BACKGROUND OF THE INVENTION 1. Field of the Invention

[0001] The invention relates to a spark plug.

2. Description of Related Art

[0002] Pre-ignition sometimes occurs in an internal combustion engine provided with a spark plug. Regarding this, Japanese Patent Application Publication No. 2000-133411 (JP 2000-133411 A) describes a spark plug with an integrated coil in which the main fixture is made of a copper alloy or an aluminum alloy. In JP 2000-133411 A, a heat resistant spark plug with an integrated coil, that reduces the occurrence of pre-ignition, is realized by improving heat dissipation through heat conduction, such that an external electrode and the main fixture will not become high in temperature, using this main fixture.

[0003] It is now known that pre-ignition occurs due to an air-fuel mixture that remains in a plug pocket (or gas pocket) formed between a housing and an insulator being subjected to heat and becoming high in temperature. One conceivable way to reduce the temperature of the air-fuel mixture that remains in the plug pocket is to form the housing (i.e., the main fixture) with a copper alloy or an aluminum alloy, like the spark plug with an integrated coil described in JP 2000-133411 A, for example.

[0004] However, when the housing is made of a copper alloy or an aluminum alloy, the copper alloy or the aluminum alloy is also used for a portion of the housing that contacts the insulator. In this case, the housing will become high in temperature due to heat conduction from the insulator, so it is difficult to dissipate heat from the plug pocket.

SUMMARY OF THE INVENTION

[0005] To solve the forgoing problem, the invention provides a structure of a spark plug for an internal combustion engine, that is capable of inhibiting pre-ignition from occurring due to an air-fuel mixture that remains in a plug pocket and becomes high in temperature.

[0006] One aspect of the invention relates to a spark plug that includes an insulator, a housing within which the insulator is housed, and a plug pocket that is formed between the housing and the insulator. The housing includes a first metal that forms a base material, and a second metal that has a thermal conductivity higher than that of the first metal, and the second metal forms the least part of a portion of the housing, the portion being located around the plug pocket.

[0007] In the spark plug according to the one aspect of the invention, the second metal may be copper, a copper alloy, an aluminum alloy, a tungsten alloy, brass, or a brass alloy. The least part made of the second metal may be provided along an axial direction of the housing.

[0008] In the spark plug according to the one aspect of the invention, the at least part made of the second metal may be a rod-shaped member, and may be provided in plurality in a circumferential direction of the portion of the housing, the portion being located around the plug pocket.

[0009] In the spark plug according to the one aspect of the invention, the at least part made of the second metal may be embedded in the housing main body.

[0010] According to the aspect of the invention, the occurrence of pre-ignition caused by the air-fuel mixture that remains in the plug pocket and becomes high in temperature is able to be inhibited.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Features, advantages, and technical and industrial significance of exemplary embodiments of the invention will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:

FIG. 1A is a sectional view of the main portions of a spark plug according to an embodiment of the invention;

FIG. IB is a bottom view of the main portions of the spark plug according to an embodiment of the invention;

FIG. 2 is a graph of an example of the relationship between ignition timing and the number of times self-ignition occurs;

FIG. 3A is a sectional view of the main portions of a spark plug according to an embodiment of the invention;

FIG. 3B is a bottom view of the main portions of the spark plug according to an embodiment of the invention;

FIG. 3C is a view of a part of the spark plug according to an embodiment of the invention;

FIG. 3D is a view of a part of the spark plug according to an embodiment of the invention;

FIG. 3E is a sectional view of the main portions of a spark plug according to an embodiment of the invention;

FIG. 3F is a bottom view of the main portions of the spark plug according to an embodiment of the invention;

FIG. 3G is a sectional view of the main portions of a spark plug according to an embodiment of the invention;

FIG. 3H is a bottom view of the main portions of the spark plug according to an embodiment of the invention;

FIG. 4A is a sectional view of the main portions of a spark plug according to an embodiment of the invention;

FIG. 4B is a bottom view of the main portions of the spark plug according to an embodiment of the invention;

FIG. 4C is a sectional view of the main portions of a spark plug according to an embodiment of the invention;

FIG 4D is a bottom view of the main portions of the spark plug according to an embodiment of the invention;

FIG. 4E is a sectional view of the main portions of a spark plug according to an embodiment of the invention; FIG. 4F is a bottom view of the main portions of the spark plug according to an embodiment of the invention;

FIG. 5 A is a sectional view of the main portions of a spark plug according to an embodiment of the invention;

FIG. 5B is a bottom view of the main portions of the spark plug according to an embodiment of the invention;

FIG. 5C is a sectional view of the main portions of a spark plug according to an embodiment of the invention;

FIG. 5D is a bottom view of the main portions of the spark plug according to an embodiment of the invention;

FIG. 5E is a sectional view of the main portions of a spark plug according to an embodiment of the invention; and

FIG. 5F is a bottom view of the main portions of the spark plug according to an embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

[0012] Some embodiments of the invention will now be described with reference to the accompanying drawings.

