JP2005166298A - Spark plug - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a spark plug capable of effectively releasing the heat of a ground electrode to an engine head. <P>SOLUTION: When this spark plug 100 is screwed into a plug hole 41 formed in the engine head 40 until a gasket 10 contacts the engine head 40, the other end 61 of the ground electrode 60 and the tip 22 of a center electrode 2 are exposed to the inside of a combustion chamber 42 of an engine. Then, one end 62 of the ground electrode 60 jointed to a joint part 58 of a main fitting 5 is screwed and brought into contact with a female screw of the plug hole 41 of the engine head 40. Thereby, heat applied to the other end 61 of the ground electrode 60 is transmitted to the one end 62 of the ground electrode 60 and directly transmitted to the engine head 40 from the one end 62. Thereby, the other end 61 of the ground electrode 60 is prevented from being set at a high temperature, and excessively early ignition can be prevented. Wear by the heating of the ground electrode 60 can be prevented. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a spark plug for an engine, and more particularly, to a spark plug capable of effectively releasing heat from a ground electrode to an engine head.

  Conventionally, spark plugs for ignition are used in internal combustion engines. In this conventional spark plug, generally, a ground electrode is welded to the end surface (hereinafter referred to as “front end surface”) of the front end of the metal shell that holds the insulator in which the center electrode is inserted. Then, the other end portion of the ground electrode is opposed to the tip portion of the center electrode to form a spark discharge gap. This ground electrode is made of a Ni alloy containing Ni having a high corrosion resistance as a main component or a Fe alloy containing Fe as a main component. The ground electrode is located at the center of the combustion chamber of the engine, and further becomes hot due to spark discharge with the center electrode. In addition, due to higher output, higher efficiency, and long-time continuous operation of the internal combustion engine, the thermal load on the ground electrode of the spark plug is increased, and the ground electrode is easily consumed.

In order to solve this problem, a spark plug with a composite ground electrode with a metal core material with better thermal conductivity than the surface metal layer of the ground electrode is proposed for the purpose of reducing the temperature of the ground electrode. (For example, refer to Patent Document 1). In the spark plug described in Patent Document 1, an alloy containing Ni as a main component is used as a core material of a ground electrode formed in a square bar shape, the core material is covered with Cu, and the outer surface metal layer is coated with Ni. It has a three-layer structure coated with an alloy containing as a main component. In this spark plug, since the ground electrode is welded to the front end surface of the metal shell, the heat applied to the ground electrode is conducted to the metal shell via the welded portion, and further, the threaded portion of the metal shell, etc. It is conducted to the engine head through the contact portion with the engine head. In this spark plug, since the Cu layer is provided inside the ground electrode, there is an effect that heat conduction in the ground electrode is excellent.
JP-A-4-337271

  However, in the spark plug described in Patent Document 1, since the ground electrode is welded to the front end surface of the metal shell, the bonding area between the ground electrode and the metal shell is smaller than the heat receiving area of the ground electrode. For this reason, the heat received by the ground electrode cannot be efficiently conducted to the metal shell, and the ground electrode may become high temperature and may be prematurely ignited before spark discharge. In addition, the ground electrode is heated to be oxidized and corroded, and the ground electrode is consumed quickly.

  Here, there has been proposed a spark plug in which a metallic shell and a ground electrode are integrally manufactured of Ni alloy (for example, Japanese Patent Laid-Open No. 2001-126844). In this spark plug, since the metal shell and the ground electrode are integrally formed of Ni alloy, the work of welding the ground electrode to the tip surface of the metal shell is not required, and pre-ignition is less likely to occur. Moreover, there is an effect that the metal shell and the ground electrode are excellent in heat resistance.

  However, in the above spark plug, the metal shell and the ground electrode are integrally formed of a Ni alloy. However, since the Ni alloy has a lower thermal conductivity than the metal shell, the heat received by the insulator is transmitted through the metal shell to the engine. There was a problem that it was difficult to conduct to the head.

  The present invention has been made in order to solve the above-described problems. The spark plug can effectively release the heat of the ground electrode to the engine head, and can also effectively release the heat of the insulator to the engine head. The purpose is to extend the service life.

