JP5960494B2 - Glow plug - Google Patents

Description

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

  A glow plug including a rod-shaped ceramic heater having a heating resistor that generates heat when energized is known. This glow plug is made of metal and holds a ceramic 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 the glow plug having such a structure, when the center shaft is shaken due to vibration caused by engine driving, the vibration is transmitted from the center shaft and the internal stress of the ceramic heater is prevented from increasing. There is one in which an insulating tube is arranged (see, for example, Patent Document 1).

JP 2007-32878 A

  However, in order to insert the tube between the metal shell and the central shaft, it is necessary to secure a clearance. In Patent Literature 1, by designing the tube to be long, adhesion between the tube, the metal shell, and the central shaft is ensured at any part of the tube, and vibration of the central shaft is suppressed. The vibration resistance of the middle shaft is ensured by the portion where the tube, the metal shell, and the middle shaft are in close contact with each other. Therefore, variation in vibration resistance may occur due to variation in individual glow plugs.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide a glow plug that can reliably hold the middle shaft in the shaft hole of the metal shell and can improve vibration resistance.

  According to the first aspect, the heater is formed in a cylindrical shape having a heating resistor that generates heat when energized at the distal end portion and an axial hole extending along the axis, and the heater is held directly or indirectly at the distal end portion. A metal shell and a central shaft formed in a rod shape and disposed in the shaft hole of the metal shell with a gap from the inner peripheral surface of the shaft hole, one end of which is connected to the rear end of the heater The other end portion protrudes from the rear end of the metal shell, and the rear body portion is connected to the other end portion in the body portion between the one end portion and the other end portion; A middle shaft having a front body portion having a smaller outer diameter than that of the rear body portion, and an annular shape, and including at least a boundary portion between the front body portion and the rear body portion. The rear body portion and the shaft are disposed between the rear body portion and the shaft hole in a state. Glow plug and a close member closely to each of the is provided.

  In the glow plug according to the first aspect, the front body portion has a small diameter, and the small diameter portion functions to absorb vibration from the outside. In the present invention, the close contact member is disposed at a position closest to the front body portion in the rear body portion, including the boundary portion with the front body portion, so that even if the vibration due to the vibration of the middle shaft occurs, Since the member is in close contact with the shaft hole and the rear body portion, the rear body portion can be firmly held in the shaft hole. Therefore, the vibration due to the vibration of the central shaft can be reliably suppressed in the vicinity of the boundary portion, and the vibration transmitted to the ceramic heater due to the vibration of the central shaft is effectively suppressed in combination with the effect of providing the small diameter portion. Can do.

In a first aspect, the intimate member may be made of press-fit between the front Symbol rear body portion and the shaft hole. By press-fitting the intimate member, it is sufficient to perform processing on the outer peripheral surface of the rear trunk portion and the inner peripheral surface of the shaft hole, which is the arrangement position of the intimate member, or without using other members such as an adhesive, The close contact member can be disposed in close contact with the rear body portion and the shaft hole, so that the manufacturing effort is not required. The close contact member is in close contact with the rear body portion and the shaft hole, so that the close contact member is not displaced due to the vibration of the center shaft, and the center shaft is securely held, and vibration suppression due to vibration is maintained for a long time. can do.

1 is a longitudinal sectional view of a glow plug 1. FIG. It is a perspective view which shows the process of press-fitting the close_contact | adherence member. 1 is a longitudinal sectional view of a glow plug 101. FIG.

  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. The drawings to be referred to are used for explaining the technical features that can be adopted by the present invention, and the structure of the glow plugs described is not intended to be limited only to them, but merely illustrative examples. is there. 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, a connection ring 75, and a close contact member 9.

  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 in a substantially U shape 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 formed to be 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 exposed on the outer peripheral surface of the ceramic heater 2 at positions shifted from each other in the axis O direction.

