JP2009272044A - Spark plug - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spark plug capable of improving ignitability and suppressing rising of a discharge voltage, while reducing wearing of the center electrode. <P>SOLUTION: At a tip part 13a of the central electrode 13, an inclined surface 21 tilted from a virtual surface P, that vertically crosses the center axis O of the central electrode 13, is provided at the entire tip part 13a of the center electrode 13. A top point 22 of the inclined surface 21, which is positioned outermost in the axial direction of the central axis O of the central electrode 13, directed to a ground electrode 14 side, as viewed from above, in the axial direction of the central axis O of the central electrode 13. The central electrode 13 and the ground electrode 14 are so provided that when viewed from above, in the axial direction of the central axis O of the central electrode 13, and that the position of the tip part 13a of the center electrode 13 is displaced from a position of the other end part 14b of the ground electrode 14. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a spark plug, and more specifically, by devising the shape of the tip of the center electrode and the positional relationship between the center electrode and the ground electrode in the axial plan view of the center axis of the center electrode. The present invention relates to a spark plug used in an internal combustion engine with improved ignitability.

  In a conventional spark plug, a cylindrical metal shell, a cylindrical insulator fitted in the metal shell, and a columnar center electrode disposed in the insulator are each substantially concentric with an axis. Are arranged as follows. In addition, a columnar ground electrode is bent at an intermediate portion thereof to be formed in a substantially L shape, and one end thereof is coupled to the distal end portion of the metal shell, and the other end portion is opposed to the distal end portion of the center electrode. Has the structure. At this time, a predetermined spark discharge gap is formed between the tip of the center electrode and the other end of the ground electrode.

  The spark plug having such a structure is attached to, for example, a cylinder head of an internal combustion engine such as an engine, and is used as an ignition source for the air-fuel mixture supplied to the combustion chamber. At this time, in order to efficiently burn the air-fuel mixture by the spark plug, it is important to surely ignite the air-fuel mixture by spark discharge and to quickly propagate the flame from the ignited flame kernel to the air-fuel mixture. However, in the conventional spark plug, since the ground electrode exists in the vicinity of the upper side and the side of the center electrode, the ground electrode tends to hinder the flow of the air-fuel mixture and the flame propagation, and heat is taken away by the ground electrode. There was a dislike that would reduce the ignitability.

  Therefore, in order to cope with such a problem, a noble metal wear resistant portion is fixed to the spark discharge portion of the center electrode and the ground electrode, and the position of the other end portion of the ground electrode with respect to the tip portion of the center electrode is set to the center of the center electrode. There has been proposed a spark plug which is arranged so as to be inclined with respect to an axis so as to improve ignitability and suppress electrode consumption (see, for example, Patent Document 1). In addition, the spark plug disclosed in Patent Document 1 reduces the temperature rise by using a cylindrical member in which the size of the noble metal wear-resistant portion fixed to the center electrode is defined by the relative relationship between the radius and the length. Thus, it is said that the consumption of the noble metal wear resistant part is effectively suppressed. Furthermore, the noble metal members of the center electrode and the ground electrode are arranged so that they do not overlap in the plan view in the axial direction of the center axis of the center electrode, thereby improving both the heat resistance and strength of the ground electrode and the ignitability. An intended spark plug has also been proposed (see, for example, Patent Document 2).

JP 2004-55142 A JP 2002-289321 A

  By the way, in recent years, there has been a strong demand for improvement in fuel consumption due to increasing interest in environmental pollution, and a spark plug with excellent ignitability that can reliably ignite an air-fuel mixture having a high A / F (Air / Fuel). Is desired. From the viewpoint of improving ignitability, the gap dimension between the ground electrode and the center electrode (the gap dimension between the tip end portion of the ground electrode and the other end portion of the center electrode in an axial plan view of the center axis of the center electrode) is increased. It has been found that such a setting is preferable because there are less obstacles to propagation of the ignited flame. On the other hand, if the gap size is set to be larger, the spark discharge gap becomes substantially larger, and the discharge voltage is increased.

  Since the noble metal wear-resistant portion fixed to the center electrode is formed in a columnar shape in the spark plug described in Patent Document 1, when the flame kernel generated by the spark discharge propagates in a direction away from the ground electrode, There is a possibility that the upper plane of this noble metal wear-resistant part may hinder the propagation of the flame kernel. In addition, the problem of the discharge voltage increase due to the increase of the spark discharge gap is not taken into consideration, and there is room for further improvement from the viewpoint of improving the ignitability.