In order to solve the above-described problem, the spark plug according to the first aspect of the present invention is an insulator having a center electrode inserted on the tip side of a through hole penetrating in the axial direction, and a metal shell for holding the insulator. And a ground electrode made of Ni alloy containing Ni as a main component or Fe alloy containing Fe as a main component and having the other end joined to the metal shell and the other end facing the center electrode. A spark plug in which a spark discharge gap is formed between the other end and the tip of the center electrode,
When the spark plug is attached to the engine head, the one end portion of the ground electrode constitutes a part of a contact portion that comes into contact with the cylinder head of the metal shell, and makes contact with the engine head. .

  According to a second aspect of the present invention, there is provided a spark plug according to the first aspect of the present invention, in addition to the configuration of the first aspect, the tip of the metallic shell of the outer surface of the one end portion of the ground electrode that contacts the engine head. The area from the surface to the rear end side is a ratio of 1/8 to 1 with respect to the area of the outer surface from the front end surface to the front end side.

  According to a third aspect of the present invention, there is provided the spark plug according to the first or second aspect of the invention, in addition to the configuration of the first or second aspect of the invention, the metal shell of the outer surface of the one end portion of the ground electrode that contacts the engine head. The area from the front end surface to the rear end side is a ratio of 1/2 to 1 with respect to the area of the outer surface from the front end surface to the front end side.

  According to a fourth aspect of the present invention, there is provided a spark plug according to a fourth aspect of the present invention, in addition to the structure of the first aspect of the present invention, wherein the ground electrode comprises a surface metal layer mainly composed of Ni or Fe. Is also characterized in that a metal core made of a metal or alloy having excellent thermal conductivity is enclosed.

  Further, in the spark plug of the invention according to claim 5, in addition to the configuration of the invention according to any of claims 1 to 4, the metal core material is made of at least Cu, Ag, Al, Au or an alloy thereof. It consists of one.

  According to a sixth aspect of the present invention, there is provided a spark plug according to any one of the first to fifth aspects, wherein the discharge portion of the ground electrode includes Pt, Ir, Rh, W, Ru. , Re or an alloy thereof is provided as a noble metal.

  When the spark plug is attached to the engine head, one end portion of the ground electrode is in contact with the engine head, so that the heat of the ground electrode is in contact with the engine head. It is possible to effectively escape from one end to the engine head. Accordingly, premature ignition can be prevented, and the heat resistance of the ground electrode can be improved to prevent corrosion and wear of the ground electrode.

  Further, in the spark plug according to the first aspect of the present invention, when the spark plug is attached to the engine head, one end of the ground electrode constitutes only a part of the contact portion that contacts the cylinder head of the metal shell. Therefore, the heat received by the insulator can be effectively released to the engine head via the metal shell. In addition, since the ground electrode is a Ni alloy containing Ni having a high corrosion resistance as a main component or a Fe alloy containing Fe as a main component, heat can be effectively effectively released to the engine head. Therefore, the present invention can extend the life of the spark plug. The “main component” refers to the most contained component among the contained components.

  In addition to the effect of the invention according to claim 1, the spark plug of the invention according to claim 2 is the rear end side from the front end surface of the metal shell among the outer surfaces of the one end portion of the ground electrode in contact with the engine head. Is 1/8 to 1 with respect to the area of the outer surface from the front end surface to the front end side, so that the heat of the ground electrode is effective on the engine head from the outer surface of the ground electrode contacting the engine head. Thus, the heat of the insulator can be effectively released to the engine head. That is, it is possible to effectively extend the life of the spark plug.

  In addition to the effect of the invention described in claim 1 or 2, the spark plug of the invention described in claim 3 is located behind the front end surface of the metal shell in the outer surface of one end of the ground electrode that contacts the engine head. Since the area on the end side is a ratio of 1/2 to 1 with respect to the area of the outer side surface from the front end surface to the front end side, the heat from the ground electrode contacts the engine head from the outer surface of the ground electrode to the engine head. The heat of the insulator can be effectively released to the engine head. That is, it is possible to effectively extend the life of the spark plug.

  In addition to the effects of the invention according to any one of claims 1 to 3, the spark plug according to the invention described in claim 4 is more conductive in heat than the surface metal layer mainly composed of Ni or Fe. Since the metal core material made of a metal or alloy having excellent properties is enclosed, the heat of the ground electrode can be released to the engine head more efficiently by the metal core material.

