JP5207309B2 - Spark plug - Google Patents

Description

  The present invention relates to a spark plug used for an internal combustion engine or the like.

  In recent years, the spark plug has been required to reduce the occupied volume when attached to the engine head. In order to satisfy this requirement, measures are taken such as reducing the outer diameter of the spark plug or increasing the axial length of the screw portion on the outer peripheral surface to reduce the occupied volume of the spark plug in the engine head. .

JP 2008-78059 A

  In order to reduce the outer diameter of the spark plug, it is necessary to secure a certain thickness of the insulator in order to maintain the withstand voltage performance. However, simply reducing the wall thickness of the metal shell decreases the mechanical strength of the metal shell, so when the spark plug is attached to the engine head, the screw neck portion adjacent to the screw portion of the metal shell is the conventional spark plug. It tends to be easily stretched in the axial direction compared to. For this reason, the press-contact state between the step formed on the tip of the insulator and the end formed on the inner peripheral surface of the metal shell is loosened, and heat conduction from the insulator to the metal shell is poor. It is expected to be.

  In addition, a spark plug having a structure in which the insulator is held in the metal shell by crimping the rear end side of the metal shell while the stepped portion of the front end of the insulator is supported on the shelf of the metal shell via a packing. In this case, as the axial length of the screw portion for attachment to the engine head becomes longer, the press-contact portion between the step at the tip of the insulator and the shelf of the metal shell, and the addition of the metal shell and the insulator. There is a tendency that the distance between the fastening portions becomes longer. When a spark plug having such a structure is heated by being exposed to combustion gas, generally, the linear expansion coefficient of the metal shell is 3 ppm / ° C. or more larger than the linear expansion coefficient of the insulator. The thermal expansion is greater than that of the insulator. For this reason, even in a spark plug in which the axial length of the threaded portion is long, the pressure contact state between the step at the tip of the insulator and the shelf of the metal shell is loosened, and the heat from the insulator to the metal shell is reduced. It is expected that conduction will deteriorate.

  An object of the present invention has been made in view of the above problems, and an object of the present invention is to provide a spark plug configured to efficiently dissipate heat received by an insulator to a metal shell.

The above object of the present invention is achieved by the following configurations.
(1) a central electrode extending in the axial direction;
A cylindrical insulator holding the center electrode on its tip side;
A cylindrical metal shell that accommodates a part of the insulator while maintaining airtightness with the insulator;
A ground electrode disposed so as to form a spark discharge gap with the center electrode;
Heat dissipation that is coupled to a portion of the insulator that is closer to the distal end side in the axial direction than the hermetic holding portion with the metal shell by an interference fit and forms a heat dissipation path by connecting the insulator and the metal shell. A spark plug comprising a member,
The metal shell protrudes radially inward from the inner peripheral surface thereof, and has a shelf portion having a flat surface substantially parallel to the radial direction on the tip end side in the axial direction.
A support member that supports the heat radiating member in the axial direction with the rear end surface of the heat radiating member in contact with the flat surface of the shelf is fastened on the inner peripheral surface of the metal shell. A spark plug characterized by being joined by a screw.

(2) The spark plug according to (1), wherein the airtight holding portion between the metal shell and the insulator has a caulking structure.

(3) The spark plug according to (1), wherein the airtight holding portion between the metal shell and the insulator has a press-fit structure.

(4) Any of (1) to (3) above, wherein a frictional force between the metal shell and the support member is larger than a frictional force between the insulator and the heat dissipation member. The spark plug according to item 1.

  According to the configuration of (1), the heat dissipating member is coupled to the insulator by an interference fit, and is supported in the axial direction by the support member in contact with the shelf of the metal shell. The support member is coupled to the metal shell by an interference fit. For this reason, even if the spark plug is heated, the pressure contact state between the heat radiating member and the shelf of the metal shell can be maintained, so that the heat received by the insulator is efficiently radiated to the metal shell via the heat radiating member. be able to.

  In addition, since the heat radiating member is supported on a flat surface substantially parallel to the radial direction in the shelf of the metal shell, the heat radiating member receives a force inward in the radial direction when the support member is press-fitted and is reduced in diameter. There is nothing. When the surface on the front end side of the shelf portion is a tapered surface having a small diameter toward the rear end side, when the support member is press-fitted and the heat dissipation member is pressed against the taper surface, the heat dissipation member is radially inward. There is a risk that the diameter of the insulator is reduced due to the force, and the insulator is cracked. However, since the heat radiating member is supported on a flat surface substantially parallel to the radial direction of the shelf, there is no fear as described above, and it is possible to prevent the insulator from being damaged due to the shelf.

