JP2014211281A - Glow plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a glow plug having a pressure sensor for suppressing the heater element thereof from becoming an overhead state.SOLUTION: A glow plug comprises: a rod-shaped heater element extending in an axial direction and exposed at its front end part to a combustion chamber; an inner shaft arranged on the rear end side of the heater element for feeding an electric power to the heater element; a housing for confining a portion of the heater element and a portion of the inner shaft in its own shaft hole; a connection member for connecting the heater element and the housing singly or together with another member; and a pressure detection element for detecting the combustion pressure of the combustion chamber from the axial displacement of the heater element with respect to the housing. Further comprised are: a ring for connecting the heater element and the inner shaft electrically; and a heat transfer part arranged in the ring between the rear end part of the heater element and the front end part of the inner shaft and contacting with the rear end part of the heater element and the leading end part of the inner shaft so that it has a thermal conductivity higher than that of air.

Description

  The present invention relates to a glow plug.

  In a compression ignition type internal combustion engine such as a diesel engine, a glow plug is used as an auxiliary heat source at the time of starting. Conventionally, various types of glow plug structures have been proposed. As one of such glow plugs, there is known a glow plug with a pressure sensor incorporating a pressure sensor capable of detecting a combustion pressure in a combustion chamber of an internal combustion engine to which the glow plug is attached (see, for example, Patent Document 1). .

JP 2010-139147 A

  A glow plug with a pressure sensor generally includes a connecting member (a film-like elastic member or a bellows) together with a heater element, and the heater element is moved by the connecting member so that the heater element can move in the axial direction within the glow plug. And the housing (outer cylinder). Thus, since the heater element and the housing are not directly in contact with each other but are connected via a thin connecting member having a small cross-sectional area, the heat transfer efficiency from the heater element to the housing is low. As a result, since it is difficult to transfer heat from the heater element to the engine block side through the housing, for example, the heat dissipation efficiency of the heater element is suppressed, and the heater element is likely to be overheated.

  As the glow plug, for example, a metal member is disposed outside the heater element and brought into contact with the heater element, thereby electrically connecting the conductive portion included in the heater element and the metal member, thereby supplying power to the heater element. A configuration for forming a supply path is known. In such a glow plug, when the heater element is overheated as described above, for example, the metal member that is in contact with the heater element and has a thermal expansion coefficient larger than that of the heater element is thermally expanded. There is a possibility that the contact between the connection terminal of the conductive portion and the metal member in contact with the connection terminal becomes insufficient, and the conduction state is lowered. Further, when the heater element is overheated, the metal member having a coefficient of thermal expansion larger than that of the heater element is thermally expanded, so that oxygen easily flows between the metal member and the heater element. As a result, the oxidation of the connection terminal of the conductive portion of the heater element is likely to progress with time, and the conduction state between the connection terminal and the metal member in contact with the connection terminal may be insufficient. is there.

  In the glow plug described in Patent Document 1 described above, the pressure sensor is disposed at a position close to the rear end of the heater element. However, in the glow plug with a pressure sensor, the pressure sensor is disposed and pressure is transmitted to the pressure sensor. Various improvements have been attempted in the overall configuration including methods. However, the glow plug with a pressure sensor is common in that it uses a connecting member that connects the heater element and the housing while allowing the heater element to move in the axial direction. Therefore, a glow plug with a pressure sensor that can suppress overheating of the heater element has been desired.

  The present invention has been made to solve the above-described problems, and can be realized as the following forms.

(1) According to one aspect of the present invention, the rod-shaped heater element extending in the axial direction and having a tip portion exposed in the combustion chamber and a conductive material are disposed on the rear end side of the heater element. A central shaft for supplying electric power to the heater element, a housing that constitutes an outer wall of the glow plug, a part of the heater element and a part of the central shaft are accommodated in its own shaft hole, and the heater element is disposed in the housing From the displacement member in the axial direction of the heater element relative to the housing, a connecting member that connects the heater element and the housing alone or together with other members while allowing displacement in the axial direction, the combustion chamber And a pressure detecting element for detecting the combustion pressure of the glow plug. The glow plug is arranged between a ring for electrically connecting the heater element and the middle shaft, and a rear end portion of the heater element and a front end portion of the middle shaft in the ring. And a heat transfer section having a thermal conductivity higher than that of air.
According to the glow plug of this form, the heat transfer portion is disposed between the rear end portion of the heater element and the tip end portion of the center shaft, so that the heat of the heater element is transmitted to the center shaft via the heat transfer portion. be able to. Therefore, it can suppress that a heater element will be in an overheated state.

(2) In the glow plug of the above aspect, the heat conductivity of the heat transfer section may be smaller than the heat conductivity of the central shaft.
According to the glow plug of this embodiment, the efficiency of heat radiation from the heater element that passes through the heat transfer section and the central shaft can be further improved.

(3) In the glow plug of the above aspect, the heater element includes an insulating portion and a conductive portion that is formed in the insulating portion and generates heat when energized, and the conductive portion is the rear end of the heater element. A first potential side connection terminal exposed at the side surface of the portion and in contact with the inner wall surface of the ring; a second potential side connection terminal having a lower potential than the first potential side connection terminal; A second potential side end portion exposed in a region facing the central axis at the rear end portion of the heater element, and by providing the heat transfer section, the second potential side end of the conductive portion is provided. The end portion may be electrically insulated from the middle shaft.
According to the glow plug of this embodiment, by providing the heat transfer section, it is possible to improve the heat dissipation efficiency from the heater element and to ensure insulation between the second potential side end and the central shaft. Therefore, even when a heater element in which the second potential side end is exposed at the rear end is used, a structure for ensuring insulation between the second potential side end and the central shaft is provided. There is no need to provide it separately, and the complexity of the glow plug structure can be suppressed.

(4) In the glow plug of the above aspect, the heat transfer section may include an electrical insulating section that covers at least the end portion on the second potential side of the conductive section.
According to the glow plug of this embodiment, it is possible to ensure insulation between the end portion on the second potential side of the conductive portion and the central shaft by the electrical insulating portion provided in the heat transfer portion.

  The present invention can be realized in various forms other than those described above. For example, the present invention can be realized in the form of a method for manufacturing a glow plug or a method for radiating a heater element in the glow plug.

