JP2012256493A - Spark plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spark plug capable of restraining horizontal jump and the like of discharge by improving an anti-fouling property.SOLUTION: A spark plug has a center electrode extending in an axial line direction, a cylindrical insulator provided on an outer periphery of the center electrode, and a cylindrical main body metal fitting provided on an outer periphery of the insulator. The insulator has one or more grooves opened outward in a radial direction from the center electrode at its tip. Total of volumes occupied by a space of a groove portion from the tip of the insulator to a bottom of the groove is 1/9 or more and 1 or less to a volume of the insulator at a portion from the tip of the insulator to the bottom of the groove.

Description

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

  Conventionally, a spark plug that is attached to an internal combustion engine such as an automobile engine and used for ignition of the internal combustion engine is known. (For example, refer to Patent Document 1).

  Further, in the plasma type ignition device, a plasma type in which a groove is formed in an insulator that accommodates the center electrode and discharge is generated between the center electrode and the ground electrode through the groove in order to improve ignitability. An ignition device is known (for example, refer to Patent Document 2).

Japanese Patent No. 3702838 JP 2008-311018 A

  In such a spark plug, when the insulation resistance value is reduced due to the contamination of carbon or the like on the insulator, the discharge jumps to the inside of the housing instead of the regular gap between the center electrode and the ground electrode, and normal combustion is possible. Otherwise, engine performance may be reduced. For this reason, it is desirable to improve the fouling resistance so that the lateral discharge of the discharge can be suppressed.

  The present invention has been made in response to the above-described conventional circumstances, and an object of the present invention is to provide a spark plug capable of improving the antifouling property and suppressing the occurrence of a discharge jumping or the like. To do.

One aspect of the spark plug of the present invention is a center electrode extending in the axial direction, a cylindrical insulator provided on the outer periphery of the center electrode, a cylindrical metal shell provided on the outer periphery of the insulator,
The insulator has one or more grooves that open radially outward from the center electrode at the tip of the insulator, and the insulator extends from the tip of the insulator to the bottom of the groove. The total volume occupied by the space of the groove portion in the portion is 1/9 or more and 1 or less with respect to the volume of the insulator in the portion from the tip of the insulator to the bottom of the groove.

  In the spark plug of the present invention, a groove is formed at the tip of the insulator, and the volume of the tip of the insulator is smaller than when there is no groove. As a result, the temperature at the tip of the insulator is increased and carbon and the like are easily combusted, so that the fouling resistance can be improved. If the volume of the tip of the insulator, which is reduced by providing the groove, is too small, the effect of improving the stain resistance is not sufficient. For this reason, the total volume occupied by the groove portion in the portion from the tip of the insulator to the bottom of the groove is 1/9 or more of the volume of the insulator in the portion from the tip of the insulator to the bottom of the groove. It is preferable to do. In addition, if the volume of the tip portion of the insulator, which is reduced by providing the groove, increases too much, the volume of the portion that becomes high temperature decreases and the effect of improving the stain resistance becomes insufficient. The total volume occupied by the space of the groove portion in the portion up to the bottom of the insulator is preferably 1 or less with respect to the volume of the insulator in the portion from the tip of the insulator to the bottom of the groove. Moreover, since the edge increases at the tip end portion of the insulator due to the groove and minute discharge is easily generated, combustion of carbon or the like by the minute discharge is promoted, thereby further improving the fouling resistance.

  In the spark plug, the center electrode has a stepped portion having a small diameter on the front end side of the center electrode, and a distance b from the front end of the insulator to the stepped portion is plus the rear end side of the insulator. As a direction, it can be set as the structure which is 0 <= b <= 1.0mm. By setting it as such a structure, while the temperature of the front-end | tip part of an insulator can be raised and fouling resistance can be improved, heat resistance can be ensured.

In this case, the length H along the axial direction between the stepped portion and the bottom of the groove is:
H ≦ 0.25mm
It is preferable that the configuration be By setting it as such a structure, stain resistance can be improved more.

  ADVANTAGE OF THE INVENTION According to this invention, the spark plug which can suppress stain | pollution | contamination resistance and can suppress generation | occurrence | production of the horizontal jump of discharge etc. can be provided.

The figure which shows the whole schematic structure of the spark plug which concerns on one 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 of a modification.

  Hereinafter, details of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing an overall schematic configuration of a spark plug 100 according to an embodiment of the present invention, and FIG. 2 is an enlarged view showing a main configuration of the spark plug 100. In the following description, the axis O direction of the spark plug 100 is the vertical direction in the drawing, the lower side is the front end side of the spark plug 100, and the upper side is the rear end side.