[0013] FIG. 1 A is a sectional view taken along an axial direction of a housing of a spark plug 1A. That is, the axial direction of the housing is the direction in which a center electrode 2 of the spark plug extends. FIG. IB is a bottom view of the spark plug 1 A (i.e., a view from the side with the electrodes 2 and 3 along the axial direction). FIGS. 1A and IB are views of the main portions of the spark plug 1A provided in an internal combustion engine (such as a cylinder head 10). The spark plug 1A includes a center electrode 2, a ground electrode 3, a housing 4A, and an insulator 5. The spark plug 1 A is fastened to the cylinder head 10 via a gasket 6. The center electrode 2 extends along the axial direction of the housing 4A. The ground electrode 3 is fixed to the housing 4A. The housing 4 A houses the insulator 5. The insulator 5 is provided around the center electrode 2. A plug pocket P is formed between the housing 4 A and the insulator 5. The plug pocket P is formed around the insulator 5 and is open to a combustion chamber C of the internal combustion engine.

[0014] The housing 4A has copper cores 4a and a portion made of base material (i.e., a housing main body). A part of the housing main body is formed to fill a gap between copper cores 4a. The copper core 4a is a rod-shaped member, and is provided in a portion of the housing 4A that is located around the plug pocket P (i.e., the portion is located around the plug pocket P). A plurality (for example, 24) of the copper cores 4a are provided at equidistant intervals in a circumferential direction in the portion of the housing 4A that is located around the plug pocket P. The copper cores 4a are provided each extending along the axial direction of the housing 4A from an end portion of the copper cores 4a located on the combustion chamber C side. The copper cores 4a are embedded in the housing 4A, in a radial direction of the portion located around the plug pocket P. The copper cores 4a are able to be embedded in at least an upper portion of a portion of the housing 4A to which the ground electrode 3 is welded. The copper cores 4a may be provided in the housing main body by forming installation holes in the housing main body by machining, for example, and inserting the copper cores 4a into the formed installation holes. The housing main body is a portion that forms the main body of the housing 4A. Therefore, the housing main body is the portion of the housing body 4A other than the portion formed by the copper cores 4a.

[0015] For example, the housing main body is made of carbon steel that is a first metal. The copper cores 4a are made of a copper alloy that is a second metal. Therefore, the housing 4A is formed having the copper cores 4a and the housing main body. The housing 4A includes the housing main body made of the first metal, and at least the portion of the housing 4A that is located around the plug pocket P, and that is made of the second metal. With the spark plug 1A in which the first metal is carbon steel and the second metal is a copper alloy, a metal having thermal conductivity higher than that of the first metal is used for the second metal. The second metal may also be copper.

[0016] FIG. 2 is a graph of an example of the relationship between the ignition timing and the number of times self-ignition occurs. The vertical axis represents the number of times self-ignition occurs, and the horizontal axis represents the ignition timing. FIG 2 shows the number of times that self-ignition occurs when ignition is canceled after the internal combustion engine is operated under a predetermined condition. FIG. 2 simultaneously shows the number of times self-ignition occurs with a spark plug 1 A' as a comparison. The spark plug 1A' has a shape similar to that of the spark plug 1A. The spark plug 1 A' differs from the spark plug 1A in that the spark plug 1A' does not have the copper cores 4a, and in that the copper cores 4a are replaced, with the base material of which the housing main body is made. The spark plug 1 A' has substantially the same configuration as the spark plug 1A, other than that no copper cores 4a are used and a housing that is made only of the base material is provided instead of the housing 4 A.

[0017] As shown in FIG. 2, the number of times that self-ignition occurs increases the more the ignition timing is advanced. With the spark plug 1A, part of the portion of the housing 4A that is located around the plug pocket P is made of a copper alloy having a thermal conductivity that is higher than that of the carbon steel of which the housing 4 A is made. Therefore, a decrease in temperature of the air-fuel mixture that remains in the plug pocket P is able to be promoted. Also, part of the portion of the housing 4A that is located around the plug pocket P is made of a copper alloy, and the rest of the housing 4A is made of carbon steel, which separates the copper alloy from the insulator 5 and can prevent the copper alloy from contacting with the insulator 5. Therefore, heat conduction from the insulator 5 to the housing 4A is able to be suppressed.

[0018] Therefore, the spark plug 1A is able to inhibit the occurrence of pre-ignition due to the air-fuel mixture that remains in the plug pocket P and becomes high in temperature. Accordingly, as shown in FIG. 2, the spark plug 1 A is able to reduce the number of times that self-ignition occurs compared with the spark plug 1A', even if the ignition timing is advanced.