  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 part 26 is disposed in the metal shell 4, but the ceramic heater 2 and the metal shell 4 are positioned by the holding member 8 and are kept in non-contact. 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 hexagonal cross section, for example. 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 is inserted into the shaft hole 43 of the metal shell 4. The middle shaft 3 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 small-diameter ring engaging portion 34 for engaging with the inner periphery of the connection ring 75 at a distal end portion (hereinafter referred to as “middle shaft distal end portion”) 31. 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. Thus, the middle shaft 3 is electrically connected to the electrode extraction portion 26 of the ceramic heater 2 via the connection ring 75. 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. The middle shaft tip 31 corresponds to the “one end” of the middle shaft 3 connected to the rear end (heater rear end 23) of the heater (ceramic heater 2).

  The rear end portion of the middle shaft 3 is inserted in the rear side of the shaft hole 43 of the metal shell 4, and the middle shaft rear end portion 32 of the middle shaft 3 extends from the rear end of the metal shell 4 (in other words, the metal rear end portion 45). It protrudes. On the outer peripheral surface of the middle shaft rear end portion 32, a connection end portion 33 having a knurled surface treatment is provided. 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. The middle shaft rear end portion 32 corresponds to the “other end portion” of the middle shaft 3.

  A front side body portion 36 having a reduced outer diameter is formed on the distal end side of the middle shaft body portion 35. The front body portion 36 is connected to the center shaft tip portion 31, and the connecting portion is formed in a tapered shape. A portion of the middle shaft barrel portion 35 on the rear end side from the front barrel portion 36 is referred to as a rear barrel portion 37 for convenience. The rear trunk portion 37 is connected to the central shaft rear end portion 32. The rear trunk portion 37 has an outer diameter that is substantially constant and is formed to have an outer diameter that is substantially the same as the outer diameter of the middle shaft rear end portion 32. The front body portion 36 is also formed in a tapered shape at the connection portion with the rear body portion 37. The middle shaft 3 has a smaller diameter of the deflection of the middle shaft 3 generated by vibrations transmitted from the outside due to vibrations of the engine or the like by forming the outer diameter of the front barrel 36 smaller than that of the rear barrel 37. The front body portion 36 absorbs the vibration from being propagated to the ceramic heater 2.

  An O-ring 7 and an insulating member 6 are disposed between the rear end portion of the middle shaft 3 and the metal fitting rear end 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 into the rear end portion 32 of the middle shaft, and is positioned by a flange portion 61 formed on the rear end side coming into contact with the rear end of the metal shell 4, so that the metal shell 4 and the middle shaft 3 are maintained in an insulated state. To do. The connection end 33 of the middle shaft 3 protrudes further rearward than the insulating member 6.

  The connection terminal 5 is fixed to the middle shaft rear end portion 32 (specifically, the connection end portion 33). The connection terminal 5 includes a flange portion 51, a fixing portion 52, and a protruding portion 53. The fixing portion 52 has a cap shape that covers the connection end portion 33. The protruding portion 53 protrudes in a pin shape from the fixed portion 52 toward the rear end side. The flange portion 51 protrudes outward in the radial direction over the entire circumference at the opening end of the distal end of the fixed portion 52. When the connection terminal 5 is put on the connection end portion 33 of the middle shaft 3, the flange portion 51 comes into contact with the rear end of the insulating member 6. The fixing portion 52 is fixed to the connection end portion 33 by caulking the outer periphery of the fixing portion 52 inward in a state where the connection terminal 5 is pressed toward the tip end in the axis O direction. Since the connection end portion 33 has a knurled shape, the fixing force with the fixing portion 52 is increased, and the connection terminal 5 and the middle shaft 3 are fixed integrally, and both are electrically connected.

  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.

