JP6096580B2 - Glow plug and method of manufacturing glow plug - Google Patents

Description

  The present invention relates to a glow plug and a method for manufacturing the 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 are known. For example, a heater element that generates heat when energized, a middle shaft that is formed of a conductive material and has an external terminal attached to a rear end portion thereof, and a ring into which a rear end portion of the heater element and a front end portion of the middle shaft are fitted. There is a known configuration comprising: As the heater element, a conductive portion provided in the heater element and energized includes a first potential side (minus side) connection terminal and a second potential side (plus side) connection terminal, A configuration in which the connection terminal is exposed on the side surface of the heater element is known. When the rear end portion of such a heater element is press-fitted into the ring, the connection terminal on the second potential side and the central shaft are electrically connected via the ring. At the time of assembling such a glow plug, there are cases where the tip of the central shaft is fitted into the ring by press-fitting (see, for example, Patent Document 1).

JP 2012-63078 A

  When the end of the middle shaft is press-fitted into the ring, it is desirable that the press-fitting load during press-fitting does not become excessive. This is because if the press-fitting load is excessive, the press-fitting operation is insufficient and the connection between the center shaft and the ring may be insufficient.

  In order to press-fit the tip of the middle shaft into the ring, it is necessary to make the outer diameter of the tip of the middle shaft larger than the inner diameter of the ring. Thus, as one of the measures for suppressing the press-fitting load, a measure for reducing the difference (press-fitting allowance) between the outer diameter of the tip of the central shaft and the inner diameter of the ring can be considered. However, the press-fit load may vary due to various factors such as the outer diameter variation (tolerance) of the central shaft tip, the inner diameter tolerance of the ring, the outer diameter tolerance of the heater element, the hardness of the ring or the press-fitting conditions. . For this reason, in order to suppress the press-fitting failure due to the press-fitting load being too small, it is necessary to set the press-fitting allowance to a certain extent, and there is a limit to reducing the press-fitting load by reducing the press-fitting allowance.

  As another measure for suppressing the press-fitting load, a measure for shortening the length in the axial direction (hereinafter also referred to as press-fitting length) of the portion overlapping the ring at the tip of the central shaft press-fitted into the ring is conceivable. However, if the press-fitting length is set short, depending on the tolerance of the outer diameter of the center shaft tip, the tolerance of the inner diameter of the ring, etc., the strength of the coupling between the tip of the center shaft and the ring may be insufficient. If the strength of the coupling is insufficient, the middle shaft can be easily removed from the ring, so that it may be difficult to handle components including the middle shaft and the ring during the glow plug manufacturing process. Moreover, if the strength of the bond is insufficient, the central axis may be inclined in the subsequent manufacturing process, which may cause a problem.

  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, a heater element that includes an insulating portion and a conductive portion formed in the insulating portion, generates heat by energizing the conductive portion, and has a shape extending in the axial direction. And a center shaft formed of a conductive material, a rear end portion of the heater element, and a front end portion of the center shaft are press-fitted into the inside, and the side of the rear end portion of the heater element is inserted into the heater element. There is provided a glow plug including a ring that electrically connects a conductive portion and the central shaft. In this glow plug, a concave shape is formed at the front end portion of the middle shaft facing the rear end of the heater element in the ring.
According to the glow plug of this form, by providing the concave shape at the tip portion of the center shaft, the tip portion of the center shaft is easily deformed radially inward when the center shaft is press-fitted into the ring. Therefore, it is possible to reduce the press-fitting load when the central shaft is press-fitted. Since the press-fitting load can be reduced, the press-fitting of the center shaft into the ring can be suppressed, and the connection between the center shaft and the ring can be stabilized. Further, it is possible to increase the press-fitting allowance and strengthen the coupling force between the center shaft and the ring. Moreover, the axial length (press-fit length) of the portion overlapping the ring at the tip of the center shaft press-fitted into the ring can be secured longer, and the coupling force between the ring and the center shaft can be increased. By strengthening the coupling force between the center shaft and the ring, the handling of parts including the center shaft and the ring can be improved, or the center shaft can be prevented from tilting with respect to the ring during the glow plug manufacturing process. Become.

(2) In the glow plug of the above aspect, the recess shape is formed such that an outer periphery of a cross section of the recess shape is concentric with an outer periphery of a cross section of a tip portion of the center shaft, and the recess shape of the center shaft In the cross section of the part where the is formed, the portion including the outer wall of the central shaft may be formed in a ring shape.
According to the glow plug of this form, when the center shaft is press-fitted into the ring, the tip end portion of the center shaft can be particularly easily deformed radially inward, and the effect of reducing the press-fit load can be enhanced.

(3) In the glow plug of the above aspect, the distal end portion of the middle shaft that is press-fitted into the ring may have a solid rear end on the portion where the recess shape is formed.
According to the glow plug of this form, the strength of the coupling between the press-fitted ring and the central shaft can be increased.

(4) In the glow plug of the above aspect, the ring is formed of an alloy containing iron as a main component, and the inner wall of the ring and the side surface of the tip of the middle shaft are in direct contact, and the inner wall of the ring and the middle shaft It is good also as the press-fit length which is the length of the axial direction of the part which overlaps with the side surface of 0.5 mm or more.
According to the glow plug of this form, since it is not necessary to perform a special process on the inner surface of the ring, the manufacturing process can be prevented from becoming complicated even if the press-fitting length is increased.

(5) In the glow plug of the above aspect, the ring may have a Vickers hardness higher than that of the central shaft.
According to the glow plug of this embodiment, the tip end portion of the central shaft can be more easily deformed during press-fitting, and the effect of reducing the press-fitting load can be enhanced.

(6) In the glow plug of the above aspect, the press-fitting length, which is the length in the axial direction of the portion where the inner wall of the ring and the side surface of the middle shaft overlap, is 0.5 mm or more and 2.0 mm or less. In the concave shape, the inner diameter of the cross-section of the concave portion is 0.90 mm or more, and the concave shape has a constant inner diameter of the cross-section of 1.47 mm or more from the leading edge of the central shaft toward the rear end side. Also good.
According to the glow plug of this form, the effect of reducing the press-fit load can be enhanced by providing the concave shape.

