CN110137806B

CN110137806B - Spark plug

Info

Publication number: CN110137806B
Application number: CN201811277371.9A
Authority: CN
Inventors: 德丸裕贵; 川嶋佑典
Original assignee: NGK Spark Plug Co Ltd
Current assignee: Niterra Co Ltd
Priority date: 2018-02-09
Filing date: 2018-10-30
Publication date: 2020-06-19
Anticipated expiration: 2038-10-30
Also published as: JP2019139946A; CN110137806A; JP6757756B2

Abstract

The invention provides a structure which can improve the heat radiation performance and the ignition performance of a grounding electrode in a spark plug which can reduce the fire extinguishing effect. A spark plug (100) has a gap formed between a discharge surface (33) of a noble metal tip (32) of a ground electrode (30) and an edge (29) of a front end portion of a center electrode (20) that is disposed at a position closest to the discharge surface (33). The noble metal tip (32) is disposed so that the position (Ps) on the discharge surface (33) that is the shortest from the edge (29) is located on the tip side of the center position (Pc) of the discharge surface (33) in the axial direction.

Description

Spark plug

Technical Field

The present invention relates to a spark plug.

Background

Patent document 1 discloses an example of a spark plug. In the spark plug of patent document 1, an inclined portion provided in the ground electrode is disposed so as to be inclined with respect to the axial direction, and a protruding portion formed of a noble metal tip is provided in the inclined portion. The center electrode is disposed along the axial direction, and a spark discharge gap is formed between the leading end portion of the center electrode and the protruding portion (noble metal tip) of the ground electrode.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2017-183107

Disclosure of Invention

Problems to be solved by the invention

If the discharge surface of the noble metal tip on the ground electrode side is inclined to face the edge portion of the center electrode (the corner portion on the ground electrode side) as in the spark plug disclosed in patent document 1, an effect of reducing the fire extinguishing effect can be expected. However, there is room for further improvement in heat dissipation and ignitability of the ground electrode.

The present invention has been made to solve at least some of the above problems, and an object thereof is to provide a spark plug capable of reducing a fire extinguishing effect and having both improved heat dissipation and ignitability of a ground electrode.

Means for solving the problems

One aspect of the present invention provides a spark plug including: a cylindrical main metal case; an insulator which includes a shaft hole extending in an axial direction and is held inside the main body metal shell; a center electrode disposed on a distal end side of the axial hole; a ground electrode having one end joined to the metal shell and the other end provided with an inclined portion arranged to be inclined with respect to the axial direction, the inclined portion being arranged to face a front end of the center electrode; and a noble metal tip joined to a surface of the inclined portion on the center electrode side and having a discharge surface facing the center electrode, wherein a gap is formed between an edge portion of a tip end portion of the center electrode, which is disposed closest to the discharge surface, and the discharge surface of the noble metal tip, and wherein the noble metal tip is disposed such that a position on the discharge surface, which is the shortest distance from the edge portion, is located on a tip side of a center position of the discharge surface in the axial direction.

In the spark plug thus configured, the distance from the noble metal tip to the base end of the ground electrode can be further shortened, so that heat is easily radiated from the ground electrode side to the main metal shell side, and the heat radiation performance of the ground electrode can be effectively improved. Further, if the distance from the noble metal tip to the base end of the ground electrode becomes shorter, the region affected by the spark discharge becomes smaller in the base end side portion of the ground electrode (the portion that is closer to the base end side than the noble metal electrode), so that the loss of the base end side portion of the ground electrode can be suppressed. Further, since sparks are likely to be generated at the position closer to the axial direction tip side than the center position on the discharge surface of the noble metal tip, ignitability can be further improved.

In the spark plug, the noble metal tip may be disposed so that a position on the discharge surface where the distance from the edge portion is shortest is located inward of the outline of the discharge surface.

With this configuration, when discharge occurs near the edge of the center electrode, excessive concentration of spark near the contour line of the discharge surface can be suppressed. Therefore, the offset loss (Japanese: offset consumption) in the vicinity of the contour line can be effectively suppressed.

ADVANTAGEOUS EFFECTS OF INVENTION

The present invention can improve both the heat radiation property and the ignitability of the ground electrode in a spark plug capable of reducing the fire extinguishing effect.

