WO2018061591A1

WO2018061591A1 - Piston for internal combustion engine and method for manufacturing piston for internal combustion engine

Info

Publication number: WO2018061591A1
Application number: PCT/JP2017/031163
Authority: WO
Inventors: 一等杉本; 勝煥朴; 高橋　智一; 正登佐々木
Original assignee: 日立オートモティブシステムズ株式会社
Priority date: 2016-09-30
Filing date: 2017-08-30
Publication date: 2018-04-05
Also published as: JP6760812B2; JP2018053879A

Abstract

Provided are: a piston for an internal combustion engine with which the adhesion with a substrate and the durability can be secured and low heat conductivity and low volume specific heat can be achieved; and a method for manufacturing the piston for an internal combustion engine. This piston for an internal combustion engine is characterized by the following: comprising a substrate (1), and a surface layer (2) provided on the surface of the substrate (1); the surface layer (2) including a matrix phase (3), and hollow particles (4) that are dispersed in the matrix phase (3) and that have a void inside thereof; the matrix phase (3) comprising a metallic phase (30) constituted by a plurality of metallic particles being bonded together, and gaps (31) surrounded by portions other than the bonding portions of the metallic particles; and the hollow particles (4) being included in the gaps (31).

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 suitable as the material. It is described that there is.

JP 2015-68302 A JP 2012-47110 A

As described above, in order to increase the thermal efficiency of the internal combustion engine, the heat insulating layer is desired to have both low thermal conductivity and low volume specific heat. However, the durability and the base material (the member of the internal combustion engine provided with the heat insulating layer are further provided. It is also important to ensure sufficient adhesion. None of

Patent Documents

1 and 2 described above achieve a sufficient level for all items of durability, adhesion to a substrate, low thermal conductivity, and low volume specific heat.

In view of the above circumstances, the present invention provides a piston for an internal combustion engine capable of ensuring adhesion and durability with a base material, and realizing low thermal conductivity and low volume specific heat, and a method for manufacturing the piston for an internal combustion engine The purpose is to provide.

In order to achieve the above object, a piston for an internal combustion engine according to the present invention has a base material and a surface layer provided on the surface of the base material, and the surface layer is configured by combining metal particles. It has a void surrounded by the metal phase and a portion other than the bonded portion of the metal particles, and the voids are included in the void.

The internal combustion engine piston manufacturing method according to the present invention is a method for manufacturing an internal combustion engine piston in which a surface layer is provided on a surface of a base material. The raw material is obtained by mixing metal particles and hollow particles constituting the surface layer. A raw material mixed powder preparation step for obtaining a mixed powder, a sintering step for obtaining a sintered body by sintering the raw material mixed powder, and a joining step for joining the sintered body and the base material are included. More specific configurations of the present invention are described in the claims.

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.

Issues, configurations, and effects other than those described above will be clarified by the following description of embodiments.

It is a perspective view showing typically an example of the piston concerning the present invention. FIG. 2 is a cross-sectional perspective view taken along line AA ′ of FIG. It is sectional drawing which shows typically the 1st example of the surface layer which comprises the piston which concerns on this invention. It is an enlarged view of the metal particle which comprises the metal phase of Fig.2 (a). It is sectional drawing which shows the 1st example of the piston which concerns on this invention. It is sectional drawing which shows the 2nd example of the piston which concerns on this invention. It is sectional drawing which shows the 3rd example of the piston which concerns on this invention. It is sectional drawing which shows typically the 2nd example of the surface layer which comprises the piston which concerns on this invention. It is a flowchart which shows an example of the manufacturing method of the piston (surface layer) which concerns on this invention. It is a flowchart which shows an example of the manufacturing method (joining of a base material and a surface layer) of the piston which concerns on this invention. It is a flowchart which shows another example of the manufacturing method of the piston which concerns on this invention. It is a figure which shows typically an example of the pulse electricity supply apparatus used in the Example. 2 is a cross-sectional SEM observation photograph of a hollow particle according to Example 1. FIG. 2 is a cross-sectional SEM observation photograph of a surface layer according to Example 1. It is an enlarged photograph of FIG.7 (b). It is a schematic diagram of the apparatus used for the thermal responsiveness evaluation test of an Example. It is a graph which shows the relationship of the output of the laser beam and time in the thermal response evaluation test of an Example. It is a graph which shows the relationship between the surface temperature of a test piece and time in the thermal response evaluation test of an Example.

