JP2850540B2 - Reentrant piston and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reentrant piston having a lip portion which tapers radially inward and forms a central opening on the upper surface of a combustion chamber formed in a piston head, and a method of manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, as a combustion chamber device of a direct injection type diesel engine, there is one disclosed in Japanese Utility Model Laid-Open No. 65333/1985. In the combustion chamber device, a combustion chamber is formed at the top of a piston, and an annular heat insulating material is cast into the upper end wall surface of the combustion chamber. With this combustion chamber device, in the compression stroke, the heat insulating material is maintained at a considerably higher temperature than the other wall surfaces of the combustion chamber, and the ignition of the air-fuel mixture occurs early around the heat insulating material, thereby shortening the ignition delay, and It is intended to prevent a diesel knock and obtain a combustion chamber having durability and mass productivity.

An aluminum piston having an insert made of a different material is disclosed in Japanese Patent Publication No. 60-25619. The aluminum piston disclosed in this publication has an insert of a different material at a high load position, and the insert has an open recess filled with aluminum of the piston body. The aluminum piston has an average pore diameter of 3 to 200 μm, a layer continuing from the surface of the open pores has a thickness of at least 20 times the average pore diameter, and the porous layer is pressed in a molten state over the entire thickness of the layer. The piston body is completely filled with aluminum. Further, the thickness of the porous layer is 80 to 10 of the pore diameter.
It is 0 times.

[0004]

By the way, in the combustion chamber of the reentrant piston, the squish flow and the squish flow are formed by making the tip of the lip at the entrance of the combustion chamber, that is, the opening of the combustion chamber sharp, that is, the radius of curvature of the tip is made small. The turbulence of the reverse squish flow is increased, the mixing of the fuel and air is made uniform, and the combustion state is improved. However,
With a conventional aluminum piston, the thermal load applied to the lip that constitutes the combustion chamber causes problems such as melting of the lip and cracks. The limit was about 1.5R.

When a metal piston such as aluminum having a reentrant type combustion chamber is formed, a lip portion of an opening of the combustion chamber is made of ceramics, and heat resistance and deformation resistance of the edge portion are secured. In this case, due to poor wettability between aluminum and ceramics,
The two cannot be firmly bonded to each other, and when subjected to repeated thermal stress due to the difference in the coefficient of thermal expansion, a phenomenon occurs such that cracks and cracks occur at the boundary between the two.

[0006] The above-mentioned problems are caused, for example, by using a heat-resistant alloy such as a niresist as a base for forming the tip of the lip, or a lip made of a heat insulating material such as a combustion chamber device disclosed in Japanese Utility Model Application Publication No. A similar problem occurred when the ring was cast. In the combustion chamber device, since a lip ring is cast into the piston head portion, excessive stress is generated during operation of the engine or a large amount of backlash is generated between the piston head portion and the lip ring, and a lip ring is generated. It is the biggest bottleneck in strengthening the department. Furthermore,
If the coefficient of thermal expansion of the lip ring is large, a large thermal stress is generated due to a temperature difference generated in the combustion chamber, which also causes the combustion chamber to be broken.

An aluminum piston having an insert made of a different material disclosed in Japanese Patent Publication No. Sho 60-25619 is pressure cast by inserting a porous body at a position where heat and mechanical load are high. It is. By the way, in order to strengthen the squish flow, it is desired to sharpen the edge of the lip forming the opening of the combustion chamber. For that purpose, the heat resistance of the lip is an important requirement. However, it is considered difficult to ensure high heat resistance of the lip portion in the piston made of the porous material and aluminum disclosed in the above publication.

