Spark plug for internal combustion engine and manufacturing method thereof

Abstract

To provide a spark plug for an internal combustion engine capable of suppressing overheat of a plug cover, and to provide a method of manufacturing the same.SOLUTION: A spark plug 1 for an internal combustion engine has an insulator 3, a center electrode 4, a housing 2, a ground electrode 6, and a plug cover 5. The plug cover 5 is formed with an injection hole 51 for connecting between a sub-combustion chamber 50 and the exterior. When a thickness of the plug cover at a tip side from the ground electrode 6 is defined as t0, a thickness of a bonded part 59 of the plug cover to be bonded to a tip part of the housing 2 is defined as t1, a thickness of the tip part of the housing 2 is defined as t2, and a length of one bonding surface 11 of two bonding surfaces 11 appearing in a cross section including a plug central axis PC is defined as L, t1≥t0, t2≥1.5t1, and L≥1.5t1 are satisfied.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a spark plug for an internal combustion engine and a method for manufacturing the same. [Background technology]

[0002] For example, as disclosed in Patent Document 1, a spark plug for an internal combustion engine having a pre-combustion chamber at its tip is known. The spark plug described in Patent Document 1 specifies the ratio of the total surface area of ​​the inner wall surfaces of the housing and plug cover facing the pre-combustion chamber to the surface area of ​​the outer circumferential surface of the insulator facing the pre-combustion chamber. This is intended to prevent the pre-combustion chamber from becoming too hot, and to prevent the air-fuel mixture from igniting before the spark plug generates a discharge (i.e., pre-ignition). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-184435 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, the spark plug described in Patent Document 1 does not take into consideration heat dissipation from the plug cover to the outside via the housing. That is, the plug cover faces both the auxiliary combustion chamber and the main combustion chamber, and is therefore particularly susceptible to temperature increases. Therefore, in suppressing pre-ignition, it is particularly important to suppress overheating of the plug cover. Heat dissipation from the plug cover is mainly performed via the housing.

[0005] Therefore, how to improve the heat transfer from the plug cover to the housing is important, but the invention described in Patent Document 1 does not particularly consider this point.

[0006] The present invention has been made in view of the above-mentioned problems, and has an object to provide a spark plug for an internal combustion engine that is capable of suppressing overheating of the plug cover, and a method for manufacturing the same. [Means for solving the problem]

[0007] The present invention 1. The embodiment includes a cylindrical insulator (3), a center electrode (4) held on the inner circumferential side of the insulator and protruding from the insulator toward the tip side; a cylindrical housing (2) that holds the insulator on its inner periphery; a ground electrode (6) forming a discharge gap (G) between itself and the center electrode; a plug cover (5) joined to the tip end portion of the housing via a joining surface so as to cover the auxiliary combustion chamber (50) in which the discharge gap is arranged, The plug cover is formed with a nozzle hole (51) that communicates the auxiliary combustion chamber with the outside, The thickness of the plug cover on the tip side of the ground electrode is t0. The thickness of the joined portion (59) of the plug cover joined to the front end portion of the housing is t1, The thickness of the tip of the housing is t2, When the length of one of the two above-mentioned mating surfaces appearing on a cross section including the central axis of the plug is L, t1 ≧ t0, t2 ≧ 1.5t1, and L ≧ 1.5t1 are satisfied. death, a length h of the joining surface in the plug axial direction satisfies h≦t1, the joining surface is joined by welding, and a fusion zone is formed over the entire length of the joining surface in the plug axial direction. Found in spark plugs for internal combustion engines. A second aspect of the present invention is a cylindrical insulator (3), a center electrode (4) held on the inner circumferential side of the insulator and protruding from the insulator toward the tip side; a cylindrical housing (2) that holds the insulator on its inner periphery; a ground electrode (6) forming a discharge gap (G) between itself and the center electrode; a plug cover (5) joined to the tip end portion of the housing via a joining surface so as to cover the auxiliary combustion chamber (50) in which the discharge gap is arranged, The plug cover is formed with a nozzle hole (51) that communicates the auxiliary combustion chamber with the outside, The thickness of the plug cover on the tip side of the ground electrode is t0. The thickness of the joined portion (59) of the plug cover joined to the front end portion of the housing is t1, The thickness of the tip of the housing is t2, When the length of one of the two above-mentioned mating surfaces appearing on a cross section including the central axis of the plug is L, t1≧t0, t2≧1.5t1, and L≧1.5t1 are satisfied; The ground electrode is joined to the housing via a ground contact surface (14), and the spark plug for an internal combustion engine satisfies W≧1.5t3, where t3 is the thickness of the ground electrode as viewed from a direction perpendicular to both the extension direction of the ground electrode and the plug axial direction, and W is the length of the ground contact surface as seen in a cross section including the central axis of the plug.