  In addition to the effects of the invention according to any one of claims 1 to 4, the spark plug of the invention according to claim 5 is made of at least one of Cu, Ag, Al, Au, or an alloy thereof. Since the metal core material is provided, the heat of the ground electrode can be more efficiently released to the engine head by the metal core material.

  In addition to the effect of the invention according to any one of claims 1 to 5, the spark plug according to the invention described in claim 6 includes Pt, Ir, Rh, W, Ru, Re or Since the noble metal made of at least one of the alloys is provided, it is possible to prevent the discharge portion of the ground electrode from being consumed.

  Hereinafter, a spark plug 100 for an internal combustion engine according to a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a partial cross-sectional view of a spark plug 100 according to a first embodiment of the present invention. As shown in FIG. 1, a spark plug 100 generally includes an insulator 1 that constitutes an insulator, a metal shell 5 that is provided at a substantially central portion in the longitudinal direction of the insulator 1 and holds the insulator 1, and an insulator 1, the center electrode 2 held in the axial direction, one end of the metal shell 5 is welded, the other end is opposed to the tip 22 of the center electrode 2, and the center electrode 2 is at the upper end. The terminal fitting 4 is provided.

  Next, the insulator 1 constituting the insulator of the spark plug 100 will be described. As is well known, the insulator 1 is formed by firing alumina or the like, and a corrugation 11 for increasing the creeping distance is formed at the rear end portion (upper portion in FIG. 1). Further, a leg length portion 13 that is exposed to the combustion chamber of the internal combustion engine is provided at the tip portion (lower portion in FIG. 1) of the insulator 1. Further, a central through hole 12 is formed at the axial center of the insulator 1, and an electrode base material 21 made of Ni (nickel) alloy such as Inconel (trade name) 600 or 601 is provided in the central through hole 12. The center electrode 2 having at least the surface layer portion is held. The distal end portion 22 of the center electrode 2 protrudes from the distal end surface of the insulator 1, and the distal end portion 22 is formed on a plane orthogonal to the axial direction of the central electrode 2. The center electrode 2 is electrically connected to an upper terminal fitting 4 via a seal body 16 and a ceramic resistor 3 provided in the center through hole 12, and a high voltage cable (not shown) is connected to the terminal fitting 4. ) Are connected via a plug cap (not shown) so that a high voltage is applied.

  Next, the metal shell 5 will be described. As shown in FIG. 1, the metal shell 5 holds the insulator 1 and is provided to fix the spark plug 100 to the engine head 40 shown in FIG. 6. The insulator 1 is surrounded and supported by the metal shell 5. Has been. The metal shell 5 is formed of a low carbon steel material (for example, S15C, S20C), and is provided on a hexagonal portion 51 that is a tool engaging portion to which a spark plug wrench (not shown) is fitted, and an upper portion of the internal combustion engine (not shown). And a screw portion 52 that is screwed into the engine head. As an example of the standard of the screw portion 52, M14 or the like is used. In the metal shell 5, the caulking portion 53 is caulked, whereby the insulator 1 is supported on the step portion 56 via the plate packing 8, and the metal shell 5 and the insulator 1 are integrated. In order to complete sealing by caulking, annular ring members 6 and 7 are interposed between the metal shell 5 and the insulator 1, and talc (talc) 9 powder is interposed between the ring members 6 and 7. Filled. A flange 54 is formed at the central portion of the metal shell 5, and the gasket 10 is provided near the rear end side (the upper portion in FIG. 1) of the screw portion 52, that is, on the seating surface 55 of the flange 54. It is inserted.

  Further, the screw portion 52 is formed with a joint portion 58 that is a groove portion having a predetermined width and a predetermined depth parallel to the axial direction of the spark plug 100 from the front end portion 57 to the vicinity of the rear end portion of the screw portion 52 (see FIG. 2), a ground electrode 60 to be described later is joined to the joint 58. In addition, the opposite side dimension of the hexagonal part 51 is 16 mm as an example, and the length from the seating surface 55 of the metal shell 5 to the tip part 57 is 19 mm as an example.

