JP3535367B2 - Spark plug with resistor - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spark plug used in an internal combustion engine, and more particularly to a spark plug with a resistor incorporated with a resistor for preventing generation of radio noise.

[0002]

2. Description of the Related Art Conventionally, as a spark plug with a resistor as described above, a terminal fitting is inserted and fixed to one end of a through hole formed in the insulator in the axial direction, and the other plug is also used. Insert and fix the center electrode on the end side,
A structure is known in which a resistor is arranged between the terminal fitting and the center electrode in the through hole. Generally, between the resistor and the terminal metal or between the resistor and the center electrode,
A conductive glass seal layer for electrically connecting the two is arranged, and is manufactured by the following process, for example.

That is, after inserting the center electrode into the through hole of the insulator, the conductive glass powder is filled, then the raw material powder of the resistor composition is filled, and then the conductive glass powder is filled again. As a result, a conductive glass powder layer, a resistor composition powder layer, and another conductive glass powder layer are laminated in the through hole from the center electrode side. And
In this state, the insulator is heated to the glass softening point or higher, and the terminal metal fitting is press-fitted from the side opposite to the center electrode to axially press each layer in the laminated state, thereby compressing and sintering each layer. It becomes the conductive glass seal layer, the resistor and another conductive glass seal layer.

[0004]

By the way, in the method of manufacturing the spark plug containing a resistor, the center electrode is on the lower side, and the conductive glass powder layer, the resistor composition powder layer and another conductive glass are formed on the center electrode. The powder layers were sequentially formed, heated, and then uniaxially compressed from the side opposite to the center electrode to form each glass seal layer and resistor. In this case, in the conductive glass powder layer located at the lowermost side, the pressing force does not sufficiently act due to the friction between the filler on the upper side and the wall surface of the through hole, and the compression or flow after the glass is melted, and thus the glass seal layer. May not be fully sintered. In such a state, carbon in the glass seal layer is burnt out or the metal component is oxidized, and the electrical connection between the resistor and the center electrode through the first conductive glass seal layer becomes incomplete, For example, when a spark plug is used for a long period of time, conduction resistance may increase, which may interfere with normal ignition.

SUMMARY OF THE INVENTION An object of the present invention is to provide a spark plug containing a resistor, which enables a good electrical connection between the resistor and the center electrode with a glass seal layer interposed therebetween.

[0006]

In the spark plug with a resistor of the present invention, a terminal fitting is inserted and fixed at one end of a through hole formed in the insulator in the axial direction. In the same way, the center electrode is inserted and fixed on the other end side, and the resistor is arranged between the terminal metal fitting and the center electrode in the through hole to solve the above problems. Therefore, the axial cross-sectional diameter of the center electrode is set to be smaller than the axial cross-sectional diameter of the resistor, and the side facing the tip of the center electrode is the front side, and the through hole of the insulator has A second portion formed on the rear side of the first portion and having a diameter larger than that of the first portion and accommodating the resistor, and the second portion includes two or more reduced diameter portions with respect to the first portion. It is connected via the connection part and the position corresponding to that connection part Conductive glass seal layer is disposed between the resistor and the center electrode in, and, medium and said connecting portion
It is characterized in that a conductive glass seal layer is arranged in a gap with the core electrode .

In the above structure, two or more reduced diameter portions are provided between the large-diameter second portion in which the resistor is arranged in the through-hole of the insulator and the small-diameter first portion communicating with the center electrode. A connecting portion including the conductive glass sealing layer is formed between the resistor and the center electrode at a position corresponding to the connecting portion, and the conductive glass seal layer is provided in the gap between the connecting portion and the center electrode.
A seal layer was placed. As a result, when the glass seal layer is formed by filling conductive glass powder and heating / compressing the glass powder, the axial cross-sectional area for pressing is reduced by the amount reduced by the reduced diameter portion. Even if the pressing force is lost due to the friction between the object (for example, resistor raw material powder) and the wall surface of the through hole, a sufficient compression force can be secured. If the compressive force can be secured, the sintering of the glass seal layer will proceed sufficiently, and the carbon of the glass seal layer will be less likely to be burned and the metal components will not be oxidized. As a result, the electrical connection between the resistor and the center electrode via the glass seal layer can be easily and favorably ensured, and troubles such as an increase in electrical resistance can be avoided for a long period of time.