  Next, the close contact member 9 will be described. The close contact member 9 is a member made of a resin having heat resistance and insulation and formed in a cylindrical shape. The thickness of the close contact member 9 is formed larger than the size of the gap between the inner peripheral surface of the shaft hole 43 of the metal shell 4 and the outer peripheral surface of the rear barrel portion 37 of the middle shaft 3. Specifically, the inner diameter of the close contact member 9 is formed to be approximately the same as the outer diameter of the rear barrel portion 37 of the middle shaft 3, and the outer diameter of the close contact member 9 faces the rear barrel portion 37 of the shaft hole 43. It is formed larger than the inner diameter. The close contact member 9 is inserted into the shaft hole 43 by press-fitting from the rear end side of the metal shell 4 and is disposed between the inner peripheral surface of the shaft hole 43 and the outer peripheral surface of the rear trunk portion 37 of the middle shaft 3. As described above, the close contact member 9 disposed in the shaft hole 43 by press-fitting has a large resistance against each of the inner peripheral surface of the shaft hole 43 and the outer peripheral surface of the middle shaft 3, and is in close contact with each other. Can be reliably suppressed in the radial direction.

  The close contact member 9 includes at least a boundary portion (a portion indicated by a two-dot chain line A in FIG. 1) between the front barrel portion 36 and the rear barrel portion 37 of the middle shaft 3 (in other words, the inner periphery of the close contact member 9). In a state where the surface overlaps the boundary part), the shaft hole 43 and the rear body part 37 are disposed. In other words, the close contact member 9 disposed so as to surround the rear body portion 37 has a tip position in the axis O direction (a position indicated by a two-dot chain line B in FIG. 1) at the same position as the boundary portion A or the boundary portion A. It is located on the tip side.

  Further, the ceramic heater 2 is connected to the front end side of the middle shaft 3 via a connection ring 75. If the arrangement position of the close contact member 9 is positioned on the rear trunk portion 37 including the boundary portion A and the middle shaft 3 is firmly held at that position, the swing of the intermediate shaft 3 on the rear end side of the close contact member 9 is The influence on the opposite side across 9, that is, the stress generated in the ceramic heater 2 can be reduced. In other words, the close contact member 9 is positioned and arranged on the rear trunk portion 37 including the boundary portion A, and the middle shaft 3 is firmly held, so that the shake in the rear trunk portion 37 of the middle shaft 3 affects the ceramic heater 2. Can be reduced. Therefore, in the design of the glow plug 1, even if the length of the rear barrel 37 of the middle shaft 3 is changed, it is not necessary to consider the influence on the ceramic heater 2. Can be done freely.

  In the glow plug 1 having such a structure, a step of press-fitting the close contact member 9 into the gap between the shaft hole 43 of the metal shell 4 and the middle shaft 3 inserted into the shaft hole 43 is performed in the manufacturing process. Hereinafter, a schematic manufacturing process of the glow plug 1 will be described focusing on the press-fitting process of the close contact member 9.

  The ceramic heater 2 is manufactured through the following manufacturing process. Injection molding is performed using a conductive ceramic powder, a binder, or the like as a raw material, and an element molded body that is the original shape of the heating element 24 is formed. Mold pressing is performed using insulating ceramic powder as a raw material, and a base compact that is the original form of the base 21 is formed as a two-part compact. Press compression is performed in a state where the element molded body is held between the base molded body. After passing through a baking process such as binder removal processing and hot pressing, the outer peripheral surface is polished to form a rod-shaped ceramic heater 2 having a hemispherical tip. The manufacturing process of the ceramic heater 2 can be changed as appropriate. For example, as a manufacturing method of a base molded body, one molded body is previously molded and placed in a mold, an element molded body is placed thereon, and further, an insulating ceramic powder is filled and press-compressed. Etc. can be applied.

  The ceramic heater 2 is press-fitted and fitted into a connection ring 75 formed of a steel material such as stainless steel in a pipe shape. The electrode extraction portion 26 of the ceramic heater 2 is electrically connected to the connection ring 75. Similarly, the ceramic heater 2 is press-fitted and fitted into the holding member 8 formed into a predetermined shape. The electrode extraction part 25 of the ceramic heater 2 is electrically connected to the holding member 8. The middle shaft 3 is formed by subjecting a rod-shaped member made of an iron-based material (for example, Fe—Cr—Mo steel) cut to a certain size to plastic working or cutting. The front body portion 36 is formed by cutting the center shaft body portion 35. The ring engaging portion 34 of the middle shaft 3 is engaged with a connection ring 75 fitted to the ceramic heater 2. The joint portion between the ring engaging portion 34 and the connection ring 75 is laser welded, and the middle shaft 3 and the ceramic heater 2 are joined together.

