JPS63216282A - Spark plug for internal combustion engine - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a spark plug for an internal combustion engine used in an internal combustion engine of an automobile or the like.

, [Prior Art] As a conventionally known spark plug of this type, there is a
Some of these are disclosed in Japanese Utility Model Publication No. 3-10219 or Japanese Utility Model Publication No. 56-25194.

These spark plugs include a hollow housing, an insulator housed and fixed in the hollow part of the housing, and a part of the insulator that extends outward from the hollow part through an opening in the hollow part of the housing. a center electrode held in the open leg with its tip exposed from the end of the leg; one end provided in the housing; the other end facing the tip of the center electrode; and a ground electrode forming a spark gap between the opening and the ground electrode, an annular radial protrusion is formed on the inner periphery of the hollow part of the opening of the housing, and the protrusion allows the inner periphery of the opening of the housing to The radial gap between the outer circumferential surface of the leg portion and the outer circumferential surface of the leg portion facing the leg portion is reduced.

In such a spark plug, under normal conditions, a spark discharge occurs in a spark gap formed between a center electrode and a ground electrode, and the air-fuel mixture is ignited.

On the other hand, if carbon adheres to the outer circumferential surface of the legs of the insulator of the plug due to the operating conditions of the internal combustion engine and the leg surface insulation resistance value decreases, carbon will pass from the center electrode through the carbon layer on the outer circumferential surface of the legs. , a spark discharge occurs through the radial gap to the protrusion.

Due to this spark discharge, the air-fuel mixture comes into contact with the spark within the radial gap and is ignited, and the carbon layer on the outer peripheral surface of the leg is burned away by the spark, returning to the above-mentioned normal spark discharge state.

[Problem that the invention seeks to solve]

In the spark plug described above, if the carbon layer attached to the leg of the plug insulator is thin, the spark discharge runs from the center electrode on the surface of the carbon layer, passes through the radial gap, and reaches the protrusion; Therefore, within the radial gap, the air-fuel mixture comes into contact with a spark and ignites. However, there is a problem that the ignitability of the air-fuel mixture is extremely low under operating conditions of an internal combustion engine that generates significant carbon, such as long periods of no-load operation, low-load operation, where the air-fuel ratio is high, or when the combustion chamber temperature is low. .

That is, when a large amount of carbon adheres to the legs of the insulator and the carbon layer becomes thick, the spark discharge does not run along the surface of the carbon layer, but passes through the inside of the carbon layer and reaches the protrusion through the radial gap. This will lead to. Therefore, the distance that sparks travel within the radial gap is shortened by the thickness of the carbon layer, which makes the air-fuel mixture less susceptible to sparks, resulting in a significant drop in ignitability.

In addition, as mentioned above, in situations where carbon generation is significant,
Since the spark discharge is generated while running inside the carbon layer, the carbon layer cannot be burned away, and therefore carbon is deposited on the legs of the insulator, and the legs are opposed to the inner peripheral surface of the opening of the housing. Carbon will adhere to areas further back than the areas where the carbon is to be removed. As a result, under such adhesion conditions, spark discharge runs inside the carbon layer and is generated on the inner circumferential surface in the direction deeper than the opening of the housing. During such spark discharge, contact between the air-fuel mixture and the spark becomes more difficult, and the ignitability of the air-fuel mixture deteriorates dramatically.

[Means for solving problems]

In the present invention, carbon is attached to the outer peripheral surface of the legs of the insulator,
In addition to the spark discharge between the electrodes in normal conditions, even if a spark discharge passes through the carbon layer and occurs on the inner circumferential surface of the opening of the housing, the ignitability of the air-fuel mixture will not be significantly reduced, and the carbon will remain on the outer circumference of the leg. Spark discharge is unlikely to occur on the inner circumferential surface of the housing even if it adheres to a portion of the surface facing the inner circumferential surface of the housing at a portion deeper than the inner circumferential surface of the opening of the housing,
It is an object of the present invention to provide a spark plug for an internal combustion engine in which a decrease in ignitability of an air-fuel mixture is improved by generating a spark discharge on the inner peripheral surface of an opening of a housing.

