JP7615974B2 - Spark plugs for internal combustion engines - Google Patents

Description

The present invention relates to a spark plug for an internal combustion engine.

A spark plug equipped with a pre-combustion chamber is disclosed, for example, in Patent Document 1. In this spark plug, one end of a ground electrode provided in the pre-combustion chamber is fixed to the tip of the housing. The ground electrode extends from the tip of the housing toward the tip side and is bent toward the central axis of the plug.

JP 2021-93293 A

However, if the ground electrode protrudes too far from the tip of the housing, the temperature of the ground electrode is more likely to rise when the spark plug is in use. Furthermore, the temperature of the part of the plug cover that is located further towards the tip than the ground electrode is more likely to rise. This raises concerns about pre-ignition. On the other hand, if an attempt is made to shorten the length by which the ground electrode protrudes from the tip of the housing, it becomes more difficult to bend the ground electrode.

The present invention was made in consideration of these problems, and aims to provide a spark plug for internal combustion engines that is easy to manufacture and makes it easy to suppress pre-ignition.

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 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 ,
The stepped portion is formed around the entire inner periphery of the tip portion of the housing , and is located in a spark plug for an internal combustion engine.

In the spark plug for an internal combustion engine, the tip of the housing is provided with the step portion. 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 of the housing can be suppressed. As a result, pre-ignition can be suppressed while facilitating bending of the ground electrode.

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.

FIG. 3 is a cross-sectional explanatory view of a spark plug for an internal combustion engine according to a first embodiment , the cross-section being taken along line II in FIG. 2 . FIG. 2 is a cross-sectional view taken along line II-II of FIG. FIG. 3 is a cross-sectional view taken along line III-III in FIG. FIG. 11 is a cross-sectional view of a sub-assembly before a ground electrode and a plug cover are attached in the first embodiment; FIG. 11 is a plan view of the tip portion of the housing in the first embodiment, as viewed from the tip side. FIG. 11 is an explanatory diagram showing a state in which the electrode member is joined to the housing in the first embodiment. FIG. 11 is an explanatory diagram of a state after bending a ground electrode in the first embodiment. FIG. 11 is an explanatory diagram of a state immediately before the plug cover is attached to the housing in the first embodiment; 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 embodiment; FIG. 11 is a cross-sectional view illustrating a spark plug for an internal combustion engine according to a second embodiment. FIG. 11 is a plan view of the tip portion of the housing in the second embodiment, as viewed from the tip side. 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. FIG. 11 is a cross-sectional view of a spark plug for an internal combustion engine according to a third embodiment . FIG. 13 is an explanatory diagram of a state immediately before the ground electrode is assembled to the housing in the third embodiment;

( 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 has 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.

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.

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.

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 where the extension 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 step 22 that is open to the inner circumference is provided at the tip of the housing 2. The fixed end 61 of the ground electrode 6 is joined to the housing 2 at the step 22.

The spark plug 1 of this embodiment can be used as an ignition means in internal combustion engines of automobiles, cogeneration systems, etc. 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. 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. The direction along the circumference centered on the plug central axis C is referred to as the plug circumferential direction.

The housing 2 has a mounting thread 23 on its outer circumferential surface. The spark plug 1 is attached to the internal combustion engine by screwing this mounting thread 23 into a female thread formed in a plug hole of the internal combustion engine. This mounting thread 23 then becomes part of the heat dissipation path from the spark plug 1 to the surrounding components (such as the engine head).

As shown in FIG. 2, in this embodiment, the step portion 22 of the housing 2 is formed in a portion 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 greater 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.

The radial depth d1 of the step 22 is approximately equal to the radial thickness of the fixed end 61 of the ground electrode 6. However, the depth d1 of the step 22 can be greater than the radial thickness of the fixed end 61.

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

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 can be joined, for example, to the ceiling surface 221. Alternatively, the fixed end 61 can be joined, for example, to at least one of the inward surface 222 and the side wall surface 223. Alternatively, the fixed end 61 can be joined to the ceiling surface 221 and also to at least one of the inward surface 222 and the side wall surface 223.

As shown in Figures 1 and 3, the plug cover 5 is formed with injection holes 51 that connect the auxiliary combustion chamber 50 to the outside. In this embodiment, four injection holes 51 are formed. When viewed from the plug axial direction Z, the injection hole axis of the injection hole 51 is 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 axis of the injection hole 51 may be configured to face the plug radial direction.

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

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.

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 the center electrode 4 and the insulator 3 are assembled inside the housing 2. Here, as shown in Fig. 4 and Fig. 5, a step 22 is formed at the tip of the housing 2. This step 22 can be formed in advance by performing a cutting process or the like on the housing 2. Note that Fig. 5 is a view of the tip surface of the housing 2 as viewed from the tip side.

Next, as shown in Figures 6 and 7, the ground electrode 6 is joined to the housing 2. At this time, first, as shown in Figure 6, a rod-shaped electrode member 60, which is the ground electrode 6 before bending, is joined to the housing 2. One end of the electrode member 60 is placed 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.

Then, the electrode member 60, one end of which is fixed to the housing 2, is bent. That is, the electrode member 60 is bent toward the plug central axis C at a predetermined position. At this time, the electrode member 60 is bent while a portion of the base end side of the electrode member 60 is fixed with a fixing jig (not shown). This results in a ground electrode 6 with a bent portion 63 formed thereon, as shown in FIG. 7.

