JPH10169505A - Piston for direct injection diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the strength of a piston for a direct injection diesel engine, by compounding and reinforcing an area including the lip edge of a head part in which a combustion chamber is recessed in the top surface of a piston by a fiber integrated body to which matrix metal is permeated, and also orientating this reinforced fibers to the circumferential direction of the lip edge. SOLUTION: A piston 1 for a direct injection diesel engine, in which an aluminum-silicon alloy is formed into a matrix 10, is equipped with a head part 2, a ring land part 3 and a skirt part 4, and a combustion chamber 21 is recessed in the center of the top surface 20 of the head part 2. In this case, an annular fiber integrated body 5 is filled and compounded into the matrix 10 in an area including the lip edge 21a of the combustion chamber 21. Alumina- silica fibers are used for reinforced fibers composing the fiber integrated body 5, and this reinforced fibers are orientated to the circumferential direction of the lip edge 21a. This piston 1 can apply strength that can sufficiently resist against a high temperature/high load, especially to the lip edge 21a, therefore the improvement of the performance of a smoke and so on can be expected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improved piston for a direct injection diesel engine.

[0002]

2. Description of the Related Art In general, an engine piston plays an important role of first inheriting the generated energy of fuel under severe conditions of being exposed to high temperature and high pressure of combustion while repeating reciprocating movement at high speed. Is lightweight,
It is required to have material properties that are robust, have a low coefficient of thermal expansion, and have good thermal conductivity.

[0003] In this respect, aluminum alloys are extremely lighter than iron-based metals, and are extremely useful as piston materials because of their high thermal conductivity. However, since the thermal expansion coefficient, which is about twice that of iron, is required to be moderated, Various innovations and improvements in practical use have been attempted. For example, the inventions described in JP-A-63-53226 and JP-A-2-298652 disclose a technique in which a part of a piston is composited with a reinforcing fiber.

[0004]

In a diesel engine having a more severe combustion mechanism as compared with a gasoline engine, particularly in a direct injection type piston used in the engine,
Due to such a mechanical load, a tensile force of a circumferential tangential component acts on the lip edge of the combustion chamber, and the tension force is continuously repeated in accordance with the movement of the piston. Therefore, the head portion including the lip edge causes particularly large damage. Will receive it.

[0005] The above-mentioned known technical means attempt to mitigate the damage to the engine piston by compounding reinforcing fibers, and a tentative effect is recognized in reducing the coefficient of thermal expansion and improving the strength and the like. However, since these reinforcing fibers are randomly oriented in a plane orthogonal to the axis of the piston, a reinforcing effect sufficient to satisfy the expected strength of the piston for a direct injection diesel engine has not been obtained.

SUMMARY OF THE INVENTION An object of the present invention is to provide a piston for a direct injection diesel engine which is excellent in both physical and mechanical properties and can sufficiently withstand severe use conditions. .

[0007]

According to a first aspect of the present invention, there is provided a piston for a direct-injection diesel engine, wherein a head having a combustion chamber formed in a top surface thereof, a ring land having a ring groove formed therein, and a projecting boss. A skirt portion provided with a pin hole in the head portion, wherein at least a region including a lip edge of the combustion chamber of the head portion is compositely reinforced by a fiber aggregate impregnated with a matrix metal, and the reinforcing fibers are It is characterized by being oriented in the circumferential direction of the edge.

As the reinforcing fibers, short alumina fibers, carbon fibers, silicon carbide fibers, alumina-silica fibers, glass fibers, silicon carbide whiskers, permeable ceramic fibers and the like can be used. In this piston, the coefficient of thermal expansion of the matrix metal such as an aluminum alloy is not only improved by the selection of the reinforcing fiber, but also the top surface of the head part is oscillated in the axial direction due to the repeated high load. In particular, the larger the area near the lip edge of the combustion chamber, the larger the tensile force of the circumferential tangential component will be generated, but the reinforcing fibers oriented in the circumferential direction often resist this and sufficiently complement the insufficient strength. I do.

According to a second aspect of the present invention, in the piston according to the first aspect, the composite reinforced region by the fiber assembly includes at least a top land and a top ring groove from the entire region of the head portion. It is characterized by being extended to the area. In this piston, in addition to the head part, the area supporting the ring land part is reinforced by a single fiber assembly, so the effect of the circumferentially oriented reinforcing fiber can be further extended to the ring land part Can be.

A piston according to a third aspect of the present invention is the piston according to the first or second aspect, wherein the inner wall of the pin hole is reinforced by an independent fiber assembly. In this piston, the pin holes are also reinforced by the independent fiber aggregates. In particular, when the reinforcing fibers are oriented in the circumferential direction of the pin holes as in the piston according to claim 4, the reinforcing effect is further improved. In addition, the roundness of the pin hole can be kept good.

[0011] The piston according to the fifth aspect is characterized in that:
The piston according to 2, 3, or 4, wherein the matrix metal is an aluminum-silicon alloy. In this piston, by employing an aluminum-silicon alloy as the matrix metal, it is possible to obtain a composite reinforced piston that is sufficiently adapted to a direct injection diesel engine while taking advantage of the inherent characteristics of the matrix metal.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, 13
Piston for direct injection diesel engine (hereinafter, referred to as piston) 1 having an aluminum-silicon alloy (for example, A390) containing -30% by weight of silicon as a matrix
Includes a head portion 2, a ring land portion 3 extending downward from an outer peripheral edge of the head portion 2, and a skirt portion 4 continuing to a lower portion of the ring land portion 3. Head part 2
A combustion chamber 21 having a circular projected shape in the axial direction is formed in the center of the top surface 20 of the base member, while three ring grooves 31 are formed in the outer peripheral surface of the ring land portion 3. The ring grooves 31 and the lands 30 alternately located therewith are arranged in the order from top to bottom, 2nd, 3rd.