(7) In the glow plug of the above aspect, the press-fitting length, which is the length in the axial direction of the portion where the inner wall of the ring and the side surface of the middle shaft overlap, is 0.5 mm or more and 2.0 mm or less. In the concave shape, the inner diameter of the cross-section of the concave portion is 1.17 mm or more, and the concave shape has a constant inner diameter of the cross-section of 1.30 mm or more from the foremost end to the rear end side of the central shaft. Also good.
According to the glow plug of this form, the effect of reducing the press-fit load can be enhanced by providing the concave shape.

(8) In the glow plug of the above aspect, the press-fitting length, which is the length in the axial direction of the portion where the inner wall of the ring and the side surface of the middle shaft overlap, is 0.5 mm or more and 2.0 mm or less. In the concave shape, the inner diameter of the cross section of the concave portion is 1.43 mm or more, and the concave shape has a constant inner diameter of the cross section of 1.92 mm or more from the foremost end to the rear end side of the central shaft. Also good.
According to the glow plug of this form, the effect of reducing the press-fit load can be enhanced by providing the concave shape.

(9) In the glow plug of the above aspect, the press-fitting length, which is the length in the axial direction of the portion where the inner wall of the ring and the side surface of the middle shaft overlap, is 0.5 mm or more and 2.0 mm or less. In the concave shape, the inner diameter of the cross section of the concave portion is 1.70 mm or more, and the concave shape has a constant inner diameter of the cross section of 1.01 mm or more from the foremost end to the rear end side of the central shaft. Also good.
According to the glow plug of this form, the effect of reducing the press-fit load can be enhanced by providing the concave shape.

(10) According to another aspect of the present invention, a heater having a shape that includes an insulating portion and a conductive portion formed in the insulating portion, generates heat when the conductive portion is energized, and extends in the axial direction. A first step of preparing an element; a second step of preparing a central shaft formed of a conductive material; a third step of preparing a ring formed of a conductive material; and a tip of the heater element The heater element is press-fitted into the ring so as to protrude from the tip of the ring, and the conductive portion of the heater element and the ring are electrically connected via the side surface of the rear end portion of the heater element. There is provided a method for manufacturing a glow plug, comprising a fourth step and a fifth step of press-fitting the tip end portion of the central shaft into the rear end portion of the ring. This method for manufacturing a glow plug includes a step of forming a concave shape at the tip of the central shaft in the second step.
According to the method for manufacturing a glow plug of this aspect, by providing the concave shape at the tip of the middle shaft, the tip portion of the middle shaft is easily deformed radially inward when the middle shaft is press-fitted into the ring. Therefore, it is possible to reduce the press-fitting load when the central shaft is press-fitted. As a result, it is possible to suppress the press-fitting of the middle shaft into the ring and to stabilize the coupling between the middle shaft and the ring. Furthermore, by reducing the press-fitting load, it becomes possible to increase the press-fitting allowance, and the axial length (press-fit length) of the portion that overlaps the ring at the tip of the central shaft press-fitted into the ring is reduced. Can be secured longer. As a result, the strength of the coupling between the ring and the center shaft can be increased, so that the handling of parts including the center shaft and the ring can be improved, or the center shaft is inclined with respect to the ring during the glow plug manufacturing process. This can be suppressed.

  The present invention can be realized in various forms other than those described above. For example, the present invention can be realized in a form such as a center shaft for a glow plug or a method for press-fitting a center shaft for a glow plug into a ring.

It is a cross-sectional schematic diagram showing schematic structure of a glow plug. It is explanatory drawing showing the mode of the area | region containing the site | part which the rear-end part of a heater element and the front-end | tip part of a center axis | shaft contact | connect. It is explanatory drawing which shows the positional relationship and magnitude | size of each part which comprise a center axis | shaft and a heater element. It is explanatory drawing which shows the modification of the front-end | tip part of a center axis | shaft. It is process drawing showing the manufacturing method of the glow plug of embodiment. It is a cross-sectional schematic diagram showing schematic structure of the glow plug of 2nd Embodiment. It is explanatory drawing which shows the result of having calculated | required the press-fit load when changing the conditions of a recessed part shape variously. It is a cross-sectional schematic diagram showing schematic structure of the glow plug as a modification.

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. 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 metal shell 20, an outer cylinder 30, a heater element 40, a center shaft 50, and a ring 60 as main components. In this specification, the lower side of the glow plug 10 in the direction of the axis O in FIG. 1 will be referred to as the “front end side” of the glow plug 10 and the upper side will be referred to as the “rear end side”.

  The metal shell 20 is a substantially cylindrical member extending along the axis O, and is formed of carbon steel in this embodiment. A shaft hole 21 that penetrates the metal shell 20 along the axis O is formed inside the metal shell 20. A male screw portion 22 is formed on the outer peripheral surface on the rear end side of the metal shell 20. The glow plug 10 is fixed to the internal combustion engine by the male screw portion 22 being screwed into a female screw formed in a plug mounting hole of a cylinder head (not shown) of the internal combustion engine.

  The outer cylinder 30 is a substantially cylindrical metal member that extends along the axis O. A shaft hole 31 that penetrates the outer cylinder 30 along the axis O is formed inside the outer cylinder 30. The inner diameter of the shaft hole 31 is equal to the outer diameter of the heater element 40 or slightly smaller than the outer diameter of the heater element 40, and the heater element 40 is fitted into the shaft hole 31. The rear end portion of the outer cylinder 30 is fitted into the distal end portion of the shaft hole 21 of the metallic shell 20, and the metallic shell 20 and the outer cylinder 30 are welded at the distal end portion of the metallic shell 20.

  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 fitted in the shaft hole 31 in the outer cylinder 30 at a middle portion thereof. In the heater element 40, a portion on the distal end side with respect to the middle portion projects from the distal end of the outer cylinder 30. A portion on the rear end side with respect to the middle portion is accommodated in the shaft hole 21 of the metal shell 20. The heater element 40 generates heat when electric power is supplied. The diameter of the heater element 40 (the diameter of the rear end portion fitted in the ring 60 described later) can be, for example, 2.5 mm or more, preferably 2.9 mm or more. Further, the diameter of the heater element 40 can be 3.5 mm or less, and preferably 3.3 mm or less.

