WO2018199024A1

WO2018199024A1 - Internal-combustion engine piston, and method for manufacturing internal-combustion engine piston

Info

Publication number: WO2018199024A1
Application number: PCT/JP2018/016463
Authority: WO
Inventors: 一等杉本; 直也沖崎; 和也野々村; 助川　義寛; 高橋　智一
Original assignee: 日立オートモティブシステムズ株式会社
Priority date: 2017-04-25
Filing date: 2018-04-23
Publication date: 2018-11-01
Also published as: JP2020109257A

Abstract

Provided is an internal-combustion engine piston having a porous structure with which both adhesion to a base material and durability can be maintained, and with which low thermal conductivity and low volumetric specific heat can be achieved. Also provided is a method for manufacturing an internal-combustion engine piston. Provided is an internal-combustion engine piston characterized by comprising a base material (1) and a sintered layer (2) provided on a surface of the base material, wherein a penetration diffusion layer (4) formed by means of an insert material having a lower melting point than the base material is provided between the sintered layer and the base material. Also provided is a method for manufacturing an internal-combustion engine piston, characterized in that: a stacked body is fabricated by stacking, in this order, a base material, an insert material comprising a metal having a lower melting point than the base material, and metal powder or a metal sintered body; and a penetration diffusion layer is formed by heating the stacked body to melt the insert material, and causing the insert material to penetrate into the sintered body formed from the metal powder, or into pores in the sintered body.

Description

Piston for internal combustion engine and method for manufacturing piston for internal combustion engine

The present invention relates to a piston for an internal combustion engine and a method for manufacturing a piston for an internal combustion engine.

In order to increase the thermal efficiency that contributes to the low fuel consumption performance of an internal combustion engine, a technique for providing a heat insulating layer on the wall surface in the combustion chamber is conventionally known, and various configurations of the heat insulating layer have been proposed. As a member for an internal combustion engine provided with a heat insulating layer, for example, one described in Patent Document 1 is known. According to Patent Document 1, a heat insulating layer is provided on the surface of a member facing the engine combustion chamber, and the heat insulating layer is made of a hollow particle made of an inorganic oxide, a filler material, and a vitreous mainly composed of silicic acid. In other words, a structure is disclosed in which the vitreous material is in a non-finished state, covering the hollow particles and the filler material, and bonding. According to Patent Document 1, it is said that the hollow particles can improve the heat insulating performance of the heat insulating layer, prevent the penetration of fuel into the heat insulating layer, and maintain high heat insulating properties over a long period of time. .

By the way, since the metal and ceramics (glass) which comprise the conventional heat insulation layer have a large volumetric specific heat, the base temperature of the base material constituting the engine (the temperature of the base material when the gas temperature in the combustion chamber is the lowest) ) And the thermal responsiveness (followability) of the temperature of the combustion chamber wall surface with respect to the gas temperature decreases. When the thermal response is low, becomes a cause of increase in knocking and NO _x, the fuel combustion efficiency is lowered. Therefore, the heat insulating layer having a large volume specific heat is not provided on the entire surface of the internal combustion engine member constituting a part of the wall surface of the combustion chamber, and needs to be used in a limited range. However, in order to realize high thermal efficiency of the internal combustion engine, a heat insulating layer that can be used in a larger area is required on the combustion chamber wall surface. For this purpose, as a material constituting the heat insulating layer, in addition to low thermal conductivity, low What has a volume specific heat is calculated | required.

In order to achieve both low heat conduction and low volume specific heat, a structure in which pores are included in a solid material is considered suitable. For example, Patent Document 2 discloses a heat insulating film composed of an anodized film having a porous structure including a large number of pores, and a plurality of particles enclosed in the pores of the heat insulating film, and adjacent particles. An internal combustion engine is disclosed that includes a plurality of encapsulated particles that are encapsulated so that a gap between them becomes a gap of a preset size.

Patent Document 2 describes that the heat insulating film uses a heat insulating material having a lower thermal conductivity and a lower heat capacity per unit volume than the base material, and a heat insulating material having a hollow structure is used as the material. It is described that it is suitable.

Japanese Patent Laying-Open No. 2015-68302 JP 2012-47110 A

As described above, in order to increase the thermal efficiency of the internal combustion engine, it is desired that the heat insulating layer has both low thermal conductivity and low volume specific heat. For this purpose, it is important to provide a surface layer having a porous structure with a high porosity. is there. It is also important to ensure sufficient durability and adhesion to the base material (member of the internal combustion engine provided with the heat insulating layer). However, Patent Document 1 and Patent Document 2 described above all achieve sufficient levels for all items of porous porosity, durability, adhesion to a substrate, low thermal conductivity, and low volume specific heat. It was not a thing.

In view of the above circumstances, the present invention provides a piston for an internal combustion engine having a porous structure capable of ensuring adhesion and durability with a substrate and realizing low thermal conductivity and low volume specific heat. It aims at providing the manufacturing method of a piston.

In order to achieve the above-mentioned object according to the present invention, an insert having a base material and a sintered layer provided on the base material, and having a lower melting point than the piston base material between the sintered layer and the base material. It was set as the structure which has the osmosis | permeation diffusion layer formed with the material.