  As shown in FIG. 1, the spark plug 100 includes a cylindrical metal shell 50 that is made of a metal such as low carbon steel and extends in the direction of the axis O. On the inside of the metal shell 50, an insulator 10 (insulator) 10 is supported. The insulator 10 is made of a ceramic sintered body such as alumina or aluminum nitride and the tip portion 11 is arranged so as to protrude from the end surface of the metal shell 50. ing.

  In the shaft hole 12 of the insulator 10, the center electrode 20 is disposed so that the tip 22 protrudes from the end surface of the insulator 10. The center electrode 20 has a core 23 made of copper or copper alloy for promoting heat dissipation at the center of an electrode base material made of nickel-based alloy such as Inconel 600 and Inconel 601 (both are registered trademarks). Is a bar-shaped electrode embedded.

  The center electrode 20 is held in the shaft hole 12 at the portion where the leg portion 13 of the insulator 10 is formed. The center electrode 20 is connected to the connecting terminal 40 held in the shaft hole 12 in the portion where the rear end side body portion 18 is formed via the seal body 4 and the resistor 3 provided in the shaft hole 12. Is electrically connected. The rear end portion 41 of the connection terminal 40 is exposed from the rear end of the insulator 10, and a high voltage cable (not shown) is connected to the rear end portion 41 via a plug cap (not shown). A voltage is applied.

  The insulator 10 is a cylindrical insulating member formed by firing alumina or the like and having an axial hole 12 in the direction of the axis O. A flange portion 19 having the largest outer diameter is formed substantially at the center in the direction of the axis O, and a rear end side body portion 18 is formed on the rear end side. Further, a distal end side body portion 17 and a leg long portion 13 continuous with the distal end side body portion 17 are formed on the distal end side from the flange portion 19. The long leg portion 13 is reduced in diameter toward the distal end side. As shown in FIG. 2, one or a plurality of grooves 14 are formed at the tip of the insulator 10. The detailed configuration of the groove 14 will be described later.

  As shown in FIG. 1, the metal shell 50 surrounds the flange portion 19, the distal end side body portion 17, and the leg length portion 13 from the rear end side barrel portion 18 in the vicinity of the flange portion 19 of the insulator 10. Holding. The metal shell 50 is formed of a low carbon steel material, and includes a tool engaging portion 51 for engaging a tool such as a hexagon wrench, and a screw portion 52 for screwing into an engine head provided at the upper part of the internal combustion engine. ing.

  In addition, annular ring members 6 and 7 are disposed between the tool engaging portion 51 of the metal shell 50 and the insulator 10 rear end side body portion 18, and further between the ring members 6 and 7. Is filled with talc 9 powder. A caulking portion 53 is formed on the rear end side of the tool engaging portion 51, and by caulking the caulking portion 53, the insulator 10 is brought into the metal shell 50 via the ring members 6, 7 and the talc 9. Is pressed toward the tip side. As a result, the step portion 15 formed between the distal end side body portion 17 and the leg length portion 13 of the insulator 10 is supported by the step portion 56 formed on the inner periphery of the metal shell 50 via the plate packing 80, The metal fitting 50 and the insulator 10 are integrated. The airtightness between the metal shell 50 and the insulator 10 is maintained by the plate packing 80, and the outflow of combustion gas is prevented. A flange 54 is formed in the central portion of the metal shell 50, and a gasket 5 that prevents gas escape from the combustion chamber is fitted into a screw neck 55 between the flange 54 and the screw 52. ing.

  An outer electrode (ground electrode) 30 is fixed to the tip of the metal shell 50 by welding. The outer electrode 30 is configured by the above-described Inconel 600 (trade name), Inconel 601 (trade name), or the like. The outer electrode 30 has a substantially rectangular cross section perpendicular to the longitudinal direction of the outer electrode 30, and has a bent rectangular bar-like outer shape. The base 32 on the base end side in the shape of a square bar is welded to the front end surface 57 on the front end side in the axial direction of the metal shell 50. On the other hand, the tip 31 of the ground electrode 30 opposite to the base 32 is bent so as to face the tip 22 of the center electrode 20. A spark discharge gap is formed between the tip 22 of the center electrode 20 and the portion facing the tip 31 of the ground electrode 30.

  In the spark plug 100 of the present embodiment, as shown in FIG. 2A, a plurality of openings (in the example shown in FIG. 2A) that open radially outward from the center electrode 20 at the tip of the insulator 10. Four) grooves 14 are formed. FIG. 3 shows a configuration example in which eight grooves 14 are provided. The number of the grooves 14 may be one or more.

