JP2007134319A - Spark plug - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spark plug which has almost the same flame extension property as a spark plug of which a cross sectional shape of a ground electrode is round, even against a main metal fitting with which only a ground electrode of a small thickness having a small thickness of a top end face can be connected, and moreover has an ultra fine precious metal chip and an effective thermal conduction of the ground electrode. <P>SOLUTION: A plane face 401 is formed in an extension direction of the ground electrode and on both ends of the plane face 401, a first arc part 402 of a comparatively small curvature radius r is formed, and a second arc part 403 of a comparatively large curvature radius R connecting with both end points P1, 2 of the first arc part 402 is formed. The ground electrode 40 is welded with the top end face 58 of the main metal fitting and the precious metal chip 43 is welded on the side facing a central electrode 10. At this time, it is more desirable that the plane face 10 is positioned on the side of the central electrode 10, and a relation r<R shall be satisfied when the curvature radiuses are compared. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a spark plug that is used by being attached to an internal combustion engine, and particularly relates to a spark plug that achieves excellent flame growth.

  A spark plug is used as an ignition device for engine combustion by exposing a center electrode and a ground electrode to a combustion chamber of an internal combustion engine and performing a spark discharge with a spark discharge gap between both electrodes. Conventionally, spark wear resistance and high-temperature oxidation resistance (hereinafter referred to as spark wear resistance and resistance) are applied to the tip of one or both of the electrodes, which are the starting point of spark discharge, in order to realize a long life of the spark plug. A chip made of a noble metal alloy (hereinafter also simply referred to as a noble metal chip) excellent in high temperature oxidation property and also called durability is joined (for example, see Patent Document 1). By using a noble metal tip with excellent durability in this way, the diameter of the noble metal tip that is the starting point of the spark discharge can be reduced, so that not only a longer life but also an ignition by making the tip extremely fine. It is also possible to realize a configuration that does not hinder the spread of the flame that is the air-fuel mixture (hereinafter also simply referred to as flame growth) (see, for example, Patent Document 2).

  By the way, as a means for improving the flame growth property, various contrivances have been made before using an extremely fine noble metal tip. This is because the spark plug is used by attaching the male screw formed on the metal shell to the female screw formed on the internal combustion engine, but it is very difficult to attach in consideration of the direction of the ground electrode at the time of attachment. . For this reason, when the air-fuel mixture goes from the spark plug to the location where spark discharge occurs, and when the air-fuel mixture ignites and the flame grows, the presence of the ground electrode inhibits the movement of the air-fuel mixture and the growth of the flame. This is because there is a problem that the combustion efficiency is lowered.

In order to solve such a problem, for example, there is a configuration in which the cross-sectional shape of the ground electrode described in Patent Document 3 is circular (hereinafter also simply referred to as a round ground electrode). By adopting such a configuration, it is possible to avoid the flow of the air-fuel mixture being hindered by the ground electrode and causing the air flow to peel off, or heat is drawn by the growth flame coming into contact with the ground electrode. This is because it is possible to avoid a decrease in the growth of the flame.
JP-A-8-339880 JP 2002-313524 A Japanese Patent Laid-Open No. 11-121142

  In the automotive industry, where spark plugs are used, the size and efficiency of engines are being reduced, such as increasing the diameter of intake / exhaust ports and the placement of injectors in the vicinity of combustion chambers associated with direct fuel injection. Therefore, the spark plug is required to have a small diameter. In order to meet this requirement, the diameter of the spark plug is reduced to a small diameter such as M12 or less. However, when a high voltage that generates a spark discharge is applied, the insulator holding the center electrode is thick enough to prevent penetration failure, or a spark discharge between the insulator and the metal shell, so-called Considering the formation of a predetermined gap in order to prevent side fire from occurring, the tip surface of the metallic shell to which the ground electrode is joined is only allowed to have a very limited thickness.

