JP6230348B2 - Spark plug - Google Patents

Description

  The present invention relates to a spark plug.

  The spark plug includes an insulator having a shaft hole, a center electrode provided in the shaft hole of the insulator, a metal shell disposed on the outer periphery of the insulator, and a ground electrode having one end fixed to the tip of the metal shell And comprising. Patent Document 1 discloses a technique in which a core material containing copper is disposed inside a ground electrode in order to improve the thermal conductivity of the ground electrode.

JP 2012-169248 A International Publication No. 2010/026940 JP 2006-228522 A Japanese Patent Laid-Open No. Sho 63-138681

  In general, during operation of an internal combustion engine, the tip of the ground electrode has the highest temperature. However, the spark plug ground electrode described in Patent Document 1 has no core material disposed up to its tip. Therefore, there is room for further improvement in improving the thermal conductivity of the ground electrode.

The present invention has been made to solve the above-described problems, and can be realized as the following forms.
The first aspect of the present invention is:
An insulator having an axial hole along the axial direction;
A center electrode provided in the shaft hole;
A metal shell disposed on the outer periphery of the insulator;
A ground electrode having a base end fixed to the metal shell,
The ground electrode is a spark plug having a base material and a core material disposed inside the base material and having a higher thermal conductivity than the base material,
A metal film that contacts and covers a part of the core material is formed at the tip of the ground electrode,
The thickness of the metal film is rather smaller than the thickness of the base material,
The metal film has a thickness of 100 μm or less . The present invention can also be realized as the following forms.

(1) According to one aspect of the present invention, an insulator having an axial hole along the axial direction; a central electrode provided in the axial hole; a metal shell disposed on an outer periphery of the insulator; A ground electrode having a base end fixed to a metal shell, and the ground electrode includes a base material and a core material that is disposed inside the base material and has a higher thermal conductivity than the base material. A spark plug is provided. This spark plug is characterized in that a metal film that contacts and covers a part of the core material is formed at the tip of the ground electrode. In the case of such a spark plug, since the core material can be covered with the metal film, the core material can be arranged up to the tip of the ground electrode. Therefore, the thermal conductivity of the ground electrode can be improved.

(2) In the spark plug of the above aspect, the thickness of the metal film may be 1 μm or more. If it is such a form, it can suppress that a core material oozes and volatilizes from a metal film.

(3) In the spark plug of the above aspect, the thickness of the metal film may be 10 μm or more. If it is such a form, it can suppress more effectively that a core material oozes and volatilizes from a metal film.

(4) In the spark plug of the above aspect, the thickness of the metal film may be 100 μm or less. With such a configuration, the thermal conductivity of the ground electrode can be sufficiently improved.

(5) In the spark plug of the above aspect, the core material may include one or more of gold (Au), silver (Ag), and copper (Cu) as a main component. With such a configuration, the thermal conductivity of the ground electrode can be improved.

(6) In the spark plug of the above aspect, the metal film includes one or more of nickel (Ni) and cobalt (Co) as a main component, and chromium (Cr), aluminum (Al), yttrium ( One or more of Y) may be included. With such a form, the oxidation resistance of the metal film can be improved.

(7) In the spark plug of the above aspect, the cross-sectional area of the core member may be 8% or more of the cross-sectional area of the ground electrode in an arbitrary cross section of the ground electrode. With such a configuration, the thermal conductivity of the ground electrode can be sufficiently improved.

(8) In the spark plug of the above aspect, a cross-sectional area of the core member may gradually increase from the distal end side toward the proximal end side. If it is such a form, since the cross-sectional area of a core material becomes large as the site | part close | similar to a metal shell, the thermal conductivity of a ground electrode can be improved more effectively.

(9) In the spark plug of the above aspect, the metal film may be formed by thermal spraying. With such a form, a metal film can be easily formed on the ground electrode.

  The present invention is not limited to the above-described method for manufacturing a spark plug, and can be realized in various forms. For example, it can be realized in the form of a spark plug manufactured by the above-described manufacturing method or a vehicle including the spark plug.

