JPS5840831B2 - 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 causes sparks to fly in a spark gap between a center electrode and a ground electrode.

As shown in FIG. 1, a conventionally known spark plug for an internal combustion engine has a grounding electrode 5 on the end face of a housing 1 for mounting on an internal combustion engine.
is fixed by welding or the like, and an insulator 2 having a center electrode 4 is fixed to the housing 1 by tightening or the like, and a spark gap 7 is formed between the side surface of the center electrode 4 and the tip end surface of the ground electrode 5. The structure was such that the air-fuel mixture was ignited by blowing a spark into the spark gap 7.

In the conventional spark plug having the above structure, under no-load or light-load operating conditions of the engine, the temperature of the leg portion 2a of the insulator 2 is low, and residues such as carbon and oil adhering to the leg portion 2a are removed. The combustion fuel may not be burnt out, and the accumulation of residue and unburned fuel will eventually lower the insulation resistance of the leg portion 2a, resulting in a spark failure.

Therefore, as a solution to these drawbacks, the second
As shown in the figure, a small-diameter portion 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 spark is generated between the tip of the center electrode 4 and the side surface of the ground electrode 5. A cap is formed, and a second spark gap 8 is formed between the end face of the leg portion 2a of the insulator 2, and a second spark gap 8 is formed between the small diameter outer peripheral portion of the center electrode 4 and the inner peripheral portion of the inner hole of the leg portion 2a of the insulator 2. A spark plug with a space 6 formed therebetween has been proposed.

In this conventionally known spark plug, if carbon or the like adheres to the leg portion 2a, the insulator 2 is removed from the center electrode 4.
The sparks of the second spark gap 8 pass along the inner hole 2b of the leg portion 2a of the insulator 2, and the sparks fly through the inner hole 2b of the leg portion 2a of the insulator 2.
Carbon etc. adhering to the inside of a and the end face of the leg portion 2a can be removed.

However, the first spark gap 7', which normally causes sparks to fly, is formed between the tip end surface of the center electrode 2 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 growth of the flame kernel formed by flying sparks in the spark gap 7', the flame kernel tends to come into contact with the inner periphery of the inner hole of the leg portion 2a of the insulator 2, and the growth of the flame kernel is inhibited and mixed due to the cooling effect. It has the disadvantage of poor ignitability.

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 is difficult to adjust the first spark cap 7/ using a gauge for adjusting the spark gap. have.

The purpose of the present invention is to provide a spark plug that combines the advantages of the conventional former and latter spark plugs, in which the center electrode has an outer diameter of the tip smaller than the diameter of the inner hole of the leg of the insulator. A part of the small diameter portion on the tip side of the center electrode is made to protrude from the tip end surface of the leg of the insulator, and a portion of the small diameter portion of the center electrode located in the inner hole of the leg of the insulator is A space is formed between the side surface and the inner peripheral part of the leg inner hole of the insulator, and the side surface of the part of the small diameter part of the center electrode that protrudes from the tip end surface of the insulator leg and the tip of the ground electrode. A first spark gap is formed between the end face of the insulator, and a second spark cap is formed between the end face of the insulator leg and the side face of the ground electrode.

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

In Fig. 3, 1 is a threaded part 1 for attaching an internal combustion engine to the lower part.
2 is an insulator, and the center electrode 4 is held in a leg portion 2a of the insulator 2 that is exposed inside the combustion chamber of the internal combustion engine. are doing.

Reference numeral 2b denotes an inner hole of the leg portion 2a, and the outer diameter of the tip side of the center electrode 4 is smaller than the inner diameter of the inner hole 2b of the leg portion 2a. It protrudes from the tip end face of the portion 2a.

The insulator 2 is fixed to the housing 1 via a packing shown at 3 around its outer periphery.

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

6 is a space formed by the side surface of the small diameter portion of the center electrode 4 located inside the inner hole 2b of the leg 2a and the inner circumference of the inner hole 2b of the leg 2a, and 7' is the center electrode. A first spark gap formed between the side surface of a portion of the small diameter portion 4 that protrudes from the distal end surface of the leg 2a and the distal end surface of the ground electrode 5; This is the second spark gap formed between the

Note that the dimensions of the second spark gap 8 are set smaller than those of the first spark gap 7'.