  In order to reduce the diameter of the spark plug using such a metal shell having a small diameter, and to provide a long life and better flame growth, a configuration in which an extremely fine noble metal tip is joined to the round ground electrode is studied. However, as described above, it is not easy to sufficiently secure the thickness of the front end surface of the metal shell to which the ground electrode is joined. Since the conventional rectangular ground electrode can be joined to the front end surface of the metal shell with a width larger than the thickness of the front end surface of the metal shell, the heat extraction of the ground electrode is insufficient. It is possible to avoid the fear of becoming. However, since the cross-sectional shape of the round ground electrode is circular, only a diameter corresponding to the thickness of the front end surface of the metal shell is allowed, and it is difficult to ensure sufficient heat sinking. Although it is conceivable to form a round ground electrode using a metal such as Cu having excellent thermal conductivity as a core material, an increase in the number of manufacturing steps is inevitable with such a configuration. By solving these problems and joining ultra-fine noble metal tips, a spark plug excellent in life and flame growth can be realized.

  The present invention has been made in view of the above circumstances, and its purpose is to provide a flame growth property equivalent to that of a round ground electrode and to extend its life, and is excellent in heat extraction without having a core material inside the ground electrode. An object of the present invention is to provide a small-diameter spark plug while realizing a ground electrode at low cost.

A rod-shaped center electrode extending in the axial direction;
A cylindrical insulator that includes a shaft hole and holds the center electrode in the shaft hole in a state where the tip of the center electrode protrudes from the tip surface of the shaft hole;
A metal shell for holding the insulator;
One end is joined to the front end surface of the metal shell, and the ground electrode extends from the one end toward the other end,
A columnar noble metal tip joined to the inner surface of the ground electrode facing the center electrode;
A spark plug comprising:
When the ground electrode is viewed from the other end side in its extending direction, the ground electrode is
A plane in which the outer line of the ground electrode is a straight portion on the inner surface;
Two first arcuate portions having a radius of curvature r and located at both ends of the linear portion extending from the end of the linear portion toward the other end of the linear portion;
A second arcuate part having a radius of curvature R connecting the other ends of the first arcuate part;
It is characterized by being formed from.

  As in the above configuration, the shape of the ground electrode viewed from the other end in the extending direction, that is, the arcuate portion (first arcuate portion) having a radius of curvature in which the outline of the cross section of the ground electrode is relatively small at both ends of the straight portion The end points of the arcuate parts are connected by arcuate parts having a relatively large radius of curvature (second arcuate part) and are substantially semicircular (however, both ends of the substantially semicircular linear part are first arcuate parts, In other words, it is possible to join the front end face of the metal shell with a wider joining area than the round ground electrode. For this reason, it is possible to avoid that the heat extraction of the ground electrode becomes insufficient, and also to have excellent flame growth property which is a characteristic of the round ground electrode. By forming the first and second arc-shaped portions having this configuration and different radii of curvature, it is possible to avoid that the air current such as the air-fuel mixture is separated from the ground electrode and the combustion efficiency is deteriorated. . As a more preferred form, the length of the straight portion is preferably made larger than the thickness of the front end surface of the metal shell, and the straight portion is joined so as not to protrude from the front end surface of the metal shell. A configuration in which this desirable form is made more specific is the second configuration of the present invention.

  The second configuration of the present invention is characterized in that the radius of curvature r of the first arcuate portion and the radius of curvature R of the second arcuate portion satisfy the relationship r <R. In this way, the ground electrode is joined to the metal shell so that the plane (which looks straight from the extending direction) faces the center electrode, and the relationship between the radii of curvature r and R is set to r <R. A joining area between the ground electrode and the metal shell can be obtained. In addition, the noble metal tip is joined to the flat portion of the side surface of the ground electrode. For this reason, the joining with the ground electrode of the noble metal tip can be made more stable.

The radius of curvature r of the first arc-shaped portion in the above configuration is preferably determined as follows. that is,
The two intersections distance between virtual circle intersects the imaginary extension of the straight line portion formed by extending the outer peripheral edge of the second arc-shaped portion when the D _1,
The radius of curvature r of the first arcuate portion is that it _{D 1/9 ≦ r ≦ D} 1/5.