  In addition, the spark plug described in Patent Document 2 is configured to prevent the melted portion between the ground electrode and the noble metal member from being consumed by discharge, and preventing the noble metal member from dropping from the ground electrode. Unlike the spark plug described in Patent Document 1, there was room for further improvement from the viewpoint of improving ignitability.

  The present invention has been made in view of the above-described problems, and the purpose thereof is the shape of the tip of the center electrode, and the center electrode and the ground electrode in the axial plan view of the center axis of the center electrode. By devising the arrangement relationship, an object is to provide a spark plug that can improve ignitability, suppress an increase in discharge voltage, and reduce wear of a center electrode.

The above-described object of the present invention is achieved by the following configuration.
(1) a cylindrical metal shell;
An insulator that is held by the metal shell and the tip is exposed from the tip of the metal shell;
A columnar center electrode disposed in the insulator such that the tip is exposed from the tip of the insulator;
A columnar ground electrode, one end of which is electrically connected to the metal shell, and the other end extending from the one end toward the central axis of the center electrode,
A spark plug in which a predetermined spark discharge gap is formed between the tip of the center electrode and the other end of the ground electrode,
The tip portion of the center electrode is provided with an inclined surface that is inclined with respect to a virtual plane perpendicular to the center axis of the center electrode over the entire tip portion of the center electrode, and the inclined surface. Of the central electrode, the apex located on the most distal side in the axial direction of the central axis is facing the ground electrode side in an axial plan view of the central axis of the central electrode,
The center electrode and the ground electrode are provided so that the position of the top portion of the center electrode and the position of the other end portion of the ground electrode are shifted in an axial plan view of the center axis of the center electrode. A spark plug characterized by
(2) The gap dimension between the tip portion of the center electrode and the other end portion of the ground electrode in an axial plan view of the center axis of the center electrode is in a range from 0.0 mm to 0.1 mm. The spark plug according to (1) above, wherein
(3) The spark plug according to (1) or (2) above, wherein an angle formed by the inclined surface and the virtual surface is set in a range of 10 ° to 25 °.
(4) The center electrode is formed in a cylindrical shape, and an imaginary line connecting the center axis of the center electrode and the top in the axial plan view of the center axis of the center electrode, and the center The angle formed by an imaginary line connecting the central axis of the electrode and the radial center position of the ground electrode with respect to the central electrode is set in a range of 30 ° or less (1) Spark plug of any one of (3).

According to the configuration of (1) above, the inclined surface is provided at the tip of the center electrode, the top of the inclined surface faces the ground electrode side, and the position of the top of the center electrode and the other end of the ground electrode. Therefore, a large open space is formed on the side where the inclined surface faces. Thereby, when the flame kernel generated by the spark discharge in the spark discharge gap propagates away from the ground electrode, it is possible to suppress the inhibition of the propagation of the flame kernel by the center electrode and the ground electrode. Accordingly, even an air-fuel mixture with high fuel efficiency can be reliably burned, and the ignitability of the spark plug can be improved. In addition, when the center electrode has a cylindrical shape, if the diameter is large, the center electrode itself is likely to be an obstacle to the expansion of the flame kernel. Therefore, when the diameter of the center electrode is a relatively large diameter of 1.5 mm or more, It has been found that the effect of. Furthermore, the length of the ground electrode can be shortened, and the stress applied to the base end portion (one end portion) of the ground electrode, particularly the ground electrode fixed to the metal shell, due to the vibration of the internal combustion engine such as the engine can be reduced. Thus, damage to the ground electrode can be prevented. In addition, the temperature increase of the ground electrode is suppressed by reducing the heat receiving area of the ground electrode and shortening the heat conduction distance due to the shortening of the ground electrode, thereby improving the durability of the spark plug. .
According to the configuration of (2) above, since the gap between the tip of the center electrode and the other end of the ground electrode is set in a range from 0.0 mm to 0.1 mm, good ignition is achieved. While maintaining the characteristics, it is possible to suppress the increase of the discharge voltage, reduce the consumption of the electrode, and improve the durability of the spark plug.
According to (3) above, the angle formed by the inclined surface at the tip of the center electrode and the virtual plane perpendicular to the center axis of the center electrode is set in the range of 10 ° to 25 °. Therefore, the consumption of the center electrode can be suppressed, the life of the spark plug can be extended, and the ignitability can be improved.
According to the spark plug configured as described in (4) above, the center electrode is formed in a cylindrical shape, and the imaginary line connecting the center axis of the center electrode and the top in the axial plan view of the center axis of the center electrode, and the center electrode Since the angle formed by the imaginary line connecting the center axis of the ground electrode and the radial center position of the ground electrode with respect to the center electrode is set within a range of 30 ° or less, the spark discharge gap can be shortened, Spark discharge can be performed at a low discharge voltage.

