JP4921039B2 - 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, a spark plug has a structure in which a center electrode, an insulator holding the center electrode, and a metal shell provided with a ground electrode at the tip are supported and fixed in the metal shell. Are known. In such a spark plug, a large-diameter bowl-shaped portion of an insulator is inserted into a cylindrical metal shell, and one end of the metal shell is swaged so that the bowl-shaped portion of the insulator is formed. In general, a structure in which an insulator is supported and fixed in the metal shell by pressing in the axial direction (see, for example, Patent Document 1).

In the spark plug having the above-described structure, it is necessary to form a hook-shaped portion on the insulator in order to crimp and engage the crimping portion of the metal shell. This bowl-shaped part has a large diameter, which hinders a reduction in diameter. Therefore, a spark plug in which an insulator is supported and fixed to a metal shell by shrink fitting or the like has also been proposed (for example, see Patent Document 2).
JP 2002-164147 A JP 2002-158078 A

  Among the above-described conventional techniques, the spark plug in which the metal shell and the insulator are fixed by caulking can secure sufficient fixing strength and high reliability, but it is difficult to reduce the diameter. In addition, the spark plug in which the metal shell and the insulator are fixed by shrink fitting or the like can be reduced in diameter, but high dimensional accuracy such as the inner diameter of the metal shell is required, so that the machining accuracy is maintained at a high level. It is necessary and its material is also limited. For this reason, it is difficult to ensure sufficient reliability of the joint portion, and it has not yet been put into practical use.

  The present invention has been made to solve the above problems. It is an object of the present invention to provide a spark plug that can be reduced in diameter as compared with the prior art and that can easily ensure sufficient reliability of a coupling portion.

The spark plug of the present invention is a spark plug comprising a central electrode extending in the axial direction, a cylindrical insulator holding the central electrode, and a cylindrical metal shell having a ground electrode at the tip. A terminal fitting inserted and fixed in the through hole of the insulator and electrically connected through the central electrode and a conductive glass seal layer, and fitted to the outer peripheral surface of the insulator. In addition, an annular member fixed to the metal shell is provided, and the insulator is held by the metal shell via the ring member, and the ring member is fixed to the metal shell by welding. A welded portion, a press-fit holding portion that is fitted by press-fitting the insulator, and a protruding portion in which an axial rear end of the annular member protrudes radially inward are provided.

The spark plug of the present invention includes an annular member that is fitted to the outer peripheral surface of the insulator and fixed by welding to the metal shell, and the insulator is held by the metal shell via the annular member. Yes. As a result, there is no need to provide the insulator with a large-diameter bowl-shaped portion for engaging the crimped portion of the metal shell as in the prior art, and the spark insulator does not have such a large-diameter portion. The maximum diameter is smaller than the conventional diameter. Further, the annular member is provided with a fitting portion with an insulator that requires a high degree of accuracy and whose material is limited. For this reason, the metal shell is not required to be limited in material or highly accurate, and can be manufactured in the same manner as in the past. Since an annular member that is smaller in size and simple in structure than the metal shell may be manufactured with high accuracy using a predetermined material, sufficient reliability of the coupling portion can be easily ensured. Further, the annular member is provided with a projecting portion whose rear end portion in the axial direction projects radially inward. By providing such a protruding portion, it is possible to prevent a situation in which the insulator is completely removed from the metal shell even if the press-fit holding portion is loosened. The protruding length of this protruding portion is preferably in the range of 0.1 mm to 1 mm. When the protruding length is less than 0.1 mm, the effect of preventing the insulator from coming off is insufficient. On the other hand, if the protruding length is larger than 1 mm, the entire spark plug has a large diameter and cannot satisfy the demand for a small diameter.

  In the spark plug of the present invention, when the annular member is fixed to the metal shell at the welded portion, the welded portion and the press-fit holding portion fitted by press-fitting the insulator are separated from each other in the axial direction. It is preferable to provide the welded portion so as to be positioned at the axial end portion of the press-fit holding portion. As a result, it is possible to prevent the press-fit holding portion from becoming hard due to heat generated by welding.

  The annular member preferably has a Vickers hardness in the range of 180 to 500. If the Vickers hardness is lower than this range, a sufficient fitting strength cannot be obtained and the insulator may come off. On the other hand, if the Vickers hardness is higher than this range, the annular member may be cracked when the insulator is pressed.

  Further, the ratio (A / B) between the axial length A of the press-fit holding part fitted by press-fitting the insulator of the annular member and the radial thickness B of the press-fit holding part is 1 (A / B). The above is preferable. When this ratio is less than 1, stress concentrates on the insulator, and the possibility that the insulator is cracked increases.