It is a cross-sectional schematic diagram showing schematic structure of a glow plug. It is an expanded sectional view of the area | region X in FIG. It is an expanded sectional view of the field containing a heat transfer part. It is a cross-sectional schematic diagram showing schematic structure of a glow plug. It is a cross-sectional schematic diagram showing schematic structure of a glow plug. It is a cross-sectional schematic diagram showing schematic structure of a glow plug. It is a top view showing the structure of a heat-transfer part. It is a cross-sectional schematic diagram showing schematic structure of a glow plug. It is a cross-sectional schematic diagram showing schematic structure of a glow plug. It is a cross-sectional schematic diagram showing the modification of a glow plug. It is a cross-sectional schematic diagram showing the modification of a glow plug.

A. First embodiment:
FIG. 1 is a schematic cross-sectional view showing a schematic configuration of a glow plug 10 as a first embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view of a portion indicated as a region X in FIG. The glow plug 10 of the present embodiment is attached to an internal combustion engine such as a diesel engine, and functions as a heat source that assists ignition when starting the internal combustion engine. The glow plug 10 can also be used as a heat source for a diesel particulate filter (DPF) reactivation burner system. As shown in FIG. 1, the glow plug 10 includes a housing 20, a heater element 40, a middle shaft 50, a ring 60, and a heat transfer unit 65 as main components. The glow plug 10 further has a function as a pressure sensor for detecting the pressure (combustion pressure) in the cylinder of the internal combustion engine. The glow plug 10 includes a connecting member 70, a transmission sleeve 32, a diaphragm 33, a pressure detection element 35, and a sensor fixing member 34 as main components for realizing a function as a pressure sensor. Yes. Below, each part is demonstrated based on FIG. In the present specification, the lower side of the glow plug 10 in FIG. 1 in the direction of the axis O is called the “front end side” of the glow plug 10 and the upper side is called the “rear end side”.

  The housing 20 is formed of a conductive material (for example, a metal material such as carbon steel or stainless steel), and includes a metal shell 22 and a cap portion 24. The metal shell 22 is a substantially cylindrical member extending along the axis O. A shaft hole 21 that penetrates through the metal shell 22 along the axis O is formed inside the metal shell 22. The metal shell 22 has a threaded portion 23 formed on the outer surface on the rear end side thereof with a male screw to be screwed into a female screw formed in a plug mounting hole of a cylinder head (not shown) of the internal combustion engine. (See FIG. 1). The cap portion 24 is an annular member disposed on the front end side of the metal shell 22. A tapered portion 25 having a diameter reduced toward the distal end side is provided on the distal end surface of the cap portion 24. The tapered portion 25 is in contact with a seat surface (not shown) provided in the plug mounting hole, thereby ensuring airtightness of the combustion chamber of the engine.

  The heater element 40 is a substantially columnar member extending along the axis O, and includes an insulating portion 41 and a conductive portion 42. The heater element 40 is disposed in the shaft hole 21 at the distal end portion of the metal shell 22, and penetrates the cap portion 24 and protrudes from the distal end of the cap portion 24. The heater element 40 generates heat when electric power is supplied.

  The insulating part 41 is made of insulating ceramics. In the present embodiment, the insulating part 41 is made of silicon nitride. However, the insulating portion 41 is not limited to silicon nitride, and may be formed of other insulating ceramics such as alumina or sialon. The insulating portion 41 is a portion that forms the base of the heater element 40.

  The conductive portion 42 is embedded in the insulating portion 41, has a U-shaped structure that extends in the direction of the axis O and is bent with the tip end as a vertex, and is made of conductive ceramics that generate resistance when energized. Is formed. In the present embodiment, the conductive portion 42 is formed of tungsten carbide. However, the conductive portion 42 is not limited to tungsten carbide, and may be formed of other conductive ceramics such as molybdenum disilicide or tungsten disilicide, for example.

  Both ends of the U-shaped conductive part 42 are exposed on the outer surface of the rear end of the heater element 40. One end portion is a first potential side end portion (plus side end portion) 44, and the other end portion is a second potential side end portion (minus side) having a lower potential than one end portion. End) 43. The conductive portion 42 has a first potential side connection terminal (plus side connection terminal) exposed on the side surface of the heater element 40 in the vicinity of the first potential side end portion (plus side end portion) 44. 46 is formed. In addition, the conductive portion 42 has a heater element 40 in the vicinity of the second potential side end portion (minus side end portion) 43 at a position closer to the tip side than the first potential side connection terminal 46. A second potential side connection terminal (minus side connection terminal) 45 exposed at the side surface is formed. In the present embodiment, the first potential-side connection terminal 46 and the second potential-side connection terminal 45 are formed of the same material as other portions of the conductive portion 42, and a part of the conductive portion 42. It is formed as. However, the first potential side connection terminal 46 and the second potential side connection terminal 45 may be formed separately from other parts of the conductive portion 42.

  The middle shaft 50 has a shape extending along the axis O, and is a rod-shaped member formed of a conductive material (for example, a metal material such as stainless steel such as SUS430, aluminum, copper, and iron). In the shaft hole 21 of 22, the heater element 40 is disposed on the rear end side.

  The ring 60 is a cylindrical member formed of a conductive material (for example, a metal material such as SUS410 or SUS630), and is assembled between the middle shaft 50 and the heater element 40 inside the shaft hole 21 of the metal shell 22. It is done. Specifically, the rear end portion of the heater element 40 and the front end portion of the middle shaft 50 are fitted into the ring 60. The rear end portion of the heater element 40 is fitted into the ring 60 by press-fitting, whereby the first potential side connection terminal (plus side connection terminal) 46 exposed on the side surface of the heater element 40 is formed on the inner wall of the ring 60. Touch. As a result, the first potential side connection terminal (plus side connection terminal) 46 of the conductive portion 42 of the heater element 40 is electrically connected to the middle shaft 50 via the ring 60. In the present embodiment, the tip of the middle shaft 50 is also fitted into the ring 60 by press-fitting.

  The heat transfer part 65 is a thin plate-like member made of an electrically insulating material, and is entirely configured as an electric insulating part. The heat transfer section 65 is disposed in the ring 60 between the rear end portion of the heater element 40 and the front end portion of the middle shaft 50. The heat transfer portion 65 is in contact with both the rear end portion of the heater element 40 and the front end portion of the middle shaft 50, and is formed in the ring 60 between the rear end portion of the heater element 40 and the front end portion of the middle shaft 50. It is arranged in the space where there is no gap. By disposing the heat transfer section 65 in this way, heat is transmitted (radiated) from the heater element 40 to the middle shaft 50 via the heat transfer section 65. Moreover, in this embodiment, the heat-transfer part 65 is formed with the insulating material. Therefore, by disposing the heat transfer section 65, the second potential side end (minus side end) 43 of the conductive section 42 included in the heater element 40 and the middle shaft 50 are insulated. As an insulating material which comprises the heat-transfer part 65, the material selected from rubber | gum, resin, ceramics, and glass can be used, for example. As will be described later, the heat transfer section 65 is disposed between the rear end portion of the heater element 40 and the front end portion of the middle shaft 50 when the middle shaft 50 is press-fitted into the ring 60. From the viewpoint of reducing the above, it is preferable to use a rubber member or a resin member having a higher elastic modulus.

