JPS596472B2 - Spark plug for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a spark plug for an internal combustion engine that has good stain resistance and misfire resistance.

As shown in Fig. 1, a conventionally known spark plug for an internal combustion engine has a ground electrode 5 fixed to the end face of a housing 1 by welding or the like, and a center electrode 4 is provided on the housing 1, as shown in Fig. 1. A structure in which the insulator 2 is fixed by tightening or the like, a spark yag 7 is formed between the side surface of the center electrode 4 and the end face of the ground electrode 5, and the air-fuel mixture is ignited by sending sparks to this spark yap 7. Met.

In general conventional spark plugs having the above structure, under no-load or light-load operating conditions of the engine, the temperature of the leg part 2a of the insulator 2 is low (carbon, oil, etc. adhering to this leg part 2a). The disadvantage is that it may not be possible to burn off the residue and unburned fuel, and the accumulation of residue and unburnt fuel will eventually reduce the insulation resistance of the leg 2a, causing a spark error (misfire). was there.

Therefore, as a solution to these drawbacks, the second
As shown in the figure, a small-diameter portion 2c is provided at the tip of the center electrode 4 so that the tip is retracted from the end surface of the leg portion 2a of the insulator 2, and a first A spark gap 1 is formed, and a second spark gap 8 is formed between the end of the leg 2a of the insulator 2, and a second spark gap 8 is formed between the small diameter outer circumference of the center electrode 4 and the inner hole of the leg 2a of the insulator 2. A spark plug has been proposed in which a space 6 is formed between the center electrode 4 and the inner circumference of the leg 2a. The sparks pass through the small diameter portion 2C of the leg portion 2C and fly to the second spark gap 8, and the carbon particles adhering to the inside of the small diameter portion 2C of the inner hole of the leg portion 2a and the end surface of the leg portion 2a can be removed by the sparks.

However, the first spark gap 7, which normally causes sparks to fly, is formed between the tip end surface of the center electrode 4 and the side surface of the ground electrode 5, which are recessed from the end surface of the leg portion 2a of the insulator 2. In the process of growing the flame kernel formed from flying sparks in the spark gap 7, the leg 2
The disadvantage is that the flame kernel tends to touch the inner periphery of the small diameter portion 2a of the inner hole a, and the growth of the flame kernel is inhibited by the cooling effect, resulting in poor ignition of the air-fuel mixture.

Furthermore, since the tip end surface of the center electrode 4 is recessed from the tip end surface of the leg portion 2a of the insulator 2, it has the disadvantage that it is difficult to adjust the first spark gap 7 using a spark gap adjustment gauge. ing.

The present invention aims to solve the above-mentioned drawbacks, and provides a spark plug for an internal combustion engine that can obtain effects such as good stain resistance, improved ignition performance, and satisfactory misfire resistance. The purpose is to

The present invention will be described below with reference to embodiments shown in the drawings.

In FIGS. 3a and 3b, 1 has a threaded portion 1a at its lower part for mounting an internal combustion engine.

For example, the housing is made of a material such as carbon steel.

Reference numeral 2 represents an insulator made of a highly electrically insulating material such as alumina, and 2a represents a leg portion of the insulator 2 that is exposed inside the combustion chamber of the internal combustion engine.

This insulator 2 is provided with an inner hole 2b penetrating in the axial direction, and a small diameter portion 2C for holding the center electrode 4 is provided on the leg portion 2a side of the inner hole 2b. A large diameter portion 2d, which has a larger diameter than the small diameter portion 2c, is provided on the tip side of 2a, and both portions 2c and 2d are connected together.

The center electrode 4 protrudes from the tip of the leg portion 2a of the insulator 2 toward the combustion chamber.

A housing 1 is attached to the outer periphery of the insulator 2 via a packing 3.
is fixed.

Reference numeral 5 denotes a ground electrode whose tip end surface faces the axial side surface of the center electrode 4, and this ground electrode 5 is fixed to the tip end surface of the housing 1 by electric welding or the like.

Reference numeral 6 denotes a space formed between the axial side surface of the center electrode 4 and the thick diameter portion 2d of the inner hole 2b of the insulator 2, and is open into the combustion chamber.

A first spark gap 7 is formed between the axial side surface of the center electrode 4 and the distal end surface of the ground electrode 5, and a first spark gap 7 is formed between the distal end surface of the leg portion 2a of the insulator 2 and the side surface of the ground electrode 5. is formed by the second spark gap 8.

