JPS6117112B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention provides an internal combustion engine with mounting screw diameters of 10, 12, and 14 mm.
This relates to a long reach spark plug with a length of the cylinder head embedded part of 19 mm or more, and a flat sheet type spark plug that is screwed onto the cylinder head via a gasket.

As shown in FIG. 1, a conventional spark plug for an internal combustion engine has a porcelain insulator 3 that holds a center electrode 2 sealed in the inner cavity of a metal shell 21, and a metal shell that is screwed onto a cylinder head 26. In the case of No. 21 mounting screw diameters of 14 and 12 mm, the body length (reach) L of the cylinder head implantation part is 12.7 mm and 19 mm, respectively.
, and when the thread diameter is 10 mm, 12.7 mm is mainly used. Furthermore, the reach portion is almost fully threaded and is fastened to the cylinder head via the gasket 5.

By the way, in the above-mentioned 19mm long reach spark plugs and spark plugs with a thread diameter of 10mm and a reach of 19mm with a full thread, the strength of the metal shell deteriorates as the wall thickness becomes thinner by the root diameter, and the strength of the metal shell deteriorates due to distortion during tightening. This tends to cause deformation, resulting in incomplete airtightness with the insulator, and in severe cases, there is a risk of breakage. Furthermore, extending the insulator in the axial direction within a limited range in the radial direction tends to cause distortion during firing, which reduces productivity. Furthermore, the long threaded portion naturally makes it extremely troublesome to attach and detach the plug. In particular, these trends become more significant as the thread diameter becomes smaller;
For a 10 mm long reach plug, it is even more difficult to satisfy the above performance when a conventional thread is provided.

The present invention has been made to advantageously solve this problem, and is a half-screw type spark plug with a threaded portion only on the tip side of the main metal fitting, and prevents the gasket from falling off due to this. The purpose of the present invention is to provide a long reach flat sheet type spark plug that has an effect of preventing falling off.

Hereinafter, the present invention will be explained with reference to embodiments shown in the drawings.

FIG. 2 is a longitudinal cross-sectional view of one and a half main parts of a spark plug according to an embodiment of the present invention, showing a state in which the spark plug is attached to a cylinder head. Note that parts common to the conventional spark plug (Fig. 1) are designated by the same reference numerals. Reference numeral 1 denotes a metal shell, in which a main body 7 and a body 8 equipped with mounting screws for the cylinder head 6 are connected via a stepped flat sheet 9, and a center electrode is provided in the inner cavity of the metal shell 1 according to known specifications. A porcelain insulator holding 2 is sealed and fixed. 4 is a ground electrode welded to the end surface of the metal shell 1; 5 is a sealing gasket interposed between the upper surface of the cylinder head 6 and the flat sheet 9 and made of a generally used plate material.

In the present invention, the male screw 1a for mounting is threaded on the tip end portion of the body 8 of the metal shell 1 near the combustion chamber 10, and this portion extends approximately 1/2 of the reach L of the body's entire length. . The thread diameter A of the mounting thread is
There are various sizes of 10, 12, and 14mm, and the reach L is about 19mm. The remaining body portion of the threaded portion 1a is provided with a non-threaded portion 1b, which is formed into a columnar shape with a diameter B equal to or larger than the thread diameter A, and is connected to the flat sheet 9 via an R portion 1c. A recess 1d having an annular groove is formed between the base of the non-threaded portion 1b and the flat sheet 9, and in order to support the gasket 5 in the recess 1d and prevent it from falling off, the dimensions of the recess 1d are as described above. It is formed to have a diameter c (about 0.05 to 0.5 mm in diameter difference) that is slightly smaller than the diameter B of the non-threaded part, and a gasket is fixed in advance in the recess. That is, as shown in FIG. 3, the gasket 5 is
Insert from the tip of the metal shell 1 to the unthreaded part 1b
At the same time, the gasket is pressed (temporarily compressed) to cause the inner diameter bent portion 5a of the gasket 5 to protrude inward and engage and secure with the seat surface 1e of the recess 1d. Further, as a means for preventing the gasket from falling off, as shown in FIG.
This can also be achieved by fixing it in the recess 1d. It should be noted that the structure of the gasket used in the present invention is not limited to the embodiments, and it is also possible to form a known protrusion on the inside of the gasket to serve as a pressing force in order to improve the escape prevention effect. In short, it is sufficient that the gasket is fixed in advance to the recess 1d of the metal shell 1 so as not to fall off.