To explain the operation of the Q spark plug of the present invention having the above configuration, when the insulation resistance of the surface of the leg portion 2a of the insulator 2 is not reduced by dirt such as carbon, the spark voltage of the spark plug is The voltage that causes a spark to fly from the center electrode 4 to the second spark gap 8 through the surface of the inner hole of the leg portion 2a is higher than that at the first spark cap 7', and normally sparking occurs only in the first spark cap 7'.

This flying spark in the first spark gap 7' ignites the air-fuel mixture.

Here, when the internal combustion engine is operated with no load or light load for a long time, the temperature of the leg 2a usually becomes low and carbon etc. adhere to the leg 2a, reducing the insulation resistance of the surface of the leg 2a. However, in the case of dirt such as carbon which induces a decrease in insulation, the tips of the leg portions 2a are heavily soiled, while the gasket 3 portion of the leg portions 2a is less soiled.

Naturally, carbon and the like also adhere to the inner circumference of the inner hole 2b in the space 6.

However, when carbon etc. adheres in this way, the voltage that causes sparks to fly from the center electrode 4 to the second spark gap 8 through the surface of the inner hole 2b is lower than the voltage that causes sparks to fly to the first spark gap 7', and 2. Sparks start flying at spark cap 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 the carbon attached to the inner hole 2b, and also burns out the carbon attached to the tip of the leg 2a), and returns to the center. Electrode 4 and ground electrode 5
The sparks formed in the first spark gap 7' are restored to the normal spark state.

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 the spark plug is contaminated, it passes along the surface of the inner hole 2b and discharges into the second spark gap 8, so the wall surface of the inner hole 2b is worn out. There is little to do.

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 2.7 mm and the spark gap is 1.0 mm, and in the spark plugs shown in FIGS. 2 and 3, the tip diameter of the center electrode 4 is 1.7 mm. Omz 1st spark cap 7' at 1.0 am,
The second spark gap 8 was set to 1.7 degrees.

The results of the stain test and ignitability test are shown in Figure 4.

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 choke 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 vehicle speed of 30kj11/h, and the internal combustion engine was stopped for 3 minutes. , a driving method in which similar operations are repeated, and one cycle is the time from idling to stopping.

In FIG. 4, an x mark indicates that the operation cannot be continued, and an ○ mark indicates that the operation can be continued.

As is clear from this Fig. 4, the second spark gap 8
The conventional spark plug shown in Fig. 1, which does not have the same structure, is no longer able to cause sparks after 10 cycles, but the spark plugs with the structure shown in Figs. can.

Next, the ignitability test will be explained. This test was conducted using a four-stroke gasoline engine for automobiles, and the ignition test conditions were idling speed of 90 rpm and changing the air-fuel ratio.

As is clear from Fig. 4, the spark plug with the structure shown in Fig. 3 has the same ignition ability as the conventional spark plug shown in Fig. 1, and is superior to the spark plug with the structure shown in Fig. 2. I understand.

The reason for this is that the first spark gap 7' is formed between the side surface of the small-diameter portion of the center electrode 4 that protrudes from the distal end surface of the leg portion 2a and the distal end surface of the ground electrode 5. Compared to the spark plug shown in FIG. 2, the flame kernel formed by flying sparks in the first spark gap 7' is less likely to touch the leg 2a during the growth process, and the growth of the flame kernel is hardly inhibited. It can be understood.

It is clear that the spark plug shown in FIG. 3 is easier to adjust the first spark gap 7' than the spark plug shown in FIG. 2.

In the above embodiment, the tip of the leg 2a is connected to the housing 1.
Although the leg portions 2a protrude from the end face portions of the housing 1, the present invention is not limited thereto, and a structure may be adopted in which the tip portions of the leg portions 2a enter the inner peripheral portion of the housing 1.

Further, in the above embodiment, the ground electrode 5 is fixed to the housing 1, but the ground electrode 5 may be formed by integrally molding something corresponding to the ground electrode 5 at the end of the housing 1.

