Spark plugs for internal combustion engines

Abstract

To provide a spark plug for an internal-combustion engine, which can be easily suppressed in preignition and can be easily manufactured.SOLUTION: A spark plug 1 for an internal-combustion engine is provided, including: an insulator 3; a center electrode 4; a housing 2; a ground electrode 6; and a plug cover 5. The ground electrode 6 includes: a standing portion 62 that stands to a distal end side from a fixed end portion 61 fixed to a tip end portion of the housing 2; and an extension portion 64 that extends to a plug central axis C side via a bent portion 63 from the distal end of the standing portion 62. A distal end 41 of the center electrode 4 is arranged in more distal end side than a distal end 21 of the housing 2. A discharge gap G is formed in a portion where the extension portion 64 of the ground electrode 6 and the distal end 41 of the center electrode 4 are opposite to a plug axis direction Z. A level-difference portion 22 opened to an inner peripheral side is provided in the tip end portion of the housing 2. The fixed end portion 61 of the ground electrode 6 is joined to the housing 2 in the level-difference portion 22.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a spark plug for an internal combustion engine. [Background technology]

[0002] A spark plug equipped with an auxiliary combustion chamber is disclosed in, for example, Patent Document 1. In this spark plug, one end of a ground electrode provided in the auxiliary combustion chamber is fixed to a front end of a housing. The ground electrode extends from the front end of the housing toward the front end side and is bent toward the central axis of the plug. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-93293 Summary of the Invention [Problem to be solved by the invention]

[0004] However, if the ground electrode protrudes too far from the tip of the housing, the temperature of the ground electrode is likely to rise during use of the spark plug. Furthermore, the temperature of a portion of the plug cover that is located further toward the tip than the ground electrode is likely to rise. This raises concerns about pre-ignition. On the other hand, if an attempt is made to shorten the length of the ground electrode protruding from the tip of the housing, it becomes difficult to bend the ground electrode.

[0005] The present invention has been made in view of the above problems, and has an object to provide a spark plug for an internal combustion engine that is easy to manufacture and that easily suppresses pre-ignition. [Means for solving the problem]

[0006] One 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) provided at a tip end of the housing so as to cover a sub-combustion chamber (50) in which the discharge gap is disposed, The ground electrode has a standing portion (62) standing toward the front end side from a fixed end (61) fixed to the front end portion of the housing, and an extension portion (64) extending from the front end of the standing portion toward the plug central axis (C) side via a bent portion (63), The tip (41) of the center electrode is disposed further forward than the tip (21) of the housing, the discharge gap is formed at a portion where the extension portion of the ground electrode and the tip of the center electrode face each other in the plug axial direction (Z), A step portion (22) that is open to the inner periphery is provided at the tip end of the housing, The fixed end of the ground electrode is joined to the housing at the stepped portion. And, The step portion is formed around the entire inner periphery of the tip portion of the housing. , in spark plugs for internal combustion engines. Effect of the Invention

[0007] In the spark plug for an internal combustion engine, the step portion is provided at the tip end of the housing. This allows the fixed end of the ground electrode to be positioned closer to the base end. Therefore, even if a certain length of the erected portion is secured, the protruding length of the ground electrode from the tip end of the housing can be suppressed. As a result, it is possible to easily bend the ground electrode and suppress pre-ignition.

[0008] As described above, according to the above aspect, it is possible to provide a spark plug for an internal combustion engine that is easy to manufacture and that easily suppresses pre-ignition. 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]

[0009] [Figure 1] FIG. 3 is an explanatory cross-sectional view of a spark plug for an internal combustion engine according to a first embodiment, the cross-sectional view being taken along line II in FIG. 2. [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 taken along line III-III in FIG. [Figure 4] FIG. 4 is a cross-sectional explanatory view of a sub-assembly before a ground electrode and a plug cover are attached in the first embodiment; [Diagram 5] FIG. 11 is a plan view of the tip portion of the housing in the first reference embodiment, as viewed from the tip side. [Figure 6] FIG. 11 is an explanatory diagram showing a state in which an electrode member is joined to a housing in the first embodiment. [Figure 7] FIG. 11 is an explanatory diagram of a state after bending the ground electrode in the first embodiment. [Figure 8] FIG. 11 is an explanatory diagram of a state immediately before the plug cover is attached to the housing in the first embodiment. [Figure 9] FIG. 11 is an explanatory diagram of a state immediately before a ground electrode bent in advance is assembled into a housing in the first reference embodiment. [Figure 10] FIG. 6 is an explanatory cross-sectional view of a spark plug for an internal combustion engine according to a second embodiment. [Figure 11] FIG. 11 is a plan view of the tip portion of the housing in the second embodiment, as viewed from the tip side. [Figure 12] FIG. 11 is a plan view of the base end portion of the plug cover in the second embodiment, as viewed from the base end side. [Figure 13] FIG. 11 is an explanatory cross-sectional view of a spark plug for an internal combustion engine according to a third embodiment. [Figure 14] FIG. 13 is an explanatory diagram of a state immediately before the ground electrode is attached to the housing in the third reference embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] ( Reference form 1 ) An embodiment of a spark plug for an internal combustion engine 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.