Further, the method for manufacturing a piston for an internal combustion engine according to the present invention includes a method of forming a permeation diffusion layer by using a metal having a melting point lower than that of the base material as an insert material, and the insert material permeates the pores of the sintered body. did.

ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the piston for internal combustion engines which can ensure the adhesiveness and durability with a base material, and can implement | achieve low thermal conductivity and low volume specific heat, and a piston for internal combustion engines is provided. be able to.

(A) is a perspective view which shows typically an example of the piston which concerns on this invention, (b) is the sectional view on the AA 'line of (a). (A) shows the enlarged view of the cross section of the crown surface 101 of the piston 100 which concerns on this invention, (b) is an enlarged view of the metal particle 32 which comprises the metal layer 30 of Fig.2 (a). 6 is a cross-sectional view schematically showing an example of a sintered layer constituting a piston according to Example 2. FIG. (A) is sectional drawing which shows the 1st example of the piston concerning this invention, (b) is sectional drawing which shows the 2nd example of the piston concerning this invention, (c) is 3rd of the piston concerning this invention. FIG. 6 is a cross-sectional view schematically showing an example of a sintered layer constituting a piston according to Example 3. FIG. It is a flowchart which shows an example of the manufacturing method of the sintered layer 2 used for the piston which concerns on this invention. It is a flowchart which shows an example of joining with the base material 1 and the sintered layer 2 of the piston which concerns on this invention. FIG. 10 is a flowchart showing another example of the method for manufacturing the piston according to the second embodiment. It is a figure which shows an example of a pulse electricity supply apparatus typically. (A) is a cross-sectional SEM observation photograph of a hollow particle according to Experimental Example 1, (b) is a cross-sectional SEM observation photograph of the sintered layer 2 according to Experimental Example 1, (c) is an enlarged photograph of (b), (d). Is an optical micrograph of the surface layer section including the sintered layer 2 and the permeation diffusion layer. It is a schematic diagram of the apparatus used for the thermal responsiveness evaluation test of the experiment example. (A) is a graph showing the relationship between the output of laser light and time in the thermal response evaluation test of the experimental example, and FIG. 10 (b) shows the relationship between the surface temperature of the test piece and time in the thermal response evaluation test of the experimental example. It is a graph to show.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1A is a perspective view schematically showing an example of a piston according to the present invention, and FIG. 1B is a cross-sectional view taken along the line AA ′ of FIG.

The piston 100 for an internal combustion engine according to the present invention (hereinafter also simply referred to as “piston”) has a crown surface 101 on the upper surface and a piston receiving portion 102 on the side surface. The crown surface 101 is a part which becomes a part of the inner wall of the combustion chamber, and is a part where a heat insulating layer is provided in order to improve combustion efficiency. In the present invention, a “surface layer” having both low thermal conductivity and low volume specific heat characteristics is provided on the crown surface (surface) of the piston 100. Hereinafter, this surface layer will be described in detail.

FIG. 2A shows an enlarged view of a cross section of the crown surface 101 of the piston 100 according to the present invention. As shown in FIG. 2 (a), the crown surface 101 of the piston 100 according to the present invention includes a piston base material 1 (hereinafter simply referred to as “base material”) and a firing provided on the surface of the base material 1. It has a tie layer 2.

The sintered layer 2 includes a metal layer 30 formed by bonding a plurality of metal particles and a void surrounded by a portion other than the bonded portion of the metal particles (in other words, a void formed between the metal particles). ) 31. The metal layer 30 is composed of a sintered metal in which metal particles are bonded by sintering. For convenience, the metal layer 30 and the gap 31 are collectively referred to as a parent phase 3.

FIG. 2 (b) is an enlarged view of the metal particles 32 constituting the metal layer 30 of FIG. 2 (a). As shown in FIG. 2B, it is preferable that some of the metal particles 32 are bonded together by sintering and have a neck 33. The space between the metal particles 32 can be secured by the neck 33 and the gap 31 can be formed. Further, the ratio of the voids 31 can be controlled by controlling the sintering density. A method for producing such a sintered metal will be described later.

Between the sintered layer 2 and the substrate 1, there is a permeation diffusion layer 4. The permeation diffusion layer 4 is a layer in which an insert material having a melting point lower than that of the base material is dissolved in a part of one side of the matrix 3 and is permeated and diffused, and a part of the void 31 provided in the original sintered body. Is buried by absorbing the insert material. FIG. 2A shows a structure in which the parent phase 3 exists up to the BB part. By adopting such a structure, it is possible to ensure adhesion with the base material 1 by the permeation diffusion layer 4 having a higher density than the sintered layer 2 while ensuring voids in the sintered layer 2. Therefore, it is possible to ensure adhesion and durability with the substrate, and to achieve low thermal conductivity and low volume specific heat.

Moreover, it is preferable that the base material 1 and the osmosis | permeation diffusion layer 4 contain the same metal as each main component. Specifically, the base material 1 is preferably an aluminum (Al) alloy, and the permeation diffusion layer 4 is preferably an Al alloy. In this way, by forming the base material 1 and the permeation diffusion layer 4 with the same metal, a strong solid-phase junction is formed at the interface between the base material 1 and the permeation diffusion layer 4 having a porous structure to ensure adhesion. In addition, a piston having excellent durability can be provided. Similarly, the permeation diffusion layer 4 and the sintered layer 2 preferably contain the same metal as their main component. By forming the metal layer 30 that constitutes the main part of the permeation diffusion layer 4 and the sintered layer 2 with the same metal, a solid phase bonded portion can be formed at the interface between the permeation diffusion layer 4 and the sintered layer 2 having a porous structure. It is possible to provide the sintered layer 2 which is formed to ensure adhesion and is excellent in durability.