As described in detail above, in the present invention, the outer diameter of the distal end side of the center electrode 4 is made smaller than the diameter of the inner hole 2b of the leg portion 2a, and the small diameter portion of the center electrode 4 is formed on the distal end surface of the leg portion 2a. By making it protrude more, the leg portion 2a of the small diameter portion of the center electrode 4 is
A first spark gap 7' is formed between the side surface of the portion protruding from the tip end surface of the ground electrode 5 and the tip end surface of the ground electrode 5, and is located within the inner hole 2b of the leg portion 2 of the small diameter portion of the center electrode 4. Since a space 6 is formed between the side surface of the part and the inner circumference of the inner hole 2b of the leg 2a, and a second spark gap 8 is formed between the tip end surface of the leg 2a and the ground electrode 5,
If the leg portion 2a is not contaminated with carbon or the like, the first spark gap 7' can be ignited by sparks, and if the leg portion 2a is contaminated with carbon or the like, the spark will flow along the inner hole 2b of the leg portion 2a. through the second spark gap 8
This has the excellent effect of being able to remove dirt such as carbon by the high-pressure spark at the same time as the air-fuel mixture is ignited, thereby restoring the first spark gap 7 to its normal spark state.

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

In addition, sparks fly to the creeping surface of the inner hole 2b of the leg portion 2a only when it is contaminated, so wear and tear on the wall surface (creeping discharge part) of the inner hole 2b can be suppressed as much as possible, resulting in a high-performance, long-life spark. Plug can be provided.

In addition, due to the above effects, the spark plug of the present invention can always spark normally and ignite the mixture, so the engine can be operated normally without misfire, and as a result of the normal spark, the engine can be operated 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, since the outer diameter of a part of the center electrode 4 is only made thinner than the inner diameter of the inner hole 2b of the insulator leg 2a, there is no problem in mass production, and therefore, compared to conventional spark plugs, there is no problem in mass production. This has the excellent effect of allowing high-performance, long-life spark plugs to be mass-produced at low cost.

Further, since the first spark gap 7' is formed between the side surface of the center electrode protruding from the distal end surface of the leg portion 2b and the distal end surface of the ground electrode 5, the first spark gap 7'
The flame kernel formed by the flying sparks is difficult to touch the leg 2b and is not subjected to much cooling effect, so the growth of the flame kernel is not inhibited, and it is easy to grow into a large flame kernel, so it is said that the ignition of the mixture is good. It has excellent effects.

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

[Brief explanation of the drawing]

1 and 2 are partial cross-sectional views showing the spark discharge part which is the main part of a conventional spark plug for an internal combustion engine, and FIG. 3 shows the main part of an embodiment of the spark plug for an internal combustion engine according to the present invention. FIG. 4, which is a partial sectional view showing a certain spark discharge portion, is a graph showing the results of a stain test and an ignitability test. 1...Housing, 2...Insulator, 2
a...leg, 2b...inner hole, 4...
... Center electrode, 5 ... Ground electrode, 6 ...
...Space part, 7'...1st spark gap,
8...Second spark gap.

Claims (1)

[Claims] 1. A center electrode, an insulator holding the center electrode,
In a spark plug for an internal combustion engine that has a housing fixed to the outer periphery of the insulator and a ground electrode provided on the end face of the housing, the outer diameter of the tip is set within the combustion chamber of the internal combustion engine within the insulator. By making a part of the small-diameter portion on the tip side of the center electrode, which is smaller than the diameter of the exposed leg inner hole, protrude from the tip end surface of the leg of the insulator, the small-diameter portion of the center electrode is A space is formed between a side surface of a portion of the leg of the insulator located in the inner hole and an inner peripheral portion of the leg inner hole of the insulator, and a space is formed between the side surface of the portion of the leg of the insulator located in the inner hole, and the leg of the insulator is formed in the small diameter portion of the center electrode. A first spark gap is formed between a side surface of a portion protruding from a distal end surface of the leg and a distal end surface of the ground electrode, and a second spark gap is formed between a distal end surface of the insulator leg and a side surface of the ground electrode. A spark plug for an internal combustion engine, characterized by forming: