JP5102530B2 - Glow plug and manufacturing method thereof - Google Patents

Description

  The present invention relates to a glow plug used for preheating a diesel engine and the like and a method for manufacturing the same.

  As glow plugs used for preheating diesel engines, those using a sheath heater are widely used. The glow plug includes a cylindrical metal shell having an inner hole and a sheath heater attached to the inner hole in a state of protruding from the distal end side of the metal shell.

  The sheath heater has a configuration in which the coil member and the insulating powder are enclosed in a metal sheath tube whose tip is closed, and the sheath tube and an energizing terminal shaft for energizing the coil member are integrated. The sheath tube is held in a state in which the distal end protrudes by fixing (press fitting) the rear portion of the sheath tube to the fitting portion in the inner hole of the metal shell in an interference fit (see, for example, Patent Document 1). .

The glow plug configured as described above is attached to the diesel engine with the tip of the sheath tube protruding into the combustion chamber. The combustion chamber is preheated by the heat generated by the sheath heater before the engine is started.
JP 2003-51371 A

  In recent years, the demand for diesel engines with better fuel efficiency and lower carbon dioxide emissions than gasoline engines has increased, and the use in ordinary passenger cars has increased rapidly. For this reason, the design of more compact diesel engines has increased, and there is a tendency for water jackets around the glow plug to be reduced. In other words, the environment is becoming unable to sufficiently cool the glow plug. As a result, the glow plug may be softened by high heat, and a problem may occur in that the bonding force between the metal shell and the sheath tube is reduced. If excessive combustion pressure is applied to the sheath tube toward the base end of the glow plug while the joint force between the two is reduced, the sheath tube may be displaced toward the base end of the glow plug, and eventually from the metal shell. There is also a risk of falling out.

  In the prior art, as in the glow plug described in Patent Document 1, as a result of press-fitting the sheath tube into the fitting portion of the metal shell, the fixing portion fixed to the fitting portion is crimped, In some cases, there is a difference in the outer diameter between the fixing portion and the portion on the tube tip side, which makes the sheath tube difficult to move.

  However, it is difficult to obtain a sufficient effect for preventing the sheath tube from coming off due to the combustion pressure or the like with the outer diameter difference generated in the press-fitting process. This is especially true when the glow plug is in a high temperature environment where it softens.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a glow plug capable of preventing the sheath tube from coming off due to combustion pressure or the like and a method for manufacturing the same.

  Hereinafter, each configuration suitable for solving the above-described problems will be described in terms of items. In addition, the effect etc. peculiar to the structure which respond | corresponds as needed are added.

Configuration 1. The glow plug of this configuration is
A sheath tube in which the tip is closed and a coil member is housed in a cylindrical shape;
In the state where the sheath tube is protruded toward the distal end of the sheath tube, the sheath tube is formed by a fitting portion formed so as to have a smaller diameter than the inner bore body of the inner bore formed along the axial direction. A glow plug with a metal shell that holds the screw in an interference fit state,
The sheath tube is
A fixing part fixed to the fitting part of the metal shell,
Formed adjacent to the distal end side in the axial direction of the fixed portion, the distal end side large diameter portion having an outer diameter equal to or larger than the inner diameter of the fitting portion;
A large diameter preventing portion formed on the distal end side in the axial direction from the large diameter portion on the distal end side and having an outer diameter larger than the outer diameter of the large diameter portion on the distal end side;
A step portion is formed between the distal end side large diameter portion and the removal preventing large diameter portion.

  In the above configuration 1, the large diameter prevention portion is provided so that the stepped portion is formed on the tip end side in the axial direction from the fixing portion fixed to the fitting portion of the metal shell. In other words, the glow plug is softened by providing a larger diameter difference in advance than the difference in outer diameter between the fixed portion and the large diameter portion on the distal end side, which occurs in the press-fitting process in which the sheath tube is tightly fitted, so that the glow plug is softened temporarily. Even when the fitting force with the tube is reduced, it is possible to more reliably prevent the sheath tube from coming off due to combustion pressure or the like.

