JP2007085578A - Glow plug with combustion pressure sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a glow plug with a combustion pressure sensor capable of being less affected by deformation of an engine head accompanying combustion pressure. <P>SOLUTION: A part on the tip end side further than a connecting point 41 (part D) of a tip end side subject fitting 50 and a rear end side subject fitting 60 structures a double pipe structure comprising the tip end side subject fitting 50, the rear end side subject fitting 60, a pressure sensor sleeve 90, and a part of a cylindrical body comprising an intermediate sleeve 95 and a supporting member 70, and direct pressuring force due to deformation of the engine head is not applied to the part of the cylindrical body on the inner side. When the connecting part 41 is formed at a center part C of a tip end part A of a seal part 53 and a rear end part B of a screw part 67, or at a part further on the rear end side than the center part C, even when a subject fitting 40 deforms between the seal part 53 and the screw part 67 by deformation of the engine head, it hardly affects the displacement of the heater member 10. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a glow plug with a combustion pressure sensor that is integrally provided with a combustion pressure sensor for detecting a change in the combustion pressure of the internal combustion engine and assists starting of the internal combustion engine.

  2. Description of the Related Art A known glow plug for assisting the start of an internal combustion engine is provided with a combustion pressure sensor for detecting the combustion pressure of the internal combustion engine. In such a glow plug with a combustion pressure sensor, piezoelectric ceramics are generally used as a sensor element for detecting the combustion pressure. Then, a heater member in which a heater (heating element) is joined to the tip of the middle shaft that is inserted through the shaft hole of the metal shell (housing) is joined by fixing or brazing at the tip of the metal shell, It is fixed. Moreover, it has the structure by which a piezoelectric ceramic is hold | maintained in the state to which the preload was added between the rear-end part of a heater member, and the rear-end part of a metal shell (for example, refer patent document 1).

When such a glow plug with a combustion pressure sensor is attached to the mounting hole of the engine head, the outer peripheral surface of the front end of the metal shell is also brought into contact with the inner peripheral surface of the mounting hole on the combustion chamber side as a seal Thus, the male screw portion formed on the outer periphery of the metal shell is screwed into the female screw portion of the mounting hole. That is, the metal shell is locked to the engine head by the tip portion and the male screw portion. When the engine head is deformed by the combustion pressure generated by the driving of the internal combustion engine, the metal shell receives a pressing force at the tip and is compressed between the male screw part, so that the body part expands in the radial direction. Elastically deforms. As a result, the distance between the front end portion of the metal shell and the male screw portion is shortened, and the heater member fixed to the front end portion is displaced relative to the metal shell. Then, the preload applied to the piezoelectric ceramic is reduced, and the combustion pressure is detected by detecting the change in the electric charge of the piezoelectric ceramic at that time.
JP 2004-124910 A

  However, since the deformation of the body of the metal shell that causes the displacement between the metal shell and the heater member is due to the deformation of the engine head, the deformation of the engine head due to the combustion pressure generated in other cylinders also Displacement may occur and may be detected as noise. In addition, when the glow plug with a combustion pressure sensor is attached to an engine head having different rigidity, the amount of deformation of the engine member due to the combustion pressure differs, resulting in a difference in the displacement of the heater member and a different output (combustion pressure). Detection value) may be obtained. For this reason, it is necessary to perform calibration after attaching the glow plug with the combustion pressure sensor to correct the detected combustion pressure so that the detected value and the detected value are correct.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a glow plug with a combustion pressure sensor that can be hardly affected by the deformation of the engine head due to the combustion pressure.

  In order to achieve the above object, a glow plug with a combustion pressure sensor according to a first aspect of the present invention includes a metal shell having an axial hole extending along the axial direction, a heater that generates heat when energized, and a rear end side of the heater. A heater member that is positioned and electrically connected to the heater, the heater member being disposed in the shaft hole so as to be displaced along the axial direction; and a combustion pressure of the internal combustion engine A combustion pressure sensor that detects a combustion pressure transmitted through the heater member that is displaced in the axial direction according to the above, and a protrusion that protrudes from the inner wall surface of the shaft hole and holds the heater member, The metal shell is formed on its outer peripheral surface with a screw portion that is screwed into the mounting hole of the internal combustion engine, and a seal portion that is in contact with the inner peripheral surface of the mounting hole on the tip side of the screw portion, Of the protrusions, the shaft holes The coupling portion with the surface is at a central portion between the axial tip portion of the seal portion and the axial rear end portion of the screw portion, or at a rear end side portion relative to the central portion. It is characterized by that.