  As the rubber constituting the heat transfer section 65, for example, a rubber selected from butyl rubber, fluorine rubber, silicone rubber, and ethylene propylene rubber (EPDM) can be used. As resin which comprises the heat-transfer part 65, resin selected from a fluorine resin, a silicone resin, and an epoxy resin can be used, for example. Any material that is stable under the environmental conditions (temperature, atmosphere, etc.) of the heat transfer section 65 during use of the glow plug 10 may be used. The heat resistant temperature of the material constituting the heat transfer section 65 is preferably 100 ° C. or higher, more preferably 150 ° C. or higher, further preferably 200 ° C. or higher, and most preferably 300 ° C. or higher. preferable.

  FIG. 3 is an explanatory diagram showing a state of a region including a portion where the heat transfer portion 65 is disposed between the rear end portion of the heater element 40 and the front end portion of the middle shaft 50. Specifically, in FIG. It is a cross-sectional schematic diagram which expands and shows the area | region shown as the area | region Y. FIG. In FIG. 3, the transmission sleeve 32, the sensor fixing member 34, and the metal shell 22 in the region Y of FIG.

  In the present embodiment, the leading end of the middle shaft 50 and the rearmost end of the heater element 40 are formed as a flat surface perpendicular to the direction of the axis O. In the present embodiment, the inner shaft 50, the heater element 40, and the inner wall of the ring 60 are all formed in a circular cross section, and the heat transfer section 65 is formed in a disc shape. However, the shape of the cross section may be a shape other than a circle, for example, a semicircular shape or an elliptical shape. In addition, the shape of each part described in this specification, specifically, circular, semicircular shape, elliptical shape, cylindrical shape, columnar shape, disk shape, or the like is an error that occurs when a member including each part is manufactured. This includes shapes having distortions and deformations due to tolerances caused by the above.

  In FIG. 3, the thickness of the heat transfer part 65 is shown as thickness a. The thickness a is preferably 1 μm or more, preferably 5 μm or more from the viewpoint of suppressing a short circuit between the second potential side end portion (minus side end portion) 43 of the conductive portion 42 and the middle shaft 50. It is more preferable. The thickness a is preferably 10 μm or more from the viewpoint of suppressing damage caused by being pinched between the middle shaft 50 and the heater element 40 when the middle shaft 50 is press-fitted into the ring 60 as will be described later. . Further, the thickness a is preferably 1 mm or less from the viewpoint of suppressing an increase in the size of the glow plug 10 in the axis O direction, or from the viewpoint of securing the strength of the coupling between the middle shaft 50 and the ring 60, and 0.5 mm or less. More preferably, it is more preferably 0.1 mm or less. However, the thickness a can be less than 1 μm, and can be 1 mm or more.

  A taper that gradually decreases in diameter toward the distal end side of the middle shaft 50 may be formed on the outer wall in the vicinity of the front end of the middle shaft 50. Thereby, the operation | movement which fits the front-end | tip part of the center axis | shaft 50 in the ring 60 can be facilitated.

  On the side surface of the heater element 40, the first outer cylinder 30 is disposed on the distal end side with respect to the fitting position of the ring 60, and the second outer cylinder 31 is disposed on the distal end side with respect to the first outer cylinder 30. . The first outer cylinder 30 and the second outer cylinder 31 are cylindrical members formed of a conductive material (for example, a metal material such as SUS410 and SUS630), and the first outer cylinder 30 and the second outer cylinder 31 are in the first outer cylinder 30 and the second outer cylinder 31. The heater element 40 is assembled by press-fitting. By press-fitting the heater element 40 into the first outer cylinder 30, the second potential side connection terminal (minus side connection terminal) 45 of the conductive part 42 comes into contact with the inner wall of the first outer cylinder 30, and the conductive part 42 and the first outer cylinder 30 are electrically connected.

  A connecting member 70, a transmission sleeve 32, a diaphragm 33, and a sensor fixing member 34 are disposed between the inner wall surface of the housing 20 and the heater element 40, the middle shaft 50 and the ring 60. All of these members are formed of a conductive material. The connecting member 70 can be formed of a metal material such as stainless steel such as SUS316 or nickel alloy. The transmission sleeve 32, the diaphragm 33, and the sensor fixing member 34 can be formed of a metal material such as carbon steel or stainless steel.

  The connecting member 70 is a film-like elastic member that connects the heater element 40 and the housing 20 while allowing the heater element 40 to move along the axis O, and is disposed in the cap portion 24. A hole through which the heater element 40 passes is formed in the connecting member 70 at the center. And the inner peripheral part (the front end side of the connection member 70) in which the hole is formed is welded to the rear end part of the second outer cylinder 31 provided on the outer periphery of the heater element 40. The outer peripheral portion (the rear end side of the connecting member 70) is welded to the cap portion 24. The connecting member 70 also serves to secure the airtightness in the housing 20 by connecting the heater element 40 and the housing 20 as described above. The connecting member 70 only needs to allow movement along the axis O of the heater element 40 by elastic deformation, and may be, for example, a bellows.

  The sensor fixing member 34 is a substantially cylindrical member. The sensor fixing member 34 is disposed along the inner wall surface of the shaft hole 21 of the metal shell 22, and a flange-like flange portion 36 protruding outward in the radial direction is formed in the vicinity of the tip of the sensor fixing member 34. The flange portion 36 is welded to the front end surface of the metal shell 22 and the rear end surface of the cap portion 24.

  The transmission sleeve 32 is a substantially cylindrical member, and is disposed radially inward of the sensor fixing member 34 in the shaft hole 21 of the metal shell 22. The distal end of the transmission sleeve 32 is fitted to the outside of the first outer cylinder 30 and is welded to the first outer cylinder 30. Thereby, when the heater element 40 is displaced along the direction of the axis O, the transmission sleeve 32 is also displaced together, and the transmission sleeve 32 causes the displacement of the heater element 40 along the axis O to the rear end side (diaphragm 33). Communicate. The first outer cylinder 30 is formed thicker than the ring 60, and the transmission sleeve 32 and the ring 60 are separated from each other. For this reason, the ring 60 and the intermediate shaft 50 fitted in the ring 60 and the transmission sleeve 32 are insulated by a space.