The volume specific heat of the sintered layer 2 is preferably 1000 kJ / m ³ · K or less. The thermal conductivity is preferably 1 W / mK or less. By configuring the thermal characteristics of the sintered layer 2 in this way, the base temperature is hardly increased in the internal combustion engine. That is, the thermal responsiveness with respect to the gas temperature of the sintered layer 2 is sufficiently high, and can be instantaneously changed from a low temperature to a high temperature or from a high temperature to a low temperature in accordance with a change in the gas temperature in the combustion chamber. Thereby, even if the sintered layer 2 is applied to the entire surface of the crown surface 101 of the piston 100, higher combustion efficiency can be obtained.

In the piston 100 according to the present invention, there is no particular limitation as long as the above-described sintered layer 2 is formed on the crown surface 101 of the piston 100. As an example, the example of the location which forms the sintered layer 2 in the piston 100 is shown below.

FIG. 4A is a cross-sectional view showing a first example of the piston according to the present invention, in which a concave portion is provided on the crown surface 101 of the piston 100, and the sintered layer 2 is arranged in the concave portion.

FIG. 4B is a sectional view showing a second example of the piston according to the present invention, in which the sintered layer 2 is disposed on the entire crown surface 101.

FIG. 4C is a cross-sectional view showing a third example of the piston according to the present invention, in which a recess is provided along the shape of the crown surface 101, and the sintered layer 2 is disposed in the recess 101. is there.

As shown in FIGS. 4 (a) to 4 (c), in the pistons 100a to 100c, the place where the sintered layer 2 is formed is not particularly limited, and as shown in FIG. It may be formed, may be formed on the entire surface of the crown surface 101 as shown in FIG. 4B, and has a thickness along the surface shape of the sintered layer 2 on the crown surface 101 as shown in FIG. You may form so that may become constant.

FIG. 6A is a flowchart showing an example of a method for producing the sintered layer 2 used in the piston according to the present invention, and FIG. 6B shows the substrate 1 and the sintered layer 2 of the piston according to the present invention. It is a flowchart which shows an example of joining. First, in FIG. 6A, the metal particles 32 as the raw material of the metal layer 30 and the powder of the hollow particles 5 are mixed (S10: metal particle powder (raw material mixed powder) preparation step). Next, the mixed powder obtained in S10 is heated and sintered (S11: sintering process) to obtain a sintered body (S12). The method for sintering the mixed powder is not particularly limited as long as it is a method capable of sintering metal particles so that voids 31 are formed in the mother phase 3, but pulse current sintering, hot press sintering, Isotropic pressure sintering and cold isotropic pressure sintering are preferred. Among these, it is preferable to use pressure sintering capable of controlling the load and temperature, and the pulse current sintering method is preferable.

Pulse electric current sintering (Pulse Electric Current Sintering) is a sintering technique also called spark plasma sintering (Spark Plasma Sintering). When applying pulse current while applying pressure to the raw material mixed powder, resistance heat generation and spark discharge are generated on the powder surface, and the reaction on the powder surface is activated. As shown in FIG. It is easy to form the neck 33 at the part. Even in the case of a porous sintered body containing a large amount of voids, the metal particles can be strongly bonded at the neck 33 portion.

In the pulse current sintering method, the reaction on the powder surface is activated, so that sintering in an environment with a relatively small load is possible. By controlling the load or the amount of indentation and pressurizing, the parent phase 3 It is possible to control the ratio of the voids 31 of the above.

Subsequently, FIG. 6B will be described. In FIG. 6B, first, a piston base material is produced by casting (S13). In this casting process, for example, a rough material of a piston base material made of an Al alloy is cast by a conventional method. Subsequently, machining (land part outer diameter cutting, pin hole machining, etc.) is performed on the obtained rough material (S14). Next, an insert material having a low melting point is placed on the surface of the substrate (S14a). Next, the sintered body produced in the process shown in FIG. 6A is placed in contact with the surface of the substrate (S15).

Then, the base material and the sintered body are joined (S16). As a joining method, a technique is preferred in which the insert material is heated and melted, diffused between the sintered body and the base material, and in particular, permeated and diffused into the voids of the sintered body. Examples of the heating method include, but are not limited to, heat treatment, friction stir welding, laser welding, arc welding, and the like.

As a post-treatment after joining the sintered body and the substrate 1, a heat treatment step is performed (S17). This heat treatment is intended to remove strain generated in the joining process and make the strength uniform. For example, solution aging treatment or artificial aging treatment is performed. After the heat treatment step, finishing machining is performed as a secondary machining step (S18), and the product piston is completed (S19).

Subsequently, Example 2 will be described. This embodiment is different from the first embodiment in that the hollow particles 5 are arranged inside the matrix phase 3.