By the curvature radius r of the first arcuate portion and D _1/9 or more, from the ground electrode in the air flow flowing toward the center from the outside of the spark plug inflection point changes to the first arcuate portion from the second arcuate portion It can suppress that it peels and combustion efficiency deteriorates. Further, by suppressing the curvature radius r to D _1/5 or less, it is possible to secure a sufficient plane to facilitate bonding of the noble metal tip.

Focusing on this noble metal tip, the outer diameter φd of the noble metal tip and 0.4 mm ≦ d ≦ 0.8 mm, and it is desirable that the _D 1 -2r ≧ 1.5d. If the outer diameter φd of the noble metal tip is less than 0.4 mm, it is difficult to achieve a long life even for a noble metal excellent in spark wear resistance and high temperature oxidation resistance. On the other hand, if φd exceeds 0.8 mm, flame growth is hindered, which is not within the scope of the present invention. When such a noble metal tip is provided, D ₁ -2r, that is, if the length of the flat portion of the ground electrode is 1.5 d or more, the noble metal tip is bonded to the ground electrode with sufficient strength. It becomes possible.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an overall view of a spark plug 100 of the present invention. The spark plug 100 is generally configured by combining a center electrode 10, a terminal electrode 20, an insulator 30, a ground electrode 40 and a metal shell 50. Hereinafter, each member will be described. In FIG. 1, the lower side of the drawing will be described as the front end side, and the upper side will be described as the rear end side.

  The center electrode 10 is formed in a substantially rod-like shape having a base 11 made of a Ni-based alloy such as Inconel 600 (registered trademark) and having a flange 11 at the rear end. A Cu alloy constitutes the core 12 for the purpose of improving thermal conductivity at the center of the base material made of Ni-based alloy. Further, the inner tip 13 made of a noble metal alloy containing Pt, Ir or the like and having excellent durability is joined to the tip of the center electrode 10. In this embodiment, this joining is performed by so-called laser welding in which a laser beam is irradiated and pressed.

  On the other hand, the ground electrode 40 provided in the metal shell 50 is made of a Ni-based alloy as a base material, is formed in a rod shape, and is joined to the tip of the metal shell 50. The ground electrode 40 is bent at a substantially right angle so as to form a spark discharge gap G with the inner chip 13 having one side surface joined to the center electrode 10 on one side. An outer tip 43 made of a noble metal alloy is joined to one side surface of the ground electrode 40 in the same manner as the center electrode 10 for the purpose of improving ignitability, flame growth and durability. The outer tip 43 corresponds to a “noble metal tip”. The detailed configuration of the ground electrode 40, which is the main point of the present invention, will be described later.

  The metal shell 50 is formed into a substantially cylindrical shape by subjecting an iron-based metal member such as S15C or S25C or a metal member such as stainless steel to plastic processing, and its rough shape is formed after finishing such as cutting. A threaded portion 51 for attaching the spark plug 100 to an internal combustion engine (not shown) is rolled on the distal end side of the outer peripheral surface of the metal shell 50. On the rear end side of the threaded portion 51, a flange portion 52 having a seat surface that hermetically seals the combustion chamber via the gasket 8 when attached to the internal combustion engine is formed. On the rear end side of 52, a tool engaging portion 53 having a hexagonal cross section, for example, is formed to which a tool such as a plug wrench engages when attached to the internal combustion engine. Between the tool engaging portion 53 and the flange portion 52 of the metal shell, it is formed thin so as to be buckled when the insulator 30 is assembled (FIG. 1 shows the shape after buckling). ing). In the present embodiment, the opposite side dimension of the tool engaging portion 53 is configured as HEX14.

