JP2005100754A - Spark plug for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase a distance S1 between firing parts while preventing degradation of a withstand voltage characteristic of an insulator 11, in a spark plug equipped with a plurality of center electrodes 12 and 13. <P>SOLUTION: In the plurality of center electrodes 12 and 13, respective center axes Z2 and Z3 of the plurality of center electrodes 12 and 13 are disposed to form a predetermined angle θ so as to set the mutual distance between tip parts of the plurality of center electrodes 12 and 13 larger than than the mutual distance between the opposite tip part sides of the plurality of center electrodes 12 and 13. Thereby, since the mutual distance between the opposite tip part sides of the center electrodes 12 and 13 located at positions close to an intense electric field is relatively small, the thickness (t) of the intense electric field part of the insulator 11 is restrained from being reduced. Since the mutual distance between the tip part sides of the center electrodes 12 and 13 is relatively large, the distance S1 between the firing parts can be increased as compared with a conventional one. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an ignition plug for an internal combustion engine used for automobiles, cogeneration, gas pressure pumps, and the like.

In a conventional spark plug in which two center electrodes and two ground electrodes are provided to form two ignition portions (discharge gaps), the two center electrodes are arranged in parallel to each other (see, for example, Patent Document 1).
JP-A-57-193777

  As a device to further improve the ignitability of the plug in which the two center electrodes are arranged in parallel to each other, an attempt was made to move the two center electrodes to the outside in the radial direction of the insulator, The wall thickness became thin, and the problem that the withstand voltage property of an insulator fell occurred.

  In view of the above points, an object of the present invention is to enable an increase in the distance between firing parts while suppressing a decrease in the voltage resistance of an insulator.

  In order to achieve the above object, in the first aspect of the present invention, the tip of the electrode located on the combustion chamber side of the center electrode (12, 13, 13A) is disposed to face the ground electrode (20, 21, 21A). The spark plug is provided with a plurality of center electrodes, and the plurality of center electrodes are such that the distance between the electrode tip portions of the plurality of center electrodes is wider than the distance between the plurality of center electrodes on the counter electrode tip portion side. As described above, the center axes (Z2, Z3, Z4) of the plurality of center electrodes are arranged at a predetermined angle (θ).

  According to this, the counter electrode tip side in the central electrode, which is a portion close to the strong electric field part, is relatively narrow, so that it is possible to suppress the thinning of the strong electric field part in the insulator. . Further, since the distance between the electrode tip portions in the center electrode is relatively wide, the distance between the firing portions can be made larger than before. Therefore, it is possible to improve the ignitability by increasing the distance between the firing portions while securing the thickness of the strong electric field portion of the insulator and suppressing the decrease in the voltage resistance of the insulator.

  By the way, if the distance between the ignition parts is increased, the pocket gap (gap between the insulator and the housing) is narrowed, and it is easy to fly sideways at the time of smoldering, so that the ignitability is lowered. The angle (θ) is preferably more than 0 ° and not more than 6 °.

  The invention according to claim 3 is characterized in that the predetermined angle (θ) is more than 1.5 ° and not more than 4.5 °. According to this, when the variation in design and manufacture is taken into consideration, the thickness of the strong electrolysis portion of the insulator can be surely ensured.

  In the invention according to claim 4, the center electrode (12, 13) is insulated and held by the cylindrical insulator (11), the insulator is accommodated in the cylindrical housing (10), and the ground electrode (20, 21) is provided. A spark plug joined to the housing, and the surfaces (201, 211) of the ground electrode facing the tip of the center electrode are inclined with respect to the surface orthogonal to the central axis (Z1) of the insulator. It is characterized by.

 According to this, when compared with a spark plug (see FIG. 1) that employs a so-called overhang type ground electrode in which the surface of the ground electrode facing the electrode tip of the center electrode is parallel to the surface perpendicular to the central axis of the insulator, When the so-called slant-type ground electrode (see FIG. 6) is used as in the invention according to claim 4, the distance S1 between the ignition parts can be further increased.

  In addition, the code | symbol in the bracket | parenthesis of each said means shows the correspondence with the specific means as described in embodiment mentioned later.

(First embodiment)
Hereinafter, the present invention will be described based on embodiments. 1A is a front cross-sectional view showing the overall configuration of the spark plug according to the first embodiment of the present invention, FIG. 1B is a bottom view of FIG. 1A, and FIG. 2 is the spark plug of FIG. It is an expanded sectional view near an ignition part.

  The spark plug 1 shown in FIGS. 1 and 2 is formed with a pair of ignition portions (discharge gaps) G1 and G2 in order to perform one-cylinder two-point ignition. Then, these ignition parts G1 and G2 are mounted on the cylinder head so as to face one combustion chamber of an internal combustion engine (not shown), and are discharged by the ignition parts G1 and G2 to ignite the air-fuel mixture in the combustion chamber. It is.

  The spark plug 1 has a substantially cylindrical housing 10 made of a conductive steel material. The housing 10 includes a male screw 101 that is screwed into a female screw of a cylinder head in an internal combustion engine. An insulator 11 made of alumina ceramic is fixed inside the housing 10, and both ends of the insulator 11 protrude from the housing 10.

