JP2017194358A - Pressure sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make measurement error small with a member for receiving heat.SOLUTION: A pressure sensor includes: a housing; a diaphragm connected to a tip side of the housing through a junction part, and configured to bend according to pressure; a sensor part having an electric characteristic varying according to pressure; a connection part connecting the diaphragm and the sensor part; and a heat receiving plate arranged on a tip side of the diaphragm, directly and indirectly connected to the diaphragm, and configured to receive heat. When a minimum value of an area of a virtual minimum inclusion region, which including, on a cross section perpendicular to an axial line, a cross section of a portion from a heat receiving part to the diaphragm and whose entire length of a contour becomes minimum, is defined as a connection area Sn; on a projection surface in a case of projecting the diaphragm and the heat receiving plate on the projection surface perpendicular to the axial line, an area of a region surrounded by the junction part is defined as a diaphragm effective area Sd; and a thickness of the heat receiving plate is defined as t, the following relationships are satisfied: t≥0.21 mm, and (Sn/Sd)≤0.25.SELECTED DRAWING: Figure 2

Description

  The present specification relates to a pressure sensor for measuring a pressure in a combustion chamber of an internal combustion engine.

  As a pressure sensor, a metal shell attached to the engine head, a pressure receiving member having a diaphragm and a pressure receiving rod, a press screw screwed into the pressure receiving rod, and a piezoelectric element sandwiched between the head of the press screw and the metal shell. A sensor having a sensor has been proposed. When the diaphragm receives the combustion pressure, the diaphragm is pushed rearward, whereby a load is transmitted to the piezoelectric sensor through the pressure receiving rod. The piezoelectric sensor converts a change in load into a change in electrical output. Here, in order to reduce the amount of thermal deformation of the diaphragm due to the high-temperature combustion gas, a heat shielding plate is disposed on the front surface of the diaphragm.

JP 7-318448 A

  However, there has been a case where the amount of deformation of the diaphragm cannot be sufficiently reduced because a member for receiving heat such as a heat shielding plate is not sufficiently devised. As a result, there is a possibility that the pressure measurement error of the pressure sensor cannot be made sufficiently small.

  The present specification discloses a technique capable of reducing a pressure measurement error in a pressure sensor having a member for receiving heat.

  The technology disclosed in the present specification can be realized as, for example, the following application examples.

[Application Example 1] A cylindrical casing;
A diaphragm that is joined to the front end side of the housing via a joint portion, expands in a direction intersecting the axis of the housing, and bends according to the received pressure,
A sensor unit disposed in the housing and having an electrical characteristic that varies with the pressure;
A connecting portion for connecting the diaphragm and the sensor portion;
A heat receiving plate that is disposed on the distal end side of the diaphragm and that is directly or indirectly connected to the diaphragm to receive heat;
A pressure sensor comprising:
On the cross section perpendicular to the axis, connect the minimum value of the area of the minimum inclusion area that is a virtual area including the cross section of the portion from the heat receiving plate to the diaphragm and having the minimum total length of the contour. Let the area Sn be
When projecting the diaphragm and the heat receiving plate on a projection plane perpendicular to the axis, on the projection plane,
The area of the region surrounded by the joint is defined as a diaphragm effective area Sd,
When the thickness of the heat receiving plate is t,
A pressure sensor satisfying t ≧ 0.21 mm and (Sn / Sd) ≦ 0.25.

  According to the said structure, a measurement error can be made small using a heat receiving plate.

[Application Example 2] The pressure sensor according to Application Example 1,
An absolute value of an angle θ formed by a surface on the rear end side of the heat receiving plate and a direction perpendicular to the axis in a cross section including the axis is within 20 degrees.

  According to the above configuration, the measurement error can be further reduced.

  The technology disclosed in the present specification can be realized in various modes, for example, in a mode of a pressure sensor, an internal combustion engine equipped with the pressure sensor, or the like.

It is explanatory drawing which shows the pressure sensor 10 as 1st Embodiment. 3 is an enlarged cross-sectional view of a tip portion of the pressure sensor 10. FIG. 3 is an exploded perspective view of an element unit 50. FIG. It is explanatory drawing of operation | movement of the pressure sensor. It is explanatory drawing of operation | movement of the pressure sensor 10x of a reference example. It is explanatory drawing of the parameter of the pressure sensor 10 of 1st Embodiment. It is a graph which shows the example of the waveform of the pressure measured by a pressure sensor. It is explanatory drawing of the pressure sensor 10a of 2nd Embodiment. It is explanatory drawing of the parameter of the pressure sensor 10a (FIG. 6) of 2nd Embodiment. It is explanatory drawing of the pressure sensor 10b of 3rd Embodiment. It is explanatory drawing of the pressure sensor 10c of 4th Embodiment. It is a figure which shows the modification of 2nd Embodiment.

A. First embodiment:
A-1. Configuration of Pressure Sensor 10 FIG. 1 is an explanatory diagram showing a pressure sensor 10 as a first embodiment. The pressure sensor 10 of this embodiment is attached to an internal combustion engine and used to detect the pressure in the combustion chamber of the internal combustion engine. As shown in FIG. 1, the pressure sensor 10 includes a cylindrical first metal fitting 20, a second metal fitting 80, a third metal fitting 35, a pressure receiving part 40, a heat receiving part 90, and an element part as main components. 50 and a cable 60. The central axis CL is the central axis of the pressure sensor 10. Hereinafter, the central axis CL is also referred to as an axis line CL, and a direction parallel to the axis line CL is also referred to as an “axis direction”. The radial direction of the circle centered on the axis CL is also simply referred to as “radial direction”, and the circumferential direction of the circle centered on the axis CL is also simply referred to as “circumferential direction”. A direction from the first metal fitting 20 toward the pressure receiving portion 40 along the axis CL is referred to as a “front end direction Df”, and a direction opposite to the front end direction Df is referred to as a “rear end direction Dr”. The front end direction Df side is referred to as “front end side”, and the rear end direction Dr side is also referred to as “rear end side”.

  FIG. 1 shows a cross-sectional configuration on the left side of the axis line CL of the tip side portion of the pressure sensor 10. This cross section is a flat cross section (cross section cut along a plane) including the axis CL. FIG. 1 shows an external configuration of another part of the pressure sensor 10. In the present embodiment, the axis CL of the pressure sensor 10 is also the central axis of each of the first metal fitting 20, the second metal fitting 80, the third metal fitting 35, the pressure receiving part 40, the heat receiving part 90, and the element part 50.

  The first metal fitting 20, the second metal fitting 80, and the third metal fitting 35 have a cylindrical shape in which a cross section perpendicular to the axis CL (hereinafter also referred to as a transverse cross section) has an annular shape and extends in the axial direction. In this embodiment, the 1st metal fitting 20, the 2nd metal fitting 80, and the 3rd metal fitting 35 are formed with stainless steel. However, other materials (for example, steel such as low carbon steel, various metal materials) may be adopted.

  The first metal fitting 20 is formed with a shaft hole 21 that is a through-hole centered on the axis CL. In addition, a screw portion 22 and a tool engagement portion 24 are provided on the outer peripheral surface of the first metal fitting 20 on the rear end side. The screw portion 22 includes a screw groove for fixing the pressure sensor 10 to the cylinder head of the internal combustion engine. The tool engaging portion 24 has an outer peripheral shape (for example, a hexagonal cross section) that engages with a tool (not shown) used for attaching and detaching the pressure sensor 10.

  FIG. 2 is an enlarged cross-sectional view of the distal end portion of the pressure sensor 10, specifically, the portion indicated as the region X in FIG. This cross section is a flat cross section including the axis CL. The second metal fitting 80 is disposed on the front end side of the first metal fitting 20, and is joined to the front end of the first metal fitting 20 via the joining portion 26. The joint portion 26 is a melted portion when the first metal fitting 20 and the second metal fitting 80 are welded (for example, laser welding) (hereinafter, the joint portion 26 is referred to as “welded portion 26” or “weld trace 26”). Also called). The joint portion 26 is a portion where the first metal fitting 20 and the second metal fitting 80 are integrated. The joint portion 26 includes a component of the first metal fitting 20 and a component of the second metal fitting 80. The third metal fitting 35 is disposed on the distal end side of the second metal fitting 80, and is joined to the second metal fitting 80 via a joining portion 89. The joint portion 89 is a melted portion when the second metal fitting 80 and the third metal fitting 35 are welded (for example, laser welding) (hereinafter, the joint portion 89 is referred to as “welded portion 89” or “weld trace 89”). Also called). The joint portion 89 is a portion where the second metal fitting 80 and the third metal fitting 35 are integrated. The joint portion 89 includes the component of the second metal fitting 80 and the component of the third metal fitting 35. A diameter-expanded portion 34 that increases in diameter from the front end side toward the rear end side is formed at the front end portion of the third metal fitting 35. When the pressure sensor 10 is attached to the internal combustion engine, the enlarged diameter portion 34 is in close contact with the cylinder head of the internal combustion engine.

  The second metal fitting 80 is formed with a shaft hole 81 that is a through hole centered on the axis CL. The third metal fitting 35 is formed with a shaft hole 39 that is a through-hole centered on the axis CL. The shaft hole 21 of the first metal fitting 20, the shaft hole 81 of the second metal fitting 80, and the shaft hole 39 of the third metal fitting 35 form a continuous through hole communicating with the shaft hole 21 of the first metal fitting 20. Yes. In the shaft hole 81 of the second metal fitting 80, the element portion 50 and the holding screw 32 are arranged in order from the front end side to the rear end side. A pressure receiving portion 40 is disposed in the shaft hole 39 of the third metal fitting 35.