[Piston for internal combustion engine]
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. A crown surface 101 constituting the upper surface of a piston for internal combustion engine (hereinafter, also simply referred to as “piston”) 100 according to the present invention is a portion that becomes a part of the inner wall of the combustion chamber, so as to improve combustion efficiency. This is a portion where a conventional heat insulating layer is provided. In the present invention, a “surface layer” having both low thermal conductivity and low volume specific heat is provided on the surface of the piston. Hereinafter, this surface layer will be described in detail.

FIG. 2A is a cross-sectional view schematically showing a first example of the surface layer constituting the piston according to the present invention. As shown in FIG. 2 (a), the piston according to the present invention has a piston base material (hereinafter simply referred to as “base material”) 1 and a surface layer 2 provided on the surface of the base material 1. The surface layer 2 includes a mother phase 3 and hollow particles 4 dispersed in the mother phase 3. The hollow particles 4 are particles having pores (fine pores) 40 inside. The parent phase 3 is composed of a metal phase 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, formed between the metal particles). The voids 31 have a configuration in which the hollow particles 4 are included. The volume ratio in which the voids 31 of the matrix 3 and the pores 40 of the hollow particles 4 occupy the surface layer 2 is referred to as “porosity”. In the present invention, the porosity of the entire surface layer 2 is increased to 50% by volume by combining both the void 31 of the matrix 3 and the void 40 of the hollow particle 4.

As described above, in order to promote the combustion of fuel, in order to provide a heat insulating layer over a wide range on the crown surface 101 of the piston, the heat insulating layer has a sufficient heat insulating performance and at the same time minimizes heat storage. It is important not to raise the temperature inside the internal combustion engine. That is, it is necessary to achieve both low thermal conductivity and low volume specific heat, and it is considered suitable for such a layer to have a porous structure incorporating pores. However, as in Patent Document 1 and Patent Document 2, when a porous body such as ceramics is bonded to a metal piston base material, the adhesion at the interface cannot be maintained sufficiently, and sufficient durability is achieved. It cannot be realized. Therefore, in the present invention, the parent phase 3 constituting the main part of the surface layer 2 that is a porous body is the metal phase 30, thereby ensuring adhesion and durability with the base material 1 made of metal. did.

In order to obtain high low thermal conductivity, it is considered effective to increase the gap 31 of the matrix 3. However, if the gap 31 is excessively increased, the strength of the matrix 3 is reduced and the surface layer 2 is reduced. Cannot withstand the harsh environment (temperature and pressure) in an internal combustion engine. Therefore, in the present invention, the hollow particles 4 are contained in the voids 31 of the matrix 3 and the voids 31 in the matrix 3 and the pores 40 of the hollow particles 4 are combined to reduce the porosity of the entire surface layer 2. The strength of the surface layer 2 is maintained while suppressing the amount of voids 31 in the mother phase 3 while ensuring sufficient.

The metal phase 30 is preferably composed of a sintered metal in which metal particles are bonded by sintering. FIG. 2B is an enlarged view of the metal particles constituting the metal phase 30 of FIG. 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 neck 33 can secure a space between the metal particles and form the gap 31. 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 in detail later.

The base material 1 and the metal phase 30 preferably contain the same metal as their main component. Specifically, it is preferable that the base material 1 is an aluminum (Al) alloy and the metal phase 30 is Al. In this way, by forming the metal phase 30 constituting the main part of the base material 1 and the surface layer 2 with the same metal, a strong solid phase junction is formed at the interface between the base material 1 and the surface layer 2 having a porous structure. Thus, it is possible to provide the surface layer 2 that ensures adhesion and is excellent in durability.