[0008] An object of the present invention is to solve the above-mentioned problems, and a tip of a lip around a combustion chamber opening formed in a piston head is formed of reactive sintered ceramics.
A ceramic whisker preform is arranged on the outer periphery of the reaction-sintered ceramics, and then the pores of the whisker molded body are impregnated with molten aluminum alloy to form a composite, and further, an aluminum alloy head body is formed on the outer periphery of the composite. In addition, the shrinkage of the reaction sintered ceramic during sintering is almost the same level as the shrinkage of the whisker molded body, so that the reaction sintered ceramic and the whisker molded body can be easily sintered to form an integrated structure. It is an object of the present invention to provide a reentrant piston having a sharpened tip portion of a lip portion so as to prevent the tip portion from being melted even at a high temperature, thereby suppressing generation of HC and particulates, and a method of manufacturing the same.

[0009]

The present invention is configured as follows to achieve the above object. That is,
The present invention relates to a reentrant piston having a lip portion that tapers inward in the radial direction to form a loop-shaped opening on the upper surface of a cavity formed in a piston head, and has a porosity of 15% or more having high temperature strength with high heat resistance. A tip portion of the lip portion made of a reaction sintered ceramic of
The present invention relates to a composite made of ceramic and metal having a volume ratio of 60% or less and joined to the outer periphery of the tip, and a reentrant piston having a head body made of metal joined to the outer periphery of the composite.

In this reentrant piston, the ceramic of the composite is a ceramic whisker, and the metal of the composite, the ceramic of the tip portion, the metal of the head body, and the ceramic of the composite are three-dimensionally. The complex and the tip, and the head body, and the complex are joined together.

In this reentrant piston, a thin film layer made of dense ceramic is formed on the surface of the reaction sintered ceramic at the tip.

Alternatively, the present invention provides a step of producing a first molded body with a slurry containing silicon powder as a main component, a step of arranging the first molded body in a center of a cavity of a mold having a porous body on a bottom surface, A step of injecting a slurry containing ceramic whiskers or ceramic particles into the mold and absorbing and solidifying the slurry to produce a composite molded body in which the second molded body is joined to the first molded body; Baking in a gas atmosphere to convert silicon of the first molded body into a reaction sintered ceramic and slightly sintering the ceramic of the second molded body into a sintered body; And a step of impregnating the aluminum alloy melt with the molten aluminum alloy.

Alternatively, the present invention provides a step of injecting a slurry containing ceramic whiskers or ceramic particles into a cavity of a rotating cylindrical porous mold, and depositing the slurry on the porous mold to form a first molded body. Forming, injecting a slurry containing silicon powder as a main component into the inside of the first compact, solidifying the slurry by water absorption, and adding a second slurry to the first compact.
A step of preparing a composite molded body in which the molded bodies are joined, firing the composite molded body in a nitrogen gas atmosphere to convert silicon of the first molded body into a reaction sintered ceramic,
The present invention relates to a method for manufacturing a reentrant piston, comprising: a step of slightly sintering a ceramic of a formed body to form a sintered body; and a step of impregnating a pore portion of the sintered body with a molten aluminum alloy.

In the method of manufacturing a reentrant piston, after firing the composite molded body in a nitrogen gas atmosphere, the composite molded body is immersed in an organic silicon polymer liquid to adhere the organic silicon polymer, and then the organic silicon polymer is thermally decomposed. Thus, a dense ceramic thin film layer is formed on the surface.

[0015]

The reentrant piston and the method of manufacturing the same according to the present invention are constructed as described above, and operate as follows. That is, this reentrant piston is rich in heat resistance, has high-temperature strength, and has a porosity of 15%.
A composite formed at the tip of a lip portion made of the above reaction sintered ceramics and bonded around the tip made of ceramic and metal having a volume ratio of 60% or less, and a metal bonded around the composite The sintering rate of the reaction-sintered ceramic during sintering is almost the same as that of the whisker compact, and the reaction-sintered ceramic and the whisker compact are easily sintered. integrated structure is configured, therefore the tip portion can be formed sharply up to about 0.5 R, to increase the turbulence of the squish flow and the reverse squish flow, mixing of fuel and air is made uniform, NO _X, A good combustion state in which the generation of HC, smoke, and the like is suppressed.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a reentrant piston according to the present invention and a method for manufacturing the same will be described below with reference to the drawings. FIG. 1 is a schematic sectional view showing an embodiment of a reentrant piston according to the present invention, and FIG. 2 is an enlarged sectional view of a portion A in FIG.

