Pressure Detector

Abstract

To provide a pressure detection device in which the effect upon other regions due to the contact of a weld bead in a welded section is suppressed.SOLUTION: The pressure detection device comprises: a cylindrical tip-side housing 31; a piezoelectric element 41 for detecting a pressure change and provided in this tip-side housing 31; a tip electrode member 42 for conveying pressure to the piezoelectric element 41 and arranged adjacent to the piezoelectric element 41 in this tip-side housing 31; a pressure member 49 for causing a load to act upon the piezoelectric element 41 and fixed to the tip-side housing 31 so as to press this tip electrode member 42 toward the axial direction of the tip-side housing 31; and an abutment pipe 57 for fixing the pressure member 49 in place in the inside of the tip-side housing 31 by being welded to the tip-side housing 31. Meanwhile, the pressure member 49 includes a retreat part 494 for avoiding the welded section of the tip-side housing 31 and the abutment pipe 57 while being fixed in place by the abutment pipe 57.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to a pressure detection device that detects pressure using a detection element. [Background technology]

[0002] 2. Description of the Related Art As a device for detecting pressure in a combustion chamber of an internal combustion engine or the like, a device using a detection element such as a piezoelectric element has been proposed.

[0003] For example, Patent Document 1 describes a pressure detection device comprising a cylindrical housing, a diaphragm attached to the front end of the housing, a piezoelectric element arranged on the rear end side of the diaphragm within the housing and detecting pressure acting through the diaphragm, a pressure transmission section arranged between the diaphragm and the piezoelectric element within the housing in contact with both the diaphragm and the piezoelectric element and transmitting the pressure acting through the diaphragm to the piezoelectric element, and a pressure member fixed to the housing so as to apply pressure to the pressure transmission section in the axial direction of the housing, thereby applying a load to the piezoelectric element, with the housing and pressure member fixed by laser welding. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5820759 Summary of the Invention [Problem to be solved by the invention]

[0005] In a pressure detection device, laser welding may be used to attach multiple components constituting a housing together, or to attach the housing to components such as a diaphragm head or a support member. When laser welding is performed, a weld bead is generated, which causes the welded portion of the component to bulge. When a weld bead is generated, the raised portion of the weld bead may come into contact with a component that is disposed near the welded portion but spaced apart from the welded portion. This may cause an effect such as an injury to the component that the weld bead comes into contact with. The present invention aims to suppress the influence of a weld bead at a welded portion of a pressure detection device on other portions due to contact with the weld bead. [Means for solving the problem]

[0006] The pressure detection device of the present invention that achieves the above object includes a cylindrical housing, a piezoelectric element provided within the housing and detecting a change in pressure, a pressure transmission part disposed within the housing in contact with the piezoelectric element and transmitting pressure to the piezoelectric element, a pressure member fixed to the housing so as to apply pressure to the pressure transmission part in the axial direction of the housing and apply a load to the piezoelectric element, and a fixing member welded to the housing to fix the pressure member within the housing. The pressure member has a retracted part that avoids the welded portion between the housing and the fixing member when fixed by the fixing member. Here, the retracted portion of the pressure member may be at least a portion of the pressure member that faces the welded portion between the housing and the fixed member, and may be formed lower than an adjacent portion. More preferably, a groove extending in a direction along the welded portion may be formed in a portion facing the welded portion as the retracted portion of the pressure member. In addition, the retracted portion of the pressure applying member may be provided at least in a portion of the pressure applying member facing the welded portion between the housing and the fixed member, and a portion of the pressure applying member adjacent to the retracted portion may be formed higher than the retracted portion. Also, preferably, the pressure member is conductive and electrically connected to the piezoelectric element, and the housing and the fixing member are conductive and electrically insulated from the pressure member and the piezoelectric element. In addition, in the above pressure detection device, the pressure application member is cylindrical and has a protrusion that protrudes outward from its outer peripheral surface, and the pressure application member is fixed by welding the housing and the fixing member with the inner peripheral surface of the housing and the fixing member sandwiching the protrusion of the pressure application member through the insulating member, and the portion of the outer peripheral surface of the pressure application member that is different from the protrusion and that faces the insulating member when fixed inside the housing is formed higher than the portion facing the welded point and comes into contact with the insulating member. Another pressure detection device of the present invention that achieves the above object includes a detection element that detects pressure changes, a first housing that is conductive and accommodates the detection element therein and is electrically connected to the detection element, a second housing that is conductive and accommodates the first housing therein and is electrically insulated from the detection element, and a fixing member that fixes the first housing by being welded to the second housing. The first housing has a recess in a portion facing a portion where a member will swell due to welding to the second housing, to avoid contact with the swell of the member. Here, the first housing may be configured such that a groove is formed in a portion opposite to a portion where a bulge occurs in a member due to welding, the groove extending in a direction along the welded portion of the second housing. Effect of the Invention

[0007] According to the present invention, it is possible to suppress the influence of the weld bead at the welded portion of the pressure detection device on other portions due to contact with the weld bead. [Brief description of the drawings]

[0008] [Figure 1] 1 is a schematic configuration diagram of a pressure detection system according to an embodiment. [Diagram 2] FIG. [Diagram 3] 3 is a cross-sectional view (a cross-sectional view taken along line III-III in FIG. 2) of the pressure detection device. [Figure 4] FIG. 2 is an enlarged cross-sectional view of the tip side of the pressure detection device. [Diagram 5] FIG. [Figure 6] FIG. [Figure 7] 5 is an enlarged view of the first welded portion and the retreated portion in the cross section shown in FIG. 4. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. [Pressure detection system configuration] FIG. 1 is a schematic configuration diagram of a pressure detection system 1 according to an embodiment. This pressure detection system 1 includes a pressure detection device 20 that detects the pressure (combustion pressure) in the combustion chamber C of the internal combustion engine 10, a control device 80 that supplies power to the pressure detection device 20 and controls the operation of the internal combustion engine 10 based on the pressure detected by the pressure detection device 20, and a connection cable 90 that electrically connects the pressure detection device 20 and the control device 80.

[0010] Here, the internal combustion engine 10, which is the target of pressure detection, has a cylinder block 11 in which a cylinder is formed, a piston 12 that reciprocates in the cylinder, and a cylinder head 13 that is fastened to the cylinder block 11 and constitutes a combustion chamber C together with the piston 12, etc. The cylinder head 13 is provided with a communication hole 13a that communicates the combustion chamber C with the outside. The pressure detection device 20 is attached to the internal combustion engine 10 by inserting the tip end of the pressure detection device 20 into this communication hole 13a and fixing a rib portion 312b (see FIG. 2 described later) provided on the pressure detection device 20 to the cylinder head 13. Here, the cylinder block 11, the piston 12, and the cylinder head 13 that constitute the internal combustion engine 10 are made of a metallic material having electrical conductivity, such as cast iron or aluminum.

[0011] [Configuration of pressure detection device] Fig. 2 is a side view of the pressure detection device 20. Fig. 3 is a cross-sectional view (cross-sectional view taken along line III-III in Fig. 2) of the pressure detection device 20. Fig. 4 is an enlarged cross-sectional view of the tip side of the pressure detection device 20.

[0012] The pressure detection device 20 of this embodiment has a housing part 30 exposed to the outside, a detection mechanism part 40 including various mechanisms for detecting pressure, which is almost entirely housed in the housing part 30 and partly exposed to the outside (a connection member 54 described later), and a seal part 70 attached to the outer circumferential surface of the housing part 30. The pressure detection device 20 is attached to the internal combustion engine 10 shown in FIG. 1 so that the left side in FIG. 2 (the part where the housing part 30 is exposed) faces the combustion chamber C (the lower side in FIG. 1) and the right side in FIG. 2 (the part where the detection mechanism part 40 is exposed) faces the outside (the upper side in FIG. 1). In this state, the seal part 70 is located inside the communication hole 13a provided in the cylinder head 13. In the following description, the side facing the left in FIG. 2 is referred to as the "front end side" of the pressure detection device 20, and the side facing the right in FIG. 2 is referred to as the "rear end side" of the pressure detection device 20. In the following description, the center line direction of the pressure detection device 20 indicated by the dashed line in FIG. 2 will be simply referred to as the center line direction.

[0013] [Housing configuration] The housing portion 30 includes a front end housing 31 , a diaphragm head 32 attached to the front end side of the front end housing 31 , and a rear end housing 33 attached to the rear end side of the front end housing 31 .

[0014] (Tip side housing) The tip side housing 31 is a member having a hollow structure and a cylindrical shape as a whole. The tip side housing 31 is made of a metal material such as stainless steel that is conductive and has high heat resistance and acid resistance. The axial direction of the cylindrical tip side housing 31 coincides with the above-mentioned center line direction. The tip side housing 31 is an example of a housing and an example of a second housing.

[0015] The tip side housing 31 has a first tip side housing 311 located relatively closer to the tip side, and a second tip side housing 312 located relatively closer to the rear end side. Here, the tip side housing 31 is configured such that the outer peripheral surface of the rear end side of the first tip side housing 311 and the inner peripheral surface of the tip side of the second tip side housing 312 are laser welded together to form an integrated body. The diaphragm head 32 is attached to the tip side of the first tip side housing 311 by laser welding, and the rear side housing 33 is attached to the rear end side of the second tip side housing 312 by fitting.

[0016] Here, a recess 311a is provided on the outer circumferential surface of the first tip side housing 311 for mounting a first seal member 71 (details of which will be described later) constituting the seal portion 70. Also, inside the first tip side housing 311, there is a portion on the tip side set to a first diameter, and a portion on the rear end side set to a second diameter larger than the first diameter, and an inner step portion 311b connecting the two portions is provided at the boundary between these two portions.

[0017] Meanwhile, a recess 312a is provided on the outer circumferential surface of the second tip side housing 312 for mounting a second seal member 72 (described in detail later) which constitutes the seal portion 70 together with the first seal member 71. Also, a ring-shaped rib portion 312b protruding outward is provided on the outer circumferential surface of the second tip side housing 312, on the rear end side of the recess 312a. As described above, this rib portion 312b is used to fix the pressure detection device 20 to the internal combustion engine 10 (more specifically, the cylinder head 13).