  A cylindrical metal shell 4 is formed from an iron-based material such as S45C, and a thread is rolled on the mounting portion 42. Cutting or the like is performed to enlarge the diameter of the shaft hole 43 in the metal rear end portion 45 to form a tapered portion 47. The central shaft 3 integrated with the ceramic heater 2 or the like is inserted into the shaft hole 43 of the metal shell 4, and the inner periphery of the metal tip 41 is engaged with the metal fitting portion 83 of the holding member 8. The joint portion of the metal shell 4 and the holding member 8 is laser-welded, and both are joined together.

  Next, the close contact member 9 is press-fitted. The close contact member 9 is formed into a cylindrical shape by injection molding using a resin or the like as a material. As described above, the inner diameter of the close contact member 9 is formed to be approximately the same as the outer diameter of the rear barrel portion 37 of the middle shaft 3, and the outer diameter of the close contact member 9 faces the rear barrel portion 37 of the shaft hole 43. It is formed larger than the inner diameter. As shown in FIG. 2, the close contact member 9 is fitted to the middle shaft rear end portion 32 and moved to the front end side in the axis O direction. The outer diameter of the middle shaft rear end portion 32 is substantially the same as the outer diameter of the rear barrel portion 37, and the close contact member 9 can move to the tip side without receiving a large resistance.

  When the inner diameter of the shaft hole 43 is reduced through the tapered portion 47, the close contact member 9 receives insertion resistance, and therefore the close contact member 9 is press-fitted using the press-fitting jig 90. The press-fitting jig 90 includes a cylindrical pressing portion 91 that extends in the direction of the axis O, and a stopper 92 that is connected to the rear end of the pressing portion 91 and can contact the rear end surface of the metal shell 4. The pressing portion 91 has an inner diameter larger than the outer diameter of the rear body portion 37 of the middle shaft 3 and an outer diameter smaller than the inner diameter of the shaft hole 43. The length D of the pressing portion 91 is determined from the length between the boundary portion A of the middle shaft 3 and the position C (see FIG. 1) of the rear end surface of the metal shell 4 in the axis O direction. It is set to the length of the length excluding the length of or slightly longer than that.

  In the press-fitting process, the close contact member 9 is pressed from the rear end side by the press-fit jig 90, and the close contact member 9 is pressed between the shaft hole 43 and the rear trunk portion 37. When the stopper 92 comes into contact with the rear end surface of the metal shell 4, the close contact member 9 is positioned at the front end side of the boundary portion A or at the front end side of the boundary portion A. Since the press-fitting jig 90 does not move further to the front end side, the close contact member 9 includes at least the boundary portion A, and the outer peripheral surface of the rear barrel portion 37 of the middle shaft 3 and the shaft hole 43 of the metal shell 4 are formed. It arrange | positions between inner peripheral surfaces. The close contact member 9 is sandwiched between the outer peripheral surface of the rear body portion 37 and the inner peripheral surface of the shaft hole 43 and is in close contact with each other. In other words, the close contact member 9 firmly holds the rear body portion 37 of the middle shaft 3 in the shaft hole 43. The close contact member 9 generates a sufficient resistance against the shake of the middle shaft 3 due to vibration from the outside to suppress the shake of the middle shaft 3, and the outer peripheral surface of the rear body portion 37 and the inner peripheral surface of the shaft hole 43 The close state of can be maintained.

