JP4741316B2 - Spark plug - Google Patents

Description

  The present invention relates to a spark plug used for an internal combustion engine such as an automobile engine.

  Conventionally, as a spark plug, a center electrode, an insulator holding the center electrode, and a metal shell having a ground electrode at the tip and a tool engaging portion for engine mounting are insulated in the metal shell. A structure in which an insulator is supported and fixed is known. Such a spark plug has a structure in which the insulator is supported and fixed in the metal shell by inserting the insulator into the cylindrical metal shell and crimping one end of the metal shell. It is general (see, for example, Patent Document 1).

In the spark plug having the above-described structure, it is necessary to form a flange-shaped large diameter portion on the insulator in order to crimp and engage the crimped portion of the metal shell. For this reason, the maximum diameter of the spark plug cannot be reduced. Therefore, a spark plug has been proposed in which an insulator is supported and fixed to a metal shell by welding, adhesive bonding, shrink fitting, or the like (see, for example, Patent Document 2).
JP 2002-164147 A JP 2002-158078 A

  In the above prior art, the spark plug in which the metal shell and the insulator are fixed by caulking can secure a sufficient fixing strength and has high reliability, but it is difficult to reduce the size. In addition, it is possible to reduce the size of a spark plug in which the metal shell and the insulator are fixed by welding, adhesive bonding, shrink fitting, etc., but ensuring vibration resistance and sufficient reliability of the joint. However, since it is difficult, it has not yet been put into practical use.

  The present invention has been made to solve the above problems. SUMMARY OF THE INVENTION An object of the present invention is to provide a spark plug that can be reduced in size as compared with the prior art and that can ensure vibration resistance and sufficient reliability of a coupling portion.

  The spark plug of the present invention is a cylindrical shape having a center electrode extending in the axial direction, a cylindrical insulator holding the center electrode, a ground electrode at the tip, and a tool engaging portion for mounting the engine. A metal plug, wherein the metal shell is fitted to hold the insulator by press-fitting, shrink fitting, or cold fitting at least on the rear end side of the tool engaging portion. It is characterized by comprising a joint.

  In the spark plug of the present invention, the insulator is held in the fitting portion of the metal shell by any one of press fitting, shrink fitting, and cold fitting. This eliminates the need to provide the insulator with a large-diameter portion for engaging the caulking portion of the metal shell as in the prior art, and the large-diameter portion for the insulator to engage the caulking portion of the metal shell. Therefore, the maximum diameter of the spark plug is smaller than the conventional one. That is, the size can be reduced as compared with the conventional case. Further, by providing the fitting portion on the rear end side with respect to the tool engaging portion, when the tool is engaged with the tool engaging portion and the spark plug is fastened to the engine block, the torsion torque or An axial force can be prevented from being applied, and the reliability of the fitting support in the fitting portion can be improved. Further, by supporting the insulator on the rear end side of the metal shell, the vibration frequency when the insulator vibrates can be increased, and the vibration resistance can be improved.

As the means for holding the insulator in the fitting portion, press-fitting can be selected, and in this case, the fitting portion of the insulator is closer to the tip side than the portion in contact with the fitting portion of the insulator. It is preferable to provide a press-fitting introduction part having a diameter smaller than that of the part in contact with . Moreover, when this press-fitting introduction part is made into a taper, it is preferable that the taper makes the taper angle with respect to the said axis line 1-5 degree | times. As a result, it is possible to manufacture in a simpler process and to secure a sufficient removal load. Furthermore, after the insulator is press-fitted into the fitting portion of the metallic shell, heat treatment is performed, so that the removal load can be increased. This is because the contact state of the fitting part is in a point contact state before heat treatment, but the point contact part is locally subjected to high surface pressure, and heat is applied to this state to soften the metal shell material. It is considered that the contact state changes from point to surface contact due to plastic deformation, and the true contact area of the fitting portion increases.

  Further, the spark plug of the present invention is the contact of the spark plug according to any one of the above-described spark plugs, wherein the insulator is pressed into the inner portion of the fitting portion and the insulator is pressed into the rear end side. A portion is formed, and a cutout portion is formed which is not in contact with the insulator in a state where the insulator is press-fitted on the tip side. By making the fitting part formed in the metal shell into such a structure, it is possible to suppress an increase in the press-fitting load necessary for press-fitting and to prevent the insulator from being damaged.