Drawings

Fig. 1 is a partially schematic sectional view showing an example of a spark plug according to embodiment 1.

Fig. 2 is an enlarged view showing a part of the spark plug of fig. 1 in an enlarged manner for a specific example.

Fig. 3 is a cross-sectional view schematically showing a cross-section of the spark plug of fig. 1 cut at the front end position of the center electrode.

Fig. 4 is an enlarged view of a portion of the spark plug of fig. 1, viewed from a different direction than fig. 2.

Fig. 5 is an explanatory view showing a pattern in which the noble metal tip and a part of the center electrode are projected on a virtual plane.

Description of the reference numerals

10. An insulator; 12. a shaft hole; 20. a center electrode; 29. an edge portion; 30. a ground electrode; 31B, an inclined part; 32. a noble metal tip; 33. a discharge surface; 50. a main body metal case; 100. a spark plug; x, axis.

Detailed Description

1. Embodiment 1

1-1. Integral structure of spark plug

Fig. 1 is a partial cross-sectional view of a spark plug 100 according to embodiment 1, and in fig. 1, the external shape of the spark plug 100 is shown on one side and the cross-sectional shape of the spark plug 100 is shown on the other side, with the axis X of the spark plug 100 being taken as a boundary. In the following description, a direction parallel to the axis X is referred to as an axial direction, a side (lower side in fig. 1) on which the ground electrode 30 is provided in the axial direction is referred to as a front end side, and a side (upper side in fig. 1) on which the terminal metal shell 40 is exposed is referred to as a rear end side.

As shown in fig. 1, the spark plug 100 includes an insulator 10, a center electrode 20, a ground electrode 30, a terminal metal shell 40, and a main metal shell 50.

The insulator 10 is an insulating ceramic formed by sintering a ceramic material (e.g., alumina or the like), and is a cylindrical member having a shaft hole 12 formed at the center thereof, the shaft hole being capable of accommodating both the center electrode 20 and the terminal metal shell 40. The shaft hole 12 is formed as a through hole extending in the axial direction. A central body portion 19 having a large outer diameter is formed at the axial center of the insulator 10. A rear-end-side body portion 18 for insulating the terminal metal shell 40 and the main-body metal shell 50 is formed on the insulator 10 on the rear end side of the central body portion 19. A front-end side body portion 17 having an outer diameter smaller than that of the rear-end side body portion 18 is formed on the insulator 10 on the front end side of the center body portion 19, and a leg portion 13 having an outer diameter smaller than that of the front-end side body portion 17 is formed on the front-end side body portion 17, the leg portion 13 having an outer diameter smaller than that of the front-end side body portion 17 and having an outer diameter smaller toward the front end side. The outer peripheral portion of the insulator 10 is held by the main body metal shell 50.

The center electrode 20 is disposed on the front end side of the insulator 10, a part of the center electrode 20 is accommodated in the axial hole 12, the remaining part protrudes from the front end of the insulator 10, and the outer peripheral portion of the center electrode 20 is held by the insulator 10. The center electrode 20 is a rod-shaped member in which a core member 25 having a thermal conductivity superior to that of the electrode base member 21 is embedded in the electrode base member 21 formed in a bottomed cylindrical shape. The electrode base material 21 is formed of a nickel alloy containing nickel as a main component, and the core material 25 is formed of copper or an alloy containing copper as a main component. The center electrode 20 is inserted into the axial hole 12 of the insulator 10 in a state where the tip of the electrode base material 21 protrudes from the axial hole 12 of the insulator 10, and is electrically connected to the terminal metal case 40 via the ceramic resistor 3 and the sealing body 4.

The ground electrode 30 is a member having one end side joined to the metal shell 50, and is electrically connected to the engine cover 200 via the metal shell 50. The ground electrode 30 itself has a rear end portion joined to a front end portion of the metal shell 50, and the ground electrode 30 extends further toward the front end side than the front end portion of the metal shell 50. The ground electrode 30 includes a bent rod-shaped base 31 and a noble metal tip 32 (ground electrode tip) joined to the base 31, and a spark gap, which is a gap for generating a spark, is formed between the noble metal tip 32 and the tip of the center electrode 20. The details of the ground electrode 30 and the center electrode 20 will be described later.

