JP2006038405A - Glow plug - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a glow plug having a center shaft that hardly folds even when it receives stress from the outside. <P>SOLUTION: A large diameter section 45 of which diameter is larger than the inner diameter of a small diameter section 44 is formed near the rear end of a shaft hole 43 of a main body fitting 4 of the glow plug. The rear end of the center shaft 3 is projected from the rear end, and is engaged with an annular insulating ring 5. The outer periphery of a barrel section 51 of the insulating ring 5 engages with the inner periphery of the large diameter section 45, and the inner periphery of a center hole 53 engages with the outer periphery of the center shaft 3. The outer diameter of the center shaft 3 part positioned inside the center hole 53 of the insulating ring 5 is set to 3.15 mm or longer, and the hardness of the insulating ring 5 is 18 or more in Vickers hardness HV, so that the center shaft 3 hardly bows even when the stress by an external force is added to the center shaft 3 to prevent folding or bending of the center shaft 3. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a glow plug for assisting starting of a diesel engine.

  Conventionally, glow plugs used to assist in starting a diesel engine have a metallic metal shell and are held with the tip of a rod-shaped heater protruding from the inside tip. ing. Further, the central shaft protrudes from the rear end side of the metal shell, and is held inside the metal shell in an insulated state. Both electrodes for energizing the heater are electrically connected to the metal shell and the central shaft, respectively.

  In recent years, as the size of engines has been reduced, glow plugs of, for example, M10 or less (the nominal diameter of the thread formed on the metal shell to be screwed into the engine head is 10 mm or less) have been developed for use in such engines. In such a small-diameter glow plug, a thread is provided on the rear end portion of the central shaft protruding from the rear end of the metal shell, and a plug cap for connecting to an external circuit is screwed to this to secure connection. (For example, refer to Patent Document 1).

In addition, with the aim of improving the freedom of design around the engine head and the workability of connecting the plug cap after installing the glow plug, a part that connects to the plug cap of the central shaft has been proposed as a pin terminal shape. (For example, refer to Patent Document 2). Such a pin terminal is manufactured separately from the middle shaft, and can be manufactured by fitting it to the rear end portion of the middle shaft and fixing it by caulking, so that pin terminals of various shapes can be manufactured according to the plug cap. it can. In this way, by using a configuration in which power is separately supplied to each glow plug through the plug cap, management of each glow plug becomes possible. For example, by measuring the current value supplied to each glow plug, it is possible to detect degradation of the glow plug performance, detection of disconnection, or the like.
JP 2002-367760 A Japanese Patent Laid-Open No. 2002-260827

  However, in order to achieve the hardness required for the metal shell of such a small-diameter glow plug, the metal shell needs to have a corresponding thickness. In particular, in a glow plug of M8 or less, there is no room in the space inside the metal shell, so that if the wall thickness of the metal shell is increased, the outer diameter of the central shaft must be reduced accordingly. When the intermediate shaft having such a thin outer diameter is subjected to an external force from a direction different from the axial direction, there is a possibility that the middle shaft is bent and bent. Then, the pin terminal fixed to the center shaft is inclined with respect to the axial direction of the mounting hole of the engine head, so that the plug cap cannot be connected normally, or even if the pin terminal protrudes from the shaft hole. There arises a problem that it becomes difficult to attach and remove the plug cap. In order to prevent this, for example, if the inner diameter of the mounting hole is increased, there has been a problem in that it is harmful to downsizing the engine.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a glow plug having a central shaft that is difficult to bend even when subjected to external stress.

  In order to achieve the above object, a glow plug according to a first aspect of the present invention has an axial hole penetrating in the axial direction, and a large-diameter portion that expands the axial hole on the rear end side in the axial direction. The formed metal shell and the shaft hole are inserted, and one end of the metal shell has a middle shaft protruding from the rear end of the metal shell, and a middle hole through which the middle shaft is inserted. A glow plug including an annular insulating member interposed between the large-diameter portion of the metal shell and the middle shaft, and a pin terminal covering the rear end portion of the middle shaft exposed from the insulating member, The outer diameter of the middle shaft in the portion located in the middle hole of the insulating member is 3.15 mm or more, and the hardness of the insulating member is 18 or more in terms of Vickers hardness HV. .

