JPH036823Y2 - - Google Patents

Description

[Detailed description of the invention] Industrial application field The present invention makes the cap forming the lower wall of the sub-combustion chamber of a swirl chamber type diesel engine made of ceramics (hereinafter referred to as the ceramic cap), and a metal ring is attached to the cap. This invention relates to a diesel engine auxiliary combustion chamber structure constructed from shrink-fitted materials.

Prior Art When the base that forms the lower wall of the sub-combustion chamber of a swirl chamber type diesel engine is made of ceramics that have excellent heat resistance and low thermal conductivity, a metal ring is baked around the outer periphery of the ceramic base to improve thermal shock resistance. The fitting technique is known (for example, Utility Model Publication No. 106506/1983, Japanese Patent Publication No. 4938/1983).

There are two methods for fixing a metal ring shrink-fit type cap in the recess of the cylinder head: a ceramic cap with a metal ring shrink-fitted thereon is press-fitted into the cylinder head recess and fixed from the periphery, and a second method is to loosely fit the cap into the cylinder head recess. There is a method in which the cap is fixed from above and below using a stepped surface of the recess and a cylinder block via a gasket.

Fixation by press-fitting is seen in Utility Model Application No. 53-106506, but in this type of fixing, the lower surface of the ceramic cap is recessed upward from the surface of the metal ring during the machining process that aligns the bottom surface of the cap with the bottom surface of the cylinder head after press-fitting. may be done. However, this retraction is not the retraction of the entire cap including the metal ring, but only the ceramic cap, and is merely a retraction to meet the processing requirements, and it occurs in ceramic caps. It is not intended for stress relief. This is because in such fixing, no vertical tightening force is applied to the ceramic cap, so there is no need to retract it to reduce the vertical load.

On the other hand, in fixation by clamping the cylinder block through the step of the recess and the gasket, conventionally,
In order to securely fix the cap when assembling the engine, the bottom surface of the cap 1 and the bottom surface of the cylinder head 2 should be
It has been thought that it is better to have the lower surface of the mouthpiece 3 protrude downward from the lower surface of the cylinder head 4, as shown in the figure, or alternatively, as shown in FIG.

However, in the conventional structure, a compressive load in the vertical direction was actually applied to the upper end of the thin-walled cylindrical skirt portion of the ceramic cap due to fixation during assembly, and circumferential stress was generated in this portion. Furthermore, under actual machine loads, thermal stress due to the temperature difference inside and outside the sub-combustion chamber was applied in the same direction, resulting in an excessive load being applied to the ceramic cap.

Furthermore, if a ceramic cap with the lower end retracted above the metal ring as in the above-mentioned Utility Model Application No. 53-106506 is loosely fitted into the cylinder head recess and tightened in the vertical direction, it will not be retracted. A large compressive load in the vertical direction acts on the metal ring that is not in place, and the top end of the metal ring is distorted, affecting the ceramic cap and generating large stress at the top of the ceramic cap. It was also difficult to repurpose it.

Purpose of the invention The object of the present invention is to reduce the circumferential stress near the upper end of the ceramic base in a diesel engine sub-combustion chamber structure using a metal ring shrink-fit type ceramic base. That is,
To minimize assembling stress generated in a ceramic cap when assembling an engine to a necessary minimum, and to securely fix the cap.

Structure of the Invention In order to achieve this object, in the diesel engine auxiliary combustion chamber structure of the present invention, a cap configured by shrink-fitting a metal ring around the outer periphery of a ceramic cap is inserted into the recess of the cylinder head, and the recess and the cap are inserted into the recess of the cylinder head. An auxiliary combustion chamber is formed between the cylinder head and the cylinder head, and the lower surface of the mouthpiece is provided above the lower surface of the cylinder head. In this case, it is desirable that the lower surface of the mouthpiece be provided above the lower surface of the cylinder head by an amount greater than 0 and less than 200 microns.

Effect of the invention Normally, a head gasket is fastened together between the cylinder head and cylinder block, and when the cylinder head is assembled, a large surface pressure is generated on the head gasket, deforming the head gasket, and the mouthpiece is pressed against the stepped surface of the recess. It is clamped and fixed by the cylinder block through the deformed head gasket. However, in the diesel engine auxiliary combustion chamber structure with the above configuration, the bottom surface of the cap, that is, both the bottom surface of the ceramic cap and the bottom surface of the metal ring,
Since it is retracted into the recess from the lower surface of the cylinder head, the contact of the deformed head gasket to the mouthpiece is weakened. Therefore, the cap is fixed in the recess with the circumferential stress generated at the upper end of the cap being reduced, and since the head gasket is in contact with the cap, there is no chance of the cap swinging or being damaged.

Effects of the invention Therefore, according to the present invention, since the bottom surface of the cap is retracted into the recess from the bottom surface of the cylinder head, the compressive load from the head gasket applied to the cap is weakened, and the stress in the circumferential direction at the top end of the ceramic cap is reduced. The effect is that the strength and reliability of the sub-combustion chamber structure is improved.

Embodiments Hereinafter, preferred embodiments of the diesel engine auxiliary combustion chamber structure according to the present invention will be described with reference to the drawings.

