JPH0318317B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement in a spark plug used in a spark-ignition internal combustion engine.

[Prior art and its problems] Conventional spark plugs used in spark-ignition internal combustion engines include, for example, the spark plug described in FIG. For example, a ground electrode 3' having a rectangular cross section faces the top end surface 8' of a rod-shaped center electrode 2' with a predetermined discharge interval, and FIG. Or, as described in FIG. 2 of Japanese Utility Model Application Publication No. 55-44565, and as shown in FIG. There is a model in which the surfaces 5'' face each other with a predetermined discharge interval, but in all of these, the discharge occurs between parallel surfaces, so it is difficult to discharge between the planes. As the discharge voltage increases, the spark discharge becomes weaker because the discharge position is not fixed in one place.In addition, when the discharge occurs between parallel surfaces, the discharge interval is determined by the shadow of the ground electrode. Therefore, not only is it difficult for the air-fuel mixture to flow into the discharge interval, but the ground electrode itself prevents the flame kernel generated within the discharge interval from growing throughout the combustion chamber. The direction of growth is limited to the direction parallel to both surfaces in the discharge interval, and the growth of the flame kernel is narrow.Furthermore, the flame kernels generated in the discharge interval between the mutually parallel surfaces are widely in contact with both surfaces, Since the so-called quenching effect, in which much heat is transferred and absorbed by both electrodes via both surfaces, is large, the flame kernel becomes weaker.

As a result, the spark ignition is poor and the ignition becomes unstable, causing ignition failure especially at low load and low rotation speeds such as when the engine is idling, resulting in a decrease in output and an increase in harmful exhaust gases. So it was warm.

SUMMARY OF THE INVENTION An object of the present invention is to provide a spark plug that solves this problem by changing the shape of each ground electrode relative to the center electrode without impairing durability.

[Means for solving problems]

Therefore, a first invention provides a spark plug comprising a center electrode having a circular cross section and protruding from the center of the mounting thread, and a plurality of ground electrodes integrally projecting from the mounting thread. The tip of each ground electrode is bent so as to be inclined inward toward the center electrode, while the end surface at the tip of each ground electrode is formed into an inclined surface that is inclined outward with respect to the center line of the center electrode. Then, the angle of inclination of this inclined end face with respect to the center line of the center electrode is set to 30 to 80 degrees, and between the inner corner of the inclined end face near the center electrode and the outer peripheral surface of the center electrode, A predetermined discharge interval is formed in the radial direction, and the position along the center line of the center electrode at the inner corner is set near the top end surface of the center electrode, while each of the ground electrodes has a rectangular cross section. The inner corner of the rod-shaped body is formed into a straight line extending in a direction substantially parallel to the top end surface of the center electrode and substantially perpendicular to the center line of the center electrode.

In addition to the first invention, a second invention is such that, in addition to the first invention, a groove is provided on the top end surface of the center electrode, extending from an intermediate portion of each ground electrode toward the center of the center electrode.

〔Example〕

Examples of the present invention are shown in the drawings (Fig. 3 and 4) below.
In the figure, the reference numeral 2 is
A center electrode with a circular cross section that extends and protrudes on the center line of the mounting screw part 1 that is screwed into the cylinder head etc.
Reference numeral 3 indicates a connection from the mounting screw portion 1 to the center electrode 2.
each showing at least two or more grounding electrodes integrally protruding so as to extend substantially parallel to the center line 6 of the
The tip 4 of each ground electrode 3 is bent inward toward the center electrode 2 so as to be inclined by an appropriate opening degree β with respect to the center line 6 of the center electrode 2. The end surface 5 of the portion 4 is set outward at an appropriate angle α with respect to the center line 6 of the center electrode 2.
only tilt.

Of the end faces 5 of the tip portions 4 of each of the ground electrodes 3, inner corner portions 7 closer to the center electrode 2
A predetermined discharge interval C is formed in the radial direction between the inner corner 7 and the outer peripheral surface of the center electrode 2, and the height position in the direction along the center line 6 of the center electrode 2 at the inner corner 7 It is set at approximately the same height as the top end surface 8 of the electrode 2.