As the hollow particles 4, 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 insulation performance of the surface layer 2. It is preferable to use a material having low thermal conductivity, and it is particularly preferable to use silica. Silica is a material having relatively low thermal conductivity among ceramics and 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.

In the surface layer 2, the ratio of the hollow particles 4 to the metal phase 30 is preferably in the range of 30 to 70% by volume (30 to 70% by volume). When the volume is smaller than 30% by volume, it is difficult to ensure a sufficient porosity in the entire surface layer 2, and when the volume is larger than 70% by volume, the binding between the metal particles constituting the metal phase 30 is inhibited. As a result, the strength of the surface layer 2 is impaired.

The particle diameter of the metal particles constituting the metal phase 30 and the particle diameter of the hollow particles 4 are preferably the same. When the particle diameter of the hollow particles 4 is larger than the particle diameter of the metal particles, it is difficult to form a bond between the metal particles, and the strength of the metal phase 30 that is a sintered body may be reduced. On the other hand, when the particle diameter of the hollow particles 4 is smaller than the particle diameter of the metal particles, the formation of the voids 31 between the metal particles is hindered and a high porosity cannot be realized.

As described above, the porosity of the surface layer 2 is the sum of the ratio of the voids 31 of the parent phase and the voids 40 of the hollow particles 4. Of these, the volume of the voids 40 of the hollow particles 4 is Is preferably larger than the volume of the void 31 of the parent phase 3. When the voids in the mother phase 3 increase, the bond between the metal particles of the metal phase 30 becomes weak, and the strength (durability) of the surface layer 2 cannot be maintained. By making the volume of the voids 40 of the hollow particles 4 larger than the volume of the voids 31 of the matrix 3, it becomes possible to achieve both a predetermined porosity and strength of the surface layer 2.

In the present invention, the porosity of the surface layer 2 is preferably greater than 40% by volume and 63% by volume or less. If it is 40% by volume or less, a sufficiently low volume specific heat cannot be realized, and if it is more than 63% by volume, it is difficult to maintain the strength of the surface layer 2. In addition, when the surface layer 2 is composed only of the parent phase 3 including the voids 31 and does not include the hollow particles 4, the strength is maintained when the porosity (ratio of the voids 31) of the surface layer 2 is 40% by volume or more. It becomes difficult. Further, when the parent phase 3 does not include the voids 31 and includes only the hollow particles 4, the voids 31 that become the spaces including the hollow particles 4 are eliminated, so that the volume ratio of the hollow particles 4 is limited, and the pores of 30 volume% or more It becomes difficult to ensure the rate. In the present invention, by combining the voids 31 included in the matrix 3 and the voids 40 of the hollow particles 4, it is possible to ensure a porosity greater than 40% by volume.

The volume specific heat of the surface layer 2 is preferably 1000 kJ / m ³ · K or less. By setting the volume specific heat of the surface layer 2 to 1000 kJ / m ³ · K or less, the base temperature is hardly increased in the internal combustion engine. That is, the thermal responsiveness with respect to the gas temperature of the surface 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. As a result, the surface layer 2 can be applied to the entire surface of the piston crown surface 101, and higher combustion efficiency can be obtained.

In the piston 100 according to the present invention, the place where the surface layer 2 described above is formed is not particularly limited. The example of the location which forms the surface layer 2 in the piston 100 is shown below. 3A is a cross-sectional view showing a first example of the piston according to the present invention, and FIG. 3B is a cross-sectional view showing a second example of the piston according to the present invention. ) Is a cross-sectional view showing a third example of the piston according to the present invention. As shown in FIGS. 3A to 3C, the location where the surface layer 2 is formed in the pistons 100a to 100C is not particularly limited, and is formed in the central portion of the crown surface 101 as shown in FIG. Alternatively, it may be formed on the entire surface of the crown surface 101 as shown in FIG. 3B, and the thickness may be constant along the surface shape of the crown surface 101 as shown in FIG. You may form in.