  A glow plug according to a second aspect of the present invention is the glow plug according to the first aspect, wherein a part of the insulating member is interposed between the large-diameter portion of the metal shell and the middle shaft. In the cross section orthogonal to the axis of the metal shell, the difference between the inner diameter of the large-diameter portion of the shaft hole and the outer diameter of the insulating member at a portion interposed in the large-diameter portion, and the insulating member The total difference between the inner diameter of the middle hole and the outer diameter of the middle shaft is 0.32 mm or less.

  A glow plug according to a third aspect of the invention includes the outer peripheral portion of the insulating member interposed in the large-diameter portion of the shaft hole in the axial direction in addition to the configuration of the invention according to the first or second aspect. The length of the portion parallel to the inner periphery of the large diameter portion is 0.4 mm or more.

  In the glow plug of the invention according to claim 1, particularly in the case of a small-diameter glow plug in which the nominal diameter of the male thread portion of the metal shell is M8 or less, the shaft hole in the metal shell is formed on the rear end side of the metal shell. An annular insulating member is interposed between the inserted middle shaft and the metal shell, but the outer diameter of the portion of the middle shaft located in the inner hole of the insulating member is 3.15 mm or more. Can be increased. For this reason, even when a stress having a component in a direction orthogonal to the axial direction is applied to the central axis, the central axis can withstand the stress with sufficient strength, so that the possibility that the central axis is bent or broken is reduced. Can do.

  In addition, when a stress having a component in a direction orthogonal to the axial direction is applied to the central axis, the insulating member is pressed against the central axis. In the glow plug of the invention according to claim 1, since the hardness of the insulating member is 18 or more in terms of Vickers hardness HV, the insulating member is not easily deformed even when the insulating member is pressed against the center shaft, and the gap between the two Expansion can be prevented. And since the middle shaft is held without bending by the insulating member that is difficult to deform, the middle shaft can be prevented from being bent or bent.

  Moreover, in the glow plug of the invention according to claim 2, in addition to the effect of the invention according to claim 1, the inner diameter of the large diameter portion of the shaft hole and the outer diameter of the insulating member at the portion interposed in the large diameter portion The sum of the difference and the difference between the inner diameter of the inner hole of the insulating member and the outer diameter of the central shaft is set to 0.32 mm or less, so that when stress is transmitted from the outside to the central shaft via the pin terminal, Since the bending of the middle shaft with respect to the axis of the plug is suppressed to the range of the difference between the outer diameters and the inner diameters, that is, 0.16 mm or less, the middle shaft can be prevented from being bent or bent.

  More preferably, the three central axes of the metal shell, the insulating member, and the middle shaft are aligned, and in this state, the gap between the shaft hole and the insulating member, and the middle hole and the middle shaft is viewed in the radial direction from the axis. The sum of the difference between the inner diameter of the large-diameter portion of the shaft hole and the outer diameter of the insulating member, and the difference between the inner diameter of the inner hole of the insulating member and the outer diameter of the central shaft may be 0.16 mm or less.

  Further, in the glow plug of the invention according to claim 3, in addition to the effect of the invention according to claim 1 or 2, the outer peripheral portion of the insulating member interposed in the large diameter portion of the shaft hole is parallel to the inner periphery of the large diameter portion. The length of the important part was 0.4 mm or more. When a stress is applied to the middle shaft from the outside via a pin terminal, a load is applied when the outer peripheral surface of the insulating member pressed by the middle shaft contacts the inner circumference of the large-diameter portion of the metal shell. Since the thickness is 4 mm or more, the load is dispersed, and damage to the insulating member can be prevented. Further, in the case of damage, the middle shaft may bend by the thickness of the damaged insulating member. However, since the deflection is prevented by preventing the insulation member from being damaged, it is possible to prevent the middle shaft from being bent.

