JP2007298265A - Glow plug and its mounting structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a glow plug having improved durability by suppressing early breakage of a control coil. <P>SOLUTION: The glow plug 1 comprises a main fitting 3, a tube 4 whose front end 4a is closed and which is fixed into the main fitting 3 in the state of protruding its front end 4a from a front end 3a of the main fitting 3, a heating coil 5 whose front end 5a is joined to the front end 4a of the tube 4 in the tube 4, and the control coil 6 whose front end 6a is joined to a rear end 5b of the heating coil 5 via a joint portion CP in the tube 4. The tube 4 has a thin portion 45 for covering the radial outside of the heating coil 5 and the joint portion CP, and a thick portion 8 whose radial thickness is greater than the radial thickness of the thin portion 45, for covering at least part of radial outside of the control coil 6. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a glow plug.

  Patent Documents 1 and 2 disclose conventional glow plugs. This glow plug has a cylindrical metal shell extending in the axial direction and a cylindrical metal shell extending in the axial direction, with its tip end closed and the metal tip protruding from the tip of the metal shell. A tube fixed inside, a heating coil in which the tip of the tube is joined to the tip of the tube, and a control in which the tip of the tube is joined to the rear end of the heating coil and the joint in the tube A coil.

  A conventional glow plug having such a configuration is attached to a mounting hole of a cylinder head such that the tip of the tube protrudes into the combustion chamber, and is used for preheating of a diesel engine or the like. At this time, the control coil controls the temperature characteristics of the heat generating coil by increasing the electric resistance at high temperatures.

JP 11-294768 A Japanese Patent Laid-Open No. 11-294769

  By the way, in recent years, with a high performance and miniaturization of a diesel engine, a glow plug is required to be small. For this reason, the outer diameter of the part which covers the radial direction outer side of the heat generating coil which is a part which protrudes from a main metal fitting among a tube, and a control coil also exists in the tendency to reduce in diameter.

  However, when the diameter of the tube is reduced, the strength of the tube is reduced. For example, if the tube is accidentally dropped during installation and a large impact is applied, the tube and the heating coil and the control coil inside the tube are easily damaged. Further, when the tube is reduced in diameter, the outer diameter of the heating coil is also reduced, so that it may be difficult to obtain necessary heat generation performance and temperature rise characteristics. Further, as the diameter of the tube is reduced, the heat generating coil easily comes into contact with the inner surface of the tube, and a problem that the heat generating coil and the tube are short-circuited easily occurs.

  For this reason, in the conventional glow plug, the outer diameter of the heating coil and the control coil and the inner diameter and the outer diameter of the portion covering the heating coil and the portion of the tube covering the control coil are related to the portion of the tube covering the heating coil and the control coil. By defining the relationship with the diameter and the like, the above-described problems can be suppressed and the necessary heat generation performance can be exhibited while the tube has a small diameter.

  However, even in the conventional glow plug described above, there is a case where the control coil is disconnected early due to repeated energization, and further improvement in durability has been demanded.

  The present invention has been made in view of the above-described conventional situation, and it is an object to be solved to provide a glow plug capable of improving durability by suppressing early disconnection of a control coil. .

  The inventors conducted intensive research on the mechanism of early disconnection of the control coil by repeatedly energizing the glow plug, and elucidated the mechanism as follows.

  That is, when energized repeatedly, generation and separation of the oxide film are repeated on the outer surface of the tube, and the outer surface of the tube tends to be gradually consumed. At this time, the portion covering the radially outer side of the heating coil on the distal end side of the tube is cooled by swirl (the flow of fuel gas in the combustion chamber), but the portion covering the radially outer side of the control coil on the root side is Since it does not protrude from the lower surface of the cylinder head into the combustion chamber, it is difficult to be cooled by the swirl. Therefore, the outer surface of the tube is consumed more heavily in the portion covering the control coil than in the portion covering the heating coil, and the wall thickness is gradually reduced. . For this reason, in the part which covers a control coil, discharge | release of a heat | fever becomes weak from the control coil via a tube, it becomes easy to accumulate heat in a control coil, and a control coil becomes easy to disconnect. The inventors have arrived at the present invention based on this mechanism.