Note that the dimensions of the second spark gap 80 are set smaller than the dimensions of the first spark gap 7.

Also, the voltage for the spark to fly from the connecting part between the small-diameter part 2C and the large-diameter part 2d of the inner hole 2b of the insulator 2 to the second spark gap 8 through the creeping surface of the large-diameter part 2d constituting the space part 6 is also determined. is set to be higher than the voltage required to cause sparks to fly to the first spark gap 7.

To explain the operation of the spark plug of the present invention having the above structure, when the insulation resistance of the surface of the leg portion 2a of the insulator 2 is reduced/good due to dirt such as carbon, the spark voltage of the spark plug is Center electrode 4 than 7
The force of the voltage that spreads to the second spark gap 8 along the connecting part between the small diameter part 2c and the large diameter part 2d of the leg part 2a and along the large diameter part 2d is high, and the spark usually occurs only in the first spark gap 7. This sparking at the first spark gap 7 ignites the air-fuel mixture.

If the internal combustion engine is operated with no load or light load for a long period of time, the temperature of the leg 2a will normally be low (and carbon etc. will adhere to the leg 2a, reducing the insulation resistance of the surface of the leg 2a). However, in the case of contamination such as carbon which induces a decrease in insulation, the tips of the leg portions 2a are heavily contaminated, and the gasket 3 portion of the leg portions 2a is less contaminated.

Naturally, carbon etc. also adhere to the creeping surface (inner circumferential portion) of the large diameter portion 2d in the space portion 6.

However, if carbon or the like is attached to the center electrode 4, the voltage that spreads to the second spark gap 8 through the connecting part between the small diameter part 2C and the large diameter part 2d and the creeping surface of the large diameter part 2d is higher than that of the center electrode 4. The voltage is lower than the voltage that causes sparks to fly to the first spark gap 7, and sparks start to spark at the second spark gap 8.

The air-fuel mixture is ignited by this flying spark from the second spark gap 8, and at the same time, the high-voltage spark completely burns out carbon, etc. attached to the surface of the thick diameter portion 2d, and also burns out carbon, etc. attached to the tip of the leg portion 2a.) The spark in the first spark gap I formed by the center electrode 4 and the ground electrode 5 is restored to the normal spark state again.

Therefore, there is no deterioration in insulation due to contamination with carbon or the like.

In the spark plug according to this embodiment, sparks always fly in the first spark gap 7, and only when contaminated, sparks pass through the creeping surface of the thick diameter portion 2d and fly to the second spark gap 8. Therefore, the creeping surface of the thick diameter portion 2d is There is almost no wear and tear.

Next, the spark plug according to the present invention shown in FIG.
The performance of the conventionally known spark plug shown in the figure and the conventionally known spark plug shown in FIG. 1 will be compared and described by a fouling test and an ignitability test.

In the spark plug shown in FIG. 1, the tip diameter of the center electrode 4 is 2.7wn, and the spark gap is 1.7wn. Orrrm Toshi,
In the spark plug shown in FIG. 2, the tip diameter of the center electrode 4 is 1. O
yy+m, the first spark gap 7 is set to 1.0, the second spark gap 8 is set to 0.7rrrm, a in Fig. 3,
For the spark plug b, the tip diameter of the center electrode 4 is 2.7 r
rrm, the diameter of the thick diameter part 2d of the insulator leg part 2a is 3.71
Mt, the first spark gap 7 was 1.0 mm, and the second spark gap 8 was 0.7 m.

The results of the stain test and ignitability test are shown in Figure 6.

First, I will explain the dirt test.
A cycle gasoline engine was used, and cycle operation was carried out under conditions in which the spark plugs were likely to be contaminated with carbon.

That is, the yoke valve of the internal combustion engine's carburetor was closed, the engine was idled for 3 minutes, then racing was performed 5 times, the vehicle was driven for 300 m at a speed of 30 km/h, and the internal combustion engine was stopped. This is an operating method in which the operation is repeated for 3 minutes, and then the same operation as in 1 is repeated. ■cycle refers to the time from idling to stopping the operation.

In FIG. 6, the X mark indicates that the operation cannot be continued, and the O mark indicates that the operation can be continued.

