JP2964101B2 - Adiabatic piston head 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 composite ceramic and a method for manufacturing the same, and more particularly, to a heat insulating piston head and a method for manufacturing the same.

[0002]

[Prior art]

[0003] New ceramic materials have recently been used as component materials for cylinder liners, cylinder heads, pistons, connecting rods and the like of internal combustion engines because of their mechanical strength being equal to or superior to that of metals. It became so.

[0004] Further, a ceramic material has a heat insulating effect greater than that of a metal and a property that its mechanical strength does not decrease so much even when exposed to a high temperature. It is frequently used for parts. Although silicon nitride materials were used in pistons of early heat-insulating engines to obtain a considerable heat-insulating effect, many attempts have been made to further enhance the heat-insulating effect to improve the thermal efficiency of the heat-insulating engine. For example,
The piston of an insulated engine described in Japanese Patent Application Laid-Open No. 63-302164 is one such attempt.

FIG. 2 is a sectional view showing the structure of the piston described in the above-mentioned publication, and the structure of the piston of the conventional heat-insulated engine will be described with reference to this drawing. As apparent from FIG. 2, the piston comprises a piston head 1 and a metal piston skirt 2.

The piston head 1 has a dish-shaped base 1a at the center. At the center of the lower surface of the base 1a, a boss 1b for attaching to the piston skirt 2 is provided.
And are formed integrally with it. On the side of the boss 1b,
A depression 1c used when the piston head 1 is incorporated into the piston skirt 2 is formed. The base 1
a is made of a sintered body of silicon nitride. Reference numeral 1d denotes a piston cylinder having a flat cylindrical shape, which is also made of a sintered body of silicon nitride, and has a step portion 1e for receiving the peripheral edge of the base 1a inside. 1f is a heat insulating layer made of a material such as potassium titanate whisker and zirconia fiber. 1 g is a ceiling plate made of a thin silicon nitride sintered body.
Is bonded to the inner side of the upper portion by a CVD method.

The piston skirt 2 is made of aluminum, has a shape in which a cup is turned upside down, and is provided with a plurality of grooves 2a for fitting a piston ring at an upper end on a lateral side. . In the center of the upper plate portion 2b of the piston skirt portion 2, there is provided a hole 2c through which a boss portion 1b provided below the piston head portion 1 passes. The piston skirt 2 has a piston
A piston pin boss portion 2d for supporting the piston is provided.

[0008] The combination of the piston head 1 and the piston skirt 2 is performed first by the boss 1b of the piston head 1.
A plate-shaped heat-resistant buffer plate 3 is fitted into the neck, and a sealing material 4 made of carbon is disposed between the lower surface of the piston cylinder 1d and the upper peripheral edge of the piston skirt portion 2. At the same time, the boss portion 1b of the base 1a is The retainer ring 5 is inserted into the recess 1c of the boss 1b while pressing the piston head 1 in the direction of the piston skirt 2 by inserting the piston head 1 into the hole 2c of the skirt 2 so that the piston head 1 and the piston skirt 2 are joined together. Assemble. Reference numeral 6 denotes a heat insulating space layer formed between the piston head 1 and the piston skirt 2.

In the conventional heat insulating engine as described above, the entire piston cylinder 1d is formed to be considerably thick in order to maintain the strength of the piston head portion 1. Moreover, since the piston cylinder 1d is made of silicon nitride having high thermal conductivity, a large amount of heat generated in the combustion chamber escapes toward the metal piston skirt 2 through the piston cylinder 1d.

In the conventional piston assembly of the heat-insulating engine, a plate-shaped heat-resistant buffer plate 3 is fitted into the neck of the boss 1b of the piston head 1, and the lower surface of the piston cylinder 1d and the upper peripheral edge of the piston skirt 2 are fitted. The sealing material 4 made of carbon is disposed between the
The piston head 1 is inserted into the hole 2c of the piston skirt 2 and the retainer ring 5 is fitted into the recess 1c of the boss 1b while pressing the piston head 1 in the direction of the piston skirt 2. And the piston skirt 2 are assembled. However, since the structure is complicated, the number of assembling steps is increased, and the parts here are required to have high dimensional accuracy.