To describe specific dimensions of the present invention, for example, the thread diameter A of the metal shell 1 is 10 mm, and the unthreaded part 1 is 10 mm.
The diameter B of b is 12 mm, the inner diameter of the gasket 5 is 12 mm, and the outer diameter of the recess 1 d of the metal shell 1 is 11.85 mm.
mm to fix the gasket in the recess 1d. This spark plug is for cylinder head 6.
10mm female thread 6a and non-threaded part 1b of metal shell 1
With a gap of approximately 0.2 to 1.0 mm between the fitting hole 6b
It is screwed onto the cylinder head 6 which is equipped with a cylinder head. In this way, in the present invention, by setting the diameter of the non-threaded portion 1b of the metal shell 1 to be equal to or larger than the outer diameter of the screw, the strength of the metal shell is increased, and this dimension prevents the gasket from falling off. This makes it easy to install the plug from the cylinder head to the cylinder head.

As described above, the long reach flat sheet type spark plug of the present invention has a screw diameter of 10, 12, or 14 mm that is screwed into the cylinder head on the tip side of the metal shell.
A threaded portion of any type such as the above is threaded, and the unthreaded body portion is provided with a diameter equal to or larger than the threaded diameter on the base side following this threaded portion, and is loosely fitted between it and the cylinder head. A recess with a diameter slightly smaller than the outside diameter of the unthreaded part is provided between the unthreaded part and the flat seat, and the gasket is fixed in advance in this recess to prevent it from falling off, so that the main body when installing the spark plug is By increasing the strength of the metal fittings, gas leakage between the fittings and the insulators can be effectively prevented, and the production of the insulators becomes easier. The half-thread type not only makes it easier to attach and detach the plug, but also has the effect of preventing the gasket from falling off, so it maintains airtightness without the gasket falling off even when the plug is attached and detached several times. I can do it. In particular, spark plugs with a small thread diameter of 10 mm and a long reach of 19 mm can be advantageously developed without sacrificing performance. Furthermore, since the clearance between the cylinder head and the metal shell can be uniformly reduced, there is a thermally advantageous effect.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of the main part showing how the cylinder head of a conventional spark plug is installed, FIG. 2 is a cross-sectional view of the main part showing how the cylinder head of the spark plug of the present invention is installed, and FIG. FIG. 4 is a cross-sectional view of the main parts of the spark plug shown in the figure showing how the gasket is fitted, and FIG. 4 is a cross-sectional view of the main parts showing how the gasket of another embodiment of the present invention is fitted. DESCRIPTION OF SYMBOLS 1... Metal shell, 1a... Threaded part, 1b... Unthreaded part, 1d... Recessed part, 5... Gasket, 6
... Cylinder head, 7 ... Body, 8 ... Body, 9 ... Flat seat.

Claims (1)

[Claims] 1. The body 8 equipped with a mounting screw screwed into the cylinder head and the large diameter main body 7 are connected via a stepped flat sheet 9, and a gasket is placed between the flat sheet and the cylinder head to ensure airtightness. In a spark plug having a metal shell holding a body, the tip of the body is formed as the mounting threaded portion 1a for the cylinder head 6, and the remaining body 8 is a threadless portion 1 that loosely fits into the cylinder head 6.
b is the outer diameter of at least the mounting screw 1a.
The outer diameter of the non-threaded portion 1 is larger than the outer diameter of the non-threaded portion 1b between the flat sheet 9 and the non-threaded portion 1b.
A recessed portion 1d having a diameter slightly smaller than the outer diameter of b is provided,
A long reach flat sheet type spark plug is characterized by having a gasket fixed in advance in this recess to prevent it from falling off.