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. To fine-tune the size of this discharge gap G, the position of the extension portion 64 is fine-tuned. In other words, the discharge gap G is fine-tuned by fine-tuning the bending angle of the bent portion 63. This fine-tuning 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 the size of the discharge gap G can be easily observed, for example, by a camera.

After fine-tuning the discharge gap G, the plug cover 5 is joined to the tip end of the housing 2, as shown in Figures 8 and 1. As described above, the plug cover 5 is formed with the accommodating recess 52 (see Figure 5). The plug cover 5 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 tip end of the housing 2 with a portion of the erected portion 62 of the ground electrode 6 accommodated in the accommodating recess 52. The abutting portion between the housing 2 and the plug cover 5 is then joined by laser welding or the like.
In this manner, the spark plug 1 as shown in FIG. 1 is assembled.

As shown in FIG. 9, the ground electrode 6 that has been 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 fine-tuned. This fine-tuning of the discharge gap G is basically performed by deforming the ground electrode 6 in a direction that brings the base end side surface of the extension portion 64 closer to the tip 41 of the center electrode 4. Therefore, it is desirable that the angle α between the erect 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 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).

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. 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 restricted. As a result, it is possible to easily bend the ground electrode 6 while restricting pre-ignition.

In other words, if the step portion 22 were not formed in the housing 2, the fixed end 61 of the ground electrode 6 would be abutted against the tip 21 of the housing 2 and joined. This would increase the length of the ground electrode 6 protruding from the tip 21 of the housing 2. In this case, when the spark plug is installed in 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 would be more difficult to suppress pre-ignition.

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

In this embodiment of the spark plug 1, a step portion 22 is provided at the tip of the housing 2, so that the length of the erected portion 62 of the ground electrode 6 can be ensured while the amount of protrusion of the ground electrode 6 from the tip 21 of the housing 2 can be reduced. As a result, bending of the ground electrode 6 can be facilitated, and pre-ignition can be more easily suppressed.

The plug cover 5 also has a recess 52. This ensures that the plug cover 5 is thick in areas other than the recess 52. This allows heat to be dissipated smoothly from the plug cover 5 through the housing 2. Furthermore, the plug cover 5 having the recess 52 allows the plug cover 5 to be positioned in the circumferential direction 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 specified positional relationship.

As described above, this embodiment makes it possible to provide a spark plug for an internal combustion engine that is easy to manufacture and that easily suppresses pre-ignition.

(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. In the embodiment shown in FIG.

As shown in FIG. 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 plug radial depth and a constant plug axial depth over the entire circumference. In other words, the step portion 22 is formed uniformly over the entire circumference. The plug radial depth d1 of the step portion 22 is desirably equal to or greater than the plug radial thickness of the fixed end portion 61 of the ground electrode 6.

As shown in Figs. 10 and 12, the base end of the plug cover 5 has a protrusion 54 that fits into the step 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 circumference of the plug circumferential direction, except for the part where the ground electrode 6 is fixed.

The rest is the same as in Reference Example 1. Note that, among the reference symbols used in the second and subsequent embodiments, the reference symbols that are the same as those used in the previous embodiments represent the same components, etc. as those in the previous embodiments, unless otherwise specified.

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 tip 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.
The rest of the effects are the same as those of the first embodiment .

( Reference Form 3 )
13 and 14, this embodiment is an embodiment in which the shape of the ground electrode 6 is modified from that of Reference Embodiment 1. 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.

In addition, 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 at least half 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.

In this embodiment, as shown in FIG. 14, the ground electrode 6 is prepared with a bent portion 63 before the ground electrode 6 is joined to the housing 2. However, before joining, it is desirable that the angle α between the standing portion 62 and the extension portion 64 is an obtuse angle. For example, it is desirable that the angle α is 90°<α<135°. At this stage, there is no particular distinction between the standing portion 62 and the extension portion 64.

Then, one end of the ground electrode 6 is disposed in the step portion 22, and the ground electrode 6 is joined to the housing 2. Thereafter, the discharge gap G is finely adjusted.
The rest is the same as in the first embodiment .

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.
In addition, the present embodiment has the same effects as the first embodiment .

The present invention is not limited to the above-described embodiments, and can be applied to various embodiments without departing from the spirit of the present invention.

1...spark plug for internal combustion engine, 2...housing, 21...tip (of housing), 22...stepped portion, 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...extended portion, C...plug central axis, Z...plug axial direction

Claims (4)

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. The spark plug for an internal combustion engine according to claim 1, wherein the step portion has a ceiling surface (221) facing a tip side at a base end portion in the plug axial direction, and the fixed end portion is joined to the ceiling surface . The spark plug for an internal combustion engine according to claim 1 or 2, wherein the plug cover has a receiving recess (52) in a portion of the circumferential direction of the plug on the inner peripheral surface along the plug axial direction, in which a portion of the erected portion of the ground electrode is received. A spark plug for an internal combustion engine according to any one of claims 1 to 3, wherein the ground electrode has a length (L1) of the erected portion in the erecting direction and a length (L2) of the extended portion in the extending direction that are equal to each other.

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