  The press-fitting jig 90 is extracted, and the O-ring 7 is inserted into the shaft hole 43 as shown in FIG. Next, the insulating member 6 is fitted into the middle shaft 3. Further, the connection terminal 5 is fitted into the rear end portion 32 of the middle shaft, and the insulating member 6 is pressed toward the tip side. The insulating member 6 presses the O-ring 7 toward the tip side at the tip surface, and is sandwiched between the taper portion 47 of the metal shell 4. The O-ring 7 is deformed and abuts against the distal end surface of the insulating member 6, the tapered surface of the tapered portion 47 of the metal shell 4, and the outer peripheral surface of the middle shaft 3 to ensure the airtightness of the shaft hole 43. In this state, the fixing portion 52 of the connection terminal 5 is caulked inward in the radial direction, and the connection terminal 5 is fixed to the connection end portion 33 of the middle shaft 3 to complete the glow plug 1.

  As described above, in the glow plug 1 according to the present invention, the front barrel portion 36 of the middle shaft 3 has a smaller diameter than the rear barrel portion 37, and the portion functions to absorb external vibration. If the close contact member 9 is disposed at a position closest to the front body portion 36 on the outer peripheral surface of the rear body portion 37 so as to include the boundary portion A between the front body portion 36 and the rear body portion 37, Even if the vibration due to vibration occurs, the close contact member 9 is in close contact with the shaft hole 43 and the rear body part 37, so that the rear body part 37 can be firmly held in the shaft hole 43. Therefore, the vibration due to the vibration of the middle shaft 3 can be surely suppressed in the vicinity of the boundary portion A, and combined with the effect of providing the small-diameter front body portion 36, the ceramic heater 2 is caused by the vibration of the middle shaft 3. The vibration transmitted to can be effectively suppressed.

  In addition, since the arrangement position of the close contact member 9 is positioned in the rear trunk portion 37 including the boundary portion A, the deflection of the center shaft 3 on the rear end side from the close contact member 9 does not affect the ceramic heater 2. Therefore, in the design of the glow plug 1, the length of the rear trunk portion 37 of the middle shaft 3 can be freely changed, and the design change for the increase in the length of the glow plug 1 can be freely performed. Furthermore, since the close contact member 9 only needs to be able to hold the middle shaft 3 in the rear body portion 37 including the boundary portion A, there is no need to form it long in the direction of the axis O like a silicon tube used in a conventional glow plug, Manufacturing costs can be reduced.

  Further, by pressing the close contact member 9 between the metal shell 4 and the middle shaft 3, the outer peripheral surface of the rear body portion 37 and the inner peripheral surface of the shaft hole 43, which are the positions where the close contact member 9 is disposed, are processed, Even if other members such as an adhesive are not used, the close contact member 9 can be disposed in close contact with the rear body portion 37 and the shaft hole 43, and the manufacturing effort is not required. The close contact member 9 is in close contact with the rear body portion 37 and the shaft hole 43, so that the close contact member 9 is not displaced due to the vibration of the intermediate shaft 3, and the intermediate shaft 3 is securely held, and the vibration due to vibration Can be maintained over a long period of time.

  The present invention can be variously modified. The outer peripheral edge of the close contact member 9 may be chamfered so that it can be easily press-fitted at the time of press-fitting. When the close contact member 9 is disposed between the inner peripheral surface of the shaft hole 43 of the metal shell 4 and the outer peripheral surface of the rear barrel portion 37 of the intermediate shaft 3, the tip position B of the close contact member 9 is the boundary portion of the intermediate shaft 3. You may arrange | position so that it may correspond with A (refer FIG. 1). The arrangement position of the close contact member 9 in the shaft hole 43 is determined by the length D of the pressing portion 91 of the press-fitting jig 90. For example, a slightly protruding hook-like or protruding stopper is provided on the outer periphery of the middle shaft 3. The press-fitting position of the close contact member 9 may be positioned. Alternatively, the outer diameter of the center shaft of the press-fitting position is slightly increased, and the pressing force of the press-fitting jig 90 at the time of press-fitting is measured. When the pressing force is equal to or greater than a predetermined value, it is assumed that the close contact member 9 has reached the press-fitting position, and press-fitting may be stopped.

