shrinkability.

[0111] Furthermore, a method for manufacturing a piezoelectric module 400 to which the present invention is applicable includes an arrangement step of arranging a piezoelectric element 41, which outputs an electrical signal in response to pressure applied in the axial direction from the tip end to the rear end in the axial direction, a conductive tip electrode member 42, and a conductive rear electrode member 44, in the order of tip electrode member 42, piezoelectric element 41, and rear electrode member 44 along the axial direction; a first tube installation step of installing a cylindrical insulating tube 50 that is insulating and heat-shrinkable so that both openings of the insulating tube 50 are aligned along the axial direction and the inner circumferential surface of the insulating tube 50 faces the outer circumferential surfaces of the tip electrode member 42, piezoelectric element 41, and rear electrode member 44; a second tube installation step of installing a cylindrical conductive tube as a conductive layer 501 that is conductive so that both openings of the conductive tube are aligned along the axial direction and the inner circumferential surface of the conductive tube faces the outer circumferential surface of the insulating tube 50; and a heat shrinking step of heating the insulating tube 50 and the conductive tube to shrink them toward their inner circumferential surfaces.

[0112] Here, the heat shrinking step may be characterized in that after the insulating tube 50 is heated and shrunk, the conductive tube serving as the conductive layer 501 is heated and shrunk. As a result, the insulating tube 50 is heated and shrunk, and then the conductive tube serving as the conductive layer 501 is heated and shrunk. As a result, the insulating tube 50 and the conductive tube are heated separately, and it becomes possible to heat them for a heating time and at a heating temperature that matches the thermal shrinkage rate of each heat-shrinkable tube.

[0113] In addition, the heat shrinking step may be characterized in that the insulating tube 50 and the conductive tube serving as the conductive layer 501 are simultaneously heated and shrunk. This causes the insulating tube and the conductive tube serving as the conductive layer 501 to be heated and shrunk simultaneously. As a result, the insulating tube 50 and the conductive tube are heated and shrunk at the same time, which makes it possible to shorten the time required for the heat shrinking process.

[0114] Although the present embodiment has been described above, the technical scope of the present invention is not limited to the above embodiment. Various modifications and alternative configurations that do not deviate from the scope of the technical concept of the present invention are included in the present invention. In the above embodiment, a piezoelectric element 41 is used in the detection mechanism section 40 of the pressure detection device 1, but the configuration of the detection mechanism section 40 can be replaced with various types of detection mechanisms that are conventionally known. For example, a strain gauge or the like may be used instead of the piezoelectric element 41. When a strain gauge is used, in addition to the above embodiment, it is necessary to provide a power supply path for supplying power to the strain gauge in the pressure detection device.

[0115] Furthermore, for example, in the above-described embodiment, the boundary between the conductive member 47 and the holding member 48 is tightly joined by insert molding, but this is not limiting. For example, the conductive member 47 and the holding member 48 may be disposed as separate members. In this case, friction or the like may occur between the conductive conductive member 47 and the conductive holding member 48, which may disrupt the charge balance and cause the above-described "step misalignment." Therefore, a configuration similar to the configuration shown in Figures 5(A) to 5(D) may be employed, i.e., a configuration in which a conductive layer is provided on the outer peripheral surface of the conductive member 47 on the radially outer side. [Explanation of symbols]

[0116] 1...pressure detection device, 10...internal combustion engine, 35...first internal housing, 41...piezoelectric element, 42...tip electrode member, 43...tip insulating member, 44...rear electrode member, 47...conductive member, 48...holding member, 49...pressure member, 50...insulating tube, 51...first insulating member, 52...second insulating member, 53...support member, 400...piezoelectric module, 431, 484, 501, 521, 522...conductive layer

Claims

1. a piezoelectric element that outputs an electrical signal according to a pressure applied in an axial direction from one end to the other end; a first electrode member that is electrically conductive and is disposed on the one end side of the piezoelectric element; a second electrode member that is conductive and is disposed on the other end side of the piezoelectric element; an insulating tube having a cylindrical shape and insulating properties, accommodating at least one of the first electrode member, the piezoelectric element, and the second electrode member arranged along the axial direction, and having an inner circumferential surface in contact with an outer circumferential surface of at least one of the first electrode member, the piezoelectric element, and the second electrode member; a pressure member that is cylindrical and conductive, that accommodates the first electrode member, the piezoelectric element, the second electrode member, and the insulating tube therein, and that is electrically connected to the first electrode member; a conductive layer having electrical conductivity is formed on the outer peripheral surface of the insulating tube, Pressure detection device.