FIG. 3 shows the structure of a diesel engine sub-combustion chamber according to an embodiment of the present invention. In the figure, a stepped recess 12 is formed on the lower surface of the cylinder head 11, and a mouthpiece 13 is loosely fitted into the recess 12 with a slight gap between the inner surface of the recess 12 and the outer periphery of the mouthpiece 13. . A sub-combustion chamber 14 is formed between the substantially hemispherical ceiling surface of the recess 12 and the nozzle 12, and the sub-combustion chamber 14 is connected to the nozzle hole 1 formed in the nozzle 13.
It communicates with the main combustion chamber 16 via 5. Base 1
3, the upper end is in contact with the step 17 of the recess 12, the lower end is in contact with the head gasket 18, and the recess 1
It is held between the lower surface of the second stage 17 and a cylinder block 19 via a head gasket 18.

The cap 13 is composed of a ceramic cap 20 made of ceramics and a highly heat-resistant metal ring 21 shrink-fitted to the outer periphery of the ceramic cap 20. The ceramic cap 20 consists of a lower disk-shaped portion and a cylindrical skirt portion that rises upward from the outer periphery and becomes thinner as it goes upward, and the nozzle hole 15 is formed in the disk-shaped portion. The metal ring 21 consists of a cylindrical ring. The lower end of the metal ring 21 is aligned with the lower end of the ceramic cap 20, and the upper end of the metal ring 21 is aligned with the upper end of the ceramic cap 20. The lower surface of the cap 13 is provided above the lower surface of the cylinder head 11 and is retracted into the recess 12. The amount by which the lower end of the cap 13 is retracted from the lower surface of the cylinder head 11 is:
It is greater than 0 and less than 200 microns. When the bottom surface of the mouthpiece 13 is retracted from the bottom surface of the cylinder head 11 in this way, the head gasket 18
When the cylinder head 11 and the cylinder block 19 are fastened together, the cylinder receives surface pressure and bites into the lower surface of the mouthpiece 13, and comes into contact with the lower surface of the mouthpiece 13 in this state.
The reason why the retraction amount is set larger than 0 is to obtain the effect of reducing the contact pressure of the head gasket 18 against the bottom surface of the base 13, and the reason why the retraction amount is set to 200 microns or less is as follows.
This is because if the force is made larger than this, the force for holding the cap 13 will be reduced, which may cause the cap 13 to swing.

In the diesel engine auxiliary combustion chamber structure constructed as described above, the mouthpiece 13 is clamped and fixed in the recess 12 by the cylinder rod 19 via the step 17 and the head gasket 18. Since the bottom surface of the cap 13 is located above the bottom surface of the cylinder head 11, the cap 1 of the head gasket 18
3 is weakened, and the vertical compressive load on the base 13 is weakened.

Figure 4 shows the cylinder head 11 on the bottom surface of the base 13.
It shows the relationship between the upward retraction amount X microns from the bottom surface and the strain Y at the upper end of the ceramic cap 20, where curve A shows the circumferential strain and curve B shows the vertical strain. As shown in the figure, the amount of retraction
The larger the value, the smaller the distortion Y becomes. It can be seen that when X is larger than 0, the distortion reduction effect becomes noticeable, and the vertical distortion approaches 0 at about 2000 microns.
If the vertical strain is not greater than 0, the cap 13 will become trapped, so X must be less than 200 microns. In addition, in order to obtain the proper holding effect of the cap 13, it is desirable that X is in the range of 80 microns to 123 microns from the appropriate vertical strain Y.
From the viewpoint of appropriate circumferential strain, it is desirable that X be in the range of 75 microns to 130 microns. Therefore, from the standpoint of both distortions, it is desirable that X be in the range of 80 microns to 125 microns.

Therefore, according to the present invention as described above, the lower surface of the cap 13 is set above the lower surface of the cylinder head 11, which reduces strain and stress at the upper end of the ceramic cap, which is particularly problematic in terms of strength. This has the effect of improving the strength and reliability of the diesel engine sub-combustion chamber structure.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of a conventional diesel engine sub-combustion chamber structure, Fig. 2 is a cross-sectional view of a conventional diesel engine sub-combustion chamber structure different from Fig. 1, and Fig. 3 is an embodiment of the present invention. FIG. 4, which is a sectional view of the structure of the sub-combustion chamber of a diesel engine, is a characteristic diagram showing the relationship between the retraction amount of the cap and the distortion of the ceramic cap. 11...Cylinder head, 12...Recess, 13
...Match, 14...Sub-combustion chamber, 15...Nozzle hole, 1
6... Main combustion chamber, 17... Stage, 18... Head gasket, 19... Cylinder block, 20...
Ceramics cap, 21...metal ring.

Claims (1)

[Claims for Utility Model Registration] (1) A diesel engine in which a cap made by shrink-fitting a metal ring around the outer periphery of a ceramic cap is inserted into a recess in the cylinder head, and an auxiliary combustion chamber is formed between the recess and the cap. In the sub-combustion chamber structure of the engine, the cap is loosely fitted into the recess, and the cap is fixed from above and below by the cross section of the recess and the cylinder block via the gasket, and the lower surface of the cap is provided above the lower surface of the cylinder head. Diesel engine auxiliary combustion chamber structure featuring (2) The diesel engine auxiliary combustion chamber structure according to claim 1, wherein the lower surface of the mouthpiece is provided above the lower surface of the cylinder head by an amount greater than 0 and less than 200 microns.