  The pressure receiving unit 40 includes a diaphragm 42 and a rod 44. The diaphragm 42 is a substantially circular film centered on the axis line CL. The outer edge 42o of the diaphragm 42 is welded to the tip of the second metal fitting 30 over the entire circumference (for example, laser welding). A rod 44 is connected to the center of the surface on the rear end side of the diaphragm 42. The rod 44 is a cylindrical portion centering on the axis CL, and extends from the diaphragm 42 toward the rear end direction Dr. The element portion 50 is connected to the rear end portion 49 of the rod 44. The diaphragm 42 and the rod 44 are integrally formed using stainless steel (for example, forging or shaving). However, after the diaphragm 42 and the rod 44 are separately formed, the diaphragm 42 and the rod 44 may be integrated by welding or the like. Moreover, you may employ | adopt other materials (For example, steel, such as low carbon steel, various metal materials).

  A heat receiving portion 90 is joined to the surface on the distal end side of the diaphragm 42 (for example, laser welding). The heat receiving unit 90 is a disk-shaped plate member centered on the axis CL (also referred to as a heat receiving plate). When the pressure sensor 10 is viewed in the rear end direction Dr, substantially the entire diaphragm 42 is hidden by the heat receiving unit 90. The heat receiving part 90 is joined to the diaphragm 42 (and thus the pressure receiving part 40) via the joining part 99. The joint portion 99 is a portion where the heat receiving portion 90 and the diaphragm 42 (and thus the pressure receiving portion 40) are melted during welding (hereinafter, the joint portion 99 is also referred to as “welded portion 99” or “weld mark 99”). Such a joint portion 99 is a portion where the heat receiving portion 90 and the diaphragm 42 are integrated. Further, the joint portion 99 includes a component of the heat receiving portion 90 and a component of the diaphragm 42. The joint 99 is formed at the center of the heat receiving part 90. The heat receiving portion 90 is formed using stainless steel in the present embodiment, but may be formed using other metals.

  The diaphragm 42 closes the shaft hole 39 at the tip of the third metal fitting 35. The diaphragm 42 is exposed in the combustion chamber of the internal combustion engine, and the surface 42f on the tip end direction Df side of the diaphragm 42 forms a pressure receiving surface. In the present embodiment, the pressure receiving surface 42 f can receive the pressure in the combustion chamber through the gap 95 between the diaphragm 42 and the heat receiving portion 90. Further, the diaphragm 42 can receive a load corresponding to the pressure in the combustion chamber through the heat receiving portion 90. And the diaphragm 42 deform | transforms according to the pressure in a combustion chamber. The rod 44 is displaced along the axis CL according to the deformation of the diaphragm 42, thereby transmitting a load corresponding to the pressure received by the diaphragm 42 to the element portion 50 on the rear end side. As the diaphragm 42 is made thinner, the diaphragm 42 is more easily deformed, so that the sensitivity of the pressure sensor 10 can be increased.

  The holding screw 32 is attached to the rear end side of the shaft hole 81 of the second metal fitting 80. The holding screw 32 is formed with a shaft hole 36 that is a through-hole centered on the axis CL. A male screw 37 is formed on the outer peripheral surface of the holding screw 32. A female screw 88 corresponding to the male screw 37 of the holding screw 32 is formed on the inner peripheral surface of the rear end side portion of the shaft hole 81 of the second metal fitting 80. The holding screw 32 is screwed into the shaft hole 81 from the rear end side of the second metal fitting 80. The element unit 50 is sandwiched between the holding screw 32 and the rod 44 of the pressure receiving unit 40. The holding screw 32 applies a preload to the element unit 50. By adjusting the number of rotations of the holding screw 32 when the holding screw 32 is screwed into the second metal fitting 80, an appropriate preload can be easily realized. Therefore, the accuracy of pressure measurement can be improved. Note that the holding screw 32 is made of stainless steel. However, other materials (for example, steel such as low carbon steel, various metal materials) may be adopted.

  The element unit 50 includes two electrodes 52, a piezoelectric element 51 sandwiched between the two electrodes 52, a pressing plate 54 disposed on the front end side of the front end electrode 52, and an electrode 52 on the rear end side. A lead portion 53, a pressing plate 54, and an insulating plate 55 are arranged in order in the rear end direction Dr. As shown in FIG. 2, the pressing plate 54, the electrode 52, the piezoelectric element 51, the electrode 52, the lead portion 53, the pressing plate 54, and the insulating plate 55 are laminated in this order from the front end side to the rear end side. Yes. The surface on the rear end side of the insulating plate 55 is supported by the surface on the front end side of the press screw 32. The rear end portion 49 of the rod 44 is in contact with the front end surface of the front end holding plate 54. The piezoelectric element 51 is connected to the rod 44 via a tip-side electrode 52 and a pressing plate 54. The whole of the rod 44, the holding plate 54 on the distal end side, and the electrode 52 forms a connection portion 100 that connects the diaphragm 42 and the piezoelectric element 51.

  FIG. 3 is an exploded perspective view of the element unit 50. As shown in the drawing, the piezoelectric element 51 and the electrode 52 are disk-shaped plate members centered on the axis CL. The holding plate 54 and the insulating plate 55 are annular plate-like members centered on the axis line CL. The piezoelectric element 51 is formed using quartz in the present embodiment, but a piezoelectric element formed of another material may be adopted. On the piezoelectric element 51, an electric charge is generated according to the load transmitted through the rod 44 from the pressure receiving portion 40 (FIG. 2). The piezoelectric element 51 outputs an electric charge (for example, an electric signal) corresponding to the load through the two electrodes 52. Based on the output electric signal, the deformation amount of the diaphragm 42, that is, the pressure in the combustion chamber can be specified. Thus, the piezoelectric element 51 has an electrical characteristic that varies depending on the pressure received by the pressure receiving unit 40. The electrode 52 and the pressing plate 54 are formed using stainless steel in the present embodiment, but may be formed using other metals. The insulating plate 55 is a member for insulating between the lead portion 53 and the holding screw 32 (FIG. 2). In this embodiment, the insulating plate 55 is formed of alumina, but may be formed of other types of insulating materials.

  The lead part 53 includes a disk part 57 that is a substantially disk-shaped plate member, and a terminal part 56 that extends from the center part of the disk part 57 toward the rear end direction Dr. The terminal portion 56 passes through the through hole 54h of the pressing plate 54 and the through hole 55h of the insulating plate 55 and protrudes toward the rear end direction Dr (FIG. 2). The lead portion 53 is formed using stainless steel in the present embodiment, but may be formed using other metals. The lead part 53 can be produced by punching out the shape of the disk part 57 and the terminal part 56 from a stainless steel flat plate, and then bending the part to be the terminal part 56.

  In the shaft hole 81 of the second metal fitting 80 (FIG. 2), the lead portion 53 is arranged such that the disk portion 57 is in surface contact with the electrode 52 and the terminal portion 56 extends to the rear end side. The terminal portion 56 passes through the through hole 54 h at the center of the pressing plate 54 and the through hole 55 h at the center of the insulating plate 55. The rear end portion of the terminal portion 56 is disposed in the shaft hole 36 in a state of being separated from the inner wall surface of the shaft hole 36 of the presser screw 32.

  Each member (excluding the insulating plate 55) constituting the element unit 50 is disposed in the shaft hole 81 of the second metal fitting 80 so as to be separated from the inner wall surface of the second metal fitting 80. The electrode 52 on the rear end side of the piezoelectric element 51 is electrically connected to a lead portion 53 (in this embodiment, further a holding plate 54), and the first metal fitting 20, the second metal fitting 80, and the third metal fitting 35 are connected. It is electrically separated from. The electrode 52 on the distal end side of the piezoelectric element 51 is electrically connected to the third metal fitting 35 through the holding plate 54 on the distal end side, the rod 44, and the diaphragm 42. In the present embodiment, in order to make the distribution of the load applied to the piezoelectric element 51 uniform, the pressing plate 54 is disposed not only on the rear end side but also on the front end side of the piezoelectric element 51.

  A cable 60 is disposed in the shaft hole 21 of the first metal fitting 20. The cable 60 is a member for transmitting the electric charge of the piezoelectric element 51 to an electric circuit (not shown) for detecting the combustion pressure of the internal combustion engine based on the electric charge of the piezoelectric element 51. In this embodiment, noise is reduced by using a so-called shielded wire having a multilayer structure as the cable 60. The cable 60 includes an inner conductor 65, an insulator 64, a conductive coating 63, an outer conductor 62, and a jacket 61 arranged from the center toward the outer peripheral side. The inner conductor 65 is composed of a plurality of conductive wires. The outer side of the inner conductor 65 in the radial direction is surrounded by an insulator 64. A conductive coating 63 is provided on the outer peripheral surface of the insulator 64. An outer conductor 62 that is a mesh shield is provided on the outer side in the radial direction of the conductive coating 63. The outer peripheral surface of the outer conductor 62 is covered with a jacket 61. A cable including a plurality of members arranged coaxially in this way is also called a coaxial cable.