[0008] The present invention Third The embodiment is a method for manufacturing a spark plug for an internal combustion engine, the spark plug having a cylindrical insulator (3), a center electrode (4) held on an inner periphery of the insulator and protruding from the insulator toward a tip end thereof, a cylindrical housing (2) holding the insulator on its inner periphery, a ground electrode (6) forming a discharge gap (G) between the center electrode and the ground electrode, and a plug cover (5) joined to a tip end portion of the housing so as to cover an auxiliary combustion chamber (50) in which the discharge gap is located, The plug cover is formed with a nozzle hole (51) that communicates the auxiliary combustion chamber with the outside, a connecting portion (59) of the plug cover is brought into contact with the front end portion of the housing, and an abutting surface (11a) is welded to connect the plug cover to the front end portion of the housing; The dimensions of each part before welding are as follows: The thickness of the plug cover on the tip side of the ground electrode is t0a, The thickness of the joined portion to be joined to the front end portion of the housing is t1a, The thickness of the tip of the housing is t2a. When the length of one of the two abutment surfaces appearing in a cross section including the central axis of the plug is La, t1a ≧ t0a, t2a ≧ 1.5t1a, and La ≧ 1.5t1a are satisfied. death, a length ha of the abutment surface in the plug axial direction satisfies ha≦t1a, the abutment surface is joined by welding, and welding is performed so that a fusion zone is formed over the entire length of the abutment surface in the plug axial direction. The present invention relates to a method for manufacturing a spark plug for an internal combustion engine. A fourth aspect of the present invention is a manufacturing method of a spark plug for an internal combustion engine, the spark plug having a cylindrical insulator (3), a center electrode (4) held on an inner periphery of the insulator and protruding from the insulator toward a tip side, a cylindrical housing (2) holding the insulator on its inner periphery, a ground electrode (6) forming a discharge gap (G) between the center electrode and the ground electrode, and a plug cover (5) joined to a tip portion of the housing so as to cover a sub-combustion chamber (50) in which the discharge gap is located, The plug cover is formed with a nozzle hole (51) that communicates the auxiliary combustion chamber with the outside, a connecting portion (59) of the plug cover is brought into contact with the front end portion of the housing, and an abutting surface (11a) is welded to connect the plug cover to the front end portion of the housing; The dimensions of each part before welding are as follows: The thickness of the plug cover on the tip side of the ground electrode is t0a, The thickness of the joined portion to be joined to the front end portion of the housing is t1a, The thickness of the tip of the housing is t2a. When the length of one of the two abutment surfaces appearing in a cross section including the central axis of the plug is La, t1a ≧ t0a, t2a ≧ 1.5t1a, and La ≧ 1.5t1a are satisfied; The ground electrode is joined to the housing via a ground joint surface (14), a portion (69) of the ground electrode is brought into contact with a part of the housing, and an abutting surface (14a) is welded to join the ground electrode to the housing; The dimensions of each part before welding are as follows: The present invention relates to a method for manufacturing a spark plug for an internal combustion engine, in which Wa ≧ 1.5ta3 is satisfied, where ta3 is a thickness of the ground electrode when viewed from a direction perpendicular to both the extending direction of the ground electrode and the plug axial direction, and Wa is a length of the abutment surface appearing in a cross section including the central axis of the plug. Effect of the Invention

[0009] In the above spark plug for an internal combustion engine, the thickness t0, the thickness t1, the thickness t2, and the length L satisfy t1≧t0, t2≧1.5t1, and L≧1.5t1. This ensures a sufficient heat dissipation path from the plug cover to the housing via the joint surface. This makes it possible to suppress overheating of the plug cover. As a result, it is possible to suppress pre-ignition in the spark plug.

[0010] In the above-mentioned method for manufacturing a spark plug for an internal combustion engine, the dimensions of each part before welding, ie, thickness t0a, thickness t1a, thickness t2a, and length La, satisfy t1a≧t0a, t2a≧1.5t1a, and La≧1.5t1a. This makes it possible to sufficiently secure a heat dissipation path from the plug cover to the housing via the joint surface in the resulting spark plug. Therefore, it is possible to suppress overheating of the plug cover. As a result, it is possible to suppress pre-ignition in the spark plug.

[0011] As described above, according to the above aspect, it is possible to provide a spark plug for an internal combustion engine that is capable of suppressing overheating of the plug cover, and a method for manufacturing the same. In addition, the symbols in parentheses described in the claims and the means for solving the problems indicate a correspondence with the specific means described in the embodiments described below, and do not limit the technical scope of the present invention. [Brief description of the drawings]