In order to obtain a sufficient low thermal conductivity, it is considered effective to increase the gap 31 of the matrix 3. However, if the gap 31 is increased too much, the strength of the matrix 3 is lowered, and the sintered layer 2 is reduced. Cannot withstand the harsh environment (temperature and pressure) in an internal combustion engine.

Therefore, in this embodiment, the hollow particles 5 are contained in the voids 31 of the matrix 3 and the voids 31 of the matrix 3 and the voids 50 of the hollow particles 5 are combined, whereby the porosity of the sintered layer 2 as a whole. The strength of the sintered layer 2 was maintained while ensuring sufficient.

FIG. 3 is a cross-sectional view schematically showing a case where the hollow particles 5 are included in the parent phase 3 as described above, and the hollow particles 5 are included in the parent phase 3. The hollow particles 5 are particles having pores (fine pores) 50 inside. A combination of the voids 31 included in the matrix 3 and the voids 50 included in the hollow particles 5 is a volume ratio of voids (hereinafter referred to as “porosity”) occupying the sintered layer 2.

In the present invention, the porosity of the entire sintered layer 2 is increased to 50% by volume by combining both the void 31 of the matrix 3 and the void 50 of the hollow particle 5.

Further, it is preferable that hollow particles 5 are also included in the permeation diffusion layer 4. If the hole 50 of the hollow particle 5 is a closed hole, an insert material does not enter and the hole is maintained as it is. Further, even if the hole 50 is an open hole, the insert material is less likely to enter compared to the gap 31, and the hole remains. As a result, the permeation diffusion layer 4 has a structure having pores and a structure having a lower porosity than the sintered layer 2.

As the hollow particles 5, various porous oxides such as silica (SiO ₂ ), alumina (Al ₂ O ₃ ), and zirconia (ZrO ₂ ) can be used, but in order to ensure the heat insulating performance of the sintered layer 2. It is preferable to use a material having a low thermal conductivity, and it is particularly preferable to use silica.

Silica has a relatively low thermal conductivity among ceramics and is a material having a relatively high strength even when hollow. Examples of the hollow particles mainly composed of silica include ceramic beads, silica airgel, porous glass, glass beads, volcanic white sand, diatomaceous earth, and processed powders thereof, but are not limited thereto.

The particle diameter of the metal particles constituting the metal layer 30 and the particle diameter of the hollow particles 5 are preferably substantially the same. When the particle diameter of the hollow particles 5 is larger than the particle diameter of the metal particles 32, the bonds between the metal particles 32 are hardly formed, and the strength of the metal layer 30 that is a sintered body may be reduced. On the other hand, when the particle diameter of the hollow particles 5 is smaller than the particle diameter of the metal particles 32, there is a possibility that the formation of the voids 31 between the metal particles 32 is hindered and a high porosity cannot be realized. Therefore, in this embodiment, the particle diameter of the metal particles 32 and the particle diameter of the hollow particles 5 are substantially the same.

Next, a method for manufacturing a piston according to the present invention will be described. As a method of forming the sintered layer 2 on the base material 1, first, the metal particles 32 and the hollow particles 5 constituting the metal layer 30 are sintered to form a sintered body in advance, and this sintered body is used as the base material. 1 and the mixed powder of the metal particles 32 and the hollow particles 5 that are the raw material powder of the sintered layer 2 are placed on the surface of the substrate 1, and the sintering of the metal particles 32 and the bonding to the substrate 1 are performed. The method of performing simultaneously is mentioned. FIG.6 (c) is a flowchart which shows another example of the manufacturing method of the piston which concerns on a present Example. In FIG. 6C, the production of the sintered body (S1 in FIG. 6A) and the joining of the sintered body and the base material (S2 in FIG. 6B) are performed simultaneously. The piston base material casting (S13) and the primary machining (S14) are the same as in FIG. 6B. An insert material for forming a permeation diffusion layer is placed on the surface of the base material 1 subjected to the primary machining process (S14a), and a mixed powder of metal particles and hollow particles 5 serving as a raw material powder for the sintered layer 2 thereon Is installed (S15 '). At this time, the insert material or the mixed powder may be powdered and placed on the surface of the substrate 1, but the powder is preliminarily formed by applying pressure to a molded body having a predetermined shape, for example, powder. The green compact may be pressed into a biscuit shape and placed on the surface of the base material 1 (piston crown surface).

Then, by applying a load from the upper part of the mixed powder and heating it, the mixed powder is sintered and at the same time the mixed powder and the piston base material are joined (S16 ′). Since the subsequent heat treatment (S17) to piston completion (S19) are the same steps as in the first embodiment, the description thereof is omitted.

In this example, the pulse current sintering method was used as in Example 1. In the pulse current sintering method, since the reaction on the powder surface is activated, it is possible to sinter in an environment where the load is relatively small, and the shape of the hollow particles can be contained without breaking. . In the present invention, by applying pulse current to the mixed powder, a metal layer (sintered metal) 30 in which the metal particles are connected to each other is formed, and the void 31 is formed in a portion other than the joint portion between the metal particles. The hollow particles 5 can be included without breaking the shape.

Further, the porosity of the sintered layer 2 is not particularly limited but is preferably 50% or more.

Subsequently, Example 3 will be described. This embodiment is different from the second embodiment in that a sealing layer 51 made of a sealing material is provided on the surface of the sintered layer 2.