FIG. 4 is a sectional view schematically showing a second example of the surface layer constituting the piston according to the present invention. As shown in FIG. 4, in the second example, a sealing layer 50 made of a sealing material is formed on the surface of the surface layer 2. When the fuel soaks into the gap 31 of the surface layer 2, the fuel that contributes to combustion decreases, and the combustion efficiency deteriorates. Therefore, it is preferable to seal the voids on the surface of the surface layer 2 as shown in FIG. 4 to prevent the fuel from penetrating to the back of the surface layer 2 (base material 1 side). When the sealing layer 50 is provided on the surface of the surface layer 2, the sealing material is not only the surface of the surface layer 2 (portion indicated by reference numeral 51 in FIG. 4), but also the gap 31 near the surface (reference numeral 52 in FIG. 4). The surface layer 2 according to the present invention secures the porosity of the entire surface layer 2 with the voids 31 of the matrix 3 and the pores 40 of the hollow particles 4. Since the sealing material does not enter the internal pores 40, even if a part of the gap 31 of the matrix 3 is sealed with the sealing material, the entire surface layer 2 has a sufficient porosity. can do.

The sealing material is not particularly limited, but an insulating paint is suitable. By constituting the sealing material with an insulating material, adhesion of carbon deposits can be suppressed. More specifically, examples of the sealing material include, but are not limited to, polysilazane, polysiloxane, silica alkoxide, polyamide, polyamideimide, polyimide, and various resins. A method for forming the sealing layer 50 will be described in detail later. 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 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.

[Method of manufacturing piston for internal combustion engine]
Next, a method for manufacturing a piston according to the present invention will be described. As a method for forming the surface layer 2 on the substrate 1, first, a sintered body is formed by sintering the metal particles and the hollow particles 4 constituting the metal phase, and the sintered body is joined to the substrate 1. And the method of installing the mixed powder of the metal particle used as the raw material powder of the surface layer 2, and the hollow particle 4 on the surface of the base material 1, and sintering the metal particle and joining to the base material 1 simultaneously is mentioned. First, the former example will be described.

FIG. 5A is a flowchart showing an example of a method for manufacturing a piston (surface layer) according to the present invention, and FIG. 5B is a method for manufacturing a piston according to the present invention (joining of a base material and a surface layer). It is a flowchart which shows an example. First, in FIG. 5A, the metal particles that are the raw material of the metal phase 30 and the powder of the hollow particles 4 are mixed (S10: 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 it is considered that the pulse current sintering method is suitable. Pulse electric current sintering (Pulse Electric Current Sintering) is a sintering method also called spark plasma sintering (Spark Plasma Sintering). When pulse current is applied while pressing the raw material 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. The neck 33 can be easily formed. 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, 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 phase (sintered metal) 30 in which the metal particles are connected to each other is formed, and in the void 31 configured other than the bonded portion between the metal particles. The hollow particles 4 can be included without breaking the shape. If the pulse current sintering method is used, it is possible to control the ratio of the voids 31 in the mother phase 3 by controlling the load or the amount of indentation and pressurizing.

In FIG. 5B, first, a piston base material is manufactured 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, the sintered body produced in the process shown in FIG. 5A is placed in contact with the surface of the substrate (S15). And a base material and a sintered compact are joined (S16). As a joining method, it is preferable to use a joining method in which a metal constituting the sintered body and a metal constituting the substrate are directly bonded to each other. Specific examples include diffusion bonding, friction stir welding, laser welding, and arc welding, but are not limited thereto.

As a post-treatment after joining the sintered body and the substrate, a heat treatment step is performed (S17). This heat treatment is intended to remove the strain generated in the joining process and to 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).

FIG. 5 (c) is a flowchart showing another example of the manufacturing method of the piston according to the present invention. In FIG.5 (c), preparation of a sintered compact (S1 of Fig.5 (a)) and joining of a sintered compact and a base material (S2 of FIG.5 (b)) are implemented simultaneously. The piston base material casting (S13) and primary machining (S14) are the same as in FIG. 5B. On the surface of the base material 1 subjected to the primary machining process, the mixed powder of the metal particles and the hollow particles 4 as the raw material powder of the surface layer 2 is placed (S15 ′). At this time, the mixed powder may be placed on the surface of the substrate 1 in the form of powder. However, the mixed powder is formed into a molded body having a predetermined shape, for example, a pre-molding by applying pressure in advance to the powder. A green compact pressed into a shape may be used, and this green compact may be placed on the surface of the substrate 1 (piston crown surface).