It is a fragmentary sectional view of a spark plug. It is explanatory drawing which shows the detailed structure of a ground electrode. It is explanatory drawing which shows the detailed structure of a ground electrode. It is a figure which shows the thickness of a metal film. It is a graph which shows the result of the 1st test regarding the thickness of a metal film. It is a graph which shows the result of the 2nd test regarding the thickness of a metal film. It is a graph which shows the result of the 3rd test regarding the thickness of a metal film. It is a graph which shows the result of the test regarding the cross-sectional area of a core material. It is a schematic diagram which shows other embodiment of a ground electrode.

A. Spark plug configuration:
FIG. 1 is a partial cross-sectional view of the spark plug 1. In FIG. 1, the axial direction OD of the spark plug 1 is defined as the vertical direction in the drawing, and the lower side is described as the front end side and the upper side as the rear end side. In FIG. 1, the right side of the axis O indicated by a one-dot broken line indicates the appearance of the spark plug 1, and the left side of the axis O indicates a cross section passing through the central axis of the spark plug 1.

  The spark plug 1 includes an insulator 10 as an insulator, a metal shell 50, a center electrode 20, a ground electrode 30, and a terminal metal fitting 40. In the metal shell 50, an insertion hole 26 penetrating in the axial direction OD is formed. The insulator 10 is inserted and held in the insertion hole 26. The center electrode 20 is held in the axial hole 12 formed in the insulator 10 along the axial direction OD. The distal end portion of the center electrode 20 is exposed on the distal end side of the insulator 10. The ground electrode 30 is fixed to the distal end portion (the lower end portion in FIG. 1) of the metal shell 50. The terminal fitting 40 is provided on the rear end side (the upper end portion in FIG. 1) of the center electrode 20. The rear end portion of the terminal fitting 40 is exposed on the rear end side of the insulator 10.

  As is well known, the insulator 10 is formed by firing alumina or the like, and has a cylindrical shape in which an axial hole 12 extending in the axial direction OD is formed. A flange portion 19 having the largest outer diameter is formed substantially at the center in the axial direction OD, and a rear end side body portion 18 is formed on the rear end side. A front end side body portion 17 having an outer diameter smaller than that of the rear end side body portion 18 is formed on the front end side from the flange portion 19. Further, a leg length portion 13 having a smaller outer diameter than the distal end side body portion 17 is formed on the distal end side of the distal end side body portion 17. The long leg portion 13 is reduced in diameter toward the tip side, and is exposed to the combustion chamber when the spark plug 1 is attached to the engine head 70 of the internal combustion engine.

  The metal shell 50 is a substantially cylindrical metal fitting for fixing the spark plug 1 to the engine head 70 of the internal combustion engine. The metal shell 50 holds the insulator 10 so as to surround a portion from a part of the rear end side body part 18 to the leg long part 13. That is, the insulator 10 is inserted into the insertion hole 26 of the metal shell 50, and the front end and the rear end of the insulator 10 are exposed from the front end and the rear end of the metal shell 50, respectively. The metal shell 50 is formed of a low carbon steel material, and is entirely plated with nickel or zinc. A hexagonal column-shaped tool engaging portion 51 with which a spark plug wrench (not shown) is engaged is provided at the rear end portion of the metal shell 50. The metal shell 50 includes a mounting screw portion 52 formed with a screw thread that is screwed into a mounting screw hole 71 of an engine head 70 provided at an upper portion of the internal combustion engine.

  Between the tool engaging portion 51 and the mounting screw portion 52 of the metal shell 50, a bowl-shaped seal portion 54 is formed. An annular gasket 5 formed by bending a plate is fitted into a screw neck 59 between the mounting screw portion 52 and the seal portion 54. When the spark plug 1 is attached to the engine head 70, the gasket 5 is crushed and deformed between the seat surface 55 of the seal portion 54 and the opening peripheral portion 75 of the attachment screw hole 71. Due to the deformation of the gasket 5, the space between the spark plug 1 and the engine head 70 is sealed, and airtight leakage in the internal combustion engine through the mounting screw hole 71 is prevented.