  As shown in FIG. 2, the outer conductor 62 that is not covered by the jacket 61 is exposed from the portion covered by the jacket 61 toward the distal end side at the distal end portion of the cable 60. Further, the insulator 64 that is not covered by the external conductor 62 is exposed from the portion where the external conductor 62 is exposed toward the tip side. Further, the inner conductor 65 that is not covered by the insulator 64 is exposed from the portion where the insulator 64 is exposed toward the tip side.

  The internal conductor 65 exposed at the distal end portion of the cable 60 is connected to the terminal portion 56 of the element portion 50 through the flat plate conductive wire 75 and the small diameter conductive wire 74. Specifically, the flat conductor 75 is welded to the tip of the inner conductor 65, and the rear end of the thin conductor 74 wound in a coil shape is welded to the tip of the flat conductor 75, The distal end of the small diameter conductive wire 74 is welded to the rear end portion of the terminal portion 56. The flat conductive wire 75 and the thin conductive wire 74 can transmit the electric charge of the piezoelectric element 51 from the terminal portion 56 to the internal conductor 65. In addition, as a structure for connecting the internal conductor 65 and the terminal part 56, it replaces with the structure using the flat conducting wire 75 and the thin diameter conducting wire 74, and can employ | adopt other arbitrary structures.

  From the tip of the terminal portion 56 to the position on the rear end side of the welded portion connecting the terminal portion 56 and the thin wire 74, the range including the entire terminal portion 56 and the tip of the thin wire 74 is Covered by a heat-shrinkable tube 72. Thereby, the reliability of the electrical insulation between the terminal part 56 and the holding screw 32 is improved. When manufacturing the pressure sensor 10, the integration of the lead portion 53 having the terminal portion 56 and the thin lead wire 74 by welding and the covering with the heat shrinkable tube 72 may be performed prior to the entire assembly.

  A grounding conductor 76 extending from the distal end of the external conductor 62 to the distal end side is connected to the distal end portion of the external conductor 62. The grounding conductor 76 is composed of a stranded wire formed continuously from the outer conductor 62. The front end portion of the grounding conductor 76 is welded to the rear end portion of the holding screw 32. As a result, the outer conductor 62 is grounded through the grounding conductor 76, the holding screw 32, the second metal fitting 80, the third metal fitting 35, and the cylinder head of the internal combustion engine.

  When manufacturing the pressure sensor 10, the rod 44 is inserted into the shaft hole 39 from the distal end side of the third metal fitting 35. The diaphragm 42 and the third metal fitting 35 are welded (for example, laser welding) to form the joint portion 45. The joint portion 45 is a portion where the diaphragm 42 and the third metal fitting 35 are melted during welding (hereinafter, the joint portion 45 is also referred to as “welded portion 45” or “weld mark 45”). Such a joint portion 45 is a portion where the diaphragm 42 and the third metal fitting 35 are integrated. Further, the joint portion 45 includes a component of the diaphragm 42 and a component of the third metal fitting 35. Further, the joint portion 45 joins the diaphragm 42 and the third metal fitting 35. The holding screw 32 is screwed into the shaft hole 81 from the rear end side of the second metal fitting 80. At this stage, the holding screw 32 is temporarily fixed to the second metal fitting 80. Thereafter, the element unit 50 is inserted into the shaft hole 81 from the distal end side of the second metal fitting 80. The terminal portion 56 of the lead portion 53 of the element portion 50 is integrated with the small-diameter conductive wire 74 and the heat shrinkable tube 72 in advance. And the thin diameter conducting wire 74 is inserted from the front end side of the shaft hole 36 of the holding screw 32, and the small diameter conducting wire 74 is drawn out from the rear end side of the shaft hole 36. The rear end surface of the insulating plate 55 is supported by the front end surface of the cap screw 32. After these, the third metal fitting 35 is disposed on the distal end side of the second metal fitting 80. As a result, the element unit 50 is sandwiched between the holding screw 32 and the rod 44. And the 3rd metal fitting 35 and the 2nd metal fitting 80 are welded, and the joined part 89 is formed. Thereafter, a preload is applied to the element portion 50 by rotating the holding screw 32 with respect to the second metal fitting 80. By adjusting the number of rotations of the holding screw 32, the preload can be adjusted.

  Then, the rear end of the small-diameter conductive wire 74 drawn from the rear end side of the holding screw 32 (specifically, the shaft hole 36) and the front end of the internal conductor 65 are welded to the flat plate conductive wire 75. Further, the front end portion of the grounding conductor 76 and the rear end portion of the holding screw 32 are welded. Further, the cable 60 is passed through the shaft hole 21 of the first metal fitting 20, and the tip of the first metal fitting 20 and the second metal fitting 80 are welded to form the joint portion 26. Thereafter, molten rubber is injected into the shaft hole 21 of the first metal fitting 20 to fill the shaft hole 21 with a rubber layer (not shown), and the pressure sensor 10 is completed. By forming the rubber layer, the waterproof property in the pressure sensor 10 is improved and the vibration proof property is also improved. Note that molten resin may be injected into the shaft hole 21 instead of the molten rubber.

  In addition, as an assembly order of the second metal fitting 80, the third metal fitting 35, the element portion 50, and the holding screw 32, other various orders can be adopted instead of the above-described order. For example, the diaphragm 42 is welded to the third metal fitting 35, the second metal fitting 80 is welded to the third metal fitting 35, the element portion 50 is inserted into the shaft hole 81 from the rear end side of the second metal fitting 80, and the second metal fitting 35 is inserted. An order in which the holding screw 32 is screwed into the shaft hole 81 from the rear end side of 80 may be adopted.

A-2. Operation of Pressure Sensor 10 FIG. 4 is an explanatory diagram of the operation of the pressure sensor 10. In the drawing, a plane cross section including a part of the axis CL on the tip side of the pressure sensor 10 is shown. The pressure receiving surface 42 f of the diaphragm 42 can receive the pressure Pc in the combustion chamber through the gap 95 between the diaphragm 42 and the heat receiving portion 90. Further, the diaphragm 42 can receive a load corresponding to the pressure Pc through the heat receiving portion 90. The diaphragm 42 bends (deforms) according to the pressure Pc in the combustion chamber. In the embodiment of FIG. 4, the diaphragm 42 bends in the axial direction. The rod 44 is displaced approximately parallel to the axis CL in accordance with the bending (deformation) of the diaphragm 42. As a result, the rod 44 transmits a load corresponding to the pressure Pc to the element unit 50.

  Further, the heat receiving portion 90 is disposed on the tip side of the diaphragm 42, that is, on the combustion chamber side. The heat receiving unit 90 can receive heat from the combustion chamber instead of the diaphragm 42. For example, heat generated by the combustion of the fuel can be conducted to the surface on the front end side of the heat receiving unit 90 through the gas in the combustion chamber. Further, high-temperature combustion gas can come into contact with the surface on the front end side of the heat receiving unit 90. As described above, the temperature of the heat receiving unit 90 (particularly, the tip side surface) can be increased. Since the diaphragm 42 is disposed on the rear end side of the heat receiving unit 90, it is less likely to receive heat from the combustion chamber than the heat receiving unit 90. Therefore, the thermal expansion of the diaphragm 42 is suppressed.

  FIG. 5 is an explanatory diagram of the operation of the pressure sensor 10x of the reference example. In the drawing, a plane cross section including an axis CL of a part of the tip side of the pressure sensor 10x is shown. The only difference from the pressure sensor 10 of the embodiment of FIG. 4 is that the heat receiving portion 90 is omitted. The configuration of the other part of the pressure sensor 10x is the same as the configuration of the corresponding part of the pressure sensor 10 of the embodiment.

  The pressure receiving surface 42f of the diaphragm 42 receives the pressure Pc in the combustion chamber, similarly to the pressure receiving surface 42f of the embodiment of FIG. Further, in the reference example of FIG. 5, unlike the embodiment of FIG. 4, the heat receiving portion 90 is omitted, so that the portion (for example, the pressure receiving surface 42 f) on the tip end direction Df side of the diaphragm 42 is from the combustion chamber. Receive heat. Thereby, the part by the side of the front-end | tip direction Df among the diaphragms 42 can be thermally expanded locally. In the reference example, the outer edge 42 o of the diaphragm 42 is joined to the third metal fitting 35. Therefore, the diaphragm 42 tends to extend toward the inner peripheral side (axis line CL side) due to thermal expansion. In this case, the thermal expansion of the diaphragm 42 can apply a force parallel to the axis CL to the rod 44. For example, in the reference example of FIG. 5, the thermal expansion of the pressure receiving surface 42 f of the diaphragm 42 applies a force F in the distal direction Df to the rod 44. Thereby, the load applied to the element part 50 becomes small. As described above, in the pressure sensor 10x of the reference example, the load applied to the element unit 50 can fluctuate greatly depending on the temperature of the combustion gas, so that the error of the signal from the element unit 50 increases.

  In the embodiment shown in FIG. 4, thermal expansion of the diaphragm 42 is suppressed by the heat receiving unit 90. Therefore, as compared with the reference example of FIG. 5, in the first embodiment, the error of the signal from the element unit 50 can be reduced.

