JP2014119219A - Glow plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a glow plug capable of maintaining a stable connection state between a middle axis whose material is softer than a connection terminal and the connection terminal.SOLUTION: A female thread part 54 of a connection terminal 5 is screwed to a male thread part 33 of a middle axis rear end part 32 of a middle axis 3 whose Vickers hardness is lower than the material of the connection terminal 5, and an outer peripheral surface of a fixing part 52 is caulked inward in radial direction, thus a caulking part 55 is formed. Outside diameters X of portions A-C corresponding to the caulking part 55 are smaller than an outside diameter Y of not-corresponding portions D and E. At the portion A, slopes on both sides of the thread ridge of the male thread part 33 tightly contact the thread ridge of the female thread part 54. At portions B-E, a slope on the side opposite to the portion E of the thread ridge of the male thread part screw part 33 respectively tightly contacts to the thread ridge of the female screw part 54. The connection terminal 5 is surely fixed to the middle axis 3 in the direction of axial line O, and the tightly contacting state between the slopes of the threads extends a long way in conical state, to assure a wide contact area, resulting in stable electrical connection.

Description

  The present invention relates to a glow plug used for assistance in starting a diesel engine.

  A glow plug including a heater having a heating resistor that generates heat when energized is known. The glow plug is made of metal and holds a heater at the tip of a cylindrical metal shell, and one electrode of the heating resistor is electrically connected to the metal shell. In addition, the other electrode of the heating resistor is electrically connected to a metal rod-shaped central shaft that is disposed in an insulated state from the metallic shell in the shaft hole of the metallic shell. The glow plug is used for applications in which the heating resistor generates heat by energization between the metal shell and the central shaft, and assists the start of the diesel engine or heats the fluid.

  In recent years, there has been a demand for smaller and lighter glow plugs, and there is a glow plug in which the material of the central shaft (shaft member) is made of aluminum or an aluminum alloy in order to reduce the weight (for example, see Patent Document 1). In the glow plug of Patent Document 1, a connection terminal (external terminal) is fixed to a rear end portion of a central shaft protruding from a rear end of a metal shell (metal main body). The connection terminal has a mounting hole that opens in the center on the tip side. After inserting the rear end of the center shaft into this mounting hole, the outer peripheral surface corresponding to the mounting hole is crimped to the center shaft. It is fixed. A knurled process is applied to the rear end portion of the center shaft in order to ensure contact friction with the inner peripheral surface of the connection hole of the connection terminal by caulking and to ensure electrical connection with the connection terminal. A stainless steel alloy or the like is usually used for the connection terminal, but the center shaft using an aluminum alloy or the like is softer in material than the connection terminal. For this reason, with caulking, there is almost no deformation of the inner peripheral surface of the connection terminal, but the knurl on the side of the central shaft is crushed and the contact area with the connection terminal is expanded, thereby ensuring electrical connection between the central shaft and the connection terminal. Is done.

JP 2012-63078 A

  However, the knurl of the middle shaft may be further crushed by the vibration of the engine to which the glow plug is attached, and when the axial force with the connection terminal decreases, the contact area with the connection terminal decreases and the contact resistance increases. There was a risk of it. In addition, since the fixed state of both is maintained by contact friction between the inner peripheral surface of the connection terminal and the tip of the knurled shaft, if the contact friction is reduced by vibration of the engine, the fixed state of both may be loosened. .

  The present invention has been made to solve the above-described problems, and an object thereof is to provide a glow plug that can maintain a stable connection state between a middle shaft and a connection terminal whose material is softer than the connection terminal. And

  According to the embodiment of the present invention, a rod-shaped heater having a heating resistor that generates heat when energized at its tip portion and a cylindrical hole having an axial hole extending along the axis are formed, and the heater is directly or indirectly formed at the tip portion. A metal shell that is held in a bar, and a central shaft that is formed in a rod shape and is disposed in the shaft hole of the metal shell with a gap with respect to the inner peripheral surface of the shaft hole, the tip portion being the rear end of the heater An intermediate shaft having a rear end projecting from a rear end of the metal shell and having an external thread formed on at least a part of the outer peripheral surface of the rear end, and at least the rear end of the middle shaft It is a connection terminal that covers a part and bears direct or indirect connection with an external circuit, has a bottomed cylindrical shape with an open end surface, and has an internal thread formed on an inner peripheral surface. A connection terminal formed by screwing the male screw; The connection terminal has a crimped portion in which at least a part of the outer peripheral surface corresponding to the inner peripheral surface on which the female screw is formed is crimped inward, and the Vickers hardness of the middle shaft is determined by the connection terminal The outer diameter of the first portion corresponding to the caulking portion of the rear end portion of the middle shaft is lower than the Vickers hardness of the middle shaft when viewed through the axis and along the axis. A glow plug is provided that has a smaller diameter than the outer diameter of the second portion of the rear end portion that does not correspond to the caulking portion.