  A thin caulking portion 53 is provided on the rear end side of the metal fitting 50 from the tool engaging portion 51. In addition, a thin compression deformation portion 58 is provided between the seal portion 54 and the tool engagement portion 51 as in the caulking portion 53. Between the inner peripheral surface of the metal shell 50 from the tool engaging portion 51 to the crimping portion 53 and the outer peripheral surface of the rear end side body portion 18 of the insulator 10, the annular first wire packing 6 and the second wire packing 6 are provided. The wire packing 7 is interposed. A talc (talc) 9 is filled between the first wire packing 6 and the second wire packing 7.

  When the spark plug 1 is manufactured, the compression deforming portion 58 is compressed and deformed by pressing the caulking portion 53 inward so as to be bent inward. Due to the compression deformation of the compression deformation portion 58, the insulator 10 is pressed toward the front end side in the metal shell 50 through the second wire packing 7, the talc 9, and the first wire packing 6. By this pressing, the second step portion 15 of the insulator 10 is pressed through the plate packing 8 to the first step portion 56 formed at the position of the mounting screw portion 52 on the inner periphery of the metal shell 50, The metal shell 50 and the insulator 10 are integrated. At this time, the airtightness between the metal shell 50 and the insulator 10 is maintained by the plate packing 8, and the outflow of combustion gas is prevented. Further, by this pressing, the talc 9 is compressed in the axial direction OD direction, and the airtightness in the metal shell 50 is enhanced.

  The center electrode 20 is made of nickel or an alloy containing nickel as a main component, such as Inconel (trade name) 600, or copper or an alloy containing copper as a main component, which is superior in thermal conductivity to the base material. It is a rod-shaped electrode having a structure in which a core material made of is embedded. The center electrode 20 extends in the shaft hole 12 toward the rear end side, and is electrically connected to the rear terminal fitting 40 via the seal body 4 and the ceramic resistor 3. A high voltage cable (not shown) is connected to the terminal fitting 40 via a plug cap (not shown), and a high voltage is applied. A noble metal tip may be fixed to the tip of the center electrode 20.

The base end 34 of the ground electrode 30 is fixed to the front end portion 57 of the metal shell 50 by welding. The ground electrode 30 is bent so that the inner surface of the tip portion 35 faces the tip of the center electrode 20 on the axis O. The cross-sectional area in an arbitrary cross section of the ground electrode 30 is preferably 1.5 mm ² or more, and more preferably 2.0 mm ² or more. The cross-sectional area is preferably 4.5 mm ² or less. A noble metal tip may be fixed to the inner surface of the tip portion 35 of the ground electrode 30 so as to face the tip of the center electrode 20.

  2 and 3 are explanatory diagrams showing the detailed configuration of the ground electrode 30. FIG. 2 shows a cross-sectional configuration of the ground electrode 30, and FIG. 3 shows a cross section taken along the line AA of FIG. The ground electrode 30 includes a base material 31 and a core material 32 having a higher thermal conductivity than the base material 31. In the present embodiment, the base material 31 is formed of Inconel 600, which is a nickel alloy. The core material 32 is formed of copper or a copper alloy containing 90% or more of copper. The core material 32 may be formed of a material containing one or more kinds as a main component among gold (Au), silver (Ag), and copper (Cu). As shown in FIGS. 2 and 3, the core material 32 is disposed inside the base material 31. Such a ground electrode 30 can be formed by performing a drawing process on a composite material in which the periphery of the core material 32 is covered with a base material 31 and cutting the composite material to a predetermined size. In the present embodiment, the front end surface 36 of the core member 32 is exposed from the base material 31. The cross-sectional area of the core member 32 is preferably 8% or more of the cross-sectional area of the ground electrode 30 in any cross section of the ground electrode 30. In the present embodiment, the cross-sectional shape of the ground electrode 30 and the cross-sectional shape of the core member 32 are substantially rectangular.