2. The insulating tube is heat-shrinkable. The pressure detection device according to claim 1.

3. the conductive layer is a conductive tube that is tubular, conductive, and heat-shrinkable, that accommodates at least one of the first electrode member, the piezoelectric element, the second electrode member, and the insulating tube that are arranged along the axial direction, and whose inner circumferential surface contacts the outer circumferential surfaces of the insulating tubes. The pressure detection device according to claim 1 or 2.

4. The conductive layer is made of a fluororesin containing a conductive material. The pressure detection device according to claim 1 or 2.

5. a piezoelectric element that outputs an electrical signal according to a pressure applied in an axial direction from one end to the other end; a first electrode member that is electrically conductive and is disposed on the one end side of the piezoelectric element; a second electrode member that is conductive and is disposed on the other end side of the piezoelectric element; a rod-shaped conductive member having electrical conductivity, to which the second electrode member is electrically connected; a holding member having a cylindrical shape and insulating properties, the holding member accommodating the other end of the conductive member therein to hold the conductive member; a support member having a cylindrical shape and being conductive, the support member accommodating the one end side of the holding member and the one end side of the support member being accommodated inside a conductive pressing member, A conductive layer having conductivity is formed on the outer peripheral surface of the holding member. Pressure detection device.

6. The support member accommodates the one end side of the holding member therein to support the holding member constantly or temporarily.

6. The pressure detection device according to claim 5.

7. a piezoelectric element that outputs an electrical signal according to a pressure applied in an axial direction from one end to the other end; a first electrode member that is electrically conductive and is disposed on the one end side of the piezoelectric element; a second electrode member that is conductive and is disposed on the other end side of the piezoelectric element; a cylindrical, electrically conductive pressure member that accommodates the first electrode member, the piezoelectric element, and the second electrode member therein and is electrically connected to the first electrode member; an insulating member having an annular shape and insulating properties, and disposed on an outer periphery of the pressure member; a cylindrical, conductive housing that accommodates the pressure member and the insulating member therein; A conductive layer having conductivity is formed on the outer peripheral surface or the inner peripheral surface of the insulating member. Pressure detection device.

8. a piezoelectric element that outputs an electrical signal according to a pressure applied in an axial direction from one end to the other end; a first electrode member that is electrically conductive and is disposed on the one end side of the piezoelectric element; a second electrode member that is conductive and is disposed on the other end side of the piezoelectric element; an insulating tube having a cylindrical shape and insulating properties, accommodating the first electrode member, the piezoelectric element, and the second electrode member arranged along the axial direction, and having an inner circumferential surface of the insulating tube in contact with the outer circumferential surfaces of the first electrode member, the piezoelectric element, and the second electrode member; a conductive layer having electrical conductivity is formed on the outer peripheral surface of the insulating tube, Piezoelectric module.

9. The insulating tube is heat-shrinkable. The piezoelectric module according to claim 8 .

10. an arrangement step of arranging a piezoelectric element that outputs an electric signal according to pressure applied in an axial direction from one end side to the other end side, a first electrode member having conductivity, and a second electrode member having conductivity in the order of the first electrode member, the piezoelectric element, and the second electrode member along the axial direction; a first tube installation step of installing a cylindrical insulating tube having insulating properties and heat shrinkability such that both openings of the insulating tube are aligned along the axial direction and the inner peripheral surface of the insulating tube faces the outer peripheral surfaces of the first electrode member, the piezoelectric element, and the second electrode member; a second tube installation step of installing a cylindrical conductive tube such that both openings of the conductive tube are aligned along the axial direction and the inner peripheral surface of the conductive tube faces the outer peripheral surface of the insulating tube; a heat shrinking step of heating the insulating tube and the conductive tube to shrink them toward their inner circumferential surfaces; 2. A method for manufacturing a piezoelectric module, comprising:

11. In the heat shrinking step, the insulating tube is heated to shrink, and then the conductive tube is heated to shrink. The method for manufacturing a piezoelectric module according to claim 10.

12. In the heat shrinking step, the insulating tube and the conductive tube are simultaneously heated and shrunk. The method for manufacturing a piezoelectric module according to claim 10.

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