According to the present invention, as a result of intensive research by the present inventor in order to achieve such an object, the present invention includes a hollow housing, a housing accommodated in the hollow part of the housing,
A fixed insulator, and a leg part of the insulator that is opened to the outside of the hollow part through the opening of the hollow part of the housing, so that the tip thereof is exposed from the end of the leg part. and a second electrode having one end disposed in the housing and the other end facing the tip of the center electrode to form a spark gap therebetween. An annular radial space is formed between the outer circumferential surface of the leg and the inner circumferential surface of the housing opposite to the outer circumferential surface of the leg; A first annular radial space formed between an inner circumferential surface at the opening and an outer circumferential surface of the leg opposite thereto, and excluding the inner circumferential surface at the opening of the housing. a second annular radial cavity formed between an inner circumferential surface and an outer circumferential surface of the leg portion opposite thereto;
and the first cavity has a radial gap between the inner circumferential surface of the opening of the housing and the outer circumferential surface of the leg opposite thereto in a predetermined axial range thereof. The radial gap is shorter than the radial gap between the inner circumferential surface of the housing excluding the opening and the outer circumferential surface of the leg opposite thereto in the second cavity; The length of the range in the predetermined axial direction is H
(in) When the minimum value of the radial gap of the first cavity is S (++un) and the radial gap of the second recess is A (mm), 0.7 (mm) The following relationship is adopted: ≦H≦4.0 (mm) S≧1.3 (mm) A≧S+0.15 (shir).

[Effect]

In the present invention, when carbon adheres to the outer peripheral surface of the legs of the insulator due to the operating conditions of the internal combustion engine where carbon is likely to be generated, and a spark discharge is generated on the inner peripheral surface of the housing, the above-mentioned S.

By satisfying H, spark discharge occurs within the radial gap of the first cavity, and the ignitability of the air-fuel mixture at the time of carbon adhesion can be ensured. In addition, since the above-mentioned S is satisfied, even if a large amount of carbon adheres to the legs and the carbon layer becomes thick, the thickness of the carbon layer is covered by the size of S, and therefore the inside of the carbon layer is A spark from a spark discharge passing through the radial gap of the first cavity can ignite the air-fuel mixture.

On the other hand, carbon adhesion to the legs of the insulator progresses,
Even if carbon adheres to the inner circumferential surface of the housing excluding the opening, that is, to the outer circumferential surface of the leg opposite to the inner circumferential surface further from the opening, the outer circumferential surface of the leg opposite the inner circumferential surface from the opening of the housing. A second contact with the inner circumferential surface of the housing opposite to this
The radial gap of the first cavity is wider than the radial gap of the first cavity between the inner circumferential surface of the opening of the housing and the opposing leg, and the above-mentioned S.

Since the relationship A is also satisfied, spark discharge is suppressed from occurring within the radial gap of the second cavity toward the inner circumferential surface in the rearward direction from the opening of the housing, and the carbon adhesion situation is suppressed. However, the chances of spark discharge occurring within the radial gap of the first cavity can be increased.

〔Effect of the invention〕

As described in detail above, according to the present invention, even if carbon adheres to the outer circumferential surface of the leg of the plug insulator and there is a chance of spark discharge occurring on the inner circumferential surface of the hollow part of the housing, the The spark discharge can be concentrated on the inner circumferential surface of the opening of the housing, and therefore the spark discharge can be ensured at a position where the air-fuel mixture can be easily touched, and the ignitability of the air-fuel mixture will not be significantly reduced.

〔Example〕

The present invention will be explained in detail below using specific examples. 1st
The figure is a partially broken sectional view showing the tip side, which is the main part of the spark plug of the present invention, and the part on the opposite side to the tip side is omitted because it has a well-known configuration. Now, in the figure, a spark plug 1 is housed in a hollow metal housing 10 in which a threaded part 11 for mounting a cylinder head of an internal combustion engine (not shown) is formed, and is housed and fixed in the hollow part of the housing 10. and an insulator 20. The insulator 20 has a shoulder portion 21 placed on an annular shoulder portion 14 that protrudes radially inward inside the hollow portion of the housing IO, with an annular metal packing 30 interposed therebetween.