  According to the present invention, the ignitability is improved by devising the shape of the tip of the center electrode and the positional relationship between the center electrode and the ground electrode in the axial plan view of the center axis of the center electrode. It is possible to provide a spark plug that can suppress an increase in the discharge voltage and reduce the consumption of the center electrode.

Hereinafter, preferred embodiments of the spark plug according to the present invention will be described with reference to the drawings.
FIG. 1 is a sectional view of a spark plug according to the present invention. FIG. 2 is an enlarged view of a main part of the spark plug in FIG. FIG. 3 is a side view taken along arrow III in FIG. FIG. 4 is a plan view in an axial plan view of the central axis for explaining the apex position angle (described later) of the present invention.

As shown in FIG. 1, the spark plug 100 according to the present invention includes a metal shell 11 formed in a cylindrical shape and a through hole 16 formed in the axial direction inside. The insulator 12 fitted and held and the tip 12a is exposed from the tip 11a of the metal shell 11, and the through-hole of the insulator 12 so that the tip 13a is exposed from the tip 12a of the insulator 12 One end side (base end portion) 14a is joined by welding to the center electrode 13 inserted and arranged at one end portion 16 and the distal end portion 11a of the metal shell 11, and the intermediate portion 14c is bent. The other end portion 13b mainly includes a ground electrode 14 formed so as to extend from the base end portion 14a toward the central axis O of the center electrode 13.
In the following description, the side on which the center electrode 13 is disposed in the axial direction of the center axis O of the center electrode 13 will be described as the front side, and the opposite side (side on which the terminal fitting is disposed) will be described as the rear side.

  The metal shell 11 is made of carbon steel or the like, and an external male screw 15 for mounting to a cylinder head of an internal combustion engine such as an engine is formed on the outer peripheral surface of the metal shell 11 in the circumferential direction. The insulator 12 is formed of a ceramic fired body such as alumina, and the terminal fitting 17 is exposed at the rear end (upper side in the drawing) of the through hole 16 of the insulator 12, and the tip end portion 17a is exposed. The center electrode 13 is inserted and fixed at the front end (downward in the figure) with the tip end portion 13a exposed.

In addition, a resistor 18 is disposed in an intermediate portion between the terminal fitting 17 and the center electrode 13 in the through-hole 16, and conductive glass seal layers 19, 20 is arranged. That is, the center electrode 13 and the terminal fitting 17 are electrically connected through the resistor 18 and the conductive glass seal layers 19 and 20. The conductive glass seal layers 19 and 20 and the resistor 18 form a conductive coupling layer.
Note that the resistor 18 may be omitted, and the terminal fitting 17 and the center electrode 13 may be joined with a single conductive glass seal layer. When the resistor 18 is provided, the conductive glass seal layer 19 between the center electrode 13 and the resistor 18 can be omitted.

The center electrode 13 is formed in a cylindrical shape by a Ni alloy having excellent heat resistance and corrosion resistance, such as Inconel (trade name), and the tip 13a of the center electrode 13 has iridium as a main component. A columnar noble metal tip 13 'made of an alloy containing 5% by mass of platinum (Ir-5Pt) is fixed and disposed by laser welding or the like.
In the present embodiment, the central electrode 13 including the noble metal tip 13 'is referred to. In the present embodiment, the description will be made assuming that the noble metal tip 13 ′ is provided. However, the noble metal tip 13 ′ may not be provided. It will be appreciated that various embodiments can be included without departing from the scope of the invention.

  The ground electrode 14 is formed in a prismatic shape from a Ni alloy having excellent heat resistance and corrosion resistance, and the other end portion 14b includes, for example, an alloy containing platinum as a main component and containing 20% by mass of rhodium (Pt-20Rh). The noble metal tip made of may be fixed by laser welding or resistance welding.