Next, an electrode fixing protrusion protruding outward from the outer peripheral surface of the center electrode can be formed at the rear end of the center electrode. Then, the connecting portion is formed with a convex portion receiving surface for receiving the electrode fixing convex portion in such a manner as to be continuous with the rear end edge of the first portion and project outward from the inner peripheral surface of the first portion. can do. In this case, the connecting portion straddles both of the extended surfaces of the convex receiving surface and the outer extending surface of the second portion corresponding to the intersection of the extending surface of the second portion to the convex receiving surface side. It is possible to form a projecting surface that projects inward in shape.

Projections protruding from both of the extension receiving surfaces corresponding to the positions where the outward extension surfaces of the protrusion receiving surfaces and the extension surfaces of the second portion toward the protrusion receiving surface side intersect. If the surface is the protruding surface), the protruding portion reduces the space volume between the side surface of the electrode fixing protrusion and the second portion, so that the compressive force to the conductive glass powder to be filled is reduced. And the effect of the present invention can be remarkably achieved.

Further, by providing such a protrusion, the following other effects can be achieved together. That is, the radio noise prevention effect of the spark plug with a resistor generally tends to improve as the length of the resistor increases. However, when the outer dimensions of the insulator are determined by the spark plug standard and the like, there is a limit to the increase in the length of the resistor. In this case, one method is to move the position of the convex receiving surface toward the tip of the center electrode to extend the axial length of the second portion of the through hole and increase the length of the resistor accordingly. . However,
In this method, the insulator becomes thin at the position of the convex receiving surface, so that the strength of the portion tends to be insufficient.
In this case, in particular, the intersection between the convex portion receiving surface and the second portion may act as a kind of notch, so that a problem in strength is particularly likely to occur.

However, according to the above construction, even if the position of the convex receiving surface is changed to extend the axial length of the second portion, the convex receiving surface and the second portion extend over the respective extension surfaces. Since the projecting portion is formed by, the thinning of the insulator as described above can be avoided, and the crossing portion of each extension surface is also filled with the projecting portion to reduce the notch effect. As a result, it is possible to increase the length of the resistor while ensuring the strength of the insulator sufficiently, and it is possible to realize the resistor-containing spark plug excellent in the radio noise prevention performance.

In the above-described resistor-containing spark plug of the present invention, in the cross section including the central axis of the insulator, from the connection point P between the convex receiving surface and the first portion to the connection point S between the protruding surface and the second portion. Is 1 and the distance in the central axis direction from the connection point P to the rear end edge of the central electrode is L, and 1 / L is preferably 0.5 or more.
When l / L is less than 0.5, the narrow gap portion between the protruding surface and the side surface of the electrode-fixing convex portion of the center electrode becomes excessively long along the center axis direction of the insulator, The conductive glass seal layer may be insufficiently filled in the portion.

The second portion of the through hole can be specifically formed in a substantially cylindrical surface shape, and the protruding surface of the connecting portion is connected to the convex portion receiving surface and is arranged concentrically with the second portion. And a substantially cylindrical main body surface, and a reduced diameter surface connecting the second portion and the main body surface to each other. The connecting portion having the above-described shape is particularly excellent in strength and has an advantage that the withstand voltage of the insulator can be improved.

Further, it is preferable to adjust d / D in the range of 0.5 to 0.95, where D is the inner diameter of the second portion of the through hole and d is the inner diameter of the body surface. When d / D is less than 0.5, the diameter of the connecting portion is excessively reduced, and the gap between the main body surface and the side surface of the convex portion for fixing the electrode is extremely narrowed, which hinders the filling of the conductive glass seal layer. There is. On the other hand, when d / D exceeds 0.95, the diameter reduction of the connection portion becomes insufficient and the effect of increasing the compression force on the conductive glass powder cannot be expected so much.
As a result, the desired effects of the present invention may not be achieved. The above d / D is more preferably 0.7.
It is preferable to adjust in the range of 5 to 0.8.

Further, the reduced diameter surface of the projecting surface can be formed as a taper surface which has an upward slope toward the outside when the insulator is placed upright so that the first portion of the through hole faces downward. In this case, the tapered surface forms a reduced diameter portion at a position close to the end face of the resistor, so that the compression effect of the conductive glass powder is enhanced at that position and the glass between the resistor and the center electrode is increased. The conduction state through the seal layer can be further improved. Further, the angle formed by the second portion of the through hole and the reduced diameter surface becomes an obtuse angle, and the notch effect is relatively unlikely to occur at the connection point between them, which has the advantage of improving the strength of the insulator. In this case, it can be said that it is desirable that the above-mentioned convex portion receiving surface also has the same tapered surface.

