JP2020060333A - Glow plug - Google Patents

Abstract

To provide a glow plug capable of suppressing fracture around a boundary between a body part and an enlarged diameter part of a housing.SOLUTION: A glow plug comprises a cylindrical housing surrounding a heater and a center shaft. The housing comprises: a body part having a screw part in a rear end part thereof; an enlarged diameter part positioned closer to the rear end than the body part; and a transition part positioned between the enlarged diameter part and the body part and directly connected to both of them. The transition part has a projecting part that projects radially inward so that the inner peripheral surface of the transition part is positioned radially inside the inner peripheral surface of the screw part. A linear distance from the outer peripheral surface to the inner peripheral surface in any position of the transition part is equal to or larger than the radial length of the boundary between the body part and the transition part. An annular seal member made of an insulation material is disposed between the housing and the center shaft closer to the rear end than the projecting part.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a glow plug, and more particularly to a glow plug in which a seal member seals a gap between a center shaft connected to a heater and a housing.

  The glow plug is used as an auxiliary heat source for an internal combustion engine such as a diesel engine of compression ignition type. The housing of the glow plug disclosed in Patent Document 1 includes a screw portion, a tool engaging portion (expanding portion) located on the rear end side of the screw portion, and a rear end connecting the tool engaging portion and the screw portion. And a side trunk portion. This glow plug has a step portion so as to be connected to the rear end side body portion and the tool engaging portion, and a seal is provided between the inner surface of the step portion and the outer peripheral surface of the center shaft connected to the heater. The member is arranged. The glow plug is attached to the internal combustion engine by engaging the tool with the tool engaging portion and tightening the screw portion in the screw hole of the internal combustion engine.

JP, 2013-204947, A

  By the way, in order to prevent the seal member arranged at the step portion from entering between the inner peripheral surface of the rear end side body portion and the outer peripheral surface of the center shaft, the rear end side body portion may have a smaller diameter. However, if the diameter of the rear end side body is made smaller, excessive tightening torque is applied to the tool engagement part, and the vicinity of the boundary between the step part and the rear end side body part where stress concentration is likely to occur due to torsion moment is broken. May occur.

  The present invention has been made to solve this problem, and an object of the present invention is to provide a glow plug that can prevent breakage near the boundary between the main body portion and the expanded diameter portion of the housing.

  In order to achieve this object, the glow plug of the present invention comprises a heater having a heating element, which extends in the axial direction from the front end side to the rear end side, a middle shaft connected to the rear end side of the heater and extending in the axial direction, and a heater. A cylindrical housing that surrounds the heater and the center shaft in a state where the tip end side of the housing protrudes from the tip of itself, the housing has a main body portion having a threaded portion having a screw formed on the outer peripheral surface at the rear end portion of itself. It is located between the enlarged diameter portion and the main body portion, and is directly connected to the enlarged diameter portion, which is located on the rear end side of the main body portion and has an outer peripheral surface whose diameter is larger than the outer peripheral surface of the main body portion. And a transition section. The transitional portion is provided with a convex portion that bulges inward in the radial direction so that the inner peripheral surface of the transitional portion is located radially inward of the inner peripheral surface of the threaded portion. The linear distances to the surfaces are both equal to or longer than the radial length at the boundary between the main body portion and the transition portion, and an annular seal member made of an insulating material is provided between the housing and the center shaft on the rear end side of the convex portion. It is arranged.

  According to the glow plug of claim 1, the transition portion is provided with the convex portion that bulges inward in the radial direction, and the seal member is disposed between the housing and the center shaft on the rear end side of the convex portion. Therefore, the seal member can be prevented from moving toward the tip side of the convex portion. In addition, since the linear distance from the outer peripheral surface to the inner peripheral surface of the transitional portion is equal to or greater than the radial length at the boundary between the main body portion and the transitional portion, the thickness of the transitional portion where the stress concentration due to the torsional moment easily occurs is sufficient. It can be greatly increased. Therefore, breakage of the transition portion can be suppressed.