  Hereinafter, an embodiment of a glow plug embodying the present invention will be described with reference to the drawings. First, the structure of a glow plug 1 as an example of a glow plug in the present embodiment will be described with reference to FIGS. FIG. 1 is a partial cross-sectional view of the glow plug 1. FIG. 2 is an enlarged cross-sectional view of the rear end portion of the glow plug 1. FIG. 3 is a cross-sectional view orthogonal to the axis O of the glow plug 1 as viewed from the direction of the arrows along the one-dot chain line B-B ′ in FIG. 2. In FIG. 1, the glow plug 1 will be described with the axis O direction as the vertical direction in the drawing, the lower side as the front end side, and the upper side as the rear end side.

  As shown in FIG. 1, in the glow plug 1, a round bar-shaped heater 2 and a middle shaft 3 for taking out the electrode thereof are arranged along an axis O, and the circumference of the middle shaft 3 is surrounded and held by a cylindrical metal shell 4. It has a structure.

  The metal shell 4 is a cylindrical metal member having a shaft hole 43 penetrating in the direction of the axis O, and a male screw portion 41 that is screwed into a mounting hole (not shown) of the engine head is formed on the rear end side. . In the present embodiment, the male thread portion 41 of the metal shell 4 having a nominal diameter of M8 is used. In addition, a tool engaging portion 42 having a hexagonal cross section in the axial line is formed at the rear end of the metal shell 4 and engages with a tool used for attachment to the engine head. The shaft hole 43 of the metal shell 4 is formed as a small-diameter portion 44 having substantially the same diameter over the entire length excluding a part thereof, and has a large diameter near the rear end in the tool engaging portion 42 that is larger than the inner diameter of the small-diameter portion 44. A portion 45 is formed. Further, the end surface 46 on the rear end side of the tool engaging portion 42 is formed as a surface orthogonal to the axis O. A joint portion between the inner periphery of the large diameter portion 45 and the end face 46 is chamfered in a tapered shape. Thereby, the O-ring 7 and the body portion 51 of the insulating ring 5 described later can be easily inserted into the large-diameter portion 45.

  The cylindrical heater 2 is press-fitted into the shaft hole 43 of the metal shell 4 and protrudes from the tip of the shaft hole 43. The heater 2 is provided with a conductive heating coil 24 and a control coil 23 wound in a spiral shape inside a cylindrical sheath tube 21 made of a conductive metal whose tip is closed to a spherical shape. The magnesia powder 22 is filled. One end of the heating coil 24 is electrically connected to the sheath tube 21, and the other end is welded to one end of the control coil 23. The other end of the control coil 23 connected in series with the heating coil 24 is connected to the middle shaft 3 described later. The magnesia powder 22 maintains the heat generating coil 24, the control coil 23, and the inner peripheral surface of the sheath tube 21 in an insulated state except for the conductive portion.

  The middle shaft 3 is a metal rod made of columnar carbon steel (for example, S45C) extending along the axis O, and is inserted through the shaft hole 43 of the metal shell 4. Both end portions of the middle shaft 3 protrude from both ends of the shaft hole 43. An engaging portion 31 having a smaller diameter than the body portion is formed at the tip of the middle shaft 3, and the other end of the control coil 23 of the heater 2 is welded and electrically connected. In this state, the distal end portion including the engaging portion 31 of the middle shaft 3 is inserted and fixed in the sheath tube 21 of the heater 2. Further, an insulator 32 made of heat-resistant rubber or the like is interposed between the outer peripheral surface of the middle shaft 3 and the inner peripheral surface of the sheath tube 21 to insulate them.

  Next, the rear end portion of the glow plug 1 will be described with reference to FIG. As shown in FIG. 2, the rear end of the middle shaft 3 protrudes from the rear end of the metal shell 4. An annular insulating ring 5 is fitted on the protruding portion of the middle shaft 3. The insulating ring 5 includes a body portion 51 in which an intermediate hole 53 penetrating in the direction of the axis O is formed, and a flange portion 52 provided thick on the rear end side. And the outer periphery of the trunk | drum 51 is engaged with the inner periphery of the large diameter part 45 of the rear end of the metal shell 4, and the inner periphery of the inner hole 53 is engaged with the outer periphery of the middle shaft 3, thereby Positioning and insulation of the central shaft 3 with respect to the metal fitting 4 are performed. The insulating ring 5 corresponds to an “insulating member” in the present invention.