  A metal film 33 is formed on the tip portion 35 of the ground electrode 30. The metal film 33 is in contact with and covers a part (tip surface 36) of the core material 32. The metal film 33 includes one or more of nickel (Ni) and cobalt (Co) as a main component, and one or more of chromium (Cr), aluminum (Al), and yttrium (Y). Is formed by. More preferably, the metal film 33 includes one or more of Ni and Co as a main component, Cr as an essential component, and may include at least one of Al and Y. More preferably, all of Ni, Co, Cr, Al, and Y are included. The composition of the metal film 33 is preferably, for example, 25 to 40% of Ni. The composition of the metal film 33 is preferably 30.5 to 45.5% of Co. The metal film 33 may contain Cr, Al, and Y. If the metal film 33 is formed of such a material, the oxidation resistance of the metal film 33 can be improved.

  The metal film 33 is formed by thermal spraying (in this embodiment, high-speed flame spraying). In addition, the metal film 33 may be formed by, for example, plasma spraying or cold spraying. Thermal spraying is performed, for example, after the ground electrode 30 is welded to the front end portion 57 of the metal shell 50. The ground electrode 30 is bent after spraying. At the time of thermal spraying, the insulator 10 and the center electrode 20 may be assembled in the metal shell 50 or may not be assembled. During thermal spraying, portions other than the portion where the metal film 33 is formed are masked so that the metal film is not formed.

  FIG. 4 is a diagram showing the thickness of the metal film 33. The thickness T of the metal film 33 at the portion in contact with the core member 32 is preferably 1 μm or more, and more preferably 10 μm or more. The thickness T of the metal film 33 is preferably 100 μm or less. As shown in FIG. 4, the thicknesses T of the metal film 33 are measured at three positions where the tip surface 36 is equally divided into four (t1, t2, t3) in the cross section of the core member 32, Is an average value (= (t1 + t2 + t3) / 3).

  In the spark plug 1 of the present embodiment described above, the core material 32 is disposed up to the tip portion 35 of the ground electrode 30. Therefore, the heat extraction performance (thermal conductivity) of the ground electrode 30 can be significantly improved. Moreover, since the part (tip surface 36) exposed from the base material 31 of the core material 32 is covered with the metal film 33, the core material 32 becomes the ground electrode when the spark plug 1 is used in a high temperature environment. Volatilization from 30 is suppressed. Therefore, according to the spark plug 1 of the present embodiment, it is possible to realize both improvement of the heat extraction performance and durability of the ground electrode 30. Further, according to the present embodiment, since the heat extraction performance of the ground electrode 30 is improved, when the noble metal tip is fixed to the ground electrode 30, consumption of the noble metal tip can be suppressed.

B. Evaluation test:
FIG. 5 is a graph showing the results of the first test regarding the thickness of the metal film 33. The inventors of the present application, when the core material 32 in the ground electrode 30 is exposed from the base material 31 and the exposed portion is covered with the metal film 33 as in the above embodiment, the metal film 33 It has been found for the first time that the main component (copper) of the core material 32 exudes from the metal film 33 depending on the thickness and the operating temperature of the spark plug 1. Therefore, the test described below was performed. In this test, four types of ground electrodes 30 having different combinations of the composition of the metal film 33 and the composition of the core material 32 were prepared. Specifically, the first ground electrode having the metal film 33 having the following composition (1) and the core 32 having the following composition (a), and the following composition (2): The second ground electrode having the metal film 33 and the core material 32 having the following composition (a), the metal film 33 having the following composition (1), and the following (b) ) A third grounding electrode having a core material 32 having the composition (2), a metal film 33 having the following composition (2), and a fourth grounding having the core material 32 having the composition (b) below. And an electrode. In all of the first to fourth ground electrodes, the base material 31 is Inconel 600. Each of these ground electrodes has a vertical width H of 1.5 mm and a horizontal width W of 2.8 mm in the cross section (see FIG. 3). Further, the cross-sectional area of the core member 32 is about 2.1 mm ² . Further, for these four types of ground electrodes, samples were prepared in which the thickness of the metal film 33 was changed to 0.2 μm, 0.6 μm, and 1.0 μm, respectively.