  Next, the ground electrode 60 will be described. The ground electrode 60 is made of a metal having high corrosion resistance. As an example, a Ni alloy such as Inconel (trade name) 600 or 601 is used. The ground electrode 60 is joined to the joint portion 58 on the side surface of the screw portion 52, and has a substantially rectangular cross section orthogonal to the longitudinal direction of the ground electrode 60. The one end portion 62 of the ground electrode 60 has a bent rectangular bar-like outer shape. Is joined to the joint 58 by welding. The other end portion 61 of the ground electrode 60 faces the tip portion 22 of the center electrode 2 in the axial direction of the center electrode 2, and the gap between the facing surfaces of the center electrode 2 and the ground electrode 60 forms a spark discharge gap. ing.

  Next, the manufacturing process of the metal shell 5 will be described with reference to FIGS. 2 is a plan view of the metal shell 5 after cutting, FIG. 3 is a partially cutaway view of the metal shell 5 after cutting, and FIG. 4 is a diagram of the metal shell 5 after the ground electrode 60 is joined. FIG. 5 is a partially cutaway view of the metal shell 5 after the ground electrode 60 is joined. First, the metal shell 5 is formed by cold working a carbon steel bar. In this state, the joint 58 and the screw thread are not yet formed on the metal shell 5. Next, as shown in FIG. 2 and FIG. 3, from the front end portion 57 (corresponding to the “end surface” of the configuration of the present invention) of the side surface (the thread is not yet formed) of the screw portion 52 of the metal shell 5. A joining portion 58 that is a groove portion having a predetermined width and a predetermined depth is formed by cutting to the vicinity of the rear end portion of the screw portion 52 in parallel with the axial direction of the metal shell 5. For example, the width of the joint 58 is slightly larger than the width of the ground electrode 60, and the depth is substantially the same as the thickness of the ground electrode 60. 4 and 5, the ground electrode 60 is joined to the joint 58 by welding (for example, resistance welding, laser welding, arc welding, etc.). Then, the thread rolling process of the thread part 52 is performed. By this thread rolling process, a thread is also formed on the outer surface of the one end 62 of the ground electrode 60. Next, assembly of the insulator 1 and the like, caulking processing of the metal shell 5, bending processing of the tip portion of the ground electrode 60, and the like are performed.

  Next, a state where the spark plug 100 is assembled to the engine head 40 will be described with reference to FIG. FIG. 6 is a longitudinal sectional view showing a state in which the spark plug 100 is assembled to the engine head 40. As shown in FIG. 6, when the spark plug 100 is screwed into the plug hole 41 provided in the engine head 40 and formed with an internal thread until the gasket 10 contacts the engine head 40, the other end 61 of the ground electrode 60 and the center electrode Two end portions 22 are exposed in the combustion chamber 42 of the engine. At this time, the outer surface of the one end 62 of the ground electrode 60 joined to the joint 58 of the metal shell 5 is screwed into contact with the female thread of the plug hole 41 of the engine head 40. Accordingly, the heat applied to the other end portion 61 of the ground electrode 60 is conducted to the one end portion 62 of the ground electrode 60 and is conducted directly from the one end portion 62 to the engine head 40. Therefore, it can prevent that the other end part 61 of the ground electrode 60 becomes high temperature, and can prevent premature ignition. Further, it is possible to prevent the ground electrode 60 from being consumed by heating the ground electrode 60.

Next, with reference to FIG. 7 and Table 1, the results of the desktop heat drawing evaluation test and the actual machine durability evaluation test will be described. FIG. 7 is a plan view of the metal shell 5 as seen from the side surface side of the ground electrode 60 after the ground electrode 60 is joined, and Table 1 is a table showing the results of the evaluation test. In the evaluation test described below, as shown in FIG. 7, the outer side surface (the surface shown in FIG. 7) of the ground electrode 60 is used as a boundary from the front end portion 57 (end surface) of the metal shell 5 to be behind the front end portion 57. The outer side surface on the end side is A part, and the outer side surface on the tip side from the tip part 57 is B part.

  In this desktop heat pulling evaluation test and actual machine durability evaluation test, the outer diameter of the threaded portion 52 of the metal shell 5 is a spark plug of M14, the ground electrode 60 is composed of Inconel (trade name) 600, and the thickness is 1.3 mm. The one with a width of 2.7 mm was used.