  The rear end side of the tool engaging portion 53 is formed in a thin cylindrical shape so that a caulking lid 60 serving as the rearmost end portion of the metal shell 50 is formed when the spark plug 100 is completed. The inner hole 57 of the metal shell 50 is formed with a small-diameter hole 54 at a position in the direction of the axis O where the threaded portion 51 is formed, and a shelf 55 protruding radially inward is formed at the distal end side of the small-diameter hole 54. Is formed. On the rear end side connected to the small-diameter hole 54, a large-diameter hole 56 is formed up to the rear end at a position in the direction of the axis O where the flange portion 52 is formed. The ground electrode 40 is joined to the tip of the metal shell 50 formed in this way. This joining is performed by resistance welding, and after removing the welding sag, the metal shell 50 is plated with zinc or the like together with the ground electrode 40.

  The insulator 30 is manufactured by mixing an insulating ceramic powder such as alumina or aluminum nitride with a binder, etc., forming a rough shape by a press, grinding and shaping with a grindstone, and firing. The insulator 30 has a substantially cylindrical shape, and has a shaft hole 31 formed therein, and a flange-shaped middle body portion 32 protruding outward in the radial direction is formed at a substantially center of the outer surface in the axis O direction. A front end side body portion 34 having a stepped portion 33 facing the front end is formed on the front end side of the middle body portion 32. On the other hand, a rear end side barrel portion 35 having substantially the same outer diameter is formed on the rear end side of the middle barrel portion 32. Note that the tip end side of the stepped portion 33 formed on the tip end side body portion 34 constitutes a leg length portion 36 that is exposed to the combustion gas when the spark plug 100 is completed. In the shaft hole 31, a support step portion 37 that supports the flange portion 11 of the center electrode 10 is formed on the rear end side of the leg long portion 36, and the inner end of the shaft hole 31 has a rear end on the tip side of the support step portion 37. It is thinner than the side.

  The assembly of the insulator 30, the center electrode 10, and the terminal electrode 20 will be described. The center electrode 10 is inserted into the shaft hole 31 of the insulator 30 so that the tip thereof is downward. A glass sealing material prepared by mixing and metal powder and a resistance material prepared by changing the mixing ratio of these raw material powders are filled. The terminal electrode 20 is inserted from the rear end of the insulator 30 so that the leg portion 21 of the terminal electrode 20 formed in a shaft shape is embedded in the filled glass sealing material. With the terminal electrode 20 inserted, the insulator 30 is put into a heating furnace, heated to a predetermined temperature, and pressed to position the terminal electrode 20 at a predetermined position. Thereafter, the insulator 30 is removed from the heating furnace, whereby the glass sealing material and the resistance material are cured, so that the glass seals 5 and 5 and the resistor 6 are formed, respectively. It is fixed in an electrically conductive state. This process is generally called a glass sealing process. In addition, you may perform simultaneously the glaze of the glaze layer formed in the outer surface of a rear-end side trunk | drum at the time of this glass sealing process.

  Each member is configured as described above, and the metal shell 50 including the insulator 30 including the center electrode 10 and the terminal electrode 20 and the ground electrode 40 includes the plate packing 7, the wire packing 8, 8. The caulking lid 60 is formed by a known caulking process using talc (talc) 9 or the like, and the spark plug 100 is completed.

  Now, the ground electrode 40 which is the gist of the present invention will be described in detail with reference to FIG. FIG. 2 shows a state in which the ground electrode 40 is joined to the front end surface 58 of the metal shell 50. It should be noted that the outer electrode 43 is welded to the ground electrode 40, but shows a state before bending.

  As shown in FIG. 2, when the ground electrode 40 is viewed in its own extending direction (corresponding to the front and back direction of the paper surface), the outer peripheral shape is a plane in which the center electrode 10 side (upper side in the drawing) is a straight portion 401 ′. 401, both ends of the straight line portion 401 ′ are formed as inner arc-shaped portions 402 that draw a substantially ¼ arc having a radius of curvature r. Furthermore, an outer arc-shaped portion 403 that draws an arc having a radius of curvature of R (> r) is formed so as to connect the end points of the arcs of the inner arc-shaped portions 402 on both sides. The inner arc-shaped portion 402 and the outer arc-shaped portion 403 correspond to a “first arc-shaped portion” and a “second arc-shaped portion”, respectively.

