JPS6229622Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a combustion chamber formed at the top of a piston of a diesel engine, and more particularly to relieving thermal stress in a combustion chamber structure in which a minute lip is formed at the periphery of the combustion chamber inlet.

Contained in diesel engine exhaust gas
To reduce NOx, delaying the timing of fuel injection is a well-known technical measure.

However, delaying the timing of fuel injection has the disadvantage of increasing smoke, HC, etc. in the exhaust gas.

For this reason, there is a limit to how much the timing can be delayed, making the NOx reduction effect insufficient.

In order to improve the above-mentioned drawbacks, a combustion chamber has been proposed in which a lip is formed at the periphery of the inlet of the combustion chamber and protrudes toward the center of the combustion chamber.

Providing such a lip 2 reduces the amount of smoke in the exhaust gas, making it possible to further delay the timing of fuel injection. Therefore, the NOx reduction effect is improved.

However, the above combustion chamber has the following drawbacks.

Since the thickness of the lip 2 is not sufficient, there is a possibility that a crack may be formed in the lip 2 due to thermal stress, and this crack may gradually extend and extend over the entire top surface of the piston.

Therefore, an object of the present invention is to prevent damage caused by thermal stress in the combustion chamber of a diesel engine provided with a lip.

A detailed explanation will be given below with reference to the drawings.

Referring to FIGS. 2 and 3, a combustion chamber 4 consisting of a recess is formed in the top surface of the piston 3. A lip 5 protruding toward the center O--O is provided on the periphery of the inlet portion of the combustion chamber 4, and the lip 5 is formed over the entire circumference.

The length of the lip 5 is the same as that in FIG. 1, so a description thereof will be omitted.

One or more notches 6 are formed around the combustion chamber inlet. In this embodiment, they are provided at three locations, but in this case it is desirable that the spacing be 120°. Furthermore, in the case of N pieces, the interval is set to 360°/
It is desirable to set it to N.

The shape of the notch 6 consists of a straight slit 7 and a circular hole 8 at the inner end of the slit 7. The hole 8 may have a circular shape.

The drilling direction of the hole 8 has an angle α with respect to the O-O line, and although this α is determined by the shape of the inner wall of the combustion chamber 4, it is preferable that it be smaller.

The sizes of the slit 7 and the hole 8 are appropriately selected depending on the size of the piston 3 and the temperature during use, but in a normal piston, the width of the slit 7 is t=0.1.
2 mm, and the diameter d of the hole 8 is 1 to 10 mm.

The depth of the notch 6, that is, H in Figures 2 and 3
should be at least as long as the protruding length of the lip 5, thereby preventing cracks from occurring in the lip 5.

According to the present invention described above, the following effects are achieved.

Conventionally, it has been known to provide a slit as a means to prevent damage due to repeated thermal stress, but in the present invention, a slit is provided in the lip of the combustion chamber of a diesel engine so that the length of the lip can be freely selected. , the lip length can be selected to maximize the smoke reduction effect. In particular, the necessity and importance of smoke reduction measures are strongly demanded by society, and it is desirable to reduce smoke as much as possible. Since the lip length has a significant effect on the amount of smoke emitted, the ability to freely select the lip length is a significant advantage beyond simply preventing thermal breakdown.

When the notch is a combination of a slit and a hole, there is no thermal damage caused by the notch, resulting in an effective notch structure.

By making the notch approximately the length of the lip, thermal breakage can be effectively prevented, and at the same time, squishing and reverse squishing during the compression and expansion strokes will not be adversely affected.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a known micro-skip combustion chamber, FIG. 2 is a sectional view of a piston showing an embodiment of the present invention, and FIG. 3 is a plan view of the piston shown in FIG. 2.

Claims (1)

[Claims for Utility Model Registration] (1) In a diesel engine having a combustion chamber consisting of a recess formed at the top of the piston and having a slight lip along the entire periphery of the inlet of the combustion chamber, A combustion chamber for a diesel engine, characterized in that a notch having a straight slit with a width of 0.1 mm to 2 mm is provided at the entrance of the combustion chamber. (2) The combustion chamber of a diesel engine according to claim 1, wherein the cutout has a circular or oval hole at the inner end of the slit.