Next, 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 ′). The joining method is the same as S16 described above.

Furthermore, although not shown, in order to form the sealing layer 50 described above, a sealing layer forming step may be included in any step after the formation of the sintered body. As a method for forming the sealing layer, 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 heated at 400 to 500 ° C. for 1 to 2 hours to be dried. Can be formed.

5 (b) and FIG. 5 (c), the sealing material forming step is a step of joining the sintered body and the base material (S16 or S16 ′), heat treatment step (S17), or secondary machining step ( It is possible to carry out between any steps of S18). According to the present invention, the sealing layer 50 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.

Hereinafter, the present invention will be described in more detail based on examples.

[Evaluation of hollow particle ratio and sintering state, porosity and thermal response]
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 (Examples 1 to 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 surface layer 2 (a raw material powder for the surface layer), a raw material mixed powder prepared by mixing Al particles as metal particles constituting the metal phase 30 and SiO ₂ particles as hollow particles 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. 6 is a diagram schematically illustrating an example of the pulse energization device used in the example. In the vacuum chamber 64, the above-mentioned mixed powder (raw material powder) 61 is placed in an annular carbon die 62, and the carbon punch 63 is driven in the direction of the arrow in FIG. A pulse current was applied to the mixed powder through (the upper electrode 65 and the 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 powders of the surface layers of Examples 1 to 3 and Reference Examples 1 to 2, and the evaluation results of the sintered state and the porosity (P) are shown in Table 1 described later. In the present specification, the “reference example” has a surface layer according to the present invention, but the ratio of hollow particles is not within the preferred range (30 to 70% by volume) of the present invention. In Table 1, the porosity P of the surface layer was calculated from the following formula.

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). 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%.

FIG. 7A is a cross-sectional SEM observation photograph of the hollow particles according to Example 1, FIG. 7B is a cross-sectional SEM observation photograph of the surface layer according to Example 1, and FIG. It is an enlarged photograph of (b). 7B and 7C, the white part is Al, the gray part is SiO ₂ , and the black part is voids and holes. As shown in FIGS. 7B and 7C, it can be seen that the hollow silica 72 is contained in the void 73 formed between the Al particles 71 while maintaining its shape.

In Examples 1 to 3 and Reference Example 1, a good sintered state could be secured, whereas in Reference Example 2 in which the content of the hollow particles was increased to 75%, the hollow particles became excessive, and the metal particles Bonding was inhibited, resulting in poor sintering, and the sintered body shape could not be maintained.

In order to evaluate the thermal response characteristics in the surface layer, a thermal response evaluation test was performed in which the temperature of the surface layer was evaluated using a laser heat source. FIG. 8 is a schematic view of an apparatus used in the thermal responsiveness evaluation test of the example. As shown in FIG. 8, 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. 9A is a graph showing the relationship between laser light output and time in the thermal response evaluation test of the example. FIG. 9B is a graph showing the surface temperature and time of the test piece in the thermal response evaluation test of the example. It is a graph which shows a relationship. FIG. 9B shows the surface temperature at the time of laser irradiation in FIG. In FIG. 9B, the peak temperature recorded during the first laser irradiation was T ₁ , and the peak temperature recorded during the third laser irradiation was T ₃ . Laser irradiation was carried out by applying a black body paint for absorbing laser to the test piece.