[0018] (Diaphragm head) The diaphragm head 32 is a member having a disk shape as a whole. The diaphragm head 32 is made of a metal material such as stainless steel that is conductive and has high heat resistance and acid resistance. In particular, in this example, the diaphragm head 32 and the tip side housing 31 are made of the same material.

[0019] The diaphragm head 32 has a recess 32b formed in the center of the tip side, a pressure receiving surface (front surface) 32a exposed to the outside (combustion chamber C side) and receiving pressure, a recess 32c formed by cutting out an annular shape in the back surface of the pressure receiving surface 32a, and a protrusion 32d protruding from the center (the portion where the recess 32b is formed) of the pressure receiving surface 32a to the rear end side due to the presence of the recess 32c. The diaphragm head 32 is provided so as to close the opening on the tip side of the first tip side housing 311. The boundary between the diaphragm head 32 and the first tip side housing 311 is laser welded around the entire circumference of the outer circumferential surface.

[0020] (Rear end housing) The rear end housing 33 is a member having a hollow structure and a cylindrical shape as a whole. The rear end housing 33 is made of a metal material such as stainless steel that is conductive and has high heat resistance and acid resistance. However, since the rear end housing 33 is located outside the internal combustion engine 10 when the pressure detection device 20 is attached to the internal combustion engine 10, a material having lower heat resistance and acid resistance than the front end housing 31 can be used for the rear end housing 33. The axial direction of the cylindrical rear end housing 33 coincides with the above-mentioned center line direction.

[0021] The rear housing 33 has a first rear housing 331 located relatively closer to the front end and a second rear housing 332 located relatively closer to the rear end. Here, the rear housing 33 is configured such that the first rear housing 331 and the second rear housing 332 are integrated together by fitting the outer peripheral surface of the front end of the second rear housing 332 into the inner peripheral surface of the rear end of the first rear housing 331. The front housing 31 (more specifically, the second front housing 312) is attached to the front end of the first rear housing 331 by fitting, and a connection member 54 (described in detail later) is attached to the rear end of the second rear housing 332 by fitting.

[0022] [Detection mechanism configuration] The detection mechanism 40 includes a piezoelectric element 41, a front electrode member 42, and a rear electrode member 43. The detection mechanism 40 also includes an insulating ring 45, a first coil spring 46, a conductive member 47, and a holding member 48. The detection mechanism 40 also includes a pressure member 49, a support member 50, a second coil spring 51, and a housing member 52. The detection mechanism 40 also includes a circuit board 53, a connection member 54, a ground plate 55, and an O-ring 56. The detection mechanism 40 also includes a butting pipe 57. The detection mechanism 40 also includes an insulating pipe 60, a first insulating member 61, a second insulating member 62, a third insulating member 63, a fourth insulating member 64, and a fifth insulating member 65.

[0023] (Piezoelectric element) The piezoelectric element 41 is a member having a cylindrical shape as a whole. The piezoelectric element 41 is an example of a detection element that detects changes in pressure. The piezoelectric element 41 includes a piezoelectric body that exhibits a piezoelectric action of the piezoelectric longitudinal effect. The piezoelectric longitudinal effect means that when an external force is applied to a stress application axis in the same direction as the charge generation axis of the piezoelectric body, a charge is generated on the surface of the piezoelectric body in the charge generation axis direction. The piezoelectric element 41 is disposed inside the tip side housing 31 and on the rear end side of the diaphragm head 32. The piezoelectric element 41 is housed in the tip side housing 31 so that the center line direction is the direction of the stress application axis. Here, the piezoelectric element 41 is disposed inside the pressure member 49 provided inside the tip side housing 31 and inside the insulating pipe 60 provided inside the pressure member 49. The outer diameter of the piezoelectric element 41 is slightly smaller than the inner diameter of the insulating pipe 60 that houses the piezoelectric element 41 inside. The tip side surface of the piezoelectric element 41 is in contact with the rear end side surface of the tip electrode member 42. On the other hand, the rear end surface of the piezoelectric element 41 is in contact with the front end surface of the rear end electrode member 43. Also, the outer circumferential surface of the piezoelectric element 41 faces the inner circumferential surface of the insulating pipe 60. By providing the insulating pipe 60 between the inner circumferential surface of the pressure applying member 49 and the outer circumferential surface of the piezoelectric element 41 in this manner, the pressure applying member 49 and the piezoelectric element 41 are not in direct contact with each other.

[0024] Next, a case where the piezoelectric transverse effect is used in the piezoelectric element 41 will be illustrated. The piezoelectric transverse effect means that when an external force is applied to a stress application axis at a position perpendicular to the charge generation axis of the piezoelectric body, a charge is generated on the surface of the piezoelectric body in the charge generation axis direction. A plurality of thin piezoelectric bodies formed in a thin plate shape may be laminated, and by laminating them in this way, the charge generated in the piezoelectric body can be efficiently collected and the sensitivity of the sensor can be increased. Examples of piezoelectric bodies that can be used in the piezoelectric element 41 include Langasite-based crystals (Langasite, Langatate, Langhanite, LTGA), quartz, and gallium phosphate, which have a piezoelectric longitudinal effect and a piezoelectric transverse effect. In the piezoelectric element 41 of this embodiment, a LTGA single crystal is used as the piezoelectric body.

[0025] (Tip electrode material) The tip electrode member 42 is a member having a cylindrical shape as a whole. The tip electrode member 42 is an example of a pressure transmitting part. The tip electrode member 42 is made of a metal material such as stainless steel that has electrical conductivity and high heat resistance. In addition, an insulating coating 42a is formed on the center of the tip side surface of the tip electrode member 42 by coating with an insulating ceramic material including alumina, zirconia, etc. Here, the insulating coating 42a has, for example, a circular shape, and its diameter is larger than the diameter of the protrusion 32d provided on the back surface of the diaphragm head 32 and smaller than the diameter of the opening provided on the tip side of the pressure member 49.

[0026] The tip electrode member 42 is disposed inside the pressure member 49 provided inside the tip housing 31. The tip electrode member 42 is disposed on the rear end side of the diaphragm head 32, on the tip side of the piezoelectric element 41. However, unlike the above-mentioned piezoelectric element 41, the tip electrode member 42 is not housed in the insulating pipe 60. The outer diameter of the tip electrode member 42 is slightly smaller than the inner diameter of the pressure member 49 that houses the tip electrode member 42. The central area of ​​the tip side surface of the tip electrode member 42 where the insulating film 42a is provided is in contact with the rear end side surface of the protrusion 32d provided on the back surface of the diaphragm head 32. The peripheral area of ​​the tip side surface of the tip electrode member 42 where the insulating film 42a is not provided is in contact with the rear side surface of the opening provided on the tip side of the pressure member 49. On the other hand, the rear end side surface of the tip electrode member 42 is in contact with the tip side surface of the piezoelectric element 41. Further, the outer peripheral surface of the tip electrode member 42 faces the inner peripheral surface of the pressure member 49 .

[0027] (First rear electrode member) The rear electrode member 43 is a member having an overall disk shape and is made of a metal material such as stainless steel that has electrical conductivity, high heat resistance, and a small difference in thermal expansion with respect to the piezoelectric element 41.

[0028] The rear electrode member 43 is disposed inside the pressure member 49 provided inside the front housing 31. The rear electrode member 43 is disposed on the rear end side of the piezoelectric element 41. The rear electrode member 43 is disposed inside the insulating pipe 60 provided inside the pressure member 49. The outer diameter of the rear electrode member 43 is approximately the same as the outer diameter of the piezoelectric element 41 and is slightly smaller than the inner diameter of the insulating pipe 60. The front surface of the rear electrode member 43 is in contact with the rear end surface of the piezoelectric element 41. Meanwhile, the rear end surface of the rear electrode member 43 is in contact with the front end surface of the insulating ring 45. The outer peripheral surface of the rear electrode member 43 faces the inner peripheral surface of the insulating pipe 60. By providing the insulating pipe 60 between the inner peripheral surface of the pressure member 49 and the outer peripheral surface of the rear electrode member 43 in this way, the pressure member 49 and the rear electrode member 43 do not come into direct contact with each other.

[0029] (insulation ring) The insulating ring 45 is an annular member as a whole, and is made of a ceramic material such as alumina that has insulating properties and high heat resistance.

[0030] The insulating ring 45 is disposed inside the pressure member 49 provided inside the tip side housing 31. The insulating ring 45 is located on the rear end side of the rear electrode member 43 and on the tip side of the support member 50. Here, the second convex portion 47b at the tip of the conductive member 47 and the first coil spring 46 attached to the second convex portion 47b are disposed inside the through hole provided in the insulating ring 45. The outer diameter of the insulating ring 45 is slightly smaller than the inner diameter of the pressure member 49. The inner diameter of the through hole of the insulating ring 45 is slightly larger than the outer diameter of the first coil spring 46. The surface on the tip side of the insulating ring 45 is in contact with the surface on the rear end side of the rear electrode member 43. On the other hand, the surface on the rear end side of the insulating ring 45 is in contact with the surface on the tip side of the support member 50. The outer peripheral surface of the insulating ring 45 faces the inner peripheral surface of the pressure member 49. Furthermore, the inner circumferential surface of the insulating ring 45 faces the first coil spring 46 .

[0031] (First coil spring) The first coil spring 46 is a member having a helical shape as a whole, and expands and contracts in the direction of the center line. The first coil spring 46 is made of a metal material such as brass that is conductive and has a higher conductivity than the distal end housing 31, and its surface is gold plated.

[0032] The first coil spring 46 is provided inside the front-end housing 31, and is disposed inside the pressure member 49 and inside the support member 50. The first coil spring 46 is disposed on the rear end side of the rear-end electrode member 43 and on the front end side of the conductive member 47. That is, the first coil spring 46 is disposed across the rear-end electrode member 43 and the conductive member 47. Here, the front end side of the first coil spring 46 is in contact with the surface on the rear end side of the rear-end electrode member 43 in the through hole of the insulating ring 45, and the rear end side of the first coil spring 46 is wound around the second convex portion 47b provided on the front end side of the conductive member 47. The inner diameter of the first coil spring 46 is larger than the outer diameter of the second convex portion 47b provided on the front end side of the conductive member 47 and smaller than the inner diameter of the first convex portion 47a. On the other hand, the outer diameter of the first coil spring 46 is smaller than the inner diameter of the through hole of the insulating ring 45. As a result, the tip of the first coil spring 46 abuts against the surface of the rear end electrode member 43 inside the through hole of the insulating ring 45. In contrast, the rear end of the first coil spring 46 abuts against the boundary (step) between the first convex portion 47a and the second convex portion 47b of the conductive member 47. In addition, the outer periphery of the portion of the first coil spring 46 exposed from the insulating ring 45 faces the inner circumferential surface of the support member 50 via an air gap. In this way, by providing an air gap between the inner circumferential surface of the support member 50 and the first coil spring 46, the support member 50 and the first coil spring 46 do not come into direct contact with each other.