According to the present invention, as shown in FIG. 1, a lip portion 3 is formed on a top surface of a cavity which is a combustion chamber 1 formed in a piston head 2 and has a loop-shaped opening 4 extending inward in a radial direction to form a tapered shape. In particular, the present invention relates to a reentrant type piston, in which the piston head 2 is formed sharply by securing the heat resistance of the tip portion of the lip portion so as to enhance the squish flow and the reverse squish flow. And a composite body 6 made of ceramics and metal joined to the outer periphery of the tip 5 and a head body 7 made of metal joined to the outer periphery of the composite 6. is there.

In this reentrant type piston, as shown in FIG. 2, the tip 5 of the lip 3 is made of reaction sintered ceramics 9 having high heat resistant high temperature strength and porosity 8 having a porosity of 15% or more. A composite body 6 joined to the outer periphery of the tip 5 made of a ceramic 10 and a metal 11 having a volume ratio of 60% or less, and further having a head body 7 made of a metal 12 joined to the outer periphery of the complex 6 It is.
In FIG. 2, a groove 15 is formed on the outer peripheral surface of the tip 5 along the circumferential direction.
Is formed, and the complex 6 is inserted into the groove 15, so that the tip 5 and the complex 6 are further strongly connected structurally.

Ceramics 1 constituting part of composite 6
Reference numeral 0 denotes a ceramic sintered body obtained by slightly sintering a ceramic whisker such as silicon nitride (Si ₃ N ₄ ) or silicon carbide (SiC) or a slurry containing ceramic particles such as silicon nitride or silicon carbide to such an extent that pores remain. The metal 11 impregnated in the pores of the ceramics 10 of the composite 6 is the same metal as the metal constituting the head main body 7, and here is an aluminum-based aluminum alloy. The metal 11 of the composite 6 and the ceramics 9 of the tip 5 of the lip 3 are entangled three-dimensionally, and the composite 6 and the tip 5 are joined. Further, the metal 12 of the head body 7
The ceramics 10 of the composite 6 are intertwined with the ceramics 10 in a three-dimensional manner, and the composite 6 and the head body 7 are connected.

Further, in this reentrant piston, a thin film layer 13 made of dense ceramic is formed on the surface 14 of the reaction sintered ceramic 9 at the tip 5 of the lip 3. This thin film layer 13 is, for example,
An organic silicon polymer solution such as a polycarbosilane solution or a polysilazane solution diluted with toluene is applied to the surface 14 of the reaction-sintered ceramic 9, and the organic silicon polymer is heated at 900 ° C.
Can be formed by thermal decomposition in nitrogen gas. By forming the ceramic thin film layer 13 on the surface 14 of the reaction sintered ceramics 9, the pores 8 are closed on the surface of the tip 5, and the strength and the thermal conductivity of the tip 5 can be improved.

Next, an embodiment of a method for manufacturing a reentrant piston according to the present invention will be described. The method of manufacturing the reentrant piston includes a step of producing a first molded body with a slurry containing silicon powder as a main component, a step of arranging the first molded body in a center of a cavity of a mold having a porous body on a bottom surface, A step of injecting a slurry containing ceramic whiskers or ceramic particles into the mold and absorbing and solidifying the slurry to produce a composite molded body in which the second molded body is joined to the first molded body; Baking in a gas atmosphere to convert silicon of the first molded body into a reaction sintered ceramic and slightly sintering the ceramic of the second molded body into a sintered body, and pores of the sintered body And a step of impregnating the portion with a molten aluminum alloy.

