JPH11121142A - Multipole spark plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multipole spark plug of which ignitability is not degraded even if it is screwed at an angle with which gaseous mixture can be fed from the back of an outer electrode. SOLUTION: A double-pole spark plug A has a cylindrical main fitting 1, an insulating insulator 2 having a shaft hole 20 which is screwed into the main fitting 1 with its front end 21 projecting from a fitting end surface 11, a center electrode 3 fitted to the shaft hole 20 with a center electrode tip 31 projecting from an insulator end surface 211, and outer electrodes 4 (cross-sectionally almost circular cylinder-shaped) which are clad in a Cu alloy and are welded to the fitting end surface 11, each having a noble metal chip 42 welded to an igniting part opposite to the periphery of the center electrode, and spark discharge is executed in between the igniting part and the center electrode end 31.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multipolar spark plug having two or more outer electrodes.

[0002]

2. Description of the Related Art Conventionally, in order to prevent electrode wear, Cu
There is known a bipolar spark plug 100 in which a good heat conductive metal such as a metal is clad, and an outer electrode 102 having a rectangular cross section in which a noble metal tip 101 is arranged at a firing portion is welded to a metal tip surface 104 of a metal shell 103 (FIG. 10).

[0003]

In the bipolar spark plug 100, the outer electrode 102 and the flow of the air-fuel mixture are shown in FIG.
In the case of an inappropriate position as shown in FIG.
2 makes it difficult for the mixture 107 to reach the spark gap g where the spark 106 is flying.

A parallel spark plug 200 shown in FIG.
However, there is a possibility that the air-fuel mixture 202 is screwed from behind the outer electrode 201 at an angle. However, the bipolar spark plug 100 is more likely to be used since it has a plurality of outer electrodes 102.

[0005] In particular, when the above-described conventional two-pole spark plug 100 is mounted on a lean burn engine that performs lean burn, the ignitability varies depending on the position of the outer electrode. In addition, vibrations due to combustion have become severe, and it is also desired to increase the strength of the outer electrode.

A first object of the present invention is to provide a multipolar spark plug whose ignitability does not decrease even if it is screwed at an angle such that an air-fuel mixture is fed from behind an outer electrode. A second object of the present invention is to prevent ignitability from lowering even when screwed at an angle such that an air-fuel mixture is fed from behind the outer electrode, and to prevent breakage of the outer electrode during use at high temperature where vibration is severe. It is an object of the present invention to provide a multi-polar spark plug excellent in resistance and electrode wear resistance.

[0007]

In order to solve the above-mentioned problems,
The present invention employs the following configuration. (1) a cylindrical metal shell, an insulator with a shaft hole fitted to the metal shell, and a center electrode fitted to the shaft hole;
An outer electrode that includes a good heat conductive metal and is welded to the front end surface of the metal fitting and has a noble metal member disposed on a firing portion facing the outer peripheral direction of the center electrode, between the firing portion and the front end portion of the center electrode. In the multipolar spark plug which performs spark discharge in the above, the outer electrode has a columnar shape with a substantially circular cross section.

(2) The structure of the above (1), wherein the total length of the good heat conductive metal is L, and the cross sectional area of the good heat conductive metal at the portion where the cross sectional area of the good heat conductive metal is maximum. S _max , the cross-sectional area of the good heat conductive metal in an arbitrary cross section is S, the total length of the outer electrode is L ₀ , and the cross sectional area of the outer electrode in a portion where the cross sectional area of the good heat conductive metal is maximum is If S _0max, and the cross-sectional area of the outer electrode in an arbitrary cross section is a _{S 0, (1/16) ≦ (} S ma x / S 0max), and (S / S
₀ ) ≦ (１ ／), and (L / L ₀ ) ≧ 0.
S, S _max , S ₀ , S _0max , L, and L ₀ were set so as to satisfy 3.

[0009]

[Action and effect of the invention]

(1) A multi-electrode spark plug which includes a noble metal member at a firing portion of an outer electrode which includes a good heat conductive metal and is welded to a front end surface of a metal shell and is opposed to an outer peripheral direction of a center electrode. Has a columnar shape with a substantially circular cross section. For this reason, even when the spark plug is screwed at an angle such that the air-fuel mixture is sent from behind the outer electrode (see FIG. 6), the air-fuel mixture wraps around the inside of the outer electrode and sparks are flying. Since the gap is reached, there is almost no variation in ignitability.