  Further, as shown in FIG. 2B, a step portion 21 having a small diameter on the tip side (upper side in FIG. 2B) is formed at the tip portion 22 of the center electrode 20, and this step portion. A gap 25 is formed between the outer surface of the center electrode 20 and the inner surface of the insulator 10 on the tip side from 21. By providing the gap 25 between the center electrode 20 and the insulator 10 as described above, a minute discharge is easily generated, and the stain resistance can be improved.

In FIG. 2B, symbol a is the distance (insulator position) from the tip (tip surface) of the metal shell 50 to the tip (tip surface) of the insulator 10, and symbol b is the tip of the insulator 10. The distance from the (tip surface) to the step portion 21 (step portion position), the symbol c is the thickness of the insulator 10, and the symbol H ₁ is the axis between the tip portion (tip surface) of the insulator 10 and the bottom of the groove 14. The length along the direction (groove depth), the symbol H indicates the length (groove depth) along the axial direction between the step portion 21 and the bottom of the groove 14. 2 indicates the width of the groove 14.

  In the spark plug 100 of the present embodiment, the total volume occupied by the space of the groove 14 in the portion from the tip of the insulator 10 to the bottom of the groove 14 is the insulation in the portion from the tip of the insulator 10 to the bottom of the groove 14. It is in the range of 1/9 to 1 with respect to the volume of the insulator 10.

In other words, when the groove 14 is not provided, the volume from the tip of the insulator 10 to the length H ₁ portion is reduced by 10% to 50% by providing the groove 14. By reducing the volume of the tip portion of the insulator 10 as described above, the temperature of the tip portion of the insulator 10 is increased and carbon and the like are easily burned, so that the fouling resistance can be improved. Moreover, since the edge is increased at the tip portion of the insulator 10 due to the groove 14 and micro discharge is easily generated, combustion of carbon or the like due to the micro discharge is also promoted, thereby further improving the fouling resistance. .

  If the volume of the tip portion of the insulator 10 that is reduced by providing the groove 14 as described above is too small, the effect of improving the stain resistance is not sufficient. Further, if the volume of the tip portion of the insulator 10 that is reduced by providing the groove 14 is excessively large, the volume of the portion that becomes high temperature is decreased, and the effect of improving the stain resistance is not sufficient. For this reason, in this embodiment, the total volume occupied by the space of the groove 14 in the portion from the tip of the insulator 10 to the bottom of the groove 14 is the insulator in the portion from the tip of the insulator 10 to the bottom of the groove 14. It is in the range of 1/9 to 1 with respect to 10 volumes. That is, the groove 14 is provided so that the volume is reduced in the range of 10% or more and 50% or less compared to the case where the groove 14 is not provided. Thereby, stain resistance can be improved.

  For Examples 1 to 19 and Comparative Examples 1 to 5, a 4-cylinder engine with a displacement of 1.5 liters was used to measure pre-delivery pollution (pre-delivery pollution) with a temperature of -20 ° C. and an operation pattern of JIS D1606. Table 1 below shows the results of the heat resistance test using a single-cylinder engine with a displacement of 0.125 liter and full throttle (WOT (Wide Open Throttle)) at 9000 rpm.

  In the measurement of pre-delivery fouling property, specifically, the engine was started, racing was performed several times, and then the third speed was driven at 35 km / h for 40 seconds, the idling was performed for 90 seconds, and then again at the third speed at 35 km / h. Drive for 2 seconds to stop the engine. Then, complete cooling is performed until the temperature of the cooling water reaches room temperature, the engine is started again, racing is performed several times, and after 15 seconds of driving at a speed of 15 km / h for 15 seconds, the engine is stopped twice for 30 seconds and then again at the first speed. Drive again at 15 km / h for 15 seconds to stop the engine. This series of test patterns was taken as one cycle, and a plurality of cycles were repeatedly tested. Then, at the end of each cycle, the insulation resistance value between the spark plug metal shell and the connection terminal was measured, and the number of cycles when the value was less than 100 MΩ was confirmed.

  In addition, in the evaluation result of the predelivery fouling property shown in Table 1, when the insulation resistance value was 100 MΩ attainment cycle was 7 cycles or more, ◎ 5 cycles or more and less than 7 cycles were ○, less than 5 cycles What was there is indicated by x. In the evaluation results of heat resistance, it is indicated by ◎ when the pre-ignition generation ignition timing is 43 degrees or more (no reduction in heat resistance level), and when the pre-ignition generation ignition timing is less than 43 degrees (heat resistance level reduction).