  Not only is the male screw of the central shaft and the female screw of the connection terminal screwed together to fix the connection terminal to the central shaft, but the connection terminal is further connected at the site where the male screw of the central shaft and the female screw of the connection terminal are screwed together. Since the caulking part is formed by caulking inward in the radial direction, the male screw of the central shaft and the female screw of the connection terminal are engaged with each other. Can be fixed to.

  In addition, by making the Vickers hardness of the middle shaft lower than the Vickers hardness of the connection terminal, deformation of the middle shaft occurs when the connection terminal is crimped to the rear end of the middle shaft, and the first part has a smaller diameter than the second part. It becomes possible. Then, the deformation of the middle shaft is caused in a portion where the male screw of the middle shaft and the female screw of the connection terminal are screwed together, so that the male screw of the middle shaft and the female screw of the connection terminal are more engaged with each other. And the adhesion of the connection terminal is ensured, and electrical connection can be reliably performed.

  In an embodiment of the present invention, when the cross section is viewed, at least one of the threads of the male screw in the first part has two inclined surfaces facing the axial direction, both of the connection terminals. You may closely contact the thread of the female thread. Since the thread of the male screw of the first part corresponding to the caulking part is in close contact with the thread of the female thread of the caulking part so as to stretch on both sides in the axial direction, the electrical connection between the central shaft and the connection terminal must be made securely. Can do.

  In an embodiment of the present invention, when the cross section is viewed, at least one of the threads of the male screw in the second part is the first part side of two inclined surfaces facing the axial direction. The slope may be in non-contact with the thread of the female screw, and the slope on the side opposite to the first part may be in close contact with the thread of the female screw. The second part is not deformed by caulking, and the thread of the male screw in the second part is in close contact with the thread of the female screw of the connection terminal toward the opposite side of the first part. And the connection terminal can be securely connected.

  In an embodiment of the present invention, the second part may be located on both sides of the first part in the axial direction. On the both sides in the axial direction of the first portion corresponding to the caulking portion of the connection terminal, second portions not corresponding to the caulking portion are respectively positioned. If the formation position of the crimped part is not the extreme end part of the male screw formation range at the rear end part of the middle shaft, the male screw of the middle axis exerts a drag force so as to stretch on both sides in the axial direction around the position corresponding to the crimped part. As a result, the connection terminal can be more securely fixed to the center shaft.

1 is a longitudinal sectional view of a glow plug 1. FIG. It is a perspective view which shows the mode of the crimping part 55 formed in the connection terminal 5 to the center axis | shaft 3 (refer FIG. 1). It is sectional drawing which cut | disconnects along the dashed-two dotted line LL of FIG. 2, and shows the fixed state to the center axis | shaft 3 of the connecting terminal 5 seen from the arrow direction.

  Hereinafter, an embodiment of a glow plug embodying the present invention will be described with reference to the drawings. With reference to FIG. 1, the overall structure of an exemplary glow plug 1 will be described. Note that the drawings to be referred to are used for explaining technical features that can be adopted by the present invention, and the structure of the glow plug described is merely an illustrative example rather than a limitation. In the following description, the axis of the metal shell 4 is defined as the axis O, and the axis O is used as a reference for explaining the positional relationship, orientation, and direction of each component constituting the glow plug 1 assembled to the metal shell 4. To do. In the extending direction of the axis O (hereinafter also referred to as “axis O direction”), the side where the ceramic heater 2 is disposed (the lower side in FIG. 1) is the tip side of the glow plug 1.

  A glow plug 1 shown in FIG. 1 is attached to a combustion chamber (not shown) of a direct injection diesel engine, for example, and is used as a heat source for assisting ignition at the time of engine start. The glow plug 1 includes a metal shell 4, a holding member 8, a ceramic heater 2, a center shaft 3, a connection terminal 5, an insulating member 6, an O-ring 7, and a connection ring 75.