Configuration 2. The glow plug of this configuration is the same as that of Configuration 1,
The large diameter prevention portion and the stepped portion are configured to be spaced from the end face facing the tip formed at the tip end in the axial direction of the fitting portion toward the tip end in the axial direction.

  In general, since the sheath tube is formed by swaging or the like, the length of the sheath tube may vary with the diameter of the sheath tube. For this reason, if the design is such that the large diameter preventing portion (stepped portion) comes into contact with the end face facing the tip of the fitting portion, there may be a problem that the press-fitting load increases excessively even at the contact stage. On the other hand, by adopting the above configuration 2, it is possible to absorb variations in the press-fit length of the sheath tube, and consequently variations in the press-fit load.

Configuration 3. The glow plug in this configuration is
The length in the axial direction of the large diameter portion on the tip end side is in the range of 0.3 mm to 1.5 mm.

  According to the configuration 3, the length in the axial direction of the large diameter portion on the distal end side, that is, the separation distance between the step portion of the sheath tube and the end surface facing the distal end of the fitting portion is within a range of 0.3 to 1.5 mm. Yes. If the length (separation distance) of the distal end side large diameter portion is less than 0.3 mm, there is a possibility that the forming error of the sheath tube cannot be absorbed. On the other hand, if it exceeds 1.5 mm, there is a possibility that it will not function sufficiently to prevent the sheath tube from coming off.

Configuration 4. The glow plug of this configuration is any one of configurations 1 to 3,
The sheath tube is
A base end side large diameter portion formed adjacent to the base end side in the axial direction of the fixed portion and having an outer diameter equal to or larger than the inner diameter of the fitting portion;
A small diameter portion formed on the proximal side in the axial direction from the large diameter portion on the proximal end side and having an outer diameter smaller than the outer diameter of the large diameter portion on the proximal end side and the inner diameter of the fitting portion;
A taper portion formed between the base end side large diameter portion and the small diameter portion, and having an outer diameter gradually expanding from the small diameter portion toward the base end large diameter portion;
The angle formed between the stepped portion of the sheath tube and the tip side portion of the stepped portion of the axis is β,
When the angle between the tapered portion of the sheath tube and the tip side portion of the tapered portion of the axis is γ,
γ <β
It is characterized by satisfying the relationship.

  According to the configuration 4, by providing the tapered portion, the sheath tube can be easily press-fitted into the fitting portion of the metal shell, and the sheath tube can be easily shifted to the center, so that the eccentricity of the sheath tube can be suppressed. However, if the angle γ of the tapered portion is set to be the same as the angle β of the stepped portion for preventing the sheath tube from coming off, such an effect cannot be obtained. Therefore, in the configuration 4, at least γ <β. It is set to satisfy the relationship. In other words, it can be said that the angle β of the stepped portion is set so as to satisfy the relationship of γ <β because the angle β is difficult to enter at the fitting portion of the metal shell.

Configuration 5. The glow plug of this configuration is any one of configurations 1 to 4,
The angle formed by the tip-facing end surface formed at the tip end portion in the axial direction of the fitting portion and the tip-side portion of the tip end portion from the tip-end facing end surface of the axis line is α,
When the angle between the step portion of the sheath tube and the tip side portion of the step portion of the axis is β,
α <β ≦ 90 °
It is characterized by satisfying the relationship.

  If it is the said structure 5, the level | step-difference part of a sheath tube will become easy to be hooked with respect to the front end direction end surface of a fitting part, and the effect of the said structure 1 etc. will be show | played more reliably. Furthermore, in order to obtain the above action more effectively, it is more preferable that 15 ° ≦ α <β. If the angles α and β are less than 15 °, the step becomes gentle, so that the effect of preventing the sheath tube from coming off may not be sufficiently obtained. In addition, undercuts having angles α and β exceeding 90 ° are not preferable because they may complicate the forming operation of the metal shell and the sheath tube and may increase the manufacturing cost.