[0010] [Claim 2] When the good heat conductive metal is included, the mechanical strength of the outer electrode is reduced as compared with the case where the metal is not included. Therefore, the following numerical limitation is required.
If the total length L of the good heat conductive metal included is short and L (total length of the good heat conductive metal) / L ₀ (total length of the outer electrode) is less than 0.3, the effect of heat removal of the outer electrode is reduced. In addition, the effect of reducing electrode consumption is reduced.

Further, the cross-sectional area of the good heat conductive metal included is too large, and S (cross-sectional area of the good heat conductive metal in an arbitrary cross section) / S ₀ (cross-sectional area of the outer electrode in an arbitrary cross section) is (1/1). When the value exceeds 3), the mechanical strength of the outer electrode tends to decrease, and the metal easily breaks even if the overall length L of the good heat conductive metal is shortened. From the viewpoint of heat drawing, S _max (the cross-sectional area of the good heat conductive metal at the portion where the cross sectional area of the good heat conductive metal is the maximum) / S
_0max (the cross-sectional area of the outer electrode at the portion where the cross-sectional area of the _good heat conductive metal is maximum) is set to (1/16) or more.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First and second embodiments of the present invention (corresponding to claims 1 and 2) will be described with reference to FIGS. As shown in the figure, the bipolar spark plugs A and B are composed of a cylindrical metal shell 1, an insulator 2 having a shaft hole 20, and a shaft hole with the center electrode tip 31 protruding from the insulator tip surface 211. 20
Electrode 3 to be fitted on the body and metal fitting end surface 1 of metal shell 1
1 and an outer electrode 4 to be welded.

The metal shell 1 is made of low-carbon steel, and has a male screw 12 for disposing the engine threaded around the distal end. The insulator 2 is formed of a ceramic sintered body mainly composed of alumina, and is fitted to the metal shell 1 with the front end 21 protruding from the metal tip surface 11 of the metal shell 1.

The center electrode 3 is formed by cladding a highly heat conductive metal (copper alloy) in a sheath material (made of nickel alloy).
The base (both not shown) is formed through the shaft hole 2 through the sealing glass.
Sealed within 0. The center electrode tip portion 31 protruding from the insulator tip surface 211 is composed of a truncated cone portion 311 whose diameter decreases toward the front and a noble metal tip 312 welded to the tip surface of the truncated cone portion 311.

Outer electrode 4 (φ1.5) in which a Cu alloy 41 is clad in a sheath material (nickel alloy; Irc600)
Is bent so that the ignition portion faces the outer periphery 32 of the center electrode (the outer periphery of the truncated cone portion 311), and is resistance-welded to the front end face 11 of the metal fitting, and the noble metal tip 42 (φ0.8, Pt−2) is attached to the ignition portion.
0Ni) by laser welding.

The total length of the Cu alloy 41 is L, and the cross-sectional area of the Cu alloy 41 where the cross-sectional area of the Cu alloy 41 is maximum is S.
_max , the cross-sectional area of the Cu alloy 41 at an arbitrary cross section is S, the total length of the outer electrode 4 is L ₀ , the cross-sectional area of the outer electrode 4 at the portion where the cross-sectional area of the Cu alloy 41 is the largest is S _0max , When the sectional area of the electrode 4 is S ₀ , the bipolar spark plug A sets (S _max / S _0max ) to １ ／ and sets (S / S ₀ ) to (１ ／) or less. , (L / L
₀ ) is set to 0.9. The two-pole spark plug B sets (S _max / S _0max ) to _に and sets (S / S
₀ ) is set to (1/3) or less, and (L / L ₀ ) is set to 0.9.
Is set to

Next, an over-high-speed durability test for examining break durability and a continuous high-speed durability test for examining electrode wear resistance will be described. [Over-high-speed endurance test] A 2400 cc DOHC 4-cylinder engine was equipped with a spark plug of the specifications shown in Table 1 for 570
0 rpm × W. O. A test was performed at T to check whether the outer electrode 4 was broken. The cross-sectional area S of the Cu alloy 41 in any cross section of the outer electrode 4 is
It has been found that when the cross-sectional area S ₀ is larger than that of the Cu alloy 41, the Cu alloy 41 is easily broken even if the total length L is short. From the test results in Table 1, to prevent breakage of the outer electrode 4, (S /
S ₀ ) is desirably set to (１ ／) or less.