  First, the ceramic heater 2 will be described. The ceramic heater 2 has a round bar shape, and has a base 21 made of an insulating ceramic whose tip (hereinafter referred to as “heater tip”) 22 is hemispherically curved. A heating element 24 having a substantially U-shaped cross section made of conductive ceramic is embedded in the base 21. The heating element 24 includes a heating resistor 27 and lead portions 28 and 29. The heating resistor 27 is disposed at the heater tip 22, and both ends are folded back toward the rear according to the curved surface of the heater tip 22. The lead portions 28 and 29 are respectively connected to both ends of the heating resistor 27 and extend substantially parallel to each other toward the rear end portion (hereinafter referred to as “heater rear end portion”) 23 of the ceramic heater 2. The cross-sectional area of the heating resistor 27 is smaller than the cross-sectional area of the lead portions 28 and 29, and heat is generated mainly in the heating resistor 27 when energized. In addition, on the rear end side from the center of the ceramic heater 2, electrode extraction portions 25 and 26 protrude in the radial direction from the lead portions 28 and 29, respectively. The electrode extraction portions 25 and 26 are provided at positions shifted from each other in the direction of the axis O, and are respectively exposed on the outer peripheral surface of the ceramic heater 2.

  Next, the holding member 8 will be described. The holding member 8 is a cylindrical metal member extending in the direction of the axis O. The holding member 8 holds the body portion of the ceramic heater 2 in the radial direction in the cylindrical hole 84. The heater front end portion 22 and the heater rear end portion 23 are exposed from both ends of the holding member 8. A thick collar portion 82 is formed on the rear end side of the body portion 81 of the holding member 8. At the rear end of the collar portion 82, a stepped metal fitting portion 83 that engages with a tip portion (hereinafter referred to as “metal tip portion”) 41 of a metal shell 4 described later is formed. Of the electrode extraction portions 25 and 26 of the ceramic heater 2, the electrode extraction portion 25 formed on the distal end side is in contact with the inner peripheral surface of the cylindrical hole 84 of the holding member 8, and the electrode extraction portion 25, the holding member 8, Are electrically connected.

  A cylindrical connecting ring 75 made of metal is press-fitted into the heater rear end portion 23 exposed from the metal fitting engaging portion 83 of the holding member 8 to the rear end side. The electrode extraction part 26 of the ceramic heater 2 is in contact with the inner peripheral surface of the connection ring 75, and the electrode extraction part 26 and the connection ring 75 are electrically connected. The electrode leading end portion 41 of the metal shell 4 to be described later is joined to the metal fitting engaging portion 83 of the holding member 8, whereby the electrode extraction portion 25 is electrically connected to the metal shell 4 through the holding member 8. The connection ring 75 connected to the electrode extraction portion 26 is disposed in the metal shell 4, but the holding member 8 positions the ceramic heater 2 and the metal shell 4 in a non-contact state. Therefore, the connection ring 75 and the metal shell 4 are insulated.

  Next, the metal shell 4 will be described. The metal shell 4 is a long and thin cylindrical metal member having a shaft hole 43 penetrating in the direction of the axis O. The metal fitting tip 41 is engaged with the metal fitting engaging portion 83 of the holding member 8 and is electrically connected to the electrode extraction portion 25 of the ceramic heater 2 via the holding member 8. Laser welding is applied to the joint portion of the metal fitting tip 41 and the metal fitting engagement portion 83, and the metal shell 4 and the holding member 8 are joined together. A metal shell portion 44 between the metal front end portion 41 and a rear end portion (hereinafter referred to as “metal rear end portion”) 45 is formed long in the axis O direction. On the outer peripheral surface on the rear end side of the metal shell body portion 44, there is provided an attachment portion 42 in which threads for attaching the glow plug 1 to an engine head (not shown) of the internal combustion engine are formed. The metal fitting rear end portion 45 is formed with a tool engaging portion 46 with which a tool used when the glow plug 1 is attached to the engine head is engaged. The tool engaging portion 46 has a cross-sectional shape with respect to the axis O, for example, a hexagonal shape. Within the tool engaging portion 46, the inner periphery of the shaft hole 43 is larger in diameter than the metal shell body portion 44, and portions having different diameters are connected by a tapered portion 47 that is tapered toward the rear end side. ing.

  Next, the middle shaft 3 will be described. The middle shaft 3 is a rod-shaped metal member extending in the direction of the axis O, and in the present embodiment, the middle shaft 3 is made of, for example, an aluminum alloy. The middle shaft 3 is inserted into the shaft hole 43 of the metal shell 4 and is disposed with a gap with respect to the inner peripheral surface of the shaft hole 43, that is, in a non-contact state. The middle shaft 3 has a distal end portion (hereinafter referred to as “middle shaft distal end portion”) 31 with an enlarged diameter, and a small-diameter ring engaging portion 34 is formed at the distal end to engage with the inner periphery of the connection ring 75. . In a state where the ring engaging portion 34 is engaged with the connection ring 75, laser welding is performed on a joint portion between the central shaft tip portion 31 and the connection ring 75. The middle shaft tip 31 and the connection ring 75 are integrally joined, and the ceramic heater 2 and the middle shaft 3 are integrally coupled along the axis O via the connection ring 75. Thereby, the middle shaft 3 is electrically connected to the electrode extraction portion 26 of the ceramic heater 2 via the connection ring 75. Therefore, the metal shell 4 and the central shaft 3 function as electrodes for applying a voltage to the heating resistor 27 of the ceramic heater 2.