  Further, as shown in FIG. 3, the close contact member 9 of the present embodiment may be applied to the glow plug 101 in which a thread is formed on the middle shaft rear end portion 132 of the middle shaft 103. The middle shaft 103 of the glow plug 101 has a fixed end portion 133 having a knurled surface processed at the rear end portion 132 of the middle shaft, and a mounting end portion 134 having a thread formed on the rear end side. An annular caulking nut 155 that functions in the same manner as the fixed portion 52 of the connection terminal 5 of the present embodiment is fitted to the fixed end portion 133. A terminal screw 156 used for connecting a current-carrying cable is fitted to the attachment end portion 134. The glow plug 101 having such a structure is attached to the engine by fastening the attachment end 134 to a conducting electrode (not shown) called a glow plate. At the time of fastening, the middle shaft 103 receives a torsional stress due to screw fastening. As described above, the close contact member 9 firmly holds the rear body portion 37 of the middle shaft 103 in the shaft hole 43 of the metal shell 4 by press-fitting. That is, the close contact member 9 is in close contact with the inner peripheral surface of the shaft hole 43 and the outer peripheral surface of the rear body portion 37. Therefore, even if the middle shaft 103 receives a twisting stress due to screwing at the attachment end portion 134, the close contact member 9 firmly holds the rear trunk portion 37 so as to suppress the twisting of the middle shaft 103. The torsional stress applied to the front body portion 36 having an outer diameter smaller than 37 can be reduced. Further, the rear barrel portion 37 having a diameter larger than that of the front barrel portion 36 causes the twisting stress applied to the middle shaft 103 with a smaller holding force than when the close contact member 9 holds the middle shaft 103 in the front barrel portion 36. Can be reduced.

  The press-fitting position of the close contact member 9 is positioned at the rear barrel portion 37 including the boundary portion A between the front barrel portion 36 and the rear barrel portion 37 of the intermediate shaft 3, and the intermediate shaft 3 is firmly held by the close contact member 9. Thus, an evaluation test for confirming that the vibration resistance and impact resistance of the central shaft 3 can be improved was performed by analysis by simulation. In this evaluation test, the length of the rear barrel portion 37 of the middle shaft 3 and the metal barrel portion 44 of the metal shell 4 in the direction of the axis O is appropriately changed with an example equivalent product having the same structure as the glow plug 1 of the present embodiment. A plurality of types of glow plugs were prepared by simulation. Further, as a comparative example, in the glow plug 1, an equivalent of the conventional example in which the close contact member 9 is not disposed between the shaft hole 43 and the rear body portion 37 and a silicon tube is inserted instead, and the middle shaft 3 is the same as described above. A plurality of types of glow plug simulated bodies in which the lengths in the axis O direction of the rear barrel portion 37 and the metal barrel portion 44 of the metal shell 4 are appropriately changed were created by simulation.

  First, the frequency at which resonance occurs in the middle shaft 3 when ultrasonic waves of different frequency bands are continuously input to the middle shaft 3 of each glow plug simulated body was obtained by simulation analysis. As a result of the analysis, the resonance frequency in the simulated glow plug equivalent to the conventional example varied depending on the shape (specifically, the length of the central shaft 3), and varied in the range of 800 to 4000 Hz. On the other hand, the resonance frequency in the simulated glow plug of the equivalent product of Example was 4000 Hz regardless of the shape (the length of the central shaft 3). As the resonance frequency is higher, the shake of the central shaft 3 is suppressed. As a result of analysis, in the glow plug equivalent to the example, the central shaft 3 is firmly held by the close contact member 9 in the vicinity of the boundary portion A, so that the vibration of the entire central shaft 3 is suppressed and vibration resistance is obtained. Was confirmed.