[0011] The center electrode 4 is held on the inner periphery of the insulator 3 and protrudes from the insulator 3 toward the tip side. The housing 2 holds the insulator 3 on the inner periphery. The ground electrode 6 forms a discharge gap G between the center electrode 4 and the ground electrode 6. The plug cover 5 is provided at the tip of the housing 2 to cover the auxiliary combustion chamber 50 in which the discharge gap G is located.

[0012] The ground electrode 6 has an erected portion 62 and an extended portion 64. The erected portion 62 is a portion that erects toward the tip side from a fixed end portion 61 that is fixed to the tip portion of the housing 2. The extended portion 64 is a portion that extends from the tip of the erected portion 62 via a bent portion 63 toward the plug central axis C side.

[0013] As shown in Fig. 1, the tip 41 of the center electrode 4 is disposed further forward than the tip 21 of the housing 2. A discharge gap G is formed at a portion where the extension portion 64 of the ground electrode 6 and the tip 41 of the center electrode 4 face each other in the plug axial direction Z. A stepped portion 22 that is open toward the inner periphery is provided at the tip of the housing 2. The fixed end portion 61 of the ground electrode 6 is joined to the housing 2 at the stepped portion 22.

[0014] The spark plug 1 of this embodiment can be used as an ignition means in an internal combustion engine of an automobile, a cogeneration system, or the like. One end of the spark plug 1 in the plug axial direction Z is disposed in the main combustion chamber of the internal combustion engine. In the plug axial direction Z, the side exposed to the main combustion chamber is referred to as the tip side, and the opposite side is referred to as the base side. Also, the direction perpendicular to the central axis of the spark plug 1 (i.e., the plug central axis C) is referred to as the plug radial direction. Also, the direction along the circumference centered on the plug central axis C is referred to as the plug circumferential direction.

[0015] The housing 2 has an attachment thread portion 23 on its outer circumferential surface. The spark plug 1 is attached to the internal combustion engine by screwing this attachment thread portion 23 into a female thread portion formed in a plug hole of the internal combustion engine. This attachment thread portion 23 forms a part of the heat dissipation path from the spark plug 1 to peripheral members (such as the engine head).

[0016] 2, in this embodiment, the step portion 22 of the housing 2 is formed in a part of the plug circumferential direction. The width W of the step portion 22 is equal to or greater than the width of the fixed end portion 61 of the ground electrode 6. In this embodiment, the width W of the step portion 22 is slightly larger than the width of the fixed end portion 61 of the ground electrode 6. Here, the width W of the step portion 22 and the width of the fixed end portion 61 are lengths in a direction perpendicular to both the plug axial direction Z and the plug radial direction.

[0017] Further, the depth d1 of the step portion 22 in the plug radial direction is approximately equal to the thickness of the fixed end portion 61 of the ground electrode 6 in the plug radial direction. However, the depth d1 of the step portion 22 can also be made larger than the thickness of the fixed end portion 61.

[0018] 1, the stepped portion 22 has a ceiling surface 221 facing the tip side at the base end side in the plug axial direction Z. The stepped portion 22 also has an inward surface 222 facing the inner periphery side at the outer periphery side in the plug radial direction. Also, as shown in FIG. 2, the stepped portion 22 has a pair of side wall surfaces 223 facing each other on both sides in the plug circumferential direction.