Opening 1 in the hollow part of the housing lo of the insulator 20
A center electrode 40 is held in the leg portion 22 which is open to the outside of the hollow portion via the leg portion 2 . The tip of the center electrode 40 is exposed by the end 22a of the leg 20. The center electrode 40 is electrically connected to a terminal shaft (not shown) that is inserted through and fixed to the center of the head (not shown) of the insulator 20 at a position opposite to the legs. A ground electrode 5 is provided on the end surface 10a of the housing 10 on the opening 12 side.
One end of the ground electrode 50 is electrically connected and fixed by welding, and the other end of the ground electrode 50 faces the tip of the center electrode 40,
A spark gap G is formed between the tip and the tip. Note that the spark gap G may be formed by making the other end surface of the ground electrode 50 face the axial side surface (circumferential surface) of the center electrode 40.

As shown, an annular radial space 60 is formed between the outer circumferential surface of the leg portion 22 of the insulator 20 and the inner circumferential surface of the hollow portion of the housing 10 facing the outer circumferential surface.

This radial cavity 60 is a first annular radial cavity 61
and a second annular radial cavity 62.

The first cavity 61 includes the inner circumferential surface 10b of the opening 12 of the housing 10 and the leg portion 22 of the insulator 20 opposite thereto.
is formed between the outer circumferential surface of the

On the other hand, in the second cavity 62, an annular radial recess 13 is formed in the inner circumferential surface 10c of the housing 10 excluding the opening 12 by boring to the vicinity of the shoulder 21. Bottom surface 13a of location 13 and leg portion 22 opposite thereto
is formed between the outer circumferential surface of the

Said radial recess 13 of the housing 10
1 except for the opening 12, and therefore, the opening 12 has a length H within a predetermined axial direction along the axial direction of the housing 10, as shown in FIG. Also,
The radial gap S1 within the range in the H direction in the first cavity where the opening 12 is located is shorter than the radial gap A in the second cavity.

In the present invention, the minimum value S of the radial gap S1,
The radial gap A and the above-mentioned H are designed to satisfy a predetermined relationship, which will be explained below.

When carbon is attached to the outer periphery of the insulator and a spark discharge passes through the carbon layer, the ignition performance of the mixture is influenced by the minimum value S of the radial gap S and the radial gap A. This was confirmed through experiments by the present inventor. In order to find the relationship between A and S, the following experiment was conducted.

First, the spark discharge is transmitted through the carbon layer to the housing 1.
In order to clarify the S dimension when it occurs on the inner circumferential surface 10b of the opening 12 of 0.0, the plug shown in FIG. The difference between the maximum and minimum rotation speeds was investigated.

The plug shown in Figure 2 is manufactured by Nippondenso Co., Ltd., model number W2.
The basic form of this plug is a 0EX-U plug, and an annular radial recess 13 is formed on the inner circumferential surface of this plug by boring, and the opening 12 is formed in a triangular cross-section with a pointed tip. It is something. The above recess 13 by boring
The axial length of the recess 13 is approximately 9 mm, which is the minimum value of the radial gap between the bottom surface 13a of the recess 13 and the outer circumferential surface of the leg 22 facing thereto (since the leg 22 is a tapered surface, the recess The innermost part) is about 1.9 mm, and the maximum value (the part near the opening) is about 2.4 mm.

Further, the legs 22 of the insulator 20 are coated with a conductive coating 70 made by baking silver paste so that spark discharge occurs at the opening 12 of the housing 10.

That is, when an internal combustion engine was operated with this plug, in addition to spark discharge between the center electrode 40 and the ground electrode 50, discharge was also observed at the opening 12 of the housing 10.

The test was carried out at an ambient temperature of -10°C, which is the most severe condition imaginable in normal use, and 4 cycles of 160°C.
A 0 cc internal combustion engine was cold started and operated at an idling speed of about 70 rpm for 3 minutes, and the rotational fluctuation range at that time was measured for plug spark gaps C (mm) of 0.8 and 1.1.