[0018]

[Table 1]

[Continuous high-speed endurance test] (S_max/ S_0max)
And (L / L₀) Of 21 different spark plugs
A set (six in each set; see FIG. 4) is manufactured and a 2000 cc D
5000 rpm with each set mounted on an OHC 6 cylinder engine
× W. O. Test at T
The gap increase (mm) was measured. Test results shown in FIG.
From the result graph, to reduce the electrode consumption, (S_max
/ S _0max) Is (1/16) or more, and (L / L₀)
It turned out that it is necessary to make it 0.3 or more.

From the results of both tests, (1/16) ≦ (S
_max / S _0max), and satisfies the _{(S / S 0) ≦ (} 1/3), and, as satisfy _{(L / L 0) ≧ 0.3} , S, S
_{max, S 0, S 0max,} L, and that it is desirable to set the L ₀ were found.

Next, the ignitability evaluation test will be described.
A group of two-pole spark plugs A, 2000cc DOHC
Idling x 6 cylinder engine as follows
The test was performed with no load, and the number of HC spikes / min was measured. The results are shown in FIG. In addition, the group of the bipolar spark plugs B had almost the same result. For comparison, the outer electrode 3 having a rectangular cross section
Similarly, the number of HC spikes / minute was measured using a bipolar spark plug 300 obtained by welding No. 01 to a metal fitting tip surface 303 of a metal shell 302. Thick line: Installed at an angle such that the mixture 202 is sent from behind the outer electrode 4 Thin line: Installed at an angle such that the mixture 202 is sent from the side of the outer electrode 4

The advantages of the two-pole spark plugs A and B will be described. [A] The bipolar spark plugs A and B are mounted at an angle such that the air-fuel mixture 202 is fed from the side surface of the outer electrode 4 even if the air-fuel mixture is sent from behind the outer electrode 4. However, the air-fuel mixture 202 wraps around the inside of the outer electrode 4 and reaches the spark gap g where the spark is flying (see FIG. 6).

That is, the two-pole spark plugs A and B are connected to the air-fuel mixture 2 from behind the outer electrode 4.
Even when the spark plug is screwed at an angle such that the air-fuel mixture 202 is fed from the side surface of the outer electrode 4, there is almost no change in the ignitability (the direction of the outer electrode 4). Has little effect on ignitability). Therefore, a cylinder screwed at an angle such that the air-fuel mixture 202 is sent from behind the outer electrode 4 and a cylinder screwed at an angle such that the air-fuel mixture 202 is sent from the side surface of the outer electrode 4 are mixed. Smooth engine operation can be obtained.

[A] The two-pole spark plug A is (S _max
/ S _0max ) is set to ４, and (L / L ₀ ) is set to 0.9. The two-pole spark plug B is (S _max
/ S _{0m ax)} is set to 1/3, it is set to 0.9 (L / L _0). That is, (1/16) ≦ (Cu alloy 41
Area S of the Cu alloy 41 at the portion where the cross-sectional area of
_max / the cross-sectional area S _0max of the outer electrode 4 at the portion where the cross-sectional area of the Cu alloy 41 is the maximum is satisfied, and
(Total length L of Cu alloy 41 / total length L _{0 of} outer electrode 4) ≧
0.3 is satisfied. For this reason, two-pole spark plug A
Is that the outer electrode 4 is hardly broken and has excellent electrode wearability (excellent durability).

The present invention includes the following embodiments in addition to the above embodiment. a. In Claims 1 and 2, "the outer electrode which is welded to the front end face of the metal shell and has a noble metal member disposed on the ignition portion facing the outer peripheral direction of the center electrode" is a creeping discharge type spark plug as described below. May be the above [A],
The same operation and effects as those of [A] are exhibited. The creeping discharge type bipolar spark plug C includes a cylindrical metal shell 1, an insulator 2 with a shaft hole 20 fitted into the metal shell 1 with a front end 21 protruding from the metal tip surface 11, Center electrode tip 3
The center electrode 3 fitted into the shaft hole 20 with the first member 1 protruding from the front end face 211 of the insulator, and a firing portion that contains a good heat conductive metal and is welded to the front end face 11 of the metal fitting, and faces the center electrode outer peripheral direction. Outer electrode 4 in which a noble metal tip 42 is disposed
And discharges sparks along the insulator front end face 211 between the ignition portion and the center electrode tip portion 31 (see FIG. 7;
Example).

B. In Claims 1 and 2, "the outer electrode in which the noble metal member is disposed on the ignition portion facing the outer peripheral direction of the center electrode and which is welded to the front end surface of the metal shell and the ..." (Cross-sectional shape), and the same operation and effects as those of the above [A] and [A] can be obtained (see the bipolar spark plugs D and E in FIGS. 8 and 9; the fourth and fifth embodiments).