  The diaphragm 33 is an annular member. In the center of the diaphragm 33, an opening 37 through which the middle shaft 50 passes is provided. The rear end of the transmission sleeve 32 is welded to the inner periphery of the diaphragm 33. For this reason, when the heater element 40 is displaced along the axis O in response to the pressure (combustion pressure) of the combustion gas, the displacement amount is transmitted to the diaphragm 33 by the transmission sleeve 32, and the diaphragm 33 is deformed. The rear end of the sensor fixing member 34 is welded to the outer periphery of the diaphragm 33. In the present embodiment, the diaphragm 33 is fixed near the central portion in the housing 20 by the sensor fixing member 34.

  A pressure detection element 35 that detects pressure based on the deformation amount of the diaphragm 33 is provided on the upper surface (the rear end side surface) of the diaphragm 33 (see FIG. 2). In the present embodiment, a piezoresistive element is used as the pressure detection element 35. In the present embodiment, a piezoresistive element is used as the pressure detection element 35, but a different type of sensor element, for example, a piezoelectric element may be used.

  The resistance value of the pressure detection element 35 (piezoresistive element) according to the present embodiment changes according to the deformation amount of the diaphragm 33. An integrated circuit (not shown) provided at a predetermined portion in the housing 20 is electrically connected to the pressure detection element 35. The integrated circuit detects the combustion pressure of the internal combustion engine by detecting a change in the resistance value of the pressure detection element 35. The integrated circuit outputs an electric signal indicating the combustion pressure thus detected to an external ECU or the like through a wiring (not shown) inserted from the rear end of the housing 20.

  Returning to FIG. 1, a protective cylinder 72 is attached to the rear end side of the housing 20. A terminal fitting 73 that is electrically connected to the middle shaft 50 is disposed inside the protective cylinder 72.

  In the glow plug 10 configured as described above, when power is supplied from the terminal fitting 73, power is supplied to the conductive portion 42 through the central shaft 50, the ring 60, and the first potential side connection terminal 46, and the heater element 40 generates heat. At this time, the connection terminal 45 on the second potential side of the conductive portion 42 is grounded through the first outer cylinder 30, the transmission sleeve 32, the diaphragm 33, the sensor fixing member 34, the housing 20, and the cylinder head of the internal combustion engine.

  Below, the manufacturing method of the glow plug 10 is demonstrated. When manufacturing the glow plug 10, first, the front end of the heater element 40 is inserted from the rear end side of the ring 60 to the front end side, and the heater element 40 is press-fitted into the ring 60. As a result, the first potential side connection terminal (plus side connection terminal) 46 of the conductive portion 42 contacts the inner wall of the ring 60, and the conductive portion 42 and the ring 60 are electrically connected. At this time, the heater element 40 is press-fitted into the ring 60, so that the contact state between the connection terminal 46 on the first potential side and the inner wall of the ring 60 is enhanced, and the conductive portion 42 and the ring 60 are electrically connected. Resistance at the time of connection is sufficiently suppressed.

  Thereafter, the heater element 40 is press-fitted into the first outer cylinder 30 and the second outer cylinder 31, and the distal end portion of the heater element 40 protrudes from the distal end of the second outer cylinder 31. As a result, the second potential side connection terminal (minus side connection terminal) 45 of the conductive portion 42 is brought into close contact with the inner wall surface of the first outer cylinder 30, and the conductive portion 42 and the first outer cylinder 30 are electrically connected. Is done.

  Next, the heat transfer part 65 is affixed to the most advanced flat surface (hereinafter also referred to as the front end surface) of the middle shaft 50. The heat transfer part 65 may be attached to the middle shaft 50 using an adhesive that is stable under the environmental conditions (temperature, atmosphere, etc.) of the heat transfer part 65 during use of the glow plug 10. As the adhesive, for example, a silicone-based adhesive can be used. Although the thickness a of the heat transfer section 65 provided in the glow plug 10 has already been described, the thickness of the heat transfer section 65 used for pasting is set in consideration of the collapse due to the press-fitting of the distal end portion of the center shaft 50 described later. That's fine.

  Then, the front-end | tip part of the center axis | shaft 50 which affixed the heat-transfer part 65 on the rear-end side of the ring 60 is press-fit, and the ring 60 and the center axis | shaft 50 are fixed by welding. When the intermediate shaft 50 is press-fitted into the ring 60, the intermediate shaft 50 may be inserted into the ring 60 until the tip of the intermediate shaft 50 to which the heat transfer section 65 is attached contacts the rear end of the heater element 40. . The ring 60 and the middle shaft 50 may be welded at a position (indicated by an arrow W1 in FIG. 3) where the rear end of the ring 60 and the outer surface of the middle shaft 50 are in contact with each other. In this embodiment, the heater element 40 is press-fitted into the first outer cylinder 30 and the second outer cylinder 31 before the intermediate shaft 50 is press-fitted into the rear end side of the ring 60 in which the heater element 40 is fitted. The order of these steps may be reversed. That is, the step of press-fitting the heater element 40 into the first outer cylinder 30 and the second outer cylinder 31 may be performed after the step of press-fitting the center shaft 50 to the rear end side of the ring 60.

  In the present embodiment, the heat transfer portion 65 is attached to the tip of the middle shaft 50 and then the middle shaft 50 is press-fitted into the ring 60. However, a different configuration may be used. For example, before the rear end portion of the heater element 40 is press-fitted into the ring 60 or after the rear end portion of the heater element 40 is press-fitted into the ring 60, the flat surface (hereinafter referred to as the rear end surface) of the heater element 40 is The heat transfer section 65 may be attached to the above. Further, the heat transfer portion 65 is not attached to the tip end portion of the intermediate shaft 50 and the heat transfer portion 65 is not attached to the rear end portion of the heater element 40, so that the intermediate shaft 50 is press-fitted into the ring 60. The heat transfer section 65 may be sandwiched between the heater 50 and the heater element 40.

  Next, the transmission sleeve 32, the diaphragm 33, the sensor fixing member 34, and the metal shell 22 are further assembled to the intermediate member including the heater element 40, the middle shaft 50, and the ring 60 described above. Here, the transmission sleeve 32, the diaphragm 33, and the sensor fixing member 34 are welded at predetermined positions, and the heater element 40 and the like are provided in a through hole that penetrates the transmission sleeve 32 disposed inside in the direction of the axis O. An intermediate member is disposed. Further, the metal shell 22 is disposed on the outer peripheral side of the sensor fixing member 34 (see FIG. 2).