[0033] (Conductive material) The conductive member 47 is a rod-shaped member as a whole. The conductive member 47 is made of a metal material such as brass having electrical conductivity, and its surface is gold-plated. The conductive member 47 is provided at its tip with the above-mentioned first convex portion 47a and second convex portion 47b, and at its rear end with a rear end side convex portion 47c that has a smaller diameter than the central portion in the center line direction and that protrudes toward the rear end side.

[0034] The conductive member 47 is provided inside the tip side housing 31, and almost all parts except the tip and rear end (rear end side convex part 47c) are arranged inside the holding member 48. The tip side of the conductive member 47 is located inside the pressure member 49, the rear end side of the conductive member 47 is located inside the housing member 52, and the intermediate part located between the tip side and the rear end side is located inside the second coil spring 51. The conductive member 47 is located on the rear end side of the first coil spring 46 and on the tip side of the circuit board 53. The conductive member 47 is arranged so as to pass through a through hole provided in the holding member 48 along the center line direction. The outer diameter of the tip part (part not covered by the holding member 48) of the conductive member 47 is smaller than the inner diameter of the support member 50. The outer diameter of the rear end part (rear end side convex part 47c) of the conductive member 47 is approximately the same as the inner width of the holding part provided in the holding member 48. Furthermore, the outer diameter of the central portion of the conductive member 47 in the center line direction is substantially the same as the inner diameter of the holding member 48. The rear end side of the first coil spring 46 is attached to the second protrusion 47b of the conductive member 47, so that the conductive member 47 is in contact with the first coil spring 46. Meanwhile, the rear end side protrusion 47c of the conductive member 47 is fitted into a holding portion provided on the holding member 48. The outer peripheral surface of the tip end of the conductive member 47 faces the inner peripheral surface of the support member 50 via an air gap. The outer peripheral surface of the central portion of the conductive member 47 in the center line direction faces the second coil spring 51 via the holding member 48 and the air gap. The outer peripheral surface of the rear end of the conductive member 47 faces the outer peripheral surface of the accommodation member 52 via the air gap and the holding member 48. In this way, by providing the air gap and the holding member 48 between the inner peripheral surface of the support member 50 and the outer peripheral surface of the conductive member 47, the support member 50 and the conductive member 47 do not come into direct contact with each other. Furthermore, by providing an air gap and retaining member 48 between the inner peripheral surface of second coil spring 51 and the outer peripheral surface of conductive member 47, second coil spring 51 and conductive member 47 do not come into direct contact with each other. Furthermore, by providing an air gap between the inner peripheral surface of accommodating member 52 and the outer peripheral surface of conductive member 47, accommodating member 52 and conductive member 47 do not come into direct contact with each other.

[0035] (holding member) The holding member 48 is a member formed by integrating a cylindrical portion located at the front end side and a plate-shaped portion located at the rear end side. The holding member 48 includes a base material made of synthetic resin material such as PPT (Polypropylene Terephthalate) having insulating properties, and wiring and terminals made of metal material such as copper having conductivity. The cylindrical portion located at the front end side of the holding member 48 houses the conductive member 47, and the plate-shaped portion located at the rear end side of the holding member 48 is attached to the circuit board 53. In this way, the holding member 48 has the function of holding the conductive member 47 and the circuit board 53.

[0036] The portion (outer circumferential surface) of the holding member 48 facing the support member 50, the second coil spring 51, and the housing member 52 is made of synthetic resin material so that no metal material is exposed at this portion. In addition, the portion (inner circumferential surface) of the holding member 48 facing the intermediate portion located between the front end and rear end of the conductive member 47 is also made of synthetic resin material so that no metal material is exposed at this portion. In addition, a holding portion made of metal material is provided at the rear end side of the cylindrical portion of the holding member 48, into which the rear end side protrusion 47c of the conductive member 47 is fitted and held. Wiring for electrically connecting with a signal input terminal (not shown) of the circuit board 53 is attached to this holding portion.

[0037] This holding member 48 is provided straddling the inside of the front-end housing 31 and the inside of the rear-end housing 33. The front-end side of holding member 48 is located inside the pressure member 49, the rear-end side of the conductive member 47 is located inside the accommodating member 52, and an intermediate portion located between the front-end side and the rear-end side is located inside the second coil spring 51. Holding member 48 is disposed on the rear-end side of insulating ring 45 and on the front-end side of connecting member 54.

[0038] The outer diameter of the cylindrical portion located on the tip side of holding member 48 is smaller than the inner diameter of support member 50, and the outer diameter of the plate-like portion located on the rear end side of this covering member is smaller than the inner diameter of accommodating member 52 at this portion. In addition, the outer peripheral surface on the tip side of the cylindrical portion of holding member 48 faces the inner peripheral surface of support member 50 and the inner peripheral surface of second coil spring 51 via an air gap. Furthermore, the outer peripheral surface on the rear end side of the cylindrical portion of holding member 48 and the outer peripheral surface of the plate-like portion are in contact with the inner peripheral surface of accommodating member 52 or face the inner peripheral surface of accommodating member 52 via an air gap.

[0039] (Pressure member) The pressure member 49 is a member having a cylindrical shape as a whole. The pressure member 49 is made of a metal material such as stainless steel that has electrical conductivity and high heat resistance. The pressure member 49 is an example of a first housing.

[0040] Fig. 5 is a perspective view of the pressure member 49. Below, the configuration of the pressure member 49 will be described with reference to Fig. 5. In Fig. 5, the lower left side in the figure is the leading end side, and the upper right side in the figure is the rear end side.

[0041] The pressure member 49 of this embodiment includes a tip tubular portion 491 located at the most distal end side and having an opening at the tip, a rear end tubular portion 493 located at the rear end side of the tip tubular portion 491, and an annular protruding portion 492 provided on the rear end tubular portion 493. In this pressure member 49, the protruding portion 492 has a larger outer diameter than the tip tubular portion 491 and the rear end tubular portion 493, and the rear end tubular portion 493 has a larger outer diameter than the tip tubular portion 491. In the pressure member 49, a step portion 49a is formed at the boundary between the tip tubular portion 491 and the rear end tubular portion 493. More specifically, the step portion 49a is located at the most distal end side of the portion on the tip side of the protruding portion 492 in the rear end tubular portion 493, and is a surface facing the tip side that forms a step between the tip tubular portion 491 and the rear end tubular portion 493, which have different outer diameters. Also, a first pressing surface 49b is provided on the tip side of the protruding portion 492, and a second pressing surface 49c is provided on the rear end side of the protruding portion 492. The inner diameter of the pressing member 49 is the same size except for the opening provided at the tip. Therefore, in this pressing member 49, the thickness of the rear end tubular portion 493 is greater than the thickness of the front end tubular portion 491. Therefore, in the pressing member 49, the front end tubular portion 491 is more flexible (more likely to function as a spring) than the rear end tubular portion 493. Also, in the rear end tubular portion 493, the thickness of the protruding portion 492 is greater than the thickness of the portion other than the protruding portion 492. Furthermore, as will be described in detail later, a retracted portion 494, which is a portion with a thin thickness, is formed on the rear end side of the protruding portion 492 in the rear end tubular portion 493.

[0042] The pressure member 49 is provided inside the tip end housing 31 so that the tip end tubular portion 491 is at the tip end side. The pressure member 49 accommodates the piezoelectric element 41, the tip end electrode member 42, the rear end electrode member 43, the insulating ring 45, the tip end side of the support member 50, the insulating pipe 60, the first coil spring 46, the tip end side of the conductive member 47, and the tip end side of the holding member 48. The pressure member 49 is disposed on the rear end side of the diaphragm head 32 and on the tip end side of the accommodation member 52. The outer diameter of the pressure member 49 differs between the tip end tubular portion 491, the protruding portion 492, and the rear end tubular portion 493, but is smaller than the inner diameter of the tip end housing 31 at all positions. Furthermore, the inner diameter of the pressure applying member 49 is slightly larger than the outer diameters of the tip electrode member 42 and the insulating pipe 60 (piezoelectric element 41, rear electrode member 43, insulating ring 45) at the portion facing the tip electrode member 42 and the insulating pipe 60, and is approximately the same as the outer diameter of the support member 50 at the portion facing the support member 50.

[0043] Here, a butt pipe 57 is disposed between an outer peripheral surface of a rear end cylindrical portion 493 provided on the rear end side of the pressure member 49 and an inner peripheral surface on the rear end side of the first tip side housing 311. The butt pipe 57 is an example of a fixing member. As will be described in detail later, the protruding portion 492 of the pressure member 49 is sandwiched between the inner step portion 311b of the first tip side housing 311 and the butt pipe 57 via the fourth insulating member 64 and the fifth insulating member 65, whereby the pressure member 49 is fixed inside the tip side housing 31.

[0044] The surface (front surface of the opening) of the tip end tubular portion 491 of the pressure member 49 faces the recess 32c of the diaphragm head 32 through an air gap. On the other hand, the rear end side of the rear end tubular portion 493 faces the first insulating member 61 through an air gap. The outer peripheral surface of the tip end tubular portion 491 faces the inner peripheral surface of the first tip side housing 311 through an air gap, and the step portion 49a faces the inner step portion 311b of the first tip side housing 311 through an air gap. The first pressing surface 49b of the protruding portion 492 of the pressure member 49 and the outer peripheral surface of the rear end tubular portion 493 located on the tip side of the first pressing surface 49b face the fourth insulating member 64 arranged in contact with the inner step portion 311b of the tip end tubular portion 491. The outer peripheral surface of the protruding portion 492 faces the inner peripheral surface of the first tip side housing 311 via an air gap. The second pressing surface 49c of the protruding portion 492 and the outer peripheral surface of the rear end tubular portion 493 at a portion adjacent to the rear end side of the second pressing surface 49c face the fifth insulating member 65. The outer peripheral surface of the rear end tubular portion 493 faces the inner peripheral surface of the butt pipe 57 via an air gap. In this way, by providing the air gap, the fourth insulating member 64, and the fifth insulating member 65 between the outer peripheral surface of the pressure member 49 and the inner peripheral surface of the first tip side housing 311 and the inner peripheral surface of the butt pipe 57, the pressure member 49 does not come into direct contact with the first tip side housing 311 and the butt pipe 57.