The method for producing the reentrant piston will be described in detail. As a step of producing a first molded body using a slurry containing silicon powder as a main component, an average particle diameter of 10 μm is used.
Then, water and a peptizer were added to the silicon Si powder of m, and mixed by a ball mill for 24 hours to obtain a slurry A. Inner diameter φ by slip casting using the slurry A
A ring-shaped first molded body having a diameter of 36 mm and an outer diameter of 50 mm and having grooves 15 (see FIG. 2) formed along the outer periphery was produced. On the other hand, as a step of preparing a slurry containing ceramic whiskers or ceramic particles, similarly, water and a peptizer were added to silicon nitride whiskers and mixed to prepare a slurry B containing silicon nitride whiskers.

Next, the first compact is placed on a gypsum mold, which is a porous body, and a solid cylinder having an inner diameter of 70 mm and a height of 50 mm centering on the first compact is converted to a gypsum mold. It was placed upright. Slurry B into this cylinder
Was injected, water was absorbed from the slurry B, and solidified, and the core was removed. As a result, a first molded body composed only of silicon particles was formed inside, and a second molded body composed of ceramic whiskers was formed outside the first molded body. That is, a composite molded body in which the first molded body and the second molded body were integrally joined was produced. Such a forming method is disclosed in, for example, Japanese Patent Application No. Hei.
-246328 and the like.

After the composite molded body is dried, the composite molded body is fired at a temperature of 1400 ° C. or less in a nitrogen gas atmosphere to convert silicon of the first molded body into reactive sintered ceramic and to form the second molded body. The whisker ceramic body was fired to a degree that the whisker ceramic was slightly sintered into a state in which pores were present, to obtain a sintered body. That is, a sintered body composed of the reaction sintered ceramic part and the whisker ceramic preform part was produced.

Next, the surface of the portion made of the reaction sintered ceramic is immersed in a polycarbosilane solution diluted with toluene, which is an organic silicon polymer solution, to apply the organic silicon polymer to the surface. The organosilicon polymer is thermally decomposed in an atmosphere to form a dense ceramic thin film layer 1 on the surface of the reaction sintered ceramic portion.
3 (see FIG. 2).

Next, a sintered body composed of a reaction sintered ceramic and a sintered body of whisker ceramics is put into a crucible for forming the piston head 2 and Al is pressed under high pressure.
-Metal alloy melt (hereinafter referred to as "Metal alloy melt")
Then, the molten aluminum alloy was impregnated into pores formed in the whisker ceramic preform portion, and the sintered body impregnated with the aluminum alloy was cut to produce a piston head 2 of a reentrant type piston. Therefore, this piston head 2 was able to obtain a structure in which the three components of reaction sintered ceramics, ceramic whisker preform, and aluminum alloy were integrated.

Another embodiment of the method for manufacturing a reentrant piston according to the present invention will be described. This method of manufacturing a reentrant piston includes a step of injecting a slurry containing ceramic whiskers or ceramic particles into a rotating cylindrical porous mold cavity, and depositing the slurry on the porous mold to form a first molded body. Forming,
A step of injecting a slurry containing silicon powder as a main component into the inside of the first molded body and solidifying the slurry by water absorption to produce a composite molded body in which a second molded body is joined to the first molded body; Baking the body in a nitrogen gas atmosphere to convert silicon of the first compact into a reaction-sintered ceramic and slightly sintering the ceramic of the second compact into a sintered body; In which the pores are impregnated with a molten aluminum alloy.

The method of manufacturing the reentrant piston of the above embodiment will be specifically described. The slurry A and the slurry B manufactured in the above embodiment are used. The plaster mold as a cylindrical porous mold has a radial thickness of 50 mm and an inner diameter of 70 m.
m, an outer diameter of 170 mm and a medium thickness of 60 mm were formed into a donut-shaped mold, and both sides of the cavity, that is, the hole, were sealed with a rubber mold. At the center of the rubber mold, a hole having a diameter of 10 mm is formed, and constitutes a slurry inlet capable of supplying a slurry. While rotating the gypsum mold, a predetermined amount of slurry B containing ceramic whiskers or ceramic particles is injected from the slurry injection port. As such a molding method,
For example, Japanese Patent Application No. 2-246 filed with the present applicant.
No. 328 and the like.