(1) Co is 45.5%, Ni is 25%, Cr is 21%, Al is 8%, Y is 0.5%
(2) Co 30.5%, Ni 40%, Cr 21%, Al 8%, Y 0.5%
(A) 99% Cu
(B) 90% Cu

  In this test, the tip portion 35 (that is, the portion on which the metal film 33 is formed) of each sample prepared as described above is heated with a burner for 2 minutes and then cooled for 1 minute for 1000 cycles. A cold test was conducted. In this cold test, heating was performed to a target temperature while measuring the temperature of the tip portion 35 of each ground electrode using a radiation thermometer. And the ratio of the copper component of the front end surface of a ground electrode was measured by EDS (energy dispersive X-ray analysis), and the temperature at which the ratio exceeded 1% is shown in the graph of FIG. That is, FIG. 5 shows the temperature at which the copper, which is the main component of the core material 32 oozes out from the metal film 33 after the cooling test.

  According to the test results shown in FIG. 5, when the thickness of the metal film 33 is less than 1.0 μm, the temperature at which the copper component on the tip surface of the ground electrode exceeds 1% is the temperature at which the spark plug 1 is used. It can be understood that the temperature is lower than 900 ° C. That is, when the thickness of the metal film 33 is less than 1.0 μm, the core material 32 oozes out from the metal film 33 and volatilizes with the use of the spark plug 1, and the thermal conductivity of the ground electrode 30 deteriorates. End up. Therefore, in order to endure the normal use environment of the spark plug 1, it was confirmed that the thickness of the metal film 33 is preferably 1.0 μm or more.

FIG. 6 is a graph showing the results of the second test regarding the thickness of the metal film. In this test, Inconel 600 was used as the base material 31, and a ground electrode having the metal film 33 having the composition (1) and the core material 32 having the composition (a) was prepared. In the horizontal cross section (see FIG. 3) of the ground electrode, the vertical width H is 1.5 mm, the horizontal width W is 2.8 mm, and the cross-sectional area of the core member 32 is about 2.1 mm ² . And about such a ground electrode, the sample which changed the thickness of the metal film 33 with 0 micrometer, 10 micrometer, 50 micrometer, 90 micrometer, 100 micrometer, 110 micrometer, and 130 micrometer is prepared, and the front-end | tip part 35 of each sample is 1000 degreeC with a burner. After heating, the temperature after 5 seconds was measured. FIG. 6 shows the temperature.

  According to the test results shown in FIG. 6, it can be understood that when the thickness of the metal film 33 exceeds 100 μm, the heat drawability of the ground electrode is lowered. Therefore, it was confirmed that the thickness of the metal film 33 is preferably 100 μm or less.

  FIG. 7 is a graph showing the results of a third test relating to the thickness of the metal film. In this test, a sample was prepared in which the thickness of the metal film 33 was changed to 1 μm, 5 μm, 10 μm, 15 μm, and 20 μm for the same type of ground electrode as in the second test described above. Then, a thermal test was performed in which the tip portion 35 of each sample was heated to 1000 ° C. for 2 minutes by a burner, and then the cycle of cooling for 1 minute was repeated 1000 cycles. FIG. 7 shows a result of measuring the area where copper of the core material 32 is deposited from the metal film 33 on the front end surface of each sample by image analysis as a result of the cooling test. In addition, when copper of the core material 32 is deposited from the metal film 33, the portion turns black, so that the area can be measured by image analysis.

  According to the test results shown in FIG. 7, if the thickness of the metal film 33 was 10 μm or more, the copper of the core material 32 did not precipitate from the metal film 33. Therefore, it was confirmed that the thickness of the metal film 33 is more preferably 10 μm or more.