  In the spark plug of the present invention, in any of the above spark plugs, airtightness is maintained between an inner portion of the fitting portion of the metal shell and an outer portion of the insulator. And Thus, the structure for airtight maintenance can be simplified by maintaining airtightness by the fitting part.

  Moreover, in the spark plug of the present invention, in any one of the above spark plugs, in addition to the fitting portion, a second fitting portion in which the metal shell and the insulator are fitted is provided. It is characterized by that. By this, by supporting with a some fitting part, higher support force can be obtained and heat drawing can be assisted. The second fitting portion is preferably provided in a portion other than the screw portion for mounting the engine on the metal shell. Thereby, it can prevent that screw precision falls by fitting.

  Further, the spark plug of the present invention is the spark plug according to any one of the above, wherein the insulator is removed by being engaged with a locking portion formed on the outer periphery of the insulator. It is characterized in that it is provided with a mechanism for preventing the slipping out. In this way, by adopting a configuration provided with a removal prevention mechanism, it is possible to prevent a situation in which the insulator is pulled out of the metallic shell due to the pressure from the inside.

  According to the spark plug of the present invention, it is possible to provide a spark plug that can be reduced in size as compared with the prior art and that can ensure vibration resistance and sufficient reliability of the coupling portion.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a state before the insulator is assembled to the metal shell, and FIG. 2 shows the spark plug according to the embodiment of the present invention after the assembly. The spark plug 100 includes a substantially cylindrical metal shell 1 and a substantially cylindrical insulator 2 that is fitted into the metal shell 1 so that the tip portion protrudes. A central electrode 3 is disposed along the axial direction of the central portion in the insulator 2, and a tip portion of the central electrode 3 protrudes from the insulator 2. And the ground electrode 10 is arrange | positioned so that the front-end | tip part of this center electrode 3 may be opposed. One end of the ground electrode 10 is coupled to the metal shell 1, and a spark discharge gap having a predetermined interval is formed between the ground electrode 10 and the center electrode 3.

  The insulator 2 is formed in a substantially cylindrical shape by a ceramic sintered body such as alumina or aluminum nitride, and has a through-hole for fitting the center electrode 3 along its own axial direction. . The terminal fitting 4 is inserted and fixed on one end side of the through hole, and the center electrode 3 is inserted and fixed on the other end side. A resistor 11 is disposed between the terminal fitting 4 and the center electrode 3 in the through hole. Both ends of the resistor 11 are electrically connected to the center electrode 3 and the terminal fitting 4 through the conductive glass seal layer.

  The metal shell 1 is formed in a cylindrical shape by a metal such as carbon steel or stainless steel, for example, S35C, S45C, SUS430, SUS630, etc., and constitutes a housing of the spark plug 100 and has a distal end side (lower in the figure). A threaded portion 7 for attaching the spark plug 100 to an engine block (not shown) is formed on the outer peripheral surface. A tool engaging portion 8 for engaging a tool such as a spanner or a wrench when the metal shell 1 is attached to the engine block is provided on the outer peripheral portion on the rear end side of the screw portion 7. A fitting portion 9 is provided further on the rear end side than the tool engaging portion 8.

  The fitting portion 9 is for fitting and holding the insulator 2. In this embodiment, the fitting portion 9 is fitted and held in the radial direction by press-fitting the insulator 2. ing. In this manner, by providing the fitting portion 9 on the rear end side with respect to the tool engaging portion 8, the fitting is performed when the tool is engaged with the tool engaging portion 8 and the spark plug 100 is fastened to the engine block. It is possible to prevent torsion torque and axial force from being applied to the joint portion 9 and to improve the reliability of the joint portion (fitting holding) in the fitting portion 9. In other words, even if the spark plug 100 is repeatedly attached to and detached from the engine block many times, no torsion torque or axial force is applied to the fitting portion 9, so that the coupling state with the insulator 2 is loosened. It does not occur. Moreover, by supporting the insulator 2 on the rear end side of the metal shell 1, the vibration frequency when the insulator 2 vibrates can be increased, and the vibration resistance can be improved.

