JP2023039630A - Spark plug for internal-combustion engine - Google Patents

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

The present invention relates to spark plugs for internal combustion engines.

A spark plug with an auxiliary combustion chamber is disclosed, for example, in US Pat. In this spark plug, one end of a ground electrode provided inside the sub-combustion chamber is fixed to the tip of the housing. The ground electrode extends from the distal end of the housing toward the distal end and is bent toward the central axis of the plug.

JP 2021-93293 A

However, if the ground electrode protrudes significantly from the distal end portion of the housing toward the distal end side, the temperature of the ground electrode tends to rise during use of the spark plug. Furthermore, the temperature of a portion of the plug cover arranged on the tip side of the ground electrode tends to rise. Then, pre-ignition becomes a concern. On the other hand, if the projecting length of the ground electrode from the tip of the housing is to be shortened, it becomes difficult to bend the ground electrode.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a spark plug for an internal combustion engine that can easily suppress pre-ignition and is easy to manufacture.

One aspect of the present invention is a tubular insulator (3),
a center electrode (4) held on the inner peripheral side of the insulator and protruding from the insulator to the tip side;
a cylindrical housing (2) that holds the insulator on the inner peripheral side;
a ground electrode (6) forming a discharge gap (G) with the center electrode;
A spark plug (1) for an internal combustion engine, comprising: a plug cover (5) provided at the tip of the housing so as to cover an auxiliary combustion chamber (50) in which the discharge gap is arranged;
The ground electrode has an upright portion (62) standing upright from a fixed end portion (61) fixed to the front end portion of the housing, and a bending portion (63) extending from the tip of the upright portion. an extending portion (64) extending toward the plug central axis (C),
The tip (41) of the center electrode is arranged on the tip side of the tip (21) of the housing,
The discharge gap is formed at a portion where the extended portion of the ground electrode and the tip of the center electrode face each other in the axial direction (Z) of the plug,
A stepped portion (22) opened to the inner peripheral side is provided at the tip of the housing,
The fixed end of the ground electrode is in a spark plug for an internal combustion engine joined to the housing at the step.

In the spark plug for an internal combustion engine, the front end portion of the housing is provided with the stepped portion. As a result, the fixed end of the ground electrode can be arranged closer to the proximal side. Therefore, even if the length of the standing portion is secured to some extent, it is possible to suppress the projection length of the ground electrode from the tip of the housing. As a result, it is possible to suppress pre-ignition 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 can easily suppress pre-ignition and is easy to manufacture.
It should be noted that the symbols in parentheses described in the claims and the means for solving the problems indicate the corresponding relationship with the specific means described in the embodiments described later, and limit the technical scope of the present invention. not a thing

FIG. 3 is a cross-sectional explanatory view of the spark plug for the internal combustion engine according to the first embodiment, and is a view corresponding to the cross section taken along the line II of FIG. 2; FIG. 2 is a cross-sectional view taken along the line II-II in FIG. 1; A cross-sectional view taken along line III-III in FIG. FIG. 4 is a cross-sectional explanatory view of the sub-assembly before assembling the ground electrode and the plug cover according to the first embodiment; FIG. 4 is a plan view of the distal end portion of the housing as viewed from the distal end side in the first embodiment; FIG. 4 is an explanatory diagram of a state in which the electrode member is joined to the housing according to the first embodiment; FIG. 4 is an explanatory diagram of a state after the ground electrode is bent according to the first embodiment; FIG. 4 is an explanatory diagram of the state immediately before the plug cover is assembled to the housing in the first embodiment; FIG. 4 is an explanatory diagram of a state immediately before the pre-bent ground electrode is assembled to the housing in the first embodiment; FIG. 5 is a cross-sectional explanatory diagram of a spark plug for an internal combustion engine according to Embodiment 2; The top view which looked at the front-end|tip part of the housing in Embodiment 2 from the front-end|tip side. FIG. 8 is a plan view of the base end portion of the plug cover viewed from the base end side in the second embodiment; FIG. 8 is a cross-sectional explanatory diagram of a spark plug for an internal combustion engine according to Embodiment 3; FIG. 11 is an explanatory diagram of a state immediately before the ground electrode is assembled to the housing according to the third embodiment;

(Embodiment 1)
An embodiment of a spark plug for an internal combustion engine will be described with reference to FIGS. 1 to 9. FIG.
A spark plug 1 for an internal combustion engine of 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 peripheral side of the insulator 3 and protrudes from the insulator 3 toward the tip side. The housing 2 holds the insulator 3 on the inner peripheral side. The ground electrode 6 forms a discharge gap G with the center electrode 4 . The plug cover 5 is provided at the tip of the housing 2 so as to cover the auxiliary combustion chamber 50 in which the discharge gap G is arranged.