That is, the glow plug of the present invention has a cylindrical metal shell extending in the axial direction and a cylindrical shape extending in the axial direction, and its tip is closed, and its tip protrudes from the tip of the metal shell. A tube that is fixed in the metal shell in a state of being held, a heating coil in which the tip of the tube is joined to the tip of the tube, and a tip of the tube that is fixed in the tube. In the glow plug including the rear end portion and the control coil joined at the joint portion,
The tube covers a radially outer portion of the heating coil and the joint portion, and covers a radially outer portion of at least a part of the control coil, and has a diameter larger than a radial thickness of the thin portion. And a thick portion having a large thickness in the direction.

  The glow plug of the present invention having such a configuration is attached to a mounting hole formed in the cylinder head so that the tip of the tube protrudes into the combustion chamber, and is used for preheating of a diesel engine or the like. In this glow plug, the tube covers a thin-walled portion that covers the radially outer side of the heating coil and the joint, and at least a portion of the control coil that is radially outer, and the tube has its own thickness rather than the radial thickness of the thin-walled portion. And a thick portion having a large radial thickness. Thereby, since the heat of the control coil is easily released to the metal shell by the thick wall portion, the outer surface of the portion of the tube that covers the radially outer side of the control coil is less likely to be consumed. In addition, this glow plug is energized repeatedly, so that the outer surface of the tube covers the outer side in the radial direction of the control coil, and even if the wall thickness gradually decreases, At least part of the portion that covers the outer side in the radial direction of the control coil is provided with a thick wall portion that is thicker than the thin wall portion that covers the outer side in the radial direction of the heating coil and the joint portion. The time when it becomes difficult to be released into the metal shell can be delayed. For this reason, the time which heat accumulates in a control coil and it heats excessively can be delayed, and it can control that a control coil breaks early.

  Therefore, the glow plug of the present invention can improve durability by suppressing early disconnection of the control coil.

  Note that the glow plug disclosed in Japanese Utility Model Laid-Open No. 1-74463 and Japanese Patent Application Laid-Open No. 2001-208347 has a thickness of only a part of the tube on the tip side of the portion covering the radially outer side of the heating coil. It is said to be thinner than the thickness of the other parts. This is because these glow plugs are intended to improve the heat generation performance of the heat generating coil. For this reason, these glow plugs do not contribute at all to suppressing early disconnection of the control coil.

  In the glow plug of the present invention, the control coil is located on the spiral side of the spiral portion and on the tip side of the spiral portion and extends in the axial direction, and its tip portion is connected to the rear end portion of the heat generating coil. It is preferable that an extension part joined at a joining part is provided, and a tip of the thick part is opposed to the spiral part. In this case, since the thick portion is not formed in the portion of the tube that covers the radially outer side of the extension portion, the heat generating coil and the thick portion are separated by at least the length of the extension portion. Becomes difficult to be released to the thick part. Therefore, in this glow plug, it is possible to prevent the control coil from being disconnected early without deteriorating heat generation characteristics such as rapid temperature rise of the glow plug.

  In the glow plug of the present invention, it is preferable that a difference between a radial thickness of the thick portion and a radial thickness of the thin portion is 0.05 to 0.15 mm. If the difference in wall thickness is smaller than 0.05 mm, the effect of suppressing the control coil from being disconnected early may not be sufficiently obtained. Also, if the difference in wall thickness is greater than 0.15 mm, the clearance between the inner peripheral surface of the thick wall portion and the control coil becomes minute, and a short circuit occurs between the control coil and the thick wall portion, or the outer diameter of the tube is reduced. The size of the glow plug may increase and the glow plug itself may increase in size. On the other hand, the glow plug of the present invention has a thickness difference of 0.05 to 0.15 mm, so that the glow plug can be enlarged while preventing a short circuit between the control coil and the thick part. Therefore, it is possible to further obtain an effect of suppressing the control coil from being disconnected early.