Furthermore, by manufacturing each of the ground electrodes 3 as a rod-shaped body with a rectangular cross section, the inner corner 7 of the tip 4 is substantially parallel to the top end surface 8 of the center electrode 2 and It is formed into a straight line extending in a direction substantially perpendicular to the center line 6 of.

With this configuration, the linear inner corner portion 7 of the end surface 5 of the tip portion 4 of each ground electrode 3 formed in a rectangular cross section, which is closer to the center electrode 2, and the outer peripheral surface of the center electrode 2, which has a circular cross section, are different from each other. By approaching a predetermined discharge distance C at one location, a spark discharge occurs at the location where the inner corner 7 of each ground electrode 3 and the center electrode 2 are closest to each other. Therefore, the location of the spark discharge is as follows. By being in a fixed position and concentrating on one place, strong sparks can be stably obtained and the discharge voltage can be lowered.

Further, while the end surface 5 at the tip 4 of each ground electrode 3 with respect to the center electrode 2 is inclined outward by an appropriate angle α with respect to the center line 6 of the center electrode 2, the end surface at the tip 4 of the ground electrode 3 is 5, the inner corner 7 is located at approximately the same position as the top end surface 8 of the center electrode 2, so that the discharge interval between the inner corner 7 and the center electrode 2 is controlled by the intake air mixture in the combustion chamber that these electrodes look into. Since the ground electrode 3 is not in the shadow of the air flow, the air-fuel mixture can easily flow into the discharge interval, and furthermore, due to the discharge between the inner corner 7 and the center electrode 2, the air-fuel mixture is The flame nucleus generated is
The end face 5 at the tip 4 of the ground electrode 3 grows widely over the entire area of the combustion chamber, and both electrodes 2 and 3 of the flame kernel
Since the contact area with the electrode is reduced, the so-called flame-extinguishing effect in which the heat of the flame kernel is transferred to both electrodes 2 and 3 is also significantly reduced, and together these factors significantly improve the ignitability of the air-fuel mixture. be.

Then, there are processing errors when fixing each ground electrode 3 to the mounting screw part 1 by welding or the like, and when bending the tip 4 of each ground electrode 3 inward toward the center electrode 2. Due to machining errors, the tip 4 of each ground electrode 3 is displaced from the center point of the center electrode 2 when viewed from the direction of the center line 6 of the center electrode 2.

In this case, each ground electrode 3 is, for example,
As shown in FIG. 4 of U.S. Pat. No. 2,324,616, if the inner corner 7 of each ground electrode 3 has a circular cross section like the center electrode 2, the inner corner 7 of each ground electrode 3 will have an arc shape. Inner corner 7 and center electrode 2
The point where the arcuate outer circumferential surface is closest to is
Due to the deviation due to errors during machining in each ground electrode 3, the outer circumferential surface of the center electrode 2 is displaced in the circumferential direction, and the discharge distance C at the relevant location changes significantly.In other words, each of the ground electrodes Due to the machining error in step 3, the intervals along the circumferential direction of the center electrodes at each discharge location become irregular, and the dispersion of the discharge interval C becomes large.As a result, for a large number of spark plugs, Predetermined ignition characteristics cannot be obtained.

In contrast, in the present invention, each ground electrode 3 is formed to have a rectangular cross section, and the inner corner 7 of each ground electrode 3 is substantially parallel to the top end surface 8 of the center electrode 2 and Since each ground electrode 3 is formed in a straight line extending in a direction substantially perpendicular to the center line 6, the inner corner 7 of the straight line approaches the center electrode 2 having a circular cross section. Part 1
Due to processing errors when fixing to the center electrode 3 or bending the tip 4 of each ground electrode 3, the tip 4 of each ground electrode 3 is not the center electrode when viewed from the direction of the center line 6 of the center electrode 2. For the center point of 2,
Even if the inner corner portion 7 is shifted upward or downward in the paper in FIG. Discharge during that time〓
The interval C does not change significantly; in other words,
Reliably prevents uneven spacing of the center electrodes 2 along the circumferential direction at each discharge location and large variations in the discharge distance C due to machining errors in each ground electrode 3. It can be done.