The ground electrode 6 has a standing portion 62 and an extending portion 64 . The erected portion 62 is a portion erected from the fixed end portion 61 fixed to the distal end portion of the housing 2 toward the distal end side. The extended portion 64 is a portion extending from the tip of the erected portion 62 toward the plug center axis C via the bent portion 63 .

As shown in FIG. 1 , the tip 41 of the center electrode 4 is arranged on the tip side of the tip 21 of the housing 2 . A discharge gap G is formed in a portion where the extended portion 64 of the ground electrode 6 and the tip 41 of the center electrode 4 face each other in the axial direction Z of the plug. A front end of the housing 2 is provided with a stepped portion 22 that opens toward the inner circumference. A fixed end portion 61 of the ground electrode 6 is joined to the housing 2 at the stepped portion 22 .

The spark plug 1 of this embodiment can be used, for example, as ignition means in internal combustion engines such as automobiles and cogeneration systems. One end of the spark plug 1 in the plug axial direction Z is arranged in the main combustion chamber of the internal combustion engine. In the axial direction Z of the plug, the side exposed to the main combustion chamber is called the front end side, and the opposite side is called the base end side. Further, the direction orthogonal to the central axis of the spark plug 1 (that is, the plug central axis C) is called the plug radial direction. Also, the direction along the circumference centered on the plug central axis C will be referred to as the plug circumferential direction.

The housing 2 has a mounting screw portion 23 on its outer peripheral surface. The spark plug 1 is attached to the internal combustion engine by screwing the attachment threaded portion 23 into a female threaded portion formed in a plug hole of the internal combustion engine. This mounting screw portion 23 forms part of a heat radiation path from the spark plug 1 to peripheral members (engine head, etc.).

As shown in FIG. 2, in this embodiment, the stepped portion 22 of the housing 2 is formed partially in the plug circumferential direction. The width W of the stepped 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 stepped 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 stepped portion 22 and the width of the fixed end portion 61 are the lengths in the direction orthogonal to both the plug axial direction Z and the plug radial direction.

Further, the depth d1 of the stepped portion 22 in the plug radial direction is substantially 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 stepped portion 22 can be made larger than the above thickness of the fixed end portion 61 .

As shown in FIG. 1, the stepped portion 22 has a ceiling surface 221 facing the tip side on the base end side in the axial direction Z of the plug. Further, the stepped portion 22 has an inward surface 222 facing the inner peripheral side on the outer peripheral side in the plug radial direction. Further, 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.

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

As shown in FIGS. 1 and 3, the plug cover 5 is formed with an injection hole 51 that communicates the auxiliary combustion chamber 50 with the outside. In this embodiment, four injection holes 51 are formed. When viewed from the axial direction Z of the plug, the injection hole axis of the injection hole 51 is inclined with respect to the radial direction of the plug. However, the number, direction, shape, etc. of the injection holes 51 are not particularly limited. For example, when viewed from the axial direction Z of the plug, the injection hole axis of the injection hole 51 may face the radial direction of the plug.

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

The plug cover 5 is made of nickel alloy, for example. The housing 2 is made of low carbon steel, for example. 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 having a center electrode 4 and an insulator 3 assembled inside the housing 2 is prepared. Here, as shown in FIGS. 4 and 5, a stepped portion 22 is formed at the tip portion of the housing 2 . The stepped portion 22 can be formed in advance by cutting the housing 2 or the like. In addition, FIG. 5 is the figure which looked at the front end surface of the housing 2 from the front end side.

Next, the ground electrode 6 is joined to the housing 2 as shown in FIGS. At this time, first, as shown in FIG. 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 rod-shaped electrode member 60 is placed on the stepped portion 22 of the housing 2 and erected so that the longitudinal direction of the electrode member 60 extends along the axial direction Z of the plug. Then, one end of the electrode member 60 is joined at the stepped portion 22 by laser welding or the like.

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 toward the central axis C of the plug at a predetermined position. At this time, the electrode member 60 is bent while a part of the proximal end of the electrode member 60 is fixed by a fixing jig (not shown). Thereby, as shown in FIG. 7, the ground electrode 6 having the bent portion 63 is obtained.

A discharge gap G is formed between the base end side surface of the extended portion 64 of the ground electrode 6 and the tip 41 of the center electrode 4 . In order to finely adjust the dimension of the discharge gap G, the position of the extended portion 64 is finely adjusted. That is, fine adjustment of the discharge gap G is performed by finely adjusting the bending angle of the bending portion 63 . This fine adjustment of the discharge gap G is performed while observing the discharge gap G. FIG. Here, since the tip 41 of the center electrode 4 is positioned closer to the tip than the tip 21 of the housing 2, the dimension of the discharge gap G can be easily observed with a camera or the like.