The metal shell 50 is a cylindrical member that holds the insulator 10 therein. The metal shell 50 is a cylindrical metal shell that surrounds and holds the portion of the insulator 10 from a part of the rear-end-side body portion 18 to the leg portion 13, and is formed of, for example, mild steel. The metal shell 50 includes a tool engagement portion 51, a mounting screw portion 52, and a seal portion 54. The tool engagement portion 51 is a portion into which a tool (not shown) for attaching the spark plug 100 to the engine cover 200 is fitted. The mounting screw portion 52 has a thread (male screw portion) for screw-engagement with the mounting screw hole 201 of the engine cover 200. The sealing portion 54 is formed in a flange shape so as to protrude outward from the vicinity of the base end portion of the mounting screw portion 52, and an annular gasket 5 is fitted between the sealing portion 54 and the engine cover 200. The front end surface 57 of the metallic shell 50 is hollow, that is, annular, and a part of the leg portion 13 of the insulator 10 protrudes from the center side of the front end surface 57. A part (near the tip end) of the center electrode 20 protrudes from the tip end of the leg 13.

A thin crimping portion 53 is provided on the rear end side of the tool engagement portion 51 of the metal shell 50. Further, a thin compression deformation portion 58 is provided between the seal portion 54 and the tool engagement portion 51, similarly to the crimping portion 53.

Annular ring members

6, 7 are disposed between the inner peripheral surface of the metal shell 50 from the tool engagement portion 51 to the crimp portion 53 and the outer peripheral surface of the rear-end-side body portion 18 of the insulator 10, and talc 9 powder is filled between the two

ring members

6, 7.

The main body metal shell 50 has a metal shell inner stepped portion 56 formed on the inner peripheral side of the mounting threaded portion 52. The inner stepped portion 56 of the metal shell is pressed by the electroceramic stepped portion 15 located at the base end portion of the leg portion 13 of the insulator 10 via the annular plate seal 8. The plate packing 8 is a member for maintaining airtightness between the metal shell 50 and the insulator 10, and the plate packing 8 functions to prevent the combustion gas from flowing out.

The spark plug 100 configured as described above is attached to an attachment screw hole 201 provided in an engine head 200 of an internal combustion engine via a metal shell 50. In use, a high voltage (e.g., a high voltage of about 2 to 3 ten thousand volts) is applied to the terminal metal shell 40, and the spark plug 100 operates in response to the high voltage to generate a spark in the spark gap formed between the center electrode 20 and the ground electrode 30.

1-2. Detailed structure of center electrode and ground electrode

Next, details of the center electrode and the ground electrode will be described.

Fig. 2 is an enlarged view showing the vicinity of the tip end portion of the spark plug 100 shown in fig. 1 in an enlarged manner. In fig. 2, the upper side is the front end side and the lower side is the rear end side, which is vertically opposite to fig. 1.

As shown in fig. 2, the center electrode 20 has a center electrode tip 27 at its leading end. The center tip 27 has a substantially cylindrical shape extending in the axial direction (direction parallel to the axis X), and the center tip 27 is formed mainly of a noble metal having a high melting point in order to improve spark wear resistance. The center tip 27 can be formed of, for example, iridium (Ir) or an Ir alloy containing Ir as a main component and containing 1 or more metals selected from platinum (Pt), rhodium (Rh), ruthenium (Ru), palladium (Pd), and rhenium (Re). The distal end surface 28 of the center electrode tip 27 is a flat surface perpendicular to the axial direction.

Fig. 3 shows the relationship between the distal end surface 28 of the center electrode 20 and the base portion 31 of the ground electrode 30 in a cross-sectional view taken along a cross-sectional plane perpendicular to the axis X and passing through an intersection position Px, which is a position where the distal end surface 28 of the center electrode 20 intersects the axis X. Note that, although the cross section of the noble metal tip 32 is actually shown in the cross section cut by the cross section, the cross section of the noble metal tip 32 is omitted in fig. 3. In the cross-section shown in fig. 3, when the center of gravity (center of the figure) of the cross-section of the base 31 is Py, a direction parallel to a straight line passing through both the center of gravity (center of the figure) Py and the intersection position Px is referred to as a relative direction. A direction orthogonal to the opposing direction and also orthogonal to the axial direction is referred to as a lateral direction.