[0045] (Support member) The support member 50 is a member having an overall cylindrical shape and is made of a metal material such as stainless steel that has electrical conductivity and high heat resistance.

[0046] The support member 50 is provided inside the tip side housing 31, and its tip side is located inside the pressure member 49, and its rear end side protrudes outside the pressure member 49. The support member 50 accommodates the first coil spring 46, the tip side of the conductive member 47, and the tip side of the holding member 48 inside. The support member 50 is disposed on the rear end side of the insulating ring 45 and on the tip side of the housing member 52. The outer diameter of the support member 50 is approximately the same as the inner diameter of the pressure member 49. The inner diameter of the support member 50 varies depending on the position in the center line direction, but is larger than the outer diameter of the first coil spring 46 at a portion facing the first coil spring 46, larger than the outer diameter of the conductive member 47 at a portion facing the conductive member 47, and larger than the outer diameter of the holding member 48 at a portion facing the holding member 48. The surface on the tip side of the support member 50 (the surface on the front side of the opening) is in contact with the surface on the rear end side of the insulating ring 45. On the other hand, the rear end side surface of the support member 50 faces the housing member 52 via an air gap. The tip side of the outer peripheral surface of the support member 50 contacts the inner peripheral surface of the pressure member 49, and the rear end side of the outer peripheral surface of the support member 50 contacts the tip side of the second coil spring 51. Here, the pressure member 49 and the support member 50 are joined and fixed by a second welded portion 59 obtained by laser welding the inner peripheral surface of the rear end side of the pressure member 49 and the outer peripheral surface of the support member 50 facing this portion over one circumference. On the other hand, the inner peripheral surface of the support member 50 faces the first coil spring 46, the conductive member 47, and the holding member 48 via an air gap. In this way, by providing an air gap between the inner peripheral surface of the support member 50 and the first coil spring 46, the conductive member 47, and the holding member 48, the support member 50 does not directly contact the first coil spring 46, the conductive member 47, and the holding member 48.

[0047] (Second coil spring) The second coil spring 51 is a member having a helical shape as a whole, and expands and contracts in the direction of the center line. The second coil spring 51 is made of a metal material such as stainless steel that is conductive and highly heat resistant, and its surface is gold plated. In this manner, in this embodiment, the first coil spring 46 and the second coil spring 51 are made of different materials.

[0048] The second coil spring 51 is provided inside the tip housing 31, and its tip side is located on the rear end side and outside of the support member 50, and its rear end side is located on the tip side and outside of the storage member 52. That is, the second coil spring 51 is disposed across the support member 50 and the storage member 52. The outer diameter of the second coil spring 51 is smaller than the inner diameter of the tip housing 31 (more specifically, the second tip housing 312). The inner diameter of the second coil spring 51 is slightly smaller than the outer diameter of the rear end side of the support member 50 and the outer diameter of the tip side of the storage member 52. The outer periphery of the second coil spring 51 faces the inner peripheral surface of the tip housing 31 via an air gap. In this way, by providing an air gap between the outer periphery of the second coil spring 51 and the inner peripheral surface of the tip housing 31, the second coil spring 51 and the tip housing 31 do not come into direct contact with each other.

[0049] (Housing material) The housing member 52 is a member having a cylindrical shape as a whole. The housing member 52 is made of a metal material such as brass or stainless steel that is conductive and has a higher conductivity than the tip side housing 31, and its surface is gold plated.

[0050] Fig. 6 is a perspective view of the housing member 52. Below, the configuration of the housing member 52 will be described with reference to Fig. 6. Note that in Fig. 6 as well, the lower left side in the figure is the leading end side, and the upper right side in the figure is the rear end side.

[0051] The storage member 52 of this embodiment includes a first cylindrical portion 521 located at the most distal end side and having an opening at the distal end, a second cylindrical portion 522 arranged at the rear end side of the first cylindrical portion 521, a third cylindrical portion 523 arranged at the rear end side of the second cylindrical portion 522, and a fourth cylindrical portion 524 arranged at the rear end side of the third cylindrical portion 523. In this storage member 52, the outer diameters increase in the order of the first cylindrical portion 521, the second cylindrical portion 522, the third cylindrical portion 523, and the fourth cylindrical portion 524. That is, in this storage member 52, the diameter increases in a stepped manner (four steps) from the distal end side to the rear end side. The housing member 52 further includes a first step portion 52a connecting the first cylindrical portion 521 and the second cylindrical portion 522 at the boundary between them, a second step portion 52b connecting the second cylindrical portion 522 and the third cylindrical portion 523 at the boundary between them, and a third step portion 52c connecting the third cylindrical portion 523 and the fourth cylindrical portion 524 at the boundary between them. Unlike the above-mentioned pressurizing member 49, the housing member 52 has a wall thickness set to a constant size regardless of the position in the center line direction. Therefore, in the pressurizing member 49, the inner diameters of the first cylindrical portion 521, the second cylindrical portion 522, the third cylindrical portion 523, and the fourth cylindrical portion 524 increase in this order.

[0052] The housing member 52 is provided so that the first cylindrical portion 521 is at the front end side, straddling the inside of the front end housing 31 and the inside of the rear end housing 33. The rear end side of the conductive member 47, the rear end side of the holding member 48, the circuit board 53, and the ground plate 55 are housed inside the housing member 52. The housing member 52 is disposed at the rear end side of the support member 50 and at the front end side of the connection member 54. The outer diameter of the housing member 52 is different between the first cylindrical portion 521, the second cylindrical portion 522, the third cylindrical portion 523, and the fourth cylindrical portion 524, but is smaller than the inner diameter of the front end housing 31 and the rear end housing 33 at all positions. The inner diameter of the housing member 52 is also different between the first cylindrical portion 521, the second cylindrical portion 522, the third cylindrical portion 523, and the fourth cylindrical portion 524, but is larger than the outer diameter of each member housed therein.

[0053] Here, a first insulating member 61 is disposed between the rear end side and second step portion 52b of the second cylindrical portion 522 in the accommodating member 52 and the inner circumferential surface of the second tip side housing 312. A second insulating member 62 is disposed between the rear end side and third step portion 52c of the third cylindrical portion 523 in the accommodating member 52 and the inner circumferential surface of the second tip side housing 312. Furthermore, a third insulating member 63 is disposed between the fourth cylindrical portion 524 in the accommodating member 52 and the first rear end side housing 331.

[0054] The surface of the tip side of the first cylindrical portion 521 in the housing member 52 (the surface on the front side of the opening) faces the surface of the rear end side of the support member 50 via an air gap. The first cylindrical portion 521 is in contact with the second coil spring 51. Meanwhile, the rear end side of the fourth cylindrical portion 524 faces the holding member 48. The outer peripheral surfaces of the first cylindrical portion 521 and the first step portion 52a face the inner peripheral surface of the second tip side housing 312 via an air gap. Furthermore, the outer peripheral surface of the second cylindrical portion 522 faces the inner peripheral surface of the second tip side housing 312 via the air gap and the first insulating member 61. Furthermore, the second step portion 52b faces the inner peripheral surface of the second tip side housing 312 via the first insulating member 61. Further, the outer peripheral surface of the third cylindrical portion 523 faces the inner peripheral surface of the second tip side housing 312 via the air gap and the second insulating member 62. Furthermore, the outer peripheral surface of the third step portion 52c faces the inner peripheral surface of the second tip side housing 312 via the second insulating member 62. The outer peripheral surface of the fourth cylindrical portion 524 faces the inner peripheral surface of the second tip side housing 312 via the air gap, and faces the inner peripheral surface of the first rear side housing 331 via the air gap and the third insulating member 63. In this way, by providing the air gap, the first insulating member 61, the second insulating member 62, and the third insulating member 63 between the outer peripheral surface of the accommodating member 52 and the second tip side housing 312 and the first rear side housing 331, the accommodating member 52 does not directly contact the second tip side housing 312 and the first rear side housing 331.

[0055] (Circuit board) The circuit board 53 is a member having a rectangular plate shape as a whole. The circuit board 53 performs various processes using an electric circuit on the electric signal generated by the weak electric charge output by the piezoelectric element 41 in response to the pressure received, and is configured by a so-called printed wiring board. The circuit board 53 is provided across the inside of the front end housing 31 and the inside of the rear end housing 33. The circuit board 53 is disposed on the rear end side of the conductive member 47 and on the front end side of the connecting member 54. The circuit board 53 is mounted on the holding member 48 and is disposed entirely inside the housing member 52.

[0056] This circuit board 53 is equipped with an integration circuit that integrates the input signal (charge signal) input from the piezoelectric element 41 and converts it into a voltage signal, an amplifier circuit that amplifies the voltage signal input from the integration circuit and produces an output signal, and a power supply circuit that serves as the power source for elements such as operational amplifiers that constitute the integration circuit and amplifier circuit (all not shown).

[0057] (Connection parts) The connection member 54 is a columnar member as a whole. The connection member 54 includes a base material made of a synthetic resin material such as PPT having insulating properties, and wiring and terminals made of a metal material such as copper having electrical conductivity. However, the portion (outer peripheral surface) of the connection member 54 that contacts or faces the second rear end side housing 332 is made of a synthetic resin material, so that the metal material is not exposed at this portion. In addition, an opening having a concave shape and opening toward the rear end side is provided at the rear end side of the connection member 54. Then, a board side connector 54a that protrudes toward the front end side and is electrically connected to the circuit board 53 is provided at the front end side of the connection member 54. Meanwhile, a cable side connector 54b that protrudes toward the rear end side and is to be connected to the connection cable 90 shown in FIG. 1 is provided at the rear end side of the connection member 54, inside the opening. Also, a recess is provided around the entire circumference of the outer peripheral surface of the front end side of the connection member 54, and an O-ring 56 is attached to this recess.