  Thereafter, the flange portion 36 at the tip of the sensor fixing member 34 and the tip of the metal shell 22 are welded, and the heater element 40 (specifically, the first outer cylinder 30) and the tip of the transmission sleeve 32 are welded. . Further, between the rear end portion of the connecting member 70 and the front end portion of the sensor fixing member 34 and between the front end portion of the connecting member 70 and the heater element 40 (specifically, the rear end portion of the second outer cylinder 31). Weld. Further, the cap portion 24 is fitted from the front end side of the heater element 40, and is further press-fitted into the front end portion of the sensor fixing member 34, and the flange portion 36 of the sensor fixing member 34 and the cap portion 24 are welded (see FIG. 2). Thereafter, the protective cylinder 72 is attached to the rear end side of the metal shell 22 and the center shaft 50 and the terminal metal fitting 73 are connected to complete the glow plug 10.

  According to the glow plug 10 of the present embodiment configured as described above, the heat transfer portion 65 is disposed between the rear end portion of the heater element 40 and the front end portion of the center shaft 50, and thus the heat transfer portion 65. The heat of the heater element 40 can be transmitted to the middle shaft 50 via For this reason, the heater element 40 can be prevented from being overheated.

  That is, the glow plug 10 of the present embodiment is a glow plug with a pressure sensor in which the heater element 40 and the housing 20 are connected by the connecting member 70 having a small cross-sectional area and low heat transfer efficiency. The heat transfer efficiency to the housing 20 is low. Further, in the glow plug of the present embodiment, the transmission sleeve 32 and the sensor fixing member 34 are also interposed between the heater element 40 and the housing 20, but these members also have a small cross-sectional area. Is not efficient enough to transmit to the housing 20. Further, in the glow plug 10 of the present embodiment, heat can be radiated from the heater element 40 to the middle shaft 50 via the ring 60. However, since the cross-sectional area of the ring 60 is small, heat transfer via the ring 60 is possible. The efficiency is also low. In the present embodiment, by further providing the heat transfer section 65, a new heat radiation path from the heater element 40 to the middle shaft 50 can be secured, and overheating of the heater element 40 can be suppressed.

  Since overheating of the heater element 40 can be suppressed as described above, the thermal expansion of the metal member (the ring 60 or the first outer cylinder 30) into which the heater element 40 is fitted is larger than that of the heater element 40 and is suppressed. Can do. As a result, the contact between the first potential side connection terminal (plus side connection terminal) 46 and the ring 60 included in the heater element 40 or the second potential side connection terminal (minus side connection terminal) 45 and the first potential terminal. It is possible to suppress the contact between the outer cylinder 30 and the conduction state from being lowered.

  Further, in this embodiment, since the overheating state of the heater element 40 can be suppressed, the progress of oxidation over time at the connection terminals (the first potential side connection terminal 46 and the second potential side connection terminal 45) is suppressed. Further, it is possible to suppress a decrease in the conduction state between the connection terminal and the metal member (the ring 60 or the first outer cylinder 30) due to the oxidation of the connection terminal. That is, since the coefficient of thermal expansion is different between the heater element 40 and the ring 60, the difference between the degree of expansion of the heater element 40 and the ring 60 increases as the temperature increases. When the difference between the degree of expansion of the heater element 40 and the ring 60 increases, oxygen flows between the heater element 40 and the ring 60, and the connection terminal is easily oxidized. In this embodiment, by suppressing the overheating state of the heater element 40 and suppressing the progress of oxidation of the connection terminals, the conduction state between the connection terminals and the metal member in contact with these connection terminals is not good. It can be suppressed that it becomes sufficient.

  As described above, in the present embodiment, it is possible to suppress overheating of the heater element 40 by providing the heat transfer portion 65 made of a material having a higher thermal conductivity than air. Here, the heat transfer section 65 has higher performance for transferring heat as the thermal conductivity of the constituent material is higher. For example, since the thermal conductivity of air at normal temperature is 0.0257 (W / m · K), in order to increase the heat dissipation efficiency from the heater element 40, the heat of the constituent material of the heat transfer section 65 at normal temperature is used. The conductivity is preferably 0.10 (W / m · K) or more, and more preferably 0.20 (W / m · K) or more.

  In the case where heat is transferred to the middle shaft 50 via the heat transfer section 65 as in the present embodiment, the structure of the heat transfer section 65 is improved in order to improve the heat radiation efficiency from the heater element 40 to the middle shaft 50. It is desirable that the thermal conductivity of the material be lower than the thermal conductivity of the constituent material of the central shaft 50. In other words, it is desirable that the thermal conductivity of the constituent material of the middle shaft 50 be higher than the thermal conductivity of the constituent material of the heat transfer section 65. In the present embodiment, as described above, the middle shaft 50 is formed of a metal material such as stainless steel, aluminum, and iron. The thermal conductivity of such a metal material is higher than that of an insulating material (for example, a material selected from rubber, resin, ceramics, and glass) constituting the heat transfer section 65. Therefore, the heat radiation efficiency from the heater element 40 to the middle shaft 50 via the heat transfer section 65 can be increased. That is, since the thermal conductivity of the middle shaft 50 is high, the heat dissipation efficiency of the middle shaft 50 itself is high, and the heat of the heat transfer section 65 can be transmitted to the middle shaft 50 without any delay. In addition, the approximate thermal conductivity at normal temperature of these materials which comprise the center shaft 50 and the heat-transfer part 65 is shown below. The thermal conductivity of the constituent material of the central shaft 50 is, for example, 16 to 26 (W / m · K) for stainless steel, 237 (W / m · K) for aluminum, and 80.3 (W / m · K) for iron. It is. The heat conductivity of the constituent material of the heat transfer section 65 is, for example, 0.13 (W / m · K) for natural rubber, 0.35 (W / m · K) for epoxy resin, and 1.03 for glass. (W / m · K).

  Here, in the present embodiment, the heater element 40 that generates heat, the ring 60 to which heat is transmitted from the heater element 40, the heat transfer portion 65, and the middle shaft 50 are arranged apart from the diaphragm 33 and the pressure detection element 35. . Further, the diaphragm 33 and the pressure detection element 35 are disposed on the rear end side of the front end portion of the central shaft 50 and the heat transfer portion 65, and a greater distance from the heater element 40 is ensured. Therefore, in the present embodiment, excessive temperature rise of the diaphragm 33 and the pressure detection element 35 can be suppressed, and the pressure detection accuracy can be prevented from being lowered due to overheating of the pressure detection element 35. In particular, in the present embodiment, the diaphragm 33 and the pressure detection element 35 are disposed at the rear end of the housing 20. As described above, the heater element 40 and the housing 20 are connected by a member having a small cross-sectional area, and the heat transfer efficiency from the heater element 40 to the housing 20 is low. Therefore, the effect of suppressing excessive temperature rise of the diaphragm 33 and the pressure detection element 35 can be enhanced.