  As a specific structure of the annular member, the first annular portion and a second annular portion having an inner diameter and an outer diameter larger than the first annular portion are connected, and the first annular portion is connected. The portion may be fitted to the outer peripheral surface of the insulator, and the second annular portion may be fixed to the metal shell. By adopting such a structure, the fitting portion with respect to the insulator and the welded portion with the metal shell can be separated in the axial direction, and the fitting portion is burned during welding as described above. Can be prevented. In addition, since the structure of the annular member is simple, its manufacture is facilitated.

  The insulator pressed into the annular member is preferably 10.5 mm or less in diameter. Thus, the diameter of the entire spark plug can be reduced by using a small-diameter insulator.

  Moreover, it is preferable that the difference of the thermal expansion coefficient of an annular member and an insulator and the difference of the thermal expansion coefficient of an annular member and a main metal fitting shall be 8 ppm / degrees C or less. When the difference in thermal expansion coefficient is greater than 8 ppm / ° C., there is a possibility that the air tightness in the press-fitting holding part is impaired due to temperature fluctuations. It can be prevented from being damaged.

  According to the spark plug of the present invention, it is possible to provide a spark plug in which the diameter can be reduced as compared with the prior art and sufficient reliability of the coupling portion can be easily secured.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a state before an insulator of a spark plug 100 according to an embodiment of the present invention is assembled to a metal shell, and FIG. 2 shows an enlarged main part after the assembly.

  As shown in FIG. 1, the spark plug 100 includes a substantially cylindrical metal shell 1 and a substantially cylindrical insulator 2 fitted into the metal shell 1 so that the tip portion protrudes. A center electrode 3 is disposed along the axial direction of the central portion in the insulator 2, and the tip of the center electrode 3 is in a state of protruding from the tip surface of the insulator 2. A ground electrode 10 is provided on the front end side of the metal shell 1. One end of the ground electrode 10 is coupled to the metal shell 1, and the other end is folded into an L shape after assembling the metal shell 1 and the insulator 2, whereby the ground electrode 10 and the center electrode 3 are It is arranged so as to face the tip of the center electrode 3 with spark discharge gaps formed at predetermined intervals therebetween. FIG. 1 shows a state before the ground electrode 10 is bent into an L shape.

  The insulator 2 is formed in a substantially cylindrical shape by a ceramic sintered body such as alumina, and has a through-hole through which the center electrode 3 is inserted 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 a plug mounting hole (not shown) of the engine is formed on the outer peripheral surface. A tool engaging portion 8 that engages a tool such as a spanner or a wrench when the spark plug 100 is attached to the plug attachment hole of the engine is provided on the outer peripheral portion on the rear end side from the screw portion 7.

  Between the metal shell 1 and the insulator 2, for example, an annular member 9 formed in an annular shape by the same metal as the metal shell 1, S35C, S45C, SUS430, SUS630, or the like is disposed. As shown in FIG. 2, the annular member 9 includes a first annular portion 95 disposed on the rear end side (upper side in the drawing) and a front end side (lower side in the drawing) from the first annular portion 95. The second annular portion 96 which is arranged and has an inner diameter and an outer diameter larger than the first annular portion 95 is connected by a connecting portion thinner than the annular portions 95 and 96. The first annular portion 95 is fixed to the insulator 2 by press-fitting the insulator 2 into the press-fit holding portion 90, and the second annular portion 96 is attached to the metal shell 1 at the welded portion 91. It is fixed by welding. The metal shell 1, the insulator 2, and the annular member 9 are formed by pressing the insulator 2 into the annular member 9 and then inserting the insulator 2 and the annular member 9 into the metal shell 1. 1 or by welding the annular member 9 to the metal shell 1 and then press-fitting the insulator 2 into the annular member 9. Further, the fixing of the annular member 9 and the metal shell 1 is not limited to joining by welding, but may be by adhesion, brazing, press fitting, or the like.

  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. A taper of a predetermined angle is formed at the end of the large diameter portion 23 on the middle diameter portion 22 side, and serves as a press-in introduction portion 24 for press-fitting into the annular member 9. 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. As the insulator 2, it is preferable to use the insulator having a diameter of the large diameter portion 23 press-fitted into the annular member 9 of 10.5 mm or less. Thus, by using the small-diameter insulator 2, the diameter of the entire spark plug 100 can be reduced.