  The insulating part 41 is made of an insulating ceramic. In the present embodiment, the insulating part 41 is made of silicon nitride. However, the insulating part 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 a conductive ceramic that generates 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 is a first potential side end (minus side end) 43, and the other end is a second potential side end (plus side) that has a higher potential than one end. End) 44. In addition, the conductive portion 42 has a second potential side connection terminal (plus side connection terminal) exposed on the side surface of the heater element 40 in the vicinity of the second 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 first potential side end portion (minus side end portion) 43 and at a position closer to the tip side than the second potential side connection terminal 46. A first potential side connection terminal (minus side connection terminal) 45 exposed at the side surface is formed. The first potential side connection terminal (minus side connection terminal) 45 of the conductive portion 42 comes into contact with the inner wall of the shaft hole 31 by the heater element 40 being fitted into the shaft hole 31 in the outer cylinder 30, and It is electrically connected to the cylinder 30. A connection terminal (plus connection terminal) 46 on the second potential side of the conductive portion 42 contacts the ring 60 as described later. In the present embodiment, the first potential side connection terminal 45 and the second potential side connection terminal 46 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 45 and the second potential side connection terminal 46 may be formed separately from other portions of the conductive portion 42.

  The middle shaft 50 has a shape extending along the axis O and is a rod-like member formed of a conductive material, and is disposed on the rear end side of the heater element 40 in the shaft hole 21 of the metal shell 20. . The hardness (Vickers hardness) of the conductive material constituting the middle shaft 50 is preferably HV 150 to 250, and more preferably HV 200 to 250. The middle shaft 50 can be formed of a conductive material that satisfies such hardness conditions, for example, a ferritic stainless steel such as SUS430, an aluminum alloy such as A6061 and A7075, and a metal material selected from carbon steel such as S45C. . The outer diameter of the middle shaft 50 is formed smaller than the inner diameter of the shaft hole 21 of the metal shell 20, and a gap that electrically insulates both is formed between the middle shaft 50 and the inner wall of the shaft hole 21. . In the present embodiment, the front end portion of the middle shaft 50 is in contact with the rear end portion of the heater element 40, and the structure of the front end portion of the middle shaft 50 is characteristic. The details of the structure of the front end portion of the middle shaft 50 will be described in detail later. To do. In the glow plug 10, a metal terminal fitting 70 is further fixed by caulking at the rear end portion of the middle shaft 50.

  The ring 60 is a cylindrical member made of a conductive material, and is assembled between the middle shaft 50 and the heater element 40 inside the shaft hole 21 of the metal shell 20. Specifically, the rear end portion of the heater element 40 and the front end portion of the middle shaft 50 are press-fitted into the ring 60. When the rear end portion of the heater element 40 is press-fitted into the ring 60, the second potential side connection terminal (positive connection terminal) 46 exposed on the side surface of the heater element 40 contacts the inner wall of the ring 60. As a result, the second 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.

  The hardness (Vickers hardness) of the conductive material constituting the ring 60 is preferably higher than the Vickers hardness of the conductive material constituting the middle shaft 50, and the difference between the two Vickers hardness values is more than 20. preferable. The hardness (Vickers hardness) of the conductive material constituting such a ring 60 is preferably HV270 to 400, and more preferably HV270 to 330. The ring 60 is preferably formed of an alloy (iron-based material) containing iron as a main component, which is a conductive material satisfying such Vickers hardness. Specifically, the ring 60 is formed of a metal material selected from, for example, a material obtained by adjusting the hardness of martensitic stainless steel such as SUS410 by heat treatment, a precipitation hardening stainless steel such as SUS630, and carbon steel that has been subjected to a strong rolling finish. can do.

  In addition, a cylindrical shape is provided at the rear end portion of the metallic shell 20 so as to be interposed between the inner wall of the shaft hole 21 of the metallic shell 20 and the middle shaft 50 and between the rear end of the metallic shell 20 and the terminal fitting 70. An insulating member 72 is disposed. The insulating member 72 positions the middle shaft 50 in the metal shell 20 to form a gap that electrically insulates the middle shaft 50 from the metal shell 20, and between the terminal metal fitting 70 and the metal shell 20. Insulate electrically. The insulating member 72 can be formed of a material having insulating properties and heat resistance according to the use environment, for example, an insulating resin such as nylon (registered trademark) or PPS resin (polyphenylene sulfide resin).

  A cylindrical sealing member 74 is disposed between the inner wall of the shaft hole 21 of the metal shell 20 and the middle shaft 50 on the tip side of the insulating member 72. The sealing member 74 seals the inside of the metal shell 20 by being in close contact with each of the middle shaft 50, the insulating member 72, and the metal shell 20. The sealing member 74 can be formed of a material having insulating properties, elasticity, and heat resistance according to the use environment, for example, an elastic body such as fluorine rubber or silicone rubber.

  In the glow plug 10 configured as described above, when electric power is supplied from the terminal fitting 70, electric power is supplied to the conductive portion 42 through the central shaft 50, the ring 60, and the connection terminal 46 on the second potential side, and the heater element 40 generates heat. At this time, the connection terminal 45 on the first potential side of the conductive portion 42 is grounded through the outer cylinder 30, the metal shell 20, and the cylinder head of the internal combustion engine.

  FIG. 2 is an explanatory diagram showing a state of a region including a portion where the rear end portion of the heater element 40 and the front end portion of the middle shaft 50 are in contact with each other. Specifically, FIG. 2A is a schematic cross-sectional view illustrating an enlarged configuration of a region surrounded by a broken line as the region X in FIG. FIG. 2B is a cross-sectional view illustrating a state of the 2-2 cross section in FIG. In FIG. 2, the description of the metal shell 20 in the region X of FIG. 1 is omitted.