  Further, in the glow plug with a combustion pressure sensor of the invention according to claim 2, in addition to the structure of the invention according to claim 1, the coupling part is more than the part at the tip end in the axial direction of the screw part or the part thereof. It exists in the site | part of the front end side, It is characterized by the above-mentioned.

  In the glow plug with a combustion pressure sensor according to the first aspect of the present invention, since the protrusion is interposed between the heater member and the metal shell, the heater member is not directly fixed to the metal shell. Even if the deformation occurs and the metal shell is subjected to a pressing force between the seal portion and the screw portion, the deformation of the heater member can be hardly affected. Furthermore, the joint part of the metal shell and the protruding part is located at the center part of the front end part of the seal part of the metal shell and the rear end part of the threaded part or at the rear end side of the central part. If formed, the influence of the deformation of the metal shell on the displacement of the heater member can be more reliably reduced. In addition, when there is a joint part in the tip side part from the central part, if the metal shell receives a pressing force compressed between the seal part and the screw part by the combustion pressure, the seal part and the joint part In addition to the deformation of the metal shell, the metal shell is easily deformed between the coupling site and the threaded portion, and the coupling site may be displaced in the axial direction. Then, there is a possibility that the heater member is displaced together with the protruding portion coupled to the coupling site, and is detected as noise by the combustion pressure sensor.

  Further, as in the glow plug with a combustion pressure sensor according to the second aspect of the present invention, if the coupling portion is formed at the tip portion of the screw portion or at the tip side of the portion, the main portion from the combustion chamber of the internal combustion engine. The high-temperature combustion gas that has entered between the inner periphery of the metal fitting and the outer periphery of the protruding portion does not enter the rear end side from the coupling site, and does not reach the screw portion. For this reason, it is difficult for the thermal load due to the combustion gas to be applied to the screw portion, and it is possible to prevent occurrence of loose attachment of the screw portion due to thermal expansion.

  Hereinafter, an embodiment of a glow plug with a combustion pressure sensor embodying the present invention will be described with reference to the drawings. First, the structure of the glow plug 1 of the present embodiment as an example of a glow plug with a combustion pressure sensor will be described with reference to FIGS. FIG. 1 is a partially cutaway longitudinal sectional view of the glow plug 1. FIG. 2 is an enlarged cross-sectional view of the tip side of the glow plug 1 attached to the engine head 200. In the direction of the axis O, the side where the ceramic heater 20 is disposed (the lower side in FIG. 1) is the front end side of the glow plug 1, and the side where the combustion pressure sensor 100 is disposed (the upper side in FIG. 1) is the rear end side. explain.

  The glow plug 1 of the present embodiment is attached to, for example, an engine head of a diesel engine, and is used as a heat source that assists ignition at the start of the engine. As shown in FIG. 1, the ceramic heater 20 is disposed on the front end side of the metal shell 40, and is mechanically connected to and integrated with the central shaft 30 inserted through the shaft holes 51 and 61 of the metal shell 40. The heater member 10 is configured. The ceramic heater 20 of the heater member 10 is exposed at the front end side in the combustion chamber, and is displaced in the direction of the axis O when receiving a pressing force due to the combustion pressure, and the pressing pressure is provided on the rear end side of the metal shell 40. It is comprised so that it may be transmitted.

  As shown in FIGS. 1 and 2, the metal shell 40 has shaft holes 51 and 61 penetrating in the direction of the axis O, and two components divided in the direction of the axis O are welded at the joint portion 41. It is a thin cylindrical metal member. The distal end side metal shell 50 on the distal end side from the joining portion 41 has a long and thin cylindrical body portion 56, and the inner diameter of the shaft hole 51 is reduced at the distal end portion 55. A seal portion 53 having a tapered surface 54 that tapers toward the tip side is formed at the tip portion 55. The seal portion 53 has its tapered surface 54 abutted against a locking surface 220 (see FIG. 3) formed on the distal end side (lower combustion chamber side in the drawing) of the mounting hole 210, and the inner peripheral surface of the mounting hole 210. This is a part for preventing combustion gas from entering between the outer peripheral surface of the metal shell 40 and the outer peripheral surface of the metal shell 40.