Configuration 6. The glow plug in this configuration is
β <90 °
It is characterized by satisfying the relationship.

  When β = 90 ° is set, there is a concern that the strength of the sheath tube may be reduced when a load in the pull-out direction is applied to the sheath tube compared to when β <90 ° is set. Therefore, it is more preferable to set β <90 ° as in the configuration 6.

Configuration 7. The glow plug of this configuration is any one of configurations 1 to 6,
The difference in diameter between the outer diameter of the large diameter portion on the tip side and the outer diameter of the large diameter portion for preventing slippage is
It is characterized by being set larger than the diameter difference between the outer diameter of the fixing portion and the outer diameter of the distal end side large diameter portion.

  In order to prevent the sheath tube from coming off due to combustion pressure, etc., the difference in diameter between the outer diameter of the large diameter on the tip side and the outer diameter of the large diameter for preventing slipping is the outer diameter of the fixed portion, which is the deformation amount due to press fitting. It is preferable that the diameter difference is set to be larger than the diameter difference from the outer diameter of the distal end side large diameter portion. Therefore, when the configuration 7 is used, the operational effects of the configuration 1 and the like are more reliably achieved.

Configuration 8. The glow plug of this configuration is any one of configurations 1 to 7,
The difference in diameter between the outer diameter of the large tip side diameter portion and the outer diameter of the large diameter prevention portion is set to 0.02 mm or more.

  By setting it as the said structure 8, the fall prevention effect of a sheath tube can be improved significantly. If it is formed as in the above configuration 7, it is possible to set the difference in diameter between the outer diameter of the distal end side large diameter portion and the outer diameter of the large diameter prevention portion to be smaller than 0.02 mm. If the diameter difference is less than 0.02 mm, the diameter difference is too small and the sheath tube removal prevention effect may not be sufficiently obtained. Therefore, it is preferable to ensure an absolute amount of 0.02 mm or more. On the other hand, if the difference in diameter exceeds 1.00 mm, it may be difficult to ensure a predetermined amount of clearance between the inner hole of the metal shell and the large diameter prevention portion. Therefore, it is more preferable that the difference in diameter between the outer diameter of the large tip side diameter portion and the outer diameter of the large diameter prevention portion is in the range of 0.02 to 1.00 mm.

Configuration 9 This configuration is a method for manufacturing a glow plug according to any one of the above configurations 1 to 8,
A metal fitting forming step for forming a metal shell having a small diameter hole portion to be the fitting portion;
A tube forming step for forming a sheath tube having the progressing large-diameter portion that becomes the fixed portion and the distal-end-side large-diameter portion, and the large diameter-preventing diameter portion having an outer diameter larger than the outer diameter of the large-diameter portion When,
A press-fitting step of press-fitting the sheath tube into the small-diameter hole portion of the metal shell from the distal end side of the metal shell,
In the press-fitting step, by pressing the progress large-diameter portion into the small-diameter hole portion, the fixing portion fixed to the fitting portion, and the fitting portion on the distal end side in the axial direction from the fitting portion. A large diameter portion on the front end side having an outer diameter equal to or larger than the inner diameter is formed, and the large diameter prevention portion and the stepped portion are fixed at a position separated from the end-facing end surface of the fitting portion toward the front end in the axial direction. It is characterized by that.

  According to the above-described configuration 9, in the tube forming process before the press-fitting process, the fixed portion and the tip generated in the press-fitting process are formed in advance by forming the large diameter portion for preventing slipping having an outer diameter larger than the large diameter portion. It is possible to form the stepped portion having a relatively large diameter difference from the outside diameter difference with the large side diameter portion.

