JPS5853034Y2 - spark plug - Google Patents

Description

[Detailed explanation of the idea] The present invention relates to a spark plug with improved ignitability.

In automobile engines, it is desired to operate at a lean air-fuel ratio for exhaust purification, and it is effective to increase the ignition advance angle, especially during idling, in order to further reduce fuel consumption and improve output.

However, when the ignition advance angle is increased, the flame kernel generated by spark discharge during the compression process when idling, etc.
According to the movement of the piston B, the spark plug C moves from the position A shown in the figure to the position A' on the center electrode side of the ignition plug C, and the flame kernel is thus subjected to a greater extinguishing effect of the center electrode, and the flame kernel The extinguishing effect of the electrode and the relative position of the spark relative to the outer electrode are the dominant factors for ignition errors in light load, low speed rotation ranges such as idling.

Conventionally, there have been spark plugs with grooves formed in the center electrode or outer electrode to improve ignition performance, but these spark plugs were formed with grooves without taking the above facts into account, so they did not improve ignition performance. That was enough.

The object of the present invention is to provide a spark plug that can reliably reduce the extinguishing rate of the flame kernel and can effectively prevent ignition errors particularly in low-speed rotation and light load ranges such as idling.

In the present invention, a heat-resistant insulating layer is provided in the middle portion of the tip surface 30 of the center electrode and/or the outer electrode surface 20 opposite to the tip surface, excluding the ends in the directions 11 and 12 on both sides of the outer electrode, and the heat-resistant insulating layer is The main idea is to form a main discharge gap in the unattached portion, thereby selectively generating a flame core in positions where the flame extinguishing effect of both the center electrode and the outer electrodes is weak.

Next, the present invention will be explained based on an embodiment shown in FIGS. 2 to 4.

10 is a metal shell of the ignition plug; 1 is an outer electrode protruding from the end surface; 2 is an insulator fixed in the metal shell 10; and 3 is a center electrode penetrated through the insulator 2.

4 and 5 are heat-resistant insulating layers according to the present invention, and 4 is coated on the center electrode tip surface 30 at the middle portion of both sides of the outer electrode excluding the 11° and 12 direction ends 31 and 32; is the outer electrode surface 20 facing the center electrode tip surface 30
The upper part is attached to the intermediate part excluding the opposite ends 13 and 14.

The heat-resistant insulating layers 4 and 5 are formed on the center electrode tip surface 3, respectively.
A ceramic having excellent electrical insulation and heat resistance, such as alumina, silica, or mullite, is thermally sprayed onto the electrode surface 20 and the outer electrode surface 20 to a thickness of 0.1 to 4 mm.

In this spark plug, the proportion of spark discharge occurring in areas where the heat-resistant insulating layers 4 and 5 are not formed is large, so spark discharge occurs in areas E and F shown in the figure, and the proportion of spark discharge occurring in areas G and H is low. Noticeably small.

These regions E and F are far from the surfaces of the center electrode 3 and the outer electrode 1, and the heat-resistant insulating layer generally has excellent heat insulation properties, so that the flame core generated by the spark is not easily extinguished.

The same applies when a flame kernel generated by a spark moves toward the center electrode.

On the other hand, in the conventional spark plug shown in Fig. 5, when a discharge occurs in the region G, it comes in contact with the outer electrode over a wide area and receives a large extinguishing effect; The end surface 15 of the outer electrode 1 shown in FIG.
comes to the position 15' displaced in the direction of the center axis of the center electrode 3, so the flame kernel moves toward the center electrode in response to the movement of the piston during the compression process, increasing the contact area with the center electrode and suppressing the flame extinguishing effect. received greatly.

The heat-resistant insulating layers 4 and 5 may form shallow grooves in the center electrode tip surface 30 and the outer electrode surface 20, respectively, and may be fixed within the grooves.

Further, the heat-resistant insulating layer is formed on the center electrode tip surface 30 as in the above embodiment.
Although it is desirable that the oxide is provided on both the outer electrode surface 20 and the outer electrode surface 20, the ignitability can be improved even when it is provided on only one of them.

In this case, the flame kernel generated by the spark discharge receives more of the extinguishing action of the center electrode, so the center electrode tip surface 3
When a heat-resistant insulating layer is formed on the 0, the effect of improving ignitability becomes greater.

Furthermore, the ignition plug of the present invention has a center electrode distal end surface 3 due to use.
0 and/or the part of the outer electrode surface 20 that is not covered with the heat-resistant insulating layer is worn away, and if the heat-resistant insulating layer is lost in this state, the tip of the center electrode and/or the center electrode of the outer electrode The side portions become wedge-shaped, and the rate at which the flame kernel receives the extinguishing effect from the convex surface of the center electrode or the outer electrode decreases, improving ignitability.

As described above, the spark plug of the present invention is provided with an insulating layer so that the spark discharge is concentrated on both sides of the outer electrode, so that the generated flame kernel has an advantageous effect on the extinguishing effect of the center electrode and the outer electrode. It is possible to reliably prevent the occurrence of ignition errors in low speed rotation ranges such as during idling.

[Brief explanation of the drawing]

Fig. 1 is a schematic sectional view of the combustion chamber of an engine, Fig. 2 is a side view of the discharge gap portion of the spark plug according to the present invention, Fig. 3 is the front view, Fig. 4 is a plan view, and Fig. 5 is a conventional spark plug. The side view of the discharge gap is shown. In the figure: 1: Outer electrode, 2: Insulator, 3: Center electrode, 4, 5: Heat-resistant insulating layer.

Claims (1)

[Scope of utility model registration request] A spark plug characterized in that a heat-resistant insulating layer is formed in the middle part of the tip surface 30 of the center electrode and/or the outer electrode surface 20 opposite to the tip surface, excluding the ends in the directions 11 and 12 on both sides of the outer electrode.