  A concave shape 52 that is recessed toward the rear end side in the direction of the axis O is formed at the tip of the middle shaft 50, leaving a portion in the vicinity of the side surface including the side surface of the middle shaft 50. Specifically, the concave shape 52 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 portion of the middle shaft 50. It is formed to be a concentric circle. By forming such a recessed portion 52, a portion including the outer wall of the middle shaft 50 is formed in a ring shape in the cross section of the tip portion of the middle shaft 50. In the ring 60, the leading end of the front end portion of the middle shaft 50 is in contact with the rear end portion of the heater element 40. In addition, the shape of each part described in this specification, specifically, a shape such as a circle, a concentric circle, and a constant diameter is a shape having distortion or deformation due to tolerance caused by an error in manufacturing a member including each part. Is included.

  FIG. 3 is an explanatory view showing the positional relationship and the size of each part constituting the both by showing the front end part of the middle shaft 50 and the rear end part of the heater element 40 apart from each other. The concave shape 52 is formed so that the diameter of the cross section becomes a constant length over a predetermined range from the front end of the central shaft 50 toward the rear end side. A range when a portion having a constant cross-sectional diameter in the concave shape 52 is projected onto a plane perpendicular to the axis O is shown as a range Y in FIG. Further, a range when the end portion 43 on the first potential side exposed at the rear end portion of the heater element 40 is projected onto a plane perpendicular to the axis O is shown as a range Z in FIG. As shown in FIG. 3, the range Z overlaps the range Y in a state of being separated from the outer periphery of the range Y. That is, the first potential side end 43 of the conductive portion 42 is formed at a position overlapping the region where the concave shape 52 is formed at the tip of the central shaft 50 in the direction of the axis O.

  In FIG. 3, the thickness of the portion of the concave portion 52 in which the diameter of the cross section of the concave portion 52 is constant (the thickness of the portion where the cross section at the tip of the central shaft 50 is formed in a ring shape) is shown as the thickness a. . The thickness a may be a value that the intermediate shaft 50 has sufficient strength for performing the operation of press-fitting the intermediate shaft 50 into the ring 60, and is desirably, for example, 50 μm or more. Further, in FIG. 3, the distance between the inner wall of the front end portion of the middle shaft 50 and the first potential side end portion (minus side end portion) 43 of the conductive portion 42 exposed at the rear end portion of the heater element 40 is b. Show. This distance b is preferably 0.12 mm or more and 0.2 mm or more in order to suppress a short circuit between the first potential side end 43 and the inner wall of the tip of the central shaft 50. More preferably. Further, the above-described distance b is preferably 1 mm or less, and more preferably 0.8 mm or less, in order to suppress an increase in the diameter of the cross section of the glow plug 10.

  Further, in FIG. 3, in the concave shape 52 provided at the front end portion of the middle shaft 50, the axial line O of the portion formed so that the inner diameter of the cross section becomes constant from the foremost end to the rear end side of the middle shaft 50. The length in the parallel direction is shown as the recess depth c. The recess depth c is preferably 0.2 mm or more, and more preferably 0.5 mm or more in order to suppress a short circuit between the first potential side end 43 and the central shaft 50. The recess shape 52 can be formed deeper in the middle shaft 50. For example, the recess shape 52 may be formed just before the position where the terminal fitting 70 is fitted in the middle shaft 50. In other words, the portion of the middle shaft 50 that is housed in the metal shell 20 may have a hollow structure in which the concave shape 52 is formed to extend in the direction of the axis O. In FIG. 3, the inner diameter of the cross section of the concave shape 52 (the inner diameter of the cross section of the concave shape 52 at the foremost end of the central shaft 50) is shown as the concave diameter d, and the tip of the central shaft 50 press-fitted into the ring 60 is shown. The length in the direction of the axis O of the portion that overlaps and contacts the ring 60 is shown as a press-fit length e. In the present embodiment, the press-fitting length e is 0.5 mm or more.

  Furthermore, in the present embodiment, the middle shaft 50 is formed with a bowl-shaped stepped portion 54 whose outer diameter suddenly increases toward the rear end side on the outer wall in the vicinity of the front end portion (see FIGS. 2 and 3). ). The middle shaft 50 is in contact with the rear end of the ring 60 at the step portion 54. As described above, in this embodiment, the press-fit length e is set to 0.5 mm or more, and the stepped portion 54 comes into contact with the rear end of the ring 60 when the set press-fit length e is realized. It is provided in the position.

  FIG. 4 is an explanatory view showing a modification of the tip portion of the middle shaft 50. As in this example, a taper 56 that gradually decreases in diameter toward the distal end side of the middle shaft 50 may be formed on the outer wall including the tip 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. In FIG. 4, the angle of inclination of the taper 56 (the angle formed by the inclined surface of the taper 56 with respect to the outer surface of the central shaft 50) is shown as the taper angle θ. The taper angle θ can be set to, for example, 5 to 20 °. In FIG. 4, the recess depth c and the press-fit length e are also shown. As described above, the press-fit length e is defined as the length in the direction of the axis O of the portion that overlaps and contacts the ring 60 at the tip of the middle shaft 50. Since the taper 56 is not pushed against the inner wall of the ring 60 during press-fitting and hardly contributes to the press-fitting load, the press-fitting length e when the taper 56 is provided is a stepped portion from the rear end of the taper 56 as shown in FIG. The length in the direction of the axis O is 54.

  FIG. 5 is a process diagram showing the method for manufacturing the glow plug 10 according to the first embodiment of the present invention. When the glow plug 10 is manufactured, first, the central shaft 50 in which the concave shape 52 is formed is prepared (step S100). The concave shape 52 may be formed, for example, by cutting the tip of a metal rod-like member that becomes the central shaft 50. Alternatively, the middle shaft 50 having the concave shape 52 may be produced by forging.

  Further, the front end of the heater element 40 is inserted from the rear end side to the front end side of the ring 60, and the heater element 40 is press-fitted into the ring 60 (step S110). As a result, the positive 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, when the heater element 40 is press-fitted into the ring 60, the close contact state between the positive connection terminal 46 and the inner wall of the ring 60 is enhanced, and the conductive portion 42 and the ring 60 are electrically connected. The resistance is sufficiently suppressed.