In the thermal response evaluation test, in order to simulate the engine environment first, the laser irradiation conditions are set so that the peak temperature of the aluminum alloy test piece without the surface layer is about 200 ° C. which is close to the actual engine environment. Selected. Specifically, as shown in FIG. 9 (a), a step of irradiating an 800 W laser for 1 second and naturally cooling for 5 seconds was taken as one set, and a total of three 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 the temperature exceeds 500 ° C., “over 500 ° C.” is described. 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 Examples 1 to 3, both T ₁ and T ₃ were 400 ° C. or higher, whereas in Reference Example 1, a sufficient temperature rising effect was not obtained, and the thermal responsiveness was not sufficient. It was. Reference Example 2 could not be tested because the shape of the sintered body collapsed before the test. 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.

From the above results, it was shown that a surface layer having high thermal responsiveness can be obtained by setting the hollow particle content in the range of 30 to 70% by volume.

[Evaluation of porosity and sintered state]
Next, test pieces in which the porosity of the surface layer was changed under the condition that the hollow particle ratio was fixed to 50% were prepared (Examples 4 and 5 and Reference Example 3). The sintered state of the obtained test piece was evaluated. The composition of the raw material powder of the surface layers of Examples 4 and 5 and Reference Example 3, and the evaluation results of the pores and the sintered state are shown in Table 2 described later. Table 2 also shows the evaluation results of the composition, pores, and sintered state of the raw material powder of Example 1. In Examples 1, 4 and 5, the sintered state was good, whereas in Reference Example 3 having a porosity of 67%, the shape of the sintered body could not be maintained, and the sintered state was poor. became. As a result, it was found that the porosity is preferably 63% or less. Further, from the results of Table 1, it can be said that Reference Example 1 having a porosity of 40% did not exhibit sufficient thermal responsiveness, so that the porosity is preferably controlled to a range of more than 40% and not more than 63%. .

For Examples 1 to 3 and Reference Examples 1 to 2, the specific heat capacity was measured using a differential scanning calorimetry (DSC (Differential Scanning calorimetry) method), and the specific volume heat was calculated from the density measured separately. A sample having a volume specific heat of 1000 kJ / m ³ · K or less was evaluated as “pass”, and a sample having a volume specific heat exceeding 1000 kJ / m ³ · K was evaluated as “fail”. The evaluation results are also shown in Table 1. Volume specific heat greatly depends on the porosity. Reference Example 1 with a porosity of 40% exceeded 1000 kJ / m ³ · K, but Examples 1 to 3 with a porosity of 48% or more had 1000 kJ / m ³ · K. The evaluation results were “passed” as follows. In Reference Example 2, measurement was not performed because the sintered body shape could not be maintained.

[Production of piston and fuel efficiency evaluation]
A piston having a surface layer having the same configuration as that of Example 1 was manufactured by the method shown in FIGS. 5A and 5B (Example 6). 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. 5A and processed into a diameter of 70 mm and a thickness of 3 mm. In accordance with the manufacturing process of FIG. 5B, 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 sintered body prepared in advance was placed in the concave portion of the crown surface of the piston, and the sintered body and the piston base material were sufficiently brought into contact with a restraining jig (S15), and diffusion bonding was performed in a heat treatment furnace (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).

Also, as Example 7, a sealing layer forming step was performed on the piston surface after the secondary machining (S18) for the piston produced in Example 6. 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.

The produced pistons of Examples 6 and 7 were subjected to an engine test to confirm fuel efficiency. In either case, the fuel efficiency was improved as compared with the piston without the surface layer, but it was confirmed that the fuel consumption was less in Example 7 in which the sealing layer was provided. 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.

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.

100, 100a, 100b, 100c ... piston, 101 ... piston crown surface, 1 ... base material, 2 ... surface layer, 3 ... parent phase, 30 ... metal phase, 31 ... void, 32 ... metal particles, 33 ... neck, 4 ... hollow particles, 40 ... holes, 5 ... piston pin receiving part, 50 ... sealing layer, 51 ... sealing material on the surface layer, 52 ... sealing material that has entered the voids of the mother phase, 61 ... surface layer Raw material powder, 62 ... carbon die, 63 ... carbon punch, 64 ... vacuum chamber, 65 ... upper electrode, 66 ... lower electrode, 67 ... pulse power supply, 71 ... Al particles, 72 ... hollow silica, 73 ... void, 81 ... test Piece 82 ... Vacuum chamber 83 ... Infrared camera 84 ... Laser heat source.