  According to the configuration of (2), the airtightness between the metal shell and the insulator can be ensured by the caulking structure.

  According to the configuration of (3), the airtightness between the metal shell and the insulator can be ensured by the press-fitting structure.

  According to the configuration of (4), since the frictional force between the metal shell and the support member is set larger than the frictional force between the insulator and the heat radiating member, the spark plug is heated or the like. When the insulator expands and contracts in the axial direction relative to the metal shell, displacement in the axial direction occurs between the insulator and the heat radiating member, and no displacement occurs between the metal shell and the support member. For this reason, the press-contact state of the heat radiating member and the shelf of the metallic shell is maintained. In addition, since the insulator and the heat dissipation member are coupled by an interference fit, even if axial displacement occurs between the insulator and the heat dissipation member, the heat dissipation from the insulator to the heat dissipation member does not change. . Therefore, even if the insulator expands and contracts in the axial direction relative to the metal shell, the heat received by the insulator can be efficiently radiated to the metal shell via the heat dissipation member.

  According to the structure of the spark plug according to the present invention, the heat radiating member is coupled to the insulator by an interference fit, and is supported in the axial direction by the support member in contact with the shelf of the metal shell. The support member is coupled to the metal shell by an interference fit. Therefore, the heat received by the insulator when the spark plug is heated can be efficiently radiated to the metal shell via the heat radiating member.

  In addition, the airtightness between the metal shell and the insulator is ensured by a caulking structure or a press-fitting structure, and combustion gas leakage can be prevented.

  Furthermore, since the frictional force between the metal shell and the support member is set larger than the frictional force between the insulator and the heat dissipation member, the insulator can be expanded and contracted in the axial direction with respect to the metal shell. The pressure contact state between the heat dissipation member and the metal shell shelf is maintained, and the pressure contact state between the heat dissipation member and the metal shell shelf does not loosen. Therefore, heat is radiated stably from the insulator to the metal shell via the heat radiating member.

It is sectional drawing which shows 1st Embodiment of the spark plug which concerns on this invention. It is an expanded sectional view of the important section showing the tip side composition of a spark plug. It is a partially cutaway perspective view which shows the structure of a heat radiating member and a supporting member. It is an expanded sectional view of the principal part which shows the rear end side structure of a spark plug. It is sectional drawing which shows 2nd Embodiment of the spark plug which concerns on this invention. It is an expanded sectional view of the principal part which shows the rear end side structure of a spark plug.

  Hereinafter, preferred embodiments of a spark plug according to the present invention will be described in detail with reference to the drawings.

First Embodiment FIG. 1 is a cross-sectional view showing the overall structure of a spark plug according to the present invention, FIG. 2 is an enlarged cross-sectional view showing the structure of the main part of the tip side of the spark plug, and FIG. FIG. 4 is an enlarged cross-sectional view showing a main configuration of the rear end side of the spark plug.

  The spark plug 1 shown in the first embodiment is attached to the engine head A as shown in FIG. The spark plug 1 is attached with the seating surface 20, which is the tip side surface of the gas seal portion 23, facing the attachment surface portion B of the engine head A. In the description of the present specification, the upper side of FIG.

  The spark plug 1 includes a cylindrical metal shell 2, a cylindrical insulator 3 that is fitted into the metal shell 2, and its tip 3 a is exposed from the tip 2 a of the metal shell 2, and the insulator 3. A central electrode 4 disposed in the insulator 3 so that the tip 4a of the tip 4a is exposed from the tip 3a, a heat dissipating member 5 which is tightly coupled to the insulator 3, and the insulator 3 and the main body A support member 6 that supports the heat radiating member 5 in the axial direction by being tightly fitted and coupled to the inner peripheral surface of the metal shell 2 from a gap E formed between the metal shell 2 and the tip 2a of the metal shell 2 is fixed. The ground electrode 14 and the like.

  In addition, the front end side structure of the spark plug 1 including the center electrode 4 and the heat dissipation member 5 will be described in detail later with reference to FIGS. 2 and 3.

  The fixing structure of the metal shell 2 and the insulator 3 will be described in detail later with reference to FIG.