  In the tube forming process, since the sheath tube is generally formed by swaging or the like, there is a possibility that the length of the sheath tube may vary with the diameter reduction of the sheath tube. For this reason, if the design is made such that the large diameter preventing portion comes into contact with the end surface facing the tip of the fitting portion, there may be a problem that the press-fitting load increases excessively even at the contact stage. In that respect, if the design is made so that the large diameter prevention portion is previously fixed at a position spaced from the end face facing the front end of the fitting portion as in the above configuration 9, the variation in the press-fit length, and the press-fit load It is also possible to absorb the variation of.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1A is an overall view showing an example of a glow plug, and FIG. 1B is a longitudinal sectional view thereof.

  As shown in FIGS. 1A and 1B, the glow plug 1 includes a cylindrical metal shell 2 and a sheath heater 3 attached to the metal shell 2.

  The metal shell 2 has an inner hole 4 penetrating in the direction of the axis C1, and the outer peripheral surface thereof has a hexagonal cross section for engaging a screw portion 5 for attachment to a diesel engine and a tool such as a torque wrench. The tool engaging portion 6 is formed.

  The sheath heater 3 is configured by integrating a sheath tube 7 and a current-carrying terminal shaft 8 in the direction of the axis C1.

  The sheath tube 7 is a metal tube having a closed tip, and a coil member, specifically, a heating coil arranged on the tip side, and a control coil connected in series at the rear end thereof are magnesia inside. It is enclosed with insulating powder such as powder. The distal end portion of the resistance coil is joined to the distal end side of the sheath tube 7.

  The energizing terminal shaft 8 has its tip inserted into the sheath tube 7, is electrically connected to the rear end of the control coil, and is inserted into the inner hole 4 of the metal shell 2. The rear end of the current-carrying terminal shaft 8 protrudes from the rear end of the metal shell 2, and the rear end of the metal shell 2 includes an O-ring 12 made of rubber, an insulating bush 13 made of resin, and an insulating bush 13. The holding ring 14 for preventing the drop-off and the energizing cable connecting nut 15 are fitted into the energizing terminal shaft 8 in this order.

  Here, the joining configuration of the metal shell 2 and the sheath tube 7 will be described in detail with reference to FIG. FIG. 2 is a partially enlarged cross-sectional view showing the periphery of the joint between the metal shell 2 and the sheath tube 7.

  The metal shell 2 and the sheath tube 7 are joined by a so-called interference fit (press fit). For this reason, the diameter of the metal shell 2 is narrowed, and a fitting portion 17 having a diameter smaller than that of the main body of the inner hole 4 is formed. The fitting part 17 includes a fitting surface 18 extending along the direction of the axis C1, a tip-facing end surface 19 formed on the tip side of the axis C1 direction, and a base-end-facing end surface 20 formed on the base side of the axis C1 direction. It has. The distal-facing end surface 19 is formed in a tapered shape that gradually increases in diameter toward the distal end side in the axis C1 direction, and the proximal-facing end surface 20 is formed in a tapered shape that gradually increases in diameter toward the proximal end side in the axis C1 direction. Yes. In the present embodiment, the metal shell 2 is set such that the inner diameter D1 of the inner hole 4 body is 5.50 mm and the inner diameter D2 of the fitting portion 17 is 4.36 mm.

  On the other hand, when the sheath tube 7 is fixed to the metal shell 2 by an interference fit (press-fit), the sheath tube 7 is fixed to the fitting portion 17 (fitting surface 18) and the sheath tube 7 is placed inside the metal shell 2. A small-diameter portion 23 having an outer diameter smaller than the inner diameter D2 of the fitting portion 17 and a proximal-end side of the fixing portion 21 in the direction of the axis C1. Is formed between the small-diameter portion 23 and the proximal-side large-diameter portion 24, and is formed between the small-diameter portion 23 and the proximal-side large-diameter portion 24. A tapered portion 25 having a diameter that gradually increases from the small-diameter portion 23 toward the proximal-side large-diameter portion 24, and is formed adjacent to the distal end side in the direction of the axis C <b> 1 of the fixing portion 21. Formed on the distal end side in the axis C1 direction from the distal end side large diameter portion 26 having an outer diameter and the distal end side large diameter portion 26 And is formed between the large diameter prevention portion 27 having an outer diameter larger than the outer diameter of the distal end side large diameter portion 26, and between the large distal end side portion 26 and the large diameter portion 27 for preventing prevention. A tapered step portion 28 having a diameter that gradually increases from the distal end side large portion 26 toward the removal preventing large portion 27 is provided.