  A tapered step portion 47 is provided between the small diameter portion 44 and the large diameter portion 45 of the shaft hole 43 of the metal shell 4, and the O-ring 7 is disposed on the step portion 47. The O-ring 7 abuts against each of the stepped portion 47, the outer peripheral surface of the middle shaft 3, and the front end surface of the insulating ring 5 while being pressed against the insulating ring 5, thereby sealing the inside and outside of the shaft hole 43 of the metal shell 4. The state is maintained.

  Further, a pin terminal 6 is fitted into a portion of the middle shaft 3 protruding from the rear end of the insulating ring 5. The pin terminal 6 is made of a metal composed of a cap-shaped body portion 62 that covers and covers the rear end of the middle shaft 3, and a pin-shaped protrusion portion 61 that extends rearwardly along the axis O from the body portion 62. Terminal. The outer periphery of the body 62 is caulked, whereby the pin terminal 6 is fixed to the rear end of the middle shaft 3 and is electrically connected to the middle shaft 3. The pin terminal 6 is fixed to the middle shaft 3 in a state where the pin terminal 6 is pressed toward the metal shell 4 (toward the tip end side of the glow plug 1), and between the pin terminal 6 and the metal shell 4. Insulation between the two is achieved by interposing the flange 52 of the insulating ring 5.

  In the small-diameter glow plug 1 having such a structure, the inner diameter of the small-diameter portion 44 of the shaft hole 43 of the metal shell 4 whose nominal diameter of the male screw portion 41 is M8 is 4.4 mm. Since the thickness of the middle shaft 3 is limited, it is desirable to increase the thickness of the middle shaft 3 in order to prevent the middle shaft 3 from being bent or bent even under stress. Therefore, in the present embodiment, the outer diameter of the middle shaft 3 is defined as 3.15 mm or more. For example, as shown in FIG. 2, when a stress having a component in a direction perpendicular to the direction of the axis O (for example, a direction indicated by an arrow A in the figure) is applied to the pin terminal 6 of the glow plug 1, the pin terminal 6 is insulated from the pin terminal 6. Since the ring 5 and the ring 5 are not fixed to each other, the load is most applied to the portion located in the inner hole 53 of the insulating ring 5 of the middle shaft 3. For this reason, if the outer diameter of at least the portion of the middle shaft 3 located in the inner hole 53 is set to 3.15 mm or more based on the test results described later, it is difficult to bend or bend even if stress is applied to the middle shaft 3. .

  Further, for example, the middle shaft 3 may be subjected to stress due to vibrations generated from the operation of the internal combustion engine. Therefore, in the present embodiment, the hardness of the insulating ring 5 that supports the middle shaft 3 at the rear end of the shaft hole 43 of the metal shell 4 is defined to be 18 or more in terms of Vickers hardness HV. That is, if the hardness of the insulating ring 5 is 18 or more in terms of Vickers hardness HV, even if the intermediate shaft 3 receives external stress and presses the insulating ring 5, the insulating ring 5 resists the pressing force. It becomes difficult to deform. In this way, the middle shaft 3 is held in the inner hole 53 of the insulating ring 5 and the bending of the middle shaft 3 is suppressed, so that the middle shaft 3 can be hardly bent.

  Further, when a stress having a component in a direction orthogonal to the axis O direction is applied to the pin terminal 6 in this way, the stress is transmitted to the insulating ring 5 through the middle shaft 3, but the insulation that is not easily deformed as described above. In the case of the ring 5, the movable range when the middle shaft 3 is deformed is limited. That is, as shown in FIG. 3, in the cross section orthogonal to the axis O including the trunk portion 51 of the insulating ring 5 (the cross section viewed from the direction of the arrow in the dashed line BB ′ in FIG. 2), The size of the clearance formed by the sum of the difference between the inner diameter C of the diameter portion 45 and the outer diameter D of the body portion 51 of the insulating ring 5 and the difference between the inner diameter E of the inner hole 53 of the insulating ring 5 and the outer diameter F of the middle shaft 3. Determines the distance that the middle shaft 3 can bend. That is, the middle shaft 3 can be half the size of the clearance from the position of the axis O. If this bending is large, the middle shaft 3 may be bent or bent. In order to prevent this, it is necessary to reduce the bending of the middle shaft 3 as much as possible. Therefore, in the present embodiment, the clearance is defined to be 0.32 mm or less. That is, the bending of the middle shaft 3 is suppressed to 0.16 mm or less with respect to the axis O. By doing so, it is possible to suppress the large bending of the middle shaft 3 and to prevent the middle shaft 3 from being bent.