It is preferable that the plane perpendicular to the central axis of the through hole is used as a reference plane, and the angle of inclination of the diameter reducing surface with respect to the reference plane is adjusted within the range of 20 to 80 °. When the inclination angle is less than 20 °, the direction of the tapered surface is largely opposed to the direction of compression of the conductive glass powder, which impedes the flow of the powder and makes the formation of the conductive glass seal layer non-uniform, resulting in a resistance. The electrical connection between the body and the central electrode may return and deteriorate. On the other hand, if the inclination angle exceeds 80 °, the length of the tapered surface in the direction of the central axis of the through hole becomes very long, and the desired diameter reduction effect and thus the compression effect of the conductive glass powder cannot be achieved. There is.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Some embodiments of the present invention will be described below with reference to the drawings. A spark plug 100 including a resistor, which is an example of the present invention shown in FIG. 1, includes a tubular metal shell 1, an insulator 2 fitted into the metal shell 1 so that a tip portion thereof projects, and an inside of the insulator 2. One end is connected to the provided center electrode 3 and the metal shell 1, and the center electrode 3
The grounding electrode 4 and the like are arranged so as to face each other, and a spark gap g is formed between the grounding electrode 4 and the center electrode 3. On the other hand, the base end side of the ground electrode 4 is fixed and integrated with the metal shell 1 by welding or the like. Further, the metal shell 1 is formed of carbon steel or the like, and as shown in FIG. 1, a screw portion 12 for attachment to an engine is formed on the outer peripheral surface thereof. The center electrode 3 is made of Ni alloy or the like. Furthermore, the insulator 2 is made of a ceramics sintered body such as alumina.

A through hole 50 is formed in the axial direction of the insulator 2, one end of which has the terminal fitting 13 inserted and fixed thereto, and the other end of which has the center electrode 3 inserted and fixed therein. Has been done. In addition, in the through hole 50, the terminal fitting 1
A resistor 15 is arranged between the center electrode 3 and the center electrode 3.
Both ends of the resistor 15 have conductive glass seal layer 1
The center electrode 3 and the terminal fitting 13 are electrically connected via 6 and 17, respectively. The resistor 15 is formed of a resistor composition obtained by mixing glass powder and conductive material powder (and ceramic powder other than glass if necessary) and sintering the mixture by hot pressing or the like. The conductive glass seal layers 16 and 17 are made of Cu, Fe.
(Or alloys thereof) is composed of glass mixed with metal powder.

Next, the axial cross-sectional diameter of the center electrode 3 is determined by the resistor 15
It is set smaller than the shaft cross-sectional diameter of. Here, with the side facing the tip of the center electrode 3 as the front side, the through hole 50 of the insulator 2 has a first portion 51 through which the center electrode 3 is inserted,
A second portion 52 is formed on the rear side (upper side in the drawing) of the first portion 51 to have a larger diameter than that and accommodates the resistor 15. The second portion 52 is connected to the first portion 51 via a connecting portion 55 including two reduced diameter portions, and the resistor 15 and the center electrode 3 are connected to the connecting portion 55 at a position corresponding to the connecting portion 55. The conductive glass seal layer 16 is disposed between the two.

FIG. 2 is a cross-sectional view of an essential part near the connecting portion 55 by a plane including the central axis O of the insulator 2. That is,
An electrode fixing projection 3a is formed on the rear end of the center electrode 3 so as to project outward from the outer peripheral surface thereof. The electrode fixing projection 3 is formed on the connecting portion 55 of the through hole 50.
The convex receiving surface 20 for receiving a is formed so as to be continuous with the rear end edge of the first portion 51 and project outward from the inner peripheral surface of the first portion 51. Also, the connecting portion 55
Corresponding to the intersection C between the outward extension surface 20a of the convex portion receiving surface 20 and the extension surface 52a of the second portion 52 toward the convex portion receiving surface 20. A projecting portion 60 is formed so as to straddle, and the surface thereof is a projecting surface 53.