  The metal shell 2 is made of carbon steel or the like, and the surface thereof is galvanized as necessary. The hardness of the metal shell 2 is set in the range of 180 to 500 Hv, preferably in the range of 300 to 450 Hv. A male screw (not shown) is formed on the outer peripheral surface 2b on the front end side of the metal shell 2, and a female screw is formed on the inner peripheral surface a of the mounting hole opened in the engine head A. The spark plug 1 is fixed to the head A.

  A gas seal portion 23 protruding outward in the radial direction is formed on the rear side of the metal shell 2, and a gasket 7 is disposed on the front side of the gas seal portion 23. The contact surface of the engine head A that contacts the gasket 7 is the mounting surface portion B.

  The gas seal portion 23 has a circular shaft cross-sectional shape, the tool engagement portion 25 on the rear side of the gas seal portion 23 has a hexagonal cross-sectional shape, and a tool is used to fix the spark plug 1 to the engine head A. The spark plug 1 is screwed into the engine head A by engaging a mounting tool with the engaging portion 25. A press-fit portion 2 g is formed on the rear side of the tool engaging portion 25.

The insulator 3 is made of a ceramic fired body such as alumina, and a through hole 8 is formed in the axial direction in the inside thereof, and a terminal fitting 9 is provided at the rear end side of the through hole 8 at the rear end portion 9a. It is inserted and fixed with the exposed. Further, the distal end side of the terminal fitting 9 is electrically connected to the center electrode 4 through a conductive glass seal 11a, a resistor 12, and a conductive glass seal 11b.
A copper core 4 b is provided in the center electrode 4.

  The overall structure of the spark plug 1 has been described above. Next, the configuration of the tip side of the spark plug 1 will be described with reference to FIGS.

  As shown in FIG. 2, a small diameter portion 3 b is formed at the distal end portion of the insulator 3, and the gap between the outer peripheral surface of the small diameter portion 3 b and the inner peripheral surface of the opening portion 2 d formed at the distal end portion of the metal shell 2. A gap E is formed. The small-diameter portion 3b of the insulator 3 has a generally tapered shape by forming a tapered surface in part, but the interference fit coupling position of the heat dissipating member 5 is not formed on the tapered surface. The annular heat radiating member 5 shown in FIGS. 2 and 3 is coupled to the small diameter portion 3b by an interference fit. As the interference fit, press-fitting, shrink fitting, and cold fitting can be employed.

  The heat radiating member 5 and the support member 6 are manufactured as separate members from the metal shell 2 and the insulator 3, and both the heat radiating member 5 and the support member 6 are formed in an annular shape as shown in FIG. . The inner diameter d1 of the heat dissipating member 5 and the outer diameter d11 of the insulator 3 at the interference fit engagement position of the heat dissipating member 5 are formed as d1 <d11. The heat dissipating member 5 is fastened to the insulator 3 by this diameter difference. Fit, for example, by press fitting.

  The support member 6 is formed in an annular shape as shown in FIG. 3, and the outer diameter d2 and the inner diameter d22 of the metal shell 2 are formed as d2> d22. If the support member 6 is fastened to the metal shell 2 due to this diameter difference, Therefore, for example, they are connected by press-fitting.

  The support member 6 is preferably made of the same material as the metal shell 2. If the support member 6 and the metal shell 2 are made of the same material, the linear expansion coefficient is the same. Therefore, even when the spark plug 1 is heated, the coupling force due to the diameter difference between the support member 6 and the metal shell 2 is maintained. Will be.

  Further, the outer diameter d21 of the heat dissipating member 5 and the inner diameter d22 of the metal shell 2 are formed as d21 <d22. Is formed. Further, the inner diameter d31 of the support member 6 and the outer diameter d11 of the insulator 3 are formed such that d31> d11, and due to this diameter difference, a gap e2 is formed between the outer peripheral surface of the insulator 3 and the inner peripheral surface of the support member 6. Is formed.

  The heat radiating member 5 is manufactured using a metal having a hardness of less than 250 Hv and a linear expansion coefficient of 8 to 20 ppm / ° C., preferably 10 to 16 ppm / ° C.

  When the heat radiating member 5 is fastened to the insulator 3 and is joined by press-fitting, for example, the insulator 3 is assembled to the metal shell 2, and then heat is radiated from the gap E shown in FIG. 2 to the small diameter portion 3b of the insulator 3. The member 5 is fitted and press-fit as it is. Then, when the rear end portion 5a of the heat radiating member 5 comes into contact with the shelf portion 2e formed on the metal shell 2, the press-fitting is stopped. Here, the surface of the shelf 2e on the tip side is formed as a flat surface substantially parallel to the radial direction.