  The insulator 11 is provided with two holes 111, 112 extending in the direction of the central axis Z1 of the insulator 11. In each of the holes 111, 112, cylindrical center electrodes 12, 13 made of a conductive steel material, carbon Resistors 14 and 15 and columnar stems 16 and 17 made of a conductive steel material are embedded, and a sealing glass is sealed between these components.

  Tips 18 and 19 made of a noble metal or an alloy thereof are joined to the front end surfaces of the center electrodes 12 and 13 located on the combustion chamber side. The heads of the stems 16 and 17 are each provided with a terminal to which a line for guiding a high voltage is connected. The terminals are formed integrally or separately with the stems 16 and 17. Further, the terminal is buried in the insulator 11 in order to keep the insulation distance between the terminals.

  On the other hand, a pair of ground electrodes 20 and 21 made of a conductive steel material are joined to the end of the housing 10. Surfaces 201 and 211 of the ground electrodes 20 and 21 facing the tip portions of the center electrodes 12 and 13 are parallel to a surface orthogonal to the insulator center axis Z1. The tip 18 of the first center electrode 12 and the first ground electrode 20 face each other across the first ignition part G1, and the tip 19 of the second center electrode 13 and the second ground electrode 21 separate the second ignition part G2. Facing each other.

  The two holes 111 and 112 of the insulator 11 are parallel to the insulator center axis Z1 in the portion where the resistors 14 and 15 and the stems 16 and 17 are embedded, and the portion where the center electrodes 12 and 13 are embedded is the insulator center axis. Inclined with respect to Z1. Specifically, the portion where the center electrodes 12 and 13 are embedded in the two holes 111 and 112 of the insulator 11 is from the portion where the resistors 14 and 15 and the stems 16 and 17 are embedded to the ground electrodes 20 and 21 side. As it goes, it is inclined so as to gradually move away from the insulator central axis Z1, and the portions of the two holes 111 and 112 of the insulator 11 where the center electrodes 12 and 13 are embedded are in a C shape.

  As a result, the central axes Z2 and Z3 of the two central electrodes 12 and 13 form a predetermined angle θ (where θ> 0 °), and the distance between the tip portions of the central electrodes 12 and 13 is the center electrode 12, 13 is wider than the mutual distance on the opposite end side. Accordingly, the distance S1 between the first ignition part G1 and the second ignition part G2 (hereinafter referred to as the “inter-ignition part distance”) S1 can be made larger than before, and specifically, the male screw 101 of the housing 10 is In the case of the M14 plug, the distance S1 between the ignition parts can be increased by 1 mm or more. However, since the pocket clearance S2 between the insulator 11 and the housing 10 is narrowed when the distance S1 between the ignition parts is large, and it becomes easy to fly sideways when smoldering, the predetermined angle θ is preferably 6 ° or less. .

  Moreover, since the mutual space | interval is relatively narrow in the center electrode 12 and 13 side which is a site | part close | similar to a strong electric field part, since mutual space | interval is relatively narrow, it suppresses that the thickness t of the strong electric field part in the insulator 11 becomes thin. Can do. However, in consideration of design and manufacturing variations, in order to ensure the thickness of the strong electrolysis part of the insulator, the predetermined angle θ exceeds 1.5 ° and is 4.5 ° or less. Is desirable.

  Next, with respect to the spark plug having the above-described configuration, the ignitability was evaluated using the distance S1 between the ignition portions as a parameter.

  As an evaluation product, a plug having an ignition part distance S1 of 5 mm and 10 mm was prepared. In addition, a conventional plug was prepared for comparison. In the conventional plug, the two center electrodes are parallel to each other, and the distance S1 between the firing parts is 3 mm. In any plug, the male screw 101 of the housing 10 is M14.

  The evaluation test was carried out under the conditions of 34 Nm / 1600 rpm and stoichiometric air-fuel ratio, with the evaluation product mounted on an internal combustion engine with a displacement of 1800 cc. The ignitability was evaluated by the flame volume with respect to the elapsed time from the start of discharge in the ignition parts G1 and G2. FIG. 3 shows the results, in which the vertical axis represents the flame volume, the horizontal axis represents the elapsed time from the start of discharge, and the longer the plug S1, the faster the flame grows and the better the ignitability. Was confirmed.

  According to the above-described embodiment, since the distance between the opposite ends of the center electrodes 12 and 13 is relatively narrow, the thickness t of the strong electric field portion in the insulator 11 can be suppressed from being reduced. On the other hand, since the space | interval of the front-end | tip part in the center electrodes 12 and 13 is relatively wide, the distance S1 between ignition parts can be taken larger than before. Therefore, while ensuring the thickness t of the strong electric field portion of the insulator 11 and suppressing a decrease in the voltage resistance of the insulator 11, the ignition portion distance S1 can be increased to improve the ignitability.