[0058] The front end side of the connecting member 54 is located inside the second rear end housing 332, and the rear end side is located outside the second rear end housing 332. An O-ring 56 attached to the outer circumferential surface of the connecting member 54 contacts the inner circumferential surface of the second rear end housing 332 inside the second rear end housing 332.

[0059] The outer diameter of the cylindrical portion located on the tip side of the connecting member 54 is smaller than the inner diameter of the second rear end housing 332. In contrast, the outer diameter of the cylindrical portion located on the rear end side of the connecting member 54 is approximately the same as the outer diameter of the second rear end housing 332. In addition, the tip side of the connecting member 54 faces the inner circumferential surface of the second rear end housing 332 via an air gap or an O-ring 56.

[0060] (Ground plate) The ground plate 55 is a band-shaped member as a whole. The ground plate 55 is made of a metal material such as phosphor bronze having electrical conductivity, and its surface is gold-plated.

[0061] The ground plate 55 is provided across the inside of the front housing 31 and the inside of the rear housing 33, with its front end located inside the housing member 52 and above the circuit board 53, and its rear end protruding rearward beyond the rear end of the housing member 52. The front end side of the ground plate 55 is electrically connected to the ground terminal (not shown) of the circuit board 53, and the rear end side of the ground plate 55 is electrically connected to the inner circumferential surface of the fourth cylindrical portion 524 of the housing member 52.

[0062] (O-ring) The O-ring 56 is a member having an overall annular shape and is made of a synthetic resin material such as PTFE (Polytetrafluoroethylene), which has insulating properties and is highly heat-resistant, moisture-resistant, and acid-resistant.

[0063] This O-ring 56 is attached to the outer peripheral surface of the connecting member 54, and is arranged to be sandwiched between the outer peripheral surface of the connecting member 54 and the inner peripheral surface of the second rear-end housing 332 when the connecting member 54 is attached to the second rear-end housing 332.

[0064] (Butt Pipe) The butt pipe 57 is a member having a cylindrical shape as a whole, and is made of a metal material such as stainless steel that has electrical conductivity and high heat resistance.

[0065] The butt pipe 57 is disposed inside the first tip housing 311 in the area where the first tip housing 311 and the second tip housing 312 overlap. The butt pipe 57 is located on the rear end side of the protruding portion 492 of the pressure member 49 and on the tip side of the first insulating member 61. The outer diameter of the butt pipe 57 is approximately the same as the inner diameter of the rear end side of the first tip housing 311 that houses the butt pipe 57. Meanwhile, the inner diameter of the butt pipe 57 is larger than the outer diameter of the rear end tubular portion 493 of the pressure member 49. The surface on the tip side of the butt pipe 57 is in contact with the fifth insulating member 65 disposed on the rear end side of the protruding portion 492 of the pressure member 49. Meanwhile, the surface on the rear end side of the butt pipe 57 faces the surface on the tip side of the first insulating member 61 via an air gap. The outer peripheral surface of the butt pipe 57 is in contact with the inner peripheral surface of the rear end side of the first tip side housing 311. Here, the first tip side housing 311 and the butt pipe 57 are joined and fixed by a first welded portion 58 obtained by laser welding the inner peripheral surface of the rear end side of the first tip side housing 311 and the outer peripheral surface of the butt pipe 57 facing this portion over one circumference. Meanwhile, the inner peripheral surface of the butt pipe 57 faces the outer peripheral surface of the rear end tubular portion 493 of the pressure member 49 via an air gap. In this way, by providing the fifth insulating member 65 and the air gap between the protruding portion 492 and the rear end tubular portion 493 of the pressure member 49 and the butt pipe 57, the butt pipe 57 and the pressure member 49 do not come into direct contact with each other.

[0066] (First welded part) The first welded portion 58 is a portion formed by laser welding the inner peripheral surface of the rear end side of the first tip side housing 311 and the outer peripheral surface of the butt pipe 57 around the circumference. A weld bead (a bulge of a member caused by welding) may be formed by laser welding at the first welded portion 58 and its vicinity. The location and shape of the welded bead vary depending on the structure, shape, and welding method of the welded portion. Depending on the structure of the first tip side housing 311 that fixes the pressure member 49 and the butt pipe 57 and the thickness of the butt pipe 57, a welded bead may be formed on the inner peripheral surface of the butt pipe 57. For example, in the case of a welding method in which a laser beam is irradiated to melt and solidify a base material, a welded bead may be formed on the inner peripheral surface of the butt pipe 57, which has a thin wall thickness.

[0067] (Second welded part) The second welded portion 59 is a portion formed by laser welding, around the entire circumference, the inner circumferential surface of the rear end side of the pressure member 49 and the outer circumferential surface of the support member 50. A weld bead may be formed in the vicinity of the second welded portion 59 by laser welding.

[0068] (insulated pipe) The insulating pipe 60 is a member having a cylindrical shape as a whole. The insulating pipe 60 is made of a synthetic resin material such as LCP (Liquid Crystal Polymer) having insulating properties. The insulating pipe 60 is disposed inside the pressure member 49 provided inside the front-end housing 31. The piezoelectric element 41 and the front-end side of the rear-end electrode member 43 are accommodated inside the insulating pipe 60. The insulating pipe 60 is located on the rear-end side of the front-end electrode member 42 and on the front-end side of the insulating ring 45. The outer diameter of the insulating pipe 60 is slightly smaller than the inner diameter of the pressure member 49. The inner diameter of the insulating pipe 60 is slightly larger than the outer diameters of the piezoelectric element 41 and the rear-end electrode member 43. The front-end side of the insulating pipe 60 faces the rear-end side surface of the front-end electrode member 42. On the other hand, the rear-end side of the insulating pipe 60 faces the front-end side surface of the insulating ring 45. The outer peripheral surface of the insulating pipe 60 faces the inner peripheral surface of the pressing member 49. Furthermore, the inner peripheral surface of the insulating pipe 60 faces the outer peripheral surfaces of the piezoelectric element 41 and the rear end electrode member 43. By providing the insulating pipe 60 between the pressure applying member 49 and the piezoelectric element 41 and the rear end electrode member 43 in this manner, the pressure applying member 49 and the rear end electrode member 43 do not come into direct contact with each other.

[0069] (First insulating member) The first insulating member 61 is a member having a cylindrical shape at its front end and an annular shape at its rear end, and is made of a ceramic material such as alumina that has insulating properties and high heat resistance.

[0070] The first insulating member 61 is disposed inside the tip side housing 31. The first insulating member 61 is disposed outside the second cylindrical portion 522 and the second step portion 52b (see FIG. 6) of the accommodating member 52. The outer diameter of the first insulating member 61 is slightly smaller than the inner diameter of the second tip side housing 312 at a corresponding portion, and the inner diameter of the first insulating member 61 is slightly larger than the outer diameter of the accommodating member 52 at a corresponding portion. The outer peripheral surface of the first insulating member 61 is in contact with the second tip side housing 312, and the inner peripheral surface of the first insulating member 61 is in contact with the accommodating member 52.

[0071] (Second insulating member) The second insulating member 62 is an annular member as a whole, and is made of a ceramic material such as alumina that has insulating properties and high heat resistance.

[0072] The second insulating member 62 is disposed inside the tip housing 31 at a position closer to the rear end than the first insulating member 61. The second insulating member 62 is disposed outside the third cylindrical portion 523 and the third step portion 52c (see FIG. 6) of the housing member 52. The outer diameter of the second insulating member 62 is slightly smaller than the inner diameter of the second tip housing 312 at a corresponding portion, and the inner diameter of the second insulating member 62 is slightly larger than the outer diameter of the housing member 52 at a corresponding portion. The outer peripheral surface of the second insulating member 62 is in contact with the second tip housing 312, and the inner peripheral surface of the second insulating member 62 is in contact with the housing member 52.

[0073] In this way, by providing an air gap, the first insulating member 61 and the second insulating member 62 between the tip side housing 31 (second tip side housing 312) and the accommodating member 52, the tip side housing 31 and the accommodating member 52 are not in direct contact with each other.

[0074] (Third insulating member) The third insulating member 63 is a member having an overall cylindrical shape and is made of a ceramic material such as alumina that has insulating properties and high heat resistance.

[0075] The third insulating member 63 is disposed inside the rear housing 33 at a position closer to the rear end than the second insulating member 62. The third insulating member 63 is disposed outside the fourth cylindrical portion 524 of the accommodating member 52. The outer diameter of the third insulating member 63 is substantially the same as the inner diameter of the first rear housing 331, and the inner diameter of the third insulating member 63 is larger than the outer diameter of the fourth cylindrical portion 524 of the accommodating member 52. The outer peripheral surface of the third insulating member 63 contacts the inner peripheral surface of the first rear housing 331, and a part of the inner peripheral surface of the third insulating member 63 on the tip side contacts the accommodating member 52, and the rest faces the accommodating member 52 via an air gap.

[0076] (Fourth insulating member) The fourth insulating member 64 is an annular member as a whole and is made of a ceramic material such as zirconia, which has insulating properties and high heat resistance.

[0077] The fourth insulating member 64 is disposed so that its front surface contacts the inner step portion 311b of the first front housing 311 and its rear surface contacts the first pressing surface 49b of the protruding portion 492 of the pressure member 49. The outer diameter of the fourth insulating member 64 is approximately the same as the second diameter, which is the larger of the inner diameters of the first front housing 311, and the outer peripheral surface of the fourth insulating member 64 contacts the inner peripheral surface of the first front housing 311. The inner diameter of the fourth insulating member 64 is approximately the same as the outer diameter of the rear end tubular portion 493 of the pressure member 49, and the inner peripheral surface of the fourth insulating member 64 contacts the outer peripheral surface of the rear end tubular portion 493 on the front side of the protruding portion 492 of the pressure member 49. The thickness of the fourth insulating member 64 is greater than the difference between the outer diameter of the rear end tubular portion 493 of the pressure member 49 and the outer diameter of the protrusion 492, in other words, the height of the outer circumferential surface of the protrusion 492 relative to the outer circumferential surface of the rear end tubular portion 493.

