JPH0373750B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a piston for an internal heat engine, and more particularly to a piston made of a light alloy material such as an aluminum alloy.

As is well known, pistons for internal combustion engines are
Light alloy materials such as aluminum alloys are often used to reduce weight and inertia. However, large repeated stress acts near the pin hole where the piston pin is inserted, that is, the pin boss, and fatigue failure is likely to occur in that area. When used, this tendency is remarkable. Conventionally, as a measure to improve the strength of the boss part of such a piston made of light alloy material, a measure has been adopted to increase the wall thickness of the boss part, but increasing the wall thickness increases the weight of the piston. Therefore, this goes against the original purpose of using light alloy materials, which is weight reduction. A method is also known in which the strength of the boss portion is improved by forming ribs on the boss portion, but this also has the problem of increasing the weight of the piston. Furthermore, in order to improve the strength of the boss part,
A piston constructed as shown in FIG. 1 has also been proposed. That is, the piston shown in FIG.
A strut 1 made of a high-strength material such as steel in the form of a long plate or rod is embedded in the piston head portion 2, and a high-strength wire 4 is embedded so as to surround the strut 1 and the pin hole 3 to form a boss portion 5. Although such a piston is strong against the force in the tensile direction between the boss part 5 and the head part 2, it is not strong enough against the force in the compressive direction.
Moreover, since the strut 1 is embedded, there is a problem in that the weight of the piston increases as described above.

This invention has been made in view of the above circumstances, and it is an object of the present invention to provide a piston mainly made of a light alloy material, which improves the strength of the boss portion without causing the problems described above, and also prevents thermal expansion. The purpose is to

That is, the present invention provides a piston based on a light alloy material, in which at least the portion including the boss portion around the pin hole is made of a plain woven fabric with heat-resistant long fibers as the weft and warp, and one of the weft and warp. One is oriented in the circumferential direction of the piston and the other is oriented in a direction parallel to the axis of the piston, and the plain fabric is embedded continuously in the circumferential direction of the piston, and the plain fabric is integrated into a composite with the light alloy material of the base material. The area around the boss is strengthened by embedding heat-resistant long fiber plain weave, and by making the plain weave continuous in the circumferential direction. It suppresses thermal expansion.

The piston of the present invention will be explained in more detail below.

FIGS. 2 and 3 show an example of a piston according to the present invention, and this piston is made of a light alloy material such as an aluminum alloy or a magnesium alloy as a base material 6. A plain woven fabric 7 made of heat-resistant long fiber warps and wefts is embedded over a predetermined thickness, and the outer periphery of the predetermined thickness is made of a fiber/light alloy composite material 8. That is, the entire outer periphery including the outer periphery side portion of the boss portion 5 around the pin hole 3 is made of the fiber/light alloy composite material 8. Further, in the plain woven fabric 7, one of the warp and weft, for example, the warp, is oriented in a direction parallel to the axis of the entire piston, and the other, for example, the weft, is oriented in the circumferential direction of the piston.

In the above example, the warp of the plain fabric 7 in the fiber/light alloy composite material 8 has strength against repeated loads applied to the boss portion 5 in a direction parallel to the piston axis;
It plays the role of increasing the steel properties, and the weft plays the role of suppressing the thermal expansion of the entire piston. Therefore, due to repeated loads applied to the boss portion 5, the boss portion 5
It can effectively prevent fatigue failure and cracks from occurring in the vicinity, and it can also suppress thermal expansion to prevent seizure between the piston and cylinder due to a reduction in the clearance between the piston and the inner wall of the cylinder due to thermal expansion. can also be effectively prevented from occurring.

It is desirable that the fibers used in the plain weave 7 have sufficient heat resistance to withstand the operating temperature of the piston and also have excellent strength, such as carbon fiber, boron (B), etc. ) fiber, alumina (Al ₂ O ₃ ) fiber, silicon carbide (SiC)
It is desirable to use fiber or the like. In addition, the blending ratio of fibers in the fiber/light alloy composite material 8, which is made by integrating the plain woven fabric 7 with a light alloy material, is 10 to 70% by volume.
It is desirable to keep it at a certain level. If it is less than 10% by volume, it is difficult to sufficiently achieve the desired objectives such as strengthening the boss and suppressing thermal expansion, while if it exceeds 70% by volume,
In manufacturing on an industrial scale, it is difficult to integrate fibers and light alloy materials into one composite body.