  More preferably, the three central axes of the metal shell 4, the insulating ring 5 and the middle shaft 3 are aligned with the axis O, and in this state, the gap between the shaft hole 43 and the insulating ring 5 and the middle hole 53 and the middle shaft 3 is increased. As seen in the radial direction from the axis O, the difference between the inner diameter of the large-diameter portion 45 of the metal shell 4 and the outer diameter of the insulating ring 5 and the difference between the inner diameter of the inner hole 53 of the insulating ring 5 and the outer diameter of the inner shaft 3. It is desirable that the total of these is 0.16 mm or less.

  In this embodiment, the insulating ring 5 is made of, for example, reinforced nylon mixed with 30% by weight of glass fiber, polyphenylene sulfide, polyetheretherketone, polybutylene terephthalate mixed with 45% by weight of glass fiber, or glass fiber. A material such as polyphthalamide mixed with approximately 30% by weight is used. If the clearance is close to 0 mm, it is necessary to press-fit the insulating ring 5 into the metal shell 4. However, if the insulating ring 5 is formed using the above materials, the insulating ring 5 is pressed into the metal shell 4 during assembly. Or the operation of inserting the middle shaft 3 through the middle hole 53 is easy. Further, each of the above materials has a Vickers hardness HV of 18 or more and has an insulating property, so that it can be suitably used as a material for the insulating ring 5 of the present embodiment.

  Further, in the present embodiment, of the outer peripheral surface of the body portion 51 of the insulating ring 5 that faces the inner peripheral surface of the large-diameter portion 45 of the metal shell 4, it is parallel to the inner peripheral surface of the large-diameter portion 45 in the axis O direction. Of the length of the large portion 45, that is, the length of the portion facing the tapered portion of the large-diameter portion 45 in the length from the tip surface of the insulating ring 5 to the tip side surface of the flange portion 52 in the direction of the axis O is excluded. The length L (see FIG. 2) is defined to be 0.4 mm or more. Similarly to the above, when a stress having a component in a direction orthogonal to the axis O direction is applied to the middle shaft 3 through the pin terminal 6, the stress is transmitted from the middle shaft 3 to the insulating ring 5. At this time, the outer peripheral surface of the trunk portion 51 of the insulating ring 5 is opposed to the inner peripheral surface of the large-diameter portion 45 of the metal shell 4 that comes into contact, so that a load is applied to the trunk portion 51. For this reason, if the length L of the parallel part in the axis O direction of the body part 51 facing the large-diameter part 45 is set to 0.4 mm or more, such a load can be sufficiently resisted, and the insulating ring 5 can be damaged. In the case of breakage, the middle shaft 3 can be bent by the thickness of the broken body portion 51. However, the bending can be prevented and the bending of the middle shaft 3 can be made difficult to occur. Of the outer peripheral surface of the body portion 51 of the insulating ring 5, the portion parallel to the inner peripheral surface of the large diameter portion 45 in the axis O direction is not necessarily continuous, and the parallel portions are in total. If it is 0.4 mm or more, a sufficient effect can be obtained in preventing the deflection of the central shaft 3.

  Thus, by defining the material and dimensions of the middle shaft 3 and the insulating ring 5 in the small-diameter glow plug 1, the strength against bending of the middle shaft 3 can be increased. Therefore, in order to confirm the effect, the following four evaluation tests were performed.

[Example 1]
First, an evaluation test was performed on the relationship between the outer diameter of the central shaft and the amount of plastic deformation of the central shaft by pressing the pin terminal, that is, the bending condition. This evaluation test was performed according to the following conditions. The glow plug used for the test was a male screw with a nominal diameter of M8. The outer diameter of the small-diameter portion of the shaft hole of this glow plug is 4.4 mm, and the metal shell and the center shaft are both made of metal. Therefore, taking into account the dimensional margin for inserting the center shaft into the shaft hole, The outer diameter was up to 3.5 mm. Moreover, the thing which made the diameter of the hole of an insulating ring different according to the outer diameter of a center axis | shaft was prepared, and it combined so that the said clearance at the time of assembling a glow plug might be 0.32 mm. The insulating ring used had a hardness of 18 in terms of Vickers hardness HV.