[0019] The fixed end 61 of the ground electrode 6 is accommodated in the step portion 22. The fixed end 61 is fixed to the housing 2 at the step portion 22 by welding or the like. The fixed end 61 may be joined to the ceiling surface 221, for example. Alternatively, the fixed end 61 may be joined to at least one of the inward surface 222 and the side wall surface 223, for example. Alternatively, the fixed end 61 may be joined to the ceiling surface 221 and also to at least one of the inward surface 222 and the side wall surface 223.

[0020] 1 and 3, the plug cover 5 is formed with injection holes 51 that communicate the auxiliary combustion chamber 50 with the outside. In this embodiment, four injection holes 51 are formed. When viewed from the plug axial direction Z, the injection hole axes of the injection holes 51 are inclined with respect to the plug radial direction. However, the number, orientation, shape, etc. of the injection holes 51 are not particularly limited. For example, when viewed from the plug axial direction Z, the injection hole axes of the injection holes 51 may be configured to face the plug radial direction.

[0021] The plug cover 5 has a generally cup shape, and an open end thereof is joined to the tip portion of the housing 2. As shown in Fig. 1 and Fig. 3, the plug cover 5 has an accommodating recess 52 in a part of the plug circumferential direction on an inner circumferential surface 53 along the plug axial direction Z. A part of the erected portion 62 of the ground electrode 6 is accommodated in the accommodating recess 52. In this embodiment, a part of the bent portion 63 of the ground electrode 6 is also disposed in the accommodating recess 52.

[0022] The plug cover 5 is made of, for example, a nickel alloy. The housing 2 is made of, for example, low carbon steel. The ground electrode 6 is made of, for example, a nickel alloy.

[0023] Next, a method for manufacturing the spark plug 1 of this embodiment will be described. First, as shown in Fig. 4, a sub-assembly is prepared in which a center electrode 4 and an insulator 3 are assembled inside a housing 2. Here, as shown in Figs. 4 and 5, a step portion 22 is formed at the front end of the housing 2. This step portion 22 can be formed in advance by performing cutting or the like on the housing 2. Note that Fig. 5 is a view of the front end surface of the housing 2 as viewed from the front end side.

[0024] 6 and 7, the ground electrode 6 is joined to the housing 2. At this time, first, a rod-shaped electrode member 60, which is the ground electrode 6 before bending, is joined to the housing 2 as shown in Fig. 6. One end of the electrode member 60 is arranged and erected in the stepped portion 22 of the housing 2 so that the longitudinal direction of the rod-shaped electrode member 60 is along the plug axial direction Z. Then, one end of the electrode member 60 is joined to the stepped portion 22 by laser welding or the like.

[0025] Next, the electrode member 60, one end of which is fixed to the housing 2, is bent. That is, the electrode member 60 is bent at a predetermined position toward the plug central axis C. At this time, the electrode member 60 is bent while a part of the base end side of the electrode member 60 is fixed by a fixing jig (not shown). As a result, the ground electrode 6 having a bent portion 63 formed thereon is obtained, as shown in FIG.

[0026] Further, a discharge gap G is formed between the base end side surface of the extension portion 64 of the ground electrode 6 and the tip 41 of the center electrode 4. In order to finely adjust the size of this discharge gap G, the position of the extension portion 64 is finely adjusted. That is, the bend angle of the bent portion 63 is finely adjusted to finely adjust the discharge gap G. This fine adjustment of the discharge gap G is performed while observing the discharge gap G. Here, the tip 41 of the center electrode 4 is located closer to the tip side than the tip 21 of the housing 2, so that the size of the discharge gap G can be easily observed by, for example, a camera.

[0027] After fine-tuning the discharge gap G, as shown in Fig. 8 and Fig. 1, the plug cover 5 is joined to the front end of the housing 2. As described above, the accommodating recess 52 is formed in the plug cover 5 (see Fig. 5). The accommodating recess 52 is aligned in the plug circumferential direction so that the position of the accommodating recess 52 matches the position of the erected portion 62 of the ground electrode 6. As a result, the plug cover 5 is placed at the front end of the housing 2 with part of the erected portion 62 of the ground electrode 6 accommodated in the accommodating recess 52. The abutting portions of the housing 2 and the plug cover 5 are then joined by laser welding or the like. Through the above steps, the spark plug 1 as shown in FIG. 1 is assembled.