  In the glow plug of the present invention, it is preferable that an inner diameter of the thick part is smaller than an inner diameter of the thin part. In this case, since the thick portion of the glow plug protrudes from the thin portion to the inside of the tube, the thick portion can be formed without increasing the outer diameter of the tube. That is, it is possible to prevent the control coil from being disconnected early without increasing the size of the glow plug.

  Among the glow plugs of the present invention, in the glow plug in which the inner diameter of the thick part is smaller than the inner diameter of the thin part, the outer diameter of the control coil is preferably smaller than the outer diameter of the heating coil. In this case, since a sufficient clearance between the inner peripheral surface of the thick portion and the control coil can be secured, it is possible to prevent a short circuit between the control coil and the thick portion.

A glow plug mounting structure in which the glow plug of the present invention is mounted in a mounting hole formed in a cylinder head with a tube tip projecting into a combustion chamber of a diesel engine. It is preferable to have a glow plug mounting structure in which the glow plug is mounted so that at least a part is disposed in the mounting hole and the thick portion is disposed in the mounting hole.
In a diesel engine, the tip end side of the glow plug tube jumps out into the combustion chamber. Therefore, an attachment hole is formed in the cylinder head so as to connect to the combustion chamber, and the glow plug is attached to the attachment hole. And at least one part of a control coil may be arrange | positioned in an attachment hole. In this case, depending on the projecting dimension of the tube into the combustion chamber, a part of the thick wall portion may protrude and be disposed in the combustion chamber. In this case, the thick part and the control coil itself are cooled by the swirl, and further, the heat of the control coil is released to the metal shell by the thick part, so that the control coil is cooled more than necessary. As a result, the temperature of the heating coil cannot be controlled, and the heating coil may generate heat abnormally. In contrast, in the glow plug mounting structure of the present invention, since the thick wall portion is accommodated in the mounting hole of the cylinder head, the control coil is prevented from being disconnected early without cooling the control coil more than necessary. can do. The combustion chamber includes a sub-combustion chamber (vortex combustion chamber, pre-combustion chamber, etc.) in addition to the main combustion chamber.

In the glow plug mounting structure of the present invention, when the glow plug is mounted in the mounting hole of the cylinder head, when viewed along the axial direction, the tip of the thick portion and the combustion chamber of the mounting hole The shortest distance from the opening edge on the side is preferably 10 mm or less.
If this shortest distance is greater than 10 mm, the portion of the tube covering the control coil that corresponds to the tip of the thick portion and the opening edge of the mounting hole on the combustion chamber side is not exposed to the combustion chamber, so swirl Since it is difficult to cool, the consumption of the outer surface of the part becomes severe, and the heat emission from the control coil through the tube may be weakened. On the other hand, in the glow plug mounting structure of the present invention, since the shortest distance is 10 mm or less, it is possible to further obtain the effect of suppressing the control coil from being disconnected early.

  A first embodiment of the present invention will be described below with reference to the drawings.

  As shown in FIGS. 1 and 2, the glow plug 1 of the first embodiment has a cylindrical metal shell 3 extending in the direction of the axis O and a cylindrical shape extending in the direction of the axis O, and the tip end portion 4a thereof is closed. The tube 4 fixed in the metal shell 3 with the tip portion 4 a of the metal shell 3 protruding from the tip 3 a of the metal shell 3, and the tip portion 5 a of the tube 4 is joined to the tip portion 4 a of the tube 4. The heating coil 5, the control coil 6 having its tip 6 a joined to the rear end 5 b of the heating coil 5 in the tube 4, and a rod extending in the direction of the axis O, and disposed in the metal shell 3, The front end portion 7 a of the own device is located in the tube 4 and joined to the rear end portion 6 b of the control coil 6, and the rear end portion 7 b of the own device includes the middle shaft 7 protruding from the rear end 3 b of the metal shell 3. The heating coil 5 and the control coil 6 are enclosed in the tube 4 together with magnesia powder as an insulating material.