  Thereafter, the heater element 40 is press-fitted into the outer cylinder 30 from the rear end side of the shaft hole 31, and the front end portion of the heater element 40 is projected from the front end of the outer cylinder 30 (step S120). Thereby, the minus side connection terminal 45 of the conductive part 42 is brought into close contact with the inner wall surface of the shaft hole 31, and the conductive part 42 and the outer cylinder 30 are electrically connected.

  Next, the front end portion of the middle shaft 50 is press-fitted into the rear end side of the ring 60, and both are fixed by welding (step S130). Specifically, the press-fitting is performed so that the press-fitting length e becomes a preset value of 0.5 mm or more. At the time of press-fitting, the distal end portion of the intermediate shaft 50 can be deformed radially inward depending on the strength of the portion where the recessed portion 52 is formed at the distal end portion of the intermediate shaft 50. By performing the press-fitting, as described above, the middle shaft 50 contacts the rear end of the ring 60 at the stepped portion 54, and the front end (front end) of the middle shaft 50 is the rear end portion (rear end surface) of the heater element 40. To touch. The ring 60 and the center shaft 50 may be welded at a position (indicated by an arrow W1 in FIG. 2) where the rear end of the ring 60 and the stepped portion 54 contact each other. However, if the strength of the coupling between the center shaft 50 and the ring 60 is sufficient, the center shaft 50 and the ring 60 may not be welded. In the present embodiment, the heater element 40 is press-fitted into the outer cylinder 30 before the middle 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 steps S120 and S130 is described below. May be reversed. Further, the step of preparing the central shaft 50 in which the concave shape 52 is formed (step S100) may be after step S110 or step S120.

  Next, the middle shaft 50 is inserted into the shaft hole 21 of the metal shell 20, and the front end portion of the metal shell 20 is assembled to the rear end portion of the outer cylinder 30 (step S140). At this time, the space between the outer cylinder 30 and the metal shell 20 is fixed by welding.

  Thereafter, the sealing member 74, the insulating member 72, and the terminal fitting 70 are attached to the rear ends of the metal shell 20 and the middle shaft 50 (step S150), and the glow plug 10 is completed.

  According to the glow plug 10 of the present embodiment configured as described above, by providing the recessed portion 52 at the tip of the middle shaft 50, when the middle shaft 50 is press-fitted into the ring 60, the tip portion of the middle shaft 50 is It becomes easy to deform inward in the radial direction. In particular, in the present embodiment, the outer periphery of the cross-section of the concave shape 52 is concentric with the outer periphery of the cross-section of the tip portion of the middle shaft 50, and the portion including the outer wall of the middle shaft 50 in the cross-section of the tip portion of the middle shaft 50 is It has a ring shape. Therefore, when the middle shaft 50 is press-fitted, the tip of the middle shaft 50 is particularly easily deformed radially inward. Therefore, the press-fit load for press-fitting the middle shaft 50 into the ring 60 to achieve the desired press-fit length e can be reduced. As a result, it is possible to suppress the press-fitting of the middle shaft 50 into the ring 60, for example, the formation of a gap between the stepped portion 54 of the middle shaft 50 and the rear end of the ring 60. Thereby, the coupling | bonding of the center axis | shaft 50 and the ring 60 can be stabilized.

  In the present embodiment, as described above, the press-fitting of the middle shaft 50 into the ring 60 is suppressed, and the middle shaft 50 is press-fitted until the leading end of the middle shaft 50 contacts the rear end of the heater element. Therefore, a sufficiently long press-fit length e can be ensured. Accordingly, the middle shaft 50 is prevented from coming off from the ring 60, and during the subsequent manufacturing process of the glow plug 10 (for example, from the press-fitting of the middle shaft 50 into the ring 60 to the welding of the middle shaft 50 and the ring 60). Further, it is possible to improve the handleability of parts including the middle shaft 50 and the ring 60. Further, since a sufficiently long press-fit length e can be secured and the coupling between the middle shaft 50 and the ring 60 can be strengthened, the middle shaft 50 can be prevented from tilting with respect to the ring 60 during the subsequent manufacturing process of the glow plug 10. . According to the present embodiment, it is possible to realize a press-fit length e longer than the conventional one, for example, a press-fit length e of 0.5 mm or more, by suppressing the press-fit load by facilitating deformation of the tip portion of the middle shaft 50. It becomes possible.

  Further, according to the present embodiment, since the press-fit load can be reduced, when the press-fit is performed, the ring 60 moves relative to the heater element 40 relative to the heater element 40 due to the press-fit load being excessive. Inconvenience can be suppressed. Therefore, the disadvantage that the electrical connection between the conductive portion 42 of the heater element 40 and the ring 60 due to the relative movement of the ring 60 is impaired can be suppressed. Furthermore, in this embodiment, since the press-fitting load is suppressed by facilitating the deformation of the tip of the middle shaft 50, the difference between the outer diameter of the tip of the middle shaft 50 and the inner diameter of the ring 60 (press-fit allowance Δφ) is further increased. The strength of the coupling between the middle shaft 50 and the ring 60 can be increased.

  Further, according to the present embodiment, since the ring 60 has a higher Vickers hardness of the constituent material than the middle shaft 50, the tip portion of the middle shaft can be more easily deformed during press-fitting, and the press-fitting load is reduced. The effect can be enhanced. Even if the ring 60 and the middle shaft 50 have the same Vickers hardness of the constituent material, or the middle shaft 50 has a higher Vickers hardness of the constituent material than the ring 60, the concave portion 52 is formed at the tip of the middle shaft 50. It is possible to obtain the effect of reducing the press-fitting load by providing.