  A rear end portion (hereinafter referred to as “middle shaft rear end portion”) 32 of the middle shaft 3 protrudes from a rear end (in other words, the rear end portion 45 of the metal fitting). The middle shaft rear end portion 32 is formed with a male screw portion 33 having a screw thread for securing an electrical connection by attaching a connection terminal 5 to be described later to the entire outer peripheral surface. A middle shaft body portion 35 between the middle shaft front end portion 31 and the middle shaft rear end portion 32 extends long in the direction of the axis O within the shaft hole 43.

  A portion closer to the middle shaft rear end portion 32 of the middle shaft body portion 35 is located in a portion of the tool engagement portion 46 of the metal shell 4 where the inner circumference of the shaft hole 43 is expanded. In this portion, the O-ring 7 and the insulating member 6 are disposed between the central shaft body portion 35 and the metal fitting rear end portion 45. The O-ring 7 is formed in an annular shape using a material having heat resistance, insulation and elasticity, for example, fluorine rubber, acrylic rubber, silicon rubber or the like. The O-ring 7 is disposed in contact with the tapered surface of the tapered portion 47 of the shaft hole 43 of the metal shell 4, the outer peripheral surface of the middle shaft 3, and the front end surface of the insulating member 6 to be described later, thereby improving the airtightness of the shaft hole 43. keep.

  The insulating member 6 is a cylindrical body formed of a member having heat resistance and insulating properties, such as nylon (registered trademark), for example, in order to prevent a short circuit due to contact between the metal shell 4 and the center shaft 3 and the connection terminal 5 (described later). It is. The insulating member 6 is inserted through the rear end portion 32 of the middle shaft and is disposed in the middle shaft barrel portion 35. The insulating member 6 is positioned by contacting the rear end of the metal shell 4 with a flange portion 61 formed on the rear end side. And the middle shaft 3 are maintained in an insulated state. The male screw portion 33 of the middle shaft rear end portion 32 is disposed further rearward than the insulating member 6.

  The connection terminal 5 is a cap-shaped metal member that is fixed to the middle shaft rear end portion 32 of the middle shaft 3. In this embodiment, the connection terminal 5 is made of, for example, sulfur composite free-cutting steel. The connection terminal 5 includes a flange portion 51, a fixing portion 52, and a protruding portion 53. The fixed portion 52 has a bottomed cylindrical shape with an open front end surface, and a female screw portion 54 having a thread is formed on at least a part of the inner peripheral surface. The female screw portion 54 may be formed over the entire inner peripheral surface of the fixed portion 52. On the side surface on the distal end side of the fixing portion 52, a flange portion 51 that protrudes radially outward is formed over one circumference. A protrusion 53 is formed at the rear end of the fixed portion 52 so as to protrude rearward in a pin shape.

  The connection terminal 5 is formed with a crimped portion 55 in which at least a part of the outer peripheral surface of the fixing portion 52 is crimped inward in a state where the female screw portion 54 is screwed onto the male screw portion 33 while being covered with the rear end portion 32 of the central shaft. By doing so, it is fixed to the middle shaft 3. In the present embodiment, the fixing portion 52 is formed so that the outer diameter of the portion between the flange portion 51 and the rear end portion is narrow. At least an internal thread portion 54 is formed on the inner peripheral surface of the fixing portion 52 corresponding to the small-diameter portion. The caulking portion 55 is formed at the small diameter portion corresponding to the formation portion of the female screw portion 54. Although details will be described later, the screw thread of the male screw part 33 of the central shaft rear end part 32 is deformed by the formation of the caulking part 55, and the adhesiveness is enhanced between the screw thread of the female screw part 54 of the fixing part 52. A reliable electrical connection is made. Further, the fixing force between the female screw portion 54 and the male screw portion 33 is increased, and the connection terminal 5 and the middle shaft 3 are fixed integrally.

  When the fixing portion 52 is attached to the rear end portion 32 of the middle shaft, the flange portion 51 abuts on the rear end of the insulating member 6 and maintains the state in which the insulating member 6 is pressed toward the front end in the axis O direction by screwing. In this state, since the fixing portion 52 is fixed to the rear end portion 32 of the middle shaft, the insulating member 6 is in a state in which the O-ring 7 is pressed toward the front end at the front end surface within the tool engaging portion 46 of the metal shell 4. Positioning is fixed. The O-ring 7 is pressed by the insulating member 6 and contacts the tapered surface of the tapered portion 47 of the shaft hole 43 and the outer peripheral surface of the middle shaft 3 as described above, and ensures the airtightness of the shaft hole 43.

