JPH10281002A - Metallic base composite reinforcing piston for internal combustion engine and manufacture therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve joining strength between a lip part made of metallic base composite material and a piston main body by forming a joint interface of the lip part and the piston main body on many recessed and projecting surfaces in a piston which constitutes the opening edge of a combustion chamber and has the lip part extending toward the inside of this opening. SOLUTION: When a metallic base composite reinforcing piston is manufactured, aluminium borate whisker is fed in distilled water at first and the distilled water is agitated till whisker is split. Next, whisker aggregate split is moved within a forming jig, the aggregate is compressed and formed and a forming body is formed. This forming body is put in a freezing chamber together with the jig and moisture in the forming body is freezed. Next, the forming body freezed is taken out from the jig, heated and dried. Subsequently, an aluminium alloy molten metal is injected within a mold of a high pressure casting device for manufacturing piston and the molten metal is solidified in a pressurizing state after this forming body is preheated and is arranged within the mold of this high pressure casting device. Thus, a metallic base composite reinforcing piston in which a lip part is combined and reinforced is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal-based composite reinforced piston for an internal combustion engine and a method of manufacturing the same, and more particularly to a metal-based composite piston having a combustion chamber used for a direct injection diesel engine or the like. The present invention relates to a metal-based composite reinforced piston reinforced with a material and a method of manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, a metal-based composite for an internal combustion engine having a metal piston body having a combustion chamber and a metal-based composite material lip forming an opening edge of the combustion chamber and projecting into the opening. A reinforced piston is known (for example, see Japanese Patent Application Laid-Open No. 4-166649).

[0003] The sharper the lip at the inlet of the combustion chamber, the more uniform the mixture of fuel and air, and the better the combustion state. However, if the lip is formed of a metal such as an aluminum alloy as in the case of the piston body, melting of the lip and generation of cracks are likely to occur, so that there is a limit to the sharpness of the lip. In order to increase the heat resistance of the lip, it is conceivable to form the lip with ceramics or the like. However, in this case, the joint strength is low due to low wettability between the ceramic of the lip portion and the metal portion of the piston body, and cracks due to thermal stress occur at the joint interface due to a difference in thermal expansion between the two. there were.

[0004] As a countermeasure, the above-mentioned publication aims to improve the heat resistance of the lip portion, improve the joining strength with the metal piston body, and reduce the thermal stress by forming the lip portion with a metal matrix composite material. It is. In order to produce a piston whose lip is reinforced with a metal-based composite material as described above, a molded body (preform) of ceramic fiber or the like serving as a reinforcing material of the composite material was previously formed, and the molded body was arranged. In a mold, the piston body is cast while impregnating the molded body with a molten metal of a metal such as an aluminum alloy for the piston body by a high-pressure casting method or the like.

However, at the time of this casting, as shown schematically in FIG. 1, various particles are generated at a high temperature in the molten metal M. The generated particles P act as a body and accumulate along the outer surface S of the formed body. Then, when the deposition concentration of the particles P increases, there is a problem that the joining strength at the joining interface S between the metal composite material lip portion V and the metallic piston main body M is significantly reduced.

[0006]

SUMMARY OF THE INVENTION Accordingly, the present invention is directed to a metal matrix composite for an internal combustion engine in which the strength of the joint between the lip portion and the main body is increased by reducing the concentration of the metal when the reinforcing material is impregnated with the molten metal. It is an object of the present invention to provide a reinforced piston and a method for manufacturing the same.

[0007]

According to a first aspect of the present invention, there is provided a metal piston body having a combustion chamber opened to a head, and an opening edge of the combustion chamber, which is formed into the opening. A metal-based composite reinforced piston for an internal combustion engine having a protruding metal-based composite material lip portion, wherein a joining interface between the metal-based composite material lip portion and the metal piston body is formed of a number of uneven surfaces. And a metal-reinforced composite piston for an internal combustion engine.