[0028] As shown in FIG. 9, the ground electrode 6 bent in advance can be fixed to the housing 2. In this case, the fixed end 61 of the ground electrode 6 is joined to the step portion 22 of the housing 2, and then the discharge gap G is finely adjusted. This fine adjustment of the discharge gap G is basically performed by deforming the ground electrode 6 in a direction in which the base end side surface of the extension portion 64 approaches the tip end 41 of the center electrode 4. Therefore, it is preferable that the angle α between the standing portion 62 and the extension portion 64 of the ground electrode 6 before being fixed to the housing 2 is an obtuse angle. For example, it is preferable that the angle α is 90°<α<135°. After that, the plug cover 5 is joined to the housing 2 in the same manner as above (see FIG. 8 and FIG. 1).

[0029] Next, the effects of this embodiment will be described. In the above spark plug 1 for an internal combustion engine, a step portion 22 is provided at the tip portion of the housing 2. This allows the fixed end portion 61 of the ground electrode 6 to be located closer to the base end side. Therefore, even if a certain length of the standing portion 62 is ensured, the protruding length of the ground electrode 6 from the tip portion 21 of the housing 2 can be reduced. As a result, the bending process of the ground electrode 6 can be easily performed and pre-ignition can be suppressed.

[0030] That is, if the step portion 22 were not formed in the housing 2, the fixed end 61 of the ground electrode 6 would be joined by abutting it against the tip 21 of the housing 2. In this case, the protruding length of the ground electrode 6 from the tip 21 of the housing 2 would be large. In this case, when the spark plug is attached to an internal combustion engine, the ground electrode 6 would be closer to the center of the main combustion chamber and would be more likely to become hotter. Also, in this case, the tip of the plug cover 5 would be closer to the center of the main combustion chamber and would be more likely to become hotter. As a result, it becomes more difficult to suppress pre-ignition.

[0031] In addition, it is desirable that the standing portion 62 of the ground electrode 6 has a certain degree of length in consideration of the ease of forming the bent portion 63. In other words, it is desirable to ensure that the standing portion 62 has a sufficient length as a portion to be held by a jig or the like when bending the ground electrode 6.

[0032] Therefore, in the spark plug 1 of this embodiment, by providing the step portion 22 at the tip portion of the housing 2, it is possible to reduce the amount of protrusion of the ground electrode 6 from the tip portion 21 of the housing 2 while ensuring the length of the standing portion 62 of the ground electrode 6. As a result, it is possible to facilitate bending of the ground electrode 6 and to facilitate suppression of pre-ignition.

[0033] In addition, the plug cover 5 has an accommodating recess 52. This ensures the thickness of the plug cover 5 in places other than the accommodating recess 52. This allows heat to be dissipated smoothly from the plug cover 5 via the housing 2. Furthermore, the plug cover 5 has an accommodating recess 52, which makes it possible to position the plug cover 5 in the circumferential direction of the plug relative to the housing 2 and the ground electrode 6. This makes it easy to set the positional relationship of the injection hole 51 of the plug cover 5 relative to the main combustion chamber and the ground electrode 6 to a predetermined positional relationship.

[0034] As described above, according to the present embodiment, it is possible to provide a spark plug for an internal combustion engine that is easy to manufacture and that can easily suppress pre-ignition.

[0035] (Embodiment 2) In this embodiment, as shown in FIGS. 10 to 12, a step portion 22 is formed over the entire inner periphery of the tip portion of the housing 2. As shown in FIG.

[0036] 11, when the housing 2 is viewed from the tip side in the plug axial direction Z, the step portion 22 is formed in an annular shape. The step portion 22 is formed with a constant depth in the plug radial direction and a constant depth in the plug axial direction over the entire circumference. That is, the step portion 22 is formed uniformly over the entire circumference. The depth d1 of the step portion 22 in the plug radial direction is desirably equal to or greater than the thickness of the fixed end portion 61 of the ground electrode 6 in the plug radial direction.

[0037] 10 and 12, the base end of the plug cover 5 has a protrusion 54 that fits into the stepped portion 22. The protrusion 54 protrudes from a part of the inner periphery of the base end of the plug cover 5 toward the base end so as to follow the inner periphery 53 of the plug cover 5. As shown in Fig. 12, the protrusion 54 is formed continuously around the entire circumferential circumference of the plug except for the portion where the ground electrode 6 is fixed.

[0038] Others: Reference form 1 In addition, among the reference characters used in the second and subsequent embodiments, the same reference characters as those used in the previous embodiments represent the same components, etc. as those in the previous embodiments, unless otherwise specified.