  Due to the arrangement relationship between the center electrode 13 and the ground electrode 14, a spark discharge gap g is formed between the tip portion 13 a of the center electrode 13 and the other end portion 14 b of the ground electrode 14. The distance D of the spark discharge gap g (the axial distance of the central axis O of the central electrode 13) is preferably set to about 0.9 mm, for example. In this state, a high voltage is applied between the ground electrode 14 and the center electrode 13 to cause a spark discharge in the spark discharge gap g, so that the spark plug 100 according to the present invention is attached to an internal combustion engine such as an engine. It will function as a fire source.

Furthermore, as shown in FIGS. 2 and 3, the tip portion 13 a of the center electrode 13 has an inclined surface 21 that is inclined with respect to a virtual plane P perpendicular to the center axis O of the center electrode 13. The electrode 13 is provided over the entire tip portion 13a. The apex (top) 22 of the inclined surface 21 that is located on the outermost side in the axial direction of the central axis O of the central electrode 13 (that is, the most distal end side of the central electrode 13) is the central electrode 13. Is set to face the ground electrode 14 side in a plan view in the axial direction of the central axis O.
At this time, an angle θ1 formed by the inclined surface 22 and the virtual surface P (hereinafter also referred to as an inclined surface angle θ1) is set in a range of 10 ° to 25 °.
In the present invention, the position of the top portion 22 of the center electrode 13 and the position of the other end portion 14b of the ground electrode 14 are shifted, i.e., do not overlap, in the plan view in the axial direction of the center axis O of the center electrode 13. A center electrode 13 and a ground electrode 14 are provided. In the present embodiment, the “top” in the claims is a point as the apex 22. However, the present invention is not limited to this, and the other end of the ground electrode 14 is also applied to a portion occupying a certain range. What is necessary is just to provide so that it may have shifted | deviated with respect to the part which occupies a certain range of the part 14b.

  Further, the center electrode 13 and the ground electrode 13 are grounded so that the tip end portion 13a (that is, the top portion 22) of the center electrode 13 and the other end portion 14b of the ground electrode 14 are shifted in a plan view in the axial direction of the center axis O of the center electrode 13. Electrodes 14 are respectively disposed. At this time, the gap dimension between the tip end portion 13a of the center electrode 13 and the other end portion 14b of the ground electrode 14 in the axial plan view of the center axis O of the center electrode 13 (hereinafter also referred to as radial electrode gap). C is set in a range from 0.0 mm to 0.1 mm.

Furthermore, according to the present invention, as shown in the example of FIG. 4, the virtual line 31 connecting the central axis O of the central electrode 13 and the vertex 22 in the axial plan view of the central axis O of the central electrode 13, An angle θ2 (hereinafter also referred to as apex position angle θ2) formed by a virtual line 30 connecting the center axis O of the electrode 13 and the center position of the ground electrode 14 in the radial direction (the radial direction of the center electrode 13) is 30 °. The following ranges are set. In other words, assuming that the counterclockwise rotation about the central axis O of the center electrode 13 is positive (plus), the vertex 22 of the center electrode 13 is within a range of ± 30 ° from the virtual line 30, and the ground electrode 14 It is arranged at a close position and faces the ground electrode 14 side.
In the present embodiment, as apparent from FIG. 3, the vertex position angle θ2 is set to 0 °.

  As described above, according to the spark plug 100 of the present invention, the inclined surface 21 is provided at the tip portion 13a of the center electrode 13, and the top portion 22 of the inclined surface 21 faces the ground electrode 14 side, and the center Since the tip end portion 13a of the electrode 13 and the other end portion 14b of the ground electrode 14 are displaced, that is, do not overlap, a large open space is formed on the side where the inclined surface 21 faces. Thereby, when the flame nucleus produced by the spark discharge in the spark discharge gap g propagates in the direction away from the ground electrode 14, the inhibition of the propagation of the flame nucleus by the center electrode 13 and the ground electrode 14 can be suppressed. . Accordingly, even an air-fuel mixture with high fuel efficiency can be reliably burned, and the ignitability of the spark plug 100 can be improved. Furthermore, the length of the ground electrode 14 can be shortened, and the stress applied to the ground electrode 14, particularly the base end portion 14a of the ground electrode 14 fixed to the metal shell, due to the vibration of the internal combustion engine such as the engine can be reduced. Thus, damage to the ground electrode 14 can be prevented. In addition, the temperature increase of the ground electrode 14 is suppressed by reducing the heat receiving area of the ground electrode 14 and shortening the heat conduction distance accompanying the shortening of the ground electrode 14, thereby improving the durability of the spark plug 100. Can be increased.