According to a second aspect of the present invention, there is provided a metal piston body having a combustion chamber opened to a head, and a metal matrix composite material forming an opening edge of the combustion chamber and projecting into the opening. In the method for manufacturing a metal-based composite reinforced piston for an internal combustion engine having a lip portion, a molded body of the reinforcing material for the composite material is arranged in a mold, and the molten metal for the piston body is poured into the mold. When casting the piston body while impregnating the melt with the molten metal in the molded body, the volume of the molded body is set to a minimum volume necessary for forming the lip portion, for an internal combustion engine. It is also achieved by a method for manufacturing a metal matrix composite reinforced piston.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The manufacturing process of a piston according to the present invention is the same as that of the prior art. A molded body of a reinforcing material such as ceramic fiber is formed, and aluminum is formed by a high-pressure casting method or the like in a mold in which the molded body is placed. The piston body is cast while the molded body is impregnated with a molten metal such as an alloy. However, the first invention differs from the prior art in that the interface between the lip and the main body is made up of a number of uneven surfaces, so that the outer surface of the reinforcing material molded body corresponding to the shape of the lip also corresponds to this. Is formed as a roughened uneven surface.

Further, the second invention is characterized in that the volume of the molded body is set to a minimum volume necessary for forming the lip. Referring to FIG. 1, the concentration of the deposit P captured on the outer surface of the molded body by the filtering action of the molded body during the impregnation of the molten metal into the molded body depends on the amount of molten metal flowing into the molded body, that is, the volume of the molded body, that is, the lip portion volume V It is proportional to the outer surface of the formed body to be the deposition surface, that is, inversely proportional to the area S of the final bonding interface.

In the first aspect of the present invention, since the bonding interface has a structure having a large number of uneven surfaces as described above, the area of the bonding interface can be significantly increased, thereby significantly reducing the concentration of the volume. Can be. The bonding interface composed of a large number of uneven surfaces according to the first invention can be easily formed, for example, by forming the outer peripheral surface of the molded body into a gear-shaped zigzag contour as shown in FIG.

In the second aspect of the present invention, the volume of the compact can be reduced by reducing the volume of the compact. Hereinafter, the present invention will be described in more detail with reference to more specific examples.

[0013]

【Example】

Example 1 A metal-based composite reinforced piston according to the first invention was manufactured. First, aluminum borate whiskers (manufactured by Shikoku Chemicals Co., Ltd., diameter: 0.5 to 1 μm, length: 10 to 30 μm)
m) was put into distilled water and stirred with a propeller until the whiskers were sufficiently defibrated.

Next, the defibrated whisker aggregate containing water was transferred into a molding jig and compression-molded to obtain a molded body having a gear-shaped contour shown in FIG. 2 and a height of 15 mm. The gear has a distance r ₁ = 34 mm from the center to the top of the gear and a distance r ₂ = 27 mm from the bottom of the gear valley, and the slope between the top and the bottom of the gear is straight. The molded body was put together with the jig in a freezer maintained at -50 ° C, and held until the moisture in the molded body was sufficiently frozen.

The frozen compact was taken out of the jig, heated by a heater and dried sufficiently. As a result, a molded article in which aluminum borate whiskers were randomly oriented at a volume ratio of 25% was obtained. Preheat this compact to 600 ° C,
After being placed in the mold of a high pressure casting machine for piston production,
A molten metal of JIS standard AC8A aluminum alloy at 800 ° C. is poured into the mold, and about 1000 k
Pressure was applied at a pressure of gf / cm ² , and this pressurized state was maintained until the molten metal was completely solidified.

After the molten metal was completely solidified, the solidified body was removed from the mold with a knockout pin. As a result, a metal-based composite reinforced piston whose lip was compositely reinforced with aluminum borate whiskers was obtained. Example 2 A metal-based composite reinforced piston was manufactured according to the second invention.

The shape of the molded body is 60 mm in outer diameter and 30 m in inner diameter.
A metal-based composite reinforced piston was produced under the same conditions as in Example 1 except that a hollow cylinder having a height of m and a height of 15 mm was used. [Comparative Example] For comparison, the shape of the molded body was 60 m in outer diameter.
A metal-based composite reinforced piston was produced under the same conditions as in Example 1 except that the solid cylinder was m and a height of 15 mm.