  In addition, "the linear distance from the outer peripheral surface of the transitional portion to the inner peripheral surface" refers to the linear distance from a predetermined location on the outer peripheral surface of the transitional portion to an arbitrary location on the inner peripheral surface.

  According to the glow plug of the second aspect, the recessed portion that is recessed radially inward is formed on the outer peripheral surface of the transition portion. The convex portion is provided at least over the entire length in the axial direction inside the concave portion. Thereby, the convex portion can be easily formed in the transition portion. On the other hand, since the recess is formed in the transition portion, stress concentration due to the torsional moment easily occurs in the transition portion. However, since the straight line distance from the outer peripheral surface to the inner peripheral surface of the transition portion is set to be not less than the radial length T1 of the boundary, it is possible to sufficiently increase the wall thickness of the transition portion where a torsion moment is likely to occur. Therefore, even if the recess is formed in the transition portion, breakage of the transition portion can be suppressed.

  According to the glow plug of the third aspect, since the convex portion further extends radially inward of the expanded diameter portion, the thickness of the transition portion can be increased by the amount of the convex portion. Therefore, in addition to the effect of claim 1 or 2, breakage of the transition portion can be further suppressed.

  According to the glow plug of claim 4, the bulge on the rear end side of the convex portion gradually decreases toward the rear end of the convex portion, and the front end side of the convex portion gradually decreases toward the front end of the convex portion. The bulge becomes smaller. Therefore, in addition to the effect according to any one of claims 1 to 3, breakage of the housing at the rear end and the front end of the convex portion can be suppressed.

  According to the glow plug of the fifth aspect, since the convex portion is provided at least over the entire inner circumference of the transitional portion, in addition to the effect of any one of the first to fourth aspects, the entire circumference is provided. The breakage of the housing can be suppressed.

It is sectional drawing of the glow plug in 1st Embodiment. It is a fragmentary sectional view of a glow plug. It is a fragmentary sectional view of the glow plug in a 2nd embodiment. It is a fragmentary sectional view of the glow plug in a 3rd embodiment. It is a fragmentary sectional view of the glow plug in a 4th embodiment.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a sectional view including an axis O of the glow plug 10 according to the first embodiment. In FIG. 1, the lower side of the paper is the front end side of the glow plug 10 and the upper side of the paper is the rear end side of the glow plug 10 (the same applies to FIGS. 2 to 5). The glow plug 10 mainly includes a housing 11, a heater 25, a center shaft 32, and a seal member 34.

  As shown in FIG. 1, the housing 11 is a substantially cylindrical metal member (for example, carbon steel, stainless steel, or the like) having a shaft hole formed along the axis O. The housing 11 includes a main body portion 12, a transition portion 13 adjacent to the rear end side of the main body portion 12, and an enlarged diameter portion 14 adjacent to the rear end side of the transition portion 13.

  A screw portion 15 is formed on the rear end portion 12a of the main body portion 12. The screw portion 15 is a portion that engages with a screw hole formed in an internal combustion engine (not shown), and has a screw formed on the outer peripheral surface. The enlarged diameter portion 14 is a tool engagement portion with which a tool such as a wrench engages with the outer peripheral surface. The outer peripheral surface of the enlarged diameter portion 14 is made larger in diameter than the outer peripheral surface of the main body portion 12. The transition portion 13 directly connects the main body portion 12 and the expanded diameter portion 14. Details of the transition unit 13 will be described later.

  An outer cylinder 24 is connected to the tip of the main body 12. The outer cylinder 24 is a substantially cylindrical metal member (for example, stainless steel) that extends in the axial direction, and holds the heater 25. The front end side and the rear end side of the heater 25 project from the front end and the rear end of the outer cylinder 24, respectively.

  The heater 25 includes a base 26, a heating element 27 embedded in the base 26, and a pair of lead portions 28.

