JPS592151B2 - internal combustion engine spark plug - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in spark plugs used in spark-ignited internal combustion engines.

In spark-ignition internal combustion engines, it is necessary to ensure ignition even in lean air-fuel mixture regions where misfires are likely to occur. Various improvements have also been made to plugs.

As an example of these improvements, a spark plug as shown in FIG. 1 has been proposed.

In this spark plug, a spark gap between a center electrode 1 and a ground electrode 2 is surrounded by an electric insulator 3 such as ceramic to form a discharge space 4 with a small volume, and plasma generated in this space during spark discharge. The gas is ejected from the ejection hole 5 into the fuel mixture.

That is, unlike ordinary large-spot plugs that directly heat and ignite the air-fuel mixture by spark discharge, this spark plug first generates a spark between the center electrode 1 and the side electrodes 2 to fill the discharge space. A high-temperature, high-energy plasma-like gas is generated in the discharge space 4, and then the plasma-like gas is ejected from the ejection hole 5 into the air-fuel mixture by the pressure increase in the discharge space 4 due to thermal expansion of the plasma-like gas. A high-energy ejected gas flow forms a large number of flame kernels in the air-fuel mixture to ensure ignition.

However, in the conventional spark plug shown in FIG. 1, the inner diameter 6a of the threaded portion 6 of the plug body is in close contact with the electric insulator 3 surrounding the discharge space 4, so the heat value of the plug is so-called. It is a "cold type" and when the load is low or the rotation speed is low, "plug fogging" occurs and fuel carbon deposits and other engine oil etc. adhere to the inner wall of the discharge space 4, resulting in a short circuit.

The drawback was that no spark discharge occurred, resulting in misfire.

The present invention was invented in view of the conventional situation, and the electrical insulator is made into a tapered shape so that the wall thickness of the electrical insulator in the vicinity of the discharge space is thin, and the outside of the thin wall portion is connected to the combustion gas. The purpose of the present invention is to provide a plug that is open to the outside so as to come in contact with the mold, and by bringing the heat value of the plug closer to that of the baking mold, the plug has a self-purifying action and solves problems such as misfires.

Hereinafter, the present invention will be explained based on the drawings.

FIG. 2 is a diagram showing the ignition plug of the present invention together with a power supply circuit, and FIG. 3 is a bottom view of the ignition plug of FIG. 2.

In this spark plug, the plug screw portion 6 is formed so that the ground electrode portion 2 is substantially flush with the wall surface of the combustion chamber when the spark plug is installed in an engine.

The electrical insulator 3 has a tapered outer diameter,
As a result, a thin wall portion 3a is formed near the discharge space 4.

An annular gas space 7 is formed between the outside of the thin wall portion 3a and the inner surface 6a of the plug threaded portion, and this gas space 7 is connected to the ground electrode 2 and the plug body (the inner surface 6a of the plug threaded portion).
a) is open to the outside of the plug through a gap 8.8, and combustion gas is introduced into the gas space 7.

On the other hand, a power supply circuit 20 is connected to the center electrode 1 of this spark plug.
is connected.

This power supply circuit 20 consists of a high voltage power supply circuit 20a and a low voltage power supply circuit 20b.

The high voltage power supply circuit 20a is similar to a power supply circuit used in a normal spark discharge type ignition plug, and includes a cam 21 that rotates in synchronization with engine rotation, a contact arm 22 and a contact 22a, an ignition coil 23, power supply 2
It is composed of 4.

On the other hand, the low voltage power supply circuit 20b includes a resistor 25 and a coil 26.
and capacitor 27 are connected in series, and resistor 2
8 and a power supply 29 is connected to the capacitor 27.
It is configured by connecting in parallel.

Both power supply circuits 20a and 20b are connected to the center electrode 1 via diodes 30 and 31, respectively.

Now, when the contact arm 22 is driven by the cam 21 rotating in synchronization with the engine rotation and the contact point 22a opens, the primary current flowing through the primary coil 23a of the ignition coil 23 is cut off, and a high voltage is applied to the secondary coil 23b. occurs, the discharge space 4 between the center electrode 1 and the side electrodes 2
A spark discharge takes place within.

At this time, the insulation in the discharge space 4 is broken, so spark discharge is possible even at a relatively low voltage, and spark discharge continues in the discharge space 4 due to the direct current supplied from the low voltage power supply circuit 20b. It is done.