  Further, the rear end-side metal shell 60 on the rear end side from the joining portion 41 is formed with a threaded portion 67 for attaching the glow plug 1 to the attachment hole 210 (see FIG. 3) of the engine head 200 on the outer peripheral surface thereof. Yes. As shown in FIG. 1, a tool engagement portion 66 that engages with a tool used for attachment to the engine head 200 is formed on the rear end side of the screw portion 67. The inner diameter of the shaft hole 61 of the rear end side metal shell 60 is expanded in the tool engaging portion 66, and is configured as an expanded diameter portion 63. At the rear end of the tool engaging portion 66, a combustion pressure sensor 100, which will be described later, is fixed to the rear end side metal shell 60. Therefore, the cross section orthogonal to the axis O is annular, and the wall faces toward the rear end in the axis O direction. A base end portion 62 protruding in a shape is provided.

  As shown in FIGS. 1 and 2, a convex portion 64 protruding from the inner wall surface of the shaft holes 51, 61 of the metal shell 40 is formed at the tip side of the threaded portion 67 of the rear metal shell 60. Is formed. Furthermore, the outer diameter of the front end side of the convex portion 64 is reduced in two stages, and a rear end portion 92 of a pressure detection sleeve 90 described later is engaged with the outer periphery of the small diameter portion 65 on the most front end side. In the present embodiment, the metal shell 40 is composed of a front end side metal shell 50 and a rear end side metal shell 60, and the shaft hole 51 of the front end side metal shell 50 and the shaft of the rear end side metal shell 60. The holes 61 are connected to form shaft holes 51 and 61 of the metal shell 40. That is, the shaft hole is connected at the joint portion 41 between the front end side metal shell 50 and the rear end side metal shell 60, and the convex portion 64 protrudes into the shaft holes 51 and 61 from the joint portion 41. It becomes. In the present embodiment, the joint portion between the shaft holes 51 and 61 and the convex portion 64 is located in the vicinity of the joint portion 41.

  A metal center shaft 30 made of an iron-based material (for example, Fe—Cr—Mo steel) extending in the direction of the axis O is inserted into the shaft holes 51 and 61 of the metal shell 40. A small-diameter engaging portion 31 is formed at the tip of the middle shaft 30, and a metal cylindrical connection ring 15 is fitted into the engaging portion 31. Then, when a rear end portion 29 of a ceramic heater 20 described later is press-fitted into the connection ring 15, the middle shaft 30 and the ceramic heater 20 are mechanically connected via the connection ring 15, and the heater member 10 is integrally formed. Composed.

  As shown in FIG. 1, a small-diameter rear end portion 32 is formed on the rear end side of the middle shaft 30. The rear end portion 32 is disposed at a position where the rear end portion 32 is inserted through a combustion pressure sensor 100 described later, and the rear end portion is exposed behind the combustion pressure sensor 100. A connection terminal 80 for electrical connection with an external circuit for energizing the ceramic heater 20 is fixed to the exposed portion of the rear end portion 32 by caulking.

  Next, the combustion pressure sensor 100 is provided at the base end portion 62 of the rear end side metal shell 60. The combustion pressure sensor 100 includes a known semiconductor strain gauge (a strain detection element 120 described later) in which a piezoresistive element is formed on a semiconductor substrate such as silicon, for example, and is disposed on the diaphragm. It is a sensor that detects the combustion pressure by bending. The strain member 110 fixed to the base end portion 62 of the rear end side metal shell 60 includes a ring-shaped locking portion 111 that surrounds and engages with the outer periphery of the base end portion 62, and an edge of the locking portion 111. It is comprised from the diaphragm part 112 which consists of a thin annular | circular metal plate which makes it a periphery and makes an axis line O direction into a thickness direction. The diaphragm portion 112 has flexibility and has an opening at the center, and is inserted so that the rear end portion 32 of the middle shaft 30 does not contact the opening.

  A plurality of strain detection elements 120 are pasted on the diaphragm portion 112 of the strain member 110. The strain detecting element 120 is distorted when the diaphragm portion 112 is bent, and its own resistance value changes according to the degree of the distortion. Further, a relay substrate 130 is disposed on the rear end side of the strain member 110 so as to face the diaphragm portion 112. On the relay substrate 130, an ASIC 131 or the like including a known electric circuit for converting the resistance value of the strain detection element 120 into a voltage value, amplifying it, and outputting it as a detection value is disposed. The strain detecting element 120 is electrically connected to the relay substrate 130 by a gold wire or a flexible cable (not shown). In addition, a connection cable 132 for making an electrical connection with an external circuit (not shown) such as an ECU is connected to the relay board 130.