First, the desktop heat pulling evaluation test will be described. In this desktop heat pulling evaluation test, the metal shell 5 in which the ground electrode 60 is joined to a water-cooled engine head simulation material made of an aluminum alloy is attached. Next, the tip of the ground electrode 60 is heated with a burner for 30 seconds and then air-cooled. The temperature from the burner heating to the air cooling is measured by a thermocouple attached to the ground electrode 60, and the time until the temperature is lowered to the maximum temperature and room temperature is measured. In the metal shell 5 used in this desktop heat pulling evaluation test, the area of the A part of the ground electrode 60 is 6.5 mm ² (the ratio of the area of the A part / the area of the B part is 1/15, hereinafter “first” The area of the A part of the ground electrode 60 is 12.0 mm ² (the ratio of the area of the A part / the area of the B part is 1/8, hereinafter “second electrode”). The area of the A part of the ground electrode 60 is 48.0 mm ² (the ratio of the area of the A part / the area of the B part is ½, hereinafter “third electrode”). The area of the A portion of the ground electrode 60 is 96.0 mm ² (the ratio of the area of the A portion / the area of the B portion is 1/1, hereinafter “fourth”. and those called.) ground electrode 60 "of the embodiment, the area of the a portion of the ground electrode 60, the ratio of the area of the area / B section of 116.0mm ² (a portion 6/5, (Hereinafter referred to as the “ground electrode 60 of the fifth embodiment”) and the conventional product, the ground electrode 60 is welded to the tip of the threaded portion 52 of the metal shell 5, and the area of the A portion of the ground electrode 60 is Six types of 0 mm ² (the ratio of the area of the A part / the area of the B part is 0, hereinafter referred to as “the ground electrode 60 of the comparative example”) were prepared, and the test was performed under the above conditions.

  First, Table 1 shows the results of the desktop heat drawing evaluation test. In Table 1, “◎” indicates that the maximum temperature is less than 700 ° C., “◯” indicates that the maximum temperature is 700 ° C. or more and less than 800 ° C., and “Δ” indicates that the maximum temperature is 800 ° C. or more and less than 900 ° C. The case where the maximum temperature is 900 ° C. or higher is indicated by “x”. Also, the temperature drop time to room temperature was displayed as “◎” when less than 40 seconds, “◯” when 40 seconds or more and less than 50 seconds, “Δ” when 50 seconds or more and less than 60 seconds, and “X” when 60 seconds or more. As shown in Table 1, in the ground electrode 60 of the first example, both the maximum temperature and the temperature lowering time to room temperature were evaluated as Δ. In the ground electrode 60 of the second example, both the maximum temperature and the temperature lowering time to room temperature were evaluated as good. In the ground electrode 60 of the third example, both the maximum temperature and the temperature lowering time to room temperature were evaluated as ◎. In the ground electrode 60 of the fourth example, both the maximum temperature and the temperature lowering time to room temperature were evaluated as ◎. In the ground electrode 60 of the fifth example, both the maximum temperature and the temperature lowering time to room temperature were evaluated as ◎. In the ground electrode 60 of the comparative example, both the maximum temperature and the temperature lowering time to room temperature were evaluated as x.

  Next, an actual machine durability evaluation test will be described. In this actual machine durability evaluation test, a grounding heat resistance evaluation test and an insulator heat resistance evaluation test were performed. First, the grounding heat resistance evaluation test will be described. In the grounding heat resistance evaluation test, the spark plug having the metal shell 5 to which the ground electrode 60 of the first to fifth embodiments and the comparative example is welded is mounted on a 4-cylinder 2.0 L gasoline engine. It was. The test is performed alternately for 1 minute at 5000 rpm and 1 minute for idling, and after 100 hours, the oxide film thickness of the cross section perpendicular to the longitudinal direction of the ground electrode 60 is measured 3 mm from the tip of the ground electrode 60. did. When grain boundary oxidation is observed, it is included in the film thickness. The results of the grounding heat resistance evaluation test are shown in Table 1. In Table 1, “◯” indicates that the thickness of the oxide film is less than 180 μm, “Δ” indicates that the thickness of the oxide film is 180 μm or more and less than 210 μm, and “x” indicates that the thickness of the oxide film is 210 μm or more. did. As shown in Table 1, in the ground electrode 60 of the first example, the oxide film thickness was evaluated as x. In the ground electrode 60 of the second example, the oxide film thickness was evaluated as Δ. In the ground electrode 60 of the third example, the oxide film thickness was evaluated as o. In the ground electrode 60 of the fourth example, the oxide film thickness was evaluated as ◯. In the ground electrode 60 of the fifth example, the oxide film thickness was evaluated as ○. In the ground electrode 60 of the comparative example, the oxide film thickness was evaluated as x.