After finely adjusting the discharge gap G, the plug cover 5 is joined to the tip of the housing 2 as shown in FIGS. As described above, the plug cover 5 is formed with the housing recess 52 (see FIG. 5). Positioning of the plug in the circumferential direction is performed so that the position of the housing recess 52 matches the position of the standing portion 62 of the ground electrode 6 . As a result, the plug cover 5 is arranged at the distal end portion of the housing 2 in a state in which part of the standing portion 62 of the ground electrode 6 is accommodated in the accommodation recess 52 . Then, the abutting portions of the housing 2 and the plug cover 5 are joined by laser welding or the like.
As described above, the spark plug 1 as shown in FIG. 1 is assembled.

In addition, as shown in FIG. 9, the pre-bent ground electrode 6 can also be fixed to the housing 2 . Also in this case, the discharge gap G is finely adjusted after the fixed end portion 61 of the ground electrode 6 is joined to the stepped portion 22 of the housing 2 . 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 extended portion 64 approaches the tip end 41 of the center electrode 4 . Therefore, it is desirable that the ground electrode 6 before being fixed to the housing 2 has an obtuse angle α between the standing portion 62 and the extending portion 64 . For example, it is preferable to set 90°<α<135°. After that, the plug cover 5 is joined to the housing 2 in the same manner as described above (see FIGS. 8 and 1).

Next, the effects of this embodiment will be described.
In the spark plug 1 for an internal combustion engine, a stepped portion 22 is provided at the tip portion of the housing 2 . Thereby, the fixed end portion 61 of the ground electrode 6 can be arranged closer to the base end side. Therefore, even if the length of the standing portion 62 is secured to some extent, the length of the ground electrode 6 protruding from the tip 21 of the housing 2 can be suppressed. As a result, it is possible to suppress pre-ignition while facilitating bending of the ground electrode 6 .

That is, if the housing 2 were not formed with the stepped portion 22, the fixed end portion 61 of the ground electrode 6 would be brought into contact with the front end 21 of the housing 2 and joined. As a result, the projection length of the ground electrode 6 from the tip 21 of the housing 2 is increased. In this case, when the spark plug is attached to the internal combustion engine, the ground electrode 6 will be closer to the center of the main combustion chamber, and will likely become hotter. Also, in this case, the tip of the plug cover 5 is closer to the center of the main combustion chamber, and is likely to reach a higher temperature. As a result, it becomes difficult to suppress pre-ignition.

Considering ease of forming the bent portion 63, it is desired that the standing portion 62 of the ground electrode 6 has a certain length. That is, when bending the ground electrode 6, it is desirable to secure a sufficient length of the upright portion 62 as a portion to be held by a jig or the like.

Therefore, in the spark plug 1 of this embodiment, by providing the stepped portion 22 at the tip portion of the housing 2 , the length of the ground electrode 6 from the tip 21 of the housing 2 is secured while the length of the standing portion 62 of the ground electrode 6 is secured. 6 can be suppressed. As a result, bending of the ground electrode 6 can be facilitated, and preignition can be easily suppressed.

The plug cover 5 also has a housing recess 52 . As a result, the thickness of the plug cover 5 can be ensured at locations other than the accommodation recess 52 . Therefore, heat can be smoothly dissipated from the plug cover 5 through the housing 2 . In addition, since the plug cover 5 has the housing recess 52 , it is possible to position the plug cover 5 with respect to the housing 2 and the ground electrode 6 in the plug circumferential direction. This facilitates setting the positional relationship of the injection hole 51 of the plug cover 5 with respect to the main combustion chamber and the ground electrode 6 to a predetermined positional relationship.

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

(Embodiment 2)
In this embodiment, as shown in FIGS. 10 to 12, the stepped portion 22 is formed along the entire inner circumference of the distal end portion of the housing 2 .

As shown in FIG. 11, when the housing 2 is viewed from the tip side in the axial direction Z of the plug, the stepped portion 22 is formed in an annular shape. Moreover, the stepped portion 22 is formed with a constant depth in the radial direction of the plug and a constant depth in the axial direction of the plug over the entire circumference. That is, the stepped portion 22 is formed uniformly over the entire circumference. Moreover, it is desirable that the depth d1 of the stepped portion 22 in the plug radial direction is equal to or larger than the thickness of the fixed end portion 61 of the ground electrode 6 in the plug radial direction.

Further, as shown in FIGS. 10 and 12, the proximal end of the plug cover 5 has a projecting portion 54 that fits into the stepped portion 22 . The protruding portion 54 protrudes from a portion of the inner peripheral side of the proximal end portion of the plug cover 5 toward the proximal end along the inner peripheral surface 53 of the plug cover 5 . Further, as shown in FIG. 12, the protruding portion 54 is continuously formed on the entire circumference of the plug in the circumferential direction except for the portion where the ground electrode 6 is fixed.