As shown in fig. 2, the ground electrode 30 includes a base 31 and a noble metal tip 32 (ground tip), and the rear end of the base 31 is welded to the front end surface 57 of the main metal shell 50.

The base portion 31 is a rod-like member having a substantially rectangular shape in cross section (a cross section in a direction orthogonal to the extending direction), and an upright portion 31A that stands along the axial direction is provided on one end side (base end side), and an inclined portion 31B that extends while being bent from the upright portion 31A is provided on the other end side (tip end side). The material of the base 31 is, for example, Ni or an alloy containing Ni as a main component.

The base end (rear end) of the base 31 has a width Wb in the lateral direction shown in fig. 4 larger than a width Wa in the opposite direction shown in fig. 2, and the base 31 has a width in the lateral direction larger than the width in the opposite direction as a whole from the base end to the front end. With this configuration, the distance between the surface of the base 31 on the side of the center electrode 20 and the center electrode 20 can be easily secured, and sparks heading toward the base 31 can be easily suppressed.

The inclined portion 31B is arranged obliquely with respect to the axial direction so that the distal end side is closer to the center electrode 20 side, and is arranged to face the distal end portion of the center electrode 20. When a virtual plane passing through both the intersection position Px and the center of gravity (center of the figure) Py shown in fig. 3 and passing through the axis X (fig. 2) is denoted as F, the base 31 extends along the plane F, and the center position of the base 31 in the lateral direction is substantially located on the plane F over the entire range from the base end to the tip end of the base 31.

The noble metal tip 32 (ground tip) shown in fig. 2 is provided to improve spark wear resistance of the ground electrode 30, and the noble metal tip 32 is provided so as to protrude from the surface of the inclined portion 31B on the side of the center electrode 20 toward the center electrode 20. The noble metal tip 32 is composed of a noble metal having a high melting point as a main component, for example, platinum (Pt), Pt — Ni alloy, or the like. The noble metal tip 32 has a columnar shape, and one end surface (back surface) of the noble metal tip 32 is joined to one surface (surface on the center electrode 20 side) of the inclined portion 31B by laser welding or the like.

The surface (surface facing the center electrode 20) of the noble metal tip 32 opposite to the surface (back surface) fixed to the inclined portion 31B is a discharge surface 33, and the discharge surface 33 is disposed facing the tip of the center electrode 20. In the example of fig. 2, the angle formed by the axial direction and the discharge surface 33 (the angle on the acute angle side) is less than 90 °, and the discharge surface 33 is disposed so as to be inclined toward the axis X as it goes toward the distal end side in the axial direction. The angle θ formed by the discharge surface 33 and the axis X (i.e., the angle formed by the plane direction of the discharge surface 33 and the axis direction) is, for example, in the range of 30 ° to 60 °. In the configuration of fig. 2, the plane F (fig. 3) and the discharge surface 33 are orthogonal to each other.

The edge portion 29 shown in fig. 2 is a corner portion disposed at a position closest to the discharge surface 33 on the distal end surface 28 of the center electrode 20, and is an end portion (end portion on the side closer to the ground electrode 30) in the facing direction of the distal end surface 28. In the example of fig. 3, the position on the above-mentioned plane F in the contour line (outer edge) of the front end face 28 is the position of the edge portion 29.

As shown in fig. 2, in the present configuration, the edge portion 29 is located within a range AR in which the discharge surface 33 is present in the axial direction. That is, the edge portion 29 is located on the rear end side of the front end Pb of the discharge surface 33 and on the front end side of the rear end Pa of the discharge surface 33 in the axial direction. As shown in fig. 4, the edge portion 29 is located in a range where the discharge surface 33 exists in the lateral direction. That is, the edge portion 29 is located on the other end side (right end side) than one end in the lateral direction of the discharge surface 33 (left end of the discharge surface 33 in fig. 4), and is located on the one end side (left end side) than the other end in the lateral direction of the discharge surface 33 (right end of the discharge surface 33 in fig. 4).