  Next, the insulator heat resistance evaluation test will be described. In this insulator heat resistance evaluation test, five spark plugs having the metal shell 5 to which the ground electrode 60 of the first to fifth embodiments and the comparative example are welded are prepared, and a 4-cylinder 1.6L gasoline engine is prepared. The test was carried out by mounting it on. In the test, the ignition advance angle was advanced during full load operation at 5500 rpm, and the average of five ignition advance angles at which pre-ignition occurred was measured. When the ignition advance angle at which this pre-ignition occurred was 40 ° or more, “◯” was given, and when the ignition advance angle at which pre-ignition occurred was less than 40 °, “X” was given. As shown in Table 1, the ground electrode 60 of the first example was evaluated as o. The ground electrode 60 of the second example was evaluated as “good”. The ground electrode 60 of the third example was evaluated as o. The ground electrode 60 of the fourth example was evaluated as “good”. The ground electrode 60 of the fifth example was evaluated as x. The ground electrode 60 of the comparative example was evaluated as “good”.

  Next, with reference to Table 1, the comprehensive evaluation based on the results of the above-mentioned desk heat pulling evaluation test and the actual machine durability evaluation test will be described. In this comprehensive evaluation, even if one of the desktop heat pulling evaluation test and the actual machine durability evaluation test was evaluated as x, it was evaluated as comprehensive x evaluation. , X evaluation and △ evaluation were not evaluated as overall ○ evaluation. As shown in Table 1, the ground electrode 60 of the third embodiment (the area of the A portion of the ground electrode 60 / the value of the area of the B portion is 1/2) and the ground electrode 60 of the fourth embodiment (the ground electrode 60). The ground electrode 60 having an area value of A part / B part area of 1/1) was evaluated as an overall evaluation. Further, the ground electrode 60 of the second example (the ratio of the area of the A portion / the area of the B portion of the ground electrode 60 is 1/8) of the ground electrode 60 was evaluated as an overall Δ evaluation. Therefore, it is preferable that the value of the area of the A part / the area of the B part of the ground electrode 60 is 1/8 to 1/1, and the value of the area of the A part of the ground electrode 60 / the area of the B part is 1/2 to It can be seen that the case of 1/1 is more preferable.

  As described above, in the spark plug 100 according to the first embodiment, when the spark plug 100 is attached to the engine head, the one end 62 of the ground electrode 60 is in contact with the engine. Therefore, heat is directly conducted from the ground electrode 60 to the engine head, the temperature of the ground electrode 60 can be reduced, and high temperature corrosion of the ground electrode 60 can be prevented. Also, premature ignition can be prevented.

  Further, when the spark plug 100 is attached to the engine head, one end portion 62 of the ground electrode 60 made of Ni alloy having a high corrosion resistance or a Fe alloy mainly containing Fe is used as the cylinder head of the metal shell 5. Only a part of the contact portion that comes into contact with. Therefore, the heat received by the insulator 1 can be effectively released to the engine head through the metal shell 5 made of a low carbon steel material. Therefore, the life of the spark plug 100 can be extended.

  Next, the spark plug 101 according to the second embodiment will be described with reference to FIG. FIG. 8 is a partially enlarged sectional view of the metal shell 5 portion. The spark plug 101 of the second embodiment has the same structure as that of the spark plug 100 of the first embodiment. The only difference is the internal structure of the ground electrode 60. Accordingly, only the internal structure of the ground electrode 60 of the spark plug 101 of the second embodiment will be described here, and the description of the other structure will be omitted with the description of the first embodiment described above. . As shown in FIG. 8, the ground electrode 60 of the spark plug 101 according to the second embodiment has a metal core 63 encapsulated therein along the longitudinal direction thereof. The metal core 63 extends from the other end 61 to the one end 62 of the ground electrode 60 inside the ground electrode 60. The material of the metal core 63 is a metal (as an example) that forms the surface metal layer of the ground electrode 60. , Ni alloy), or a metal or alloy (as an example, a metal composed of at least one of Cu, Ag, Al, Au, or an alloy thereof) having better thermal conductivity. By configuring the ground electrode 60 in this way, the thermal conductivity of the ground electrode 60 is increased, the thermal conductivity from the ground electrode 60 to the engine head is improved, and the other end portion 61 of the ground electrode 60 is improved. The temperature can be reduced, and the other end portion 61 of the ground electrode 60 can be prevented from high temperature corrosion. Also, premature ignition can be prevented.