  FIG. 8 is a graph showing the results of a test related to the cross-sectional area of the core material. In this test, two kinds of ground electrodes having the metal film 33 having the composition (1) and the core material 32 having the composition (a) and having different vertical width H and horizontal width W were prepared. One ground electrode has a vertical width H (see FIG. 3) of 1.5 mm and a horizontal width W of 2.8 mm, and Inconel 600 is used as the base material 31. The other ground electrode had a vertical width H of 1.3 mm and a horizontal width W of 2.7 mm, and Inconel 601 was adopted as the base material 31. For these two types of ground electrodes, samples in which the area ratio of the core material 32 in any cross section of the ground electrode was changed to 0%, 5%, 8%, 12%, 20%, 33%, 45% Each prepared. Note that the lengths of these samples were all 13 mm.

  In this test, other samples were heated under heating conditions in which the area ratio of the core material 32 was 0%, that is, the temperature at a portion 5 mm from the tip of the sample not having the core material 32 was 900 ° C. And the temperature in the part 5 mm from the front-end | tip of each sample was measured with the radiation thermometer, and the result was shown on the graph of FIG.

  According to the test results shown in FIG. 8, it is understood that, for both of the two types of ground electrodes, if the ratio of the cross-sectional area of the core member 32 to the cross-sectional area of the ground electrode 30 is increased, the heat extraction performance is improved. it can. In particular, when the area ratio is 8% or more, the temperature decrease is particularly remarkable. Therefore, in order to improve the thermal conductivity of the ground electrode 30, it is preferable that the cross-sectional area of the core member 32 is 8% or more of the cross-sectional area of the ground electrode 30 in any cross section of the ground electrode 30. confirmed.

  According to the results of the tests described above, it was confirmed that the ground electrode 30 included in the spark plug 1 has a thickness of the metal film 33 of preferably 1 μm or more, and more preferably 10 μm or more. . Moreover, it was confirmed that the thickness of the metal film 33 is preferably 100 μm or less. Furthermore, it was confirmed that the cross-sectional area ratio of the core member 32 is preferably 8% or more of the cross-sectional area of the ground electrode 30 in an arbitrary cross section of the ground electrode 30.

C. Other embodiments:
FIG. 9 is a schematic diagram showing another embodiment of the ground electrode 30. 9A to 9G, the lower stage shows the cross section of the ground electrode in each embodiment, and the upper stage shows the shape of the front end surface of the ground electrode and the cross section of the core member 32 (broken line portion). Yes. 9A to 9G show a state before the ground electrode 30 is bent.

  In the ground electrode 30a of the second embodiment shown in FIG. 9A, the core material 32 is made of a multilayer metal. That is, the core material 37 of another material is further arranged inside the core material 32 mainly composed of copper. As another material, for example, nickel or a nickel alloy can be adopted. As described above, if the core material 37 mainly composed of nickel is arranged inside the core material 32 mainly composed of copper, the thermal conductivity of the ground electrode 30 is increased by the core material 32 mainly composed of copper. It becomes possible to improve. Furthermore, it is possible to prevent the bent ground electrode 30 from returning to a straight shape by the core material 37 containing nickel as a main component.

  The ground electrode 30b of the third embodiment shown in FIG. 9B is configured such that the cross-sectional area of the core material 32 gradually increases from the distal end portion of the ground electrode 30 toward the proximal end side. If it is such a form, since the heat received by the front-end | tip part can be smoothly tell | transmitted to the metal shell 50, the thermal conductivity of the ground electrode 30 can be improved more effectively.

  In the ground electrode 30c of the fourth embodiment shown in FIG. 9C, a plurality of core members 32 are embedded in a base material 31 in parallel. Even in such a form, the thermal conductivity of the ground electrode 30 can be improved.

  The ground electrode 30d of the fifth embodiment shown in FIG. 9D is configured such that the cross-sectional area of the core member 32 gradually increases from the distal end portion of the ground electrode 30 toward the proximal end side. Further, a core material 37 of another material is embedded in the core material 32. If it is such a form, there can exist both effects of 2nd Embodiment (FIG. 9 (A)) and 3rd Embodiment (FIG. 9 (B)).

  The ground electrode 30e of the sixth embodiment shown in FIG. 9E is configured such that the cross-sectional area of the core member 32 gradually decreases from the distal end portion of the ground electrode 30 toward the proximal end side. Even in such a form, the thermal conductivity can be improved.