The first molded body is formed by depositing the slurry on a gypsum mold. Before the first molded body is completely solidified, silicon powder is mainly contained inside the first molded body. The slurry A is poured, and the slurry A is solidified by absorbing water and the first
A composite molded body in which the second molded body is joined to the molded body, that is, a composite molded body having a continuously changing composition composed of slurry A, a mixture of slurry A and slurry B, and slurry B in the radial direction is produced. Will be.

After the composite molded body has been dried, the composite molded body is fired at a temperature of 1400 ° C. or less in a nitrogen gas atmosphere to convert silicon of the first molded body into reactive sintered ceramics and to form the second molded body. The whisker ceramic body was fired to a degree that the whisker ceramic was slightly sintered into a state in which pores were present, to obtain a sintered body. That is, a sintered body composed of the reaction sintered ceramic part and the whisker ceramic preform part was produced.

Next, the surface of the portion made of the reaction-sintered ceramics is immersed in a polycarbosilane solution diluted with toluene, which is an organic silicon polymer solution, to apply the organic silicon polymer to the surface. The organosilicon polymer is thermally decomposed in an atmosphere to form a dense ceramic thin film layer 1 on the surface of the reaction sintered ceramic portion.
3 (see FIG. 3) was formed.

Next, a sintered body composed of a reaction sintered ceramic and a sintered body of whisker ceramics is put into a crucible for forming the piston head 2 and is subjected to Al under high pressure.
-Metal alloy melt (hereinafter referred to as "Metal alloy melt")
Then, the molten aluminum alloy was impregnated into pores formed in the whisker ceramic preform portion, and the sintered body impregnated with the aluminum alloy was cut to produce a piston head 2 of a reentrant type piston. Therefore, this piston head 2 was able to obtain a structure in which the three components of reaction sintered ceramics, ceramic whisker preform, and aluminum alloy were integrated.

[0033]

The reentrant piston and the method of manufacturing the same according to the present invention are configured as described above.
It has the following effects. That is, the reentrant piston according to the present invention has a heat-resistant, high-temperature strength in a reentrant piston having a lip portion that tapers inward in the radial direction to form a loop-shaped opening on the upper surface of the cavity formed in the piston head. Porosity 1
A composite part joined to the outer periphery of the tip part made of ceramic and metal having a volume ratio of 60% or less, and a metal joined to the outer periphery of the composite part; The head body of the lip is made of a reaction-sintered ceramic having excellent heat resistance, and the tip is sharpened, that is, the edge is set to 0.1 mm.
It can be formed as sharp as about 5R. as a result,
The tip of the lip does not melt even at high temperatures, maintains a sharp angle, increases the turbulence of the squish flow and reverse squish flow, makes the mixing of fuel and air uniform,
A combustion state in which the generation of particulates such as _X or HC or smoke is suppressed can be ensured.

In this reentrant piston, the ceramic of the composite is a ceramic whisker, and the metal of the composite, the ceramic of the tip portion, the metal of the head body, and the ceramic of the composite are three-dimensionally. Since the complex and the tip portion and the head body and the complex are joined to each other and intertwined, each boundary, that is, the complex between the tip portion and the intermediate portion, and the complex and the head body are subjected to thermal stress. Can be firmly joined without being affected.

In this reentrant piston, since a thin film layer made of dense ceramic is formed on the surface of the reaction sintered ceramic at the tip, pores on the surface of the tip are closed, and the tip is closed. In addition to increasing the strength of the part, heat conduction is improved, and the heat energy received at the tip is released from the tip to the composite, the head body, the piston ring, and then to the cylinder liner, and only the tip is It is possible to prevent melting and becoming a heat spot.