  Further, a cylindrical tube member 140 made of an insulating ceramic is fitted to the rear end portion 32 of the middle shaft 30, and the front end is in contact with a stepped boundary portion where the rear end portion 32 of the middle shaft 30 is formed. It is fixed in the state. The rear end of the tubular member 140 is in contact with the peripheral edge of the central opening portion of the diaphragm portion 112 of the strain member 110. When the middle shaft 30 of the heater member 10 is displaced toward the rear end side in the direction of the axis O due to the combustion pressure, the opening portion of the diaphragm portion 112 is pressed by the cylindrical member 140 and the diaphragm portion 112 is bent. Yes.

  A flanged cylindrical insulating member 150 is disposed in the gap between the outer periphery of the cylindrical member 140 and the middle shaft 30 and the inner periphery of the enlarged diameter portion 63 of the rear end side metal shell 60. 30 is insulated. Further, an O-ring 160 made of, for example, silicon rubber is formed in a gap surrounded by the distal end surface of the insulating member 150, the stepped surface on the distal end side of the enlarged diameter portion 63 of the shaft hole 61, and the outer peripheral surface of the middle shaft 30. The intermediate shaft 30 is positioned so that the airtightness in the shaft holes 51 and 61 of the metal shell 40 is maintained and the outer peripheral surface of the intermediate shaft 30 is not in contact with the inner peripheral surfaces of the shaft holes 51 and 61. Yes.

  In addition, a cover 170 is provided to cover the outer periphery and upper side (rear end side) of the strain member 110 and the relay substrate 130 disposed at the base end portion 62 of the rear end side metal shell 60. The entire outer periphery is laser-welded while being engaged with the outer periphery of the portion 111, thereby being fixed integrally with the rear end side metal shell 60. An annular insulating rubber 180 is interposed between the cover 170 and the connection terminal 80 fixed to the rear end portion 32 of the middle shaft 30 so as to insulate the two.

  Next, as shown in FIG. 2, the ceramic heater 20 disposed on the distal end side in the shaft hole 51 of the distal end side metal shell 50 has a round bar shape, and is made of an insulating ceramic in which the distal end portion 28 is processed into a curved surface shape. A heating element 24 having a substantially U-shaped cross section made of a conductive ceramic is embedded in the base 25. The heating element 24 is disposed at the tip portion 28 of the ceramic heater 20, and is connected to the heating element 21 whose both ends are folded back in a substantially U shape in accordance with the curved surface thereof, and to both ends of the heating element 21, respectively. It is comprised from the lead parts 22 and 23 embed | buried substantially parallel along the axis O toward the rear-end part 29. As shown in FIG. The heating element 21 is formed so that its cross-sectional area is smaller than the cross-sectional area of the lead portions 22 and 23, and heat is generated mainly in the heating element 21 when energized. In addition, on the outer peripheral surface of the rear end portion 29 of the ceramic heater 20, electrode extraction portions 26 and 27 protruding from the lead portions 22 and 23 are exposed at positions shifted from each other in the axis O direction. The ceramic heater 20 corresponds to the “heater” in the present invention.

  A cylindrical heater support member 70 is disposed around the outer periphery of the body portion of the ceramic heater 20. The heater support member 70 is made of a conductive metal member, and the ceramic heater 20 is fixed by press-fitting with the electrode extraction portion 26 of the rear end portion 29 exposed rearward. The electrode extraction portion 27 of the ceramic heater 20 is in contact with the inner peripheral surface of the heater support member 70, and the heater support member 70 and the lead portion 23 of the ceramic heater 20 are electrically connected. On the other hand, the electrode extraction portion 26 is in contact with the inner peripheral surface of the connection ring 15 fitted to the rear end portion 29 of the ceramic heater 20. Further, a flange 71 projecting outward is formed on the rear end side of the heater support member 70 over the entire circumference. The collar portion 71 functions as positioning when the front end portion 96 of the intermediate sleeve 95 is engaged with the outer periphery of the engaging portion 72 provided on the rear end side from the collar portion 71.

  Next, the intermediate sleeve 95 surrounds the rear end portion 29 of the ceramic heater 20 fixed to the heater support member 70 and the front end portion of the intermediate shaft 30 mechanically connected to the ceramic heater 20 via the connection ring 15. The distal end portion 96 is welded to the engaging portion 72 of the heater support member 70. The intermediate sleeve 95 is fixed in a non-contact state with the middle shaft 30, and the two are insulated with a gap. The rear end portion 97 is formed in a step shape with a small diameter, and the front end portion 91 of the pressure detection sleeve 90 is engaged and welded thereto.