Claims

A base material, and a surface layer provided on the surface of the base material,
The surface layer includes a parent phase and hollow particles dispersed in the parent phase and having pores therein,
The parent phase has a metal phase configured by combining a plurality of metal particles, and a void surrounded by a portion other than the bonded portion of the metal particles, and the hollow particles are in the void. A piston for an internal combustion engine, characterized in that it is included.
2. The piston for an internal combustion engine according to claim 1, wherein the metal phase is made of sintered metal.
3. The piston for an internal combustion engine according to claim 2, wherein the sintered metal is made of the same metal as that constituting the base material, and the sintered metal and the base material are joined.
3. The piston for an internal combustion engine according to claim 2, wherein the sintered metal is made of aluminum.
The piston for an internal combustion engine according to any one of claims 1 to 4, wherein the hollow particles are made of silica, alumina, or zirconia.
The internal combustion engine piston according to any one of claims 1 to 4, wherein a ratio of the hollow particles to the metal phase is 30 to 70% by volume.
The piston for an internal combustion engine according to any one of claims 1 to 4, wherein a joint portion of the metal particles has a neck.
The piston for an internal combustion engine according to any one of claims 1 to 4, wherein a particle diameter of the metal particles constituting the metal phase and a particle diameter of the hollow particles are the same.
5. The piston for an internal combustion engine according to claim 1, wherein in the surface layer, the volume of the holes is larger than the volume of the gap.
5. The piston for an internal combustion engine according to claim 1, wherein the sum of the ratio of the air gap and the air hole to the surface layer is greater than 40% by volume and equal to or less than 63% by volume. .
5. The internal combustion engine piston according to claim 1, wherein the volumetric heat of the surface layer is 1000 kJ / m 3 · K or less.
The piston for an internal combustion engine according to any one of claims 1 to 4, further comprising a sealing layer on a surface of the surface layer.
The piston for an internal combustion engine according to claim 12, wherein the sealing layer is made of polysilazane, polysiloxane, silica alkoxide, polyamide, polyamideimide, or polyimide.
In the method for manufacturing a piston for an internal combustion engine in which a surface layer is provided on the surface of a base material constituting the piston,
Raw material mixed powder preparation step for obtaining a raw material mixed powder by mixing metal particles and hollow particles constituting the surface layer,
A sintering step of sintering the raw material mixed powder to obtain a sintered body;
A method for manufacturing a piston for an internal combustion engine, comprising: a bonding step of bonding the sintered body and the base material.
The said sintered compact obtained at the said sintering process is installed on the said base material, The said sintered compact and the said base material are joined, The manufacturing of the piston for internal combustion engines of Claim 14 characterized by the above-mentioned. Method.
The method for manufacturing a piston for an internal combustion engine according to claim 14, wherein the raw material mixed powder is placed on the base material, and the sintering step and the joining step are simultaneously performed on the surface of the base material.
17. The internal combustion engine according to claim 16, wherein a molded body obtained by pressure-molding the raw material mixed powder is placed on the base material, and the sintering step and the joining step are simultaneously performed on the surface of the base material. Manufacturing method of piston for engine.
15. The method for producing a piston for an internal combustion engine according to claim 14, further comprising a sealing layer forming step of applying a sealing material to the surface of the sintered body and drying the sealing material.
The method for manufacturing a piston for an internal combustion engine according to claim 18, wherein the sealing material is polysilazane, polysiloxane, silica alkoxide, polyamide, polyamideimide, or polyimide.
The method for manufacturing a piston for an internal combustion engine according to claim 14, wherein the sintering step is performed by a pulse current sintering method.
The method for manufacturing a piston for an internal combustion engine according to claim 14, wherein the joining step is performed by diffusion welding, friction stir welding, laser welding, or arc welding.
The method for manufacturing a piston for an internal combustion engine according to claim 16 or 17, wherein the sintering step and the joining step are simultaneously performed by pulsed current pressure sintering.