  The heating coil 5 has, for example, an electrical specific resistance at 20 ° C. of ρ20, ρ20 of 80 to 180 μΩ · cm, an electrical specific resistance at 800 ° C of ρ800, and ρ800 / ρ20 of 0.9 to 1. It is made of about two materials (specifically, iron-chromium alloy wire or nickel-chromium alloy wire). The wire diameter of the heating coil 5 is about 0.15 to 0.4 mm, the coil length is about 5 to 12 mm, and the coil outer diameter is about 1.5 to 3 mm. Further, the winding pitch of the heating coil 5 is about 0.2 to 0.8 mm, and the number of winding turns is about 8 to 15.

  The control coil 6 is, for example, a material whose electrical resistivity at 20 ° C. is ρ20, ρ20 is 5 to 25 μΩ · cm, electrical resistivity at 800 ° C is ρ800, and ρ800 / ρ20 is about 7 to 12. (Specifically, it is composed of iron-chromium alloy wire or nickel-chromium alloy wire). The control coil 6 has a wire diameter of about 0.17 to 0.3 mm, a coil length of about 10 to 32 mm, and a coil outer diameter of about 1.5 to 3 mm. The winding pitch of the control coil 6 is about 0.2 to 0.8 mm, and the number of winding turns is about 25 to 40.

  When the electrical resistance value of the heating coil 5 is RH and the electrical resistance value of the control coil 6 is RC, the electrical resistance ratio [(RH / RC), RT between the heating coil 5 and the control coil 6 at room temperature (RT) ] Is 1 or more, and the electric resistance value [(RH / RC), 800 ° C.] at 800 ° C. is adjusted to 0.1 to 0.4.

  The heating coil 5 includes a spiral portion 5c and an extension portion 5b (rear end portion 5b) extending in the direction of the axis O on the rear end side of the spiral portion 5c. Further, the control coil 6 is formed with a spiral portion 6c and an extension portion 6a (tip portion 6a) extending substantially in the direction of the axis O on the tip side of the spiral portion 6c. And the rear-end part of the extension part 5b of the heating coil 5 and the front-end | tip part of the extension part 6a of the control coil 6 are joined by the junction part CP.

  The tube 4 is made of a metal material such as SUS310S, Inconel 601, etc., and is continuous with the thin-walled portion 45 and the thin-walled portion 45 that covers the heating coil 5 and the radially outer side of the joint CP, and at least a part of the control coil 6 And a thick portion 8 that is a portion covering the outside in the radial direction. The thick part 8 will be described later.

  Here, as shown in an enlarged view in FIG. 2, in the glow plug 1 of the first embodiment, the following dimensions are selected for the heating coil 5, the control coil 6, and the tube 4.

  First, the outer diameter φD of the portion protruding from the metal shell 3 of the tube 4 is set to 3.5 mm in order to reduce the diameter. The outer diameters φd of the heating coil 5 and the control coil 6 located in the tube 4 are both 1.8 mm. Further, the helical portion 5c length CL1 of the heating coil 5 is 6 mm (including the thickness of the distal end portion 4a of the tube 4), and the length SL1 of the extension portion 5b of the heating coil 5 is 2 mm. Furthermore, the helical part 6c length CL2 of the control coil 6 is 14 mm, and the length SL2 of the extension part 6a of the control coil 6 is 2 mm.

  Next, the thickness Th (hereinafter referred to as the thickness Th) in the radial direction of the thin portion 45 of the tube 4 is sufficient to secure a sufficient clearance to prevent short circuit with the heating coil 5 and to increase the rapid temperature rise performance. In order to improve, it is 0.5 mm. The wall thickness Th is constant. In this case, the clearance between the inner peripheral surface of the thin portion 45 and the heating coil 5 is 0.35 mm. And about thickness Tc (henceforth thickness Tc) of the radial direction of the thick part 8, in the present Example, the heating coil 5 and the control coil 6 are the above-mentioned dimensions, and the thick part 8 The temperature distribution during energization is measured using a conventional glow plug having a wall thickness Tc equal to the wall thickness Th of the thin portion 45 of the tube 4 as a design glow plug, and is determined based on the result. FIG. 3 shows a graph of the temperature distribution during energization of the design glow plug.