  Furthermore, according to the present embodiment, since the concave portion 52 is provided at the tip of the middle shaft 50 to facilitate deformation, the inner wall surface of the ring 60 is not subjected to special treatment such as plating the inner surface of the ring. Even if the intermediate shaft 50 and the side surface of the middle shaft 50 are in direct contact with each other, the press-fit load can be sufficiently reduced. When the inner wall surface of the ring is subjected to a plating process using, for example, a noble metal such as gold, the inner surface is smoothed to reduce the resistance during press-fitting of the central shaft 50, thereby suppressing the press-fitting load. . In this embodiment, since it is not necessary to perform a special surface treatment for smoothing such as a plating treatment in order to suppress the press-fitting load, the manufacturing process can be prevented from becoming complicated. In general, when the diameter of the cross section of the heater element is about 2.5 to 3.5 mm as in the glow plug 10 of the present embodiment, the press-fitting length e is required without performing a smoothing process such as a plating process. It was extremely difficult to ensure 0.5 mm or more. According to this embodiment, it becomes easy to ensure 0.5 mm or more as press-fit length e, even if it does not perform a plating process. Note that the direct contact between the ring 60 and the middle shaft 50 means that no plating layer or the like is interposed between the ring 60 and the middle shaft 50, but the entire ring 60 does not need to have a uniform composition. This includes the case where a passive layer is formed on the surface of the ring 60 when 60 is made of stainless steel.

  However, the present invention may be applied to a configuration in which the inner surface of the ring 60 is subjected to a plating process such as gold plating, and the concave shape 52 may be provided at the tip of the middle shaft 50. In this case, the press-fit length e can be secured longer. Further, the durability of the contact portion between the second potential side connection terminal (plus side connection terminal) 46 and the surface of the ring 60 can be improved, and the conduction state between the conductive portion 42 and the ring 60 can be stabilized. .

B. Second embodiment:
FIG. 6 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 the middle shaft 150 is provided instead of the middle shaft 50. FIG. 6 shows only the rear end portion of the ring 60 in which the heater element 40 is fitted and the front end portion of the middle shaft 150 among the constituent elements of the glow plug 110, and also shows the rear end portion of the middle shaft 150 and the rear end of the ring 60. The end part is shown apart. In FIG. 6, as in FIGS. 3 and 4, the recess depth c, the recess diameter d, the press-fit length e, and the taper angle θ are shown. Further, in FIG. 6, the ring diameter f that is the inner diameter of the ring 60, the taper length g that is the length of the taper 56 in the direction of the axis O, and the tip end portion of the intermediate shaft 150 that is press-fitted into the ring 60. Also shown is the central shaft diameter h, which is the diameter at the rear end side.

  As shown in FIG. 6, in the second embodiment, the concave shape 52 is not formed in the tip end portion of the central shaft 150 press-fitted into the ring 60, but is formed over the entire direction of the axis O. A solid part is further formed on the rear end side of the part to be formed. In FIG. 6, a region where the solid part is formed is shown as a region V surrounded by a broken line. In addition, in FIG. 6, from the portion (the portion corresponding to the recess depth c) formed so that the inner diameter of the transverse cross section of the recess shape 52 is constant at the distal end portion of the center shaft 150 press-fitted into the ring 60. Also, the length in the direction of the axis O of the rear end side portion is shown as the rear end side length i.

  With such a configuration, in addition to the same effects as those of the first embodiment, it is possible to obtain an effect of further increasing the strength of the coupling between the ring 60 and the center shaft 150 after the press-fitting. That is, in the rear end portion of the middle shaft 150 press-fitted into the ring 60, by providing a solid portion that is hard to be deformed by press-fitting (more rigid) on the rear end side of the portion where the concave shape 52 is provided, The middle shaft 150 is more difficult to be removed from the ring 60, and the strength of the coupling between them can be increased.

C. Effect on pressure load:
FIG. 7 is an explanatory diagram showing the result of obtaining the press-fit load by simulation when various shape parameters of the concave shape in FIG. 6 are changed. Here, the recess depth c, the recess diameter d, and the press-fitting length e (see FIG. 6) were changed, and the peak pressure of the reaction force during press-fitting was determined as the press-fitting load. The taper angle θ was 15 °, the ring diameter f was 3.08 mm, the taper length g was 0.70 mm, and the central shaft diameter h was 3.10 mm (see FIG. 6). That is, the press-fit allowance Δφ (= medium shaft diameter h−ring diameter f) was set to 0.02 mm. The Vickers hardness of the ring was HV300, and the Vickers hardness of the central shaft was HV183. In addition, the said simulation was performed using ANSYS which is FEM (finite element method) analysis software of Ansys Japan.

  FIG. 7A shows the results when the press-fit length e is set to 0.5 mm, FIG. 7B shows the results when the press-fit length e is set to 1.0 mm, and FIG. The results when the press-fit length e is set to 1.5 mm are shown, and FIG. 7D shows the results when the press-fit length e is set to 2.0 mm. The press-fit load obtained by the simulation is a relative value when the press-fit load value (hereinafter referred to as a reference value) is 100 when the press-fit is performed under the same conditions using a central shaft having no concave shape. As shown. In FIG. 7, the result of reducing the press-fit load at a rate of 5% or more and less than 10% with respect to the above-described reference value is attached with a thin hatch, and at a rate of 10% or more with respect to the above-described reference value. The result of the reduced press-fit load is marked with a dark hatch.

  Based on the results shown in FIG. 7, when the press-fit length e is in the range of 0.5 mm to 2.0 mm, the recess diameter d is 0.90 mm or more and the recess depth c is 1.47 mm or more. It can be seen that the press-fit load can be reduced at a rate of 5% or more with respect to the reference value. Further, based on the results shown in FIG. 7, in the range where the press-fitting length e is 0.5 mm or more and 2.0 mm or less, the recess diameter d is 1.17 mm or more and the recess depth c is 1.30 mm or more. It can be seen that the press-fit load can be reduced at a rate of 5% or more with respect to the above-described reference value. Further, based on the results shown in FIG. 7, in the range where the press-fitting length e is 0.5 mm or more and 2.0 mm or less, the recess diameter d is 1.43 mm or more and the recess depth c is 1.92 mm or more. It can be seen that the press-fit load can be reduced at a rate of 10% or more with respect to the above-described reference value. Further, based on the results shown in FIG. 7, in the range where the press-fitting length e is 0.5 mm or more and 2.0 mm or less, the recess diameter d is 1.70 mm or more and the recess depth c is 1.01 mm or more. It can be seen that the press-fit load can be reduced at a rate of 10% or more with respect to the above-described reference value.