The base 26 is made of an insulating ceramic such as Si ₃ N ₄ , AlN, sialon, or Al ₂ O ₃ , and is formed in a substantially columnar shape in this embodiment. The heating element 27 and the lead portion 28 contain one or more selected from W, Ta, Nb, Ti, Mo, Zr, Hf, V, Cr silicides, carbides, borides and nitrides. It is made of a conductive ceramic.

  The heating element 27 is located closer to the tip side than the tip of the outer cylinder 24. The heating element 27 is formed in a U shape, and the pair of lead portions 28 are connected to both ends of the heating element 27, respectively. Since the cross-sectional area of the heating element 27 is smaller than that of the lead portion 28, the resistance value of the heating element 27 can be made larger than that of the lead portion 28. As a result, the heating value of the heating element 27 can be made larger than the heating value of the lead portion 28, so that the heating element 27 can be selectively heated. It should be noted that it is naturally possible to adopt a material having a higher specific resistance than the specific resistance of the lead portion 28 for the heating element 27 to selectively cause the heating element 27 to generate heat.

  Electrode portions 29 and 30 are provided on the rear end sides of the pair of lead portions 28 and extend radially outward. The electrode portions 29 and 30 are portions that function as terminals to which a power supply voltage is applied, and are exposed on the surface of the base 26. The electrode portion 30 is arranged on the rear end side of the electrode portion 29, and is located on the rear end side of the outer cylinder 24. The electrode portion 29 contacts the outer cylinder 24.

  The ring member 31 is a metallic cylindrical member arranged inside the housing 11. The heater 25 is fitted on the tip side of the ring member 31. The ring member 31 contacts the electrode portion 30. The front end portion 32a of the center shaft 32 is fitted to the rear end side of the ring member 31.

  The center shaft 32 is a cylindrical member made of metal (for example, stainless steel) arranged inside the housing 11 along the axis O. The rear end side of the center shaft 32 projects from the rear end of the housing 11. The terminal 33 is attached to a portion of the center shaft 32 protruding from the rear end of the housing 11. An energizing cord (not shown) connected to an external power supply (not shown) is connected to the terminal 33.

  The seal member 34 is an annular member made of an insulating material that seals the gap between the housing 11 and the center shaft 32. The seal member 34 is arranged inside the housing 11 near the transition portion 13 and near the enlarged diameter portion 14. The seal member 34 is made of, for example, an elastic body such as fluororubber or silicone rubber. In the present embodiment, the seal member 34 is an O-ring. The seal member 34 is sandwiched between the housing 11 and the center shaft 32 and compressed.

  The insulating member 35 is a ring-shaped member that secures a gap between the center shaft 32 and the housing 11, and is arranged at the rear end of the housing 11. The insulating member 35 electrically insulates between the housing 11 and the center shaft 32 and between the housing 11 and the terminal 33. In this embodiment, the insulating member 35 is made of synthetic resin such as polyphenylene sulfide, polyphthalamide, nylon.

  FIG. 2 is a partial cross-sectional view including the axis O (see FIG. 1) of the glow plug 10 in which the vicinity of the seal member 34 is enlarged. In the housing 11, the inner diameter of the threaded portion 15 and the inner diameter of the expanded diameter portion 14 of the main body portion 12 are substantially the same size. A convex portion 18 is formed on the transition portion 13 of the housing 11. The convex portion 18 bulges radially inward of the inner peripheral surface 15a of the threaded portion 15 of the main body portion 12. The size of the gap between the portion of the convex portion 18 closest to the center shaft 32 and the center shaft 32 is smaller than the wire diameter of the seal member 34. Therefore, it is possible to prevent the seal member 34 from moving toward the tip side of the convex portion 18.

  The bulge on the tip side of the convex portion 18 gradually decreases toward the tip 19 of the convex portion 18, and the bulge on the rear end side of the convex portion 18 gradually decreases toward the rear end 20 of the convex portion 18. The rear end 20 of the convex portion 18 is located inside the radial expansion portion 14 in the radial direction, and the convex portion 18 extends at least to the radial inside of the radial expansion portion 14. In the present embodiment, the convex portion 18 is continuously provided over the entire circumference of the housing 11.