  Next, a spark plug 102 according to a third embodiment will be described with reference to FIG. FIG. 9 is a partially enlarged sectional view of the metal shell 5 portion. The spark plug 102 according to the third embodiment has the same structure as the spark plugs 100 and 101 according to the first and second embodiments, except that the ground electrode facing the center electrode 2 is different. The noble metal tip 68 is joined to the inner surface (discharge portion) of the other end portion 61 of 60. Accordingly, only the noble metal tip 68 provided on the inner surface of the other end portion 61 of the ground electrode 60 will be described here, and the description of the other structure will be described with the description of the first and second embodiments. Omitted. As shown in FIG. 9, a noble metal tip 68 is joined by welding to the inner surface (discharge part) of the other end 61 of the ground electrode 60 of the spark plug 102 of the third embodiment. As an example of the material of the noble metal tip 68, a noble metal made of at least one of Pt, Ir, Rh, W, Ru, Re or an alloy thereof is used. Therefore, the inner surface (discharge portion) of the other end portion 61 of the ground electrode 60 is provided with the noble metal tip 68 that is less likely to be consumed by spark discharge, thereby preventing the discharge portion of the ground electrode 60 from being consumed by spark discharge. it can. The noble metal tip 68 may be provided on the ground electrode 60 where the metal core 63 is not provided.

  Next, a spark plug 103 according to a fourth embodiment will be described with reference to FIG. FIG. 10 is a partial cross-sectional view of the spark plug 103 according to the fourth embodiment. The spark plug 103 according to the fourth embodiment has the same structure as that of the spark plug 100 according to the first embodiment. The difference is the fixing method of the metal shell 5 and the spark plug 103. Therefore, only the fixing method of the metal shell 5 and the spark plug 103 will be described here, and description of other structures will be omitted with the description of the first embodiment.

  As shown in FIG. 10, the metal shell 5 of the spark plug 103 according to the fourth embodiment does not have the screw portion 52, and is instead inserted into the plug hole 41 formed in the engine head 40 without the female screw. A cylindrical insertion portion 59 is formed. Therefore, the metal shell 5 does not have the hexagonal portion 51, but instead the flange portion 54 protrudes greatly. The spark plug 103 is fixed to the engine head 40 by fixing the flange portion 54 with a plug fixing bracket 43 that is fixed to the engine head 40 with a screw 44. In such a spark plug 103 without the threaded portion 52, as in the first embodiment, the ground electrode 60 is joined to the outer surface of the insertion portion 59 of the metal shell 5, and the outer surface of the ground electrode 60 is A part of the contact portion with the engine head 40 can be configured. With such a configuration, heat is directly conducted from the ground electrode 60 to the engine head 40, the temperature of the ground electrode 60 can be reduced, and high temperature corrosion of the ground electrode 60 can be prevented. Also, premature ignition can be prevented.

  Next, a spark plug 104 according to a fifth embodiment will be described with reference to FIG. FIG. 11 is a partial cross-sectional view of the spark plug 104 according to the fifth embodiment. The spark plug 104 of the fifth embodiment has the same structure as that of the spark plug 103 of the fourth embodiment, and the difference is the structure of the ground electrode 60. Therefore, only the structure of the ground electrode 60 will be described here, and the description of the other structure will be omitted by using the description of the fourth embodiment. As shown in FIG. 11, one end 62 of the ground electrode 60 of the spark plug 104 according to the fifth embodiment is formed longer than the spark plug 103 according to the fourth embodiment, and the flange 54 of the metal shell 5 is formed. It is extended to. The upper end portion 64 of the one end portion 62 of the ground electrode 60 is bent toward the radially outer side of the flange portion 54. The ground electrode 60 having this shape is joined to the outer surface of the insertion portion 59 of the metal shell 5 and the contact surface of the flange portion 54 to the engine head 40. Accordingly, since the upper end portion 64 of the one end portion 62 of the ground electrode 60 engages with the outer peripheral portion of the plug hole 41 of the engine head 40, the ground electrode 60 is mainly used in a state where the spark plug 104 is fixed to the engine head 40. It does not peel off and fall off from the outer surface of the insertion part 59 of the metal fitting 5.