In the matrix 10 of the piston 1, an annular fiber assembly 5 is filled and compounded in a required area including the lip edge 21a of the combustion chamber 21 by, for example, a high-pressure solidification casting method. Alumina-silica fibers are used as the reinforcing fibers constituting the fiber assembly 5, and the reinforcing fibers are oriented in one direction, specifically, in the circumferential direction of the lip edge 21a.

The production of such a fiber assembly 5 involves a method of electrostatically orienting and bridging the fibers dispersed in the dielectric liquid, and then sequentially sedimenting and accumulating the fibers, especially concentric. Using a bottomed container in which an upright cylindrical space is formed between the inner and outer cylinders, positive and negative electrodes are alternately embedded in the inner peripheral wall of the outer cylinder, and a filter is arranged at the lower part of the upright cylindrical space, and these A known orientation method of slowly rotating the outer cylinder and the filter body around their axes is applied.

When the piston 1 is cast by the high-pressure solidification casting method, the fiber assembly 5 is set in a mold corresponding to the outer shape of the piston 1 and then poured. The piston 1 shown in FIG. 1 is obtained by solidifying by applying a pressure of ² cm ² . FIG. 2 illustrates a piston 1A in which the entire area of the head portion 2 including the lip edge 21a is compounded by the fiber assembly 5A.

The pistons 1, 1A thus obtained
In addition to the mechanical properties inherent in aluminum-silicon alloys, the head section is not only improved in physical properties such as a decrease in the coefficient of thermal expansion in the composite area, but also simply improved in strength, and is also characterized by the high load characteristic of diesel engines. When the top surface 20 oscillates in the axial direction, an extremely large tensile force of a circumferential tangential component is generated especially in a region near the lip edge 21a of the combustion chamber 21, but the circumferential direction is oriented in the circumferential direction. The reinforced fibers resist this and sufficiently compensate for the lack of strength.

The piston ring fitted in the ring groove 31 at the top and the second position described above is a compression ring for preventing leakage. The surrounding area has already been composited with a unique reinforcing fiber, but the second embodiment of the present invention shown in FIG.
The piston 1B is shown in which the entire area of the head portion 2 including the lip edge 21a and the area including the top land 30 and the top ring groove 31 are all compositely reinforced by the fiber assembly 5B. The composite reinforced area can naturally be extended to the entire area of the ring land portion 3 as shown in FIG.

The piston 1B thus obtained is
The head portion 2 and the ring land portion 3 are a single fiber assembly 5
Since it is reinforced by B or 5C, the effect of the circumferentially oriented reinforcing fibers can be extended to the ring land portion 3 including the ring groove 31 without impairing the productivity in the casting process. . Further, the third embodiment of the present invention shown in FIG. 4 is a fiber assembly in which the inner wall portion is independent even for a pin hole 42 for supporting a piston pin provided through the projecting boss 41 of the skirt portion 4. 6 shows a piston 1C that is compositely reinforced.

In the piston 1C, particularly in the case where the reinforcing fibers are oriented in the circumferential direction of the pin hole 42, even when a strong load is applied to the pin hole 42 via the piston pin, the reinforcing action by the oriented fiber is sufficient. Resisting this, and there is no directional thermal expansion difference in the pin hole 42, the roundness of the pin hole 42 can be kept good.

[0020]

As described in detail above, the piston for a direct injection type diesel engine according to the present invention adopts the constitution described in each claim, and therefore, particularly, the high temperature and high load are applied to the lip edge of the combustion chamber. As a result, the lip edge shape can be sharpened, and the performance such as output and smoke can be expected to be improved, and further, the mixing state of air and fuel is further improved. Design can also be implemented. In addition, when the entire area of the head portion is compositely reinforced, there is an effect that can sufficiently realize more severe engine conditions.

[Brief description of the drawings]

FIG. 1 is a cutaway perspective view showing a piston according to a first embodiment of the present invention.

FIG. 2 is a sectional view showing the piston.

FIG. 3 is a sectional view showing a piston according to a second embodiment of the present invention.

FIG. 4 is a sectional view showing a piston according to a third embodiment of the present invention.

[Description of References] 1 is a piston, 2 is a head, 21 is a combustion chamber, 21a is a lip edge, 3 is a ring land, 30 is a land, 31 is a ring groove, 4 is a skirt, 42 is a pin hole, 5 , 6 is a fiber assembly

Claims (5)

[Claims] A head portion having a combustion chamber formed on the top surface thereof; a ring land portion having a ring groove formed therein; and a skirt portion having a pin hole penetrating a protruding boss. Direct injection type wherein at least a region including a lip edge of the combustion chamber is compositely reinforced by a fiber aggregate impregnated with a matrix metal, and the reinforcing fibers are oriented in a circumferential direction of the lip edge. Piston for diesel engine. 2. The composite reinforced area by the fiber assembly extends from the entire area of the head portion to at least the ring land area including a top land and a top ring groove. The described piston. 3. An inner wall portion of the pin hole is compound-reinforced by an independent fiber assembly.
Or the piston according to 2. 4. The piston according to claim 3, wherein the reinforcing fibers of the pin hole are oriented in the circumferential direction of the pin hole. 5. The method according to claim 1, wherein said matrix metal is an aluminum-silicon alloy.
The described piston.