(Example)
Next, the numerical ranges of the inclined surface angle θ1, the vertex position angle θ2, and the radial electrode gap C of the spark plug 100 described above will be described in more detail with reference to the drawings showing the evaluation test results.

<About radial electrode gap C>
First, an evaluation test was performed on the numerical range of the radial electrode C. The results of this evaluation test are shown in FIG. 5, FIG. 6, and FIG.
As a spark plug for this evaluation test, the diameter D of the center electrode 13 is 2.7 mm, the inclined surface angle θ1 is 15 °, the spark discharge gap g is 0.9 mm, and the apex position angle θ2 is 0 °. In some cases, a plurality of spark plugs were produced in which the radial electrode gap C (coverage amount a) was changed from −0.6 mm to 0.6 mm.
FIG. 5 shows that this evaluation test spark plug is attached to a 2000 cc displacement, in-line 4-cylinder, DOHC gasoline engine, and is operated while gradually increasing A / F (Air / Fuel) at an engine speed of 2000 rpm. It is a graph which shows the relationship between the limit A / F at the time of misfire, and the fogging amount a.
FIG. 6 is a graph showing the relationship between the discharge voltage and the fogging amount a at this time.
FIG. 7 is a graph comparing the stress acting on the ground electrode having a fogging amount of 1 mm (radial electrode gap C = −1 mm) and −1 mm (radial electrode gap C = 1 mm).

  Here, in FIG. 5 and FIG. 6, in the plan view in the axial direction of the central axis O of the central electrode 13, the horizontal axis represents the state from the state where the central electrode 13 and the ground electrode 14 overlap to the state where there is a gap. The fogging amount a is shown. That is, a region where the fogging amount a is negative is a state where there is a radial electrode gap C, and a region where the fogging amount a is positive indicates a state where the center electrode 13 and the ground electrode 14 overlap each other (that is, the diameter (Direction electrode gap C = -the relationship of fogging amount a).

  As shown in FIG. 5, when the fogging amount a is smaller than 0 (minus side), it ignites even with a high A / F (good ignitability), but when the fogging amount a is larger than 0 (plus side), the ignitability is low. It tends to get worse. This is because the fogging amount a is negative, that is, by providing the radial electrode gap C, it becomes difficult for the ground electrode 14 to hinder the expansion of the flame kernel caused by the spark discharge. At this time, the center electrode 13 is provided with the inclined surface 21 and the apex 22 of the inclined surface 21 faces the ground electrode 14, so that the spread of the flame kernel is prevented by the center electrode 13. This also increases the ignitability.

  On the other hand, as shown in FIG. 6, when the fogging amount a is smaller than −0.1 mm (that is, the radial electrode gap C is 0.1 mm or more), the separation distance between the discharge point of the center electrode 13 and the ground electrode 14 is increased. As a result, a phenomenon in which the discharge voltage rises rapidly is observed. This increase in the discharge voltage is not preferable because it also causes consumption of the electrode.

  Therefore, from the evaluation test results of FIGS. 5 and 6, when the fogging amount a is set in the range from −0.1 mm to 0.0 mm, that is, the radial electrode gap C is set in the range from 0.0 mm to 0.1 mm. It can be seen that in this case, while maintaining good ignitability, it is possible to suppress an increase in the discharge voltage, reduce electrode consumption, and improve the durability of the spark plug.

  In addition, by setting the radial electrode gap C in the range from 0.0 mm to 0.1 mm, the length of the ground electrode 14 can be shortened, the tip mass of the ground electrode 14 can be reduced, and grounding can be performed. The burden on the base end portion 14a of the electrode 14 can be reduced. For example, as shown in FIG. 7, the load stress acting on the ground electrode 14 is reduced to approximately 90% when the cover amount a is −1 mm, compared to the case where the cover amount a is 1 mm. Thus, it can be seen that the load stress tends to be reduced by shortening the length of the ground electrode 14. Therefore, by setting the radial electrode gap C in the range from 0.0 mm to 0.1 mm, the vibration of the ground electrode 14 caused by the vibration of the internal combustion engine such as the engine can be suppressed. It turns out that it becomes advantageous with respect to breakage.