[0019] The spark plug 1 A has the copper alloy as, the second metal provided along the axial direction of the housing 4A. Therefore, heat conduction from the portion of the housing 4A that is located around the plug pocket P to the upper portion (i.e., the portion located on the side opposite the combustion chamber C side in the axial direction of the housing 4 A when the spark plug 1 A is provided in the internal combustion engine) is also able to be promoted.

[0020] In the spark plug 1A, the copper cores 4a are made of the second metal, and a plurality of the copper cores 4a are provided along the circumferential direction in the portion of the housing 4A that is located around the plug pocket P. The copper cores 4a are provided extending in the axial direction of the housing 4A. The copper cores 4a may be embedded in a portion of the housing 4A that is located around the plug pocket P, in the radial direction of the housing 4A.

[0021] FIGS. 3 A and 3B are views showing the main portions of a spark plug IB, similar to FIGS. 1A and IB. The spark plug IB is functionally the same as the spark plug 1 A, except for that a housing 4B is provided instead of the housing 4 A. The housing 4B is configured substantially the same as the housing 4A, except for that a copper tube 4b is provided instead of the copper cores 4a, and the shape of the housing main body is different.

[0022] The copper tube 4b is a cylindrical member and is made of a copper alloy similar to the copper cores 4a. The copper tube 4b is provided in a portion of the housing 4B that is located around the plug pocket P. The copper tube 4b is provided in a portion of the housing 4B that is adjacent to the plug pocket P. A length of the copper tube 4b in the axial direction of the housing 4B is set equal to a length of the plug pocket P in the axial direction. Therefore, the copper tube 4b is adjacent to the plug pocket P around the housing 4B, in the axial direction.

[0023] An outer diameter of the copper tube 4b is set equal to an inner diameter of the housing main body of the housing 4B that is located around the plug pocket P. With the spark plug IB, part of the portion of the housing 4B that is located around the plug pocket P is made of a copper alloy, just as with the spark plug 1 A. The copper tube 4b may be provided in the housing 4B by forming an installation portion in the housing main body by machining, for example, and press-fitting the copper tube 4b into the formed installation portion.

[0024] With the spark plug IB, a decrease in temperature of the air-fuel mixture that remains in the plug pocket P is able to be promoted, and heat conduction from the insulator 5 is able to be suppressed, just as with the spark plug 1 A. Therefore, the spark plug IB is able to inhibit the occurrence of pre-ignition caused by the air-fuel mixture that remains in the plug pocket P and becomes high in temperature.

[0025] In FIGS. 3A and 3B, the copper tube 4b is shown as being cylindrical in shape, but the entire copper tube 4b does not have to be copper metal. That is, the copper tube 4b may also be a copper tube in which slits s are formed in the axial direction or the circumferential direction of the housing 4B, in a portion of the copper tube 4b, as shown in FIGS. 3C and 3D. Also, a plurality of copper tubes 4b may be formed, as denoted by reference characters 4b 1 and 4b2, in the axial direction of the housing 4B, as shown in FIGS. 3E and 3F. The copper tube 4b may also be formed divided into a plurality of sections, as denoted by reference characters 4b3, 4b4, 4b5, and 4b6, in the circumferential direction of the housing 4B, as shown in FIGS. 3 G and 3H. Alternatively, the structures illustrated in FIGS. 3E, 3F, 3G, and 3H may also be combined appropriately.

[0026] FIGS. 4A and 4B are views of the main portions of a spark plug 1C, similar to FIGS. 1 A and IB. The spark plug 1C is functionally the same as the spark plug 1A, except for that a housing 4C is provided instead of the housing 4A. The housing 4C is configured substantially the same as the housing 4A, except for that a copper ring 4c is provided instead of the copper cores 4a, and the shape of the housing main body is different.

[0027] The copper ring 4c is a ring-shaped member, and is made of a copper alloy, similar to the copper cores 4a. The copper ring 4c is provided in a portion of the housing 4C that is located around the plug pocket P. The copper ring 4c is provided in a portion of the housing 4C that is adjacent to the plug pocket P. The copper ring 4c is provided in a middle portion of the housing main body that is adjacent to the plug pocket P, in the axial direction of the housing 4C, for example.

[0028] A length of the copper ring 4c in the axial direction of the housing 4C is set shorter than a length of the plug pocket P in the axial direction of the housing 4C. Also, an inner diameter of the copper ring 4c is set smaller than an inner diameter of the housing main body that is adjacent to the plug pocket P. Therefore, at the portion where the copper ring 4c is provided, a step is formed by the copper ring 4c at a portion of the housing 4C that is adjacent to the plug pocket P. An outer diameter of the copper ring 4c is set larger than the inner diameter of the housing main body that is adjacent to the plug pocket P, within a range that enables the copper ring 4c to be housed in the housing main body.