  The pressure detection sleeve 90 is a cylindrical member made of metal such as SUS, which is thinner than the intermediate sleeve 95, and is insulated from the middle shaft 30 with a gap, like the intermediate sleeve 95. The front end portion 91 of the pressure detection sleeve 90 is engaged with the rear end portion 97 of the intermediate sleeve 95, and the rear end portion 92 is engaged with the small-diameter portion 65 at the front end of the rear end side metal shell 60. Has been. The pressure detection sleeve 90 is configured such that, when a pressure compressed in the direction of the axis O is applied, the body portion 93 can expand and bend in the radial direction.

  With such a configuration, the rear end side metal shell 60, the pressure detection sleeve 90, the intermediate sleeve 95, and the heater support member 70 are connected to each other, and the respective connected portions are integrated to maintain high airtightness. It is configured in the form of a cylindrical body. A heater member 10 composed of a ceramic heater 20 and a central shaft 30 that are integrally joined by a connection ring 15 is disposed in the cylindrical body. The ceramic heater 20 of the heater member 10 is fixed to the heater support member 70 on the front end side of the cylindrical body, and the middle shaft 30 is not in contact with the cylindrical body by an O-ring 160 disposed on the rear end side of the cylindrical body. Is supported by positioning.

  Further, the front end side metal shell 50 surrounds the outer periphery of the cylindrical body so that the convex portion 64 of the rear end side metal shell 60 is engaged with the rear end side of the shaft hole 51. In this state, the joining portion 41 is welded to form the metal shell 40 in which the front end side metal shell 50 and the rear end side metal shell 60 are integrated. At this time, the seal portion 53 of the distal end side metal shell 50 is disposed at a position surrounding the outer periphery of the heater support member 70, but does not hold (fix) the heater support member 70.

  In the present invention, the “protruding portion” refers to a portion of the cylindrical body that supports the heater member 10 in the distal end side metal shell 50 on the distal end side from the joining portion 41, and more specifically, on the rear end side. The convex part 64 of the metal shell 60, the pressure detection sleeve 90, the intermediate sleeve 95, and the heater support member 70 are referred to. The “projecting portion” constituted by these may be constituted by a plurality of members including a part of the rear end side metal shell 60 as in the present embodiment, or may be constituted by a single member. Alternatively, the rear end side metal shell 60 may be integrated. In the present invention, the “joining portion of the projecting portion with the inner wall surface of the shaft hole” is a portion near the base of the projecting portion projecting from the shaft holes 51 and 61 of the metal shell 40 (more specifically, the projecting portion). In the present embodiment, the portion of the convex portion 64 that corresponds to the vicinity of the joint portion 41 is equivalent, but the binding portion and the joint portion 41 do not necessarily coincide with each other. The site near the boundary between the hole and the protrusion corresponds to the binding site. For example, one end portion of a single member or a plurality of members corresponding to the convex portion 64, the pressure detection sleeve 90, the intermediate sleeve 95, and the heater support member 70 is directly joined to the inner wall surfaces of the shaft holes 51 and 61 of the metal shell 40. In the case of the form, the joint portion with the inner wall surface of the shaft holes 51 and 61 at one end thereof corresponds to the “binding portion” in the present invention.

  Further, as described above, the heater support member 70 is electrically connected to the lead portion 23 via the electrode extraction portion 27 of the ceramic heater 20 inside, and the rear end side metal shell 60 and the pressure detection sleeve 90 are electrically connected. The cylindrical body comprising the intermediate sleeve 95 and the heater support member 70 functions as one electrode for applying a voltage to the heating element 21. On the other hand, the engaging portion 31 of the middle shaft 30 and the rear end portion 29 of the ceramic heater 20 are connected by a metal connection ring 15. Thereby, the lead part 22 of the ceramic heater 20 and the middle shaft 30 are electrically connected, and the middle shaft 30 functions as the other electrode for applying a voltage to the heating element 21. That is, the metal shell 40 and the central shaft 30 function as two electrodes for applying a voltage to the heating element 24 of the ceramic heater 20.

  Next, the operation of the glow plug 1 when detecting the combustion pressure of the engine will be described with reference to FIGS. FIG. 3 is an enlarged cross-sectional view of the tip end side of the glow plug 1 that has been deformed due to the pressing force due to the combustion pressure. In FIG. 3, for the sake of explanation, the bending that occurs in the distal end side metal shell 50 and the pressure detection sleeve 90 is drawn exaggerating the actual size.