Further, in order to secure the strength of the upper surface of the piston, the ceiling plate 1g made of a thin silicon nitride sheet is required.
It is necessary to increase the wall thickness of the heat sink, thereby increasing the heat capacity of this portion and lowering the heat insulation.

In addition, there is a contact point between materials having different coefficients of thermal expansion, such as a piston cylinder 1d and a heat insulating layer 1f in contact therewith. This is the weak point of the heat insulation engine.

[0013]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned drawbacks, and an object of the present invention is to provide a heat-insulated engine having a piston structure which is thin even if the piston cylinder is formed thin. An object of the present invention is to provide a heat-insulating piston head in which strength is not reduced, heat insulation is sufficiently maintained, the number of parts is reduced, and breakage due to a difference in thermal expansion coefficient is minimized, and a method of manufacturing the same.

[0014]

SUMMARY OF THE INVENTION In order to achieve the above-mentioned objects, the present invention provides an insulated piston having a piston head portion made of a heat insulating material on an upper portion of a metal piston skirt portion. Wherein the piston head has a cup-shaped crown portion made of dense ceramics, the crown portion has fine pores of 10 vol% or more, and ceramic whiskers or particles are dispersed therein. A heat-insulated piston head characterized by being filled with a porous ceramic set as described above, a dense silicon nitride film is applied to the surface of the filled portion, and the filled portion is closely adhered to a crown portion. In addition, in order to manufacture this insulated piston head, ceramic particles or whiskers are added to the organosilicon polymer. Additionally, a step of kneading, the steps of forming internal pressure, by filling the dense material container this is heated below the temperature at which densification of the filling unit is started,
A step of converting the organic silicon polymer into ceramics, and a step of attaching an organic silicon polymer to the surface of the filling portion, and then performing a heat treatment to convert the same into a ceramic film. A manufacturing method is provided.

[0015]

Next, an embodiment of the present invention will be described in detail with reference to the drawings.

An organic silicon polymer, polysilazane;
A composition composed of ceramic particles or plastic whiskers is kneaded, and the mixture is pressurized and filled into a dense cylindrical or cup-shaped ceramic container.
Next, the organosilicon polymer is converted into amorphous ceramics at a temperature lower than the temperature at which the kneaded substance contained in the container is dissolved and densified.

In such a process, when the kneaded substance pressurized and filled in the ceramic container is sintered, the dimensional shrinkage is remarkably small at about 1% or less, so that the shape after molding is substantially maintained even after sintering. In addition, a structure integrated with the surrounding dense cylindrical or cup-shaped ceramic container is obtained.

Example 1 The polysilazane was diluted with toluene, and a silicon nitride whisker was added thereto to a concentration of about 60% by volume, followed by kneading in a nitrogen atmosphere to obtain an intermediate composition. This is filled in a cup-shaped crown portion formed of dense silicon nitride and constituting a piston head portion, and is pressed and molded at a pressure of about 0.2 ton / cm ² . Next, this is placed in an ammonia atmosphere at 80
By heating at 0 ° C., the intermediate composition was converted into ceramics to form a ceramic sintered body. Thereafter, polysilazane is applied to the surface of the ceramic sintered body,
By firing in an ammonia atmosphere, polysilazane was converted into dense silicon nitride to form a dense ceramic thin layer.

When the cross section of the piston head formed in this manner is closely inspected using an SEM or the like, no clear gap is formed between the crown formed in the cup shape and the sintered body. . Fine pores having a volume ratio of about 10% or more are uniformly formed inside the sintered body.

FIG. 1 shows a state in which the piston head thus obtained is assembled as an adiabatic piston.

This adiabatic piston has a piston head 1
And a piston skirt 20 made of metal.

The piston head 10 has a heat insulating material holding portion 11a having a shallow cup shape and a crown portion 11 having a boss 11b formed at the center of the lower surface of the heat insulating material holding portion 11a. The outer diameter of the heat insulating material holding portion 11 a of the crown portion 11 is the same as the outer diameter of the piston skirt portion 20. Inside the heat insulating material holding portion 11a, several shallow grooves 11c are formed all around.
Are formed. A hole 11d is provided at the center of the boss 11b. The crown portion 11 is integrally formed of a dense ceramic, for example, a ceramic sintered body obtained by compressing and sintering Si3N4 fine powder.