More specifically, when the edge portion 29 and the discharge surface 33 are projected on a virtual plane orthogonal to the above-described opposing direction (the direction in which the front end portion of the center electrode 20 and the ground electrode 30 oppose each other in the direction orthogonal to the axis X) shown in fig. 3, the edge portion 29 is projected on the projection area of the discharge surface 33. Fig. 5 shows a pattern in which the vicinity of the tip end portion (center tip 27) of the center electrode 20 and the noble metal tip 32 are projected on a virtual plane orthogonal to the opposing direction, the pattern in which the center tip 27 is projected is shown by reference numeral 27Z, and the pattern in which the noble metal tip 32 is projected is shown by reference numeral 32Z. A figure obtained by projecting the discharge surface 33 is indicated by reference numeral 33Z, and a projection area of the discharge surface 33 is indicated by hatching. The projected position of the edge portion 29 is denoted by reference numeral 29Z. As shown in fig. 5, when the edge portion 29 and the discharge surface 33 are projected on a virtual plane orthogonal to the opposing direction, the edge portion 29 is projected on the projection area of the discharge surface 33.

As shown in fig. 2, the distance between the edge portion 29 and the predetermined position Ps on the discharge surface 33 is the smallest among the distances between the center electrode 20 and the ground electrode 30. As shown in fig. 2 and 4, the noble metal tip 32 is disposed such that the predetermined position Ps (the position on the discharge surface 33 where the distance from the edge portion 29 is shortest) is located inward of the contour line 33A (outer edge) of the discharge surface 33. In fig. 2, a straight line Lp is a line extending from a perpendicular line drawn from the position of the edge portion 29 to the discharge surface 33, and a position (shortest position) Ps exists on the straight line Lp. More specifically, the noble metal tip 32 is disposed such that the position Ps is located closer to the center position Pc than the contour line 33A (outer edge) of the discharge surface 33. The distance between the edge 29 and the position Ps is the distance of the spark gap, and is, for example, 0.3mm to 1.0 mm.

As shown in fig. 2 and 4, the noble metal tip 32 is disposed such that the predetermined position Ps (the position on the discharge surface 33 where the distance from the edge portion 29 is shortest) is located on the tip side of the center position Pc of the discharge surface 33 in the axial direction. The center position Pc of the discharge surface 33 is a position of a center of gravity (center of the figure) of the discharge surface 33, and in the example of fig. 2, the center position Pc is a position of an axial center of the discharge surface 33.

1-3. Effect

In the spark plug 100, the noble metal tip 32 is disposed so that a position Ps on the discharge surface 33, which is the shortest distance from the edge portion 29, is located on the tip side of the center position Pc of the discharge surface 33 in the axial direction. With this configuration, the distance from the noble metal tip 32 to the base end of the ground electrode 30 can be further shortened, so that heat can be easily dissipated from the ground electrode 30 side to the main metal shell 50 side, and the heat dissipation performance of the ground electrode 30 can be effectively improved. Further, if the distance from the noble metal tip 32 to the base end of the ground electrode 30 becomes shorter, the region affected by the spark discharge becomes smaller in the base end side portion of the ground electrode 30 (the portion closer to the base end side than the noble metal tip 32), and therefore, the loss of the base end side portion of the ground electrode 30 can be suppressed. Further, since sparks are likely to be generated at the discharge surface 33 of the noble metal tip 32 on the axial direction tip side of the center position Pc, ignitability can be further improved.

In the present configuration, the noble metal tip 32 is disposed so that the position Ps on the discharge surface 33, which is the shortest distance from the edge portion 29, is located inward of the contour line 33A of the discharge surface 33. With this configuration, when discharge occurs near the edge portion 29 of the center electrode 20, excessive concentration of spark near the contour line 33A of the discharge surface 33 can be suppressed. Therefore, the offset loss in the vicinity of the contour line 33A can be effectively suppressed.