The results are shown in FIG. Incidentally, in all levels of this test, variations in the spark discharge position (both toward G and toward the opening 12) were observed.

Considering this result, regardless of the spark gap G, S≧
It can be seen that even if the spark discharge position fluctuates at 1.3 mm, the rotation fluctuation range is small (35 rpm or less) and stable rotation can be obtained.

Next, in order to clarify the range within the housing that the spark discharge position at the opening of the housing is allowed to be, the rotational fluctuation range of the internal combustion engine was investigated using the plug shown in FIG.

The plug shown in FIG. 4 has the axial length of the opening 12 of the housing 10 <L (Hmm), and the innermost end of the opening 12 of the housing 10 is connected to the conductive coating (made of the same material as above) of the outer peripheral part 22 of the insulator 20. It is on the same line as the innermost end. The basic form of the plug is the same as shown in FIG. From the results shown in FIG. 3, the minimum value of the radial gap at the opening 12 of this plug is S
= 1.3 inches. The test was conducted in the same manner as described above.

The results are shown in FIG. Also in this test,
Variations in the spark discharge position were observed at all levels. Also,
Considering this result, we can see that H≦4, regardless of the spark gap.
It can be seen that stable rotation can be obtained with a small rotational fluctuation range in mm.

Judging from the results shown in FIGS. 3 and 5 above, carbon adheres to the insulator of the plug, the surface insulation resistance of the leg of the insulator decreases, and spark discharge occurs between the center electrode 40 and the ground electrode 50. Even if the discharge occurs between the outer peripheral surface of the leg portion 22 of the insulator 20 and the inner peripheral surface of the housing 10, the position of the discharge is 4 mm from the end surface of the housing.
It can be seen that if the minimum gap S is maintained at 1.3 rtrm or more, the ignitability of the air-fuel mixture will hardly decrease.

Next, in order to prevent sparks from being discharged to the bottom surface 13a of the annular radial recess 13 formed by boring the housing, the present inventor designed the recess bottom surface 13a and the legs of the insulator 20 opposite thereto. The relationship between the radial gap A between the outer circumferential surface of No. 22 and the above S was found. In order to determine the relationship between A and S, the following test was conducted using the plug shown in FIG. The plug is the same as in Figure 2 <W20EX
-U was used as the basic configuration, and the rotational fluctuation range was measured by changing the gap A between the recesses 13.

Note that this gap A is the portion indicated by A in FIG.

The test was carried out at an ambient temperature of minus 10°C, which is the most severe condition imaginable in normal use, and at 160°C for 4 cycles.
Cold start a 0cc internal combustion engine and run it idling at about 150 Orpm for about 10 seconds → racing at about 50 Orpm 10 times (increase the engine speed under no-load conditions)
→ Drive 10 cycles with 30 seconds of low-speed driving at a maximum speed of 401an/H and varying the speed as needed,
The insulation resistance value of the surface of the leg of the plug is lowered, and then the same internal combustion engine is cold-started at -10°C, operated at idling for 3 minutes, and the rotational fluctuation range is measured.

The plugs used in the test were S = 1.3 and 1. ' 5 m
m spark gap = 0.8 and 1.1 mm, and various A
The value of

The results are shown in FIG. Considering this result, the rotational fluctuation width is not affected by the spark gap and S = 1
．． 3, A≧1.45nvn, preferably A≧1.
When 5+nm5S=1.5m, A≧1.65mm.

Preferably A≧1.7mm, that is, A≧S+0.15m
m.

Preferably, when A≧S + 0.2 mm, the rotation fluctuation width is small and stable rotation can be obtained. Also, A≧S+
0.2, between the center electrode 40 and the ground electrode 50 and between the outer peripheral surface of the leg 22 and the opening 1 of the housing 10.
Although spark discharge was observed between the housing 10 and the inner peripheral surface 10b of the housing 10, there was no spark discharge to the bottom surface of the recess 13' of the housing 10.