  Then, as indicated by an arrow A in FIG. 2, a load of 130 N was applied to the pin terminal from the direction orthogonal to the axis O, and the maximum value of the plastic deformation amount of the central shaft was measured. Here, the maximum value of the amount of plastic deformation is a value obtained by measuring the maximum value of the amount of displacement of the axis of the central shaft with respect to the axis O as a length in the direction in which the load is applied. . The middle shaft whose deformation amount was 0.2 mm or less was evaluated as “◯” as having a small deformation amount and sufficient strength for bending, and a material deformed larger than that was sufficient strength for bending. It was evaluated as “×” because there was no. The results of this evaluation test are shown in Table 1.

  As a result, when the central shaft having an outer diameter of 3 mm was used, the maximum value of the plastic deformation amount of the central shaft was 0.28 mm, and the evaluation was “x”. Similarly, when each of the middle shafts having an outer diameter of 3.05, 3.1, 3.15, 3.2, 3.5 (mm) is used, the maximum value of the plastic deformation amount of the middle shaft is 0.24. , 0.21, 0.18, 0.16, 0.02 (mm), and the evaluations were “×”, “×”, “O”, “O”, and “O”, respectively. Therefore, it was confirmed that if the outer diameter of the central shaft is 3.15 mm or more, sufficient strength against bending can be obtained.

[Example 2]
Next, an evaluation test was performed on the relationship between the hardness of the insulating ring and the amount of plastic deformation of the central shaft. The glow plug used for the evaluation was the same as that in Example 1, but the middle shaft having an outer diameter of 3.15 mm was used. Insulating rings with different hardnesses were prepared, and the diameter of the inner hole of each insulating ring was adjusted so that the clearance was 0.32 mm. The hardness of the insulating ring was adjusted by changing the amount of glass fiber to be mixed.

  Then, similarly to Example 1, a load of 130 N was applied to the pin terminal, and the maximum value of the plastic deformation amount of the central shaft was measured. The evaluation criteria are the same as in Example 1. The results of this evaluation test are shown in Table 2.

  As a result, when the hardness of the insulating ring is 13, 15, 18, 20 (HV), the maximum value of the plastic deformation amount of the central shaft is 0.27, 0.23, 0.18, 0.16 ( mm), and the evaluations were “×”, “×”, “O”, and “O”, respectively. Therefore, if the hardness of the insulating ring is 18 or more in terms of Vickers hardness HV, even if stress is applied to the central shaft, the insulating ring to which stress is transmitted from the central shaft is difficult to deform and supports the central shaft. It was confirmed that sufficient strength against the above could be obtained.

[Example 3]
Next, the difference between the inner diameter of the shaft hole of the metal shell and the outer diameter of the body portion of the insulating ring, the total value of the difference (clearance) between the inner diameter of the inner hole of the insulating ring and the outer diameter of the central shaft, and plastic deformation An evaluation test was performed on the relationship with the amount. The glow plug used for the evaluation was the same as in Example 1, and an insulating ring having an outer diameter of 3.15 mm and a hardness of 18 in terms of Vickers hardness HV was prepared. The clearance was adjusted by changing the outer diameter of the body portion of the insulating ring and the inner diameter of the inner hole. In this embodiment, in order to more precisely manage the clearance, the central axis of the metal shell, the insulating ring, and the central shaft are aligned with the axis O, and the clearance is measured as a radius for adjustment. Then, as in Example 1, a load of 130 N was applied to the pin terminal, and the maximum value of the plastic deformation amount of the central shaft was measured. The evaluation criteria are the same as in Example 1. The results of this evaluation test are shown in Table 3.