In the example shown in FIG. 2, the plain fabric 7 is embedded over the entire outer circumference of the piston, but in the piston of the present invention, the key point is to cover only the outer circumference of the piston.
It is sufficient that the plain fabric 7 is embedded continuously in the circumferential direction at least in a portion including the boss portion 5.

Next, the method for manufacturing a piston of the present invention will be described. For example, a plain woven fabric made of heat-resistant long fibers is prepared in advance, and a hollow cylindrical fiber molded body is created from this plain woven fabric. For this purpose, for example, the plain woven fabric may be wound around a cylindrical body until the desired thickness is achieved. The fiber molded body thus obtained was preheated and placed in a high-pressure casting mold for piston casting, and a light alloy molten metal was immediately poured into it.
So-called high-pressure casting is performed by applying a pressure of about 1500 kg/cm ² and preserving the pressure until the molten light alloy solidifies. By performing high-pressure casting in this manner, the light alloy molten metal fills the voids between the fibers, and the light alloy and the fibers are integrated into a composite body. Therefore, when the molten light alloy is removed from the mold after solidification, the plain weave continuous in the circumferential direction is embedded in the light alloy base material, creating a piston shape whose outer periphery is made of fiber/light alloy composite material. wood is obtained. Thereafter, the piston of the present invention can be obtained by appropriately machining or finishing the piston material.

Note that, of course, a centrifugal casting method may be used instead of the high-pressure casting method as described above.

A specific example of manufacturing the piston of this invention will be described below.

A piston (outer diameter 85 mm) for a 4-cylinder 2000 c.c. gasoline engine was prototyped as follows. That is,
First, carbon fiber (Toray Card, manufactured by Toray Industries, Ltd.) with a ratio of warp to weft of 3:1 was wound around a cylindrical body so that the warp was parallel to the central axis, and the outer diameter was 80 mm and the wall thickness was 4 mm.
A hollow cylindrical fiber molded body made of carbon fiber with a length of 60 mm and a height of 60 mm was created. The fiber density of this fiber molded product was adjusted so that the fiber volume percentage when finally composited with the aluminum alloy was 50%. Next, after preheating this fiber molded body to about 800°C, it is placed in a high-pressure casting mold for piston casting,
Immediately aluminum alloy (JIS standard AC8A)
molten metal is poured and pressurized with a pressure of 1000Kg/ ^mm2 ,
Moreover, the applied pressure was maintained until the molten aluminum alloy solidified. After solidification, it was removed from the mold and machined to form a piston.

It was confirmed that the obtained piston had high strength at the boss portion, had little thermal expansion, and was not impaired in lightness.

As is clear from the above description, the piston of the present invention has a plain weave made of heat-resistant filaments continuously embedded in the circumferential direction in at least the portion including the boss portion around the pin hole, and one of the warp and weft yarns. is oriented in the circumferential direction, and the other is oriented in a direction parallel to the axis, and the plain weave is integrated with the light alloy base material, so the boss part is smaller than conventional pistons made of light alloy material. Therefore, fatigue failure due to repeated loads applied to the boss can be effectively prevented, and since the boss has high strength, the wall thickness of the boss can be made smaller than before. As a result, it is even lighter than conventional pistons, and it is also lighter than conventional pistons with embedded struts, and is resistant to compressive force against the boss. Since the weft or warp yarns of the plain weave are oriented in the circumferential direction of the piston, thermal expansion is suppressed, which can produce various excellent effects such as preventing seizure between the piston and the inner wall of the cylinder. .

[Brief explanation of drawings]

FIG. 1 is a schematic perspective view showing an example of a conventional piston, FIG. 2 is a cutaway front view of essential parts showing an example of the piston of the present invention, and FIG. 3 is a bottom view from the direction of arrow A in FIG. It is a diagram. 3... Pin hole, 5... Boss part, 6... Base material, 7
...plain woven fabric.

Claims (1)

[Claims] 1. A piston based on a light alloy material,
At least in the area including the boss around the pin hole into which the piston pin is inserted, there is a plain woven fabric with heat-resistant long fibers as the weft and warp, one of the weft and warp being oriented in the circumferential direction of the piston, and the other being oriented in the circumferential direction of the piston. is embedded so as to be continuous in the circumferential direction of the piston in a state parallel to the axis of the piston, and the plain weave is compositely integrated with the light alloy material of the base material. Pistons for internal combustion engines. 2. The piston for an internal combustion engine according to claim 1, wherein the plain fabric made of the long fibers is embedded so as to be continuous in the circumferential direction over the entire outer periphery of the piston.