Others are the same as those of the first embodiment. Note that, of the reference numerals used in the second and subsequent embodiments, the same reference numerals as those used in the previous embodiments represent the same components as those in the previous embodiments, unless otherwise specified.

In the case of this embodiment, the assembly of the ground electrode 6 to the housing 2 can be made easier. That is, the stepped portion 22 is formed over the entire circumference of the plug in the circumferential direction. Therefore, the fixed end portion 61 of the ground electrode 6 can be joined at any position in the plug circumferential direction at the distal end portion of the housing 2 . Therefore, it is not necessary to position the ground electrode 6 with respect to the housing 2 in the plug circumferential direction. Therefore, it is possible to efficiently assemble the ground electrode 6 to the housing 2 .
Others have the same effects as those of the first embodiment.

(Embodiment 3)
As shown in FIGS. 13 and 14, this embodiment is a form in which the shape of the ground electrode 6 is changed with respect to the first embodiment. In the spark plug 1 of this embodiment, the ground electrode 6 has the length L1 of the standing portion 62 in the standing direction and the length L2 of the extending portion 64 in the extending direction equal to each other.

Further, in the present embodiment, the ground electrode 6 has a shape in which the erected portion 62 and the extended portion 64 are symmetrical with respect to the bent portion 63 . Also, the depth of the stepped portion 22 of the housing 2 is appropriately set according to the length of the standing portion 62 . In this embodiment, the depth of the stepped portion 22 is half or more of the length of the ground electrode 6 in the axial direction Z of the plug. Here, the length of the ground electrode 6 in the axial direction Z of the plug is substantially equal to the sum of the length L1 of the erected portion 62 and the thickness of the extended portion 64 . Note that the depth of the stepped portion 22 is not particularly limited.

In this embodiment, as shown in FIG. 14, before joining the ground electrode 6 to the housing 2, the ground electrode 6 having the bent portion 63 in advance is prepared. However, it is desirable that the angle α formed between the standing portion 62 and the extending portion 64 be an obtuse angle before joining. For example, it is desirable that the angle α be 90°<α<135°. At this stage, the erected portion 62 and the extended portion 64 are not particularly distinguished.

Then, one end of the ground electrode 6 is placed on the stepped portion 22 and the ground electrode 6 is joined to the housing 2 . After that, fine adjustment of the discharge gap G is performed.
Others are the same as those of 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 . That is, any one end of the ground electrode 6 may be joined to the housing 2 . Therefore, the work of assembling the ground electrode 6 to the housing 2 can be facilitated. As a result, productivity of the spark plug 1 can be improved.
In addition, it has the same effects as those of the first embodiment.

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

DESCRIPTION OF SYMBOLS 1... Spark plug for internal combustion engines 2... Housing 21... Tip (of housing) 22... Stepped portion 3... Insulator 4... Center electrode 41... Tip of (center electrode) 5... Plug cover 50... sub-combustion chamber 6... ground electrode 61... fixed end portion 62... standing portion 63... bending portion 64... extension portion C... plug central axis Z... plug axial direction

Claims (4)

a cylindrical insulator (3);
a center electrode (4) held on the inner peripheral side of the insulator and protruding from the insulator to the tip side;
a cylindrical housing (2) that holds the insulator on the inner peripheral side;
a ground electrode (6) forming a discharge gap (G) with the center electrode;
A spark plug (1) for an internal combustion engine, comprising: a plug cover (5) provided at the tip of the housing so as to cover an auxiliary combustion chamber (50) in which the discharge gap is arranged;
The ground electrode has an upright portion (62) standing upright from a fixed end portion (61) fixed to the front end portion of the housing, and a bending portion (63) extending from the tip of the upright portion. an extending portion (64) extending toward the plug central axis (C),
The tip (41) of the center electrode is arranged on the tip side of the tip (21) of the housing,
The discharge gap is formed at a portion where the extended portion of the ground electrode and the tip of the center electrode face each other in the axial direction (Z) of the plug,
A stepped portion (22) opened to the inner peripheral side is provided at the tip of the housing,
A spark plug for an internal combustion engine, wherein the fixed end of the ground electrode is joined to the housing at the stepped portion. 2. The spark plug for an internal combustion engine according to claim 1, wherein said stepped portion is formed along the entire inner circumference of the distal end portion of said housing. 2. The plug cover has an accommodating recess (52) in which part of the upright portion of the ground electrode is accommodated in a portion of the plug cover's inner peripheral surface along the axial direction of the plug in the plug circumferential direction. 3. Or the spark plug for internal combustion engines of 2. 4. The ground electrode according to any one of claims 1 to 3, wherein the length (L1) of the standing portion in the standing direction and the length (L2) of the extending portion in the extending direction are equal to each other. 1. A spark plug for an internal combustion engine according to 1.

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