In the spark plug 100, the distance from the connection point P between the convex receiving surface 20 and the first portion 51 to the connection point S between the protruding surface 53 and the second portion 52 in the central axis direction is l. L / is the distance from the connection point P to the rear edge of the center electrode 3 in the direction of the central axis, and 1 / L is set to 0.5 or more (desirably 1.0 or more).

Next, the inner peripheral surface of the second portion 52 of the through hole 50 is formed into a substantially cylindrical surface. However, the through hole 50
A fine taper may be attached to the inner peripheral surface of the above for the purpose of facilitating removal of the molding pin during molding. The angle of this taper is, for example, about 1 to 1.2 ° with respect to the angle formed with the central axis O. Also, the connecting portion 55
The protruding surface 53 of the second portion 5 is connected to the convex receiving surface 20.
It has a substantially cylindrical main body surface 53a arranged concentrically with 2, and a reduced diameter surface 53b connecting the main body surface 53a and the second portion 52 to each other. Here, assuming that the inner diameter of the second portion 52 is D and the inner diameter of the main body surface is d, d / D is 0.5 to 0.
It is adjusted in the range of 95 (preferably 0.75 to 0.8).

Further, the diameter-reduced surface 53b of the protruding surface 53 is a tapered surface having an upward slope toward the outside when the insulator 2 is placed upright so that the first portion 51 is on the lower side. Then, with the plane orthogonal to the central axis O of the insulator 2 (through hole 50) as the reference plane Q, the inclination angle θ of the tapered surface with respect to the reference plane Q is 20 to 80 ° (desirably 30).
Is adjusted in the range of up to 50 °. Here, in the connection portion 55, the diameter-reduced surface 53b forms the first-stage diameter-reduced portion, and the convex portion receiving surface 20 forms the second-stage diameter-reduced portion.

In the spark plug 100 containing a resistor, the center electrode 3 and the terminal fitting 13 are assembled to the insulator 2, the resistor 15 and the conductive glass seal layer 16,
Formation with 17 can be performed as follows. First, as shown in FIG. 7A, after inserting the center electrode 3 into the first portion 51 of the through hole 50 of the insulator 2,
As shown in (b), the conductive glass powder H is filled. Then, as shown in (c), the pressing rod 9 is inserted into the through hole 50.
The powder H filled by inserting 0 is pre-compressed to form the first conductive glass powder layer 71. Then, the raw material powder of the resistor composition is filled and pre-compressed in the same manner, and further the conductive glass powder is filled and pre-compressed.
As shown in (d), the first conductive glass powder layer 71, the resistor composition powder layer 72, and the second conductive glass powder layer are provided in the through hole 50 from the center electrode 3 side (lower side). 73 will be in the laminated state.

Then, as shown in FIG. 8 (a), the whole is inserted into the furnace F in this state and the glass softening point is not less than 9
After heating to 00 to 1000 ° C., the terminal fitting 13 is press-fitted into the through hole 50 from the side opposite to the center electrode 3 to axially press the laminated layers 71 to 73. Thereby, as shown in FIG. 8B, the respective layers are compressed and sintered to become the conductive glass seal layer 16, the resistor 15 and the conductive glass seal layer 17, respectively.

The advantages of the spark plug 100 with a resistor according to the present invention will be described below in comparison with a conventional example. First, in the conventional spark plug with resistor,
As shown in FIG. 1 (a), when the second portion 152 and the first portion 151 are formed in the through hole 150 of the insulator 102, these are generally one-step tapered surface (convex receiving surface) 12
0, and the center electrode 10 is connected to the tapered surface 120.
The convex portion 103a for fixing the electrode of No. 3 was supported. However, the connecting portion is formed with the single tapered surface 12 as described above.
When 0 is set, a considerably wide space U is formed between the side surface of the electrode fixing protrusion 103a and the second portion 152. Therefore, the upper layers 72, 73 during the manufacturing process
When the pressing force is reduced by the friction between the wall surface of the through hole 50 (FIG. 7D) and the conductive glass powder filled in the space U, the compressive force tends to be insufficient, so that a good bonding state is achieved. In some cases it could not be formed.