A-3. Details of Configuration Near Heat-Receiving Unit 90 and Diaphragm 42 Here, as shown in FIG. 2, the thickness (plate thickness) of the heat-receiving unit 90 that is a plate-like member is t. When the thickness t of the heat receiving unit 90 is large, the volume of the heat receiving unit 90 is larger than when the thickness t is small, and thus the amount of heat (heat capacity) that can be absorbed by the heat receiving unit 90 is large. As a result, the greater the thickness of the heat receiving portion 90, the more difficult the heat from the combustion chamber is transmitted to the diaphragm 42, so that the thermal expansion of the diaphragm 42 can be further suppressed. Signal error can be reduced.

  As shown in FIG. 2, let d be the minimum distance in the axial direction between the heat receiving portion 90 and the diaphragm 42. In the embodiment of FIG. 2, the pressure receiving surface 42 f of the diaphragm 42 and the surface on the rear end side of the heat receiving unit 90 are directly joined. Therefore, the minimum distance d is zero. When the minimum distance d is small, the high-temperature combustion gas is less likely to flow into the gaps 95 and 95a than when the minimum distance d is large. Therefore, the smaller the minimum distance d, the more the thermal expansion of the diaphragms 42 and 42a can be suppressed, and the error of the signal from the element unit 50 can be reduced. For example, the minimum distance d is preferably 0.5 mm or less, and particularly preferably 0.3 mm or less.

  Further, as shown in FIG. 2, in the cross section including the axis line CL, the surface 90f on the rear end side of the heat receiving portion 90 (that is, the surface facing the pressure receiving surface 42f of the diaphragm 42) and the direction perpendicular to the axis line are The angle formed is θ. In the example of FIG. 2, the rear end surface 90 f of the heat receiving portion 90 is slightly curved. For this reason, the angle θ is 0 degrees at the position intersecting the axis CL, and increases as it goes radially outward from the axis CL. When the angle θ is small, high-temperature combustion gas is less likely to flow into the gap 95 than when the angle θ is large. For this reason, the absolute value of the angle θ is preferably within 20 degrees. When the absolute value of the angle θ is within 20 degrees, the amount of heat transferred to the diaphragm can be further reduced by suppressing high-temperature combustion gas from flowing into the gap 95. As a result, the thermal expansion of the diaphragm 42 can be further suppressed, and as a result, the error of the signal from the element unit 50 can be reduced.

  Next, the effective area Sd of the diaphragm 42 according to the first embodiment, the connection area Sn, and the heat receiving area Sn2 of the heat receiving unit 90 will be described.

  FIG. 6 is an explanatory diagram of parameters Sn2, Sn, and Sd of the pressure sensor 10 of the first embodiment. 6 (A), 6 (C), and 6 (E) are perspective views of the distal end portion of the pressure sensor 10, and FIGS. 6 (B) and 6 (D) show the heat receiving portion 90 along the axis CL. FIG. 6F shows a projection view obtained by projecting the diaphragm 42 onto the projection plane perpendicular to the axis line CL. FIGS. 6C and 6E show a state where the heat receiving portion 90 is removed from the pressure receiving portion 40.

  6A and 6B show the heat receiving area Sn2. In the drawing, a region corresponding to the heat receiving area Sn2 is hatched. The heat receiving area Sn2 is the entire area of the heat receiving unit 90 in the projection view of FIG. In the first embodiment, the area of the surface on the tip direction Df side of the heat receiving portion 90 corresponds to the heat receiving area Sn2. The heat receiving area Sn <b> 2 indicates an area of a region where heat from the combustion chamber can be received instead of the diaphragm 42. When the heat receiving area Sn2 is large, heat from the combustion chamber is less likely to be transmitted to the diaphragm 42 than when the heat receiving area Sn2 is small. Therefore, as the heat receiving area Sn2 is larger, the thermal expansion of the diaphragm 42 is suppressed, that is, the error of the signal from the element unit 50 is reduced.

  6C and 6D show the connection area Sn. In the drawing, the region corresponding to the connection area Sn is hatched. The connection area Sn includes a cross section of a portion from the heat receiving portion 90 to the diaphragm 42 (hereinafter also referred to as a target portion) on a cross section perpendicular to the axis CL, and a virtual region where the total length of the contour is minimized. Is the minimum value of the area of the minimum inclusion region. In other words, the connection area Sn is the area of the minimum inclusion region at a specific axial position. The position in the specific axial direction is a position where the minimum inclusion region in the cross section perpendicular to the axis CL is the smallest among the positions in the axial direction in the range from the heat receiving unit 90 to the diaphragm 42. And the minimum inclusion area | region in a specific cross section is a virtual area | region where the full length of the outline containing the said target part becomes the minimum on the specific cross section. The minimum inclusion region is also called a convex hull. The minimum inclusion area is one continuous area. The area of such a minimum inclusion region can vary depending on the position of the cross section in the axial direction. The connection area Sn is the minimum value of the area of the minimum inclusion region that can change according to the position of the cross section. In this embodiment, the part from the heat receiving part 90 to the diaphragm 42 includes the heat receiving part 90, the diaphragm 42, and a part connecting the heat receiving part 90 and the diaphragm 42.

  In the first embodiment, the heat receiving portion 90 is directly connected to the diaphragm 42 by the joint portion 99, and therefore the portion connecting the heat receiving portion 90 and the diaphragm 42 is the heat receiving portion 90 of the joint portion 99. This is a portion between the rear end surface and the front end surface of the diaphragm 42. In the first embodiment, the connection area Sn, that is, the minimum area of the minimum inclusion region is the connection surface between the heat receiving unit 90 and the diaphragm 42 (that is, the heat receiving unit 90) in the cross section from the heat receiving unit 90 to the diaphragm 42. The area of the minimum inclusion region including the cross section of the joint 99 on the cross section including the rear end surface and the front end surface of the diaphragm 42). 6D shows a connection portion 93 joined to the diaphragm 42 on the surface on the rear end side of the heat receiving portion 90. FIG. The connection portion 93 corresponds to a cross section of a joint portion 99 (FIG. 2) that joins the heat receiving portion 90 and the diaphragm 42. The area of the minimum inclusion region 94 including the connection portion 93 is the connection area Sn. In the first embodiment, since the shape of the connection portion 93 is substantially circular, the shape of the minimum inclusion region 94 is approximately the same as the shape of the connection portion 93, and the connection area Sn is the area of the connection portion 93 (that is, The cross-sectional area of the joint 99) is approximately the same. The connection portion 43 in FIG. 6C is a portion corresponding to the connection portion 93 in the diaphragm 42.

  The heat receiving unit 90 can receive heat from the combustion chamber and thermally expand (that is, can deform). When the connection part 93 with the diaphragm 42 is large in the heat receiving unit 90, that is, when the connection area Sn is large, the deformation of the heat receiving unit 90 is easily transmitted to the diaphragm 42. When the diaphragm 42 is deformed due to the deformation of the heat receiving unit 90, an unintended load can be applied to the element unit 50 due to the deformation of the diaphragm 42. Therefore, the smaller the connection area Sn, the smaller the error of the signal from the element unit 50.

  FIGS. 6E and 6F show the diaphragm effective area Sd (hereinafter also simply referred to as “effective area Sd”). In the drawing, the area corresponding to the effective area Sd is hatched. The effective area Sd is an area of a region 46 surrounded by the joint 45 in the projection view of FIG. Here, the inner peripheral side contour 45i of the joint portion 45 (that is, the contour 45i of the region 46) is the inner peripheral side of the joint portion 45 on the surface of the diaphragm 42 connected to the third metal fitting 35. A contour is employed. For example, in the embodiment of FIGS. 2 and 6F, the contour on the inner peripheral side of the joint 45 on the rear end surface of the diaphragm 42 corresponds to the contour 45i of the region 46.

  In 1st Embodiment, the junction part 45 which joins the diaphragm 42 and the 3rd metal fitting 35 is cyclic | annular in the projection view of FIG.6 (F). Therefore, the part in the area | region 46 enclosed by the junction part 45 among the diaphragms 42 can deform | transform according to the pressure in a combustion chamber.

  In addition, when the ratio (Sn2 / Sd) of the heat receiving area 90 of the heat receiving section 90 to the effective area Sd of the diaphragm 42 is large, the ratio of the portion hidden in the rear end side of the heat receiving section 90 in the diaphragm 42 increases. Therefore, it is difficult for heat from the combustion chamber to be transmitted to the diaphragm 42. Therefore, the larger the ratio (Sn2 / Sd) is, the more the thermal expansion of the diaphragm 42 is suppressed, and thus the pressure error Ep can be reduced. For this reason, from the viewpoint of reducing the pressure error Ep, the ratio (Sn2 / Sd) is, for example, preferably 0.8 or more, more preferably 0.9 or more, and particularly preferably 1 or more. However, when the ratio Sn2 / Sd is large, the heat receiving portion 90 tends to come into contact with the mounting hole of the pressure sensor 10 of the cylinder head of the internal combustion engine. Therefore, the upper limit of the ratio Sn2 / Sd is preferably determined so that the heat receiving portion 90 does not contact the mounting hole of the cylinder head. For example, the ratio Sn2 / Sd is preferably 1.2 or less.

A-4. Evaluation Test For the pressure sensor 10 of the first embodiment, twelve types of samples with different thickness t of the heat receiving portion 90 and the ratio of the connection area Sn to the effective area Sd described above (Sn / Sd) were prepared. An evaluation test was conducted. Specifically, as shown in Table 1, the thickness t of the heat receiving portion 90 is any one of 0.1 mm, 0.2 mm, 0.21 mm, and 0.3 mm, and the ratio (Sn / Sd) is 0. A total of 12 types of samples were created for all combinations ((4 × 3) combinations) that were either .24 mm, 0.25 mm, or 0.26 mm.