  When the glow plug 1 is attached to the engine head (not shown), the plug cap (not shown) is fitted to the protrusion 53 of the connection terminal 5. The heating element 24 of the ceramic heater 2 includes one end side of a heating resistor 27 grounded to the engine via the holding member 8 and the metal shell 4, and the other end connected to the plug cap via the connection terminal 5 and the center shaft 3. When it is energized between the two sides, it generates heat.

  In the glow plug 1 of the present embodiment having such a configuration, as described above, the center shaft 3 is formed of, for example, an aluminum alloy, whereas the connection terminal 5 is formed of, for example, sulfur composite free-cutting steel. Yes. Generally, the Vickers hardness (HV90-130) of an aluminum alloy is lower than the Vickers hardness (HV200-230) of sulfur composite free-cutting steel. That is, the middle shaft 3 is softer in material than the connection terminal 5. Therefore, in the glow plug 1, the male screw portion 33 of the middle shaft rear end portion 32 of the middle shaft 3 and the female screw portion 54 of the fixing portion 52 of the connection terminal 5 are screwed together, and further, the outer periphery of the fixing portion 52 is crimped. A connection terminal 5 is fixed to the middle shaft 3. Hereinafter, with reference to FIGS. 1-3, the detail of fixation of the fixing | fixed part 52 of the connection terminal 5 to the center axis | shaft rear-end part 32 of the center shaft 3 is demonstrated.

  In the manufacturing process of the glow plug 1 shown in FIG. 1, the male screw portion 33 and the female screw portion 54 are screwed together so that the fixing portion 52 of the connection terminal 5 is put on the middle shaft rear end portion 32 of the middle shaft 3. In the middle shaft rear end portion 32, at least a portion where the male screw portion 33 is formed is arranged over the entire fixing portion 52 in the axis O direction. The flange 51 of the connection terminal 5 abuts on the rear end of the insulating member 6 and maintains the state in which the insulating member 6 is pressed toward the front end in the axis O direction by screwing. The insulating member 6 presses the O-ring 7 toward the tip at the tip surface within the tool engaging portion 46 of the metal shell 4. The O-ring 7 is in contact with the tapered surface of the tapered portion 47 of the shaft hole 43 and the outer peripheral surface of the middle shaft 3.

  As shown in FIG. 2, the connection terminal 5 has an outer peripheral surface corresponding to a portion where the female screw portion 54 (see FIG. 1) is formed at least on the inner peripheral surface of the fixing portion 52 (in this embodiment, the outer periphery has a small diameter). The formed portion) is caulked inward in the radial direction, and the caulking portion 55 is formed. In the present embodiment, the crimping portion 55 is crimped radially inward from four directions that are equally spaced in the circumferential direction of the fixed portion 52. The caulking portion 55 is not limited to four directions, and may be formed by caulking from a plurality of directions such as two directions, three directions, or by so-called round caulking where the entire circumference is caulked. May be. Further, the caulking portion 55 may be formed by caulking over the entire small-diameter portion of the fixing portion 52 in the axis O direction. Further, the caulking portion 55 is not limited to the flat pressing as in the present embodiment, but, for example, presses the outer peripheral surface of the fixing portion 52 using a protruding jig or the like, and a part of the outer peripheral surface is pressed. It may be achieved by partially crimping.

  As shown in FIG. 3, when the cross section of the glow plug 1 passing through the axis O and along the axis O is viewed, the caulking portion 55 deformed inward in the radial direction by caulking in the fixing portion 52 is the center shaft rear end. The part 32 is pressed inward. The internal thread portion 54 formed in the portions A to C (portions surrounded by dotted lines A to C in FIG. 3) corresponding to the crimping portion 55 is softer than the connection terminal 5 with the deformation of the crimping portion 55. It protrudes inward in the radial direction so as to bite into. By the caulking, the outer diameter X of the part A to C corresponding to the caulking part 55 (the outer diameter at the part A is taken as an example in FIG. The diameter is smaller than the outer diameter Y at the portions D and E (the portions surrounded by the dotted lines D and E in FIG. 3) that do not correspond to the portion 55. The thread of the male threaded portion 33 is compressed and deformed so as to spread to both sides in the direction of the axis O around the portion A near the center of the crimped portion 55.