  Next, the support member 6 is press-fitted from the gap E. When the rear end portion 6a of the support member 6 comes into contact with the front end portion 5b of the heat-dissipating member 5 that has been press-fitted before, the press-fitting is impossible. Stop press-fitting.

  By press-fitting the heat radiating member 5 and the support member 6 from the gap E as described above, the inner peripheral surface of the heat radiating member 5 is pressed into contact with the outer peripheral surface of the insulator 3, and the rear end portion 5a is a shelf portion of the metal shell 2. 2e. Further, the outer peripheral surface of the support member 6 comes into pressure contact with the inner peripheral surface of the metal shell 2, and the rear end portion 6 a comes into pressure contact with the front end portion 5 b of the heat radiating member 5.

  Thus, the heat radiating member 5 is coupled to the insulator 3 by an interference fit, and is supported in the axial direction while being in contact with the shelf 2e of the metal shell 2 by the support member 6, and the support member 6 Is coupled to the metal shell 2 by an interference fit, so that even if the spark plug 1 is heated, the heat radiation member 5 and the shelf 2e of the metal shell 2 can be kept in pressure contact with each other. The heat received by can be efficiently radiated to the metal shell 2 through the heat radiating member 5.

  Further, since the heat radiating member 5 is supported on a flat surface substantially parallel to the radial direction of the shelf 2e of the metal shell 2, the heat radiating member 5 exerts a force inward in the radial direction when the support member 6 is press-fitted. There is no reduction in diameter. When the surface on the front end side of the shelf 2e is a tapered surface having a smaller diameter toward the rear end side, when the support member 6 is press-fitted and the heat radiating member 5 is pressed against the taper surface, the heat radiating member 5 is in the radial direction. There is a possibility that the diameter of the insulator 3 is reduced due to the inward force, and the insulator 3 is cracked. However, since the heat radiating member 5 is supported on a flat surface substantially parallel to the radial direction of the shelf 2e, there is no fear as described above, and damage to the insulator 3 due to the shelf 2e can be prevented. .

  If F1 is a frictional force (pressure contact) between the heat dissipation member 5 and the insulator 3, and F2 is a frictional force (pressure contact) between the support member 6 and the metal shell 2, F1 <F2. Since the relationship is set, the heat dissipating member 5 is always supported by the support member 6, and it is possible to prevent the press contact state between the heat dissipating member 5 and the shelf 2e from loosening.

  That is, since the frictional force F2 between the metal shell 2 and the support member 6 is set larger than the frictional force F1 between the insulator 3 and the heat radiating member 5, the spark plug 1 is heated or the like, When the insulator 3 expands and contracts in the axial direction with respect to the metal shell 2, an axial displacement occurs between the insulator 3 and the heat radiating member 5, and no displacement occurs between the metal shell 2 and the support member 6. . For this reason, the press-contact state of the heat radiating member 5 and the shelf part 2e of the metal shell 2 is maintained. Therefore, even if the insulator 3 expands and contracts with respect to the metal shell 2 in the axial direction, the heat received by the insulator 3 can be efficiently radiated to the metal shell 2 through the heat radiating member 5.

  Here, in order to satisfy the relationship of F1 <F2, the length in the axial direction at the interference fit portion between the insulator 3 and the heat radiating member 5 is L1, and at the interference fit portion between the support member 6 and the metal shell 2. When the length in the axial direction is L2 (see FIG. 2), L2 is made larger than L1, and the contact area between the support member 6 and the metal shell 2 is larger than the contact area between the insulator 3 and the heat radiating member 5. A method that can be realized by doing this.

Next, heat conduction and heat dissipation action by the heat dissipation member 5 will be described.
When the temperature in the combustion chamber rises due to driving of the engine, the temperature at the ends of the center electrode 4 and the insulator 3 rises with this temperature rise. This heat is conducted to the heat radiating member 5 through the entire pressure contact surface between the insulator 3 and the heat radiating member 5, and is conducted directly to the metal shell 2 through the heat radiating member 5, or through the support member 6. Conducted by

  That is, the heat of the insulator 3 and the like is radiated in the radial direction via the heat radiating member 5. And since the heat radiating member 5 is manufactured as a separate part from the metal shell 2 and the insulator 3 and is assembled by press fitting as described above, bending stress is generated in the insulator due to the influence of the clearance of each member. Accidents such as destruction can be prevented.