  Further, in the present embodiment, since the heat transfer section 65 is made of an insulating material, the heater element 40 in which the second potential side end (minus side end) 43 is exposed at the rear end is used. Even so, it is possible to ensure insulation between the second potential side end portion 43 and the middle shaft 50. Further, when the center shaft 50 is press-fitted into the ring 60, the rear end portion of the heater element 40 and the heat transfer portion 65, and the heat transfer portion 65 and the tip end portion of the center shaft 50 may be press-fitted. Thus, the assembly operation can be simplified.

B. Second embodiment:
FIG. 4 is a schematic cross-sectional view illustrating a schematic configuration of the glow plug 110 according to the second embodiment. In the second embodiment, parts that are the same as those in the first embodiment are given the same reference numerals, and detailed descriptions thereof are omitted. The glow plug 110 of the second embodiment has the same configuration as the glow plug 10 of the first embodiment, except that a heat transfer unit 165 is provided instead of the heat transfer unit 65. 4, as in FIG. 3, only the region including the rear end portion of the heater element 40 and the front end portion of the middle shaft 50 is shown in an enlarged manner.

  In the second embodiment, the heat transfer section 165 is filled with a powder made of an insulating material (the resin or ceramic described above) between the rear end portion of the heater element 40 and the front end portion of the central shaft 50. It is formed by. Specifically, it is formed by filling the powder on the rear end portion of the heater element 40 in the ring 60 instead of attaching the insulator to the tip portion of the middle shaft 50 in the first embodiment. The As described above, the heat transfer section only needs to be formed of a solid made of an insulating material, and thereby the same effect as that of the first embodiment can be obtained. However, in order to simplify the operation of fitting the center shaft 50 into the ring 60 while interposing the heat transfer portion between the rear end portion of the heater element 40, the heat transfer portion is a single member. Alternatively, it is preferably formed in a state of being fixed in advance to the rear end portion of the heater element 40 or the front end portion of the middle shaft 50.

C. Third embodiment:
FIG. 5 is a schematic cross-sectional view illustrating a schematic configuration of the glow plug 210 according to the third embodiment. In the third embodiment, parts that are the same as those in the first embodiment are given the same reference numerals, and detailed descriptions thereof are omitted. The glow plug 210 of the third embodiment has the same configuration as that of the glow plug 10 of the first embodiment except that a heat transfer section 265 is provided instead of the heat transfer section 65. In FIG. 5, similarly to FIG. 2, only the region including the rear end portion of the heater element 40 and the front end portion of the central shaft 50 is shown enlarged.

  In the glow plug 210, a heat transfer portion 265 is formed on the tip surface of the middle shaft 50 as a coating made of an insulating material. The coating as the heat transfer portion 265 is, for example, a resin coating (spray) using a resin (for example, epoxy resin or polyimide) that is stable under the environmental conditions (temperature, atmosphere, etc.) of the heat transfer portion 65 during use of the glow plug 10. Etc.). Alternatively, it may be formed by a ceramic coating. The ceramic coating can be performed by, for example, a PVD method (physical vapor deposition method) such as ion plating. Moreover, you may form the film used as the heat-transfer part 265 with an insulating gel. The insulating gel film can be formed, for example, by applying silicone gel or rubber polymer. When the heat transfer portion 465 is formed of an insulating film, the insulating film may be formed on at least one of the rear end surface of the heater element 40 and the front end surface of the middle shaft 50. Even with such a configuration, the same effects as those of the first embodiment can be obtained.

  In the case where the heat transfer portion is constituted by an insulating film formed by coating, the heat transfer portion is formed more than in the case where the heat transfer portion is constituted by a thin plate member separate from the heater element 40 and the central shaft 50. Thinning becomes easy. For example, it becomes possible to easily form a heat transfer portion having a thickness a of about 0.1 to 10 μm. Thereby, the length of the ring 60 in the axis O direction and the length of the glow plug in the axis O direction can be suppressed.

D. Fourth embodiment:
FIG. 6 is a schematic cross-sectional view illustrating a schematic configuration of a glow plug 310 according to the fourth embodiment. In the fourth embodiment, parts common to the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted. The glow plug 310 of the fourth embodiment has the same configuration as the glow plug 10 of the first embodiment, except that a heat transfer unit 365 is provided instead of the heat transfer unit 65. 6, as in FIG. 2, only the region including the rear end portion of the heater element 40 and the front end portion of the middle shaft 50 is shown in an enlarged manner.

  The heat transfer unit 365 is a thin plate member similar to the heat transfer unit 65 of the first embodiment, and includes a high heat transfer unit 366 and an electrical insulating unit 367. The electrical insulating part 367 is provided so as to penetrate the heat transfer part 365 in the thickness direction, and is made of an insulating material similar to that of the heat transfer part in the first to third embodiments. The electrical insulating portion 367 is provided so as to cover the entire second potential side end portion (minus side end portion) 43 exposed at the rear end portion of the heater element 40. The high heat transfer portion 366 may be formed of a material having a higher thermal conductivity than that of the electrical insulating portion 367. For example, the high heat transfer portion 366 may be formed of a metal material having a lower thermal conductivity than the constituent material of the middle shaft 50.

  Even with such a configuration, the same effects as those of the first embodiment can be obtained. Furthermore, the heat transfer unit 365 of the present embodiment has a high heat transfer unit while ensuring insulation between the second potential side end (minus side end) 43 and the central shaft 50 by the electric insulating unit 367. By providing 366, the heat transfer efficiency of the entire heat transfer section 365 can be increased.

  FIG. 7 is a plan view illustrating the configuration of the heat transfer unit 365. FIG. 7A is a plan view of the heat transfer section 365 shown in FIG. 6, and FIG. 7B is a plan view of the heat transfer section as a modification of the fourth embodiment. In the heat transfer section of FIG. 7B, the electric insulation section 367 is provided so that the outer periphery of the electric insulation section 367 is concentric with the outer periphery of the heat transfer section. In this way, the electrical insulating portion 367 only needs to cover at least the second potential side end portion (minus side end portion) 43. Further, as long as the electrical insulating portion 367 covers at least the second potential side end portion (minus side end portion) 43, it does not penetrate the heat transfer portion 365 in the thickness direction (is in contact with the middle shaft 50). You don't have to)

E. Fifth embodiment:
FIG. 8 is a schematic cross-sectional view illustrating a schematic configuration of the glow plug 410 according to the fifth embodiment. In the fifth embodiment, parts common to the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted. The glow plug 410 of the fifth embodiment has the same configuration as the glow plug 10 of the first embodiment, except that a heat transfer unit 465 is provided instead of the heat transfer unit 65. In FIG. 8, as in FIG. 2, only the region including the rear end portion of the heater element 40 and the front end portion of the middle shaft 50 is shown in an enlarged manner.