The method of manufacturing a reentrant piston according to the present invention comprises the steps of
Forming a molded body, arranging the first molded body in the center of a cavity of a mold having a porous body on the bottom surface, injecting a slurry containing ceramic whiskers or ceramic particles into the mold and absorbing the slurry Solidifies the first
Forming a composite molded body in which the second molded body is joined to the molded body, firing the composite molded body in a nitrogen gas atmosphere to convert silicon of the first molded body into a reaction sintered ceramic, The process comprises a step of slightly sintering the ceramics of the compact to form a sintered body, and a step of impregnating the pores of the sintered body with a molten aluminum alloy. Since the shrinkage is almost the same level as the body, the reaction sintered ceramics and the ceramic whisker molded body are easily and integrally sintered.

Alternatively, in the method of manufacturing a reentrant piston according to the present invention, a step of injecting a slurry containing ceramic whiskers or ceramic particles into a rotating cylindrical porous mold cavity, and depositing the slurry on the porous mold Forming a first molded body by mixing a slurry mainly composed of silicon powder into the inside of the first molded body, solidifying the slurry by water absorption, and joining the second molded body to the first molded body. Since there is a step of producing a composite molded article, joined molded articles having different compositions can be easily produced, and moreover, a molded article whose boundary portion is firmly joined can be formed.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an embodiment of a reentrant piston according to the present invention.

FIG. 2 is an enlarged cross-sectional view showing one embodiment of a portion A in FIG.

FIG. 3 is an enlarged sectional view showing another embodiment of a portion A in FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Combustion chamber 2 Piston head 3 Lip part 4 Opening 5 Tip part 6 Composite 7 Head main body 8 Pores 9 Reaction sintered ceramics 10 Ceramics (sintered body) 11, 12 Metal 13 Thin film layer 14 Surface 15 Groove

Continuation of the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) F02F 3/00 F02F 3/00 301 F02F 3/00 302 F02F 3/26 B22D 19/08

Claims (6)

(57) [Claims] 1. A reentrant piston having a lip formed in a top surface of a cavity formed in a piston head so as to taper inward in a radial direction to form a loop-shaped opening, and has a porosity of 15% having high temperature strength and high heat resistance. A tip portion of the lip portion made of the above reaction sintered ceramics,
A reentrant piston comprising: a composite made of a ceramic and a metal having a volume ratio of 60% or less and joined to the outer periphery of the tip; and a head body made of a metal joined to the outer periphery of the composite. 2. The ceramic of the composite is a ceramic whisker, and the metal of the composite, the ceramic of the tip portion, the metal of the head body, and the ceramic of the composite are three-dimensionally entangled with each other, and The reentrant piston according to claim 1, wherein the distal end portion, the head main body, and the complex are coupled. 3. The reentrant piston according to claim 1, wherein a thin film layer made of dense ceramic is formed on the surface of the reaction sintered ceramic at the tip. 4. A step of producing a first molded body with a slurry containing silicon powder as a main component, a step of arranging the first molded body in a center of a cavity of a mold having a porous body on a bottom surface, and A step of injecting a slurry containing ceramic whiskers or ceramic particles, solidifying the slurry by water absorption to produce a composite molded body in which the second molded body is joined to the first molded body, and firing the composite molded body to form the composite molded body. (1) a step of converting the silicon of the molded body into a reaction sintered ceramic, and slightly sintering the ceramic of the second molded body into a sintered body;
And a step of impregnating the pores of the sintered body with a molten aluminum alloy. 5. A step of injecting a slurry containing ceramic whiskers or ceramic particles into a cavity of a rotating cylindrical porous mold, a step of forming the first molded body by depositing the slurry on the porous mold. A step of injecting a slurry containing silicon powder as a main component into the inside of the first molded body and solidifying the slurry by water absorption to produce a composite molded body in which a second molded body is joined to the first molded body; Firing the body to convert the silicon of the first compact into reactive sintered ceramics and slightly sintering the ceramic of the second compact to form a sintered body, and then the pores of the sintered body Impregnating a molten aluminum alloy into the piston. 6. A dense ceramic thin film layer is formed on the surface by firing an organic silicon polymer after firing the composite molded body in a nitrogen gas atmosphere, and then thermally decomposing the organic silicon polymer. 3. The method for producing a reentrant piston according to item 1.