FIG. 5 is a cross-sectional view schematically showing an example of a sintered layer constituting the piston according to the present embodiment.

If the fuel soaks into the gap 31 of the sintered layer 2, the fuel that contributes to combustion decreases and the combustion efficiency deteriorates. Therefore, as shown in FIG. 5, the gap 31 is sealed on the surface of the sintered layer 2 with a sealing layer 51 made of a sealing material, and the fuel soaks into the back of the sintered layer 2 (base 1 side). It is preferable to prevent this. When the sealing layer 51 is provided on the surface of the sintered layer 2, the sealing material is not only the surface of the sintered layer 2 (portion indicated by 52 in FIG. 5), but also the gap 31 (53 in FIG. 5) near the surface. The sintered layer 2 according to the present example secures the porosity of the entire sintered layer 2 with the voids 31 of the parent phase 3 and the pores 50 of the hollow particles 5. Since the sealing material does not enter the pores 50 inside the particles 5, even if a part of the void 31 of the mother phase 3 is sealed by the sealing material, the entire sintered layer 2 is sufficient. The porosity can be ensured.

Specific examples of the sealing material include, but are not limited to, polysilazane, polysiloxane, silica alkoxide, polyamide, polyamideimide, polyimide, and various resins.

According to the above configuration of the present invention, it is possible to provide a piston having an excellent thermal response characteristic and having a structure that can withstand long-term use, and assists in combustion of fuel to contribute to improvement of fuel consumption of the internal combustion engine. It also contributes to suppressing deposits and smoke emissions from the internal combustion engine.

Then, the formation method of the sealing layer 51 is demonstrated. The sealing material forming step is the step of joining the sintered body and the base material (S16 or S16 ′) in the steps of FIGS. 6B and 6C described in the first and second embodiments and the heat treatment step. (S17) or the secondary machining process (S18) is performed between the processes. According to the present invention, the sealing layer 51 may be formed before the heat treatment step (S17), may be formed before the secondary machining step (S18), or the secondary machining step (S18). It may be formed later. In these application processes, a heat treatment process may be further added to fix the applied sealing material on the piston surface. Further, the heat treatment step (S17) may also serve as drying of the sealing material after application.

As a method for forming the sealing layer 51, for example, when polysilazane is used as a sealing material, a coating solution containing a polysilazane precursor is applied to the surface of the sintered body, and dried by heating at 400 to 500 ° C. for 1 to 2 hours. By doing so, it can be formed.

[Production and evaluation of piston specimen]
A base material was prepared as if it were a piston crown surface, and test pieces having a surface layer in which the ratio of hollow particles was changed on the surface thereof were prepared (Experimental Examples 1-3, Reference Examples 1 and 2). The obtained test piece was evaluated for its sintered state, porosity and thermal responsiveness.

First, a disk-shaped test piece (diameter: 75 mm, thickness: 10 mm) was prepared using an Al alloy (JIS (Japan Industrial Standards) 4032-T6) close to the actual piston material. A recess having a thickness of 5 mm was formed.

As a raw material mixed powder constituting the sintered layer 2 (a raw material powder for the surface layer), a raw material mixed powder prepared by mixing Al particles as the metal particles 32 constituting the metal layer 30 and SiO ₂ particles as the hollow particles 5 was prepared. All particles were prepared with an average particle size of 30 μm. This raw material mixed powder was sintered by a pulse current sintering method to produce a sintered body.

FIG. 7 is a diagram schematically showing an example of the pulse energization device used in the examples. In the vacuum chamber 64, the above-mentioned mixed powder (sintered layer raw material powder 61) is placed in an annular carbon die 62, the carbon punch 63 is driven in the direction of the arrow in FIG. A pulse energization was applied to the mixed powder through 67 and the electrodes (upper electrode 65 and lower electrode 66), and the mixture was heated and sintered. During the pulse electric current sintering, the temperature, the load and the indentation amount of the carbon punch 63 were monitored.

The obtained sintered body was processed so as to have a shape with a diameter of 30 mm and a thickness of 3 mm, and placed in the recess of the aluminum alloy test piece described above. The sintered body and the aluminum alloy test piece were fixed using a restraining jig, and both were diffusion-bonded by heating in a heat treatment furnace.

The composition of the raw material powder of the sintered layers of Experimental Examples 1 to 3 and Reference Example 1, and the evaluation results of the sintered state and the porosity (P) are shown in Table 1 described later.

In this specification, Reference Example 1 uses pure aluminum having a melting point lower than that of a sintered body as an insert material in joining of sintered layers according to the present invention.

Further, Reference Example 2 is a test piece made of only an aluminum base material having no sintered layer. In Table 1, the porosity P of the sintered layer and the porosity Q of the permeation diffusion layer were calculated from the following formulas (1) and (2), respectively.