  The outer peripheral surface on the front end side of the metal shell 2 is screwed into the engine head A over a wide range as shown in FIG. Therefore, the heat conducted to the metal shell 2 is efficiently dissipated from the metal shell 2 to the engine head A, and various problems caused by overheating as well as overheating of the center electrode 4 and the insulator 3 can be solved.

Next, the configuration of the rear end side of the spark plug 1 will be described.
As shown in FIG. 4, the metal shell 2 is formed so that the portion directly above the attachment surface portion B is thickest, and is formed to be thin in a stepped shape toward the rear end. According to the structure of the metal shell 2, since the metal shell 2 is cylindrical, when the insulator 3 is press-fitted therein, the entire inner peripheral surface on the rear end side of the metal shell 2 is pressed against the outer peripheral surface of the insulator 3. Then, the airtight state is established between the two.

Second Embodiment Next, a second embodiment of the present invention will be described with reference to FIGS. 5 is a cross-sectional view showing the overall configuration of the spark plug, and FIG. 6 is an enlarged cross-sectional view of the main part showing the configuration on the rear end side. Further, members having the same functions as those of the first embodiment are denoted by the same reference numerals, and redundant description is omitted or simplified.

  The second embodiment relates to the configuration on the rear end side, and the front end side may have the same configuration as that of the first embodiment.

  A gap e is formed between the large-diameter portion 2f constituting the metal shell 2 and the insulator 3, and annular ring members 15 and 16 are fitted into the gap e, and talc (talc) 17 is provided. Is filled. Further, a shelf 18 whose inner diameter gradually decreases toward the distal end side is formed inside the gas seal portion 23, and an annular gap is formed in the inclined gap formed between the shelf 18 and the insulator 3. The plate packing 19 is fitted. The plate packing 19 is galvanized on the surface as necessary.

  In the manufacturing process of the spark plug 1, the rear end portion of the metal shell 2 is crimped radially inward. As a result, the gap between the rear end of the large-diameter portion 2f and the insulator 3 is closed, and the plate packing 19 is sandwiched and deformed between the shelf portion 18 and the insulator 3, and the plate packing 19 is fitted. Airtightly close the gap.

  As a result, the airtightness between the metal shell 2 and the insulator 3 can be improved, and combustion gas leakage can be prevented.

In addition, this invention is not limited to embodiment mentioned above, A deformation | transformation, improvement, etc. are possible suitably. In addition, the material, shape, dimension, numerical value, form, number, arrangement location, and the like of each component in the above-described embodiment are arbitrary and are not limited as long as the present invention can be achieved.
For example, the heat radiating member 5 may be formed in an L-shaped cross section.

DESCRIPTION OF SYMBOLS 1 Spark plug 2 Main metal fitting 3 Insulator 4 Center electrode 5 Heat radiation member 6 Support member 7 Gasket 8 Through-hole 9 Terminal metal fitting 11a, 11b Conductive glass seal 12 Resistor 15, 16 Annular ring member 17 Talc 18 Shelves 19 Plate Packing A Engine head B Mounting surface E Clearance

Claims (4)

A central electrode extending in the axial direction;
A cylindrical insulator holding the center electrode on its tip side;
A cylindrical metal shell that accommodates a part of the insulator while maintaining airtightness with the insulator;
A ground electrode disposed so as to form a spark discharge gap with the center electrode;
Heat dissipation that is coupled to a portion of the insulator that is closer to the distal end side in the axial direction than the hermetic holding portion with the metal shell by an interference fit and forms a heat dissipation path by connecting the insulator and the metal shell. A spark plug comprising a member,
The metal shell protrudes radially inward from the inner peripheral surface thereof, and has a shelf portion having a flat surface substantially parallel to the radial direction on the tip end side in the axial direction.
A support member that supports the heat radiating member in the axial direction with the rear end surface of the heat radiating member in contact with the flat surface of the shelf is fastened on the inner peripheral surface of the metal shell. A spark plug characterized by being joined by a screw.   The spark plug according to claim 1, wherein an airtight holding portion between the metal shell and the insulator has a caulking structure.   The spark plug according to claim 1, wherein an airtight holding portion between the metal shell and the insulator has a press-fit structure.   The spark according to any one of claims 1 to 3, wherein a frictional force between the metal shell and the support member is larger than a frictional force between the insulator and the heat dissipation member. plug.

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