The thickness D ₂ of the ground electrode 40 is determined as follows. Since the ground electrode 40 is joined to the front end surface 58 of the metal shell 50, the thickness thereof is set so as not to exceed the thickness of the front end surface 58 of the ground electrode 40. For example, in the case of M12, the outer diameter C1 of the front end portion of the metal shell 50 is about 10.1 mm, and the inner diameter C2 is about 7.3 mm. These numerical values are determined in consideration of the thickness of the leg length portion 36 of the insulator 30 and the gap between the leg length portion 36 and the inner diameter C2 of the small diameter hole 54 at the tip of the metal shell 50 as described above. Thus, half of the diameter difference (C1-C2) / 2 is the maximum value of as the thickness _{D 2} of the ground electrode 40.

It will be described width _{D 3} of the ground electrode 40. The end points P1 and P2 of the outer arc-shaped portion 403 are extended until they intersect with the extension line VE of the straight line portion 401 ′, respectively, and virtual arcs VA ₁ and VA ₂ are drawn. The intersections at this time are J1 and J2, respectively, and the distance between J1 and J2 is D ₁ (hereinafter referred to as the distance D ₁ between intersections). In this intersection distance D ₁ in this embodiment is equivalent to twice the radius of curvature of the outer arc-shaped portion 403 may also take a value slightly larger than when considering 2R manufacturing tolerances. Of course, the margin may be set to be smaller than 2R.

The radius of curvature r of the inner arcuate portion 402 may be set based on the intersection distance D _1. Since the radius of curvature r is too small it is less than D _1/9, cause the airflow in the combustion chamber is disturbed at the inflection point is the outer arc-shaped portion 403 and an inner arcuate portion 402 boundaries (corresponding to end points P1, P2 in FIG. 2) It can be. Specifically, the flow of the air-fuel mixture particularly from the outside of the ground electrode 40 is peeled off from the ground electrode 40 at this inflection point, and cannot reach the center electrode 10 side efficiently. Therefore, there is a concern that the combustion efficiency will deteriorate. On the other hand, if the radius of curvature r is more than D _1/5, it is impossible to take the width of the plane 401 for joining the outer tip 43 (i.e., the length of the linear portion 401 ') enough, Ya deterioration in bonding strength There is concern about the deterioration of heat pull. In addition, since the radius of curvature R of the outer arcuate portion 403 becomes small, it may be impossible to obtain the same flame growth effect as that of the round ground electrode. Therefore, the curvature radius r is set to be _D 1/9 or _D 1/5 or less. As described above, the width D ₃ of the ground electrode 40 is determined by the balance between the curvature radius r of the inner arc-shaped portion 402 and the curvature radius R of the outer arc-shaped portion 403.

The outer diameter φd of the outer tip 43 is set to be 0.4 mm or more and 0.8 mm or less from the relationship between durability and flame growth. Taking this outer diameter φd into consideration, the distance D ₁ between the intersections, the radius of curvature r of the inner arcuate portion 402 and the outer diameter φd of the outer tip 43 satisfy the relationship of D ₁ -2r ≧ 1.5d. D ₁ -2r means the possible width of the flat surface 401 on the center electrode 10 side, and if this is less than 1.5d, the bonding strength of the outer chip 43 may be reduced, such as chip dropping. It may cause a problem. Since φd is the outer diameter of the cylindrical noble metal tip, it corresponds to the outer diameter of the tip (center electrode 10 side) of the outer tip 43 after the spark plug is completed.

The distance D ₁ between the intersections, the thickness D ₂ , the width D ₃ , and the curvature radii r and R of the ground electrode 40 determined as described above have the following values in this embodiment.
D ₁ = 2.7 mm
D ₂ = 1.3 mm
D ₃ = 2.5 mm
r = 0.4mm
R = 1.3mm

  As described above, the present invention provides a round ground contact even when there is not enough such that the thread diameter of the metal shell is M12 or less or the thickness of the tip surface is, for example, 1.0 to 1.5 mm. It is possible to achieve a long life while providing the same flame growth property as the electrode.

