JPS6231615Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a lip structure for improving the thermal durability of a piston for a direct injection diesel engine, which has a lip at the opening of a combustion chamber cavity and a valve recess on the top surface of the piston.

As a piston for a direct injection diesel engine, for example, the piston No.
There is something like the picture. 1 is the cylinder head, 2
is a cylinder. Fuel is injected into a piston combustion chamber cavity 4 formed at the top of the piston 3 in the direction of each spray axis 9 from a fuel injection nozzle 8, and after being atomized and evaporated, it is mixed with air and combusted.
In a direct injection type (hereinafter abbreviated as "direct injection type") diesel engine, when the piston 3 reaches the top dead center, the distance between the bottom surface of the cylinder head 1 and the top surface of the piston 3 becomes extremely small. In order to prevent the bulk part of the exhaust valve from interfering with the piston 3, a valve recess 6 is provided at the top of the piston 3. In this case, if a lip 5 is provided at the cavity opening in order to strengthen the squish flow into the cavity 4 and the reverse squish flow flowing out of the cavity, a portion where the lip 5 and the valve recess 6 overlap is usually created. The thickness of the lip 5 at the overlapping portion is reduced, heat load is concentrated, and cracks are likely to occur in that portion. In order to avoid this, it is known that a concave conical surface 7 is formed on the top surface of the piston to avoid overlapping of the lip 5 and the valve recess 6.

However, in the case of such a conventional direct-injection type diesel engine piston, since the top surface of the piston is formed into a concave conical surface as described above, the volume of the clearance combustion chamber 10 sandwiched between the top surface of the piston and the lower surface of the cylinder head is reduced. Of course, it becomes larger by that amount.

On the other hand, the cavity volume ratio at piston top dead center {defined as = cavity volume / (cavity volume + clearance combustion chamber volume)} is one of the factors that greatly controls the output performance of a direct injection diesel engine. Although it is desirable to keep the value as large as possible, if the top surface of the piston is made into a concave conical surface as described above, the value of the cavity volume ratio becomes small and the output performance decreases. Particularly when downsizing a direct injection type engine, it is generally difficult to secure a large volume ratio, so there has been a problem that the adverse effects of the shape and configuration are significant.

This idea was created by focusing on these conventional problems, and by lowering the part of the lip that overlaps with the valve recess to prevent the thickness from decreasing, the thickness of the lip is substantially reduced over the entire circumference. The purpose is to solve the above-mentioned problems by making it uniform.

As mentioned above, this invention avoids interference with the valve recess by lowering the lip portion of the cavity opening that overlaps with the valve recess connected to the piston combustion chamber cavity bored at the top of the piston than the other portion that does not overlap. The thickness of the lip is made substantially uniform over the entire circumference.

This invention will be explained below based on the drawings.

FIG. 2 is a diagram showing an embodiment of this invention. Note that the same numbers as in FIG. 1 indicate the same (corresponding) parts, and redundant explanation will be omitted. A piston combustion chamber cavity 4 is formed on the top surface of the piston 3 on a flat surface without providing a concave conical surface as in the conventional example. Lip 5 of the opening of this cavity 4
In order to prevent the part that overlaps the valve recess 6 from being scraped due to interference with the valve recess, the lip in the overlapping part is lowered as shown in Fig. The structure is designed to ensure the same thickness.

Next, the effect will be explained.

Since a valve recess 6 is provided on the top surface of the piston, it is possible to avoid interference between the piston and the intake and exhaust valves and to reduce the clearance at the top of the piston.In addition, the top surface of the piston has a concave concave surface as in the conventional example. Since there is no clearance, the volume of the combustion chamber 10 can be kept small, and a large cavity volume ratio can be ensured.

Furthermore, since the lip 5a is provided at the opening of the piston combustion chamber cavity 4, the squishing flow obtained when the piston rises and the reverse squishing flow obtained when the piston descends are strengthened, thereby promoting the mixing of fuel and air. .

Furthermore, the thickness of the lip 5a is the same as that of the descending lip 11.
By employing this, the temperature can be kept substantially constant over the entire circumference, so the lip will not locally become high in temperature, and there is no risk of concentration of thermal stress.

As explained above, this invention is based on a piston for a direct injection diesel engine that has a lip at the opening of the piston combustion chamber cavity bored at the top of the piston, and a valve recess connected to the cavity on the top surface of the piston. In this structure, the part of the lip that overlaps with the recess is lowered than the other part that does not overlap, so that the thickness of the lip becomes substantially uniform over the entire circumference, which increases the value of the cavity volume ratio. In addition, since the lip provides a mixing effect of fuel and air, it is possible to improve the output performance of a direct injection diesel engine. This has the great effect of preventing the occurrence of cracks due to localized thermal stress concentration at the lip.

[Brief explanation of the drawing]

1a and 1b are diagrams showing an example of a conventional piston for a direct injection diesel engine, in which FIG. 1a is a top view, FIG. 1b is a sectional view taken along line A-A, and FIGS. b is a diagram showing an embodiment of the same piston according to the present invention, FIG. 2 a is a top view, and FIG.
-B sectional view. 3... Piston, 4... Piston combustion chamber cavity, 5, 5a... Lip, 6... Valve recess, 11... Clearance combustion chamber, 11... Descending type lip.

Claims (1)

[Scope of utility model registration request] In a piston that has a lip at the opening of a piston combustion chamber cavity formed at the top of the piston, and a valve recess that is connected to the cavity on the top surface of the piston, the lip portion that overlaps with the valve recess is replaced by another portion that does not overlap. A piston for a direct injection diesel engine, characterized in that the lip is lowered further so that the lip thickness is substantially uniform over the entire circumference.