[0078] (Fifth insulating member) The fifth insulating member 65 is an annular member as a whole, and is made of a ceramic material such as zirconia, which has insulating properties and high heat resistance.

[0079] The fifth insulating member 65 is disposed so that its front end surface contacts the second pressing surface 49c of the protruding portion 492 of the pressure member 49, and its rear end surface contacts the front end surface of the butt pipe 57. The fifth insulating member 65 has an outer diameter that is approximately the same as the second diameter, which is the larger of the inner diameters of the first front end housing 311, and the outer peripheral surface of the fifth insulating member 65 contacts the inner peripheral surface of the first front end housing 311. The fifth insulating member 65 has an inner diameter that is approximately the same as the outer diameter of the rear end tubular portion 493 of the pressure member 49, and the inner peripheral surface of the fifth insulating member 65 contacts the outer peripheral surface of the rear end tubular portion 493 of the pressure member 49. The thickness of the fifth insulating member 65 is greater than the difference between the outer diameter of the rear end tubular portion 493 of the pressure member 49 and the outer diameter of the protruding portion 492, in other words, the height of the outer peripheral surface of the protruding portion 492 relative to the outer peripheral surface of the rear end tubular portion 493.

[0080] By setting the thicknesses of the fourth insulating member 64 and the fifth insulating member 65 as described above, the outer circumferential surface of the pressure member 49 contacts the fourth insulating member 64 and the fifth insulating member 65, or faces the inner circumferential surfaces of the first tip side housing 311 and the butt pipe 57 via an air gap. Therefore, the pressure member 49 does not come into direct contact with the first tip side housing 311 and the butt pipe 57.

[0081] [Sealing section configuration] The seal portion 70 has a first seal member 71 located relatively toward the front end side and a second seal member 72 located relatively toward the rear end side. When the pressure detection device 20 is attached to the internal combustion engine 10, the first seal member 71 and the second seal member 72 abut against the inner circumferential surface of a communication hole 13a (see FIG. 1) provided in the cylinder head 13.

[0082] (First sealing member) The first seal member 71 is a hollow member having a cylindrical shape as a whole, and is made of a synthetic resin material such as PTFE, which has insulating properties and is highly resistant to heat and acid.

[0083] The first seal member 71 is fitted into a recess 311a provided on the outer circumferential surface of the first tip side housing 311. The inner diameter of the first seal member 71 is slightly smaller than the outer diameter of the recess 311a, and the outer diameter of the first seal member 71 is slightly larger than the inner diameter of the communication hole 13a.

[0084] (Second sealing member) The second seal member 72 is an O-ring having an overall annular shape, and is made of a synthetic resin material such as PTFE, which has insulating properties and is highly resistant to heat and acid.

[0085] The second seal member 72 is fitted into a recess 312a provided on the outer circumferential surface of the second tip side housing 312. The inner diameter of the second seal member 72 is slightly smaller than the outer diameter of the recess 312a, and the outer diameter of the second seal member 72 is slightly larger than the inner diameter of the communication hole 13a.

[0086] [Electrical connection structure in pressure detection device] Here, the electrical connection structure in the pressure detection device 20 will be described.

[0087] (Positive Path) In the pressure detection device 20, the rear end surface (positive electrode) of the piezoelectric element 41 is electrically connected to a metallic conductive member 47 via a metallic rear end electrode member 43 and a metallic first coil spring 46. The metallic conductive member 47 is electrically connected to an input terminal (not shown) provided on a circuit board 53 via a metallic holding portion, wiring, and terminals provided on a holding member 48. Hereinafter, the electrical path from the rear end surface of the piezoelectric element 41 to the circuit board 53 via the rear end electrode member 43, the first coil spring 46, the conductive member 47, and the holding member 48 is referred to as the "positive path."

[0088] (Negative Path) Meanwhile, in pressure detection device 20, the end face (negative electrode) on the tip side of piezoelectric element 41 is electrically connected to a ground terminal (not shown) provided on circuit board 53 via metal tip electrode member 42, metal pressure member 49, metal support member 50 (second welded portion 59), metal second coil spring 51, metal housing member 52, and metal ground plate 55. Hereinafter, the electrical path from the tip side surface of piezoelectric element 41 to circuit board 53 via tip electrode member 42, pressure member 49, support member 50, second coil spring 51, housing member 52, and ground plate 55 will be referred to as the "negative path."

[0089] (Case route) On the other hand, in the pressure detection device 20, the metallic diaphragm head 32 is electrically connected to the metallic rear end housing 33 (first rear end housing 331 and second rear end housing 332) via the metallic front end housing 31 (first front end housing 311 and second front end housing 312). In addition, in this pressure detection device 20, the metallic first front end housing 311 is electrically connected to the metallic butt pipe 57 (first welded portion 58). Hereinafter, the electrical path from the diaphragm head 32 to the rear end housing 33 and butt pipe 57 via the front end housing 31 is referred to as the "housing path".

[0090] (Relationship between positive and negative pathways) Here, in the pressure detection device 20 of this embodiment, the negative path exists outside the positive path. In other words, the positive path is housed inside the negative path. The positive path and the negative path are electrically insulated by the insulating pipe 60, the insulating ring 45, the holding member 48, and an air gap formed between both paths. Here, in this embodiment, the negative path is an example of the first electrical path, and the positive path is an example of the second electrical path.

[0091] (Relationship between negative path and housing path) In addition, in this pressure detection device 20, the housing path exists outside the negative path. In other words, the negative path is housed inside the housing path. The negative path and the housing path are electrically insulated by the insulating coating 42a provided on the tip electrode member 42, the fourth insulating member 64 and the fifth insulating member 65 that sandwich the protruding portion 492 of the pressure member 49, the first insulating member 61, the second insulating member 62, and the third insulating member 63, and the air gap formed between both paths.

[0092] (Relationship between the housing path and the positive path) As a result, in the pressure detection device 20, the housing path exists outside the positive path. In other words, the positive path is accommodated inside the housing path. As described above, the positive path and the negative path are electrically insulated from each other, and the negative path and the housing path are electrically insulated from each other, so that the housing path and the positive path are electrically insulated from each other.

[0093] (Retraction portion provided on the outer peripheral surface of the pressure member) Here, the retreat portion 494 provided on the outer peripheral surface of the pressure member 49 will be described. It has been mentioned that a weld bead may be formed on the first welded portion 58 by laser welding the first tip side housing 311 and the butt pipe 57. The inner peripheral surface of the butt pipe 57 and the outer peripheral surface of the pressure member 49 face each other via an air gap and are electrically insulated. However, when a weld bead is formed on the inner peripheral surface of the butt pipe 57 at the first welded portion 58 and the weld bead comes into contact with the pressure member 49, the housing path including the butt pipe 57 and the negative path including the pressure member 49 are short-circuited. The weld bead formed on the outer peripheral surface of the first tip side housing 311 at the first welded portion 58 can also be removed by grinding. However, it is not easy to grind the weld bead formed on the inner peripheral surface of the butt pipe 57 because there is only a small gap between the inner peripheral surface of the butt pipe 57 and the outer peripheral surface of the pressure member 49. Even if it is possible to grind it, there is a concern that the mechanical strength of the part will decrease. Therefore, in this embodiment, a retraction portion 494 for retracting from the weld bead is provided at a position facing first weld portion 58 (where welding is performed) on the outer circumferential surface of pressure member 49.

[0094] 7 is an enlarged view of the first welded portion 58 and the vicinity of the retreated portion 494 in the cross section shown in FIG. 4. The retreated portion 494 is formed on the outer peripheral surface of the rear end side of the protruding portion 492 in the rear end tubular portion 493 at a position facing at least the first welded portion 58. The retreated portion 494 is formed to be thinner than adjacent portions in the rear end tubular portion 493. The retreated portion 494 is a recess formed lower than the outer peripheral surface of the adjacent rear end tubular portion 493 (see FIG. 5). As an example of a specific shape of the retreated portion 494, the retreated portion 494 is formed as a groove extending in a direction along the first welded portion 58, in other words, as a groove continuing around the outer peripheral surface of the rear end tubular portion 493.

[0095] By forming the above-described retreated portion 494 on the outer peripheral surface of the pressure applying member 49, the distance between the outer peripheral surface of the pressure applying member 49 and the inner peripheral surface of the butt pipe 57 becomes wider than a portion where the retreated portion 494 is not formed. Therefore, even if a weld bead is formed on the first welded portion 58, it is possible to prevent the weld bead from coming into contact with the pressure applying member 49 and causing a short circuit between the negative path and the housing path.

[0096] The specific shape of the retreated portion 494 is not limited to the groove described above as long as the distance between the pressure member 49 and the butt pipe 57 is sufficient to prevent contact even when a weld bead is formed on the first welded portion 58. For example, the portion of the outer circumferential surface of the rear end tubular portion 493 of the pressure member 49 that contacts the fourth insulating member 64 and the fifth insulating member 65 may be formed higher than the other portions including the retreated portion 494. However, since the pressure member 49 is a member that applies a preload to the piezoelectric element 41, each of the front end tubular portion 491 and the rear end tubular portion 493 is required to have a certain degree of rigidity. Therefore, depending on the size and material of the pressure member 49, it is preferable to make only the retreated portion 494 recessed from the adjacent portions, rather than making the entire thickness of the rear end tubular portion 493 other than the portions that contact the fourth insulating member 64 and the fifth insulating member 65 thinner.

[0097] In this embodiment, a configuration has been described in which a retreat portion 494 for retreating from the weld bead of the first weld portion 58 is provided on the outer peripheral surface of the pressure member 49 facing the first weld portion 58. In contrast, a weld bead may also be generated in the second weld portion 59 formed by welding the inner peripheral surface of the pressure member 49 and the outer peripheral surface of the support member 50. However, since the support member 50 has a sufficient thickness, unlike the first weld portion 58, in this embodiment, it is not considered that a weld bead is formed on the inner peripheral surface side of the support member 50 in the second weld portion 59. In addition, since the holding member 48 made of a synthetic resin material is present inside the support member 50 at a position facing the second weld portion 59, an electrical short circuit due to contact of the weld bead does not occur. Therefore, a configuration for retreating from the weld bead in the second weld portion 59 is not provided.