[Brief description of the drawings]

FIG. 1 is a perspective view of bipolar spark plugs A and B according to a first embodiment and a second embodiment of the present invention.

FIGS. 2A and 2B are an axial explanatory view (a) and a radial explanatory view (b) of outer electrodes of the bipolar spark plugs A and B, respectively.

FIG. 3 is a side view (upper) and a structural explanatory view (lower) of the bipolar spark plugs A and B according to the first and second embodiments of the present invention.

FIG. 4 is a graph showing test results of a continuous high-speed durability test.

FIG. 5 is a graph showing a test result of an ignitability evaluation test of the bipolar spark plugs A and B according to the first embodiment and the second embodiment of the present invention.

FIG. 6 is an explanatory diagram showing a flow of the air-fuel mixture when the spark plug adopting the configuration of the present invention is mounted at an angle such that the air-fuel mixture is sent from behind an outer electrode.

FIG. 7 is a side view (top) and a structural explanatory view (bottom) of a surface discharge type bipolar spark plug C according to a third embodiment of the present invention.
It is.

FIG. 8 is a side view (top) and a structural explanatory view (bottom) of a creeping discharge type bipolar spark plug D according to a fourth embodiment of the present invention.
It is.

FIG. 9 is a side view (top) and a structural explanatory view (bottom) of a creeping discharge type bipolar spark plug E according to a fifth embodiment of the present invention.
It is.

FIG. 10 is a perspective view of a two-pole spark plug according to the related art.

FIG. 11 is a top view (a) and a side view (b) of a bipolar spark plug according to the prior art when screwed at an angle such that an air-fuel mixture is fed from behind an outer electrode.

12A and 12B are a top view (a) and a front view (b) of a parallel type spark plug in which an air-fuel mixture is screwed in from the side surface of the outer electrode.

FIG. 13 is a side view of a multipolar spark plug in which an outer electrode having a rectangular cross section is welded to a tip end surface of a metal fitting.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Metal shell 2 Insulator 3 Center electrode 4 Outer electrode 11 Metal tip surface 20 Shaft hole 21 Front end 31 Center electrode tip 41 Cu alloy (good heat conductive metal) 42 Noble metal tip 211 Insulator front end surface A, B, C, D, E Bipolar spark plug (multipolar spark plug) L Total length of Cu alloy (total length of good heat conductive metal) S Cross sectional area of Cu alloy at arbitrary cross section of outer electrode (good thermal conductivity at arbitrary cross section of outer electrode) L ₀ Total length of outer electrode S ₀ Cross-sectional area of outer electrode at arbitrary cross-section of outer electrode (cross-sectional area of outer electrode at arbitrary cross-section of outer electrode) S _max of section where cross-sectional area of Cu alloy is maximum Cross-sectional area of Cu alloy (cross-sectional area of high-thermal-conductivity metal in section where cross-sectional area of high-thermal-conductivity metal is maximum) S _{0max Cross-} sectional area of outer electrode in section where maximum cross-sectional area of Cu alloy is maximum (good heat Conductive gold Cross-sectional area of the outer electrode at the part where the cross-sectional area of

Claims (2)

[Claims] 1. A cylindrical metal shell, an insulator with a shaft hole fitted into the metal shell, a center electrode fitted into the shaft hole, and a high thermal conductive metal. A multi-electrode spark plug having an outer electrode which is welded to a metal fitting tip surface and has a noble metal member disposed on a firing portion opposed to a center electrode outer peripheral direction and performs a spark discharge between the firing portion and the center electrode tip portion; A multipolar spark plug, wherein the outer electrode has a columnar shape with a substantially circular cross section. 2. The overall length of the good heat conductive metal is L,
Good thermal conductive gold in the area where the cross-sectional area of the thermal conductive metal is maximum
The cross section of the genus is S_max, Good thermal conductivity in any cross section
S is the cross-sectional area of the metal, and L is the total length of the outer electrode.₀, Said good
The outer electrode at a portion where the cross-sectional area of the heat conductive metal is maximum.
The cross-sectional area of_0maxAnd the outer electrode in any cross section
The cross-sectional area of₀, (1/16) ≦ (S_max/
S_0max) And (S / S₀) ≦ (1/3), and
(L / L₀) ≧ S, S, S_max,
S₀, S_0max, L, and L ₀Is set.
The multi-polar spark plug according to claim 1.