  Specifically, in the part A of the caulking portion 55, the male screw portion 33 of the rear end portion 32 of the middle shaft is plastically deformed by a screw thread compressed radially inward by the female screw portion 54, and both sides in the axis O direction. Spread towards. In the portion A, the rear end facing surface 330 facing the rear end side in the axis O direction of the slope of the thread of the male thread portion 33 is rear end facing surface 330 of the thread of the female thread portion 54 due to plastic deformation of the thread. In close contact with the tip facing surface 540 of the thread. Similarly, the tip-facing surface 331 facing the tip side in the direction of the axis O in the slope of the thread of the male screw portion 33 is similarly behind the screw thread facing the tip-facing surface 331 among the threads of the female screw portion 54 by plastic deformation. Close to the end face 541. That is, the male threaded portion 33 in the part A is in a state in which the rear end facing surface 330 and the front end facing surface 331 of the screw thread generate resistance against the front end facing surface 540 and the rear end facing surface 541 of the female screw portion 54, respectively. Become. Thereby, the movement of the connection terminal 5 to both sides in the axis O direction with respect to the middle shaft 3 is restricted in the part A. In addition, an electrical connection between the male screw portion 33 and the female screw portion 54 is ensured.

  In the portion B located on the rear end side of the portion A in the caulking portion 55, the male screw portion 33 is pressed toward the rear end side in accordance with the plastic deformation of the thread in the portion A. In the portion B, the rear end-facing surface 332 facing the rear end side in the axis O direction of the inclined surface of the thread of the male screw portion 33 by the pressing of the entire male screw portion 33 is the rear end-facing surface of the thread of the female screw portion 54. Close to the tip facing surface 542 of the thread facing 332. As a result, the rear end-facing surface 332 is in a state in which a drag is generated with respect to the front-end facing surface 542. On the other hand, the tip-facing surface 333 facing the tip side in the direction of the axis O in the slope of the thread of the male screw portion 33 is a thread that faces the tip-facing surface 333 among the threads of the female screw portion 54 by pressing the entire male screw portion 33. The rear end facing surface 543 is separated. As a result, a gap is formed between the front end facing surface 333 and the rear end facing surface 543.

  Of the crimped portion 55, the portion C located on the distal end side of the portion A is the same as the portion B, and the male screw portion 33 is pressed toward the distal end side. In the portion C, the tip-facing surface 335 facing the tip side in the axis O direction on the slope of the thread of the male screw portion 33 faces the tip-facing surface 335 of the screw thread of the female screw portion 54 by pressing the entire male screw portion 33. Close contact with the face 545 facing the rear end of the thread. As a result, the front-facing surface 335 is in a state where a drag is generated with respect to the rear-end facing surface 545. On the other hand, the rear end-facing surface 334 facing the rear end side of the slope of the thread of the male thread portion 33 is a thread that faces the rear end facing surface 334 of the thread of the female thread portion 54 by pressing the entire male thread portion 33. Separate from the tip-facing surface 544. As a result, a gap is formed between the rear end facing surface 334 and the front end facing surface 544.

  On the rear end side of the part B, in the part D that does not correspond to the caulking part 55, the central shaft rear end part 32 is not subjected to radial inward compression by caulking. Is pressed toward the rear end side. Therefore, the rear end facing surface 336 facing the opposite side to the portions A to C of the slope of the thread of the male screw portion 33 in the portion D is the tip of the thread facing the rear end facing surface 336 of the threads of the female screw portion 54. It is in close contact with the facing surface 546 and is in a state where a drag is generated. Further, the tip-facing surface 337 facing the portion A to C of the slope of the thread of the male screw portion 33 in the portion D is a rear-end facing surface 547 of the screw thread facing the tip-facing surface 337 among the threads of the female screw portion 54. Separate from.

  Similarly, in the region E that does not correspond to the crimping portion 55 on the distal end side of the region C, the entire male screw portion 33 is pressed toward the distal end side without being compressed inward in the radial direction by crimping. . Therefore, the tip-facing surface 339 facing the side opposite to the portions A to C of the slope of the thread of the male screw portion 33 at the portion E is the rear end direction of the screw thread facing the tip-facing surface 339 among the threads of the female screw portion 54. The surface is brought into close contact with the surface 549, and a drag is generated. Further, the rear end facing surface 338 facing the portion A to C of the slope of the thread of the male screw portion 33 in the portion E is the tip facing surface of the screw thread facing the rear end facing surface 338 of the screw threads of the female screw portion 54. Separate from 548.

  Thus, in the glow plug 1 of the present embodiment, the male screw portion 33 of the middle shaft 3 and the female screw portion 54 of the connection terminal 5 are screwed together to fix the connection terminal 5 to the middle shaft 3. The caulking portion 55 is formed by caulking the connecting terminal 5 radially inward at a portion where the male screw portion 33 of the middle shaft 3 and the female screw portion 54 of the connecting terminal 5 are screwed together. Therefore, the male screw portion 33 of the middle shaft 3 and the female screw portion 54 of the connection terminal 5 are engaged with each other, and as a result, even if the glow plug 1 receives vibrations of the engine, the connection terminal 5 is fixed to the middle shaft 3. be able to.

