JPS5933949B2 - spark plug - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates primarily to spark plugs used in automobile gasoline engines.

Engine exhaust gas purification has become the biggest technical challenge for the automobile industry these days.

To purify exhaust gas, it is effective to thin the air-fuel mixture supplied to the engine and use a powerful spark to cause complete combustion.

Therefore, in modern engines, it is necessary to operate the engine with a lean mixture with a mixture concentration of 17, 18, or in some cases 20, which is thinner than the stoichiometric air-fuel ratio, that is, the ratio of fuel to air is 14.7. is being attempted.

However, the air-fuel ratio of the air-fuel mixture supplied to the engine and the required voltage of the plug to ensure reliable ignition when combined with this air-fuel mixture are different from each other even if other conditions such as the compression ratio are the same. As shown in Figure 1, as the air-fuel ratio increases, the required voltage tends to increase.

The characteristics shown in Figure 1 are for the 18mm plug (the outside diameter of the plug mounting screw is 18mm) that is currently widely used in automobile gasoline engines. The voltage used is about 20 to 25 kV.

Now, when the air-fuel ratio A/F is set to 18, the difference between the required voltage and the available voltage, that is, the margin voltage, is 4 kV, which is sufficient to withstand use if the plug is new, but in general, the electrodes of the plug are worn out. As the required voltage increases, the required voltage exceeds the available voltage in a short period of time, causing a misfire.

As countermeasures against this problem, two methods have been adopted: one is to use an ignition power source with a high usable voltage, and the other is to use a noble metal such as platinum as the electrode material of the spark plug to lower the required voltage.

The former method requires the capacity of the ignition power source to be increased, which has the disadvantage of increasing the overall cost, while the latter method uses precious metals as the material for the plug, which increases the cost of the plug and makes it difficult to use in cars for the general public. The equipment was inadequate.

An object of the present invention is to provide a spark plug for an internal combustion engine that requires low voltage without using special electrode materials.

The present invention is characterized in that two notch-shaped grooves that intersect are provided on the discharge end face of the center electrode, and the dimensions of the grooves are set within a specific range.

The embodiments shown in the drawings will be described below.

Fig. 2 shows a known spark plug, in which an insulator 1 is hermetically sealed by a plug metal fitting 2, and the central part ζ
A center electrode 3 is embedded here using a known method.

A ground electrode 5 is welded to the end face of the mounting screw 4 of the stopper metal fitting 2, and a spark gap 6 is formed between it and the end face of the center electrode 3.

A notched groove 13 is provided on the discharge end surface of the center electrode 3.

This known spark plug is provided with a groove in order to keep the temperature of the end face of the center electrode high, but according to experiments conducted by the present inventors, spark plugs with simple grooves have a lower temperature than those without grooves. Although this is effective, it has been found that the effect can be further improved by making the shape and dimensions of the groove special.

3 and 4 show an embodiment of the present invention, in which a cross-shaped groove 23 is provided on the discharge end face of the center electrode 3, and the width X of the groove is 0.3 degrees or more. The size is set to be 40% or less of the diameter of the center electrode 3.

Therefore, four poles 24 for discharge are formed on the discharge end surface of the center electrode 3.

FIG. 5 shows the results of the test at vehicle speeds corresponding to 50 km/h and 70 km/h using the conventional plug shown in FIG. 2 and the plug of the invention having cross-shaped grooves shown in FIGS. This figure shows the relationship between the width of the groove and the required voltage of the plug.

The engine used is the L16 installed in the 1950 Bluebird (1600cc) manufactured by Nissan Motor Co., Ltd.
It is a type engine.

The test plug was a 1f3mm plug with a center electrode diameter of 27mm, a spark gap of 0.7mm, and a groove depth of 1rnm, and the A/R of the air-fuel mixture supplied to the engine. F was kept constant at 14.7.

As is clear from this experimental result, when a groove with a width of 0.1 mm is provided, the required voltage is A in the present invention, compared to the required voltage of a spark plug with no groove at all.

As shown in A', it has decreased to 70-80%, whereas in the conventional type shown in Figure 2, it has decreased to 90% as shown in B and B'.
It has only decreased by about %.

Furthermore, when the groove width is set to 0.31n1n or more, compared to the case without grooves, the present invention reduces it to about 60%, while the conventional type shown in Figure 2 only reduces it to about 70%. do not have.

Although this characteristic is a characteristic during load operation, it was confirmed that a similar tendency is exhibited when the engine is started.

The results shown in Figure 5 were obtained using the stoichiometric air-fuel ratio of the air-fuel mixture supplied to the engine, but experiments were also conducted with lean air-fuel mixtures, and the trend was the same, except that the required voltage value increased overall. there were.

Incidentally, if the groove width is increased, the required voltage will decrease, but the reason for this is that the larger the groove width is, the more the pole 2
This is because the angle of the arc portion 4 becomes smaller, making it easier to discharge.

However, as will be described later, there is a limit to increasing the groove width without limit.

FIG. 6 shows the results when the same experiment as that described in FIG. 5 was conducted using the A12 engine installed in the 1950 model Sunny (1200CC) manufactured by Nissan Motor Co., Ltd.

In this case, the required voltage is 1 to 2 kV depending on the engine change.
However, the trend is almost the same as that shown in FIG. 5, and the effects of the present invention can be fully expected even if the engine is changed.

FIG. 7 shows the results when the center electrode of the plug was changed from 2.7 mm to 2.2 mm in the same experiment as that described in FIG. 5.