Judging from the results shown in Figures 3, 5, and 6 above, carbon adheres to the outer circumferential surface of the legs of the plug insulator, and the insulation resistance value on the leg surface decreases, causing the spark discharge position to fluctuate. Even if H≦4mm, S≧1.3trrm.

It can be seen that if A≧S+0.15 mm is ensured, the ignitability of the air-fuel mixture will hardly decrease.

However, if the above dimensions are applied to an actual plug, for example, if the housing shape is as shown in Fig. 2, that is, H = 0, the inner peripheral surface of the housing 10 will gradually wear out as spark discharge occurs, and the value of S will become large. turn into. As a result, A≧S+
The relationship of 0.15 mm no longer holds true.

Therefore, in order to determine the minimum values of the eight dimensions, the following experiment was conducted in consideration of the wear caused by flying sparks. The exam is
In an actual vehicle, the vehicle was driven for 100,000 miles, which is the life distance of a platinum plug (P16R manufactured by Nippondenso Co., Ltd.), which is a long-life plug. The plug used in the test had a conductive coating applied to the outer circumferential surface of the leg so that the spark discharge position could be varied as shown in FIG. 4, and the tests were conducted for eight different sizes.

The results are shown in FIG. Considering this result, as H increases, the amount of increase in gap S decreases rapidly, and when H = 0.7 mm, the amount of increase in S becomes 0.05.
ttm, and if you set A≧0.2 trm initially, A≧S+0.15mm even at the end of the service life.
The results shown in FIG. 6 also indicate that the ignitability of the air-fuel mixture is good.

Although the above-mentioned dimension S is S≧1.3, the upper limit is 2.7 TNR from the viewpoint of plug manufacturing.

In the present invention, the axial length l (see FIG. 1) of the recess 13 that satisfies the above-mentioned A≧S+0.15 mm is determined from the above-mentioned effect due to the existence of dimension A and from the manufacturing viewpoint.
It is desirable that it be at least 3.0M. Further, in the recess 13, the tapered surface T (see FIG. 1) is
It is desirable for the angle to be 75° or less with respect to a line perpendicular to the axis of the plug from the viewpoint of manufacturing and the effect of the recess. Furthermore, the spark gap G is practically Q, 7 tmn~1.1 mm
is desirable.

Furthermore, in the present invention, the end portion 22a of the leg portion 22 extends beyond the opening 12 of the housing 10 and protrudes outward from the end surface 10a. If the end portion 22a of the leg portion 22 protrudes from the inner part, the above-described effects of the present invention can be achieved.

FIG. 8 shows another embodiment of the present invention. In this embodiment, an annular radial recess 23 is formed in the outer circumferential surface of the leg portion 22 of the insulator 20 at a position other than the portion facing the inner circumferential surface 10b of the opening 12 of the housing 10. be.

Therefore, the first cavity in the present invention includes the outer circumferential surface of the distal end side portion of the leg portion 22 where the recess 23 is not formed, and the inner circumferential surface 10b of the opening 12 of the housing 10 facing the outer circumferential surface. is formed between. On the other hand, the second cavity in the present invention is formed between the bottom surface 23a of the recess 23 and the inner peripheral surface 10c of the housing 10 facing thereto.

In the embodiment shown in FIG. 8, the bottom surface 23 of the recess 23
a is parallel to the inner peripheral surface 10c of the housing 10,
Further, the inner circumferential surface 10b at the opening of the housing 10 and the outer circumferential surface of the tip portion of the leg portion 22 where the recess 23 is not formed are parallel to each other. Therefore, the minimum value of the radial gap in the first cavity 61 and the minimum value of the radial gap in the second cavity 62 exhibit the same values wherever these gaps are formed.

In the present invention, the bottom surfaces 13a and 23a of the annular radial recess 13 provided in the housing 10 and the annular radial recess 23 provided in the leg portion 22 are relative to the outer circumferential surface of the leg portion 22 and the housing 10. The bottom surfaces 13a, 23a may be parallel to the inner circumferential surface of the housing 10 or may not be parallel to the inner circumferential surface of the housing 10. An annular radial recess may also be formed. Note that when a protrusion is formed on the outer peripheral surface of the leg portion 22, the gap A indicates the distance from the surface of the protrusion.