  In the present embodiment, the outer diameter S1 of the small diameter portion 23 is 4.30 mm, the outer diameter S2 of the proximal end side large diameter portion 24 is 4.40 mm, the outer diameter S3 of the fixing portion 21 is 4.36 mm, and the distal end side diameter is large. The outer diameter S4 of the portion 26 is 4.40 mm, and the outer diameter S5 of the large diameter prevention portion 27 is 4.50 mm. Here, for the purpose of preventing removal of the sheath tube due to combustion pressure or the like, the difference in diameter between the outer diameter S4 of the distal end side large diameter portion 26 and the outer diameter S5 of the large diameter prevention portion 27 is 0.02 mm to It is preferable to be within a range of 1.00 mm.

  The length L1 of the distal end side large diameter portion 26 in the direction of the axis C1 is set to be within a range of 0.3 mm to 1.5 mm, and is fitted to the tapered stepped portion 28 of the sheath tube 7. The end-facing end surface 19 of the portion 17 is in a separated state. If the length L1 of the distal end side large diameter portion 26 is less than 0.3 mm, the molding error of the sheath tube 7 may not be absorbed. On the other hand, if it exceeds 1.5 mm, there is a possibility that it will not function sufficiently to prevent the sheath tube 7 from coming off.

  Further, in the present embodiment, the angle α formed between the end-facing end surface 19 of the fitting portion 17 and the axis C1 is set to 15 °, and the angle β formed between the tapered step portion 28 and the axis C1 is set to 30 °. ing. Of course, there is no problem even if the angle is set differently. However, for the convenience of forming the metal shell 2 and the sheath tube 7, it is preferable that the angle satisfy the relationship of α <β ≦ 90 °. However, if β = 90 ° is set, there is a concern that the strength of the sheath tube 7 may be reduced when a load is applied to the sheath tube 7 in the pulling direction compared to when β <90 ° is set. Is done. Therefore, it is more preferable that β <90 °. Further, when the angles α and β are less than 15 °, the step becomes gentle, and in order to prevent the sheath tube 7 from coming off, it is more preferable that 15 ° ≦ α <β.

  In the state before being press-fitted into the metal shell 2, the sheath tube 7 has a small-diameter portion 23, a tapered portion 25, and a proximal-side large-diameter portion 24, a fixed portion 21, and a large distal-end-side diameter after press-fitting. The passage large diameter portion, the tapered stepped portion 28, and the large diameter prevention portion 27 for preventing removal are only formed in the direction of the axis C1 constituting the portion 26. The progress large diameter portion in the present embodiment has an outer diameter (specifically, 4.40 mm) slightly larger than the inner diameter D2 of the fitting portion 17, and the outer diameter and the fitting portion of the progress large diameter portion. The sheath tube 7 is held in a tightly fitted state in the fitting portion 17 by the difference in the inner diameter D2 of 17 (4.40 mm−4.36 mm = 0.04 mm). Then, in the direction of the axis C1, the range fixed to the fitting surface 18 is the fixing portion 21, the portion protruding from the base end side becomes the base end side large diameter portion 24, and the portion protruding to the tip end side is the tip end. The large side diameter portion 26 is obtained.

  Here, a method for manufacturing the glow plug 1 will be described. First, a metal fitting forming process for forming the metal shell 2 will be described.

  In the metal fitting forming step, the pipe material having the hole portion that becomes the inner hole 4 is subjected to plastic working, cutting, or the like, thereby forming a small-diameter hole portion that becomes the fitting portion 17 on the inner side and the screw portion 5 on the outer side. And the tool engaging portion 6 and the like are formed to obtain the metal shell 2.

  Next, the molding process of the sheath heater 3 performed separately will be described. In the molding process of the sheath heater 3, the tip of the current-carrying terminal shaft 8 and the current-carrying terminal shaft are formed in a cylindrical sheath tube 7 that is formed with a diameter larger than the final dimension by the machining allowance and whose tip is not closed. The coil member integrated with 8 is disposed. And while the front-end | tip of the sheath tube 7 is obstruct | occluded, the front-end | tip of a coil member is joined to the said front-end | tip part. Thereafter, the sheath tube 7 is filled with insulating powder, and then the sheath tube 7 is subjected to a swaging process. Thereby, the sheath tube 7 having the small diameter portion 23, the tapered portion 25, the large diameter portion 28, the tapered step portion 28, the large diameter prevention portion 27, etc. is formed, and the sheath tube 7 is connected to the energization terminal. The sheath heater 3 is completed together with the shaft 8. Therefore, this swaging process corresponds to the tube forming process in this embodiment.

  In the subsequent press-fitting process, the progressing large-diameter portion of the sheath heater 3 is press-fitted into the small-diameter hole portion of the metal shell 2 from the tip side. As a result, the large diameter portion having the same diameter in the direction of the axis C1 is crimped by the fitting portion 17, so that the fixing portion 21 having the same diameter as the inner diameter D2 of the fitting portion 17 is obtained. The large base end side large diameter portion 24 and the distal end side large diameter portion 26 are formed. In this way, the sheath tube 7 is firmly fixed to the fitting portion 17 in an interference fit state, so that the sheath tube 7 is located at a position where the tapered step portion 28 is separated from the end face 19 facing the distal end of the fitting portion 17. In addition to being fixed, it is held in a state of protruding from the tip of the metal shell 2.

  Thereafter, the glow plug 1 is completed by fitting the O-ring 12 or the like into the rear end portion of the energizing terminal shaft 8 protruding from the rear end portion of the metal shell 2.

  As described in detail above, in this embodiment, the diameter for preventing slipping is large so that the tapered step portion 28 is formed on the tip side in the axis C1 direction from the fixing portion 21 fixed to the fitting portion 17 of the metal shell 2. A portion 27 is provided. That is, the glow plug 1 is softened temporarily by providing a diameter difference larger than the outer diameter difference between the fixing portion 21 and the distal end side large diameter portion 26 that occurs in the press-fitting process in which the sheath tube 7 is tightly fitted. Even when the fitting force between the metal shell 2 and the sheath tube 7 is reduced, it is possible to more reliably prevent the sheath tube 7 from coming off due to combustion pressure or the like.

  Further, in the present embodiment, the angle α formed between the end-facing end surface 19 of the fitting portion 17 and the axis C1 is set to 15 °, and the angle β formed between the tapered step portion 28 and the axis C1 is set to 30 °. ing. Thereby, the taper-shaped step part 28 of the sheath tube 7 becomes easy to be hooked with respect to the end-facing end surface 19 of the fitting part 17, and the above-described effects are more reliably exhibited.

  In addition, since the sheath tube 7 is fixed at a position where the tapered step portion 28 and the end face 19 of the fitting portion 17 are separated from each other, variations in press-fitting length, and consequently variations in press-fitting load. Can also be absorbed.

  Further, by providing the tapered portion 25, the sheath tube 7 can be easily press-fitted into the fitting portion 17 of the metal shell 2, and the eccentricity of the sheath tube 7 can be suppressed because the sheath tube 7 tends to be close to the center.

  In addition, it is not limited to the description content of embodiment mentioned above, For example, you may implement as follows.