  In the graph of FIG. 3, the temperature of the control coil 6 is still low in the curve A when 4 seconds have elapsed after the design glow plug is energized. Therefore, the electric resistance of the control coil 6 is low, and control is performed so that the heating coil 5 is rapidly heated so that a relatively large current flows through the heating coil 5. Then, in the curve B when 30 seconds have elapsed after energization, the heating coil 5 rises to near the target high temperature, and the temperature of the control coil 6 also rises. For this reason, the electrical resistance of the control coil 6 is increased, and control is performed so that a relatively small current flows through the heating coil 5 so that the heating coil 5 does not overheat.

  Here, in curve B when 30 seconds have passed after energization, the temperature is highest at a portion at a distance of about 15 mm from the tip portion 4 a of the tube 4. A maximum temperature position Pm, which is a position where the highest temperature is reached when used by being attached to an internal combustion engine among the portions that do not protrude into the combustion chamber 10, is determined to be about 15 mm from the distal end portion 4 a of the tube 4.

  Thereby, in the tube 4, the midpoint M between the joining position Pc corresponding to the radially outer side of the joining portion CP and the maximum temperature position Pm is determined to be about 11.5 mm from the distal end portion 4 a of the tube 4.

  In this embodiment, the thick portion 8 in which the thickness Tc of the tube 4 is larger than the thickness Th of the thin portion 45 is provided on the rear end side of the middle point M in the tube 4. Further, the thick portion 8 is continuously provided on the rear end side from the middle point M in the tube, and is in contact with the metal shell 3. In this embodiment, the contact is made directly, but the contact may be made through another member.

  The inner diameter of the thick part 8 is smaller than the inner diameter of the thin part 45. That is, the outer diameter of the tube 4 does not change, and the inner peripheral surface swells inward on the rear end side from the middle point M, so that the thickness Tc of the thick portion 8 is increased to 0.6 mm.

  The glow plug 1 according to the first embodiment having such a configuration is attached to an attachment hole 9a formed in the cylinder head 9 so that the distal end portion 4a of the tube 4 is positioned in the combustion chamber 10 as shown in FIG. And used for preheating diesel engines. At this time, the control coil 6 controls the temperature characteristics of the heating coil 5 by increasing the electrical resistance at high temperatures. In the case of the present embodiment, the control coil 6 (including the joint portion CP) and the thick portion 8 are disposed inside the mounting hole 9a. Further, when viewed along the direction of the axis O, the shortest distance h between the tip 8a of the thick portion 8 and the opening edge 9b on the combustion chamber 10 side of the mounting hole 9a is 4.5 mm.

  And this glow plug 1 can suppress that the control coil 6 disconnects early as follows.

  That is, in this glow plug 1, the tube 4 has a thick portion 8 in which its own radial thickness Tc is larger than the radial thickness Th of the thin portion 45. As a result, the heat of the control coil 6 is easily released to the metal shell 3 by the thick wall portion 8, so that the outer surface of the portion of the tube 4 that covers the outer side in the radial direction of the control coil 6 is less likely to be consumed. Further, when the glow plug 1 is repeatedly energized, the portion of the tube 4 covering the control coil 6 that does not protrude into the combustion chamber 10 becomes exhausted on the outer surface of the tube 4, and the wall thickness gradually decreases. Even so, the thickness Tc in the radial direction of the conventional glow plug is thicker than the thickness Th in the radial direction of the thin portion 45, so that the heat generated in the control coil 6 is released to the metal shell 3 through the tube 4. The time when it becomes difficult to be done can be delayed. For this reason, the time which heat accumulates in the control coil 6 and it is heated excessively can be delayed, and the control coil 6 can be prevented from being disconnected early.