[0098] (others) Here, the housing part 30 constituting the housing path is a part exposed to the outside in the pressure detection device 20, and in particular, the diaphragm head 32 is a part facing the combustion chamber C where the acidity increases with combustion. In contrast, the members constituting the positive path and the negative path are parts housed within the housing part 30 in the pressure detection device 20. For this reason, it is preferable that the members constituting the positive path and the negative path are made of a material having a higher conductivity than the members constituting the housing path (housing part 30), and it is also preferable that the members constituting the housing path (housing part 30) are made of a material having a higher acid resistance than the members constituting the positive path and the negative path.

[0099] [Pressure detection device assembly procedure] Next, the assembly procedure for the pressure detection device 20 used in this embodiment will be described.

[0100] First, the tip side of the first tip side housing 311 and the back side (the convex portion 32d side) of the diaphragm head 32 are opposed to each other and butted against each other. Then, in this state, laser welding is performed around the boundary between the first tip side housing 311 and the diaphragm head 32.

[0101] Next, the fourth insulating member 64 is inserted from the rear end side into the first tip side housing 311 in the structure including the first tip side housing 311 and the diaphragm head 32, and then the pressure member 49 is inserted with the tip tubular portion 491 at the tip side. At this time, the pressure member 49 is inserted until the first pressing surface 49b of the protruding portion 492 of the pressure member 49 abuts against the inner step portion 311b provided on the inner peripheral surface of the first tip side housing 311 via the fourth insulating member 64. As a result, the convex portion 32d of the diaphragm head 32 is inserted into the opening provided on the tip side of the tip tubular portion 491 of the pressure member 49.

[0102] Next, the fifth insulating member 65 is inserted between the inner peripheral surface of the first tip side housing 311 and the outer peripheral surface of the rear end cylindrical portion 493 of the pressure member 49 from the rear end side, and then the butt pipe 57 is inserted. At this time, the butt pipe 57 is inserted until the tip side of the butt pipe 57 butts against the fifth insulating member 65.

[0103] In this state, the rear end side of the first tip side housing 311 and the butt pipe 57 are laser-welded around the circumference to form a first welded portion 58. At this time, the protruding portion 492 of the pressure member 49 is sandwiched between the inner step portion 311b of the first tip side housing 311 and the tip side of the butt pipe 57 with the fourth insulating member 64 and the fifth insulating member 65 interposed therebetween, so that the pressure member 49 is fixed to the first tip side housing 311. This allows the pressure member 49 to be positioned relative to the first tip side housing 311 and the diaphragm head 32. Even if a weld bead is formed on the inner circumferential surface of the butt pipe 57 by welding, an electrical short circuit does not occur because the retracted portion 494 is provided on the outer circumferential surface of the pressure member 49.

[0104] Next, the front electrode member 42, the insulating pipe 60, the piezoelectric element 41, the rear electrode member 43, the insulating ring 45, and the support member 50 are inserted in this order from the rear end side into the pressure member 49 in the structure including the first front housing 311, the diaphragm head 32, the pressure member 49, and the butting pipe 57. When the front electrode member 42 is inserted into the pressure member 49, the surface on which the insulating coating 42a is formed is set as the front end side. At this time, the insulating coating 42a provided on the front side of the front electrode member 42 housed in the pressure member 49 contacts the convex portion 32d provided on the rear end side of the diaphragm head 32. The piezoelectric element 41 and the rear electrode member 43 are disposed inside the insulating pipe 60.

[0105] In this state, the position of the support member 50 relative to the pressure member 49 in the center line direction is adjusted, and the load (preload) applied to the piezoelectric element 41 via the pressure member 49 and the support member 50 is adjusted.

[0106] Then, after the position adjustment of the support member 50 in the center line direction relative to the pressure member 49 is completed, the rear end side of the pressure member 49 and the support member 50 are laser-welded around one circumference to form a second welded portion 59. At this time, the piezoelectric element 41 is fixed to the pressure member 49 via the front end electrode member 42 at its front end and via the rear end electrode member 43, the insulating ring 45, and the support member 50 at its rear end. In this state, the pressure member 49 is already fixed to the first front end housing 311 and the diaphragm head 32. Therefore, the piezoelectric element 41 housed in the pressure member 49 is fixed to the diaphragm head 32 with a predetermined preload applied. As a result, the pressure member 49, the support member 50, and the piezoelectric element 41 are positioned relative to the first front end housing 311 and the diaphragm head 32.

[0107] Next, the second protrusion 47b provided on the tip side of the conductive member 47 and the first coil spring 46 attached to the second protrusion 47b are inserted from the rear end side into the support member 50 in the structure to which the support member 50 is attached. The second coil spring 51 is inserted from the rear end side into the rear end side of the support member 50 in the structure. Furthermore, the second tip side housing 312 is screwed and attached from the rear end side into the first tip side housing 311 in the structure. Furthermore, the first insulating member 61 and the second insulating member 62 are inserted from the rear end side into the second tip side housing 312 in this order. Accordingly, the first insulating member 61 is positioned by hitting a step portion provided on the tip side in the second tip side housing 312, and the second insulating member 62 is positioned by hitting a step portion provided on the rear end side in the second tip side housing 312.

[0108] On the other hand, in a separate process from the assembly of the structure, the conductive member 47 is inserted from the tip side into the tip side of the holding member 48. Also, the circuit board 53 including the ground plate 55 is attached to the rear end side of the holding member 48. At this time, the rear end side convex portion 47c of the conductive member 47 attached to the holding member 48 and the circuit board 53 are electrically connected. Then, the holding member 48 to which the conductive member 47 and the circuit board 53 (ground plate 55) are attached is inserted from the rear end side into the housing member 52 with the conductive member 47 on the tip side. At this time, the holding member 48 is inserted until the boundary (the tip side of the plate part) between the cylindrical part and the plate part of the holding member 48 abuts against the inner peripheral surface of the second step part 52b provided in the housing member 52. Accordingly, the tip side of the cylindrical part of the holding member 48 and the tip side of the conductive member 47 exposed from the cylindrical part of the holding member 48 protrude further to the tip side than the first cylindrical part 521. Additionally, the inner peripheral surface of the housing member 52 and the rear end side of the ground plate 55 come into contact with each other.

[0109] Then, the housing member 52 including the conductive member 47, the circuit board 53 (ground plate 55) and the holding member 48 is inserted from the rear end side into the second tip side housing 312 in the structure to which the second insulating member 62 has been attached, with the first cylindrical portion 521 at the tip side. At this time, the housing member 52 is inserted until the second step portion 52b provided on the housing member 52 abuts against the first insulating member 61 attached in the second tip side housing 312 (until the third step portion 52c provided on the housing member 52 abuts against the second insulating member 62 attached in the second tip side housing 312). Accordingly, the rear end side of the second cylindrical portion 522 in the housing member 52 and the outer peripheral surface of the second step portion 52b come into contact with the inner peripheral surface and the surface on the rear end side of the first insulating member 61. Furthermore, the rear end side of the third cylindrical portion 523 of the accommodating member 52 and the outer peripheral surface of the third step portion 52c come into contact with the inner peripheral surface and the surface of the rear end side of the second insulating member 62. Furthermore, the first cylindrical portion 521 of the accommodating member 52 is inserted into the rear end side of the second coil spring 51, and the rear end of the second coil spring 51 abuts against the first step portion 52a of the accommodating member 52. As a result, the first coil spring 46 and the second coil spring 51 are compressed in the center line direction compared to before the accommodating member 52 is inserted into the structure.

[0110] Next, the first rear end housing 331 and the third insulating member 63 are inserted from the rear end side into the second front end housing 312 in the structure to which the accommodating member 52 has been attached. As a result, the outer circumferential surface of the fourth tubular portion 524 of the accommodating member 52 comes into contact with the inner circumferential surface of the third insulating member 63. In addition, the second rear end housing 332 is inserted into the first rear end housing 331 from the rear end side.

[0111] Then, the connection member 54 having the O-ring 56 attached to its outer circumferential surface is inserted from the rear end side into the second rear end housing 332 in the structure to which the second rear end housing 332 has been attached, with the board side connector 54a at the leading end side. At this time, the O-ring 56 attached to the connection member 54 enters the inside of the second rear end housing 332 and comes into contact with the second rear end housing 332. In addition, the circuit board 53 and the board side connector 54a provided on the connection member 54 are electrically connected.

[0112] Finally, in the structure to which the connection member 54 has been attached, the first seal member 71 is attached to the recess 311a of the first tip side housing 311, and the second seal member 72 is attached to the recess 312a of the second tip side housing 312. With the above, the assembly of the pressure detection device 20 is completed.

[0113] [Pressure detection operation by pressure detection device] Next, the pressure detection operation by the pressure detection device 20 will be described. When the internal combustion engine 10 is operating, the pressure (combustion pressure) generated in the combustion chamber C is applied to the pressure receiving surface 32a of the diaphragm head 32. In the diaphragm head 32, the pressure received by the pressure receiving surface 32a is transmitted to the convex portion 32d on the back side, and is further transmitted from the convex portion 32d to the front electrode member 42 through the insulating coating 42a. The pressure transmitted to the front electrode member 42 acts on the piezoelectric element 41 sandwiched between the front electrode member 42 and the rear electrode member 43, 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 to an input signal terminal (not shown) of the circuit board 53 through a positive path. The electric charge signal supplied to the circuit board 53 is subjected to various processes in a circuit mounted on the circuit board 53, and becomes an output signal. The output signal output from the circuit board 53 is transmitted to the outside (here, the connection cable 90 and the control device 80) through the connection member 54.

[0114] [Advantages of this embodiment] In the pressure detection device 20 of this embodiment, the positional relationship between the pressure member 49 and the support member 50 in the center line direction is fixed, so that the piezoelectric element 41 is sandwiched between the pressure member 49 and the support member 50, and a predetermined load is applied to the piezoelectric element 41. Then, the protruding portion 492 of the pressure member 49, which houses the piezoelectric element 41 therein, is sandwiched between the inner circumferential surface of the tip side housing 31 and the butting pipe 57, with the fourth insulating member 64 and the fifth insulating member 65 interposed therebetween, so that the pressure member 49 is fixed to the tip side housing 31. As a result, the pressure member 49 and the tip side housing 31 are electrically insulated from each other, and the piezoelectric element 41 can be fixed to the housing part 30 (tip side housing 31) via the pressure member 49 and the support member 50 in a state in which the fluctuation of the load is suppressed.