[0012] [Figure 1] 1 is a cross-sectional explanatory view of the vicinity of a tip portion of a spark plug attached to an internal combustion engine in a first embodiment. [Diagram 2] FIG. 2 is a cross-sectional view taken along line II-II in FIG. [Diagram 3] FIG. 3 is a cross-sectional view illustrating the vicinity of a joint surface between a housing and a plug cover in the first embodiment. [Figure 4] FIG. 4 is an explanatory cross-sectional view showing a state in which the joint surfaces of the housing and the plug cover are welded in the first embodiment. [Diagram 5] 3 is a micrograph showing a welded surface portion in embodiment 1. [Figure 6] FIG. 11 is a cross-sectional view illustrating a heat flow around a joint surface in a comparative example. [Figure 7] FIG. 11 is a cross-sectional view illustrating a heat flow around a joint surface in another comparative embodiment. [Figure 8] FIG. 4 is a cross-sectional view illustrating a heat flow around a joint surface in the first embodiment. [Figure 9] FIG. 11 is an explanatory cross-sectional view of the periphery of a joint surface between a housing and a plug cover in a second embodiment. [Figure 10] FIG. 11 is an explanatory cross-sectional view of the periphery of a joint surface between a housing and a plug cover in a third embodiment. [Figure 11] FIG. 13 is an explanatory cross-sectional view of the periphery of a joint surface between a housing and a plug cover in a fourth embodiment. [Figure 12] FIG. 13 is an explanatory cross-sectional view of the periphery of a joint surface between a housing and a plug cover in a fifth embodiment. [Figure 13] FIG. 13 is an explanatory cross-sectional view of the vicinity of a tip portion of a spark plug attached to an internal combustion engine in a sixth embodiment. [Figure 14] FIG. 14 is a cross-sectional view taken along line XIV-XIV in FIG. [Figure 15] FIG. 13 is an explanatory cross-sectional view of the vicinity of a tip portion of a spark plug attached to an internal combustion engine in a seventh embodiment. [Figure 16] FIG. 13 is an explanatory cross-sectional view of the vicinity of a tip portion of a spark plug attached to an internal combustion engine in an eighth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] (Embodiment 1) DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A spark plug for an internal combustion engine and a manufacturing method thereof will be described with reference to FIGS. A spark plug 1 for an internal combustion engine according to this embodiment includes a cylindrical insulator 3, a center electrode 4, a cylindrical housing 2, a ground electrode 6, and a plug cover 5, as shown in FIGS.

[0014] The center electrode 4 is held on the inner periphery of the insulator 3 and protrudes from the insulator 3 towards the tip side. The housing 2 holds the insulator 3 on the inner periphery. The ground electrode 6 forms a discharge gap G between itself and the center electrode 4. The plug cover 5 is joined to the tip of the housing 2 via a joint surface 11 so as to cover the auxiliary combustion chamber 50 in which the discharge gap G is located. The plug cover 5 is formed with an injection hole 51 that connects the auxiliary combustion chamber 50 to the outside.

[0015] The thickness of the plug cover 5 on the tip side of the ground electrode 6 is defined as t0. As shown in Fig. 3, the thickness of the joined portion 59 of the plug cover 5 that is joined to the tip end of the housing 2 is defined as t1. The thickness of the tip end of the housing 2 is defined as t2.

[0016] Of the two mating surfaces 11 appearing in a cross section including the plug central axis PC, the length of one of the mating surfaces 11 is defined as L. That is, as shown in Fig. 1, in a cross section including the plug central axis PC, two mating surfaces 11 appear on opposite sides of the plug central axis PC. The length of one of the mating surfaces 11 is defined as L.

[0017] When the dimensions of each part are defined as above, t1≧t0, t2≧1.5t1, and L≧1.5t1 are satisfied.

[0018] The plug axial direction Z refers to the axial direction of the spark plug 1 and is a direction parallel to the plug central axis PC. The plug radial direction refers to the radial direction of the spark plug 1 and is a direction perpendicular to the plug central axis PC.

[0019] The length h of the joint surface 11 in the plug axial direction Z satisfies h≧t1 / 2. The plug cover 5 is made of nickel or an alloy mainly composed of nickel, and the housing 2 is made of low carbon steel.

[0020] 1 and 3, in this embodiment, the tip end of the housing 2 is disposed on the base end side in the plug axial direction Z with respect to the joined portion 59 of the plug cover 5 via the joint surface 11, and is also disposed on the inner side in the plug radial direction via another portion of the joint surface 11. In addition, as shown in Fig. 3, when the length of the joint surface 11 in the plug axial direction Z is h, L = t1 + h.

[0021] In addition, the length h of the joint surface 11 in the plug axial direction Z satisfies h≦t1. As shown in Fig. 4, the joint surface 11 is joined by welding. The fusion zone 12 is formed over the entire length of the joint surface 11 in the plug axial direction Z.

[0022] When the fusion zone 12 is formed as shown in FIG. 3, the length h and the length L can be specified as follows. That is, as shown in Fig. 5, the central position in the plug axial direction Z of the welded surface portion 13 seen when the housing 2 and the plug cover 5 are viewed from the outer periphery side is defined as the base end 111 of the joining surface 11. Note that w in Fig. 5 represents the width of the welded surface portion 13 in the plug axial direction Z.

[0023] The length from the base end 111 of the joint surface 11 to the tip end 112 of the joint surface 11 (see FIG. 3 ) is defined as h. The length h plus the thickness t1 of the jointed portion 59 of the plug cover 5 is defined as length L. In this manner, in the completed spark plug 1, when the fusion zone 12 is formed and the joint surface 11 cannot be closely observed, each dimension of the joint surface 11 can be estimated from the welded surface portion 13, etc.