  The recess diameter d is a parameter related to the thickness of the tip end portion of the middle shaft in which the recess shape 52 is formed, and is one of the indices of the rigidity and the ease of deformation of the tip end portion of the center shaft. Further, the longer the length of the wall surface constituting the recess shape in the direction of the axis O, the more easily the tip end portion of the center shaft is deformed radially inward during press-fitting. This is one of the indices of the rigidity of the tip and the ease of deformation. The press-fitting load increases as the press-fitting allowance Δφ increases. For example, if the press-fitting allowance Δφ is in the range of 0.01 to 0.05 mm, the shape of the recess is changed even if the value of the press-fitting load varies according to the press-fitting allowance Δφ. It is considered that the degree to which the ease of deformation of the tip end portion of the central shaft changes by providing does not vary greatly. Therefore, the heater element has a cross-sectional diameter in the range of 2.5 to 3.5 mm, which is the diameter of a heater element of a general glow plug, and a thickness that is the thickness of the central shaft in the portion where the concave shape is formed. If a (see FIG. 3) is 50 μm or more and the press-fitting allowance Δφ is in the range of 0.01 to 0.05 mm, the press-fitting load at the same rate as the simulation result depending on the concave diameter d and the concave depth c. It is considered that a reduction effect can be obtained.

  When the press-fitting length e and the taper length g are constant at the front end of the central shaft, the rear end side length i (= press-fitting length e + taper length g−recess depth) increases as the value of the recess depth c increases. C) becomes shorter (see FIG. 6). This rear end side length i reflects the length of the solid portion in the direction of the axis O when the solid portion (region V) described above is provided, and from the tip of the step portion 52. In the case where the concave shape 52 is formed even on the rear end side, the extent to which the concave shape 52 extends beyond the tip of the stepped portion 52 to the rear end side is reflected. From the results shown in FIG. 7, it can be seen that the press-fit load tends to decrease as the value of the recess depth c increases, regardless of whether or not the solid portion is provided at the tip of the intermediate shaft.

D. Variations:
Modification 1 (Modification of the insulation mode of the negative side end):
In each of the embodiments described above, the range Z when the first potential side end portion (minus side end portion) 43 of the conductive portion 42 is projected onto the plane perpendicular to the axis O is the recess shape 52 perpendicular to the axis O. As overlapping with the range Y when projected onto the surface (see FIG. 3), the first potential side end 43 and the middle shaft are insulated. On the other hand, at least a part of the range Z may not overlap with the range Y, but may overlap with the range when the ring-shaped leading edge of the central axis is projected onto a plane perpendicular to the axis O. In this case, for example, the insulation between the first potential side end portion 43 and the center shaft may be ensured by separating the front end portion of the center shaft from the rear end portion of the heater element. Alternatively, an insulator is disposed between at least the exposed portion of the end portion 43 on the first potential side and the middle shaft between the front end portion of the middle shaft and the rear end portion of the heater element, so that the first potential is reached. You may ensure the insulation between the edge part 43 and the center axis | shaft of a side. In any case, by forming the concave shape 52 at the tip of the middle shaft, the same effect as that of each embodiment of reducing the press-fitting load when the tip of the middle shaft is press-fitted into the rear end of the ring 60 is achieved. Can be obtained.

Modification 2 (Modification of the mode of the end of the conductive portion 42):
In the heater element 40 of each of the above embodiments, at the rear end portion, the first potential side end portion 43 and the second potential side end portion 44 of the conductive portion 42 are exposed, and both are separated from the center shaft. However, different configurations may be used. For example, the end portion 44 on the second potential side may be in contact with the center shaft. Alternatively, in the conductive portion, at least one of the first potential side end portion 43 and the second potential side end portion 44 may not be provided, and the conductive portion may not be exposed at the rear end portion. Regardless of the manner in which the conductive portion is routed in the heater element, the same effect as in each embodiment can be obtained by forming the concave shape 52 at the tip of the central shaft.

Modification 3 (deformation of the concave shape 52):
In each of the above embodiments, the recess shape 52 is formed so that the diameter of the cross section has a constant length over a predetermined range from the leading end of the central shaft toward the rear end side, but may have a different configuration. For example, the concave shape may be a shape that gradually decreases in diameter as it becomes deeper (as the rear end side), that is, a conical shape. Moreover, in each said embodiment, although the recessed part shape and convex part shape which were provided in the front-end | tip part of the center axis | shaft were formed so that a cross section may become circular, it is good also as a different structure. Also in this case, by forming a concave shape at the tip of the middle shaft, the tip of the middle shaft is easily deformed, and the same effects as those of the embodiments can be obtained.

Modification 4 (deformation of the shape near the tip of the central shaft):
In each of the above embodiments, the outer wall near the front end of the central shaft is provided with the stepped portion 54 that abruptly increases in outer diameter toward the rear end and contacts the rear end of the ring. Such a stepped portion is provided. It's okay to not. As an example, an example in which a configuration in which the stepped portion 54 is not provided on the central shaft is applied to the first embodiment will be described as a modified example.

  FIG. 8 is a schematic cross-sectional view showing a schematic configuration of a glow plug 210 as a modification of the present invention. In the present modification, the same reference numerals are assigned to portions common to the first embodiment, and detailed description thereof is omitted. The glow plug 210 of this modification has the same configuration as that of the glow plug 10 of the first embodiment, except that a middle shaft 250 is provided instead of the middle shaft 50. In FIG. 8, as in FIG. 2, only the region including the portion where the rear end portion of the heater element 40 and the front end portion of the central shaft 250 are in contact is shown in an enlarged manner. A concave portion 52 similar to that in the first embodiment is formed at the tip of the middle shaft 250. However, the stepped portion 54 is not provided on the outer wall in the vicinity of the front end portion of the middle shaft 250, and the outer diameter of the middle shaft 250 gradually decreases from the position in contact with the rear end of the ring 60 toward the rear end side. ing. In the glow plug 210, when the center shaft 250 and the ring 60 are welded, welding may be performed at a position where the rear end of the ring 60 and the outer surface of the center shaft 250 are in contact (indicated by an arrow W2 in FIG. 8).