  Here, as shown in Table 1, a durability evaluation test was performed on the glow plug 1 of Example 1. The test method is to measure how many cycles the control coil 6 is not disconnected by repeating a cycle in which the glow plug 1 is supplied with DC 13 V for 3 minutes and then stopped for 1 minute. Further, the glow plug of the comparative example 1 having a thickness Tc of the thick part 8 equal to the maximum thickness Th of the thin part 45 is 0.5 mm, and the glow plug of the comparative example 2 having a thickness Tc of the thin part 45. Those having a thickness of 0.4 mm which is thinner than the maximum wall thickness Th were prepared and the same evaluation test was performed.

  As a result, the glow plug of the comparative example 1 corresponding to the conventional glow plug did not break the control coil 6 until 10,000 cycles, whereas the glow plug 1 of the first embodiment had a control coil of up to 12000 cycles. 6 is a result of no disconnection, and an improvement in durability was observed. On the other hand, in the glow plug of Comparative Example 2, the result was that the control coil 6 did not break until 7000 cycles, and durability was reduced. This is because the thickness Tc of the portion of the tube 4 that covers the control coil 6 that does not protrude into the combustion chamber 10 is reduced, so that the heat release of the portion of the tube 4 that covers the control coil 6 is reduced. This is thought to be due to the fact that heat easily accumulates.

  In addition, the glow plug of Reference Example 1 having a thickness Tc significantly increased to 0.8 mm was prepared and the same evaluation was attempted. However, as a result of significantly increasing the thickness Tc, the clearance between the inner peripheral surface of the thick portion 8 and the control coil 6 becomes as small as 0.05 mm in design, and as a result, a short circuit occurs and evaluation cannot be performed. . For this reason, when increasing the thickness Tc, it is necessary to pay attention to the clearance between the inner peripheral surface of the thick portion 8 and the control coil 6.

  Therefore, the glow plug 1 of the first embodiment can improve durability by suppressing early disconnection of the control coil.

  Moreover, since the front end 8a of the thick portion 8 is provided on the rear end side of the heating coil 5 and the extension portion 6a of the control coil 6 (opposite the spiral portion 6c of the control coil 6), the heat generation of the glow plug 1 is achieved. The characteristics are also good. More preferably, the tube 4 is provided on the rear end side from the midpoint M between the joining position Pc and the maximum temperature position Pm corresponding to the radially outer side of the joining portion CP.

  If the thick portion 8 is provided so that the tip 8a of the thick portion 8 faces the extension portion 6a of the control coil 6, the heat release from the heating coil 4 increases, and the glow plug 1 is rapidly heated. The heat generation characteristics such as

  In the glow plug 1, the difference between the radial thickness of the thick portion 8 and the radial thickness of the thin portion 45 is 0.05 to 0.15 mm. If the difference in thickness is 0.05 to 0.15 mm, the control coil is disconnected early without increasing the size of the glow plug 1 while preventing a short circuit between the control coil 6 and the thick portion 8. The effect of suppressing this can be further obtained.

  Further, in the glow plug 1, the inner diameter of the thick part 8 is smaller than the inner diameter of the thin part 45. That is, since the thick portion 8 protrudes from the thin portion 45 to the inside of the tube 4, the effect of the present invention can be achieved without increasing the outer diameter φD of the tube 4.

  In the glow plug 1, the outer diameter of the control coil 6 is preferably smaller than the outer diameter of the heating coil 5 in the glow plug in which the inner diameter of the thick portion 8 is smaller than the inner diameter of the thin portion 45. In this case, since a sufficient clearance between the inner peripheral surface of the thick portion 8 and the control coil 6 can be secured, it is possible to prevent a short circuit between the control coil 6 and the thick portion 8.

  Further, in the glow plug mounting structure of the present invention, the thick portion 8 is disposed in the mounting hole 9 a of the cylinder head 9. For this reason, while the thick part 8 and the control coil 6 are cooled by the swirl, the control coil 6 is cooled more than necessary due to the release of the heat of the control coil 6 by the thick part 8, and the temperature of the heating coil 5 is increased. There is no possibility that the heating coil 5 will generate heat abnormally without being controlled. That is, early disconnection of the control coil 6 can be suppressed without cooling the control coil 6 more than necessary.