  The shape, dimensions, etc. of the glow plug 1 are not limited to the above embodiment. For example, in the said embodiment, all the front end sides from the large diameter prevention diameter part 27 are comprised by the straight shape of the same diameter. However, the present invention is not limited to this, and for example, a configuration may be adopted in which a small diameter portion that is smaller in diameter than the large diameter portion 27 for preventing slipping is formed on the distal end side. By doing so, the distal end side of the sheath tube 7 is likely to generate heat, and the rapid temperature rise performance can be enhanced.

  In the above embodiment, the outer diameter S2 (4.40 mm) of the base end side large diameter portion 24 and the outer diameter S4 (4.40 mm) of the distal end side large diameter portion 26 are the outer diameter S3 ( However, the present invention is not limited to this, and the three members may be configured to have the same diameter. In FIG. 2, the three appear to have the same diameter, but there are actually diameter differences, and when these diameter differences are emphasized, as shown in the schematic diagram of FIG. 3. Become.

  Although not particularly mentioned in the above embodiment, when the tapered portion 25 is provided, the angle of the tapered portion 25 is set to be the same as the angle of the tapered step portion 28 for preventing the sheath tube 7 from coming off. The effect of the tapered portion 25 as described above cannot be obtained. Therefore, as shown in FIG. 3, at least the angle γ formed by the tapered portion 25 and the axis C1 is set smaller than the angle β formed by the tapered step portion 28 and the axis C1 (γ <β). Is preferred. In other words, it can be said that the angle β of the tapered step portion 28 is set so as to satisfy the relationship γ <β because the angle β is not easy to enter the fitting portion 17 of the metal shell 2.

  In the above embodiment, the diameter difference between the outer diameter S4 of the distal end side large diameter portion 26 and the outer diameter S5 of the large diameter prevention portion 27 (hereinafter, this diameter difference is referred to as a first diameter difference | S5-S4 |). ) Becomes 0.10 mm, and the diameter difference between the outer diameter S3 of the fixing portion 21 and the outer diameter S4 of the distal end side large diameter portion 26 (hereinafter, this diameter difference is referred to as a second diameter difference | S4-S3 |) is 0. Although the diameter difference is 04 mm, each diameter difference is not limited to this, and can be appropriately changed according to the size of the glow plug 1 and the balance with the metal shell 2.

  However, in order to prevent the sheath tube 7 from coming off due to combustion pressure or the like, the first diameter difference | S5-S4 | is larger than the second diameter difference | S4-S3 | It is preferable that they are set as follows. Therefore, in the above embodiment, the first diameter difference | S5-S4 | is described as being in the range of 0.02 mm to 1.00 mm. However, as in the above embodiment, the second diameter difference | S4-S3 | Is 0.04 mm, the first diameter difference | S5−S4 | is preferably larger than that.

  Conversely, if the first diameter difference | S5-S4 | is larger than the second diameter difference | S4-S3 |, the first diameter difference | S5-S4 | is set to be smaller than 0.02 mm. Although it is possible, it is preferable to secure 0.02 mm or more as an absolute amount.

(A) is the whole figure which shows the glow plug of this embodiment, (b) is the longitudinal cross-sectional view. It is a partial expanded sectional view which shows the junction part periphery of a main metal fitting and a sheath tube. It is a partial expanded cross-section schematic diagram which shows the junction part periphery of a main metal fitting and a sheath tube.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Glow plug, 2 ... Main metal fitting, 3 ... Sheath heater, 4 ... Inner hole, C1 ... Axis, 7 ... Sheath tube, 17 ... Fitting part, 19 ... End surface facing end, D1, D2 ... Inner diameter, 21 ... Adhering part , 24 ... large diameter on the base end side, 26 ... large diameter on the distal end side, 27 ... large diameter part for preventing slipping, 28 ... tapered stepped part, S1 to S5 ... outer diameter, α, β ... angle.