(Second Embodiment)
4 is a perspective view of an essential part of a spark plug according to a second embodiment of the present invention, FIG. 5A is a cross-sectional view taken along the line AA in FIG. 4, and FIG. FIG. 5C is a cross-sectional view taken along the line C-C in FIG. 4.

  In the first embodiment, the portions where the resistors 14 and 15 and the stems 16 and 17 are embedded in the two holes 111 and 112 of the insulator 11 are parallel to the insulator central axis Z1. Is inclined with respect to the insulator central axis Z1. Other points are common to the first embodiment.

  As shown in FIGS. 4 and 5, the axes of the two holes 111 and 112 of the insulator 11 are arranged on the side of the center electrodes 12 and 13 from the open end (the upper side in FIG. 4) on the side where the high voltage is supplied. Straight to the open end. In addition, the axes of the two holes 111 and 112 of the insulator 11 are not parallel to each other, and the two holes 111 and 112 of the insulator 11 are closest to each other in the vicinity of the strong electric field portion of the insulator 11 and the center electrodes 12 and 13. The farthest open end on the side.

  According to the present embodiment, it is possible to improve the ignitability by increasing the inter-firing portion distance S1 while securing the thickness t of the strong electric field portion of the insulator 11 and suppressing the decrease in the voltage resistance of the insulator 11. it can.

(Third embodiment)
FIG. 6 is a cross-sectional view of a main part of the spark plug according to the third embodiment of the present invention. In the first embodiment, the surfaces 201 and 211 facing the tips of the center electrodes 12 and 13 of the ground electrodes 20 and 21 are parallel to the surface orthogonal to the insulator center axis Z1, but in this embodiment, the ground electrodes The surfaces 201 and 211 facing the tip portions of the center electrodes 12 and 13 at 20 and 21 are inclined with respect to the surface orthogonal to the insulator center axis Z1. Other points are common to the first embodiment.

  Compared with the spark plug (see FIG. 1) employing the so-called overhang type ground electrodes 20 and 21 as in the first embodiment, when the so-called slant-type ground electrodes 20 and 21 as in the present embodiment are used, ignition occurs. The inter-part distance S1 can be further increased by 1 mm or more.

(Fourth embodiment)
FIG. 7 is a cross-sectional view of a main part of a spark plug according to the fourth embodiment of the present invention. In the first embodiment, two center electrodes 12, 13 and two ground electrodes 20, 21 are provided. However, in this embodiment, three center electrodes 12, 13, 13A and three ground electrodes 20, 21, 21A are provided. It is a thing. Other points are common to the first embodiment.

  And the center electrode 12,13,13A of three center electrodes 12,13,13A so that the mutual space | interval of the front-end | tip part in center electrode 12,13,13A may become wider than the mutual space | interval of the non-tip part side in center electrode 12,13,13A. By giving each central axis Z2, Z3, Z4 a predetermined angle θ, the same effect as in the first embodiment can be obtained.

(A) is front sectional drawing which shows the whole structure of the ignition plug which concerns on 1st Embodiment of this invention, (b) is a bottom view of (a). It is front sectional drawing which expands and shows the ignition part vicinity in the ignition plug of FIG. It is a figure which shows the evaluation result regarding the ignitability of the ignition plug of FIG. It is a perspective view of the principal part of the spark plug which concerns on 2nd Embodiment of this invention. (A) is sectional drawing which follows the AA line of FIG. 4, (b) is sectional drawing which follows the BB line of FIG. 4, (c) is sectional drawing which follows the CC line of FIG. It is sectional drawing of the principal part of the spark plug which concerns on 3rd Embodiment of this invention. It is sectional drawing of the principal part of the spark plug which concerns on 4th Embodiment of this invention.

Explanation of symbols

  12, 13, 13A ... center electrode, 20, 21, 21A ... ground electrode, Z2, Z3, Z4 ... center axis of center electrode, [theta] ... predetermined angle.

Claims (4)

In the spark plug in which the electrode tip located on the combustion chamber side in the center electrode (12, 13, 13A) is arranged to face the ground electrode (20, 21, 21A),
A plurality of the center electrodes;
The plurality of center electrodes are arranged such that the distance between the electrode tip portions of the plurality of center electrodes is wider than the distance between the counter electrode tip portions of the plurality of center electrodes. The internal combustion engine ignition plug is characterized in that each of the central axes (Z2, Z3, Z4) is arranged at a predetermined angle (θ). 2. The ignition plug for an internal combustion engine according to claim 1, wherein the predetermined angle (θ) is greater than 0 ° and 6 ° or less. The ignition plug for an internal combustion engine according to claim 2, wherein the predetermined angle (θ) is more than 1.5 ° and not more than 4.5 °. The center electrode (12, 13) is insulated and held by a cylindrical insulator (11), the insulator is accommodated in a cylindrical housing (10), and the ground electrode (20, 21) is joined to the housing. A spark plug,
The surface (201, 211) facing the electrode tip of the center electrode in the ground electrode is inclined with respect to a surface orthogonal to the central axis (Z1) of the insulator. The ignition plug for an internal combustion engine according to any one of 3.

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