Note that samples with different ratios (Sn / Sd) were created by fixing the effective area Sd to 16 mm ² and changing the connection area Sn by changing the dimensions of the joint 99. In addition, the heat receiving part 90 whose heat receiving area Sn2 is 16 mm < ² > was used for each sample. Therefore, in each sample, the ratio (Sn2 / Sd) of the heat receiving area Sn2 to the effective area Sd is 1. In each sample, the minimum distance d was set to 0 as shown in FIG.

  In the evaluation test, a sample sensor and a target pressure sensor (also referred to as a “target sensor”) were attached to the same cylinder (ie, combustion chamber) of the internal combustion engine. Then, by operating the internal combustion engine, a pressure waveform was obtained from each of the sample sensor and the target sensor. As the internal combustion engine, an in-line four-cylinder engine with a displacement of 1.3 L and a natural intake air was used. The internal combustion engine was operated under the condition that the maximum pressure in the combustion chamber was 20 MPa.

  FIG. 7 is a graph showing an example of a pressure waveform measured by the pressure sensor. The horizontal axis represents the crank angle CA, and the vertical axis represents the pressure (unit: kPa). A crank angle CA of zero degrees indicates a top dead center. In the graph, a reference graph G1 and a sample graph G2 are shown. The reference graph G1 shows the pressure measured by the target sensor. The sample graph G2 shows the pressure measured by the pressure sensor sample.

  As shown in the drawing, the pressure G2 measured by the pressure sensor sample may be different from the pressure G1 measured by the target pressure sensor (in the example of FIG. 7, the crank angle CA is zero to 180 degrees). Within range). The target pressure sensor is adjusted in advance so that the pressure can be measured with sufficiently good accuracy. In this evaluation test, the sample pressure G2 and the target pressure G1 were measured over five cycles. The difference between the two pressures G1 and G2 at the same timing was calculated. The maximum difference Em (FIG. 7) was specified for each cycle. The average value of the five maximum differences Em was calculated as the pressure error Ep of the pressure sensor of the sample.

  And the evaluation of the sample whose absolute value of the pressure error Ep is 2% of 20 MPa, that is, 400 kPa or less is “A”, and the evaluation of the sample exceeding 400 kPa is “B”.

  The evaluation results are as shown in Table 1. In the four types of samples with a ratio (Sn / Sd) of 0.24, the evaluation of the sample with the heat receiving portion 90 having a thickness t of 0.1 mm is “B”, and the thickness t of the heat receiving portion 90 is The evaluation of samples of 0.2 mm or more, that is, 0.2 mm, 0.21 mm, and 0.3 mm was “A”.

  In the four types of samples having a ratio (Sn / Sd) of 0.25, the evaluation of the samples having a thickness t of the heat receiving portion 90 of 0.2 mm or less, that is, 0.1 mm or 0.2 mm is “B”. The evaluation of the samples with the heat receiving portion 90 having a thickness t of 0.21 mm or more, that is, 0.21 mm and 0.3 mm was “A”.

  In the four types of samples having a ratio (Sn / Sd) of 0.26, the evaluation of the samples in which the thickness t of the heat receiving portion 90 is 0.21 mm or less, that is, 0.1 mm, 0.2 mm, 0.21 mm , “B” and the evaluation of the sample with the heat receiving portion 90 having a thickness t of 0.3 mm was “A”.

  From the above results, the thickness t of the heat receiving portion 90 is 0.21 mm or more (t ≧ 0.21 mm), and the ratio (Sn / Sd) is 0.25 or less ((Sn / Sd) ≦ 0.25), that is, in the range surrounded by the dotted line in Table 1, it was found that the pressure error Ep can be made sufficiently small.

  The reason for this is as follows. As described above, since the thermal expansion of the diaphragm 42 is suppressed as the thickness t of the heat receiving unit 90 is increased, the pressure error Ep is reduced. The smaller the ratio of the connection area Sn to the effective area Sd of the diaphragm 42a, that is, the smaller the ratio (Sn / Sd), the smaller the influence of the deformation of the heat receiving portion 90 on the deformation of the diaphragm 42. Ep becomes small. Therefore, a range in which the thickness t of the heat receiving unit 90 is relatively large and the ratio (Sn / Sd) is relatively small, specifically, t ≧ 0.21 mm and (Sn / Sd) ≦ 0. It is considered that the pressure error Ep can be sufficiently reduced within a range satisfying .25. It is considered that the thickness t is more preferably in a larger range, for example, t ≧ 0.3 mm. Further, it is considered that the ratio (Sn / Sd) is more preferably in a smaller range, for example, (Sn / Sd) ≦ 0.24.

B. Second embodiment:
FIG. 8 is an explanatory diagram of the pressure sensor 10a of the second embodiment. In the drawing, as in FIG. 4, a plane cross section including an axis CL of the tip side portion of the pressure sensor 10 a is shown. The only difference from the first embodiment of FIG. 4 is that the rod 44a extends to the tip direction Df side from the diaphragm 42a and that the heat receiving portion 90 is joined to the tip portion of the rod 44a. It is. The structure of the other part of the pressure sensor 10a is the same as the structure of the corresponding part of the pressure sensor 10 of the first embodiment.

  In the second embodiment, the pressure receiving portion 40a includes a rod 44a, a diaphragm 42a, and a fixing portion 41a. The diaphragm 42a is an annular film centered on the axis CL. The outer peripheral edge 42ao of the diaphragm 42a is welded to the tip of the third metal fitting 35 over the entire circumference (for example, laser welding). The joint portion 45 that joins the diaphragm 42a and the third metal fitting 35 is a portion melted during welding. A fixed portion 41a is connected to the inner peripheral edge 42ai of the diaphragm 42a. The fixed portion 41a is a cylindrical portion centered on the axis CL, and extends from the edge 42ai of the diaphragm 42a toward the distal direction Df. The fixed portion 41a and the diaphragm 42a are integrally formed using stainless steel (for example, forging or shaving). However, after the fixing portion 41a and the diaphragm 42a are separately formed, the fixing portion 41a and the diaphragm 42a may be integrated by welding or the like. Moreover, you may employ | adopt other materials (For example, steel, such as low carbon steel, various metal materials).

  A rod 44a is inserted into a through hole on the inner peripheral side of the fixed portion 41a and the diaphragm 42a. The rod 44a is a columnar member centered on the axis CL. The rear end surface of the rod 44 a is in contact with the surface on the front end side of the pressing plate 54 on the front end side of the element unit 50. The distal end portion of the rod 44a protrudes from the fixed portion 41a toward the distal end side. The rod 44a is formed using stainless steel in the present embodiment, but may be formed using other metals.

  The fixed portion 41a and the rod 44a are welded over the entire circumference (for example, laser welding). Thus, the diaphragm 42a is connected to the rod 44a through the fixing portion 41a. The piezoelectric element 51 is connected to the rod 44 a via the tip-side electrode 52 and the pressing plate 54. The whole of the fixing portion 41 a, the rod 44 a, the holding plate 54 on the distal end side, and the electrode 52 forms a connection portion 100 a that connects the diaphragm 42 a and the piezoelectric element 51.

  The heat receiving part 90 is joined to the tip surface of the rod 44a (for example, laser welding). The heat receiving part 90 is joined to the rod 44a via the joint 99a. The joint portion 99a is a portion where the heat receiving portion 90 and the rod 44a are melted during welding (hereinafter, the joint portion 99a is also referred to as “welded portion 99a” or “weld mark 99a”). Such a joint portion 99a is a portion where the heat receiving portion 90 and the rod 44a are integrated. Further, the joint portion 99a includes a component of the heat receiving portion 90 and a component of the rod 44a. Thus, in 2nd Embodiment, the heat receiving part 90 is connected to the diaphragm 42a via the rod 44a and the fixing | fixed part 41a. The joint portion 99a is formed at the center of the heat receiving portion 90. In 2nd Embodiment, the junction part 99a is formed over the whole end surface at the front end side of the rod 44a. The heat receiving portion 90 is formed using stainless steel in the present embodiment, but may be formed using other metals.

  When the pressure sensor 10a is viewed in the rear end direction Dr, substantially the entire diaphragm 42a is hidden by the heat receiving unit 90. Similar to the first embodiment, the heat receiving unit 90 can receive heat from the combustion chamber instead of the diaphragm 42a. Since the diaphragm 42 a is disposed on the rear end side of the heat receiving unit 90, it is less likely to receive heat from the combustion chamber than the heat receiving unit 90. Therefore, the thermal expansion of the diaphragm 42a is suppressed. Compared to the reference example of FIG. 5, in the second embodiment, the error of the signal from the element unit 50 can be reduced.

B-2. Details of Configuration Near Heat Receiving Unit 90 and Diaphragm 42a Also in the second embodiment, as shown in FIG. 8, the thickness (plate thickness) of the heat receiving unit 90, which is a plate-like member, is t. Further, as shown in FIG. 8, the minimum distance in the axial direction between the heat receiving portion 90 and the diaphragm 42a is defined as d. In the second embodiment of FIG. 8, unlike the first embodiment of FIG. 2, the heat receiving portion 90 is disposed at a position away from the pressure receiving surface 42af, which is the surface of the diaphragm 42a on the tip direction Df side, in the tip direction Df. ing. In the second embodiment, the minimum distance d is a distance between the surface on the rear end direction Dr side of the heat receiving unit 90 and the pressure receiving surface 42af of the diaphragm 42a. Similar to the first embodiment, for example, the minimum distance d is preferably 0.5 mm or less, and particularly preferably 0.3 mm or less.