P = 100−D _m / D _i × 100 Formula (1)
Q = P × {αX + β (1-X) (2)

Here, D _m is the measured density (g / cm ³ ), and was calculated by measuring the volume and weight from a rectangular parallelepiped piece taken from the test piece. D _i is the ideal density of the bulk material does not contain pores (g / cm ^3), was determined in consideration of the content ratio of the metal particles (Al) hollow particles (SiO _2). Further, in the permeation diffusion layer in which part of the pores are filled with the insert material, α is the volume ratio of the remaining portion of the voids of the sintered body, and β is the portion of the void portion of the hollow particle remaining. Volume ratio. X is a volume ratio indicating the ratio of voids of the sintered body in the pores of the original sintered layer, and 1-X is a volume ratio indicating the ratio of voids of the hollow particles. In addition, the ratio of the void | hole in a hollow particle can be measured with the true density meter using helium gas, The average ratio of the void | hole of the hollow silica used in the present Example was 59.6%.

8A is a cross-sectional SEM observation photograph of the hollow particles according to Experimental Example 1, FIG. 8B is a cross-sectional SEM observation photograph of the sintered layer 2 according to Experimental Example 1, and FIG. FIG. 8B is an enlarged photograph, and FIG. 8D is an optical micrograph observing a cross section of the surface layer portion including the sintered layer 2 and the permeation diffusion layer. In the SEM photographs of FIGS. 8B and 8C, the white portion is Al, the gray portion is SiO ₂ , and the black portion is voids and holes. As shown in FIGS. 8B and 8C, it can be seen that in the sintered layer, the hollow silica 72 is contained in the void 73 formed between the Al particles 71 while maintaining its shape.

The sintered bodies used in Experimental Examples 1 to 3 and Reference Example 1 were made of a porous sintered body using a raw material containing 50% by volume of hollow silica so that the void ratio during sintering was 32% by volume. .

As a result, the ratio x of voids in the sintered layer was 0.59. Observation of the cross-sections of the test specimens prepared in Experimental Examples 1 to 3 confirmed that the osmotic diffusion layer was completely filled with voids but all the pores remained (α = 0 and β = 1). From this, the porosity P of the sintered layer was 54%, and the porosity of the permeation diffusion layer was 22%. The bonding temperature was 470 ° C. as the temperature at which the aluminum base material was not softened.

In Examples 1 to 3 in which an aluminum alloy powder having a melting point lower than that of aluminum was used as an insert material, a good bonding state could be secured by forming a permeation diffusion layer, whereas a reference using pure aluminum powder as an insert material In Example 1, the insert material was fixed in a sintered state without melting, and the permeation diffusion layer was not formed.

In addition, in order to evaluate the thermal response characteristics in the surface layer, a thermal response evaluation test was performed to evaluate the temperature of the surface layer using a laser heat source. FIG. 9 is a schematic diagram of an apparatus used in a thermal responsiveness evaluation test of an experimental example. As shown in FIG. 9, the evaluation apparatus irradiates a test piece 81 installed in a vacuum chamber 82 with a laser beam using a laser heat source 84, and determines the surface temperature of the test piece 81 at that time using an infrared camera. 83 is used for measurement.

FIG. 10A is a graph showing the relationship between laser light output and time in the thermal response evaluation test of the experimental example, and FIG. 10B is a graph showing the surface temperature and time of the test piece in the thermal response evaluation test of the experimental example. It is a graph which shows a relationship.

FIG. 10B shows the surface temperature at the time of laser irradiation in FIG. In FIG. 10B, the peak temperature recorded at the first laser irradiation is T ₁ , and the peak temperature recorded at the third laser irradiation is T ₃ . Laser irradiation was carried out by applying a black body paint for absorbing laser to the test piece.

The thermal response evaluation test, to simulate the First engine environment, as the peak temperature T ₁ of the aluminum test piece of Reference Example 2 provided with no surface layer, the 200 ° C. approximately close to the actual engine environmental, Laser irradiation conditions were selected. Specifically, as shown in FIG. 10 (a), an 800W laser was irradiated for 1 second and naturally cooled for 5 seconds was set as one set, and a total of 3 sets of irradiation were performed. Since the upper limit of the temperature that can be quantitatively evaluated by the infrared camera 83 is 500 ° C., when it exceeds 500 ° C., it is described as “over 500 ° C.”. In order to instantly burn the fuel at the piston crown surface, it is necessary to heat to about 400 ° C. which is sufficiently higher than the ignition point (300 ° C.) of the fuel. Therefore, in this test, a surface layer having a temperature raising effect with a peak temperature of 400 ° C. or higher was selected. The values of T ₁ and T ₃ in the thermal response evaluation tests of Examples 1 to 3 and Reference Examples 1 to 2 are also shown in Table 1.

As a result of the thermal response evaluation test, in Experimental Examples 1 to 3, both T ₁ and T ₃ were 500 ° C. or higher, whereas in Reference Example 1, the sintered layer peeled off at the joint immediately after the first laser irradiation. No result was obtained. In Examples 1 to 3, peeling of the surface layer from the test piece was not observed even after the thermal responsiveness evaluation test, and it was confirmed that the film had good adhesion.

For Experimental Examples 1 to 3 and Reference Example 1, weight specific heat was measured using a differential scanning calorimetry (DSC (Differential scanning calorimetry) method), and volume specific heat was calculated from separately measured densities. Those having a volume specific heat of 1000 kJ / m ³ · K or less were evaluated as “pass”. All were 800 kJ / m ³ · K or less, and passed. The evaluation results are also shown in Table 1.