The present invention can be variously modified without departing from the gist thereof. For example, in the above embodiment, the radius of curvature R of the outer arc-shaped portion 403 has a radius R that intersects the extension line VE of the straight portion 401 ′ of the inner plane 401 when the virtual arcs VA ₁ and VA ₂ are drawn. Although it is set to be a circle, even if the ground electrode 40 is manufactured by setting in this way, a manufacturing error occurs, so that a small plane is generated at the midpoint M (see FIG. 3) of the outer arc-shaped portion 403. obtain. However, if it is very small, it can be said that there is almost no influence on the combustion efficiency. It is also possible to increase the width D ₃ of the ground electrode without lowering the combustion efficiency by varying so as to increase toward the curvature radius R of the outer arc-shaped portion 403 to the midpoint M (see FIG. 4) . Incidentally, it is possible to permit up to ₂ ≦ _{D 1} ≦ 2.5D ₂ about 1.8D is when this configuration.

  In the present embodiment, a core material is not used for the ground electrode 40, but a known Cu core or the like may be used in the case where the core material is specially manufactured for performance improvement.

  Further, when importance is attached to the spread of the flame which is the ignited air-fuel mixture, for example, as shown in FIG. 5, the second arcuate portion called the outer arcuate portion 403 in the above embodiment is centered with the straight portion 401 ′ being radially outward. The electrode 10 may be desired, and the outer tip 43 may be joined to the arc surface of the second arc-shaped portion.

1 is an overall view of a spark plug 100 of the present invention, and is a partial cross-sectional view thereof. It is the figure seen from the extending | stretching direction of the ground electrode 40 which shows the Example of this invention. It is the figure seen from the extending | stretching direction of the ground electrode 40 which shows the modification of this invention. It is the figure seen from the extending | stretching direction of the ground electrode 40 which shows another modification of this invention.

Explanation of symbols

40 Ground electrode 43 Outer (noble metal) chip 50 Tip surface 100 of main metal fitting 58 (main metal fitting) Spark plug 401 (center electrode side) plane 402 Inner (first) arc-shaped portion 403 Outer (second) arc-shaped portion

Claims (4)

A rod-shaped center electrode extending in the axial direction;
A cylindrical insulator that includes a shaft hole and holds the center electrode in the shaft hole in a state where the tip of the center electrode protrudes from the tip surface of the shaft hole;
A metal shell for holding the insulator;
One end is joined to the front end surface of the metal shell, and the ground electrode extends from the one end toward the other end,
A columnar noble metal tip joined to the inner surface of the ground electrode facing the center electrode;
A spark plug comprising:
When the ground electrode is viewed from the other end side in its extending direction, the ground electrode is
A plane in which the outer line of the ground electrode is a straight portion on the inner surface;
Two first arcuate portions having a radius of curvature r and located at both ends of the linear portion extending from the end of the linear portion toward the other end of the linear portion;
A second arcuate part having a radius of curvature R connecting the other ends of the first arcuate part;
A spark plug characterized by being formed from.   2. The spark plug according to claim 1, wherein a curvature radius r of the first arcuate portion and a curvature radius R of the second arcuate portion satisfy a relationship r <R. The ground electrode is
The two intersections distance between virtual circle intersects the imaginary extension of the straight line portion formed by extending the outer peripheral edge of the second arc-shaped portion when the D _1,
The spark plug according to claim 2, characterized in that the radius of curvature r of the first arcuate portion and the _{D 1/9 ≦ r ≦ D} 1/5. The spark plug according to claim 3, wherein the ground electrode has an outer diameter φd of the noble metal tip of 0.4 mm ≦ d ≦ 0.8 mm and D ₁ −2r ≧ 1.5 d.

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