  When the glow plug 1 shown in FIG. 1 is attached to the attachment hole 210 (see FIG. 3) of the engine head 200 of the internal combustion engine, the rear end side of the ceramic heater 20 is exposed in the combustion chamber. The threaded portion 67 of the metal shell 60 is screwed. At this time, the taper surface 54 of the seal portion 53 is brought into contact with a locking surface 220 (see FIG. 3) provided on the combustion chamber side of the attachment hole 210, and the screw portion 67 and the seal portion 53 are placed in the attachment hole 210. By being locked, the metallic shell 40 is fixed to the engine head 200.

  If the pressure in the combustion chamber increases with the operation of the engine, the engine head 200 may be deformed by the combustion pressure. As shown in FIG. 3, when the seal portion 53 receives a pressing force (indicated by an arrow U in the drawing) due to this deformation, the metal shell 40 is screwed into the seal portion 53 and the mounting hole 210. 67 and compressed. Then, the front end side metal shell 50 joined to the rear end side metal shell 60 at the joint portion 41 on the front end side of the screw portion 67 receives a pressing force compressed in the direction of the axis O, and the trunk portion 56 has a diameter. A bending (indicated by an arrow S in the figure) spreading in the direction is generated. However, since the rear end side metal shell 60 is fixed to the engine head 200 by the screw portion 67, the influence of the internal stress accompanying the deformation of the engine head 200 is hardly exerted. Therefore, the pressure detection sleeve 90, the intermediate sleeve 95, the heater support member 70, and the heater member 10 coupled to the rear end side metal shell 60 are hardly affected by the internal stress accompanying the deformation of the engine head 200. Since the heater member 10 is not fixed to the front end side metal shell 50, the heater member 10 is hardly displaced due to the deformation of the engine head 200.

  On the other hand, when the front end portion 28 of the ceramic heater 20 exposed in the combustion chamber receives a pressing force (indicated by an arrow V in the figure) due to the combustion pressure, the rear end side metal shell 60, the pressure detection sleeve 90, the intermediate sleeve 95, and The pressure detection sleeve 90 having the thinnest thickness and the lowest rigidity among the heater support members 70 undergoes a deflection (indicated by an arrow T in the drawing) that expands in the radial direction at the trunk portion 93 under the action of the pressing force. By this bending, the heater member 10 is displaced toward the rear end side in the axis O direction with respect to the rear end side metal shell 60. Then, the periphery of the opening portion of the diaphragm portion 112 of the strain member 110 is pressed toward the rear end side in the axis O direction on the rear end of the cylindrical member 140 fixed to the rear end portion 32 of the middle shaft 30. As a result, the diaphragm portion 112 bends, and strain is generated in the strain detection element 120 attached to the diaphragm portion 112. A voltage supplied from an external circuit (not shown) is applied to the strain detection element 120, and the resistance value of the strain detection element 120 that changes according to the magnitude of the distortion, that is, the magnitude of the displacement of the heater member 10. It is detected as a change in voltage value and output to the external circuit as a detected value of combustion pressure.

  As described above, in the glow plug 1, as shown in FIG. 3, the body portion 40 of the distal end side metal shell 50 is bent, that is, the metal shell 40 is deformed between the seal portion 53 and the screw portion 67. Thus, it has a structure that can reduce the influence on the displacement of the heater member 10 with respect to the deformation of the engine head 200. Here, when the joint part 41 between the front end side metal shell 50 and the rear end side metal shell 60 is brought close to the seal portion 53, the part from the joint part 41 to the screw part 67 of the rear end side metal shell 60 is the engine head. The pressing force accompanying the deformation of 200 is received. Then, the position of the front end side of the joining part 41 of the rear end side metal shell 60, that is, the position of the convex part 64 and the small diameter part 65 to which the pressure detection sleeve 90 is coupled at the front end also causes displacement. As the engine head 200 is deformed, the heater member 10 may be displaced.

  Therefore, in the present embodiment, based on the result of an evaluation test described later, as shown in FIG. 2, the central portion C of the tip portion A of the seal portion 53 and the rear end portion B of the screw portion 67, or its It is defined that the joint part 41 (part D) is located in a part on the rear end side from the central part C (a rear end from the part C). Here, the joint part 41 (part D) is used as a reference because the front end side metal part 50, the convex part 64 of the rear end side main metal part 60, the pressure detection sleeve 90, etc. This is because a double-pipe structure is constituted by a part of the cylindrical body made of the above, and a direct pressing force due to deformation of the engine head 200 is not applied to a part of the cylindrical body inside. When the joint part 41 (part D) is located at the tip part (between part A and part C) from the center part C between the tip part A of the seal part 53 and the rear part B of the screw part 67 When the metal shell 40 receives a pressing force compressed between the seal portion 53 and the screw portion 67 by the combustion pressure, in addition to the portion between the seal portion 53 and the joint portion 41 of the tip side metal shell 50, Since the part between the joint part 41 of the end-side metal shell 60 and the threaded part 67 is easily bent, the position of the convex part 64 integrated with this part in the direction of the axis O is displaced and detected as noise. There is a fear.