  Further, since the ground electrode 14 is disposed so as to protrude into the combustion chamber of the engine, it tends to become high temperature, and overheating of the ground electrode 14 leads to wear of the electrode, which is not preferable. The heat transferred to the ground electrode 14 by the combustion of the air-fuel mixture is transmitted to the ground electrode 14, the metal shell 11, and the engine block, and the ground electrode 14 is cooled. Therefore, if the length of the ground electrode 14 is shortened, the total surface area of the ground electrode 14 is reduced, so that the amount of heat received is reduced, and the heat transfer path is shortened, so that the heat extraction of the ground electrode 14 is improved. 14 can be prevented from being overheated and durability can be enhanced.

<Inclined surface angle θ1>
Next, an evaluation test was performed on a numerical range of the inclination angle θ1. The results of this evaluation test are shown in FIGS.
As a spark plug for the evaluation test, the diameter D of the center electrode 13 is 2.7 mm, the spark discharge gap g is 0.9 mm, the apex position angle θ2 is 0 °, and the fogging amount a is −0.1 mm (radial electrode A plurality of spark plugs were manufactured in which the inclined surface angle θ1 was changed in units of 5 ° from 0 ° to 35 ° at a constant gap C = 0.1 mm).
FIG. 8 shows the relationship between the inclination angle θ1 and the limit A / F when the spark plug for evaluation test is attached to a 2000 cc, in-line 4-cylinder, DOHC gasoline engine and operated at an engine speed of 2000 rpm. It is a graph.
FIG. 9 is a graph showing the relationship between the wear rate of the center electrode 13 and the inclined surface angle θ1 based on the wear amount of θ2 = 90 ° after 200 hours of operation at an engine speed of 5000 rpm. The consumption rate referred to here was evaluated by measuring the height H of the center electrode 13.
As for the measurement of the inclined surface angle θ1, the relational expression of θ1 + θ3 = 90 ° is established when the apex angle (inner angle) at the apex 22 is θ3 in the cross section including the central axis O and the apex 22 of the center electrode 13. The vertex angle θ3 was measured, and the inclined surface angle θ1 was obtained based on the measured value as θ1 = 90 ° −θ3. In addition, the measuring method of (theta) 1 is not restricted to this, You may use what kind of method.

  As shown in FIG. 8, it can be seen that the A / F is drastically improved when the inclined surface angle θ1 is 10 °. This is because the center electrode 13 is less likely to become an obstacle to the expansion of the flame kernel, and the ignitability is improved. Further, as shown in FIG. 9, the tip portion 13a of the center electrode 13 tapers as the inclined surface angle θ1 decreases, so that the consumption rate of the center electrode 13 increases, and particularly when θ1 is 25 ° or less. It can be seen that increases rapidly.

  Therefore, it can be seen from the evaluation test results of FIGS. 8 and 9 that the inclined surface angle θ1 should be set to 10 ° or more and 25 ° or less (10 ° ≦ θ1 ≦ 25 °). As a result, the life of the spark plug can be extended and the ignitability can be improved.

<Vertex position angle θ2>
Further, an evaluation test was performed on the numerical range of the vertex position angle θ2. This evaluation test is shown in FIG.
As a spark plug for this evaluation test, the diameter D of the center electrode 13 is 2.7 mm, the inclined surface angle θ1 is 15 °, the spark discharge gap g is 0.9 mm, and the radial electrode gap C is 0.1 mm. A plurality of spark plugs were produced in which the apex position angle θ2 was changed in units of 10 ° from 0 ° to 60 °.
FIG. 10 is a graph showing the relationship between the discharge voltage and the apex position angle θ2 when the spark plug is attached to a 2000 cc displacement, in-line 4-cylinder, DOHC gasoline engine and operated at an engine speed of 750 rpm.

  As shown in FIG. 10, when the apex position angle θ2 is 40 ° or more, a rapid increase in the discharge voltage is observed. This is considered to be because when the apex position angle θ2 increases, the apex 22 moves away from the ground electrode 14, and the substantial spark discharge gap increases. Therefore, it can be seen from the test results in FIG. 10 that the vertex position angle θ2 should be set within a range of 30 ° or less. In this case, the spark discharge gap g can be shortened, and the spark is reduced at a low discharge voltage. It can be discharged.