  The heat transfer portion 465 has a recessed portion 468 formed at the tip thereof. Specifically, the concave shape 468 is formed such that the outer periphery of the surface perpendicular to the axis O (hereinafter referred to as a cross section) is formed in a circular shape, and the outer periphery of the cross section is the outer periphery of the cross section of the tip of the middle shaft 50. It is formed to be a concentric circle. The front end portion of the concave shape 468 is in contact with the rear end portion of the heater element 40 in the ring 60. However, the tip of the concave portion 468 that contacts the rear end of the heater element 40 is separated from the second potential side end (minus side end) 43. Such a heat transfer part 65 can be formed of, for example, a metal material having a lower thermal conductivity than the constituent material of the middle shaft 50.

  Even with such a configuration, the same effects as those of the first embodiment can be obtained. Furthermore, the heat transfer portion 465 of the present embodiment has a general insulating property while ensuring the insulating property between the second potential side end portion (minus side end portion) 43 and the central shaft 50 by the concave shape 468. The heat transfer efficiency of the heat transfer section 465 can be increased by using a material (for example, a metal material) having a higher thermal conductivity than the material. Furthermore, according to the present embodiment, since the middle shaft 50 and the heat transfer section 465 can be formed of different metals, heat transfer can be performed while increasing the degree of freedom of selection of the metal constituting the middle shaft 50 and the heat transfer section 465. The effect of improving the heat dissipation efficiency from the heater element 40 by providing the portion can be enhanced.

  The heat transfer portion 465 is in contact with the entire front end portion of the middle shaft 50 exposed in the ring 60 on the rear end side, but may be in contact with only a part of the front end portion of the middle shaft 50. Further, the concave shape 468 is different if the portion of the front end portion of the heat transfer portion 465 that contacts the rear end portion of the heater element 40 is separated from the second potential side end portion (minus side end portion) 43. It is good also as a shape. The heat transfer part 465 is in contact with a part of the rear end part of the heater element 40 while being separated from the second potential side end part (minus side end part) 43 and at least a part of the front end part of the middle shaft 50. The same effect can be obtained by contacting with.

F. Sixth embodiment:
FIG. 9 is a schematic cross-sectional view illustrating a schematic configuration of a glow plug 510 according to the sixth embodiment. In the sixth embodiment, parts common to the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted. The glow plug 510 of the sixth embodiment has the same configuration as that of the glow plug 10 of the first embodiment, except that a middle shaft 550 is provided instead of the middle shaft 50. 9, as in FIG. 2, only the region including the rear end portion of the heater element 40 and the front end portion of the middle shaft 50 is shown in an enlarged manner.

  The intermediate shaft 550 is formed with a bowl-shaped step portion 555 whose outer diameter abruptly increases toward the rear end side on the outer wall in the vicinity of the front end portion. The middle shaft 550 is in contact with the rear end of the ring 60 at the step portion 555. In glow plug 510, welding between middle shaft 550 and ring 60 may be performed at a position where the rear end of ring 60 and stepped portion 555 are in contact (indicated by arrow W2 in FIG. 9). In addition, the structure which provides the level | step-difference part 555 in the center axis | shaft as mentioned above may be similarly applied, for example in 2nd-5th embodiment, when the structure of a heat-transfer part differs.

  Even with such a configuration, the same effect as in the first embodiment can be obtained. In the present embodiment, the center shaft 550 and the ring 60 may be welded at the position of the stepped portion 555, so that the welding operation can be facilitated. Further, in the present embodiment, the distance between the front end portion of the middle shaft 550 and the rear end portion of the heater element 40 is defined by the step portion 555, and therefore, the heat transfer portion 65 is configured by a relatively soft member. Even if it exists, damage to the heat-transfer part 65 at the time of press-fitting the center shaft 550 in the ring 60 can be suppressed.

G. Variations:
Modification 1 (deformation of thermal conductivity relationship):
In the first to sixth embodiments, the thermal conductivity of the constituent material of the heat transfer unit is made smaller than the thermal conductivity of the constituent material of the middle shaft 50, but it may be equivalent thermal conductivity. However, the thermal conductivity may be increased. Even in such a case, the same effect of improving the heat transfer efficiency from the heater element to the central shaft side can be obtained by providing the heat transfer section.

Modification 2 (Modification of the mode of the end of the conductive portion 42):
In each of the embodiments described above, the second potential side end 43 and the first potential side end 44 of the conductive portion 42 are exposed at the rear end of the heater element 40. Good. For example, the conductive portion 42 may be configured such that at least one of the second potential side end portion 43 and the first potential side end portion 44 is not provided and is not exposed at the rear end portion of the conductive portion. At this time, in the case where at least the second potential side end portion (minus side end portion) 43 is not exposed, the second potential side end portion 43 is covered with an insulating member or the second potential side end portion 43 is exposed. There is no need to separate the end 43 on the side and the tip of the central shaft 50. Alternatively, the first potential side end portion (plus side end portion) 44 exposed at the rear end portion of the heater element 40 may be in contact with the middle shaft 50. Regardless of the manner in which the conductive portion 42 is routed in the heater element 40, by providing a heat transfer portion between the rear end portion of the heater element and the front end portion of the central shaft, the same effect as in each embodiment can be obtained. .

-Modification 3 (Modification of assembly method of ring and center shaft):
In each of the above embodiments, after the front end portion of the middle shaft 50 is press-fitted into the rear end portion of the ring 60, the front end portion of the middle shaft 50 and the rear end portion of the ring 60 are welded. For example, welding may not be performed after the front end portion of the middle shaft 50 is press-fitted into the rear end portion of the ring 60. Alternatively, the outer diameter of the front end portion of the intermediate shaft 50 is formed smaller than the inner diameter of the rear end portion of the ring 60, and the front end portion of the intermediate shaft 50 is simply inserted into the ring 60, thereby fitting the inner shaft into the ring 60. Then, both may be welded. Further, the intermediate shaft 50 and the ring 60 may be fixed by caulking from the outside of the ring 60 after inserting the distal end portion of the intermediate shaft 50 into the ring 60.