[0029] By providing the copper ring 4c as described above, with the spark plug 1C, part of the portion of the housing 4C that is located around the plug pocket P is made of a copper alloy, similar to the spark plug 1A. The second metal may also protrude farther inward in the radial direction of the housing 4C than the housing main body that is adjacent to the plug pocket P, as shown by the spark plug 1C. The copper ring 4c may be provided on the base material by casting, for example.

[0030] With the spark plug 1C, a decrease in the temperature of the air-fuel mixture that remains in the plug pocket P is able to be promoted, and heat conduction from the insulator 5 is able to be suppressed, just as with the spark plug 1A. Therefore, the spark plug 1C is able to inhibit the occurrence of pre-ignition caused by the air- fuel mixture that remains in the plug pocket P and becomes high in temperature.

[0031] The spark plug 1C may be such that the copper ring 4c that is a member made of the second metal is provided on the housing 4C by casting. Therefore, the housing 4C is able to be easily manufactured because machining is not necessary for arranging the members of the housing 4C.

[0032] In FIGS. 4A and 4B, the spark plug 1C is such that one copper ring 4c is provided at a portion located around the plug pocket P. A plurality of copper rings 4c may also be formed, as denoted by reference characters 4c 1 and 4c2, in the axial direction of the housing 4C, as shown in FIGS. 4C and 4D. The copper ring 4c may also be formed divided into a plurality of sections, as denoted by reference characters 4c3, 4c4, 4c5, and 4c6, in the circumferential direction of the housing 4C, as shown in FIGS. 4E and 4F. Alternatively, the structures illustrated in FIGS. AC, 4D, 4E, and 4F may also be combined appropriately. [0033] FIGS. 5 A and 5B are views of the main portions of a spark plug ID, similar to FIGS. 1 A and IB. The spark plug ID is functionally the same as the spark plug 1 A, except for that a housing 4D is provided instead of the housing 4A. The housing 4D is configured substantially the same as the housing 4A, except for that a copper tube 4d is provided instead of the copper cores 4a, and the shape of the housing main body is different.

[0034] The copper tube 4d is a cylindrical member, and is made of a copper alloy similar to the copper cores 4a, and is provided on a portion of the housing 4D that is located around the plug pocket P. The copper tube 4d is provided so as to form the entire portion of the housing 4D around the plug pocket P. A length of the copper tube 4d in the axial direction of the housing 4D is set to be equal to a length of the plug pocket P in the axial direction. By providing the copper tube 4d in this way, with the spark plug ID, the portion of the housing 4D that is located around the plug pocket P is made of a copper alloy. The copper tube 4d is arranged at a portion on the combustion chamber C side of the housing 4D. The copper tube 4d may be provided on the base material by joining, for example.

[0035] With the spark plug ID, a decrease in temperature of the air-fuel mixture that remains in the plug pocket P is able to be promoted, and heat conduction from the insulator 5 is able to be suppressed, just as with the spark plug 1 A. Therefore, the spark plug ID is able to inhibit the occurrence of pre-ignition caused by the air-fuel mixture that remains in the plug pocket P and becomes high in temperature.

[0036] With the spark plug ID in FIGS. 5A and 5B, only one copper tube 4d is provided at the portion around the plug pocket P. A plurality of copper tubes 4d may also be formed, as denoted by reference characters 4dl and 4d2, in the axial direction of the housing 4D, as shown in FIGS. 5C and 5D. The copper tube 4d may also be formed divided into a plurality of sections, as denoted by reference characters 4d3, 4d4, 4d5, and 4d6, in the circumferential direction of the housing 4B, as shown in FIGS. 5E and 5F. Alternatively, the structures illustrated in FIGS. 5C, 5D, 5E, and 5F may also be combined appropriately. [0037] While the invention has been described with reference to specific embodiments thereof, the invention is not limited to these specific embodiments. Various modifications and variations are also possible within the scope of the invention described in the scope of the claims for patent.

[0038] For example, the second metal may be a metal other than a copper alloy

(including brass or a brass alloy) such as an aluminum alloy and a tungsten alloy. Also, for example, in the invention, the housing may be made using another metal in addition to the first and second metals. The other metal may be provided in a location that enables heat conduction from the insulator to the second metal to be suppressed by a combination of the other metal and the first metal, or by the other metal alone, for example. In this case, the other metal may be a metal having a thermal conductivity lower than that of the first metal. Alternatively, the other metal may be provided in a location that enables a decrease in the temperature of the air-fuel mixture that remains in the plug pocket to be promoted by a combination of the other metal and the second metal, or by the other metal alone, for example. In this case, the other metal may be a metal that has a thermal conductivity higher than that of the first metal.