[0024] The spark plug 1 can be used as an ignition means in an internal combustion engine of an automobile, etc. As shown in Fig. 1, the spark plug 1 is attached to an internal combustion engine 10 by screwing a threaded portion 24 of a housing 2 into a female threaded portion of a plug hole 711 of a cylinder head 71. When the spark plug 1 is attached to the internal combustion engine 10, the housing 2 is in thermal contact with the cylinder head 71 of the internal combustion engine via the threaded portion 24.

[0025] In manufacturing the spark plug 1 for an internal combustion engine of this embodiment, the joined portion 59 of the plug cover 5 is brought into contact with the front end portion of the housing 2, and the contact surface 11a is welded.

[0026] The dimensions of each part before welding are defined as follows: thicknesses t0a, t1a, t2a, and length La. That is, as shown in Fig. 1, the thickness of the plug cover 5 on the tip side of the ground electrode 6 is defined as t0a. As shown in Fig. 3, the thickness of the joined portion 59 of the plug cover 5 that is joined to the tip end of the housing 2 is defined as t1a. The thickness of the tip end of the housing 2 is defined as t2a. The length of one of the two contact surfaces 11a that appears in a cross section including the plug central axis PC is defined as La.

[0027] In this case, the thicknesses t0a, t1a, and t2a and the length La satisfy t1a≧t0a, t2a≧1.5t1a, and La≧1.5t1a. Further, the length ha of the abutment surface 11a in the plug axial direction Z satisfies ha≧t1a / 2.

[0028] The length ha of the abutment surface 11a in the plug axial direction Z satisfies ha≦t1a. The abutment surfaces 11a are joined by welding, and welding is performed so that the fusion zone 12 is formed over the entire length of the abutment surface 11a in the plug axial direction Z.

[0029] In this embodiment, the welding of the contact surface 11a is performed by laser welding. That is, a laser beam is irradiated from the outside of the contact surface 11a in the plug radial direction. The laser welding is performed over the entire outside circumference of the contact surface 11a.

[0030] Next, the effects of this embodiment will be described. In the above spark plug 1 for an internal combustion engine, the thickness t0, the thickness t1, the thickness t2, and the length L satisfy t1≧t0, t2≧1.5t1, and L≧1.5t1. This makes it possible to sufficiently secure a heat dissipation path from the plug cover 5 to the housing 2 via the joint surface 11. This makes it possible to suppress a temperature rise of the plug cover 5. As a result, pre-ignition in the spark plug 1 can be suppressed.

[0031] In other words, by satisfying t1≧t0, heat dissipation by heat transfer from the tip end side to the base end side of the plug cover 5 can be easily performed. That is, the heat from the plug cover 5 is mainly dissipated to the engine head 71 via the housing 2. Therefore, by setting the thickness t1 of the joined portion 59 of the plug cover 5 to be equal to or greater than the thickness t0 of the plug cover 5 on the tip side of the ground electrode 6, heat dissipation from the plug cover 5 can be easily performed.

[0032] Furthermore, by satisfying t2 ≧ 1.5t1, heat can be effectively transferred from the plug cover 5 to the housing 2. That is, since the thickness t2 of the front end of the housing 2 is sufficiently larger than the thickness t1 of the joined portion 59 of the plug cover 5, the heat capacity of the front end of the housing 2 becomes sufficiently large. Therefore, heat can be sufficiently released from the joined portion 59 of the plug cover 5 to the front end of the housing 2.

[0033] Particularly in this embodiment, the plug cover 5 is made of nickel or an alloy mainly composed of nickel. The housing 2 is made of low carbon steel. Therefore, the thermal conductivity of the plug cover 5 is approximately 1.5 times that of the housing 2. In this case, if the thickness t1 of the front end of the housing 2 and the thickness t2 of the joined portion 59 of the plug cover 5 are equivalent, there is a risk that heat transfer from the plug cover 5, which has a relatively high thermal conductivity, to the housing 2, which has a relatively low thermal conductivity, will not be performed efficiently. Therefore, by making t2 ≧ 1.5t1, it is possible to prevent the front end of the housing 2 from becoming the rate limiting factor for the heat flow, and to perform efficient heat dissipation.

[0034] However, even if t1≧t0 and t2≧1.5t1 are satisfied, if the length L of the joint surface 11 is insufficient, as shown in Fig. 6, for example, heat cannot be efficiently transferred from the plug cover 5 to the housing 2 via the joint surface 11. That is, in the case of the structure shown in Fig. 6, L=t1, and the length L of the joint surface 11 is short, so that heat is not efficiently transferred to the housing 2, which has a lower thermal conductivity than the plug cover 5. The arrows in Figs. 6 to 8 show an image of the heat flow.