Claims (9)

A sheath tube in which the tip is closed and a coil member is housed in a cylindrical shape;
In the state where the sheath tube is protruded toward the distal end of the sheath tube, the sheath tube is formed by a fitting portion formed so as to have a smaller diameter than the inner bore body of the inner bore formed along the axial direction. A glow plug with a metal shell that holds the screw in an interference fit state,
The sheath tube is
A fixing part fixed to the fitting part of the metal shell,
Formed adjacent to the distal end side in the axial direction of the fixed portion, the distal end side large diameter portion having an outer diameter equal to or larger than the inner diameter of the fitting portion;
A large diameter preventing portion formed on the distal end side in the axial direction from the large diameter portion on the distal end side and having an outer diameter larger than the outer diameter of the large diameter portion on the distal end side;
A glow plug characterized in that a step portion is formed between the tip side large diameter portion and the large diameter prevention portion.   2. The glow according to claim 1, wherein the large diameter prevention portion and the stepped portion are separated from the tip-facing end surface formed at the tip end portion in the axial direction of the fitting portion toward the tip end side in the axial direction. plug.   The glow plug according to claim 2, wherein a length of the large diameter portion on the tip end side in the axial direction is in a range of 0.3 mm to 1.5 mm. The sheath tube is
A base end side large diameter portion formed adjacent to the base end side in the axial direction of the fixed portion and having an outer diameter equal to or larger than the inner diameter of the fitting portion;
A small diameter portion formed on the proximal side in the axial direction from the large diameter portion on the proximal end side and having an outer diameter smaller than the outer diameter of the large diameter portion on the proximal end side and the inner diameter of the fitting portion;
A taper portion formed between the base end side large diameter portion and the small diameter portion, and having an outer diameter gradually expanding from the small diameter portion toward the base end large diameter portion;
The angle formed between the stepped portion of the sheath tube and the tip side portion of the stepped portion of the axis is β,
When the angle between the tapered portion of the sheath tube and the tip side portion of the tapered portion of the axis is γ,
γ <β
The glow plug according to claim 1, wherein the relationship is satisfied. The angle formed by the tip-facing end surface formed at the tip end portion in the axial direction of the fitting portion and the tip-side portion of the tip end portion from the tip-end facing end surface of the axis line is α,
When the angle between the step portion of the sheath tube and the tip side portion of the step portion of the axis is β,
α <β ≦ 90 °
The glow plug according to claim 1, wherein the relationship is satisfied. β <90 °
The glow plug according to claim 5, wherein the relationship is satisfied. The difference in diameter between the outer diameter of the large diameter portion on the tip side and the outer diameter of the large diameter portion for preventing slippage is
The glow plug according to any one of claims 1 to 6, wherein the glow plug is set to be larger than a diameter difference between an outer diameter of the fixing portion and an outer diameter of the tip-side large-diameter portion.   The glow plug according to any one of claims 1 to 7, wherein a difference in diameter between the outer diameter of the large distal end diameter portion and the outer diameter of the large diameter preventing portion is set to 0.02 mm or more. . A method for manufacturing a glow plug according to any one of claims 1 to 8,
A metal fitting forming step for forming a metal shell having a small diameter hole portion to be the fitting portion;
A tube forming step for forming a sheath tube having the progressing large-diameter portion that becomes the fixed portion and the distal-end-side large-diameter portion, and the large diameter-preventing diameter portion having an outer diameter larger than the outer diameter of the large-diameter portion When,
A press-fitting step of press-fitting the sheath tube into the small-diameter hole portion of the metal shell from the distal end side of the metal shell,
In the press-fitting step, by pressing the progress large-diameter portion into the small-diameter hole portion, the fixing portion fixed to the fitting portion, and the fitting portion on the distal end side in the axial direction from the fitting portion. A large diameter portion on the front end side having an outer diameter equal to or larger than the inner diameter is formed, and the large diameter prevention portion and the stepped portion are fixed at a position separated from the end-facing end surface of the fitting portion toward the front end in the axial direction. A method for manufacturing a glow plug, characterized by being made to do so.

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