That is, the capacitor 2 is connected from the power supply 29 via the resistor 28.
The charge that was charged in 7 is transferred to the discharge space 4 diode 31
, the resistor 25, and the coil 26, and during this period, spark discharge is sustained within the discharge space 4.

Therefore, a large amount of plasma-like gas is generated within the discharge space 4, and due to thermal expansion of this plasma-like gas, the plasma-like gas is ejected from the ejection hole 5 into the air-fuel mixture, thereby ensuring reliable ignition.

Since the combustion gas generated at this time is introduced into the gas chamber T from the gaps 8, 8, the thin wall portion 3a of the electrical insulator 3
This prevents the wall surface of the discharge space 4 from cooling down due to energy damage.

Therefore, even under low load or low rotation, the fuel and
Carbon deposits, other engine oil, etc. are incinerated and can be prevented from adhering to the inner wall surface of the discharge space 4, thereby preventing misfires due to such adhesion.

Other embodiments are shown in FIGS. 4 to 6.

These figures are all bottom views of the spark plug, and the shapes of the ground electrodes are 2/2 and 71°2, respectively, in order to reduce the area of the ground electrode and bring the plug closer to the baking mold. It is.

In the embodiments shown in FIGS. 5 and 6, the inner diameter of the nozzle hole 5 and the inner diameter of the discharge space 4 are made to be the same (the discharge space 4 and the nozzle hole 5 are substantially the same). .

7 and 8 show another embodiment. In this embodiment, the ground electrode 2 is made to protrude from the combustion chamber wall surface by an amount tl,
The thin wall portion 3a is brought into direct contact with the combustion gas, and the plug is brought close to the baking mold.

In the embodiment shown in FIGS. 9 and 10, the ground electrode 2 is made to protrude from the wall surface of the combustion chamber by t2, and the electrical insulator 3
A gas space 7 is formed between the outer side of the plug and the inner surface 6a of the plug screw part, and the heat value of the plug can be brought closer to that of the baking mold than in the above embodiments, and the self-cleaning effect of the plug can be enhanced. can.

Incidentally, it goes without saying that in the above two embodiments, instead of the ground electrodes having the shapes shown in FIGS. 8 and 9, ground electrodes having the shapes shown in FIGS. 4 to 6 may be used. It is.

As explained above, according to the present invention, the electric insulator is formed into a tapered shape so that the wall thickness of the electric insulator in the vicinity of the discharge space is thin, and the outside of the thin wall portion comes into contact with the combustion gas. In order to bring the heat value of the plug closer to that of the baking mold, fuel, carbon deposits, and
It also has the effect of preventing engine oil and the like from adhering to it.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway side view of a conventional spark plug, FIG. 2 is a diagram showing the spark plug of the present invention together with a power supply circuit, and FIG.
The figure is a bottom view, FIGS. 4 to 6 are bottom views of other embodiments, FIG. 7 is a partially cutaway side view of another embodiment, FIG. 8 is a bottom view thereof, and FIG. 9 is a further A partially cutaway side view of another embodiment,
FIG. 10 is a bottom view thereof. DESCRIPTION OF SYMBOLS 1... Center electrode, 2... Ground electrode, 3... Electrical insulator, 4... Discharge space, 5...-Gas nozzle hole, 7...
Gas space, 8... air gap, 20... power supply circuit, 20a
...High voltage power supply circuit, 20b...Low voltage power supply circuit.

Claims (1)

[Claims] 1. A spark gap between a center electrode and a ground electrode is surrounded by an electric insulator to form a discharge space with a small volume, and plasma-like gas generated in this space during spark discharge is transferred to the discharge space. In the spark plug for an internal combustion engine, the electric insulator is formed into a tapered shape so that the wall of the electric insulator near the discharge space is thin, and the thin wall is A spark plug for an internal combustion engine, characterized in that the outer part of the spark plug is opened to the outside of the plug so that the outer part thereof comes into contact with combustion gas. 2. The ground electrode section is made substantially flush with the wall surface of the combustion chamber, and the combustion gas is introduced from the gap formed between the ground electrode section and the plug body into the gas space formed between the thin wall external force and the plug body. A spark plug for an internal combustion engine according to claim 1. 3. The spark plug for an internal combustion engine according to claim 1, wherein the ground electrode portion protrudes from the wall surface of the combustion chamber, and a gap is formed between the ground electrode portion and the plug body.