However, in the spark plug 100 containing a resistor of the present invention, as shown in FIG. 2, the convex receiving surface 20 and the extending surface 20 to the outside of the convex receiving surface 20.
a and an extended surface 52 of the second portion 52 toward the convex receiving surface 20 side
Corresponding to the position C where a intersects with the two extended surfaces 20
A protruding portion 60 (a protruding surface 53) is formed so as to straddle a and 52a. As a result, as shown in FIG. 9, the volume of the space between the side surface of the electrode fixing protrusion 3a and the second portion 52, and thus the conductive glass powder layer 71 filled in the space.
Since the pressing cross-sectional area in the axial direction of FIG. 7 is reduced, a sufficient compression force can be secured even when the pressing force is lost due to the friction. As a result, the conductive glass powder that has been in a semi-molten state by heating often flows into a narrow gap between the electrode fixing protrusion 3a of the center electrode 3 and the protrusion 60, for example. As a result, sintering of the glass seal layer progresses sufficiently, burning of carbon in the glass seal layer and oxidation of metal components are less likely to occur, and the glass seal layer 16 is interposed between the resistor 15 and the center electrode 3 in FIG. It is possible to easily and in good condition maintain the conduction state via the.

Returning to FIG. 2, the following effects can be achieved by providing the connecting portion 55 with a protrusion. That is, the radio noise prevention effect of the spark plug with a resistor generally tends to improve as the length of the resistor increases. However, the external dimensions of the insulator cannot generally be freely changed due to the spark plug standard, etc., and there is a limit to the increase in the length of the resistor on the assumption that the same external dimensions of the insulator are maintained. . For example, in FIG.
As shown in (b), the position of the convex receiving surface 120 is moved toward the tip of the center electrode 103 to extend the axial length of the second portion 152 of the through hole 150, and the length of the resistor 115 is correspondingly increased. Can be increased. However, in this method, as shown by the arrow in FIG. 11B, the insulator 102 becomes thin at the position corresponding to the convex receiving surface 120, so that there is a drawback that the strength of the portion tends to be insufficient.
In this case, in particular, the intersection C between the convex receiving surface 120 and the second portion 152 may act as a kind of notch, so that a strength problem is particularly likely to occur.

However, according to the above configuration, as shown in FIG. 2, even if the position of the convex receiving surface 20 is changed in order to extend the axial length of the second portion 52, the convex receiving surface 20 and the second receiving portion 20 are not changed. Since the protruding portion 60 is formed so as to extend over the extension surfaces 20a, 52a of the portion 52, it is possible to avoid the thinning of the insulator 2 as described above, and further, the extension surfaces 20a, 52a.
Since the intersection C of a is embedded in the protrusion 60, the notch effect does not occur. As a result, it is possible to increase the length of the resistor 15 while sufficiently ensuring the strength of the insulator 2, and it is possible to realize a resistor-containing spark plug having excellent radio noise prevention performance.

Incidentally, FIG. 10 shows another example of the insulator 2. A locking protrusion 2e is formed, for example, in the shape of a flange in the axial center of the insulator 2 shown in FIG. 10 (a). Further, in the insulator 2, the side toward the tip of the center electrode 3 (FIG. 1) is the front side, and the rear side of the locking projection 2e is the main body 2b formed with a smaller diameter than this. ing. On the other hand, on the front side of the locking projection 2e, a first shaft portion 2g having a smaller diameter than that and a second shaft portion 2i having a diameter smaller than that of the first shaft portion 2g are formed in this order. There is.
A glaze 2d is applied to the outer peripheral surface of the main body 2b, and a corrugation 2c is formed at the rear end of the outer peripheral surface. The outer peripheral surface of the first shaft portion 2g has a substantially cylindrical shape, and the outer peripheral surface of the second shaft portion 2i has a substantially conical surface shape whose diameter decreases toward the tip.

The through hole 6 of the insulator 2 has a substantially cylindrical first portion 6a into which the center electrode 3 is inserted, and a rear portion (upper side of the drawing) of the first portion 6a having a larger diameter than this. It has a cylindrical second portion 6b. And FIG.
Similarly, the terminal fitting and the resistor are housed in the second portion 6b, and the center electrode is inserted in the first portion 6a. Then, the first portion 6a and the second portion 6 of the through hole 6
b is connected to each other in the first shaft portion 2g of FIG. 10A, and the projection receiving surface 20 and the projection 60 are formed at the connection position.