Note that the above-mentioned effects of the present invention can be further improved by combining the plug according to the present invention with a CDI ignition device or a high-energy ignition device.

[Brief explanation of the drawing]

Fig. 1 is a partially cutaway cross-sectional view showing the main parts of a spark plug that is an embodiment of the present invention, and Fig. 2 is a partially cutaway view showing a test plug used in a test to evaluate changes in performance due to changes in S. Figure 3 is a graph of test results showing changes in performance due to changes in S. Figure 4 is a partially broken cross-section showing a test plug used in a test to evaluate changes in performance due to changes in H. , 5th
The figure is a graph of test results showing changes in performance due to changes in H.
FIG. 6 is a graph of test results showing changes in performance as A changes, FIG. 7 is a graph of test results showing changes in S as H changes, and FIG. 8 shows another embodiment of the present invention. It is a partially broken sectional view. 1... Spark plug, 10... Housing, 10
b, 10c...Inner peripheral surface, 12...Housing opening. 13... Recess, 13a... Bottom of the recess, 20... Insulator. 22... Leg portion, 40... Center electrode, 50... Ground electrode. 60... Vacancy, 61... First void, 62... Second void, G... Spark gap, H... Axial range of opening, S. ...Radial gap, S...Minimum value, A...Radial gap.

Claims (5)

[Claims] (1) A hollow housing, an insulator housed and fixed in the hollow part of the housing, and a part of the insulator that is opened to the outside of the hollow part through an opening in the hollow part of the housing. a first electrode held in a leg portion with a tip thereof exposed from an end portion of the leg portion; one end provided in the housing and the other end facing the tip of the center electrode; a second electrode forming a spark gap therebetween, and an annular radial cavity between an outer peripheral surface of the leg and an inner peripheral surface of the housing opposite to the outer peripheral surface of the leg. a first annular radial cavity formed between an inner circumferential surface of the opening of the housing and an opposing outer circumferential surface of the leg; , a second annular radial space formed between an inner circumferential surface of the housing other than the inner circumferential surface of the opening and an outer circumferential surface of the leg opposing thereto; and the first cavity has a radial gap between the inner circumferential surface of the opening of the housing and the outer circumferential surface of the leg opposite thereto in a predetermined axial range thereof. The radial gap in the second cavity is shorter than the radial gap between the inner peripheral surface of the housing excluding the opening and the outer peripheral surface of the leg opposing thereto, and The length of the predetermined axial range of the cavity is H (mm), the minimum value of the radial gap of the first cavity is S (mm), and the radius of the second recess. When the direction gap is A (mm), it is characterized by satisfying the following relationships: 0.7 (mm)≦H≦4.0 (mm) S≧1.3 (mm) A≧S+0.15 (mm) Spark plugs for internal combustion engines. (2) The spark plug for an internal combustion engine according to claim 1, wherein the A (mm) satisfies A≧S+0.2 (mm). (3) The second cavity is formed by forming an annular radial recess in the inner peripheral surface of the housing excluding the opening, so that the bottom surface of the recess and the leg facing the bottom surface are formed. The first space is formed between the outer circumferential surface of the
Claims characterized in that the housing is formed between the inner circumferential surface of the opening in which the recess is not formed and the outer circumferential surface of the leg portion facing the inner circumferential surface. The spark plug for an internal combustion engine according to item 1. (4) The second cavity is formed by forming an annular radial recess in the outer circumferential surface of the leg at a position other than a portion facing the inner circumferential surface of the opening of the housing, The first cavity is formed between a bottom surface of the recess and an inner peripheral surface of the housing opposite to the bottom surface,
The recess is formed between an outer circumferential surface of the portion of the leg portion in which the recess is not formed and an inner circumferential surface of the opening of the housing that faces the outer circumferential surface. A spark plug for an internal combustion engine as described in scope 1. (5) The internal combustion engine according to any one of claims 1 to 4, wherein the end of the leg protrudes outward beyond the opening of the housing. spark plug.