A porous ceramic sintered body 12 is filled inside the heat insulating material holding portion 11a, and a dense ceramic thin layer 14 is applied thereon. The ceramic sintered body 12 sufficiently penetrates into the plurality of grooves 11c and is in close contact with the inner surface of the heat insulating material holding portion 11a including the grooves 11c.

A hollow 15 serving as a combustion chamber is formed on the upper surface of the dense ceramic thin layer 14.

The piston skirt portion 20 is made of aluminum similarly to the conventional one as described above, has a shape like an inverted cup, and has, at the upper end on the outer side surface thereof, several lines for fitting a piston ring. A groove 21 is provided. A hole 23 is provided in the center of the upper plate portion 22 of the piston skirt portion 20. A piston pin boss portion 2 for supporting a piston pin is provided inside the piston skirt portion 20.
4 are provided.

Example 2 Polysilazane was diluted with toluene, and this was diluted to about 20 vol.
% Aluminum titanate powder and about 40 vol% silicon nitride powder, and kneaded in a nitrogen atmosphere.
An intermediate composition is obtained. This is filled in a cup-shaped crown portion formed of dense silicon nitride and constituting a piston head portion, and is pressed and molded at a pressure of about 0.2 ton / cm ² . Next, this is placed in an ammonia atmosphere at 800
The intermediate composition was converted into ceramics by heating at ℃. Thereafter, polysilazane was adhered to the surface of the ceramic sintered body, and baked in an ammonia atmosphere to convert polysilazane into dense silicon nitride, thereby forming a dense ceramic thin layer.

When the cross section of the piston head formed in this manner is closely inspected using an SEM or the like, no gap is formed between the crown formed in the cup shape and the sintered body. . Fine pores having a volume ratio of about 10% or more are uniformly formed inside the sintered body.

The same sintered body as the ceramic sintered body produced in the above two embodiments was manufactured, and the strength and thermal conductivity of this material were measured. As a result, τ _3B = 200 MPa κ = 0.003 cal / Sec. cm. ° C was obtained. As described above, the ceramic sintered body of the present application has excellent properties in strength and heat insulation.

[0029]

As described above in detail, according to the present invention, the dimensional change during sintering is extremely small, the heat conductivity is low, the strength is improved, and the heat insulation engine is improved. It is possible to form a piston head portion in which no gap is formed between the crown portion formed in a cup shape and the sintered body, so that the crown portion is formed to be thinner than the conventional one. And the structure can be simplified as compared with the conventional one, for example, the ceiling plate can be omitted.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a heat-insulating piston using a heat-insulating piston head according to the present invention.

FIG. 2 is a sectional view of a conventional heat insulating piston.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Piston head part 11 ... Crown part 11a ... The heat insulating material holding part 11b ... Boss part 11c ... Groove 11d ... Hole 12 ... Ceramic sintered body 14 ... Dense ceramic thin Layer 15 ... hollow

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Claims (5)

(57) [Claims] 1. A heat-insulating piston in which a piston head portion made of a heat insulating material is provided above a metal piston skirt portion, wherein the piston head portion has a cup-shaped crown portion made of dense ceramics. The crown portion has fine pores of 10 vol% or more, contains ceramic whiskers or particles, is filled with an amorphous porous ceramic matrix, and has a dense silicon nitride film on the surface of the filled portion. Characterized in that the filling part is closely adhered to the crown part. 2. The adiabatic piston head according to claim 1, wherein said porous ceramic contains at least one of Al, Ti and Zr in addition to Si and N. 3. A step of adding and kneading ceramic particles or whiskers to an organosilicon polymer, a step of pressurizing and filling the inside of a dense material container, and a step of compacting the filled portion. Heating below the temperature
A step of converting the organic silicon polymer into ceramics, and a step of attaching an organic silicon polymer to the surface of the filling portion, and then performing a heat treatment to convert the same into a ceramic film. Production method. 4. A method according to claim 3, wherein said organosilicon polymer is either polysilazane or polycarbosilane. 5. The method according to claim 3, wherein the ceramic particles and the whiskers contain at least one of aluminum titanate and silicon nitride.