  Further, in the mounting structure of the glow plug 1 of the present invention, when the glow plug 1 is mounted in the mounting hole 9a of the cylinder head 9, when viewed along the direction of the axis O, the glow plug 1 is mounted on the tip 8a of the thick portion 8. It arrange | positions so that the shortest distance h with the opening edge 9b by the side of the combustion chamber 10 of the hole 9a may be 10 mm or less. Thereby, since the shortest distance is 10 mm or less, the effect of suppressing the control coil from being disconnected early can be further obtained.

  In the above, the present invention has been described with reference to the first embodiment. However, the present invention is not limited to the first embodiment, and it is needless to say that the present invention can be appropriately modified and applied without departing from the spirit of the present invention. .

  The present invention is applicable to a glow plug.

1 is a longitudinal sectional view of a glow plug of Example 1. FIG. It is a principal part expanded longitudinal cross-sectional view of the glow plug of Example 1, and sectional drawing of the attachment structure. 6 is a graph showing a temperature distribution during energization of a design glow plug according to the glow plug of Example 1;

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Glow plug 3 ... Main metal fitting 3a ... The front-end | tip of a main metal fitting 3b ... The rear end of a main metal fitting 4 ... Tube 4a ... The front-end | tip part of a tube 5 ... Exothermic coil 5a ..Extremity of heating coil 5b ... Extension of heating coil (rear end)
5c: Spiral part of heating coil 6 ... Control coil 6a: Extension part (tip part) of control coil
6b: Control coil rear end 6c: Control coil spiral 7: Medium shaft 7a: Medium shaft tip 7b: Medium shaft rear end 8: Thick part 45 ..Thin portion O ... Axis Tc ... Thickness of thick portion Th ... Thickness of thin portion CP ... Junction between heating coil and control coil

Claims (7)

A cylindrical metal shell extending in the axial direction;
A tube that extends in the axial direction, has its tip end closed, and a tube that is fixed in the metal shell in a state in which the tip portion protrudes from the tip of the metal shell,
A heating coil in which the tip of the tube is joined to the tip of the tube in the tube;
In the glow plug provided with a control coil in which the front end of the tube is joined at the rear end of the heating coil and the joint in the tube,
The tube
A thin-walled portion covering the radially outer side of the heating coil and the joint,
A glow plug characterized by having a thick portion that covers at least a part of the control coil in the radial direction and has a thickness greater in the radial direction than the thickness in the radial direction of the thin portion. The control coil is located at the front end side of the spiral portion and extends in the axial direction, and the control coil is extended at the front end portion of the heat generating coil and the joining portion. And
The glow plug according to claim 1, wherein a tip of the thick part is opposed to the spiral part.   The glow plug according to claim 1 or 2, wherein a difference between a radial thickness of the thick portion and a radial thickness of the thin portion is 0.05 to 0.15 mm.   The glow plug according to any one of claims 1 to 3, wherein an inner diameter of the thick portion is smaller than an inner diameter of the thin portion.   The glow plug according to claim 4, wherein an outer diameter of the control coil is smaller than an outer diameter of the heating coil. The glow plug according to any one of claims 1 to 5, wherein the glow plug is attached to an attachment hole formed in a cylinder head in a state in which a tip portion of the tube projects into a combustion chamber of a diesel engine. The mounting structure of
A glow plug mounting structure in which the glow plug is mounted such that at least a part of the control coil is disposed in the mounting hole and the thick portion is disposed in the mounting hole.   When the glow plug is attached to the attachment hole of the cylinder head, the shortest distance between the tip of the thick part and the opening edge of the attachment hole on the combustion chamber side is 10 mm when viewed along the axial direction. The glow plug mounting structure according to claim 6, wherein the glow plug mounting structure is arranged as follows.

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