  As described above, in the present embodiment, since the insulator 2 is press-fitted into the annular member 9 and is fitted and held, the large size for engaging the caulking portion of the metal shell as in the prior art. There is no need to provide a bowl-shaped portion of the diameter in the insulator 2, and the maximum diameter of the spark plug 100 can be reduced. Thereby, the diameter of the plug mounting hole for the spark plug 100 provided in the engine can be reduced, and the degree of freedom in engine design can be increased. In addition, since the annular member 9 is provided with the press-fitting holding portion 90 with the insulator 2 that is required to have a high degree of accuracy and the material of which is limited, the material of the metal shell 1 is limited to a high level of accuracy. Is not required, and can be manufactured in the same manner as in the prior art. Since the annular member 9 that is smaller and simpler in structure than the metal shell 1 may be manufactured with high accuracy using a predetermined material, sufficient reliability of the press-fit portion can be easily ensured.

  Further, by providing the annular member 9 on the rear end side with respect to the tool engaging portion 8, when the tool is engaged with the tool engaging portion 8 and the spark plug 100 is tightened to the engine, the annular member 9 is twisted. Torque and axial force can be prevented from being applied, and the reliability of the coupling portion (fitting and holding) in the annular member 9 can be improved. That is, even if the spark plug 100 is repeatedly attached to and detached from the engine many times, no torsional torque or axial force is applied to the annular member 9, so that the coupling state with the insulator 2 is loosened. There is no. 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, by providing the annular member 9 on the rear end side, the annular member 9 can be fitted on the large diameter portion 23 side of the insulator 2. The large-diameter portion 23 can be made thicker than other parts, and 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 insulator 2 can be prevented from being broken or damaged. Moreover, since it becomes comparatively low temperature when used with an engine, problems such as airtight leakage hardly occur.

  As described above, when the annular member 9 is fixed to the metal shell 1 by the welded portion 91, the welded portion 91 and the press-fit holding portion 90 into which the insulator 2 is press-fitted are separated in the axial direction. It is preferable to provide the welded portion 91 so as to be positioned at the end portion in the axial direction of the press-fit holding portion 90. Accordingly, it is possible to prevent the press-fit holding portion 90 from becoming hard due to heat generated by welding.

  The annular member 9 preferably has a Vickers hardness in the range of 180 to 500. This is based on the result of a test in which a plurality of types of annular members 9 having actually different Vickers hardnesses were manufactured and the insulator 2 was actually press-fitted. As a result of this test, when the Vickers hardness is lower than the above range, for example, when the Vickers hardness is 100, a sufficient fitting strength cannot be obtained, and the insulator 2 may come off. On the other hand, when the Vickers hardness is higher than this range, for example, when the Vickers hardness is 550, the annular member 9 may be cracked when the insulator 2 is press-fitted. On the other hand, when the Vickers hardness was 180, 200, 500, good results were obtained without any breakout or cracking. The results are shown in Table 1.

  Further, the ratio (A / B) between the axial length A of the press-fit holding portion 90 into which the insulator 2 of the annular member 9 shown in FIG. 2 is press-fitted and the thickness B in the radial direction is 1 or more. Is preferred. When this ratio is less than 1, the stress concentrates on the insulator 2 and the possibility that the insulator 2 is cracked increases.

  The difference in thermal expansion coefficient between the annular member 9 and the insulator 2 and the difference in thermal expansion coefficient between the annular member 9 and the metal shell 1 are preferably 8 ppm / ° C. or less. When the difference in thermal expansion coefficient is greater than 8 ppm / ° C., there is a possibility that the air tightness in the press-fit holding unit 90 may be impaired due to temperature fluctuation. However, by setting the difference in thermal expansion coefficient to 8 ppm / ° C. or less, air tightness Can be prevented from being damaged. When the insulator 2 is alumina, the coefficient of thermal expansion is 7.8 ppm / ° C. In this case, for example, carbon steel (12 ppm / ° C.), SUS304 (15 ppm / ° C.), or Invar (4 ppm / ° C.) can be used as the annular member 9. When the carbon steel or SUS304 is used for the annular member 9, any of these can be used for the metal shell 1. On the other hand, when invar is used for the annular member 9, invar can be used for the metal shell 1, but carbon steel and SUS304 cannot be used.

  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 because the lubricant is decomposed by heat treatment and the lubrication effect is lost, and 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. By applying heat to this state, the annular member softens, and plastic deformation causes the contact state to change from a point to a surface contact, and according to two effects for increasing the true contact area of the fitting portion Conceivable. 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, the removal load can be increased compared to the press-fit load.

  Furthermore, the annular member 9 can ensure the required airtightness between the press-fit holding portion 90 and the outside of the insulator 2. Thus, in the spark plug 100, since the airtightness is ensured in the press-fit holding portion 90, it is not necessary to fill talc powder or the like that serves as a seal to ensure airtightness as in the past, For this reason, the structure can be simplified.