[Example 1]
As described above, the joint portion (part D) is a central part C between the front part A of the seal part 53 and the rear end part B of the screw part 67, or a rear end part of the central part C ( In order to confirm the effect of being defined so as to be located at the rear end of the part C), the following evaluation test was performed.

  In this evaluation test, 11 glow plug samples prepared by changing the positions of the connecting portions of the front end side metal shell and the rear end side metal shell are assembled in order to the two types of engine heads Q and R, respectively. Sensitivity dependence was determined from the output value obtained by applying combustion pressure. The engine head R is an engine head having a large cavity around the glow plug mounting hole, and the engine head Q is an engine head having no cavity. Both are made of aluminum, and the engine head R having a cavity is deformed more greatly than the engine head Q when subjected to combustion pressure.

  As shown in FIG. 2, the glow plug sample is obtained by multiplying the ratio of the length X between the part A and the part D by the length L between the part A and the part B multiplied by 100 (hereinafter referred to as “joining”). “Position” and the unit is expressed in%.) 11 types were prepared which differed every 10% from 0% to 100%. Here, for the metal shell of each sample, the inner diameter of the front metal shell is Φ6.4, the outer diameter is Φ8.4 (thickness 1.0 mm), and the inner diameter of the rear metal shell is Φ4.4, the outer diameter. Was made Φ8.4 (thickness 2.0 mm), and both were made using S45C as a material.

Samples having the same joining position are assembled to the engine heads Q and R, the same combustion pressure is applied, and output values of the samples at the engine heads Q and R (in this embodiment, a strain detection element that changes depending on the combustion pressure) Voltage value based on the resistance value). When the output value obtained from the sample assembled on the engine head Q S _Q, the output values obtained from samples assembled on the engine head R was S _R,
(1-S _Q / S _R ) × 100 (%) (1)
4 was obtained by calculation, and the obtained value was expressed as “sensitivity dependency”, and the relationship with “joining position” was graphed. As a result, the result shown in FIG. 4 was obtained.

Since the engine head Q is not easily deformed as described above, the output value of the sample assembled to the engine head Q is due to the displacement of the heater member that receives the pressing force due to the combustion pressure. On the other hand, the output value of the sample assembled to the easily deformable engine head R is caused by the displacement of the heater member subjected to the pressing force due to the combustion pressure and the deformation of the metal shell accompanying the deformation of the engine head R. This is due to the combined displacement with the displacement of the heater member. Therefore, it can be said that as the value of S _Q / S _R approaches 0, the deformation of the metal shell accompanying the deformation of the engine head affects the magnitude of the output value obtained, that is, the displacement of the heater member. Further, it can be said that as the value of S _Q / S _R approaches 1, even if the metal shell is deformed by the deformation of the engine head, the displacement of the heater member is hardly affected.

  As shown in FIG. 4, the smaller the joining position (that is, the closer the joining part 41 (part D) approaches the part A at the tip of the seal portion 53), the higher the sensitivity dependency (that is, the heater due to deformation of the metal shell 40). It was confirmed that the influence on the displacement of the member 10 is increased). Also, the greater the joining position, that is, the closer the joining part 41 (part D) approaches the rear end part B of the threaded portion 67, the lower the sensitivity dependency, and the displacement of the heater member 10 even if the metal shell 40 is deformed. It has been confirmed that it becomes difficult to affect. Further, it was confirmed that the rate of change in sensitivity dependency with respect to the joining position is greatly different when the joining position is 50% with the inflection point as a turning point.

  From the result of this evaluation test, the joining position is 50% or more, that is, the joining part 41 (part D) is the center part C between the part A at the front end of the seal part 53 and the part B at the rear end of the screw part 67. Alternatively, if the metal shell 40 is formed so as to be located at the rear end side portion (between the portion C and the portion B) of the central portion C, the sensitivity dependency can be reduced to less than 10%, and the combustion pressure It has been found that a glow plug with a combustion pressure sensor can be produced in which the deformation of the engine head accompanying this is less likely to affect the displacement of the heater member.