  In addition, by making the Vickers hardness of the middle shaft 3 lower than the Vickers hardness of the connection terminal 5, when the connection terminal 5 is crimped to the rear end portion 32 of the middle shaft 3, the middle shaft 3 is deformed, and the crimped portion The outer diameter at the parts A to C of the central shaft rear end portion 32 corresponding to 55 can be made smaller than the outer diameter Y of the parts D and E not corresponding to the caulking part 55. Then, the deformation of the middle shaft 3 is caused in a portion where the male screw portion 33 of the middle shaft 3 and the female screw portion 54 of the connection terminal 5 are screwed together, whereby the male screw portion 33 of the middle shaft 3 and the female screw portion 54 of the connection terminal 5. And bite each other. As a result, the adhesiveness between the middle shaft 3 and the connection terminal 5 is ensured, and electrical connection can be reliably performed.

  In addition, among the threads of the male threaded portion 33 of the middle shaft rear end portion 32, at least one of the threads of the parts A to C corresponding to the caulking portion 55 is plastically deformed and stretched on both sides in the axis O direction. In this way, the screw thread of the female thread portion 54 is in close contact. Therefore, the electrical connection between the middle shaft 3 and the connection terminal 5 can be reliably performed. On the other hand, in the portions D and E, the central shaft rear end portion 32 is not deformed by caulking, and the screw thread of the male screw portion 33 faces the opposite side to the portions A to C, and the screw thread of the female screw portion 54. Close state. Therefore, the electrical connection between the middle shaft 3 and the connection terminal 5 can be reliably performed in the portions D and E.

  Further, portions D and E that do not correspond to the caulking portion 55 are respectively positioned on both sides in the direction of the axis O of the portions A to C corresponding to the caulking portion 55. If the formation position of the caulking portion 55 is not the endmost portion of the formation range of the external thread portion 33 at the rear end portion 32 of the intermediate shaft, the external thread portion 33 of the intermediate shaft 3 has the axis O around the position corresponding to the caulking portion 55. Since a drag force is generated so as to stretch on both sides in the direction, the connection terminal 5 can be more securely fixed to the central shaft 3.

  In this embodiment, due to the threaded engagement of the male threaded portion 33 and the female threaded portion 54, the close contact state between the slopes of the screw threads extends in a spiral shape, thereby ensuring a wide contact area between the central shaft 3 and the connection terminal 5. The stability of electrical connection can be obtained. Furthermore, the connection terminal 5 is securely fixed to the middle shaft 3 in the direction of the axis O by the formation of the crimping portion 55. For this reason, for example, even when at least one of the middle shaft 3 and the connection terminal 5 undergoes thermal expansion or contraction, the close state in the direction of the axis O is maintained by any one of the respective screw threads. Become. Therefore, the electrical connection between the middle shaft 3 and the connection terminal 5 can be reliably maintained.

  The present invention can be variously modified. The middle shaft 3 of the present embodiment has the male screw portion 33 formed on the entire rear end portion 32 of the middle shaft, but may be formed on a part of the rear end portion 32 of the middle shaft. For example, in a state where the connection terminal 5 is screwed to the rear end portion 32 of the middle shaft, the male screw portion 33 is formed only in the portions A to C corresponding to the crimping portion 55 to be crimped in the fixing portion 52. Good. Alternatively, the male screw portion 33 may be formed only in the portion A. That is, there is a portion where at least one screw thread of the male thread portion 33 has a rear end facing surface 330 and a front end facing surface 331 that are in close contact with the front end facing surface 540 and the rear end facing surface 541 of the thread of the female screw portion 54, respectively. It may be formed.

  In the present embodiment, sulfur composite free-cutting steel is given as an example of the material of the connection terminal 5, and aluminum alloy having a Vickers altitude lower than that of the sulfur composite free-cutting steel is given as an example of the material of the middle shaft 3. For example, brass or stainless steel may be used as the material of the connection terminal 5, and magnesium alloy, brass or the like may be used as the material of the center shaft 3. However, the Vickers hardness of the material of the middle shaft 3 is used in a combination that is lower than the Vickers hardness of the material of the connection terminal 5.

  In the present embodiment, the ceramic heater 2 corresponds to the “heater” of the present invention. The parts A to C correspond to the “first part” of the present invention, and the parts D and E correspond to the “second part” of the present invention. The rear end facing surface 330 and the front end facing surface 331 correspond to “two inclined surfaces” in claim 2. The front end facing surface 337 and the rear end facing surface 338 correspond to a “slope on the first part side” in claim 3. The front-facing surface 339 and the rear-end facing surface 336 correspond to the “slope on the side opposite to the first portion” in claim 3.