  The housing 11 has a linear distance from the outer peripheral surface 21 to the inner peripheral surface 22 of the transition portion 13 (regardless of whichever of the outer peripheral surface 21 of the transition portion 13 is selected) the main body portion 12 (screw portion 15) and the transition portion. The length 16 in the radial direction at the boundary 16 with 13 is at least T1.

  For example, as shown in FIG. 2, assuming that one predetermined position on the outer peripheral surface 21 of the transitional portion 13 is the position 17, the radial distance T2 from the position 17 to the inner peripheral surface 22 of the transitional portion 13 is at the boundary 16. The radial length is T1 or more. This relationship is not limited to the distance T2, and all the line segments cut by the outer peripheral surface 21 and the inner peripheral surface 22 of the transitional portion 13 with respect to all the straight lines passing through arbitrary points on the outer peripheral surface 21 of the transitional portion 13. The length (straight line distance) satisfies T1 or more. That is, it means that the inner peripheral surface 22 of the transition portion 13 is not located inside the virtual circle having the radius T1 centered on the point (for example, the position 17) on the outer peripheral surface 21 of the transition portion 13.

  Further, the outer peripheral surface 21 of the transition portion 13 is formed with a concave portion 23 that is recessed inward in the radial direction. In the present embodiment, the recess 23 is provided continuously over the entire circumference of the housing 11. The convex portion 18 is provided at least over the entire length in the axial direction inside the concave portion 23.

  The housing 11 is manufactured, for example, by the following method. First, a load is applied by a press die (not shown) for forming the expanded diameter portion 14 to the end portion of the cylindrical work (not shown) in the axial direction. As a result, the end of the pressed work is compressed in the axial direction, and the expanded diameter portion 14 is formed by forging. Due to this load, the concave portion 23 is formed on the outer peripheral surface of the work, the convex portion 18 is formed on the inner peripheral surface of the work, and the transition portion 13 is formed accordingly. Next, the threaded portion 15 is formed on the work by rolling or cutting.

  The glow plug 10 is attached to the internal combustion engine by tightening a screw portion 15 in a screw hole of the internal combustion engine using a tool (not shown) engaged with the expanded diameter portion 14 of the housing 11. At this time, if excessive tightening torque is applied to the expanded diameter portion 14, the transition portion 13 where stress concentration is likely to occur may be broken.

  In this respect, as in the present embodiment, in the glow plug 10, the linear distance from the outer peripheral surface 21 to the inner peripheral surface 22 of the transition portion 13 is at least the radial length T1 of the boundary 16. As a result, the thickness of the transition portion 13 where stress concentration is likely to occur when the tightening torque is applied can be made sufficiently large. Therefore, breakage of the transition portion 13 of the housing 11 when an excessive tightening torque is applied to the expanded diameter portion 14 can be suppressed.

  In the glow plug 10, the outer peripheral surface 21 of the transition portion 13 is formed with a recess 23 that is recessed radially inward. The convex portion 18 is provided at least over the entire length in the axial direction inside the concave portion 23. Thereby, the convex portion 18 can be easily formed on the transition portion 13. On the other hand, since the recess 23 is formed in the transition portion 13, stress concentration due to the torsional moment is likely to occur in the transition portion 13. However, since the straight line distance from the outer peripheral surface 21 to the inner peripheral surface 22 of the transitional portion 13 is set to be equal to or longer than the radial length T1 of the boundary 16, the wall thickness of the transitional portion 13 where a torsion moment is likely to occur is sufficiently large. it can. Therefore, even if the recess 23 is formed in the transition portion 13, breakage of the transition portion 13 can be suppressed.

  Since the convex portion 18 extends to the radially inner side of the expanded diameter portion 14, the wall thickness of the transition portion 13 can be increased by the amount of the convex portion 18. Therefore, breakage of the transition portion 13 can be further suppressed.