[Production of piston and fuel efficiency evaluation]
A piston having a surface layer having the same configuration as Experimental Example 1 was manufactured by the method shown in FIGS. 6 (a) and 6 (b). The sintered body was produced in the same manner as in Example 1 by the pulse current sintering method according to the manufacturing process of FIG. 6A, and was processed into a diameter of 70 mm and a thickness of 3 mm. In accordance with the manufacturing process of FIG. 6B, primary machining (S14) is applied to the aluminum alloy piston rough material (JIS AC8A) produced in the piston casting process (S13). A recess having a diameter of 70 mm was formed. A powder that serves as an insert material is laid in the recess, a pre-sintered sintered body is placed in the recess of the piston crown surface, and the sintered body and the piston base material are sufficiently brought into contact with a restraining jig (S15), and a heat treatment furnace Was joined (S16). Thereafter, solution treatment and artificial aging treatment (S17) were performed, and a piston having a predetermined shape was fabricated by processing into a finished shape by secondary machining (S18) (S19). This piston is referred to as Experimental Example 4.

Moreover, the sealing layer formation process was implemented with respect to the piston surface after the secondary machining (S18) with respect to the piston produced by the said method. Specifically, after secondary machining (S18), polyamide imide was applied to the piston crown surface and subjected to a dry heat treatment so that voids near the surface were sealed. However, the pores originally contained in the hollow silica have a closed structure and remain as pores. This piston is referred to as Experimental Example 5.

The produced piston was subjected to an engine test to confirm fuel efficiency. In either case, the fuel efficiency was improved compared to the piston without the surface layer, but it was confirmed that the fuel consumption of Example 5 with the sealing layer was less than that of Experimental Example 4 with no sealing layer. It was. This is considered to be because, in Example 7 in which the sealing layer is provided, higher combustion efficiency can be realized by preventing the fuel from entering the voids in the surface layer. It was confirmed that the sealing layer contributes to fuel efficiency.

The above is a brief summary of the present invention.

A piston 100 for an internal combustion engine according to the present invention includes a base material 1 and a sintered layer 2 provided on the base material 1, and the base material 1 is interposed between the sintered layer 2 and the base material 1. A permeation diffusion layer was formed on the sintered body side with an insert material having a melting point lower than that of (1). By adopting such a structure, it is possible to ensure adhesion with the base material 1 after securing the voids in the sintered layer 2. Therefore, it is possible to ensure adhesion and durability with the substrate, and to achieve low thermal conductivity and low volume specific heat. In the piston 100 for an internal combustion engine according to the present invention, the metal that is the main component of the permeation diffusion layer 4 and the sintered body 2 is aluminum, and the main component of the base material is also aluminum. By adopting such a configuration, the base layer 1, the permeation diffusion layer 4 and the metal layer 30 constituting the main part of the sintered layer 2 can be composed of the same metal, and the base layer 1 and the permeation diffusion having a porous structure. It is possible to form a solid phase bonded portion at the interface between the layer 4 and the sintered layer 2 to ensure adhesion, and to make the sintered layer 2 excellent in durability.

Moreover, the piston 100 for an internal combustion engine according to the present invention includes hollow particles 5 in the sintered body 2. By adopting such a configuration, the strength of the sintered layer 2 can be increased while ensuring the porosity of the entire sintered layer 2 by combining the voids 31 in the matrix 3 and the voids 50 of the hollow particles 5. It becomes possible to keep.

In the internal combustion engine piston 100 according to the present invention, the sintered body 2 preferably has a porosity of 50% or more.

In the internal combustion engine piston 100 according to the present invention, the insert material includes at least an aluminum alloy.

Further, in the piston 100 for an internal combustion engine according to the present invention, the aluminum alloy contained in the insert material is an Al—Mg alloy.

In the piston 100 for an internal combustion engine according to the present invention, the Al—Mg alloy contained in the insert material is Al ₁₂ Mg ₁₇ .

Moreover, in the piston 100 for an internal combustion engine according to the present invention, it is preferable in terms of strength that the thickness of the permeation diffusion layer is at least twice the average particle diameter of the metal particles contained in the sintered body.

Further, in the piston 100 for an internal combustion engine according to the present invention, the porosity of the permeation diffusion layer is lower than that of the sintered body.

In the internal combustion engine piston 100 according to the present invention, the porosity of the permeation diffusion layer may be inclined.

In the piston 100 for an internal combustion engine according to the present invention, the volume specific heat of the sintered layer is 1000 kJ / m ³ · K or less, and the thermal conductivity is 1 W / mK or less.

The thickness of the sintered layer is preferably 50 μm or more and 100 μm or less.

Further, in the method for manufacturing a piston for an internal combustion engine according to the present invention, a metal having a melting point lower than that of the base material is used as the insert material, and the insert material penetrates into the pores of the sintered body to form the permeation diffusion layer. It is characterized by.

Further, the method for manufacturing a piston for an internal combustion engine according to the present invention uses a pulse current joining method when the insert material is melted and joined.

Also, the method for manufacturing a piston for an internal combustion engine according to the present invention may use an external heat source when the insert material is melted and joined.

In the method for manufacturing a piston for an internal combustion engine according to the present invention, the insert material is powder.

Further, in the method for manufacturing a piston for an internal combustion engine according to the present invention, the powder of the insert material contains an Al alloy.