With respect to the pistons manufactured in Examples 1 and 2 and Comparative Example, the bonding interface strength between the lip portion and the piston body at 350 ° C. was measured. Table 1 compares the measurement results with the shape, volume, and surface area of the molded article (lip).
Shown in

[0019]

[Table 1]

As shown in Table 1, in the first embodiment, according to the first invention, the joining interface (outer peripheral surface) of the lip portion and the piston body is formed into a gear shape having a large number of uneven surfaces, thereby joining. As a result of an increase in the area of the interface and a decrease in the concentration of deposits at the interface, the bonding interface strength was remarkably improved from 40 MPa to 75 MPa as compared with the comparative example in which the volume of the molded body was equal and the surface area was small.

In the second embodiment, the volume of the molten metal passing through the outer surface of the molded body acting as a filter is reduced by reducing the volume of the molded body for forming the lip in accordance with the second invention. As a result of the decrease in the deposit concentration at the joint interface with the main body, the joint interface strength is still 40% as compared with the comparative example in which the surface area of the molded body is equal and the volume is large.
It was remarkably improved from MPa to 75 MPa.

In the hollow cylindrical shape of the second embodiment, FIG.
And based on the following formula, the ratio of the volume / surface area of the molded body can be set to be the minimum necessary for forming the lip. Molded product volume / molded product surface area = (r ₂ −r ₁ ) h / 2
[(R ₂ −r ₁ ) + h] Here, r ₁ = outer diameter, r ₂ = inner diameter, and h = height.

FIG. 4 shows another embodiment for reducing the volume of the compact according to the second invention. In other words, in the case where not only the lip portion but also the wear ring portion is compositely reinforced by the metal composite material, when placing the reinforcing material molded body in the mold at the time of casting,
Conventionally, as shown in FIG. 4A, a molded body A for the lip portion and a molded body B for the ring-resistant part are arranged in a mold as one set.
On the other hand, as shown in FIG.
Is set as a separate set, the volume of the molded product A for lip portion can be reduced.

[0024]

As described above, according to the present invention,
The present invention provides a metal matrix composite reinforced piston for an internal combustion engine, in which the strength of the joint between the lip portion and the main body is increased by reducing the deposition concentration at the time of impregnation of the molten metal into the reinforcing material molded body, and a method for manufacturing the same.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing a joint between a metal-based composite material lip and a metal-made piston main body of a metal-based composite reinforced piston.

FIG. 2 is a plan view showing a gear-shaped reinforcing material molded body according to the first invention.

FIG. 3 is (1) a perspective view and (2) a plan view showing a hollow cylindrical shaped reinforcing material molded body according to the second invention.

FIG. 4 is a cross-sectional view showing an embodiment (2) in which the volume of a reinforcing material molded body is reduced according to the second invention, in comparison with a conventional example (1).

[Explanation of symbols]

M: molten metal (metal piston body) V: molded body (metal composite material lip portion (area)) P: generated particles S: outer surface of molded body (area of lip portion / piston body joint interface (area)) A: Reinforcement molded body for lip part B: Reinforcement molded body for wear ring

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI F02F 3/00 F02F 3/00 G 302 302A 302B

Claims (2)

[Claims] 1. A metal for an internal combustion engine, comprising: a metal piston body having a combustion chamber opened to a head; and a lip made of a metal-based composite material forming an opening edge of the combustion chamber and projecting into the opening. A metal-based composite reinforced piston for an internal combustion engine, wherein a joint interface between the metal-based composite material lip portion and the metal piston body comprises a number of uneven surfaces. 2. A metal for an internal combustion engine having a metal piston body having a combustion chamber opened to a head, and a lip made of a metal matrix composite material forming an opening edge of the combustion chamber and projecting into the opening. In a method of manufacturing a base composite reinforced piston, a molded body of the reinforcing material for the composite material is disposed in a mold, and a molten metal for the piston body is poured into the mold and the molten metal is poured into the molded body. A method for manufacturing a metal-based composite reinforced piston for an internal combustion engine, wherein the volume of the molded body is reduced to a minimum volume necessary for forming the lip portion when the piston body is cast while being impregnated.