  Further, as shown in FIG. 8, in the cross section including the axis line CL, the surface 90f on the rear end side of the heat receiving portion 90 (that is, the surface facing the pressure receiving surface 42af of the diaphragm 42a) and the direction perpendicular to the axis line are The angle formed is θ. In the example of FIG. 8, the surface 90f on the rear end side of the heat receiving unit 90 is a surface perpendicular to the axis CL, and thus the angle θ is zero. Similar to the first embodiment, the absolute value of the angle θ is preferably within 20 degrees. In this way, it is possible to suppress the high-temperature combustion gas from flowing into the gap 95a, and to further suppress the thermal expansion of the diaphragm 42a, and to reduce the error of the signal from the element unit 50.

  Next, the effective area Sd, the connection area Sn, and the heat receiving area Sn2 of the heat receiving unit 90 of the diaphragm 42a of the second embodiment will be described.

  FIG. 9 is an explanatory diagram of parameters Sn2, Sn, Sd of the pressure sensor 10a (FIG. 6) of the second embodiment. 9A, 9C, and 9E are perspective views of the tip of the pressure sensor 10a, and FIGS. 9B and 9D illustrate the heat receiving portion 90 with the axis CL. FIG. 9F shows a projection view obtained by projecting the diaphragm 42a onto the projection plane perpendicular to the axis line CL. FIG. 9C and FIG. 9E show a state where the heat receiving portion 90 is removed from the rod 44a.

  FIG. 9A and FIG. 9B show the heat receiving area Sn2. In the drawing, a region corresponding to the heat receiving area Sn2 is hatched. The heat receiving area Sn2 is the entire area of the heat receiving unit 90 in the projection view of FIG. 9B. In the second embodiment, the area of the surface on the tip direction Df side of the heat receiving portion 90 corresponds to the heat receiving area Sn2. Similarly to the first embodiment, also in the second embodiment, the larger the heat receiving area Sn2, the more the thermal expansion of the diaphragm 42a is suppressed, that is, the error of the signal from the element unit 50 is reduced.

  9C and 9D show the connection area Sn. In the drawing, the region corresponding to the connection area Sn is hatched. In the second embodiment, the heat receiving portion 90 (FIG. 8) is indirectly connected to the diaphragm 42a via the rod 44a and the fixing portion 41a (the heat receiving portion 90 and the rod 44a are directly connected by the joint portion 99a. Connected). The part from the heat receiving part 90 to the diaphragm 42a includes the heat receiving part 90, the diaphragm 42a, and a part connecting the heat receiving part 90 and the diaphragm 42a. The portion connecting the heat receiving portion 90 and the diaphragm 42a is a portion between the rear end surface of the heat receiving portion 90 and the front end surface of the rod 44a in the joint portion 99a, and the fixed portion 41a of the rod 44a. The part from the part connected to the part connected to the heat receiving part 90, and the fixing | fixed part 41a are included. In the second embodiment, the connection area Sn, that is, the minimum area of the minimum inclusion region is the smallest in the cross-section perpendicular to the axis CL in the axial direction range from the heat receiving unit 90 to the diaphragm 42a. It is the area of the minimum inclusion region in a specific cross section. Specifically, it is the area of the minimum inclusion region in the cross section between the surface on the rear end side of the heat receiving portion 90 and the end on the front end side of the fixing portion 41a. 9D shows a connection portion 93a connected to the rod 44a on the surface on the rear end side of the heat receiving portion 90. FIG. This connection portion 93a corresponds to a cross section of a joint portion 99a (FIG. 6) that joins the heat receiving portion 90 and the rod 44a. In the second embodiment, since the shape of the connection portion 93a is the same as the cross-sectional shape of the rod 44a, the area of the minimum inclusion region 94a including the connection portion 93a is the connection area Sn. In the second embodiment, since the shape of the connection portion 93a (that is, the cross-sectional shape of the rod 44a) is substantially circular, the shape of the minimum inclusion region 94a is approximately the same as the shape of the connection portion 93a, and the connection area Sn Is approximately the same as the area of the connecting portion 93a (that is, the cross-sectional area of the joint 99a and hence the cross-sectional area of the rod 44a). The connection portion 43a in FIG. 9C is a portion corresponding to the connection portion 93a in the rod 44a.

  Similarly to the first embodiment, also in the second embodiment, the heat receiving unit 90 can be thermally expanded (that is, can be deformed) by receiving heat from the combustion chamber. When the connection portion 93a of the heat receiving unit 90 is large, that is, when the connection area Sn is large, the deformation of the heat receiving unit 90 is easily transmitted to the diaphragm 42a. Therefore, the smaller the connection area Sn, the smaller the error of the signal from the element unit 50.

  FIG. 9E and FIG. 9F show the diaphragm effective area Sd (effective area Sd). In the drawing, the area corresponding to the effective area Sd is hatched. The effective area Sd is an area of a region 46a surrounded by the joint 45 in the projection view of FIG. Here, as the inner peripheral side contour 45i of the joint portion 45 (that is, the contour 45i of the region 46a), the inner peripheral side contour of the joint portion 45 on the surface connected to the third metal fitting 35 among the surfaces of the diaphragm 42a. Is adopted. For example, in the second embodiment shown in FIGS. 8 and 9F, the contour on the inner peripheral side of the joint 45 on the rear end surface of the diaphragm 42a corresponds to the contour 45i of the region 46a.

  In 2nd Embodiment, the junction part 45 which joins the diaphragm 42a and the 3rd metal fitting 35 is cyclic | annular in the projection view of FIG.9 (F). Accordingly, a portion of the pressure receiving portion 40a (that is, the diaphragm 42a, the fixed portion 41a, and the rod 44a) in the region 46 surrounded by the joint portion 45 can be deformed according to the pressure in the combustion chamber. The effective area Sd is the entire area of the region 46 a surrounded by the joint portion 45.

  Also in the second embodiment, as in the first embodiment, the thickness t of the heat receiving unit 90 is 0.21 mm or more (t ≧ 0.21 mm) and the ratio (Sn / Sd) is 0. It is preferably 25 or less ((Sn / Sd) ≦ 0.25). In this way, the pressure error Ep can be made sufficiently small.

C. Third embodiment:
FIG. 10 is an explanatory diagram of the pressure sensor 10b according to the third embodiment. 10A shows a flat cross section including a part of the axis CL on the tip side of the pressure sensor 10b. FIGS. 10B and 10C show the heat receiving portion 90 on a projection plane perpendicular to the axis CL. The projection figure obtained by projecting is shown. The difference from the first embodiment shown in FIG. 4 is only that the joining portion 99b that joins the heat receiving portion 90 and the diaphragm 42 is annular when viewed in the axial direction. The joint portion 99b is a portion where the heat receiving portion 90 and the diaphragm 42 (and thus the pressure receiving portion 40) are melted during welding (hereinafter, the joint portion 99b is also referred to as “welded portion 99b” or “weld mark 99b”). Such a joint portion 99b is a portion where the heat receiving portion 90 and the diaphragm 42 are integrated. Further, the joint 99b includes the component of the heat receiving unit 90 and the component of the diaphragm 42. The configuration of the other part of the pressure sensor 10b is the same as the configuration of the corresponding part of the pressure sensor 10 of the first embodiment.

  FIG. 10B shows the connection portion 93b and the outline of the minimum inclusion region 94b including the connection portion 93b. The connection part 93 b is a part joined to the diaphragm 42 on the surface on the rear end side of the heat receiving part 90. In the drawing, the connecting portion 93b is hatched. In the third embodiment, the connection portion 93 b corresponds to a cross section of the joint portion 99 b on the surface on the rear end side of the heat receiving portion 90. Thus, the part (here junction part 99b) connected to the diaphragm 42 among the heat receiving parts 90 may be an annular part having a hole.

  Here, when the heat receiving part 90 is thermally expanded, the deformation of the part surrounded by the annular joint 99b in the heat receiving part 90 is easily transmitted to the diaphragm 42 through the joint 99b. The connection area Sn indicates the minimum area of the portion where the deformation of the heat receiving portion is easily transmitted. In the third embodiment, it is preferable to employ the area of the minimum inclusion region 94b including the connection portion 93b as the connection area Sn. In the third embodiment, the shape of the contour on the outer peripheral side of the connection portion 93b is substantially circular, so the shape of the contour of the minimum inclusion region 94b is approximately the same as the shape of the contour on the outer peripheral side of the connection portion 93b. As in this embodiment, when the cross section at a specific position in the range of the axial direction in the range from the heat receiving portion to the diaphragm is annular, for example, like the cross section of the joint 99b, the specific The minimum inclusion region in the cross-section at the position is a region surrounded by the outer contour (outer edge) of the annular cross-section. In FIG. 10C, the region corresponding to the connection area Sn is hatched. And it is preferable that ratio Sn / Sd calculated using such connection area Sn exists in said preferable range. Thus, it is estimated that a good pressure error Ep can be realized.