  On the rear end side of the convex portion 18, the bulge gradually decreases toward the rear end 20 of the convex portion 18, and on the front end side of the convex portion 18, the bulge gradually decreases toward the front end 19 of the convex portion 18. Thereby, breakage of the housing 11 at the rear end 20 and the front end 19 of the convex portion 18 can be suppressed. Moreover, since the convex portion 18 is provided at least over the entire inner circumference of the transition portion 13, it is possible to suppress breakage of the housing 11 over the entire circumference.

  A second embodiment will be described with reference to FIG. In the first embodiment, the housing 11 in which the recess 23 is formed in the transition portion 13 has been described. On the other hand, in the second embodiment, the housing 41 including the transition portion 42 in which the recess is not formed will be described. The same parts as those described in the first embodiment are designated by the same reference numerals, and the following description will be omitted. FIG. 3 is a partial cross-sectional view of the glow plug 40 according to the second embodiment. Similar to FIG. 2, FIG. 3 is a partial cross-sectional view including the axis O (see FIG. 1) of the glow plug 40 in which the vicinity of the seal member 51 is shown in an enlarged manner (the same applies to FIGS. 4 and 5).

  In the housing 41, the inner diameter of the threaded portion 15 of the main body 12 is smaller than the inner diameter of the expanded diameter portion 43. The sealing member 51 arranged inside the housing 41 is restricted from moving toward the rear end side by the insulating member 52. The housing 41 includes a main body portion 12, a transition portion 42, and an enlarged diameter portion 43. The housing 41 is manufactured by cutting or the like. The housing 41 has a convex portion 44 formed inside the transition portion 42. The convex portion 44 bulges radially inward of the inner peripheral surface 15 a of the threaded portion 15 of the main body portion 12.

  On the tip end side of the convex portion 44, the bulge gradually decreases toward the tip 45 of the convex portion 44. The rear end 46 of the convex portion 44 is located inside the transition portion 42 in the radial direction. In the present embodiment, the convex portion 44 is continuously provided over the entire circumference of the housing 41. The convex portion 44 can prevent the seal member 51 from moving toward the tip side of the convex portion 44.

  In the housing 41, the linear distance from the outer peripheral surface 47 of the transition portion 42 to the inner peripheral surface 48 is the same as the main body portion 12 (screw portion 15) (regardless of the outer peripheral surface 47 of the transition portion 42 is selected). It is at least the radial length T1 at the boundary 16 with the portion 42. This makes it possible to sufficiently increase the wall thickness of the transition portion 42 in which stress concentration is likely to occur when a tightening torque is applied, and thus it is possible to suppress breakage of the transition portion 42 of the housing 41. Moreover, since the bulge of the tip end side of the convex portion 44 gradually decreases toward the tip end 45 of the convex portion 44, it is possible to suppress breakage of the housing 41 at the tip end 45 of the convex portion 44.

  A third embodiment will be described with reference to FIG. The same parts as those described in the first and second embodiments are designated by the same reference numerals, and the following description will be omitted. FIG. 4 is a partial cross-sectional view of the glow plug 60 according to the third embodiment.

  The housing 61 of the glow plug 60 includes the main body portion 12, the transition portion 62, and the enlarged diameter portion 63. The housing 61 is manufactured by cutting or the like. A convex portion 64 is formed inside the transition portion 62 in the housing 61. The convex portion 64 bulges radially inward of the inner peripheral surface 15a of the threaded portion 15 of the main body portion 12.

  On the rear end side of the convex portion 64, the bulge gradually decreases toward the rear end 66 of the convex portion 64. The rear end 66 of the convex portion 64 is located radially inside the enlarged diameter portion 63. The convex portion 64 can prevent the seal member 51 from moving toward the tip side of the convex portion 64.

  In the housing 61, the linear distance from the outer peripheral surface 67 of the transition portion 62 to the inner peripheral surface 68 is the same as that of the main body portion 12 (screw portion 15) (regardless of where the outer peripheral surface 67 of the transition portion 62 is selected). It is at least the radial length T1 at the boundary 16 with the portion 62. As a result, the thickness of the transition portion 62 where stress concentration is likely to occur when the tightening torque is applied can be made sufficiently large, so that breakage of the transition portion 62 of the housing 61 can be suppressed.