As is clear from this Fig. 6, the second spark gap 8
The conventional spark plug shown in Fig. 1, which does not have a
With the spark plugs having the structures shown in , b, sparks still fly even after 50 cycles, and the internal combustion engine can be operated normally.

Next, the ignitability test will be explained. This test was conducted using a four-stroke gasoline engine for automobiles, and the ignitability test was carried out under the conditions of an idling speed of 9 oor-p"m and varying the air-fuel ratio.

As is clear from FIG. 6, the spark plugs with the structures shown in FIG. It turns out that it is superior.

The reason for this is that since the first spark cap 7 is formed between the axial side surface of the center electrode 4 and the tip end surface of the ground electrode 5, the flame kernel formed by the sparks in the first spark gap 7 grows. In the process, it is difficult to touch the leg portion 2a compared to the spark plug shown in FIG. 2 (this can be understood from the fact that the growth of the flame kernel is hardly inhibited).

It is clear that the first spark gap 7 can be adjusted more easily in the spark plugs shown in FIGS. 3a and 3b than in the spark plug shown in FIG. 2.

The present invention is not limited to the above embodiments (but can be modified in various ways as follows).

FIG. 4 shows the ground electrode 5 in the embodiment shown in FIGS. 3a and 3b.
The cross-sectional shape is changed, and a groove 5a with a U-shaped cross section is provided extending from the tip to the connection part with the housing 1.

In this embodiment, the ignition ability when spark jumps to the second spark gap 8 is improved.

In this case, for the ground electrode 5, instead of providing the U-shaped groove 5a as described above, a conventionally known method may be adopted, such as making the ground electrode 5 thinner.

FIG. 5 shows the ground electrode 5 in the embodiment shown in FIGS. 3a and 3b.
The end face shape is changed, and there is a U only at the tip of the ground electrode 5.
By providing the shaped groove 5a, the ignition ability when sparks fly to the first spark gap 7 is improved.

In this case as well, for the ground electrode 5, a conventional method may be adopted, such as making the ground electrode 5 thinner, as described above (instead of providing the U-shaped groove 5a).

Also, instead of changing the shape of the ground electrode 5 as described above, the diameter of the portion of the center electrode 4 facing the end surface of the ground electrode may be reduced (
Alternatively, a conventionally known method may be adopted for the center electrode 4, such as providing a groove in that portion.

Further, the diameter q2d of the insulator 2 may be made thicker on the end face side of the leg portion 2a (smaller on the side of the connecting portion of the thicker portion 2c, L, and formed into a tapered shape. Among them, the outer diameter of a portion corresponding to the thick diameter portion 2d of the insulator 2 may be made smaller than other portions.

In addition, in the above embodiments shown in FIGS. 3 to 5, the leg portion 2a
Although the tip of the leg 2a protrudes from the end surface of the housing 1, the structure is not limited to this, and the tip of the leg 2a may be inserted into the inner peripheral portion of the housing 1.

In addition, in the embodiments shown in FIGS. 3 to 5, the ground electrode 5 is fixed to the housing 1, but what corresponds to the ground electrode 5 is integrally molded to the end of the housing 1. It's good as well.

As described in detail above, in the present invention, the center electrode 4 is held on the side of the leg 2a of the insulator 2 that is exposed inside the combustion chamber of the internal combustion engine, of the inner hole 2b that passes through the insulator 2 in the axial direction. The leg portion 2 of the insulator 2 is provided with a small diameter portion 2c.
The tip of a has a large diameter portion 2d that is larger in diameter than the small diameter portion 2c.
A space 6 opened into the combustion i by the large diameter portion 2d is formed around the outer periphery of the center electrode 4, and a ground electrode 5 is provided on the housing 1 fixed to the outer periphery of the insulator 2. A first spark gap γ is formed between the tip end surface of the ground electrode 5 and the axial side surface of a portion of the center electrode 4 that protrudes from the tip end surface of the leg portion 2a of the insulator 2. A second spark gap 8, which is dimensionally smaller than the first spark gap 7, is formed between the tip end surface and the side surface of the ground electrode 5, and the second spark gap 8 is formed through the creepage of the thick diameter portion 2d of the inner hole 2b of the insulator 2. Since the voltage for sparking at the first spark gap 8 is set to be higher than the voltage for sparking at the first spark gap γ, if the leg 2a is not contaminated with carbon or the like, the first spark gap 7 will not fly. When the leg portion 2a is contaminated with carbon or the like, the spark passes from the center electrode 4 through the connecting portion between the large diameter portion 2d and the small diameter portion 2c, and the creeping surface of the large diameter portion 2d.
Sparks fly into spark gap 8, ignite the air-fuel mixture, and at the same time the high-pressure spark removes carbon and other dirt.
There is an excellent result in that the first spark gap 7 can be restored to its normal flying state again.