  In order to confirm the effect of fixing the connection terminal 5 to the middle shaft 3 by forming the crimping portion 55 in the fixing portion 52 in addition to the screwing of the male screw portion 33 and the female screw portion 54, an evaluation test Went. In this evaluation test, ten samples of the glow plug 1 of the present embodiment and a knurled process are applied to the central shaft rear end portion of the center shaft made of an aluminum alloy, and the inner peripheral surface is made of a sulfur composite free-cutting steel having no processing. Ten conventional glow plug samples were prepared by fitting the connection terminals and caulking the outer peripheral surface of the fixed portion of the connection terminal radially inward. In both samples, the caulking applied to the connection terminal is 5.0 mm in the opposite side (diameter thickness after caulking) and 2 mm in the caulking width (length of the caulking portion in the axis O direction). As in this embodiment, caulking was performed from four directions radially inward at equal intervals in the circumferential direction. In the sample of the glow plug 1, a male screw portion 33 having a nominal diameter of M4 and a thread pitch of 0.7 mm was formed at the middle shaft rear end portion 32 of the middle shaft 3.

  Each of the prepared samples was assembled in a test engine, and the engine was driven for a predetermined time under the same conditions, then removed from the engine, and the resistance value between the connection terminal and the metal shell was measured several times for each of the ten samples. . The glow plug 1 of this embodiment always had a resistance value of 0.2 mΩ in any sample. On the other hand, the resistance value of the conventional glow plug sample was in the range of 0.5 to 10 mΩ for each sample, and the resistance value varied with each measurement and was not stable. From the results of this test, in the conventional glow plug, the knurl tip on the center shaft side was turned by the vibration of the engine and slipped between the inner peripheral surface of the connection terminals, so that the electrical connection was stable. Decreased. On the other hand, the glow plug 1 of the present embodiment maintains the state in which the thread of the male threaded portion 33 projects in the direction of the axis O with respect to the thread of the female threaded portion 54 by forming the crimping portion 55. It was confirmed that the stability of the electrical connection can be maintained even when subjected to the vibrations.

DESCRIPTION OF SYMBOLS 1 Glow plug 2 Ceramic heater 3 Middle shaft 4 Main metal fitting 5 Connection terminal 22 Heater front-end | tip part 23 Heater rear end part 27 Heating resistor 31 Middle-axis front-end | tip part 32 Middle-shaft rear end part 33 Male screw part 41 Metal fitting front part 43 Clamping portion 330, 336, 338 Rear end facing surface 331, 337, 339 Front end facing surface

Claims (4)

A rod-shaped heater having a heating resistor that generates heat when energized at the tip;
A metal shell that is formed in a cylindrical shape having an axial hole extending along the axis, and that directly or indirectly holds the heater at the tip,
A central shaft formed in a rod shape and disposed in the shaft hole of the metal shell with a gap with respect to the inner peripheral surface of the shaft hole, and its front end is connected to the rear end of the heater, A rear shaft protruding from the rear end of the metal shell, and a middle shaft having a male screw formed on an outer peripheral surface of at least a part of the rear end of the metal shell,
A connecting terminal that covers at least a part of the rear end of the central shaft and is responsible for direct or indirect connection with an external circuit, has a bottomed cylindrical shape with an open front end, and an internal thread formed on the inner peripheral surface A connection terminal formed by screwing the female screw and the male screw of the central shaft;
With
The connection terminal has a crimped portion in which at least a part of the outer peripheral surface corresponding to the inner peripheral surface on which the female screw is formed is crimped inward,
The Vickers hardness of the central shaft is lower than the Vickers hardness of the connection terminal,
When the cross section passing through the axis and along the axis is viewed, the outer diameter of the first portion corresponding to the caulking portion of the rear end portion of the middle shaft is within the rear end portion of the middle shaft. A glow plug having a smaller diameter than the outer diameter of the second portion not corresponding to the caulking portion.   When the cross section is viewed, at least one of the threads of the male screw in the first part has two inclined surfaces facing the axial direction, both closely contacting the screw thread of the female screw of the connection terminal. The glow plug according to claim 1, wherein:   When the cross section is viewed, at least one of the threads of the male screw in the second part is a screw of the female screw, the slope of the first part among the two slopes facing the axial direction. 3. The glow plug according to claim 1, wherein a slope that is not in contact with a mountain and is opposite to the first part side is in close contact with the thread of the female screw.   The glow plug according to claim 3, wherein the second part is located on each side of the first part in the axial direction.

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