  Further, if the fitting portion 9 as described above is provided, for example, in the portion of the screw portion 7, the screw portion 7 may swell due to the press-fitting of the insulator 2, and the screw accuracy may be reduced. Thus, it can prevent that such a malfunction arises by providing in the back end side rather than the tool engaging part 8. FIG. Furthermore, generally it can be fitted on the large-diameter portion 23 side of the insulator 2 by being provided on the rear end side. Since the large-diameter portion is thick, the breaking load of the insulator 2 is higher than that of the small / medium-diameter portion. Therefore, even if the fitting force is designed to be strong, the burden on the insulator 2 can be reduced. Also, considering use in an engine, it is convenient because it is a relatively low temperature part.

  On the other hand, the insulator 2 is made into the small diameter part 21, the medium diameter part 22, and the large diameter part 23 in order from the front end side. And the taper of a predetermined angle is formed in the end part by the side of the medium diameter part 22 of the large diameter part 23, and the said part is expanded, and it press-fits into the fitting part 9 of the metal shell 1 as shown in FIG. For this purpose, a press-fit introduction section 24 is provided. The taper angle of the press-fit introduction portion 24 is preferably about 1 to 5 degrees, and more preferably about 2 to 4 degrees. This is due to the following reasons.

  That is, as shown in FIG. 4, for example, when the diameter of the large-diameter portion 23 of the insulator 2 is 9.9 mm, the diameter of the tip of the large-diameter portion 23 is 9.7 mm, and the diameter difference is 200 μm, the taper angle Changes the taper length (press-fit introduction portion length). FIG. 5 shows the relationship between the vertical axis as the taper length and the horizontal axis as the taper angle. As shown by the curve described on the lower side of the figure, when the taper angle is less than 1 degree, the taper length is abruptly increased. For this reason, the taper angle is preferably 1 degree or more, and more preferably 2 degrees or more.

  Further, with the vertical axis in FIG. 5 as the fitting allowance after removal, the upper curve in the drawing shows the relationship between the fit allowance after removal and the taper angle. The fitting allowance after removal indicates the difference in diameter (D2-D1) between the outer shape (D1) of the insulator 2 and the inner diameter (D2) of the press-fitted portion 9 when it is once pressed and then withdrawn. In order to obtain a sufficient fitting strength (a predetermined load or more), it is necessary to have a certain level of strength. In order to secure the fitting allowance after the removal, the taper angle is preferably 5 degrees or less, and more preferably 4 degrees or less. From the above, the taper angle is preferably about 1 to 5 degrees, and more preferably about 2 to 4 degrees.

  As described above, in the present embodiment, the insulator 2 is press-fitted into the fitting portion 9 to be fitted and held, so that the caulking portion of the metal shell is engaged as in the conventional case. It is not necessary to provide a large-diameter portion in the insulator 2, and the maximum diameter of the spark plug 100 can be reduced. Thereby, the diameter of the hole for attaching the spark plug 100 provided in the engine block can be reduced, and the degree of freedom in engine design can be increased. In addition to press-fitting, the insulator 2 may be fitted to the fitting portion 9 by shrink fitting, cold fitting, or a combination thereof.

  Moreover, in the spark plug of this embodiment, it is necessary to increase the reliability of the fitting portion, that is, to increase the unloading load. However, the higher the unloading load, the higher the press-fit load. In such a case, the press-fitting load can be reduced while keeping the reliability of the fitting portion high by using a lubricant during press-fitting. In this case, the removal load increases by performing heat treatment after press-fitting. This is due to the two effects that the lubricant is decomposed by heat treatment and the lubrication effect is lost, and that the point contact is changed to the surface contact. As such a lubricant, for example, Paskin M30 (trade name), cellosol (trade name) or the like can be used.

  The heat treatment is preferably performed at a temperature of 300 ° C. for about 15 minutes, for example. When such heat treatment after press-fitting is not performed, the press-fitting load and the removal load are substantially the same. However, by performing the heat treatment as described above, for example, in the case of a spark plug having a fitting portion diameter (outer diameter of the insulator) of 10 mm, an example of data actually measured is as follows. The unloading load at room temperature was 610 kg, and the unloading load at 200 ° C. was 520 kg. For example, in the case of a spark plug having a fitting portion diameter (outer diameter of the insulator) of 8 mm, an example of data actually measured is 157 kg of press-fit load and 357 kg of unloading load at room temperature. The unloading load at ℃ was 276 kg. At the time of this press-fitting, the insulator is press-fitted while supporting the seating surface of the metal shell. Since a ground electrode 10 is joined to the tip of the metal shell by a known method (see FIG. 1), in order to press fit without deforming the ground electrode 10, a seating surface is supported. It is preferable to press-fit.