  As described above, according to the spark plug 100 of the present embodiment, by optimizing the numerical ranges of the inclined surface angle θ1, the vertex position angle θ2, and the radial electrode gap C, the ignitability is improved, It is possible to suppress the increase of the discharge voltage, reduce the consumption of the center electrode 13, and improve the durability of the spark plug 100.

(Modification)
Next, a plurality of modifications according to the spark plug of the above-described embodiment will be described with reference to FIGS. FIGS. 11 to 13 are side views of main parts of the spark plugs of the first modification, the second modification, and the third modification, respectively.
In addition, since the spark plug of each modification differs only in the form of a part of a ground electrode or a center electrode, the same code | symbol or an equivalent code | symbol is attached | subjected to the same part, and detailed description is abbreviate | omitted.

(First modification)
The spark plug 101 of the first modification shown in FIG. 11 is formed such that the width W of the ground electrode 14 is narrower than the diameter of the center electrode 13. As a result, it is possible to reduce the possibility that the upward propagation of the flame kernel generated in the spark discharge gap g is hindered by the ground electrode 14 and to improve the ignitability. Since other operations and effects are the same as those of the above-described embodiment, the description thereof is omitted.

(Second modification)
In the spark plug 102 of the second modified example shown in FIG. 12, the ground electrode 14 is formed in a cylindrical shape. Thereby, since the flow around the ground electrode 14 is improved, the flame kernel generated in the spark discharge gap g easily propagates upward along the side surface of the cylindrical ground electrode 14. Thus, since the expansion of the flame kernel is not hindered by the ground electrode 14, the ignitability can be improved. Since other operations and effects are the same as those of the above-described embodiment, the description thereof is omitted.

(Third Modification)
In the spark plug 103 of the third modified example shown in FIG. 13, a portion including the apex 22 of the inclined surface 21 of the center electrode 13 (in this modified example, a portion including the upper half surface portion of the inclined surface 21) is used as a noble metal tip. 40 is fixedly formed. The noble metal used for the noble metal tip 40 is mainly composed of iridium (Ir), such as Pt, Rh, Ni, W, Pd, Ru, Re, Al, Al ₂ O ₃ , Y, Y ₂ O ₃ . Alloys containing at least one additive and alloys containing platinum (Pt) as a main component and containing at least one additive such as Ir, Rh, Ni, W, Pd, Ru, Re, etc. Examples are materials that are high and have excellent spark wear resistance.

  By the way, normally, since the spark plug is used by applying a negative high voltage to the center electrode 13 to cause a spark discharge, the center electrode 13 is greatly consumed by sparks. For this reason, the noble metal tip 40 on the side of the center electrode 13 is preferably a noble metal tip made of an iridium-based alloy having high spark wear resistance. Since other operations and effects are the same as those of the above-described embodiment, the description thereof is omitted.

  As a result, the consumption of the center electrode 13 (the noble metal tip 40) due to the discharge is greatly suppressed, stable discharge can be performed over a long period of time, and a long-life spark plug can be obtained.

(Fourth embodiment)
In the tip part 13a of the center electrode 13 of the spark plug of the fourth modification shown in FIG. 14, the inclined surface 51 is partially provided so as to partially have an end surface 51 perpendicular to the center axis O of the center electrode 13. It has been. At this time, the midpoint of the side formed between the end surface 51 and the inclined surface 51 is a top (not shown), and this top is grounded in an axial plan view of the central axis O of the center electrode 13. It is set to face the electrode 14 side. Since other operations and effects are the same as those of the above-described embodiment, the description thereof is omitted.

Note that the present invention is not limited to the above-described embodiments and modifications, and modifications, improvements, and the like can be made as appropriate.
For example, in the above-described embodiments and modifications, the center electrode is described as being formed in a cylindrical shape. Can be adopted. Moreover, although embodiment and each modification mentioned above demonstrated the inclined surface and the end surface as a flat surface, it is not restricted to this, For example, it can also be set as a curved surface to such an extent that the effect of this invention is not prevented. .