[0115] In the pressure detection device 20 of this embodiment, a retraction section 494 is provided on the outer circumferential surface of the pressure applying member 49 at a position facing a first welded section 58 formed by welding the first tip side housing 311 and the butt pipe 57. This makes it possible to prevent a short circuit between the housing path including the butt pipe 57 and the negative path including the pressure applying member 49 even if a weld bead is formed on the inner circumferential surface side of the butt pipe 57 at the first welded section 58.

[0116] In the pressure detection device 20 of this embodiment, an insulating film 42a is provided on the tip side of the tip electrode member 42 that is located between the piezoelectric element 41 and the diaphragm head 32. This makes it possible to electrically insulate the tip electrode member 42 and the diaphragm head 32.

[0117] Here, in this embodiment, the above-mentioned tip electrode member 42 and pressure member 49 are configured to also serve as the negative path of the piezoelectric element 41, and by adopting the above-mentioned configuration, this negative path can be electrically insulated from the housing path including the tip side housing 31 and the diaphragm head 32.

[0118] The pressure detection device 20 of this embodiment is attached to the internal combustion engine 10, and when this internal combustion engine 10 is installed in an automobile, noise with a frequency of the order of kHz (hereinafter referred to as low-frequency noise) generated by the horn, headlights, windshield wipers, etc., penetrates into the cylinder head 13 of the internal combustion engine 10. In this embodiment, the housing part 30 of the pressure detection device 20, which is made of metal, is attached to the cylinder head 13, which is made of metal, so that the low-frequency noise that penetrates into the cylinder head 13 is also propagated to the housing part 30 of the pressure detection device 20.

[0119] Here, in the pressure detection device 20 of this embodiment, the housing path including the housing portion 30 is electrically insulated from the positive path and the negative path from the piezoelectric element 41 to the circuit board 53. Therefore, low-frequency noise propagated from the cylinder head 13 to the housing portion 30 of the pressure detection device 20 is less likely to be transmitted to the circuit board 53 via the pressure member 49, the support member 50, the conductive member 47, etc. As a result, the fluctuation (variation) of the potential on the circuit board 53 caused by the low-frequency noise is suppressed, and it is possible to reduce the fluctuation (variation) of the output signal output from the circuit board 53 to the outside (the control device 80, etc.).

[0120] Furthermore, when the internal combustion engine 10 is mounted on an automobile, radio waves of MHz order frequencies, which are typically used in mobile phones, radios, televisions, etc., fly around the automobile. When these radio waves are irradiated to the conductive member 47 provided in the pressure detection device 20, noise of MHz order frequencies (hereinafter referred to as high-frequency noise) ends up being transmitted to the circuit board 53.

[0121] Here, in the pressure detection device 20 of this embodiment, the conductive member 47 is covered using the pressure member 49 and the support member 50. Therefore, the radio waves irradiated from the outside to the pressure detection device 20 are blocked by the pressure member 49 and the support member 50, and are less likely to be transmitted to the conductive member 47. As a result, the fluctuation (variation) of the potential in the circuit board 53 caused by high frequency noise is suppressed, and it is possible to reduce the fluctuation (variation) of the output signal output from the circuit board 53 to the outside.

[0122] Moreover, in this embodiment, the circuit board 53 is covered with a metallic housing member 52. Therefore, radio waves irradiated from the outside to the pressure detection device 20 are blocked by the housing member 52, and are less likely to reach the circuit board 53. As a result, fluctuations (variations) of the potential on the circuit board 53 caused by high-frequency noise are suppressed, and it is possible to further reduce fluctuations (variations) of the output signal output from the circuit board 53 to the outside.

[0123] [others] In this embodiment, a retraction portion 494 is provided on the outer circumferential surface of the pressure applying member 49 at a position facing a first welded portion 58 formed by welding the first tip side housing 311 and the butt pipe 57. On the other hand, with respect to a second welded portion 59 formed by welding the pressure applying member 49 and the support member 50, no configuration is provided for retracting from the weld bead on the holding member 48 located at a position facing the second welded portion 59. However, a configuration for retracting from the weld bead may also be provided for this portion of the holding member 48.

[0124] In the pressure detection device 20 of the present embodiment, in addition to the first welded portion 58 and the second welded portion 59, the joint portion between the first tip side housing 311 and the second tip side housing 312 constituting the tip side housing 31 and the boundary portion between the diaphragm head 32 and the first tip side housing 311 are laser-welded. In these portions, a configuration for retracting from the weld bead such as a recess may be provided in a portion of a member near the welded portion that faces a position where the weld bead is expected to be formed. When the weld bead is formed during welding, the weld bead is at a high temperature. Therefore, there is a possibility that the contact of the high-temperature weld bead with a member near the welded portion may cause an effect such as a change in the characteristics of the member. Therefore, by providing a configuration for retracting from the weld bead, the occurrence of such an effect can be avoided.

[0125] In this embodiment, the tip electrode member 42 constituting the negative path and the diaphragm head 32 constituting the casing path are electrically insulated from each other by providing the insulating coating 42a on the tip side of the tip electrode member 42, but this is not limited to the above. For example, an insulating plate made of a ceramic material such as alumina, which has insulating properties and high heat resistance, may be disposed between the tip electrode member 42 and the diaphragm head 32.

[0126] In the present embodiment, the first insulating member 61, the second insulating member 62, and the third insulating member 63 are disposed between the rear end side and the second step portion 52b of the second cylindrical portion 522 in the housing member 52 and the inner circumferential surface of the second tip side housing 312, between the rear end side and the third step portion 52c of the third cylindrical portion 523 in the housing member 52 and the inner circumferential surface of the second tip side housing 312, and between the fourth cylindrical portion 524 in the housing member 52 and the first rear side housing 331, respectively, to electrically insulate the housing member 52 constituting the negative path from the tip side housing 31 and the rear side housing 33 constituting the housing path, but this is not limited thereto. For example, an insulating coating formed by coating a ceramic material having insulating properties, such as alumina or zirconia, on a part of the outer circumferential surface of the housing member 52 may be formed, or an air gap may be formed between the housing member 52 and the tip side housing 31 or the rear side housing 33.

[0127] Furthermore, in this embodiment, the tip electrode member 42 is not housed within the insulating pipe 60, but this is not limited to this, and the tip electrode member 42 may be housed within the insulating pipe 60.

[0128] Furthermore, in this embodiment, an example has been described in which a piezoelectric element 41 is used as the pressure detection element in the pressure detection device 20, but this is not limited to this, and for example, a strain gauge, spaced electrodes, etc. may also be used. [Explanation of symbols]

[0129] Reference Signs List 1...pressure detection system, 10...internal combustion engine, 20...pressure detection device, 30...casing, 31...front end casing, 32...diaphragm head, 33...rear end casing, 40...detection mechanism, 41...piezoelectric element, 42...front end electrode member, 42a...insulating coating, 43...rear end electrode member, 45...insulating ring, 46...first coil spring, 47...conductive member, 48...holding member, 49...pressurizing member, 492...projection portion, 493...rear end tubular portion, 494...retraction portion, 50...support member, 51...second coil spring, 52...accommodating member, 53...circuit board, 54...connecting member, 55...ground plate, 56...O-ring, 57...butt pipe, 58...first welded portion, 59...second welded portion, 60...insulating pipe, 61...first insulating member, 62...second insulating member, 63...third insulating member, 64...fourth insulating member, 65...fifth insulating member, 70...sealing portion, 71...first sealing member, 72...second sealing member, 80...control device, 90...connecting cable

Claims

1. A cylindrical housing; a piezoelectric element disposed within the housing for detecting a change in pressure; a pressure transmitting portion disposed in the housing in contact with the piezoelectric element and configured to transmit pressure to the piezoelectric element; a pressure member fixed to the housing so as to apply pressure to the pressure transmission portion in the axial direction of the housing and apply a load to the piezoelectric element; a fixing member that is welded to the housing to fix the pressure member within the housing, the pressing member has a retreat portion that avoids a welding portion between the housing and the fixing member in a state where the pressing member is fixed by the fixing member, A pressure detection device, characterized in that a groove extending in a direction along the welded portion is formed in a portion of the pressure member facing the welded portion as the retreated portion.

2. the pressure member is conductive and electrically connected to the piezoelectric element; 2. The pressure detection device according to claim 1, wherein the housing and the fixing member are electrically conductive and electrically insulated from the pressure member and the piezoelectric element.

3. The pressure member is cylindrical and has a protrusion that protrudes outward on an outer circumferential surface thereof. the housing and the fixing member are welded together in a state in which the inner circumferential surface of the housing and the fixing member sandwich the protruding portion of the pressure member via an insulating member, thereby fixing the pressure member; 3. The pressure detection device according to claim 1, wherein a portion of the outer surface of the pressing member other than the protrusion that faces the insulating member when fixed inside the housing is formed higher than a portion that faces the welded portion and abuts against the insulating member.

4. A cylindrical housing; a piezoelectric element disposed within the housing for detecting a change in pressure; a pressure transmitting portion disposed in the housing in contact with the piezoelectric element and configured to transmit pressure to the piezoelectric element; a pressure member fixed to the housing so as to apply pressure to the pressure transmission portion in the axial direction of the housing and apply a load to the piezoelectric element; a fixing member that is welded to the housing to fix the pressure member within the housing, the pressing member has a retreat portion that avoids a welding portion between the housing and the fixing member in a state where the pressing member is fixed by the fixing member, The pressure member is cylindrical and has a protrusion that protrudes outward on an outer circumferential surface thereof. the housing and the fixing member are welded together in a state in which the inner circumferential surface of the housing and the fixing member sandwich the protruding portion of the pressure member via an insulating member, thereby fixing the pressure member; A pressure detection device characterized in that, on the outer surface of the pressurizing member different from the protrusion, a portion that faces the insulating member when fixed inside the housing is formed higher than a portion that faces the welded point and abuts against the insulating member.

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