[0035] 7, if the thickness t1 of the joined portion 59 of the plug cover 5 is too small, the thermal conduction path to the joined portion 59 of the plug cover 5 is narrowed. This makes it easier for the heat flow from the plug cover 5 to the joined portion 59 to be hindered. As a result, it becomes difficult to dissipate heat to the housing 2 efficiently.

[0036] Therefore, the spark plug 1 of this embodiment further satisfies L≧1.5t1. As a result, as shown in Fig. 8, heat can be efficiently transferred to the housing 2 via the joint surface 11 without impeding the heat flow from the tip side of the plug cover 5 to the joined portion 59. As a result, the heat dissipation property of the plug cover 5 can be improved, and the temperature rise of the plug cover 5 can be effectively suppressed. Therefore, pre-ignition can be effectively suppressed.

[0037] Furthermore, the length h of the joint surface 11 in the plug axial direction Z satisfies h≧t1 / 2, which makes it possible to easily increase the length L of the joint surface 11.

[0038] Furthermore, the length h of the joint surface 11 in the plug axial direction Z satisfies h≦t1. This allows the entire joint surface 11 to be efficiently welded. The fusion zone 12 is formed over the entire length of the joint surface 11 in the plug axial direction Z. This allows the heat dissipation from the plug cover 5 to the housing 2 to be improved.

[0039] In the above-mentioned method for manufacturing a spark plug for an internal combustion engine, the dimensions of each part before welding, that is, thickness t0a, thickness t1a, thickness t2a, and length La, satisfy t1a≧t0a, t2a≧1.5t1a, and La≧1.5t1a. This makes it possible to sufficiently secure a heat dissipation path from the plug cover 5 to the housing 2 via the joint surface 11 in the obtained spark plug 1. Therefore, it is possible to suppress a temperature rise of the plug cover 5. As a result, it is possible to suppress pre-ignition in the spark plug 1.

[0040] The thickness t0a, thickness t1a, thickness t2a, and length La can be the actual measured values ​​of each portion before welding. In this embodiment, the thickness t0a, thickness t1a, thickness t2a, and length La are substantially equal to the thickness t0, thickness t1, thickness t2, and length L, respectively. The effect of these dimensions satisfying the above relationship is the same as the effect of the thickness t0, thickness t1, thickness t2, and length L satisfying the above relationship.

[0041] As described above, according to the present embodiment, it is possible to provide a spark plug for an internal combustion engine that is capable of suppressing overheating of the plug cover, and a manufacturing method thereof.

[0042] (Embodiment 2) In this embodiment, as shown in FIG. 9, the contact surface 11a is configured by an upright surface 114a along the plug axial direction Z and an inclined surface 115a inclined with respect to the plug axial direction Z. The inclined surface 115a is inclined so as to be more inclined toward the base end side as it approaches the outer periphery side. In a cross section including the plug center axis PC, the sum of the length of the standing surface 114a and the length of the inclined surface 115a is the length L of the abutting surface 11a. The distance between the tip of the standing surface 114a and the base end of the inclined surface 115a in the plug axial direction Z is the length ha of the abutting surface 11a in the plug axial direction Z.

[0043] In this embodiment, t1a≧t0a, t2a≧1.5t1a, and La≧1.5t1a are satisfied. It is also preferable that ha≧t1a / 2 is satisfied. It is also preferable that ha≦t1a is satisfied.

[0044] Also, the joint surface 11 formed by joining the housing 2 and the plug cover 5 at this contact surface 11a can be understood directly or indirectly depending on the joining method. In this case, the length L and the length h are defined in the same way as La and ha at the contact surface 11a. This also applies to the third to fifth embodiments described later. In the obtained spark plug 1, t1≧t0, t2≧1.5t1, and L≧1.5t1 are satisfied. It is also preferable that h≧t1 / 2 is satisfied. It is also preferable that h≦t1 is satisfied.

[0045] The rest is the same as in embodiment 1. Note that, among the symbols used in embodiment 2 and onwards, the same symbols used in the previous embodiments represent the same components, etc. as in the previous embodiments, unless otherwise specified.

[0046] In the case of this embodiment as well, it is possible to provide a spark plug for an internal combustion engine that is capable of suppressing overheating of the plug cover, and a method for manufacturing the same. In addition, the same effects as those of the first embodiment can be obtained.

[0047] (Embodiment 3) In this embodiment, as shown in FIG. 10, the contact surface 11a is formed only of an inclined surface. In this embodiment, the length La of the contact surface 11a tends to be relatively short, but as long as it satisfies L≧1.5t1, the same effects as those of the first embodiment can be obtained. In addition, the second embodiment has the same configuration and effects as the first embodiment.

[0048] (Embodiment 4) In this embodiment, as shown in FIG. 11, the contact surface 11a is configured with two inclined surfaces. One of the inclined surfaces constituting the abutment surface 11a is inclined gradually toward the base end from the inner circumferential surface of the plug cover 5 toward the center in the thickness direction. The other inclined surface is inclined gradually toward the base end from the outer circumferential surface of the plug cover 5 toward the center in the thickness direction. In a cross section including the plug central axis PC, the length La of the abutment surface 11a is defined as the sum of the lengths of these two inclined surfaces. In addition, the second embodiment has the same configuration and effects as the first embodiment.