  In the ground electrode 30f of the seventh embodiment shown in FIG. 9F, the cross section of the core member 32 is formed in an ellipse. Thus, the cross section of the core member 32 is not limited to a rectangle, but may be an ellipse or another shape. Further, the cross section of the ground electrode 30 is not limited to a rectangle, and may be an ellipse or other shapes.

  In the ground electrode 30g of the eighth embodiment shown in FIG. 9G, the metal film 33 covers only the core member 32, not the entire tip of the ground electrode 30. As described above, the metal film 33 only needs to be formed so as to cover at least the core member 32 exposed from the base material 31.

  In each of the above-described embodiments, the core material 32 is exposed from the front end surface of the base material 31. However, the core material 32 is exposed not only from the front end surface of the base material 31 but also from the side surface. May be. The metal film 33 only needs to cover and cover the entire portion (for example, the front end surface and the side surface) where the core material 32 is exposed from the base material 31.

  The present invention is not limited to the above-described embodiment, and can be realized with various configurations without departing from the spirit of the present invention. For example, the technical features of the embodiments corresponding to the technical features in each embodiment described in the summary section of the invention are intended to solve part or all of the above-described problems, or part of the above-described effects. Or, in order to achieve the whole, it is possible to replace or combine as appropriate. Further, if the technical feature is not described as essential in the present specification, it can be deleted as appropriate.

DESCRIPTION OF SYMBOLS 1 ... Spark plug 3 ... Ceramic resistance 4 ... Sealing body 5 ... Gasket 6 ... 1st wire packing 7 ... 2nd wire packing 8 ... Board packing 9 ... Talc 10 ... Insulator 12 ... Shaft hole 13 ... Leg long part 15 ... 2nd step part 17 ... Front end side body part 18 ... Rear end side body part 19 ... Ridge part 20 ... Center electrode 26 ... Insertion hole 30 ... Ground electrode 31 ... Base material 32 ... Core material 33 ... Metal film 34 ... Base end 35 ... tip portion 36 ... tip surface 40 ... terminal fitting 50 ... metal shell 51 ... tool engaging portion 52 ... mounting screw portion 53 ... clamping portion 54 ... seal portion 55 ... seat surface 56 ... first step portion 57 ... tip Portion 58 ... Compression deformation portion 59 ... Screw neck 70 ... Engine head 71 ... Mounting screw hole 75 ... Opening edge

Claims (8)

An insulator having an axial hole along the axial direction;
A center electrode provided in the shaft hole;
A metal shell disposed on the outer periphery of the insulator;
A ground electrode having a base end fixed to the metal shell,
The ground electrode is a spark plug having a base material and a core material disposed inside the base material and having a higher thermal conductivity than the base material,
A metal film that contacts and covers a part of the core material is formed at the tip of the ground electrode,
The thickness of the metal film is rather smaller than the thickness of the base material,
A spark plug , wherein the metal film has a thickness of 100 μm or less . The spark plug according to claim 1,
A spark plug, wherein the metal film has a thickness of 1 μm or more. The spark plug according to claim 1 or 2, wherein
A spark plug, wherein the metal film has a thickness of 10 μm or more. The spark plug according to any one of claims 1 to 3 , wherein
The spark plug is characterized in that the core material includes one or more of gold (Au), silver (Ag), and copper (Cu) as a main component. The spark plug according to any one of claims 1 to 4 , wherein
The metal film includes at least one of nickel (Ni) and cobalt (Co) as a main component, and includes at least one of chromium (Cr), aluminum (Al), and yttrium (Y). Spark plug characterized by The spark plug according to any one of claims 1 to 5 , wherein
The spark plug according to any one of the cross-sectional areas of the ground electrode, wherein the cross-sectional area of the core member is 8% or more of the cross-sectional area of the ground electrode. The spark plug according to any one of claims 1 to 6 , wherein
A spark plug characterized in that a cross-sectional area of the core member gradually increases from the distal end portion toward the proximal end side. The spark plug according to any one of claims 1 to 7 ,
A spark plug, wherein the metal film is formed by thermal spraying.

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