  FIG. 3 shows a main configuration of a spark plug 101 according to another embodiment. In this spark plug 101, the insulator 2 is formed with a step portion 25 having a small diameter on the front end side, and the annular member 901 is disposed so that the top portion of the step member 25 is locked. The top of 1 is a crimped portion 12 that is crimped inward. With such a configuration, even if the press-fit holding portion 90 is loosened or the welding condition of the welded portion 91 becomes poor, a situation in which the insulator 2 is completely removed from the metal shell 1 occurs. Can be prevented.

  FIG. 4 shows a main configuration of a spark plug 102 according to another embodiment. In this spark plug 102, a small diameter portion 26 is formed on the rear end side of the insulator 2, and a protruding portion 92 protruding radially inward is provided on the top of the annular member 902. By providing such a protruding portion 92, it is possible to prevent a situation in which the insulator 2 is completely removed from the metal shell 1 even when the press-fit holding portion 90 is loosened. The protruding length of the protruding portion 92 is preferably in the range of 0.1 mm to 1 mm. When the protruding length is less than 0.1 mm, the effect of preventing the insulator 2 from coming off is insufficient. On the other hand, if the protruding length is greater than 1 mm, the entire spark plug 102 becomes larger in diameter and cannot satisfy the demand for smaller diameter.

  FIG. 5 shows a main configuration of a spark plug 103 according to another embodiment. In the spark plug 103, a welded portion 91 is provided on the distal end side of the press fitting holding portion 90 of the annular member 903 and on the distal end side of the tool engaging portion 8 of the metal shell 1. Thus, the position of the welded portion 91 is not limited to the rear end side from the tool engaging portion 8. Furthermore, like the spark plugs 104 to 106 of other embodiments shown in FIGS. 6 to 8, the annular members 904 to 906 may have any shape. However, even in this case, the welded portion 91 and the press-fit holding portion 90 are provided so as to be separated from each other in the axial direction, or the welded portion 91 is provided so as to be positioned at the end in the axial direction of the press-fit holding portion 90. It is preferable. As a result, it is possible to prevent the press-fit holding portion 90 from becoming hard due to welding.

  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.

The figure which shows the state before the press injection of the spark plug which concerns on embodiment of this invention. The figure which expands and shows the principal part structure of the spark plug of FIG. The figure which expands and 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. The figure which expands and 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. The figure which expands and 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.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Metal fitting, 2 ... Insulator, 3 ... Center electrode, 7 ... Screw part, 8 ... Tool engaging part, 9 ... Ring member, 10 ... Ground electrode, 100 ... Spark plug.

Claims (9)

A spark plug comprising a central electrode extending in the axial direction, a cylindrical insulator holding the central electrode, and a cylindrical metal shell having a ground electrode at the tip,
A terminal fitting inserted and fixed in the through hole of the insulator and electrically connected via the central electrode and a conductive glass seal layer;
The insulator is fitted to the outer peripheral surface of the insulator and includes an annular member fixed to the metal shell, and the insulator is held on the metal shell via the annular member,
The annular member includes a welded part fixed by welding to the metal shell, a press-fit holding part fitted by press-fitting the insulator, and an axially rear end of the annular member is radially inward. A spark plug, characterized by comprising a projecting portion projecting into the surface. The spark plug according to claim 1, wherein
The spark plug, wherein the welded portion and the press-fit holding portion are provided apart from each other in the axial direction. The spark plug according to claim 1, wherein
The spark plug according to claim 1, wherein the welded portion is provided so as to be positioned at an end portion in the axial direction of the press-fit holding portion. The spark plug according to claim 2 or 3,
A spark plug characterized in that the annular member has a Vickers hardness in a range of 180 to 500. In the spark plug according to any one of claims 1 to 4 ,
The spark plug according to claim 1, wherein a protrusion length of the protrusion is in a range of 0.1 mm to 1 mm. In the spark plug according to any one of claims 1 to 5 ,
The ratio (A / B) between the axial length A of the press-fit holding part fitted by press-fitting the insulator of the annular member and the radial thickness B of the press-fit holding part is 1 or more. Spark plug characterized by being said. The spark plug according to any one of claims 1 to 6 ,
The annular member has a shape in which a first annular portion and a second annular portion having an inner diameter and an outer diameter larger than those of the first annular portion are connected, and the first annular portion is the insulator. A spark plug, wherein the second annular portion is fixed to the metal shell. The spark plug according to any one of claims 1 to 7 ,
The spark plug, wherein the annular member is fitted to a portion of the insulator having a diameter of 10.5 mm or less. The spark plug according to any one of claims 1 to 8 ,
The spark plug characterized in that a difference in thermal expansion coefficient between the annular member and the insulator and a difference in thermal expansion coefficient between the annular member and the metal shell are 8 ppm / ° C or less.

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