  Next, the stress generated in the ceramic heater 2 when 30G sine wave vibration was input to the center shaft 3 of each glow plug simulated body was obtained by simulation analysis. As a result of analysis, the stress generated in the ceramic heater 2 in the simulated glow plug equivalent to the conventional example differs depending on the shape (the length of the central shaft 3), and varied in the range of 30 to 180 MPa. On the other hand, the stress generated in the ceramic heater 2 in the simulated glow plug equivalent to the example was 30 MPa regardless of the shape (the length of the central shaft 3). In the case of an equivalent product of the conventional example, the position where the silicon tube suppresses the deflection of the center shaft 3 is ensured by the part where the silicon tube, the metal shell 4 and the center shaft 3 are inadvertently adhered. The stress applied to the ceramic heater 2 varies due to the vibration. In the case of the product equivalent to the embodiment, the stress applied to the ceramic heater 2 due to the deflection of the central shaft 3 due to external vibration is caused by the close contact member 9 holding the central shaft 3 firmly in the vicinity of the boundary portion A. Is reliably suppressed. As a result of the analysis, in the glow plug equivalent to the example, the vibration propagated to the ceramic heater 2 integrated with the central shaft 3 through the connection ring 75 is suppressed, and the stress generated in the ceramic heater 2 can be sufficiently reduced. It was confirmed that anti-vibration properties were obtained.

  According to the simulation analysis, the vibration resistance of the glow plug equivalent to the conventional example has a larger variation as the length of the central shaft 3 is longer. Further, the longer the glow plug is, the longer the silicon tube needs to be formed, and it is difficult to insert the silicon tube into the gap between the shaft hole 43 of the metal shell 4 and the middle shaft 3. On the other hand, the glow plug equivalent to the embodiment can obtain sufficient vibration resistance regardless of the length of the middle shaft 3. Further, the press-fitting of the close contact member 9 is easy because it is only necessary to adjust the length D of the pressing portion 91 of the press-fitting jig 90. Therefore, if the close contact member 9 of the present embodiment is used for a glow plug in which the length of the middle shaft 3 is longer than that of a general glow plug, for example, the total length (length in the axis O direction) is 180 mm or more, vibration resistance In this case, a high effect can be obtained.

  Next, an impact resistance evaluation test was performed using a glow plug sample. Ten glow plugs 1 equivalent to the examples and 10 glow plugs equivalent to the conventional examples were produced, each sample was dropped from a height of 100 cm, and the presence or absence of breakage of the ceramic heater 2 was confirmed. As a result of the evaluation test, in the glow plug 1 equivalent to the example, the broken ceramic heater 2 was 0 out of 10, whereas in the glow plug equivalent to the conventional example, 2 out of 10 ceramic heaters were used. 2 broke. As a result of this test, the stress applied to the ceramic heater 2 connected to the intermediate shaft 3 via the connection ring 75 due to the impact applied to the intermediate shaft 3 by positioning the close contact member 9 of the present embodiment near the boundary A. It was confirmed that it was possible to reliably suppress

DESCRIPTION OF SYMBOLS 1,103 Glow plug 2 Ceramic heater 3,103 Middle shaft 4 Main metal fitting 9 Close contact member 23 Heater rear end part 27 Heating resistor 31 Middle shaft front end part 32,132 Middle shaft rear end part 35 Middle shaft trunk part 36 Front trunk part 37 Rear trunk part Part 41 Bracket tip 43 Shaft hole A Boundary part

Claims (2)

A heater having a heating resistor that generates heat when energized at its 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, with one end connected to the rear end of the heater and the other end Projecting from the rear end of the metal shell, and at the barrel between the one end and the other end, a rear barrel connected to the other end and a tip of the rear barrel A middle shaft having a front barrel having an outer diameter smaller than that of the rear barrel,
It is formed in an annular shape and is disposed between the rear barrel and the shaft hole in a state including at least a boundary portion between the front barrel and the rear barrel, and the rear barrel and the shaft hole. And an intimate member in close contact with each of
A glow plug characterized by comprising. The close member, the glow plug according to claim 1, characterized by being press-fitted between the front Symbol rear body portion and the shaft hole.

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