Modification 4 (deformation of the heater element and the end of the central shaft):
In each of the above embodiments, the rear end of the heater element 40 and the leading edge of the middle shaft 50 are flat surfaces, but different configurations may be used. Some irregularities may be formed in at least one of the opposed portions of the rear end portion of the heater element 40 and the front end portion of the middle shaft 50. Even in such a case, the heat transfer part is provided in contact with at least a part of the rear end part of the heater element 40 and at least a part of the front end part of the middle shaft 50, and thus the same as in each embodiment. An effect can be obtained.

-Modification 5 (Modification of the connection mode between the ring 60 and the center shaft 50)
In each said embodiment, although the front-end | tip part of the center axis | shaft 50 was engage | inserted in the ring 60, it is good also as a different structure. Even if the tip of the middle shaft 50 is not fitted in the ring 60, the tip of the middle shaft 50 and the ring 60 are electrically connected, and the rear end of the heater element 40 and the tip of the middle shaft 50 are connected to each other. If a heat transfer section having a higher thermal conductivity than that of air is disposed, the same effects as those of the embodiments can be obtained.

  FIG. 10 and FIG. 11 are cross-sectional schematic diagrams showing schematic configurations of glow plugs 610 and 710 of modifications, respectively. In FIG. 10 and FIG. 11, the same reference numerals are assigned to portions common to the first embodiment, and detailed description thereof is omitted. The glow plugs 610 and 710 have the same configuration as the glow plug 10 of the first embodiment, except that the middle shafts 650 and 750 are provided instead of the middle shaft 50. 10 and 11, as in FIG. 3, only the region including the rear end portion of the heater element 40 and the front end portion of the central shaft is shown in an enlarged manner.

  The middle shaft 650 provided in the glow plug 610 shown in FIG. 10 is in contact with the rearmost end of the ring 60 on the flat end surface. The tip surface of the middle shaft 650 and the ring 60 can be fixed by, for example, butt welding.

  In the middle shaft 750 provided in the glow plug 710 shown in FIG. 11, a concave shape 755 is formed at the tip. In the glow plug 710, the rear end portion of the ring 60 is fitted in the recess shape 755. The center shaft 750 and the ring 60 may be fixed by, for example, press-fitting the ring 60 into the concave shape 755, or may be performed by welding the leading end of the center shaft 750 and the ring 60, or by a combination thereof. Also good.

Modification 6 (Modification of the connection mode of the connection member 70):
In each of the above embodiments, the connecting member 70 has the second outer cylinder 31 interposed between the heater element 40 and the heater element 40 when connecting the heater element 40 and the housing 20, but may have a different configuration. Another member may be interposed between the connecting member 70 and the housing 20, or the heater element 40 and the housing 20 may be directly connected without any other member.

Modification 7 (Modification of connection mode of the transmission sleeve 32):
In each of the above embodiments, the transmission sleeve 32 interposes the first outer cylinder 30 when connected to the heater element 40, but may be directly connected to the heater element 40. When the transmission sleeve 32 is directly connected to the heater element 40, the transmission sleeve 32 may be connected so as to be in contact with the second potential side connection terminal (minus side connection terminal) 45.

Modification 8 (Modification of heater element configuration):
In each of the above embodiments, the heater element 40 has a configuration in which the conductive portion 42 formed of conductive ceramics is embedded in the insulating portion 41 formed of insulating ceramics, but may have a different configuration. For example, it is good also as a structure provided with the heater heat generating body exposed to the surface of the insulation part which consists of insulating ceramics. Even in such a configuration, by applying the present invention, it is possible to obtain an effect of improving the heat radiation efficiency from the heater element to the central shaft as in the embodiments.

  The present invention is not limited to the above-described embodiments, examples, and modifications, and can be realized with various configurations without departing from the spirit thereof. For example, the technical features in the embodiments, examples, and modifications corresponding to the technical features in each embodiment described in the summary section of the invention are to solve some or all of the above-described problems, or In order to achieve part or all of the above effects, replacement or combination can be performed as appropriate. Further, if the technical feature is not described as essential in the present specification, it can be deleted as appropriate.

10, 110, 210, 310, 410, 510, 610, 710 ... glow plug 20 ... housing 21 ... shaft hole 22 ... metal shell 23 ... screw part 24 ... cap part 25 ... taper part 30 ... first outer cylinder 31 ... first 2 outer cylinder 32 ... transmission sleeve 33 ... diaphragm 34 ... sensor fixing member 35 ... pressure detection element 36 ... flange part 37 ... opening 40 ... heater element 41 ... insulation part 42 ... conductive part 43 ... second potential side end 44 ... first potential side end 45 ... second potential side connection terminal 46 ... first potential side connection terminal 50, 550, 650, 750 ... middle shaft 60 ... ring 65, 165, 265, 365, 465 ... Heat transfer part 70 ... Connecting member 72 ... Protection cylinder 73 ... Terminal fitting 366 ... High heat transfer part 367 ... Electrical insulation part 468 ... Recessed shape 555 ... Stepped part 755 ... Recessed shape

Claims (4)

A rod-shaped heater element extending in the axial direction and having a tip exposed at the combustion chamber;
A central shaft that is formed of a conductive material and is arranged on the rear end side of the heater element to supply power to the heater element;
A housing that constitutes an outer wall of the glow plug and houses a part of the heater element and a part of the middle shaft in its own shaft hole;
A connecting member that connects the heater element and the housing alone or together with another member while allowing the heater element to be displaced in the axial direction within the housing;
A pressure detection element for detecting a combustion pressure in the combustion chamber from a displacement in the axial direction of the heater element with respect to the housing;
Glow plug with
A ring for electrically connecting the heater element and the central shaft;
Heat transfer that is disposed between the rear end of the heater element and the front end of the central shaft in the ring, is in contact with the rear end of the heater element and the front end of the central shaft, and has a higher thermal conductivity than air. And
A glow plug characterized by comprising. The glow plug according to claim 1,
The glow plug characterized in that the heat conductivity of the heat transfer section is smaller than the heat conductivity of the central shaft. A glow plug according to claim 1 or 2,
The heater element includes an insulating portion and a conductive portion that is formed in the insulating portion and generates heat when energized.
The conductive portion is exposed on a side surface of the rear end portion of the heater element, and has a first potential side connection terminal in contact with the inner wall surface of the ring, and a lower potential than the first potential side connection terminal. A second potential side connection terminal, and a second potential side end portion exposed in a region facing the central axis in the rear end portion of the heater element,
The glow plug according to claim 1, wherein an end portion on the second potential side of the conductive portion is electrically insulated from the central shaft by providing the heat transfer portion. The glow plug according to claim 3,
The glow plug according to claim 1, wherein the heat transfer unit includes an electrical insulating unit that covers at least an end of the conductive unit on the second potential side.

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