In the present configuration, when the edge portion 29 and the discharge surface 33 are projected on a virtual plane orthogonal to the facing direction (the direction in which the front end portion of the center electrode 20 and the ground electrode 30 face each other in the direction orthogonal to the axis X), the edge portion 29 is projected on the projection area of the discharge surface 33 (see fig. 5). In this configuration, since the discharge surface 33 and the edge portion 29 of the noble metal tip 32 are in a facing relationship in the direction orthogonal to the axis X, even when an in-cylinder flow is generated in the direction orthogonal to the axis X from the center electrode 20 side toward the ground electrode 30 side, a spark generated in the vicinity of the edge portion 29 is easily received by the discharge surface 33 of the noble metal tip 32, and the spark is less likely to spread to the base end side portion of the ground electrode 30 (the portion closer to the root side than the noble metal tip 32). Therefore, it is possible to suppress the sparks from flying toward the base end side portion of the ground electrode 30 when such an in-cylinder flow occurs, and it is possible to effectively suppress the wear of the ground electrode 30.

In particular, in this configuration, ignitability can be ensured under conditions in which the influence of the fire extinguishing action is large in a low flow velocity state, and in addition to this effect, an effect of suppressing the partial loss of the electrode in a high flow velocity state and the excessive loss in a high energy state can be produced. In particular, in the past, there has been a tendency that the in-cylinder flow is greatly increased due to the increase in performance of the engine, and the ignitability is improved by the increase in energy of the ignition coil, and therefore, there has been a further concern about the partial loss of the electrode due to the high flow rate and the excessive loss due to the high energy, but the spark plug 100 of the present configuration can effectively suppress the loss of the electrode, and is therefore particularly effective in such a severe environment.

2. Other embodiments

The present invention is not limited to the embodiments described above and illustrated in the drawings, and can be realized in various configurations without departing from the spirit and scope thereof. For example, various features of the above-described embodiments and those of the embodiments described later may be combined arbitrarily as long as they do not depart from the gist of the invention and are not contradictory. Note that, unless otherwise specified, the technical features are essential in the present specification and can be appropriately eliminated.

In the above embodiment, the center electrode 20 provided with the center electrode tip 27 is illustrated, and the distal end surface 28 of the center electrode tip 27 is configured as the distal end surface of the center electrode 20, but the center electrode tip 27 may not be provided. In this case, the distal end surface of the center electrode 20 can be configured similarly to the distal end surface 28.

In the above embodiment, the noble metal tip 32 is disposed so that the position Ps on the discharge surface 33, which is the shortest distance from the edge portion 29, is located closer to the center position Pc than the tip Pb of the discharge surface 33 in the axial direction, but the noble metal tip 32 may be disposed so that the position Ps is located closer to the tip Pb than the center position Pc of the discharge surface 33 in the axial direction.

In the above-described embodiments, the noble metal tip having a circular discharge surface is exemplified, but the discharge surface may have another shape such as an elliptical shape or a rectangular shape.

In the above embodiment, when the edge portion 29 and the discharge surface 33 are projected on a virtual plane orthogonal to the opposing direction, the edge portion 29 is projected on the projection area of the discharge surface 33 (see fig. 5). That is, when the edge portion 29 and the discharge surface 33 are projected on the virtual plane, the projection position of the edge portion 29 may be shifted from the projection area of the discharge surface 33.

Claims

1. A spark plug is provided with:

a cylindrical main metal case;

an insulator which includes a shaft hole extending in an axial direction and is held inside the main body metal shell;

a center electrode disposed on a distal end side of the axial hole;

a ground electrode having one end joined to the metal shell and the other end provided with an inclined portion arranged to be inclined with respect to the axial direction, the inclined portion being arranged to face a front end of the center electrode; and

a noble metal tip joined to a surface of the inclined portion on the center electrode side and having a discharge surface facing the center electrode,

a gap is formed between an edge portion of the tip end portion of the center electrode, which is disposed closest to the discharge surface, and the discharge surface of the noble metal tip,

the noble metal tip is disposed so that a position on the discharge surface which is the shortest from the edge portion is positioned on a tip side in the axial direction with respect to a center position of the discharge surface,

when a direction in which a front end portion of the center electrode and the ground electrode oppose each other in a direction orthogonal to the axial direction is set as an opposing direction, and the edge portion and the discharge surface are projected on a virtual plane orthogonal to the opposing direction, the edge portion is projected within a projection region of the discharge surface.

2. The spark plug of claim 1,

the noble metal tip is disposed such that a position on the discharge surface which is the shortest from the edge portion is located inward of a contour line of the discharge surface.