  Also in the third embodiment, the thickness t of the heat receiving unit 90, the angle θ of the heat receiving unit 90, the ratio Sn2 / Sd, the ratio Sn / Sd, and one or more parameters selected arbitrarily from the minimum distance d However, it is estimated that a favorable pressure error Ep can be realized by adopting a configuration in which each parameter is within the above preferable range.

  For example, in the third embodiment, as in the first and second embodiments, the thickness t of the heat receiving unit 90 is 0.21 mm or more (t ≧ 0.21 mm) and the ratio (Sn / Sd ) Is preferably 0.25 or less ((Sn / Sd) ≦ 0.25). In this way, the pressure error Ep can be made sufficiently small.

  In the embodiment of FIG. 10, the heat receiving unit 90 is directly connected to the diaphragm 42 by the joint 99b. Therefore, the minimum distance d is zero. Further, the rear end surface 90f of the heat receiving portion 90 is perpendicular to the axis line CL. Therefore, the angle θ formed by the surface 90f on the rear end side of the heat receiving portion 90 and the direction perpendicular to the axis line CL is zero.

D. Fourth embodiment:
FIG. 11 is an explanatory diagram of a pressure sensor 10c according to the fourth embodiment. In the drawing, a flat cross section including a part of the axis CL on the tip side of the pressure sensor 10c is shown. The difference from the second embodiment shown in FIG. 8 is that the heat receiving portion 90 and the rod 44c are formed by one member 120 (referred to as “heat receiving rod 120”). The structure of the other part of the pressure sensor 10c is the same as the structure of the corresponding part of the pressure sensor 10a of the second embodiment.

  The heat receiving rod 120 includes a heat receiving portion 90 and a rod 44 c connected to the rear end side of the heat receiving portion 90. The shape of the heat receiving part 90 is the same as the shape of the heat receiving part 90 of FIG. The shape of the rod 44c is a shape in which a small diameter portion 48 having a small outer diameter is locally formed on a cylinder centering on the axis CL. Similarly to the rod 44a of FIG. 8, the rod 44c is inserted into a through-hole on the inner peripheral side of the fixed portion 41a and the diaphragm 42a, and is welded to the fixed portion 41a. The small diameter part 48 is located between the heat receiving part 90 and the fixed part 41a. The heat receiving rod 120 is integrally formed as one member (for example, forging or shaving). Moreover, although the heat receiving rod 120 is formed using stainless steel in the present embodiment, it may be formed using other metals.

  The piezoelectric element 51 is connected to the rod 44 c via the tip-side electrode 52 and the pressing plate 54. The whole of the fixing portion 41a, the rod 44c, the holding plate 54 on the distal end side, and the electrode 52 forms a connection portion 100c that connects the diaphragm 42a and the piezoelectric element 51.

  In the fourth embodiment, the heat receiving part 90 is indirectly connected to the diaphragm 42a via the rod 44c and the fixing part 41a. The part from the heat receiving part 90 to the diaphragm 42a includes the heat receiving part 90, the diaphragm 42a, and a part connecting the heat receiving part 90 and the diaphragm 42a. A portion connecting the heat receiving portion 90 and the diaphragm 42a includes a portion from a portion connected to the fixed portion 41a to a portion connected to the heat receiving portion 90 in the rod 44c, and the fixed portion 41a. In the fourth embodiment, the cross section in which the area of the minimum inclusion region in the cross section perpendicular to the axis CL at the position in the axial direction from the heat receiving portion 90 to the diaphragm 42a is the portion with the smallest outer diameter of the small diameter portion 48. It is a section which passes through. The connection area Sn, that is, the minimum area of the minimum inclusion region is the area of the minimum inclusion region in the cross section of the minimum outer diameter portion of the small diameter portion 48 of the rod 44c (not shown). As described above, when the connection area Sn is small, the deformation of the heat receiving portion 90 is not easily transmitted to the diaphragm 42a, so that the error of the signal from the element portion 50 is reduced.

  The heat receiving area Sn2, the effective area Sd, and the minimum distance d are calculated in the same manner as in the second embodiment of FIG. In the fourth embodiment, the thickness t of the heat receiving unit 90, the angle θ of the heat receiving unit 90, the ratio Sn2 / Sd, the ratio Sn / Sd, and the minimum distance d are arbitrarily selected. Further, it is estimated that a favorable pressure error Ep can be realized by adopting a configuration in which one or more types of parameters are within the above-described preferable ranges of the parameters.

  For example, in the fourth embodiment, as in the first to third embodiments, the thickness t of the heat receiving unit 90 is 0.21 mm or more (t ≧ 0.21 mm) and the ratio (Sn / Sd ) Is preferably 0.25 or less ((Sn / Sd) ≦ 0.25). In this way, the pressure error Ep can be made sufficiently small.

  The small diameter portion 48 may be omitted. In this case, the connection area Sn is an area of a minimum inclusion region including a cross section of a portion between the surface on the rear end side of the heat receiving portion 90 and the end on the front end side of the fixing portion 41a in the rod 44c.

  In the fourth embodiment, the rear end surface 90f of the heat receiving unit 90 is perpendicular to the axis CL. Therefore, the angle θ formed by the surface 90f on the rear end side of the heat receiving portion 90 and the direction perpendicular to the axis line CL is zero.

E. Variations:
(1) In the second to fourth embodiments, the angle θ formed by the surface 90f on the rear end side of the heat receiving unit 90 and the direction perpendicular to the axis CL is 0, but is not limited thereto. FIG. 12 is a diagram illustrating a modification of the second embodiment. As shown in FIG. 12A, in the cross section including the axis line CL, the surface 90f on the rear end side of the heat receiving portion 90 may be inclined toward the front end side toward the radially outer side. In this case, the angle θ is preferably within 20 degrees. If it carries out like this, it can suppress that high temperature combustion gas flows in into the clearance gap 95a, and can reduce more heat amount transmitted to the diaphragm 42a. As a result, the thermal expansion of the diaphragm 42a can be further suppressed, and as a result, the signal error from the element unit 50 can be reduced.

  Further, as shown in FIG. 12A, in the cross section including the axis line CL, the surface 90f on the rear end side of the heat receiving portion 90 may be inclined toward the rear end side toward the radially outer side. . Also in this case, the angle θ is preferably within 20 degrees. In this way, even when the heat receiving unit 90 is deformed by being exposed to high-temperature combustion gas, it is possible to suppress the interference between the heat receiving unit 90 and the diaphragm 42a, and thus the element unit 50. The error of the signal from can be reduced.

(2) Various configurations can be adopted as a configuration for connecting the heat receiving portion and the diaphragm. For example, the heat receiving unit 90 and the diaphragm 42 may be directly connected as in the embodiment of FIGS. Further, as in the embodiment of FIGS. 8 and 11, the heat receiving portion 90 and the diaphragm 42a are indirectly connected via other elements (in the example of FIGS. 8 and 11, the rods 44a and 44c and the fixing portion 41a). It may be connected to.

  In the embodiment of FIG. 2, a spacer may be disposed between the heat receiving unit 90 and the diaphragm 42. As the spacer, for example, a cylindrical member having the axis CL as the center may be employed. Here, the entire diaphragm 42 (and hence the pressure receiving portion 40) and the spacer may be integrally formed as one member (for example, forging or shaving). Instead, the entire heat receiving portion 90 and the spacer may be integrally formed as one member (for example, forging or shaving). Since such a spacer is also arranged on the tip side of the diaphragm 42 and can receive heat instead of the diaphragm 42, it can be said to be a part of the heat receiving portion. In addition, a joined portion (for example, a welded portion (weld trace) melted during welding) joining the heat receiving portion 90 and the diaphragm 42 is formed so as to reach the diaphragm 42 from the heat receiving portion 90 through the spacer. Also good. Such a joint may be formed over the entire spacer when viewed in the axial direction, or alternatively may be formed in a portion of the spacer. When the joint portion is formed in a part of the spacer, a small gap may be formed between the spacer and the diaphragm connected to each other by the joint portion, like the gap 95 in FIG. In this case, the minimum distance d is zero.

  In any case, the heat receiving portion (or a member including the heat receiving portion) may be connected to the diaphragm or another element connected to the diaphragm by welding. Laser welding may be employed as the type of welding, and instead of this, other types of welding (for example, resistance welding) may be employed. When joining by welding, the joining part which joins a heat receiving part (or member provided with a heat receiving part) and a diaphragm (or other element connected to the diaphragm) is joined by welding at the time of welding. It is a part where two members are melted. Such a joint is a part where two members joined by welding are integrated. Moreover, the junction part contains each component of two members joined by welding. Moreover, as a structure of such a junction part, it can replace with the structure of the junction parts 99, 99a, and 99b of FIG.2, FIG.8, FIG.10 and can employ | adopt various other structures. For example, when viewed in the axial direction, a plurality of joint portions separated from each other may be formed. For example, three or four joint portions arranged so as to surround the axis line CL may be formed. When a plurality of joints that are separated from each other are formed, the deformation in the region surrounded by the plurality of joints of the heat receiving portion is more than the deformation outside the region surrounded by the plurality of joints. It is easy to be transmitted to the diaphragm through the joint. Therefore, as the connection area Sn, the area of the minimum inclusion region including a plurality of junctions can be adopted. For example, when three junctions are formed, the area of a substantially triangular minimum inclusion region including three cross sections of the three junctions can be adopted as the connection area Sn. When four junctions are formed, as the connection area Sn, an area of a substantially quadrangular minimum inclusion region including four cross sections of the four junctions can be employed.