  The outer peripheral surface 67 of the transition portion 62 is formed with a recess 69 that is recessed inward in the radial direction. In the present embodiment, the recess 69 is provided continuously over the entire circumference of the housing 61. The convex portion 64 is provided at least over the entire length in the axial direction inside the concave portion 69. Thereby, the convex portion 64 can be easily formed on the transition portion 62. On the other hand, since the recess 69 is formed in the transition portion 62, stress concentration due to the torsional moment easily occurs in the transition portion 62. However, since the linear distance from the outer peripheral surface 67 to the inner peripheral surface 68 of the transition portion 62 is set to be equal to or greater than the radial length T1 at the boundary 16, the wall thickness of the transition portion 62 where a torsion moment is likely to occur is sufficiently large. it can. Therefore, even if the recess 69 is formed in the transition portion 62, breakage of the transition portion 62 can be suppressed.

  A fourth embodiment will be described with reference to FIG. In the fourth embodiment, a case where a recess 79 smaller than those in the first and third embodiments is formed will be described. The same parts as those described in the first and second embodiments are designated by the same reference numerals, and the following description will be omitted. FIG. 5 is a partial cross-sectional view of the glow plug 70 according to the fourth embodiment.

  The housing 71 of the glow plug 70 includes the main body portion 12, the transition portion 72, and the enlarged diameter portion 73. The housing 71 is manufactured by cutting or the like. A convex portion 74 is formed inside the transition portion 72 in the housing 71. The convex portion 74 bulges radially inward of the inner peripheral surface 15 a of the threaded portion 15 of the main body portion 12.

  The bulge on the tip side of the convex portion 74 gradually decreases toward the tip 75 of the convex portion 74, and the bulge on the rear end side of the convex portion 74 gradually decreases toward the rear end 76 of the convex portion 74. The rear end 76 of the convex portion 74 is located radially inside the enlarged diameter portion 73. The convex portion 74 can prevent the seal member 51 from moving toward the tip side of the convex portion 74.

  In the housing 71, the straight line distance from the outer peripheral surface 77 to the inner peripheral surface 78 of the transition portion 72 is the boundary between the main body portion 12 and the transition portion 72 (regardless of the outer peripheral surface 77 of the transition portion 72 is selected). It is 16 or more in radial direction length T1. This makes it possible to sufficiently increase the thickness of the transition portion 72 where stress concentration is likely to occur when a tightening torque is applied, so that the transition portion 72 of the housing 71 can be prevented from breaking.

  On the outer peripheral surface 77 of the transition portion 72, a concave portion 79 that is recessed radially inward is formed. In the present embodiment, the recess 79 is provided continuously over the entire circumference of the housing 71. Thereby, the convex portion 74 can be easily formed on the transition portion 72. On the other hand, since the recess 79 is formed in the transition portion 72, stress concentration due to the torsional moment is likely to occur in the transition portion 72. However, since the linear distance from the outer peripheral surface 77 to the inner peripheral surface 78 of the transition portion 72 is set to be equal to or longer than the radial length T1 at the boundary 16, the wall thickness of the transition portion 72 where a torsion moment is likely to occur is sufficiently large. it can. Therefore, even if the recessed portion 79 is formed in the transition portion 72, breakage of the transition portion 72 can be suppressed.

  Although the present invention has been described based on the embodiments, the present invention is not limited to the above embodiments, and various improvements and modifications are possible without departing from the spirit of the present invention. It can be easily guessed.

  In the embodiment, the glow plugs 10, 40, 60, 70 including the heater 25 in which the heating body 27 made of a conductive ceramic is embedded in the base body 26 made of an insulating ceramic have been described, but the present invention is not limited to this. . Instead of the heater 25, it is naturally possible to employ a heater in which a heating coil (heating element) is built in a metal tube filled with insulating powder. Further, the outer shape of the heater is not limited to the circular cross section orthogonal to the axis O, and it is naturally possible to make the cross sectional shape elliptical or polygonal.