[0049] (Embodiment 5) In this embodiment, as shown in FIG. 12, an uneven surface is provided on the contact surface 11a at a portion where the plug cover 5 and the housing 2 face each other in the plug axial direction Z. The plug cover 5 and the housing 2 are fitted together at this uneven surface. In this embodiment, in a cross section including the plug central axis PC, the length La of the contact surface 11a is defined as the sum of the length along the uneven surface and the length of the standing surface 114a. In addition, the second embodiment has the same configuration and effects as the first embodiment.

[0050] (Embodiment 6) This embodiment is defined by the relationship between the thickness of the ground electrode 6 and the dimensions of the joint surface of the ground electrode 6 with the housing 2 (that is, the ground joint surface 14), as shown in Figs.

[0051] The ground electrode 6 is joined to the housing 2 via a ground contact surface 14. As shown in Fig. 13, the thickness of the ground electrode 6 when viewed from a direction perpendicular to both the extension direction of the ground electrode 6 and the plug axial direction Z is defined as t3. Furthermore, the length of the ground contact surface 14 appearing in a cross section including the plug central axis PC (i.e., the cross section shown in Fig. 13) is defined as W. In this case, W ≥ 1.5t3 is satisfied.

[0052] In this embodiment, the ground contact surface 14 is formed on the inner circumferential surface of the housing 2. The ground electrode 6 is inclined from the ground contact surface 14 toward the tip side in the plug axial direction Z as it moves toward the plug central axis PC. As shown in Fig. 14, the ground electrode 6 protrudes in the plug radial direction when viewed from the plug axial direction Z.

[0053] The inclination angle α of the ground electrode 6 with respect to the inner circumferential surface of the housing 2 is 41.8° or less. This satisfies W≧1.5t3. In this embodiment, since the inner circumferential surface of the housing 2 is approximately parallel to the plug axial direction Z, the inclination angle of the ground electrode 6 with respect to the plug axial direction Z coincides with the inclination angle α.

[0054] The cross section of the ground electrode 6 perpendicular to the extension direction has a substantially rectangular shape. The dimension of this substantially rectangular cross section in a direction perpendicular to the plug circumferential direction corresponds to a thickness t3. The ground electrode 6 is made of nickel or an alloy mainly composed of nickel. The housing 2 is made of low carbon steel.

[0055] When joining the ground electrode 6 to the housing 2, the joined portion 69 of the ground electrode 6 is brought into contact with a part of the housing 2. The ground electrode 6 is joined to the housing 2 by welding the contact surface 14a. The dimensions of each part before welding satisfy the following requirements. The thickness of the ground electrode 6 when viewed from a direction perpendicular to both the extension direction of the ground electrode 6 and the plug axial direction Z is defined as ta3. The length of the contact surface 14a that appears in a cross section including the plug central axis PC is defined as Wa. In this case, Wa ≧ 1.5ta3 is satisfied.

[0056] The ground electrode 6 can be welded to the housing 2 by resistance welding. In this case, the ground interface 14 remains as an interface that can be identified. On the other hand, the ground electrode 6 can also be welded to the housing 2 by laser welding. In this case, a molten part may be formed in the finished spark plug 1, making it impossible to closely observe the ground interface 14. In such a case, the position of the ground interface 14, etc. can be estimated by the same method as in the first embodiment. The rest is the same as in the first embodiment.

[0057] In this embodiment, overheating of the ground electrode 6 can also be effectively suppressed. That is, the thickness t3 of the ground electrode 6 and the length W of the ground interface 14 satisfy W≧1.5t3. This makes it possible to sufficiently secure a discharge path from the ground electrode 6 to the housing 2 via the ground interface 14. This makes it possible to suppress a rise in temperature of the ground electrode 6. As a result, pre-ignition of the spark plug 1 can be further suppressed.

[0058] Moreover, the ground electrode 6 is made of nickel or an alloy mainly composed of nickel, and the housing 2 is made of low carbon steel. Therefore, the thermal conductivity of the ground electrode 6 is approximately 1.5 times that of the housing 2. In this case, if the thickness t3 of the ground electrode 6 and the length W of the ground interface 14 are equivalent, there is a risk that heat transfer from the ground electrode 6, which has a relatively high thermal conductivity, to the housing 2, which has a relatively low thermal conductivity, will not be efficient. Therefore, by setting W≧1.5t3, it is possible to prevent the ground interface 14 from limiting the rate of heat flow, and to perform efficient heat dissipation.

[0059] In this way, according to this embodiment, it is possible to effectively prevent overheating of the ground electrode 6 in addition to preventing overheating of the plug cover 5. As a result, pre-ignition can be further suppressed.