Further, it has been experimentally found that the inclination angle α of the end face 5 of each ground electrode 3 should be 30 to 80 degrees.

In other words, if the inclination angle α of the end face 5 of each ground electrode 3 is set to a value exceeding 80 degrees, the inner corner 7 becomes an acute angle, so the inner corner 7 is greatly worn during discharge, and the spark plug is damaged. If the inclination angle α of the end face 5 is less than 30 degrees, the end face 5 may be parallel to the outer circumferential surface of the center electrode 2 as in the conventional case. There is no noticeable difference in ignitability, and when the inclination angle is set to 30 to 80 degrees, there is no increase in wear and tear on each ground electrode 3, and there is no decrease in the durability of the spark plug. , the ignitability could be significantly improved compared to the conventional case shown in FIGS. 1 and 2.

In addition, the height of the inner corner 7 of the end surface 5 of each ground electrode 3 relative to the top end surface 8 of the center electrode 2 may vary somewhat as shown by the dashed line or the dashed double dotted line in FIG. The discharge spacing should be set at a location that does not exceed the discharge interval dimension C on the lower and higher sides of the top end surface 8 of the center electrode 2, respectively. That is,
When the height of the inner corner 7 with respect to the top end surface 8 of the center electrode 2 increases beyond the discharge interval dimension C, the distance from the inner corner 7 to the center electrode 2 increases, causing a drop in the discharge voltage. Not only is it impossible to achieve this, but the discharge interval is in the shadow of the ground electrode 2, which causes problems with the inflow of air-fuel mixture and the growth of flame kernels. However, it has been found through experiments that when the discharge interval becomes smaller than the above-mentioned discharge interval dimension C, there is a problem in that the discharge interval becomes in the shadow of the center electrode 2 and the flame-extinguishing effect of the center electrode 2 increases.

5 to 7 show an embodiment of the second invention, which is similar to the embodiment of the first invention in which a middle portion of both ground electrodes 3, 3 is attached to the top end surface 8 of the center electrode 2. A groove 10 is provided at the center electrode 2 in a direction perpendicular to the center line 6 of the center electrode 2, and by providing the groove 10 on the top end surface 8 of the center electrode 2, the discharge interval can be adjusted. The flame kernel generated in FIG. 5 grows as shown by the dotted circle in FIG. Since it is possible to reduce the amount of the flame being carried away by the center electrode 2, the extinguishing effect of the flame kernel can be further reduced.

In this case, the groove 1 provided on the top end surface 8 of the center electrode 2
The groove 10 may be configured to extend from the intermediate portion of each ground electrode 3 toward the center point of the center electrode 2. Therefore, when there are three ground electrodes 3, the groove 10 is As shown in FIG. 7, it has a Y-shape, and when there are four ground electrodes 3, it has a cross-shape. Also,
It goes without saying that the cross-sectional shape of the groove 10 is not limited to the V-shape, but may be other cross-sectional shapes such as a U-shape.

[Action/effect of the invention]

As described above, according to the first invention, each ground electrode 3
The tip portion 4 of each ground electrode 3 is bent so as to be inclined inwardly toward the center electrode 2, while the end surface 5 of the tip portion 4 of each of the ground electrodes 3 is inclined outwardly with respect to the center line 6 of the center electrode 2. The inner corner 7 of the inclined end surface 5 near the center electrode 2 is formed into an inclined surface so that the inclined angle α of the inclined end surface 5 with respect to the center line 6 of the center electrode 2 is 30 to 80 degrees. A predetermined discharge interval C is formed in the radial direction between and the outer peripheral surface of the center electrode 2, and the position of the inner corner 7 in the direction along the center line 6 of the center electrode 2 is By setting it near the top end surface 8,
The discharge voltage between the center electrode 2 and each ground electrode 3 can be lowered, and the mixing by spark discharge can be achieved without increasing wear and tear on each ground electrode 3 or reducing the durability of the spark plug. Since the ignitability of gas can be significantly improved, ignition can be reliably and stably ignited even in low load/low rotation ranges such as when the engine is idling, and it is possible to prevent a decrease in output and an increase in harmful gases in the exhaust gas.