  In the embodiment, the case where the convex portions 18, 44, 64, 74 are continuous over the entire circumference of the housings 11, 41, 61, 71 has been described, but the present invention is not necessarily limited to this. Of course, it is possible to form the convex portion at one or a plurality of positions on the entire inner circumference of the transition portions 13, 42, 62, 72 of the housings 11, 41, 61, 71. Also in this case, since the protrusions can increase the thickness of the transition portions 13, 42, 62, 72 while restricting the positions of the seal members 34, 51 by the protrusions, breakage can be suppressed.

  In the embodiment, the case where the tips 19, 45, 65, 75 of the convex portions 18, 44, 64, 74 are located on the rear end side of the boundary 16 has been described, but the present invention is not limited to this. It is naturally possible that the tips 19, 45, 65, 75 of the convex portions 18, 44, 64, 74 are located on the tip side of the boundary 16. That is, the convex portions 18, 44, 64, 74 may be provided on the inner peripheral side of the screw portion 15.

  In the embodiment, the case where the O-ring having a circular cross section is used for the seal members 34 and 51 has been described, but the present invention is not limited to this. It is naturally possible to use an elastic body made of an annular insulating material whose cross section is rectangular, V-shaped, U-shaped, etc. as the seal member.

10, 40, 60, 70 Glow plug 11, 41, 61, 71 Housing 12 Main body part 12a Main body rear end part 13, 42, 62, 72 Transition part 14, 43, 63, 73 Expanding part 15 Screw part 15a Inner peripheral surface of screw part 16 Boundary 18,44,64,74 Convex part 19,45,65,75 Convex part tip 20,46,66,76 Convex part rear end 21,47,67,77 Transition part Outer peripheral surface 22, 48, 68, 78 Inner peripheral surface of transition portion 23, 69, 79 Recessed portion 25 Heater 27 Heat generating element 32 Medium shaft 34, 51 Seal member T1 Radial direction at boundary T2 Linear distance O Axis line

Claims (5)

A heater having a heating element extending in the axial direction from the front end side to the rear end side,
A central shaft connected to the rear end side of the heater and extending in the axial direction,
A tubular housing that surrounds the heater and the center rod in a state in which the tip end side of the heater projects from the tip end of itself,
The housing has a main body portion having a threaded portion having a thread formed on an outer peripheral surface thereof at a rear end portion thereof,
A diameter-expanded portion that is located on the rear end side of the main body portion and that has an outer peripheral surface that has a larger diameter than the outer peripheral surface of the main body portion,
A glow plug that is disposed between the enlarged diameter portion and the main body portion and includes a transition portion that is directly connected to both,
The transitional portion is provided with a convex portion that bulges inward in the radial direction such that the inner peripheral surface of the transitional portion is located radially inward of the inner peripheral surface of the threaded portion,
The linear distance from the outer peripheral surface to the inner peripheral surface of the transitional portion is equal to or greater than the radial length at the boundary between the main body portion and the transitional portion,
A glow plug in which an annular seal member made of an insulating material is disposed between the housing and the center shaft on the rear end side of the convex portion. On the outer peripheral surface of the transition portion, a recessed portion that is recessed inward in the radial direction is formed,
The glow plug according to claim 1, wherein the convex portion is provided at least over the entire length in the axial direction inside the concave portion.   The glow plug according to claim 1, wherein the convex portion further extends to the radially inner side of the expanded diameter portion.   The bulge gradually decreases toward the rear end of the convex portion toward the rear end of the convex portion, and the front end side of the convex portion gradually decreases toward the tip of the convex portion. The glow plug according to any one of 1 to 3.   The glow plug according to any one of claims 1 to 4, wherein the convex portion is provided at least over the entire inner circumference of the transition portion.

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