In the method for manufacturing a piston for an internal combustion engine according to the present invention, Al contained in the insert material is an Al—Mg alloy.
In the method for manufacturing a piston for an internal combustion engine according to the present invention, the Al—Mg alloy contained in the insert material is Al ₁₂ Mg ₁₇ .

In the method for manufacturing a piston for an internal combustion engine according to the present invention, the insert material is a sheet-like material.

Also, in the method for manufacturing a piston for an internal combustion engine according to the present invention, the sheet material of the insert material contains an Al alloy.

As described above, it is demonstrated that the piston for an internal combustion engine according to the present invention can ensure durability and adhesion to the base material, and can realize low thermal conductivity and low volume specific heat. It was done.

In addition, this invention is not limited to the above-mentioned Example, Various modifications are included. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. Further, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Further, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

DESCRIPTION OF SYMBOLS 1 ... Base material, 2 ... Sintered layer, 3 ... Mother phase, 30 ... Metal layer, 31 ... Void, 32 ... Metal particle, 33 ... Neck, 4 ... Penetration diffusion layer, 5 ... Hollow particle, 50 ... Hole, DESCRIPTION OF SYMBOLS 51 ... Sealing layer, 52 ... Sealing material on the surface of a sintered layer, 53 ... Sealing material which penetrate | invaded the space | gap of a mother phase, 61 ... Sintered layer raw material powder, 62 ... Carbon die, 63 ... Carbon punch, 64 DESCRIPTION OF SYMBOLS ... Vacuum chamber, 65 ... Upper electrode, 66 ... Lower electrode, 67 ... Pulse power supply, 71 ... Al particle, 72 ... Hollow silica, 73 ... Air gap, 81 ... Test piece, 82 ... Vacuum chamber, 83 ... Infrared camera, 84 ... Laser heat source, 100, 100a, 100b, 100c ... piston, 101 ... piston crown surface, 102 ... piston pin receiving part

Claims

A substrate and a sintered layer provided on the surface of the substrate;
A piston for an internal combustion engine having an infiltration diffusion layer formed of an insert material having a melting point lower than that of the base material between the sintered layer and the base material.
The sintered layer and the permeation diffusion layer have pores,
The porosity P of the sintered layer represented by the following formula (1) is larger than the porosity Q of the permeation diffusion layer represented by the following formula (2). Piston for internal combustion engine.
P = 100−D m / D i × 100 Formula (1)
(D m is the measured density (g / cm 3 ), D i is the ideal density of the bulk material without pores)
Q = P × {αX + β (1-X) (2)
(Α is the volume ratio of the voids in the sintered body, β is the volume ratio of the voids of the hollow particles)
2. The piston for an internal combustion engine according to claim 1, wherein a main component of the sintered layer is a metal.
The piston for an internal combustion engine according to claim 3, wherein the metal is aluminum.
The piston for an internal combustion engine according to any one of claims 1 to 4, wherein the sintered layer includes hollow particles.
The piston for an internal combustion engine according to claim 1, wherein the porosity of the sintered layer is 50% or more.
The piston for an internal combustion engine according to claim 1, wherein the insert material includes at least an aluminum alloy.
The piston for an internal combustion engine according to claim 7, wherein the aluminum alloy is an Al-Mg alloy.
9. The piston for an internal combustion engine according to claim 8, wherein the Al—Mg alloy is Al 12 Mg 17 .
2. The piston for an internal combustion engine according to claim 1, wherein the thickness of the permeation diffusion layer is at least twice the average particle diameter of the metal particles contained in the sintered layer.
2. The piston for an internal combustion engine according to claim 1, wherein the porosity of the permeation diffusion layer is inclined.
2. The piston for an internal combustion engine according to claim 1, wherein the sintered layer has a volume specific heat of 1000 kJ / m 3 · K or less and a thermal conductivity of 1 W / mK or less.
The piston for an internal combustion engine according to claim 1, wherein the sintered layer has a thickness of 50 µm or more and 100 µm or less.
A base material, an insert material made of a metal having a melting point lower than that of the base material, and a metal powder or a metal sintered body are laminated in this order to produce a laminate,
Heating the laminated body to melt the insert material, and forming a permeation diffusion layer by infiltrating the insert material into a sintered body formed from the metal powder or pores of the sintered body; A method for manufacturing a piston for an internal combustion engine, which is characterized.
The method for manufacturing a piston for an internal combustion engine according to claim 14, wherein a pulse current joining method is used when the insert material is melted.
The method for manufacturing a piston for an internal combustion engine according to claim 15, wherein an external heat source is used when the insert material is melted.
The method for manufacturing a piston for an internal combustion engine according to any one of claims 15 to 16, wherein the insert material is powder.
The method for manufacturing a piston for an internal combustion engine according to claim 17, wherein the powder of the insert material contains an Al alloy.
The method for manufacturing a piston for an internal combustion engine according to claim 18, wherein the Al alloy is an Al-Mg alloy.
The method for manufacturing a piston for an internal combustion engine according to claim 19, wherein the Al-Mg alloy is Al 12 Mg 17 .
The method for manufacturing a piston for an internal combustion engine according to any one of claims 14 to 16, wherein the insert material is a sheet-like material.
The method for manufacturing a piston for an internal combustion engine according to claim 21, wherein the sheet-like material contains an Al alloy.