  The present invention can be variously modified. For example, the joint part 41 (part D) shown in FIG. 2 is preferably formed between the part C and the part B, but the tip part E of the screw portion 67 or the tip side of the part E is closer to the tip side. It is even better if it is formed at the site. As described above, the heater support member 70 is not fixed to the front end side metal shell 50, and when the engine is operated, high-temperature combustion gas passes through the gap between the seal portion 53 and the heater support member 70. In some cases, the inner circumference of the front-end-side metal shell 50 enters between the outer circumference of the cylindrical body including the rear-end-side metal shell 60, the pressure detection sleeve 90, and the like. At this time, the combustion gas reaches the joining part 41. However, if the joining part 41 (part D) is located on the tip side of the tip part E of the screw part 67 as described above, the combustion gas does not reach the screw part 67. . With such a configuration, it is difficult for the thermal load due to the combustion gas to be applied to the screw portion 67, and it is possible to prevent the loosening of the screw portion 67 due to thermal expansion.

  In this embodiment, a piezoresistive element is used as the strain detecting element 120 of the combustion pressure sensor 100. However, when a resistor made of a metal such as copper or nickel alloy is formed on a thin insulating plate, it is meandered. For example, a strain gauge configured to increase the distance between the electrodes may be used. Alternatively, a piezoelectric charge type element may be used as the strain detection element 120. In this case, the piezoelectric charge-type element may be pressed when the center shaft is displaced by the pressing force due to the combustion pressure, and the generated charge may be output as a detection value. Alternatively, a preload may be applied to the piezoelectric charge element in advance, and the generated load may be output as a detection value so that the preload is relaxed when the center shaft is displaced by the pressing force due to the combustion pressure. Alternatively, an optical position sensor may be used to measure the displacement amount and displacement speed (or acceleration) of the central shaft, and the combustion pressure may be calculated based on the measurement result.

  Further, a temperature sensing element capable of detecting the temperature is provided on the substrate of the strain sensing element 120, and the detected value of the combustion pressure detected by the strain sensing element 120 is corrected based on the temperature information detected by the temperature sensing element. A temperature compensation circuit may be provided in the ASIC 131.

  The heater member provided in the glow plug 1 is provided with the ceramic heater 20 in the present embodiment. However, a sheath in which a coil-shaped heating resistor and a control coil are disposed in a sheath tube whose tip is closed in a hemispherical shape. A heater may be used.

  The present invention can be used for a combustion pressure sensor that detects the combustion pressure of an internal combustion engine, a glow plug equipped with a combustion pressure sensor, a temperature sensor, and the like.

2 is a partially cutaway longitudinal sectional view of the glow plug 1. FIG. 2 is an enlarged cross-sectional view of the tip side of a glow plug 1 attached to an engine head 200. FIG. FIG. 3 is an enlarged cross-sectional view of the tip side of the glow plug 1 that is deformed by receiving a pressing force due to combustion pressure. It is graphing which shows the relationship between the sensitivity dependence of a glow plug, and a joining position.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Glow plug 10 Heater member 20 Ceramic heater 30 Middle shaft 40 Main metal fitting 41 Joining part 51 Shaft hole 53 Seal part 61 Shaft hole 64 Engagement part 67 Screw part 70 Heater support member 90 Pressure detection sleeve 95 Intermediate sleeve 100 Combustion pressure sensor

Claims (2)

A metal shell having an axial hole extending along the axial direction;
A heater member having a heater that generates heat by energization and a middle shaft that is located on the rear end side of the heater and is electrically connected to the heater, and is disposed in the shaft hole so as to be displaced along the axial direction. A heater member disposed in
A combustion pressure sensor that detects a combustion pressure transmitted through the heater member that is displaced in the axial direction in accordance with a combustion pressure of an internal combustion engine;
A protrusion projecting from the inner wall surface of the shaft hole and holding the heater member,
The metallic shell is
On the outer peripheral surface, there are formed a screw portion that is screwed into the mounting hole of the internal combustion engine, and a seal portion that is in contact with the inner peripheral surface of the mounting hole on the tip side of the screw portion,
Of the protrusions, the coupling site with the inner wall surface of the shaft hole is:
Combustion pressure characterized by being in a central part between the axially leading end part of the seal part and the axially rear end part of the screw part, or in a rear end side part from the central part. Glow plug with sensor. 2. The glow plug with a combustion pressure sensor according to claim 1, wherein the coupling part is located at a part of the screw portion in the axial direction front end or a part of the front end side of the part.

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