Moreover, in the first invention, each of the ground electrodes 3 is
A rod-shaped body with a rectangular cross section, and the inner corner 7 of the tip 4 is formed into a straight line extending in a direction substantially parallel to the top end surface 8 of the center electrode 2 and substantially perpendicular to the center line 6 of the center electrode 2. By configuring the
It is possible to reliably prevent the spacing of the center electrodes 2 at each discharge location from becoming irregular in the circumferential direction and from increasing variations between the discharge points due to machining errors in each ground electrode 3. Therefore, the above-mentioned predetermined ignition performance can be reliably secured for a large number of spark plugs.

In addition to the first invention, the second invention has the effect that the ignition performance of the first invention can be further enhanced by the groove 10 provided in the top end surface 8 of the center electrode 2.

[Brief explanation of the drawing]

1 and 2 are views showing a conventional spark plug, FIG. 3 is a view showing a spark plug according to the first embodiment of the present invention, FIG. 4 is a plan view of FIG. 3, and FIG. FIG. 6 is a plan view of FIG. 5, and FIG. 7 is a plan view of another embodiment. DESCRIPTION OF SYMBOLS 1... Mounting screw part, 2... Center electrode, 3... Ground electrode, 4... Tip of ground electrode, 5... End surface,
6...Center line, 7...Inside corner, 8...Top end surface,
10...Groove, α...Angle between the end surface at the tip of the ground electrode and the center line of the center electrode, β...Angle between the tip of the ground electrode and the center line of the center electrode.

Claims (1)

[Scope of Claims] 1. A spark plug comprising a center electrode 2 having a circular cross section and projecting from the center of the mounting thread 1, and a plurality of ground electrodes 3 integrally projecting from the mounting thread 1. , the tip 4 of each ground electrode 3 is bent inwardly toward the center electrode 2, while the end surface 5 of the tip 4 of each ground electrode 3 is aligned with the center line 6 of the center electrode 2. The inclined surface is formed to be inclined outwardly, and the inclined end surface 5 has an inclination angle α with respect to the center line 6 of the center electrode 2.
is set to 30 to 80 degrees, and a predetermined discharge interval C is formed in the radial direction between the inner corner 7 of the inclined end surface 5 closer to the center electrode 2 and the outer peripheral surface of the center electrode 2. , the position of the center electrode 2 in the direction along the center line 6 at the inner corner 7 is set near the top end surface 8 of the center electrode 2, while each of the ground electrodes 3
is made into a rod-like body with a rectangular cross section, and the inner corner 7 at the tip thereof is formed into a straight line extending in a direction substantially parallel to the top end surface 8 of the center electrode 2 and substantially perpendicular to the center line 6 of the center electrode 2. An ignition plug for an internal combustion engine characterized by the following: 2. In a spark plug in which a plurality of ground electrodes 3 integrally protrude from the mounting screw portion 1 are arranged around a center electrode 2 having a circular cross section and protruding from the center of the mounting screw portion 1, each of the ground electrodes The tips 4 of the ground electrodes 3 are bent so as to be inclined inwardly toward the center electrode 2, while the end surfaces 5 of the tips 4 of each of the ground electrodes 3 are inclined outwardly with respect to the center line 6 of the center electrode 2. The sloped end surface 5 is formed at an inclined angle α with respect to the center line 6 of the center electrode 2.
is set to 30 to 80 degrees, and a predetermined discharge interval C is formed in the radial direction between the inner corner 7 of the inclined end surface 5 closer to the center electrode 2 and the outer peripheral surface of the center electrode 2. , the position of the center electrode 2 in the direction along the center line 6 at the inner corner 7 is set near the top end surface 8 of the center electrode 2, while each of the ground electrodes 3
is a rod-like body with a rectangular cross section, and the inner corner 7 of the tip 4 is formed into a straight line extending in a direction substantially parallel to the top end surface 8 of the center electrode 2 and substantially perpendicular to the center line 6 of the center electrode 2. A spark plug for an internal combustion engine, further comprising a groove 10 extending from an intermediate portion of each ground electrode 3 toward the center of the center electrode 2 on the top end surface 8 of the center electrode 2. .