  In any case, as the minimum distance d in the direction parallel to the axis of the gap between the heat receiving portion and the diaphragm, it is preferable to adopt the distance between the surface of the diaphragm on the combustion chamber side and the heat receiving portion. .

(2) As the configuration of the connecting portion for connecting the diaphragms 42 and 42a and the piezoelectric element 51, the configuration of the connecting portion 100 in FIG. 2, the configuration of the connecting portion 100a in FIG. 8, and the configuration of the connecting portion 100c in FIG. Instead of, various other configurations can be adopted. For example, the holding plate 54 on the distal end side may be omitted, and the rods 44, 44 a, 44 c may be in contact with only the electrode 52 on the distal end side among the elements of the element unit 50. Further, the pressing plate 54 and the electrode 52 on the distal end side may be omitted, and the piezoelectric element 51 may be directly connected to the rods 44, 44a, 44c. In this case, the rods 44, 44a and 44c function as electrodes. 8 and 11, the fixing portion 41a may be omitted, and the diaphragm 42a may be directly joined to the rods 44a and 44c. In the embodiment of FIGS. 8 and 11, the diaphragm 42a and the rods 44a and 44c may be integrally formed as one member (for example, forging or shaving). Also in this case, it can be said that the diaphragm 42a is connected to the rods 44a and 44c.

  In any case, the connecting portion includes a rod, and the diaphragm is directly or indirectly connected to the first portion of the rod, and the piezoelectric element 51 is connected to the second portion of the rod on the rear end side of the first portion. Are preferably connected directly or indirectly. The reason why the second portion is located on the rear end side with respect to the first portion is that the element unit 50 is generally arranged on the rear end side with respect to the diaphragm receiving the pressure in the combustion chamber. Here, as the second portion connected to the element portion 50 (that is, the piezoelectric element 51) of the rod, the rear end portion of the rod (for example, the rear end portion 49 in FIG. 2, the rear end portion 49a in FIG. 8). Instead, any part of the rod can be employed. For example, the element part 50 (for example, electrode 52) may be connected to the outer peripheral surface of the rod. In this case, the electrode 52 and the piezoelectric element 51 may be formed in an annular shape, and a rod may be inserted into the through hole between the electrode 52 and the piezoelectric element 51.

(3) As the configuration of the element unit 50, various other configurations can be adopted instead of the configurations of FIGS. For example, at least one of the front end side pressing plate 54 and the rear end side pressing plate 54 may be omitted. Further, the terminal portion 56 may be directly connected to the electrode 52. In addition, the electrode 52 and the piezoelectric element 51 may be an annular plate member surrounding the axis CL, instead of a disk-shaped plate member disposed on the axis CL, and a specific circumferential axis CL. The member arrange | positioned in the position away from may be sufficient. In general, the element unit 50 preferably includes a piezoelectric element and is configured to output a signal from the piezoelectric element to the outside of the pressure sensor. In addition, as an apparatus having an electrical characteristic that changes depending on the pressure received by the diaphragm, an electrical characteristic that changes according to the load received through the diaphragm and the connecting portion instead of the piezoelectric element (for example, voltage, resistance value, etc.) Various devices having the above can be employed. For example, a strain gauge may be employed.

(4) As a configuration of the heat receiving unit, various types of heat receiving unit 90 can receive heat from the combustion chamber instead of the diaphragm instead of the configuration of the heat receiving unit 90 of FIGS. 2, 8, 10, and 11. A configuration can be adopted. For example, the shape of the heat receiving portion viewed in the axial direction may be a rectangle instead of a circle. Generally, the heat receiving part is preferably a plate-like member that is disposed on the distal end side of the diaphragm and is directly or indirectly connected to the diaphragm. In addition, although the thickness t of the heat receiving portion is constant in each of the above-described embodiments, for example, it may be changed depending on a radial position or a circumferential position. In this case, as the thickness t of the heat receiving portion, the average thickness of a portion of the heat receiving portion excluding the portion connected to the diaphragm is employed. And the said average thickness t should just be 0.21 mm or more.

(5) In the above-described embodiment (for example, FIGS. 2 and 8), the diaphragms 42 and 42a are joined to the cylindrical casing formed by the second metal fitting 80 and the third metal fitting 35, and the housing The element part 50 is accommodated in the body. As a configuration of such a housing, various cylindrical configurations can be employed instead of the configuration using the second metal fitting 80 and the third metal fitting 35. For example, the whole of the second metal fitting 80 and the third metal fitting 35 may be formed of one member. Moreover, the whole 2nd metal fitting 80 and the holding screw 32 may be formed with one member. Moreover, the 2nd metal fitting 80, the 3rd metal fitting 35, and the holding screw 32 may be formed with one member.

  In either case, the diaphragm may be connected to the housing by welding. Laser welding may be employed as the type of welding, and instead of this, other types of welding (for example, resistance welding) may be employed. In any case, a portion where the diaphragm and the housing are melted during welding forms a joint for joining the diaphragm and the housing. Such a joining portion is a portion where the diaphragm and the housing are integrated. And the junction part contains the component of the diaphragm and the component of the housing | casing. As the contour of the region corresponding to the effective area Sd, it is possible to adopt the contour on the inner peripheral side of the joint portion that joins the housing and the diaphragm on the surface of the diaphragm connected to the housing ( For example, the outline 45i of the joint 45 in FIGS. 6 (F) and 9 (F).

(6) As a configuration for guiding the signal from the element unit 50 to the outside of the pressure sensor, various other configurations can be adopted instead of the configuration using the cable 60. For example, a terminal metal fitting may be disposed on the rear end side of the pressure sensor 10, and the terminal metal fitting and the terminal portion 56 of the element unit 50 may be connected by a middle shaft. In this case, a signal from the element unit 50 can be acquired through the terminal fitting and the first fitting 20.

  As mentioned above, although this invention was demonstrated based on embodiment and a modification, embodiment mentioned above is for making an understanding of this invention easy, and does not limit this invention. The present invention can be changed and improved without departing from the spirit and scope of the claims, and equivalents thereof are included in the present invention.

DESCRIPTION OF SYMBOLS 10, 10a, 10c, 10x ... Pressure sensor, 20 ... 1st metal fitting, 21 ... Shaft hole, 22 ... Screw part, 24 ... Tool engaging part, 26 ... Joint part , 30 ... second metal fitting, 34 ... diameter enlarged portion, 35 ... third metal fitting, 36 ... shaft hole, 39 ... shaft hole, 40, 40a ... pressure receiving portion, 41a. .. Fixing part, 42, 42a ... Diaphragm, 42f, 42af ... Pressure receiving surface, 42o, 42ai, 42ao ... Edge, 43, 43a ... Connection part, 44, 44a ... Rod, 45 ... Junction, 45i ... contour, 46 ..., 46a ... region, 49, 49a ... rear end, 50 ... element part, 51 ... piezoelectric element, 52 .. Electrode 53 ... Lead part 54 ... Presser plate 54h ... Through hole 55 ... Insulating plate 55h ... Through hole 56 ... Terminal part 57 ... Disc 60 ... cable 61 ... jacket 62 ... outer conductor 63 ... conductive coating 64 ... insulator 6 ... Inner conductor, 72 ... Heat-shrinkable tube, 74 ... Small diameter conductor, 75 ... Plate conductor, 76 ... Ground conductor, 80 ... Second metal fitting, 81 ... Shaft hole 89 ... Joint portion, 90 ... Heat receiving portion, 93, 93a, 93b ... Connection portion, 94, 94a, 94b ... Minimum inclusion area, 95, 95a ... Gap, 97 ... Plate part, 98 ... Leg part, 99, 99a, 99b ... Joint part, 100, 100a, 100c ... Connection part, X ... Area, d ... Minimum distance, G1 ... Standard Graph (pressure), G2 ... sample graph (pressure), CA ... crank angle, CL ... center axis (axis), Pc ... pressure, Sd ... diaphragm effective area (effective area), Df ... front end direction, Dr ... rear end direction, Em ... maximum difference, Sn ... connection area, Ep ... pressure error, Sn2 ... heat receiving area

Claims (2)

A cylindrical housing;
A diaphragm that is joined to the front end side of the housing via a joint portion, expands in a direction intersecting the axis of the housing, and bends according to the received pressure,
A sensor unit disposed in the housing and having an electrical characteristic that varies with the pressure;
A connecting portion for connecting the diaphragm and the sensor portion;
A heat receiving plate that is disposed on the distal end side of the diaphragm and that is directly or indirectly connected to the diaphragm to receive heat;
A pressure sensor comprising:
On the cross section perpendicular to the axis, connect the minimum value of the area of the minimum inclusion area that is a virtual area including the cross section of the portion from the heat receiving plate to the diaphragm and having the minimum total length of the contour. Let the area Sn be
When projecting the diaphragm and the heat receiving plate on a projection plane perpendicular to the axis, on the projection plane,
The area of the region surrounded by the joint is defined as a diaphragm effective area Sd,
When the thickness of the heat receiving plate is t,
A pressure sensor satisfying t ≧ 0.21 mm and (Sn / Sd) ≦ 0.25. The pressure sensor according to claim 1,
An absolute value of an angle θ formed by a surface on the rear end side of the heat receiving plate and a direction perpendicular to the axis in a cross section including the axis is within 20 degrees.

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