The dimensions of the insulator 2 will be exemplified below. -Full length L1: 30-75 mm. The length L2 of the first shaft portion 2g: 0 to 30 mm (however, the second shaft portion 2i does not include the connecting portion 2f with the locking protrusion 2e).
Including the connection portion 2h). -The length L3 of the second shaft portion 2i: 2 to 27 mm. -Outer diameter D1 of the main body portion 2b: 9 to 13 mm. -The outer diameter D2 of the locking protrusion 2e is 11 to 16 mm. -Outer diameter D3 of the first shaft portion 2g: 5 to 11 mm. -The outer diameter D4 of the base end portion of the second shaft portion 2i is 3 to 8 mm. -Outer diameter D5 of the tip of the second shaft portion 2i (however, when the outer peripheral edge of the tip surface is rounded or chamfered, in the cross section including the central axis O, the base end position of the rounded portion or the chamfered portion) Outside diameter) at: 2.5 to 7 mm. -Inner diameter D6 of the second portion 6b of the through hole 6 is 2 to 5 mm.・ Inner diameter D7 of the first portion 6a of the through hole 6: 1 to 3.5 m
m. -Thickness t1 of the first shaft portion 2g: 0.5 to 4.5 mm. -Thickness t2 of the base end portion of the second shaft portion 2i (value in the direction orthogonal to the central axis O): 0.3 to 3.5 mm. -Thickness t3 of the tip portion of the second shaft portion 2i ((value in the direction orthogonal to the central axis O; however, when the outer peripheral edge of the tip surface is rounded or chamfered, in the cross section including the central axis O, The wall thickness at the base end position of the rounded portion or the chamfered portion): 0.2 to 3 mm ・ The average wall thickness tA of the second shaft portion 2i ((t1 + t2) / 2):
0.25 to 3.25 mm.

The above-mentioned respective dimensions of the insulator 2 shown in FIG. 10A are, for example, as follows: L1 = about 60 mm, L2 = about 10 mm, L3 = about 14 mm, D1 =
About 11 mm, D2 = about 13 mm, D3 = about 7.3 mm, D
4 = 5.3 mm, D5 = 4.3 mm, D6 = 3.9 mm,
D7 = 2.6mm, t1 = 3.3mm, t2 = 1.4m
m, t3 = 0.9 mm, tA = 1.2 mm.

In the insulator 2 of FIG. 10 (b), the first shaft portion 2g and the second shaft portion 2i each have a slightly larger outer diameter than that shown in FIG. 10 (a). . The dimensions of each part are, for example, as follows: L1 = about 60 mm,
L2 = about 10mm, L3 = about 14mm, D1 = about 11m
m, D2 = about 13 mm, D3 = about 9.2 mm, D4 = 6.
9 mm, D5 = 5.1 mm, D6 = 3.9 mm, D7 =
2.7 mm, t1 = 3.3 mm, t2 = 2.1 mm, t3
= 1.2 mm, tA = 1.7 mm.

A modified example of the spark plug with a resistor according to the present invention will be described below. First, in FIG. 2, in the protruding portion 60, in the direction of the central axis O, the connecting point S between the protruding surface 53 and the second portion 52 (that is, the rear end edge position of the protruding portion 60) is the rear end edge of the center electrode 3. Although it was formed so as to be located rearward of the position, as shown in FIG. 3, the projecting portion 60 is formed so that this positional relationship is reversed in the range where l / L is 0.5 or more. You may do it.

Further, the projecting surface 53 of the projecting portion 60 is formed as a stepped surface which is a combination of the tapered surface (reduced diameter surface) 53b and the raised body surface 53a in FIG. The cross-sectional outline is a smooth convex curve as shown in FIG. 4, a linear (that is, tapered surface) as shown in FIG. 5A, and further shown in FIG. A shape in which the inner diameter of the through hole 50 is continuously reduced from the connection point S toward the connection point P, such as a concave curve shape, may be used. Further, as shown in FIG. 6, the connecting portion 55 may be formed with three or more stages of reduced diameter portions.

[0037]

EXAMPLES The resistor-containing spark plug shown in FIGS. 1 and 2 was manufactured by setting the above-mentioned d, D, θ, l and L to various values. Then, as an accelerated durability test, the temperature of the spark plug was raised to 350 ° C., and JIS B8031:
After discharging for 300 hours by the method described in Section 6.10 and returning to room temperature, the resistance value is measured and the rate of change from the desired resistance value measured in advance before the test is calculated to determine the spark endurance. The resistance change rate was calculated. The above results are shown in Tables 1 and 2.