  In such a glow plug 210, when the rear end portion of the heater element 40 is first fitted in the ring 60, the inner end of the middle shaft 250 enters the ring 60 until it abuts on the rear end portion of the heater element 40. And the intermediate shaft 250 may be press-fitted. Therefore, the operation of press-fitting the middle shaft 250 into the ring 60 can be easily performed without providing the step portion 54 and without performing special control of the fitting position of the middle shaft 250. In addition, since it is not necessary to form the stepped portion 54 that requires sufficient accuracy corresponding to the press-fit length e of the center shaft, the manufacturing process of the center shaft can be simplified. Further, since the stepped portion 54 does not excessively press the rear end of the ring 60 when the center shaft is press-fitted, it is possible to suppress the inconvenience of the ring 60 moving relative to the heater element 40 toward the front end side.

  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.

DESCRIPTION OF SYMBOLS 10,110,210 ... Glow plug 20 ... Metal fitting 21 ... Shaft hole 22 ... Male screw part 30 ... Outer cylinder 31 ... Shaft hole 40 ... Heater element 41 ... Insulating part 42 ... Conductive part 43 ... End of 1st electric potential side (Minus side end)
44: Second potential side end (plus side end)
45... First potential side connection terminal (minus side connection terminal)
46: Second potential side connection terminal (plus side connection terminal)
50, 150, 250 ... middle shaft 52 ... recessed portion 54 ... stepped portion 56 ... taper 60 ... ring 70 ... terminal fitting 72 ... insulating member 74 ... sealing member

Claims (11)

A heater element having an insulating portion and a conductive portion formed in the insulating portion and generating heat by energizing the conductive portion and extending in the axial direction; and a central shaft formed of a conductive material; A rear end portion of the heater element and a front end portion of the middle shaft are press-fitted into the inside, and the conductive portion of the heater element and the middle shaft are electrically connected via a side surface of the rear end portion of the heater element. In a glow plug comprising a ring,
A glow plug is characterized in that a concave shape is formed at a tip portion of the central shaft facing the rear end portion of the heater element in the ring. The glow plug according to claim 1,
The recess shape is formed such that the outer periphery of the cross section of the recess shape is concentric with the outer periphery of the cross section of the distal end portion of the central shaft,
A glow plug, wherein a portion including an outer wall of the central shaft is formed in a ring shape in a cross section of a portion of the central shaft where the concave shape is formed. A glow plug according to claim 1 or 2,
The glow plug is characterized in that a front end portion of the middle shaft press-fitted into the ring has a solid rear end side where the concave portion is formed. The glow plug according to any one of claims 1 to 3, wherein
The ring is formed of an iron-based alloy.
The inner wall of the ring and the side surface of the tip of the middle shaft are in direct contact;
A glow plug, wherein a press-fitting length, which is an axial length of a portion where an inner wall of the ring and a side surface of the middle shaft overlap, is 0.5 mm or more. The glow plug according to claim 4,
The glow plug characterized in that the ring has a Vickers hardness higher than that of the central shaft. A glow plug according to any one of claims 1 to 5, wherein
The press-fitting length, which is the axial length of the portion where the inner wall of the ring and the side surface of the middle shaft overlap, is 0.5 mm or more and 2.0 mm or less,
The inner diameter of the cross-section of the concave shape at the forefront of the middle shaft is 0.90 mm or more,
The glow plug is characterized in that the concave shape has a constant inner diameter in a cross section over 1.47 mm or more from the foremost end of the central shaft toward the rear end side. A glow plug according to any one of claims 1 to 5, wherein
The press-fitting length, which is the axial length of the portion where the inner wall of the ring and the side surface of the middle shaft overlap, is 0.5 mm or more and 2.0 mm or less,
The inner diameter of the concave cross section at the forefront of the central shaft is 1.17 mm or more,
The glow plug is characterized in that the concave shape has a constant inner diameter in a cross section over 1.30 mm or more from the leading end of the central shaft toward the rear end side. A glow plug according to any one of claims 1 to 5, wherein
The press-fitting length, which is the axial length of the portion where the inner wall of the ring and the side surface of the middle shaft overlap, is 0.5 mm or more and 2.0 mm or less,
The inner diameter of the cross-section of the concave shape at the forefront of the central shaft is 1.43 mm or more,
The glow plug according to claim 1, wherein the concave shape has a constant inner diameter in a cross section over a distance of 1.92 mm or more from the front end of the central shaft toward the rear end side. A glow plug according to any one of claims 1 or 5, wherein
The press-fitting length, which is the axial length of the portion where the inner wall of the ring and the side surface of the middle shaft overlap, is 0.5 mm or more and 2.0 mm or less,
The inner diameter of the concave cross section at the forefront of the central shaft is 1.70 mm or more,
The glow plug according to claim 1, wherein the concave shape has a constant inner diameter of a cross section over 1.01 mm or more from the leading end of the central shaft toward the rear end side. A first step of providing a heater element having a shape that includes an insulating portion and a conductive portion formed in the insulating portion, generates heat by energizing the conductive portion, and extends in an axial direction; and a conductive material A second step of preparing a middle shaft formed by the above, a third step of preparing a ring formed of a conductive material, and the inside of the ring so that the tip of the heater element protrudes from the tip of the ring. A fourth step of press-fitting the heater element and electrically connecting the conductive portion of the heater element and the ring through a side surface of the rear end portion of the heater element; and a rear end portion of the ring A fifth step of press-fitting the tip of the middle shaft, and a method of manufacturing a glow plug comprising:
The method of manufacturing a glow plug, wherein the second step includes a step of forming a concave shape at a tip portion of the central shaft. A method of manufacturing a glow plug according to claim 10,
The third step is a step of preparing the ring formed of an alloy containing iron as a main component,
In the fifth step, the inner wall of the ring and the side surface of the front end portion of the middle shaft are in direct contact, and the press-fitting length, which is the axial length of the portion where the ring and the middle shaft overlap, is 0.5 mm or more. The method for manufacturing a glow plug is characterized by being a step of press-fitting the central shaft into the ring.

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