It is sectional drawing of the spark plug of this invention. It is a principal part enlarged view of the spark plug in FIG. FIG. 3 is a side view taken along arrow III in FIG. 2. It is a top view of the axial direction planar view of the central axis for demonstrating the top position angle of this invention. A spark plug for evaluation test is attached to a 2000 cc displacement, in-line 4-cylinder, DOHC gasoline engine, and the engine is operated while gradually increasing the A / F (air-fuel ratio) at an engine speed of 2000 rpm. It is a graph which shows the relationship between F and the amount of fogging. It is a graph which shows the relationship between the discharge voltage when the spark plug for evaluation tests is attached to a 2000 cc displacement, in-line 4-cylinder, DOHC gasoline engine and the engine is operated at an engine speed of 750 rpm and the fogging amount. It is a graph which compares the stress which acts on the ground electrode whose fog amount is 1 mm and -1 mm (radial direction electrode gap C = 1 mm). A spark plug for evaluation test is attached to a 2000 cc displacement, in-line 4-cylinder, DOHC gasoline engine, and the engine is operated while gradually increasing the A / F (air-fuel ratio) at an engine speed of 2000 rpm. It is a graph which shows the relationship between F and inclined surface angle (theta) 1. A spark plug for evaluation test was attached to a gasoline engine with a displacement of 2000 cc, an in-line 4-cylinder, DOHC engine, and the operation rate of the center electrode after operating for 200 hours at an engine speed of 5000 rpm (θ2 = 90 ° reference) and the inclination angle θ1. It is a graph which shows a relationship. 6 is a graph showing the relationship between the discharge voltage and the apex position angle θ2 when an evaluation test spark plug is attached to a 2000 cc, in-line 4-cylinder, DOHC gasoline engine and operated at an engine speed of 750 rpm. It is a principal part side view of the spark plug which concerns on a 1st modification. It is a principal part side view of the spark plug which concerns on a 2nd modification. It is a principal part side view of the spark plug which concerns on a 3rd modification. It is a principal part front view of the spark plug which concerns on a 4th modification.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Main metal fitting 11a The front-end | tip part of a main metal fitting 12 Insulator 12a The front-end | tip part of an insulator 13 Center electrode 13a The front-end | tip part of a center electrode 14 Ground electrode 14a One end side (base end part) of a ground electrode
14b The other end of the ground electrode 16 Through hole 21 Inclined surface 22 Apex 23 Side surface on the ground electrode side 24 Side surface on the opposite side to the ground electrode 25 Ground electrode tip 30 Connect the central axis of the center electrode and the radial center position of the ground electrode Virtual line 31 Virtual line connecting the central axis and the top of the central electrode 100 Spark plug 101 Spark plug 102 Spark plug 103 Spark plug C Radial electrode gap g Spark discharge gap O Center electrode central axis θ1 Inclined surface angle θ2 Vertex position angle

Claims (4)

A cylindrical metal shell,
An insulator that is held by the metal shell and the tip is exposed from the tip of the metal shell;
A columnar center electrode disposed in the insulator such that the tip is exposed from the tip of the insulator;
A columnar ground electrode, one end of which is electrically connected to the metal shell, and the other end extending from the one end toward the central axis of the center electrode,
A spark plug in which a predetermined spark discharge gap is formed between the tip of the center electrode and the other end of the ground electrode,
The tip portion of the center electrode is provided with an inclined surface that is inclined with respect to a virtual plane perpendicular to the center axis of the center electrode over the entire tip portion of the center electrode, and the inclined surface. Of the central electrode, the apex located on the most distal side in the axial direction of the central axis is facing the ground electrode side in an axial plan view of the central axis of the central electrode,
The center electrode and the ground electrode are provided so that the position of the top portion of the center electrode and the position of the other end portion of the ground electrode are shifted in an axial plan view of the center axis of the center electrode. A spark plug characterized by The gap dimension between the tip end portion of the center electrode and the other end portion of the ground electrode in an axial plan view of the center axis of the center electrode is set in a range from 0.0 mm to 0.1 mm. The spark plug according to claim 1, wherein: The spark plug according to claim 1 or 2, wherein an angle formed by the inclined surface and the virtual surface is set in a range of 10 ° or more and 25 ° or less. The center electrode is formed in a columnar shape, and an imaginary line connecting the center axis of the center electrode and the top in an axial plan view of the center axis of the center electrode, and the center electrode The angle formed by a virtual axis connecting a central axis and a radial center position of the ground electrode with respect to the central electrode is set in a range of 30 ° or less. The spark plug according to claim 1.

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