[0038]

[Table 1]

[0039]

[Table 2]

That is, all the spark plugs within the scope of the present invention have a small rate of change in spark endurance resistance, and in particular, l / L is 0.5 or more and d / D is 0.5 to 0.
It is understood that particularly good results are obtained for those having a value of 95 and θ of 20 ° to 80 °.

[Brief description of drawings]

FIG. 1 is a front sectional view showing an example of a spark plug of the present invention.

FIG. 2 is a front sectional view showing the main part thereof.

FIG. 3 is a front sectional view of an essential part showing a first modified example of the spark plug of the present invention.

FIG. 4 is a front sectional view of an essential part showing a second modified example of the same.

FIG. 5 is a front sectional view of an essential part showing the third and fourth modifications of the same.

FIG. 6 is a front sectional view of an essential part showing a fifth modification of the same.

FIG. 7 is an explanatory view showing a manufacturing process of the spark plug of FIG.

FIG. 8 is an explanatory diagram following FIG. 7.

FIG. 9 is an explanatory view of the action of the protrusion of the spark plug of FIG.

FIG. 10 is a front cross-sectional view showing some other examples of insulators.

FIG. 11 is an explanatory view showing a conventional spark plug together with its problems.

[Explanation of symbols]

1 metal shell 2 insulator 3 Center electrode 3a Electrode fixing protrusion 4 ground electrode 15 resistor 20 convex receiving surface 20a Extension surface of convex receiving surface 100 spark plugs 50,6 through holes 51 First Part 52 Second Part 52a Extended surface of second part C intersection 53 protruding surface 53a Body surface 53b Reduced surface 55 Connection 60 Projection

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01T 13/20

Claims (5)

(57) [Claims] 1. A terminal fitting is inserted and fixed from one end of a through hole formed in the insulator in the axial direction,
Similarly, in the spark plug with a resistor, in which the center electrode is inserted and fixed from the other end side and a resistor is arranged between the terminal fitting and the center electrode in the through hole, The axial cross-sectional diameter is set to be smaller than the axial cross-sectional diameter of the resistor, and the through hole of the insulator has a first portion that communicates with the central electrode, and a first portion that communicates with the central electrode. And a second portion which has a diameter larger than that on the rear side of the portion and accommodates the resistor, and the second portion includes a reduced diameter portion having two or more stages with respect to the first portion. It is connected via a conductive glass seal layer is disposed between the center electrode and the resistor at a position corresponding to the connecting portion, 且
The conductive glass screen in the gap between the connection part and the center electrode.
A spark plug with a resistor, which is characterized by having a ruled layer . 2. A rear end portion of the center electrode is provided with an electrode fixing protrusion protruding outward from an outer peripheral surface thereof, and the connecting portion has a protrusion for receiving the electrode fixing protrusion. The receiving surface is formed so as to be continuous with the rear end edge of the first portion and project outward from the inner peripheral surface of the first portion. 2. The resistor element according to claim 1, wherein a projecting surface projecting inward is formed so as to straddle both of the extended surfaces at a position where a portion of the extended portion extending toward the convex receiving surface side intersects. Spark plug. 3. The cross section including the central axis of the insulator, the central axis from the connection point P between the convex receiving surface and the first portion to the connection point S between the protruding surface and the second portion. The resistor-containing spark plug according to claim 2, wherein 1 / L is 0.5 or more, where L is a distance in a direction. 4. The second portion is formed in a substantially cylindrical surface shape,
The projecting surface of the connecting portion connects the second portion and the body surface to each other, and a substantially cylindrical body surface that is connected to the convex portion receiving surface and is arranged concentrically with the second portion. And a diameter-reduced surface, the inner diameter of the second portion is D, and the inner diameter of the main body surface is d.
The spark plug according to claim 3, wherein / D is adjusted in the range of 0.5 to 0.95. 5. The second portion is formed in a substantially cylindrical surface shape,
The projecting surface of the connecting portion connects the second portion and the body surface to each other, and a substantially cylindrical body surface that is connected to the convex portion receiving surface and is arranged concentrically with the second portion. And a reduced diameter surface, wherein the reduced diameter surface of the protruding surface is formed as a taper surface that has an upward slope toward the outside when the insulator is erected so that the first portion faces downward. The spark plug according to claim 3 or 4, wherein a plane perpendicular to the central axis of the through hole is used as a reference surface, and an inclination angle of the tapered surface with respect to the reference surface is adjusted within a range of 20 to 80 °. .