  As a result, when the clearance size is 0.10, 0.12, 0.14, 0.16, 0.18, 0.20 (mm), the maximum value of the plastic deformation amount of the central shaft is 0, respectively. .11, 0.14, 0.16, 0.18, 0.22, 0.24 (mm), and the evaluations are “O”, “O”, “O”, “O”, “×”, It became “x”. Therefore, if the outer diameter of the body of the insulating ring and the inner diameter of the inner hole are adjusted so that the clearance is 0.16 mm or less, that is, 0.32 mm or less when viewed as the diameter, the inner shaft receives stress from the outside. It was also confirmed that sufficient hardness against bending can be obtained.

[Example 4]
Next, out of the outer peripheral surface of the trunk portion of the insulating ring facing the inner peripheral surface of the large-diameter portion of the metal shell, the length of the portion parallel to the inner peripheral surface of the large-diameter portion in the axis O direction, and the amount of plastic deformation An evaluation test was conducted on the relationship. The glow plug used for the evaluation was the same as in Example 1, with an inner diameter of 3.15 mm and an insulation with a Vickers hardness HV of 18 and different lengths in the direction of the axis O of the barrel. A ring was prepared. Then, as in Example 1, a load of 130 N was applied to the pin terminal, and the maximum value of the plastic deformation amount of the central shaft was measured. The evaluation criteria are the same as in Example 1. The results of this evaluation test are shown in Table 4.

  As a result, the length of the portion where the outer peripheral surface of the body portion of the insulating ring is parallel to the axis O direction with respect to the inner peripheral surface of the large-diameter portion of the metal shell is 0.2, 0.4, 0.6. , 0.8, 1.0 (mm), the maximum plastic deformation amount of the central shaft is 0.20, 0.19, 0.18, 0.18, 0.17 (mm), respectively. The evaluations were “×”, “○”, “○”, “○”, and “○”, respectively. Therefore, if the length of the parallel portion of the body portion of the insulating ring is 0.4 mm or more, the strength of the body portion can be sufficiently obtained even if the central shaft receives stress from the outside, so that the position of the insulating ring varies. In addition, it was confirmed that the central shaft can obtain a sufficient hardness against bending.

  Needless to say, the present invention can be modified in various ways. For example, in the present embodiment, the heater 2 is a metal heater with a built-in heating coil 24, but a ceramic heater in which a heat generating portion made of conductive ceramic or the like is embedded in an insulating ceramic base may be used.

  Applicable to glow plugs used for starting assistance of diesel engines.

2 is a partial cross-sectional view of the glow plug 1. FIG. 2 is an enlarged cross-sectional view of a rear end portion of the glow plug 1. FIG. FIG. 3 is a cross-sectional view orthogonal to the axis O of the glow plug 1 as viewed from the direction of the arrows along the one-dot chain line B-B ′ in FIG. 2.

Explanation of symbols

1 Glow plug 3 Middle shaft 4 Metal shell 5 Insulation ring 6 Pin terminal 43 Shaft hole 45 Large diameter part 53 Medium hole

Claims (3)

A metal shell having a shaft hole penetrating in the axial direction and having a large diameter portion formed by expanding the shaft hole on the rear end side in the axial direction;
A middle shaft that is inserted into the shaft hole, one end of which protrudes from the rear end of the metal shell,
An annular insulating member having an inner hole through which the intermediate shaft is inserted, and at least a part of itself interposed between the large-diameter portion of the metal shell and the intermediate shaft;
A glow plug comprising: a pin terminal covering a rear end portion of the central shaft exposed from the insulating member;
The outer diameter of the middle shaft in the portion located in the middle hole of the insulating member is 3.15 mm or more, and the hardness of the insulating member is 18 or more in terms of Vickers hardness HV. Glow plug. In a cross section perpendicular to the axis of the metal shell at a portion where a part of the insulating member is interposed between the large diameter portion of the metal shell and the middle shaft, the inner diameter of the large diameter portion of the shaft hole, The sum of the difference between the outer diameter of the insulating member and the difference between the inner diameter of the inner hole of the insulating member and the outer diameter of the inner shaft in a portion interposed in the large diameter portion is 0.32 mm or less. The glow plug according to claim 1. In the axial direction, the length of the outer peripheral portion of the insulating member interposed in the large diameter portion of the shaft hole is parallel to the inner periphery of the large diameter portion is 0.4 mm or more. The glow plug according to claim 1 or 2.

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