  In addition, this invention is not restricted to said embodiment, Various deformation | transformation are possible. For example, in each of the above embodiments, one ground electrode 60 has been described as an example. However, the number of ground electrodes 60 is not necessarily limited to one, and a plurality of ground electrodes 60 such as two, three, etc. The present invention can also be applied to a spark plug provided with an electrode. When there are a plurality of ground electrodes, all of the plurality of ground electrodes may be opposed to the tip 22 of the center electrode 2 in a direction perpendicular to the axial direction of the center electrode 2, or one ground electrode may be the center. The distal end portion 22 of the electrode 2 may be opposed to the axial direction of the central electrode 2, and the remaining ground electrode may be opposed to the distal end portion 22 of the central electrode 2 and a direction perpendicular to the axial direction of the central electrode 2.

  The present invention is not limited to a spark plug for an automobile but can be used for a spark plug for various engines such as a generator.

FIG. 1 is a partial cross-sectional view of a spark plug 100 according to a first embodiment of the present invention. FIG. 2 is a plan view of the metal shell 5 after cutting. FIG. 3 is a partially broken view of the metal shell 5 after cutting. FIG. 4 is a plan view of the metal shell 5 after the ground electrode 60 is joined. FIG. 5 is a partially cutaway view of the metal shell 5 after the ground electrode 60 is joined. FIG. 6 is a longitudinal sectional view showing a state in which the spark plug 100 is assembled to the engine head 40. FIG. 7 is a plan view of the metal shell 5 after the ground electrode 60 is joined. FIG. 8 is a partially enlarged sectional view of the metal shell 5 portion. FIG. 9 is a partially enlarged sectional view of the metal shell 5 portion. FIG. 10 is a partial cross-sectional view of the spark plug 103 according to the fourth embodiment. FIG. 11 is a partial cross-sectional view of the spark plug 104 according to the fifth embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Insulator 2 Center electrode 5 Main body metal fitting 40 Engine head 41 Plug hole 42 Combustion chamber 43 Plug fixing metal fitting 51 Hexagon part 52 Screw part 54 Gutter part 57 Tip part 58 Junction part 60 Ground electrode 61 Other end part 62 One end part 63 Metal core Material 64 Upper end 68 Precious metal tip 100 Spark plug 101 Spark plug 102 Spark plug 103 Spark plug 104 Spark plug

Claims (6)

An insulator in which a center electrode is inserted on the tip side of a through-hole penetrating in the axial direction, a metal shell holding the insulator, one end joined to the metal shell, and the other end facing the center electrode A ground electrode made of Ni alloy containing Ni as a main component or Fe alloy containing Fe as a main component, and forming a spark discharge gap between the other end of the ground electrode and the tip of the center electrode. A spark plug,
When the spark plug is attached to the engine head, the one end portion of the ground electrode constitutes a part of a contact portion that comes into contact with the cylinder head of the metal shell, and makes contact with the engine head. Spark plug.   Of the outer surface of the one end portion of the ground electrode in contact with the engine head, the area from the front end surface to the rear end side of the metal shell is 1/8 of the area of the outer surface from the front end surface to the front end side. The spark plug according to claim 1, wherein the ratio is ˜1.   Of the outer surface of the one end portion of the ground electrode in contact with the engine head, the area from the front end surface to the rear end side of the metal shell is 1/2 of the area of the outer surface from the front end surface to the front end side. The spark plug according to claim 1, wherein the ratio is ˜1.   4. A metal core made of a metal or alloy having better thermal conductivity than a surface metal layer mainly composed of Ni or Fe is enclosed in the ground electrode. A spark plug according to any one of the above.   The spark plug according to any one of claims 1 to 4, wherein the metal core material is made of at least one of Cu, Ag, Al, Au, or an alloy thereof.   The noble metal which consists of at least one of Pt, Ir, Rh, W, Ru, Re or its alloy is provided in the discharge part of the said ground electrode, The any one of Claim 1 thru | or 5 characterized by the above-mentioned. Spark plug.

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