Therefore, spark errors due to contamination with carbon or the like can be prevented.

Also, the thick diameter portion 2. of the leg portion 2a. Sparks fly to the creeping surface of d only when the spark plug is contaminated, so wear on the creeping surface of the large diameter portion 2d can be suppressed to the utmost, and a spark plug with high performance and long life can be provided.

In addition, due to the above effects, the spark plug of the present invention can always fly normally and ignite the mixture, so the engine can be operated normally without misfire, and as a result, the engine can be operated normally without using a rich mixture. This has the excellent effect of reducing the amount of harmful components in exhaust gas released into the atmosphere and not increasing fuel consumption.

Furthermore, in terms of manufacturing, the small diameter portion 2c of the leg portion 2a of the insulator 2
Since the diameter of the spark plug is simply increased, there is no problem in mass production.Therefore, compared to conventional spark plugs, spark plugs with high performance and long life can be mass produced at low cost.

Furthermore, since the first spark gap 7 is formed between the axial side surface of the center electrode protruding from the distal end surface of the leg portion 2a and the distal end surface of the ground electrode 5, the first spark gap 7 is formed by flying sparks at the first spark gap 7. It is difficult for the flame kernel to touch the leg 2a (because the flame kernel does not receive much cooling effect, the growth of the flame kernel is not inhibited, and it is easy to grow into a large flame kernel, which has the excellent effect of improving the ignition of the air-fuel mixture. be.

Another advantage is that the first spark gap 7 can be easily adjusted.

[Brief explanation of drawings]

Figures 1 and 2 are partial cross-sectional views showing the spark discharge part, which is the main part of a conventional spark plug for internal combustion engines, and Figure 3a.
3 is a partial sectional view showing a spark discharge portion which is a main part of an embodiment of a spark plug for an internal combustion engine according to the present invention, FIG. 3 is a bottom view of FIG. 3a, and FIG. FIG. 4 is a partial sectional view showing a spark discharge part which is a main part of an embodiment of the present invention, FIG. 4 is a sectional view taken along the line A-A in FIG. Partial sectional view showing a certain spark discharge part, No. 5
The figure is a view taken from arrow B in FIG. 5a, and FIG. 6 is a view of the present invention.
It is a graph showing the results of a stain test and an ignitability test. 1...Housing, 2...Insulator, 2
a...leg, 2b...inner hole, 2c...
...Small diameter part, 2d...Large diameter part, 4...
...Center electrode, 5...Ground electrode, 6...
・Space part, 7...First spark gap, 8・
...Second spark gear.

Claims (1)

[Claims] 1 An internal combustion engine in which a center electrode is held in an axially penetrating inner hole of the insulator so that the center electrode protrudes toward the combustion chamber from the tips of the legs of the insulator that are exposed inside the combustion chamber of the internal combustion engine. In the engine spark plug, a small diameter hole for holding the center electrode is provided in the inner hole of the insulator on the leg side, and a tip part of the leg has a diameter larger than the small diameter part. a large-diameter portion is provided, a space opened into the combustion chamber by the large-diameter portion is formed around the outer periphery of the center electrode, and a ground electrode is provided on the housing fixed to the outer periphery of the insulator; A first spark gap is formed between the tip end surface of the ground electrode and an axial side surface of a portion of the center electrode that protrudes from the tip end surface of the leg of the insulator, and a first spark gap is formed between the tip end surface of the leg of the insulator and the A second spark cap, which is dimensionally smaller than the first spark cap, is formed between the ground electrode and the side surface of the ground electrode, and a spark jumps to the second spark cap through the creeping surface of the large diameter portion of the inner hole of the insulator. A spark plug for an internal combustion engine, characterized in that the voltage force for causing the spark to fly to the first spark cap is set to be higher than the voltage for causing the spark to fly to the first spark cap.