[0060] In the manufacturing method of the spark plug 1 for an internal combustion engine, the dimensions of each part before welding, that is, the length Wa and the thickness t3a, satisfy Wa≧1.5t3a. This makes it possible to sufficiently secure a heat dissipation path from the plug cover 5 to the housing 2 via the joint surface 11 in the obtained spark plug 1. In addition, the same effects as those of the first embodiment are achieved.

[0061] (Embodiment 7) In this embodiment, as shown in FIG. 15 , the ground electrode 6 has a shape including a standing portion 61 extending along the plug axial direction Z and an extension portion 62 bent from the tip of the standing portion 61 toward the inside in the plug radial direction. That is, the ground electrode 6 has a substantially L-shape.

[0062] The base end of the standing portion 61 of the ground electrode 6 is joined to the housing 2. That is, the base end of the standing portion 61 becomes the joined portion 69. Here, a step portion 21 is formed in a part of the tip portion of the housing 2, which is set back toward the base end side on the inner circumferential side from the outer circumferential side in the plug radial direction. The base end of the standing portion 61 is disposed on this step portion 21 and joined to the housing 2. In this case, the ground joint surface 14 is the base end surface at the base end of the standing portion 61 and a part of the outer circumferential side surface. Therefore, the length W of the ground joint surface 14 is the sum of the thickness t3 of the ground electrode 6 and the depth d of the step portion 21. The rest is the same as in the sixth embodiment, and has the same effects.

[0063] (Embodiment 8) In this embodiment, as shown in FIG. 16, the base end surface of the standing portion 61 of the ground electrode 6 is an inclined end surface.

[0064] An inclined surface is formed at the tip end of the housing 2 to join the inclined end surface of the ground electrode 6. As a result, a ground joint surface 14, which is the joint surface between the housing 2 and the ground electrode 6, is inclined with respect to the plug axial direction Z.

[0065] In this case, the ground interface 14 is inclined with respect to the erect direction of the erect portion 61 of the ground electrode 6. This makes the length W of the ground interface 14 larger than the thickness t3 of the ground electrode 6. By making this inclination angle β 41.8° or less, it is possible to satisfy W≧1.5t3. The rest is the same as in the sixth embodiment, and has the same effects.

[0066] The present invention is not limited to the above-described embodiments, and can be applied to various embodiments without departing from the gist of the present invention. [Explanation of symbols]

[0067] 1...spark plug for internal combustion engine, 11...joint surface, 11a...contact surface, 2...housing, 3...insulator, 4...center electrode, 5...plug cover, 50...auxiliary combustion chamber, 51...nozzle hole, 59...jointed portion, 6...ground electrode, G...discharge gap

Claims

1. A cylindrical insulator (3); a center electrode (4) held on the inner circumferential side of the insulator and protruding from the insulator toward the tip side; a cylindrical housing (2) that holds the insulator on its inner periphery; a ground electrode (6) forming a discharge gap (G) between itself and the center electrode; a plug cover (5) joined to the tip end of the housing via a joining surface so as to cover a sub-combustion chamber (50) in which the discharge gap is arranged, The plug cover is formed with a nozzle hole (51) that communicates the auxiliary combustion chamber with the outside, The thickness of the plug cover on the tip side of the ground electrode is t0, The thickness of the joined portion (59) of the plug cover joined to the front end portion of the housing is t1, The thickness of the tip of the housing is t2, When the length of one of the two mating surfaces appearing in a cross section including the central axis of the plug is L, t1 ≧ t0, t2 ≧ 1.5t1, and L ≧ 1.5t1 are satisfied; a length h of the joint surface in the plug axial direction satisfies h≦t1, the joint surface is joined by welding, and a fusion zone is formed over the entire length of the joint surface in the plug axial direction.

2. 2. The spark plug for an internal combustion engine according to claim 1, wherein the ground electrode is joined to the housing via a ground contact surface (14), and where t3 is a thickness of the ground electrode when viewed from a direction perpendicular to both an extension direction of the ground electrode and an axial direction of the plug, and W is a length of the ground contact surface appearing in a cross section including a central axis of the plug, W≧1.5t3 is satisfied.

3. A cylindrical insulator (3); a center electrode (4) held on the inner circumferential side of the insulator and protruding from the insulator toward the tip side; a cylindrical housing (2) that holds the insulator on its inner periphery; a ground electrode (6) forming a discharge gap (G) between itself and the center electrode; a plug cover (5) joined to the tip end of the housing via a joining surface so as to cover a sub-combustion chamber (50) in which the discharge gap is arranged, The plug cover is formed with a nozzle hole (51) that communicates the auxiliary combustion chamber with the outside, The thickness of the plug cover on the tip side of the ground electrode is t0, The thickness of the joined portion (59) of the plug cover joined to the front end portion of the housing is t1, The thickness of the tip of the housing is t2, When the length of one of the two mating surfaces appearing in a cross section including the central axis of the plug is L, t1 ≧ t0, t2 ≧ 1.5t1, and L ≧ 1.5t1 are satisfied; The ground electrode is joined to the housing via a ground contact surface (14), and when a thickness of the ground electrode as viewed from a direction perpendicular to both an extension direction of the ground electrode and an axial direction of the plug is defined as t3, and a length of the ground contact surface as seen in a cross section including a central axis of the plug is defined as W, a relationship W≧1.5t3 is satisfied.