  Further, as shown in FIG. 3 showing an enlarged cross-sectional structure of the fitting portion 9 of the metal shell 1, the insulator 2 and the insulator 2 in a state where the insulator 2 is completely press-fitted into the inner wall portion of the fitting portion 9. A contact portion 91 that is maintained in a contact state, and provided on the distal end side of the contact portion 91. The inner diameter is set to be larger than that of the contact portion 91, and the insulator 2 is not in contact with the insulator 2 in a state where the insulator 2 is completely press-fitted. An exit 92 is provided that is maintained in contact. When the removal portion 92 is provided in this manner, the leading end portion (mainly the press-fitting introduction portion 24) of the insulator 2 reaches the removal portion 92 at the end of the press-fitting process and is in a non-contact state with the metal shell 1. Thereby, the press-fit load required when press-fitting the insulator 2 into the fitting part 9 can be reduced.

  That is, the leading end portion (mainly the press-fitting introduction portion 24) of the insulator 2 is a portion to which the most frictional force is applied during press-fitting, the surface is rubbed and roughened, and a portion having a larger friction than the other portions. It has become. Then, at the end of the press-fitting process in which the press-fitting load is increased, the large frictional portion is pulled out to the drop-out portion 92, so that the increase in the press-fitting load is alleviated.

  A comparative test was conducted to verify this effect. One is a spark plug of the present invention having a dropout portion 92 shown in FIG. 3, and the other, which is a comparative example, does not have the dropout portion 92 shown in FIG. A spark plug was used. FIG. 8 is a graph showing a comparison between the time required for press-fitting (that is, the degree of press-fitting) on the horizontal axis and the load required for press-fitting on the vertical axis. As shown in FIG. 8, it can be seen that the spark plug of the present invention provided with the removal portion 92 has an effect of alleviating the increase in press-fit load at the end of press-fit.

  Further, the contact portion 91 can ensure the required airtightness between the contact portion 91 and the outside of the insulator 2. When airtightness was measured when a pressure of 1.55 MPa was applied from the inside with the spark plug 100 attached, the leak rate was about 0 ml / min at room temperature and about 1 ml / min at 200 ° C. It was found that airtightness equivalent to or better than spark plugs by caulking was secured. As described above, in the spark plug 100 according to the present embodiment, since the airtightness is ensured in the fitting portion 9, talc powder or the like serving as a seal for securing the airtightness is filled as in the prior art. Therefore, the structure can be simplified.

  FIG. 6 shows a configuration of a main part of a spark plug 110 according to another embodiment. In the spark plug 110, a second fitting portion 95 is provided in addition to the fitting portion 9, and two places are provided. The insulators 2 are held by the metal shell 1 by the fitting portions 9 and 95. By holding the insulator 2 by the plurality of fitting portions in this way, the vibration frequency when the insulator 2 vibrates in the metal shell 1 can be further increased, and the vibration resistance is further improved. Can do. In addition, it is preferable to provide the 2nd fitting part 95 in parts other than the screw part 7 for the engine (engine) attachment of the metal shell 1. Thereby, it can prevent that screw precision falls by fitting.

  FIG. 7 shows a main configuration of a spark plug 120 according to another embodiment. In this spark plug 120, a locking portion 25 made of a stepped portion or a recessed portion is provided in a part of the insulator 2 in the circumferential direction. Further, the metal shell 1 is provided with a drop prevention mechanism 10 composed of a convex portion according to the locking portion 25. Then, after the insulator 2 is press-fitted into the metal shell 1, from the state shown in FIG. 7 (A), the slip-off prevention mechanism 10 is pressed toward the locking portion 25 to be plastically deformed, and the state shown in FIG. 7 (B). Assuming that the protruding portion of the removal preventing mechanism 10 is engaged with the locking portion 25. As a result, even when the fitting force in the fitting portion 9 is reduced, it is possible to prevent a situation in which the insulator 2 is pulled out of the metal shell 1 due to the pressure from the inside. . In addition, it is preferable that the level | step difference or recessed part depth of the latching | locking part 25 shall be about 0.1 mm-1.0 mm. If it is less than 0.1 mm, the convex portion of the drop prevention mechanism 10 is difficult to be caught, and a sufficient drop prevention effect cannot be obtained. On the other hand, if it is larger than 1.0 mm, the diameter of the insulator is reduced. From the viewpoint of reducing the diameter, it is more preferable that the step or recess depth of the locking portion 25 is about 0.1 mm to 0.5 mm.