In this case, the required voltage was lower than in the case of FIG. 5 due to the smaller diameter of the center electrode, but the trend was almost the same as in FIG.

FIG. 8 shows the required voltage when the spark gap is changed for the L16 engine used in the experiment shown in FIG.

Here, the test plug is a 181m plug, the diameter of its center electrode is 2.7mm, and the spark gap is 0.7m.
m, and the depth of the groove is l mm.

The driving conditions were a vehicle speed of 50km/h and an A/F of 1.
4.7, the required voltage was measured in a full-open sudden acceleration state in which the throttle valve opens from 1/6 of full open to full open.

The solid line is the conventional spark plug shown in Figure 2, and the broken line is the 3rd type spark plug.
The spark plug of the present invention shown in FIG. It can be seen that the required voltage is low.

Figure 9 shows the L16 type engine used in the experiment in Figure 5, with a center electrode diameter of 2.7 mm and a width of 0.5 mm.
Fig. 2 shows a plug of the present invention having a cross-shaped groove 23 with a depth of 1 inch, and a plug with a center electrode having a diameter of 2.7 mm with a single groove 13 with a width of 0.5 nm and a depth of 1 inch. Conventional plug and
The figure shows the results of measuring the required voltage for a plug with a center electrode diameter of 2.7 mm and no groove at all while maintaining the same spark gap Q and 7 mm.

The driving conditions are vehicle speed 50 km/h and A/F 14.
．． 7 is constant.

As is clear from the results, the required voltage value of the product implementing the present invention was about half that of the conventional product, and it was found that the fluctuation of the required voltage was also small.

Although it is not clear why the required voltage decreases when a groove of an appropriate width is provided on the end surface of the center voltage, when a groove is provided on the end surface of the center electrode 3, a plurality of grooves 23 are formed on the end surface of the center electrode. It is thought that this is because the formation of the individual poles 24 and the presence of the grooves 23 make it easier for the air-fuel mixture to enter the discharge gap.

That is, as shown in FIGS. 2 and 3, the cross-shaped groove 2
3, four poles 24 for discharge are formed on the end face of the center electrode 3 due to the grooves 23, and sparks are generated at the poles that are most likely to spark.
It is thought that the required voltage becomes lower because not only does the amount of fluctuation in the required voltage become smaller, but also because the air-fuel mixture enters the discharge gap between each pole more easily.

To confirm this result, we tested the plug shown in Figure 2 with one groove and the one with the cross groove shown in Figures 3 and 4. As shown in Figure 10, the groove width was the same (Q, 5 mm). It was confirmed that the required voltage of the present invention was approximately 20% lower than that of the conventional product shown in FIG.

The test conditions were that the diameter of the center electrode of the spark plug was 2.7 mm;
The depth of the groove was set to 1 mm, the spark gap was set to Q, 7 mm, and the throttle valve was opened at a vehicle speed of 50 km/h with the A/F set to 14.7 using the L16 type engine used in the experiment shown in Figure 5. The required voltage was measured in a full-open sudden acceleration state where the valve opens from 1/6 of the fully open position to fully open.

Here, the full-open sudden acceleration state is a bad state in which the A/F of the air-fuel mixture becomes diluted at the same time.

From this result, it can be seen that the plug of the present invention requires a lower voltage than the plug shown in FIG.

According to the characteristics shown in FIG. 5, the groove width is approximately constant when Q exceeds 3 mm, but if the groove width is too large, the area of the pole 24 decreases and the wear of the electrode increases.

Therefore, the life of the plug is shortened accordingly.

For plugs applied to general automobile engines, the outer diameter of the center electrode is 2, except for those that use a center electrode made of precious metal.
As shown in FIG. 1, the groove width X is preferably set to 40% or less of the diameter of the center electrode.

Figure 11 shows the relationship between the ratio of the diameter of the center electrode and the groove width In order to suppress the amount of consumption, it is desirable that x/D be 0.4 or less.

Regarding the cross-sectional shape of the groove, that is, the shape of the groove seen in the projection views of FIGS. 2 and 3, other semicircular and inverted ■-shaped shapes other than I- are also effective.

If the depth of the groove is too shallow, the groove may disappear due to electrode wear during use, so it must be set larger than the wear dimension of the electrode.

Further, when machining the grooves, mechanical cutting is generally used, and in this case, cross-shaped grooves in which the grooves intersect at right angles are preferable from the viewpoint of workability.

As explained above, according to the present invention, the required voltage can be lowered by changing the shape of the center electrode.
The use of the plug of the invention is particularly effective when the engine is operated with a lean mixture.

[Brief explanation of the drawing]

FIG. 1 is a characteristic diagram showing the relationship between the air-fuel ratio of the air-fuel mixture and the required voltage, FIG. 2 is a front view of a conventional plug, FIG. 3 is a partial front view showing an embodiment of the present invention, and FIG. The bottom view of FIG. 3 with the ground electrode removed, and FIGS. 5 to 11 are characteristic diagrams. 1... Insulator, 2... Plug fitting, 3.
...Center electrode, 13, 23...Groove, 24
...Pole, 4...:...Not installed, 5...
...Ground electrode, 6...Spark gap.

Claims (1)

[Claims] 1. In a device that has an air gap discharge gap between the ground electrode and the center electrode in the axial direction of the center electrode, two notch-shaped grooves that intersect are provided on the discharge end surface of the center electrode, and the width of this groove is Q, 3 1. A spark plug characterized by having a dimension of not less than mm and not more than 40% of the diameter of the center electrode.