[0039] In this embodiment, the ground electrode 6 can be more easily assembled to the housing 2. That is, the step portion 22 is formed over the entire circumference in the circumferential direction of the plug. Therefore, the fixed end portion 61 of the ground electrode 6 can be joined to the front end portion of the housing 2 at any position in the circumferential direction of the plug. Therefore, it is not necessary to determine the position of the ground electrode 6 relative to the housing 2 in the circumferential direction of the plug. Therefore, the ground electrode 6 can be assembled to the housing 2 efficiently. Others: Reference form 1 It has the same effect as above.

[0040] ( Reference form 3 ) As shown in Figs. 13 and 14, this embodiment is as follows: Reference form 1 2, the ground electrode 6 has a modified shape. In the spark plug 1 of this embodiment, the ground electrode 6 has a length L1 in the standing direction of the standing portion 62 and a length L2 in the extending direction of the extending portion 64 which are equal to each other.

[0041] In this embodiment, the ground electrode 6 has an upright portion 62 and an extended portion 64 that are symmetrical with respect to the bent portion 63. The depth of the step portion 22 of the housing 2 is set appropriately according to the length of the upright portion 62. In this embodiment, the depth of the step portion 22 is set to half or more of the length of the ground electrode 6 in the plug axial direction Z. Here, the length of the ground electrode 6 in the plug axial direction Z is approximately equal to the sum of the length L1 of the upright portion 62 and the thickness of the extended portion 64. The depth of the step portion 22 is not particularly limited.

[0042] In this embodiment, as shown in Fig. 14, the ground electrode 6 having the bent portion 63 is prepared before the ground electrode 6 is joined to the housing 2. However, before the joining stage, it is preferable that the angle α between the standing portion 62 and the extension portion 64 is an obtuse angle. For example, it is preferable that the angle α is 90°<α<135°. At this stage, the standing portion 62 and the extension portion 64 are not particularly distinguished from each other.

[0043] Then, one end of the ground electrode 6 is placed in the step portion 22, and the ground electrode 6 is joined to the housing 2. After that, the discharge gap G is finely adjusted. Others: Reference form 1 is the same as:

[0044] In this embodiment, before the ground electrode 6 is assembled to the housing 2, there is no particular distinction between the standing portion 62 and the extending portion 64. In other words, either end of the ground electrode 6 may be joined to the housing 2. This facilitates the assembly of the ground electrode 6 to the housing 2. As a result, the productivity of the spark plug 1 can be improved. others, Reference form 1 It has the same effect as above.

[0045] 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]

[0046] 1...spark plug for internal combustion engine, 2...housing, 21...tip (of housing), 22...step, 3...insulator, 4...center electrode, 41...tip (of center electrode), 5...plug cover, 50...auxiliary combustion chamber, 6...ground electrode, 61...fixed end, 62...standing portion, 63...bent portion, 64...extension, C...plug center axis, Z...plug axial direction

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) provided at a tip end of the housing so as to cover a sub-combustion chamber (50) in which the discharge gap is disposed, The ground electrode has a standing portion (62) standing toward the front end side from a fixed end (61) fixed to the front end portion of the housing, and an extension portion (64) extending from the front end of the standing portion toward the plug central axis (C) side via a bent portion (63), The tip (41) of the center electrode is disposed on the tip side of the tip (21) of the housing, the discharge gap is formed at a portion where the extension portion of the ground electrode and the tip of the center electrode face each other in the plug axial direction (Z), The housing has a step (22) at the tip thereof that is open to the inner periphery. the fixed end of the ground electrode is joined to the housing at the stepped portion, a step portion formed around an entire inner periphery of the tip portion of the housing;

2. A spark plug for an internal combustion engine as described in claim 1, wherein the step portion has a ceiling surface (221) facing the tip side at the base end in the plug axial direction, and the fixed end portion is joined to the ceiling surface.

3. 3. The spark plug for an internal combustion engine according to claim 1, wherein the plug cover has an accommodating recess (52) in a part of a circumferential direction of the plug on an inner circumferential surface along an axial direction of the plug, the accommodating recess (52) adapted to accommodate a part of the erected portion of the ground electrode.

4. 4. A spark plug for an internal combustion engine according to claim 1, wherein the ground electrode has a length (L1) in the standing direction of the standing portion and a length (L2) in the extension direction of the extended portion which are equal to each other.

Images