  In the above, the present invention has been described with reference to the embodiment. However, the present invention is not limited to the above-described embodiment and the like, and it is needless to say that the present invention can be appropriately modified and applied without departing from the gist thereof. For example, in addition to the L-shaped ground electrode 10 described in the present embodiment, a combination of a plurality of ground electrodes, and further, the tip of a metal shell, which is one of the so-called creeping discharge types, also serves as a spark discharge electrode. It may be a type.

  In addition, in this embodiment, although the form which hold | maintains an insulator by making only the part of the back end side rather than the tool engaging part of a metal shell into a fitting part is shown, when attaching a spark plug to an engine, it is by twisting torque. It is good also as a fitting part applied to a tool engaging part in the range which does not remove | deviate or loosen the fitting of an insulator. Moreover, it is preferable that the length of the part which contacts an insulator in a fitting part shall be 1 mm or more. However, if the length is too long, an excessive press-fitting load is required. From the viewpoint of production, it is preferable to set the inner diameter of the fitting portion as the upper limit.

The figure which shows the state before the press injection of the spark plug which concerns on embodiment of this invention. The figure which shows the state after the press injection of the spark plug of FIG. The figure which expands and shows the principal part structure of the spark plug of FIG. The figure for demonstrating the relationship between the taper angle of an introducing | transducing part, and taper length. The graph which shows the relationship between a taper angle, taper length, and the fitting margin after extraction. The figure which shows the principal part structure of the spark plug which concerns on other embodiment. The figure which expands and shows the principal part structure of the spark plug which concerns on other embodiment. FIG. 8 is a graph showing the relationship between the time required for press-fitting and the load required for press-fitting. The figure which expands and shows the principal part structure of the spark plug which concerns on a comparative example.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Metal fitting, 2 ... Insulator, 3 ... Center electrode, 7 ... Screw part, 8 ... Tool engaging part, 9 ... Fitting part, 100 ... Spark plug.

Claims (9)

A center electrode extending in the axial direction, a cylindrical insulator holding the center electrode, and a cylindrical metal shell having a ground electrode at the tip and a tool engaging portion for mounting the engine. Spark plug,
The spark plug is characterized in that the metal shell includes a fitting portion that holds the insulator by any one of press fitting, shrink fitting, and cold fitting at least on the rear end side of the tool engaging portion. The spark plug according to claim 1, wherein
The insulator is held by press-fitting at the fitting portion, and has a diameter smaller than a portion of the insulator that abuts on the fitting portion at a distal end side than a portion that abuts on the fitting portion of the insulator. A spark plug characterized in that a press-fitting introduction part is provided. The spark plug according to claim 2, wherein
A spark plug characterized in that the press-fitting introduction portion is a taper, and a taper angle formed by the taper with respect to the axis is 1 to 5 degrees. The spark plug according to claim 2 or 3,
A spark plug in which at least the fitting portion is heat-treated after the insulator is press-fitted into the fitting portion of the metal shell. In the spark plug according to any one of claims 1 to 4,
A contact portion that is in contact with the insulator in a state where the insulator is pressed into the rear end side is formed in an inner portion of the fitting portion, and the insulator is pressed in the state where the insulator is pressed into the tip side. A spark plug, characterized in that a hollow portion that is not in contact with the insulator is formed. In the spark plug according to any one of claims 1 to 5,
The spark plug is characterized in that airtightness is maintained between an inner portion of the fitting portion of the metal shell and an outer portion of the insulator. In the spark plug according to any one of claims 1 to 6,
In addition to the fitting portion, a spark plug is provided in which a second fitting portion into which the metal shell and the insulator are fitted is provided. The spark plug according to claim 7,
The spark plug is characterized in that the second fitting portion is provided in a portion other than the screw portion for attaching the engine to the metallic shell. In the spark plug according to any one of claims 1 to 8,
A spark plug characterized in that a spark plug is provided on the metal shell and is engaged with a locking portion provided on an outer peripheral portion of the insulator to prevent the insulator from coming off.

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