4. 4. The spark plug for an internal combustion engine according to claim 2, wherein said ground electrode is made of nickel or an alloy containing nickel as a main component, and said housing is made of low carbon steel.

5. 5. The spark plug for an internal combustion engine according to claim 1, wherein a length h of the joint surface in the plug axial direction satisfies h≧t1 / 2.

6. 6. The spark plug for an internal combustion engine according to claim 1, wherein the plug cover is made of nickel or an alloy containing nickel as a main component, and the housing is made of low carbon steel.

7. A method for manufacturing a spark plug for an internal combustion engine, comprising: a cylindrical insulator (3); a center electrode (4) held on an inner periphery of the insulator and protruding from the insulator toward a tip end; a cylindrical housing (2) holding the insulator on its inner periphery; a ground electrode (6) forming a discharge gap (G) between the center electrode and the ground electrode; and a plug cover (5) joined to a tip end of the housing so as to cover an auxiliary combustion chamber (50) in which the discharge gap is located, The plug cover is formed with a nozzle hole (51) that communicates the auxiliary combustion chamber with the outside, The plug cover is joined to the front end portion of the housing by abutting the joined portion (59) of the plug cover to the front end portion of the housing and welding the abutment surface (11a); The dimensions of each part before welding are as follows: The thickness of the plug cover on the tip side of the ground electrode is t0a, The thickness of the joined portion to be joined to the front end portion of the housing is t1a, The thickness of the tip of the housing is t2a, When the length of one of the two abutment surfaces appearing in a cross section including the central axis of the plug is La, t1a ≧ t0a, t2a ≧ 1.5t1a, and La ≧ 1.5t1a are satisfied; a length ha of the abutment surface in the axial direction of the plug satisfies ha≦t1a, the abutment surface is joined by welding, and the welding is performed so that a molten portion is formed over the entire length of the abutment surface in the axial direction of the plug.

8. The ground electrode is joined to the housing via a ground joint surface (14), a portion of the housing to be joined to the ground electrode and a contact surface of the ground electrode is welded to the housing; The dimensions of each part before welding are as follows:

8. The method for manufacturing a spark plug for an internal combustion engine according to claim 7, wherein, when a thickness of the ground electrode as viewed from a direction perpendicular to both an extension direction of the ground electrode and an axial direction of the plug is defined as ta3, and a length of the abutment surface appearing in a cross section including a central axis of the plug is defined as Wa, Wa ≧ 1.5ta3 is satisfied.

9. A method for manufacturing a spark plug for an internal combustion engine, comprising: a cylindrical insulator (3); a center electrode (4) held on an inner periphery of the insulator and protruding from the insulator toward a tip end; a cylindrical housing (2) holding the insulator on its inner periphery; a ground electrode (6) forming a discharge gap (G) between the center electrode and the ground electrode; and a plug cover (5) joined to a tip end of the housing so as to cover an auxiliary combustion chamber (50) in which the discharge gap is located, The plug cover is formed with a nozzle hole (51) that communicates the auxiliary combustion chamber with the outside, The plug cover is joined to the front end portion of the housing by abutting the joined portion (59) of the plug cover to the front end portion of the housing and welding the abutment surface (11a); The dimensions of each part before welding are as follows: The thickness of the plug cover on the tip side of the ground electrode is t0a, The thickness of the joined portion to be joined to the front end portion of the housing is t1a, The thickness of the tip of the housing is t2a, When the length of one of the two abutment surfaces appearing in a cross section including the central axis of the plug is La, t1a ≧ t0a, t2a ≧ 1.5t1a, and La ≧ 1.5t1a are satisfied; The ground electrode is joined to the housing via a ground joint surface (14), a portion of the housing to be joined to the ground electrode and a contact surface of the ground electrode is welded to the housing; The dimensions of each part before welding are as follows:

2. A method for manufacturing a spark plug for an internal combustion engine, wherein, when a thickness of the ground electrode as viewed from a direction perpendicular to both an extension direction of the ground electrode and an axial direction of the plug is defined as ta3, and a length of the abutment surface appearing in a cross section including a central axis of the plug is defined as Wa, the relationship Wa≧1.5ta3 is satisfied.

10. 10. The method for manufacturing a spark plug for an internal combustion engine according to claim 8, wherein the ground electrode is made of nickel or an alloy containing nickel as a main component, and the housing is made of low carbon steel.

11. The method for manufacturing a spark plug for an internal combustion engine according to any one of claims 7 to 10, wherein a length ha of the contact surface in the plug axial direction satisfies ha ≧ t1a / 2.

12. 12. The method for manufacturing a spark plug for an internal combustion engine according to claim 7, wherein the plug cover is made of nickel or an alloy mainly composed of nickel, and the housing is made of low carbon steel.

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