  Comparative Example 1 shown in Table 1 is a case of a conventional spark plug without the groove 14 at the tip of the insulator 10, and the evaluation result of the predelivery fouling property was x. In Comparative Examples 2 to 5 in which the groove 14 is provided at the tip of the insulator 10, the total volume occupied by the space of the groove 14 in the portion from the tip of the insulator 10 to the bottom of the groove 14 is the insulator 10. 1/19 (Comparative Example 2), 3/2 (Comparative Example 3), 1/19 (Comparative Example 4), 1/39 This is the case of Comparative Example 5), and the evaluation result of these predelivery fouling properties was x.

  On the other hand, the groove 14 is provided at the tip of the insulator 10, and the total volume occupied by the space of the groove 14 in the portion from the tip of the insulator 10 to the bottom of the groove 14 is from the tip of the insulator 10 to the groove 14. In Examples 1 to 19 in which 1/9 or more and 1 or less with respect to the volume of the insulator 10 in the portion up to the bottom part, the evaluation result of the predelivery fouling property was ◎ or ◯. As is clear from the evaluation results of the pre-delivery fouling properties of Examples 1 to 19, the fouling resistance was improved in Examples 1 to 19 as compared with Comparative Examples 1 to 5.

In addition, among Examples 1 to 17, Example 1 in which the evaluation result of the pre-delivery fouling property is ◯ is along the axial direction between the step portion 21 and the bottom portion of the groove 14 shown in FIG. Example 2 where the length H was 0.75 mm, and the evaluation result of predelivery fouling property was ◯ in the same manner. In Example 2, the evaluation result of predelivery fouling property was ◯ when 0.5 mm. Example 6 is a case of -0.5 mm. On the other hand, among Examples 1 to 17, the other Examples 3 to 5 and 7 to 19 in which the evaluation result of the pre-delivery fouling property is ◎ are all axes between the step portion 21 and the bottom of the groove 14. This is a case where the length H along the direction is H ≦ 0.25 mm. Therefore, the length H along the axial direction between the step 21 and the bottom of the groove 14 is:
H ≦ 0.25mm
It is preferable to be within the range.

Moreover, although the heat resistance fall was seen in Example 11, in Example 11, the distance b from the front-end | tip part (tip surface) of the insulator 10 shown to FIG. 1.5 mm. On the other hand, in another example in which a decrease in heat resistance was not observed, the distance b from the tip portion (tip surface) of the insulator 10 to the stepped portion 21 was in a range of 0 ≦ b ≦ 1.0 mm. Yes. Therefore, from the viewpoint of heat resistance, the distance b from the tip portion (tip surface) of the insulator 10 to the stepped portion 21 is:
0 ≦ b ≦ 1.0mm
It is preferable to set it as the range.

Further, the groove width W is not particularly limited, but 0.5 mm ≦ W ≦ 2.5 mm considering the ease of processing and the like.
The groove depth H ₁ is preferably about
0.25 mm ≦ H ₁ ≦ 1.5 mm
It is preferable to set the degree.

  As described above, according to the embodiments and examples of the present invention, it is possible to provide a spark plug that can improve the antifouling property and can suppress the occurrence of a lateral discharge or the like. Note that the present invention is not limited to the above-described embodiments and examples, and it is needless to say that various modifications are possible.

  DESCRIPTION OF SYMBOLS 100 ... Spark plug, 50 ... Metal fitting (housing), 10 ... Insulator, 14 ... Groove, 20 ... Center electrode, 30 ... Outer electrode.

Claims (3)

A central electrode extending in the axial direction;
A cylindrical insulator provided on the outer periphery of the center electrode;
A cylindrical metal shell provided on the outer periphery of the insulator;
A spark plug having
The insulator has at least one groove at its distal end that opens radially outward from the center electrode;
The sum of the volume occupied by the space of the groove portion in the portion from the tip of the insulator to the bottom of the groove is 1 / of the volume of the insulator in the portion from the tip of the insulator to the bottom of the groove. A spark plug characterized by being 9 or more and 1 or less. The spark plug according to claim 1, wherein
The center electrode has a step portion in which the front end side of the center electrode has a small diameter, and the distance b from the front end of the insulator to the step portion is a positive direction on the rear end side of the insulator,
A spark plug, wherein 0 ≦ b ≦ 1.0 mm. The spark plug according to claim 2, wherein
A length H along the axial direction between the step and the bottom of the groove is:
A spark plug, wherein H ≦ 0.25 mm.

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