WO2018037616A1 - Piston for internal combustion engine and method for manufacturing piston for internal combustion engine - Google Patents

Abstract

Provided is a piston for an internal combustion engine, in which cylinder or piston wear can be minimized. This piston for an internal combustion engine has a main body and a low-thermal-conductivity part. The main body, which contains an aluminum alloy, has a piston head, a piston boss, and a piston skirt. The low-thermal-conductivity part is located on a combustion-chamber side of the piston head, and comprises at least one of carbon, boron nitride, and molybdenum disulfide. The low-thermal-conductivity part has a gap in the interior thereof. The piston for an internal combustion engine is provided with a main body part formed from an aluminum alloy. The main body part has a piston head part, and a piston boss part and piston skirt part provided to the side of the piston head part opposite from the combustion chamber of the internal combustion engine. The piston furthermore is provided with a low-thermal-conductivity part that: is provided on the side of the piston head adjacent to the combustion chamber of the internal combustion engine; is formed from a low-thermal-conductivity-part-forming material containing carbon, boron nitride, or molybdenum disulfide; and has a gap in the interior thereof.

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.

Conventionally, a piston of an internal combustion engine is known (for example, Patent Document 1).

JP 2009-243355 A

In the conventional piston, the heat insulating material provided on the crown surface may fall off and the wear of the cylinder or the piston may be accelerated.

The piston of the internal combustion engine according to one embodiment of the present invention has a low heat conduction part made of a material containing a substance functioning as a solid lubricant in the piston head.

Therefore, it is possible to suppress wear of the cylinder or piston.

1 schematically shows a cross section of a part of an engine cut by a plane passing through the axis of one cylinder of the first embodiment. 1 is a perspective view of a piston according to a first embodiment. FIG. 3 is a top view of the piston according to the first embodiment viewed from the crown surface side. 1 schematically shows a cross section (hereinafter referred to as an axial cross section) in which a part of a low heat conduction portion and a piston head (hereinafter referred to as a low heat conduction portion) of the first embodiment is cut by a plane parallel to the axis of the piston. 2 is an enlarged photograph showing a part of an axial cross section of a low heat conduction portion or the like of the first embodiment. 1 schematically shows a coating process of a first embodiment. FIG. 2 is an axial sectional view schematically showing a part of the coating film after the drying step of the first embodiment. FIG. 5 is an axial cross-sectional view schematically showing a part of a low heat conduction portion and the like of a second embodiment. FIG. 5 is an axial direction cross-sectional view schematically showing a part of a low heat conduction portion and the like according to a third embodiment. FIG. 10 is an axial cross-sectional view schematically showing a part of a coating film after the coating step of the third embodiment. The material heating process and injection | pouring process of 3rd Embodiment are shown typically. FIG. 6 is an axial cross-sectional view schematically showing a part of a coating film after a spraying process of a third embodiment. FIG. 9 is an axial cross-sectional view schematically showing a part of a low heat conduction portion and the like of a fourth embodiment. FIG. 9 is an axial cross-sectional view schematically showing a part of a low heat conduction portion and the like according to a fifth embodiment. FIG. 10 is a photograph showing an enlarged part of an axial cross section of a low thermal conductive portion or the like according to a fifth embodiment. FIG. 10 is an axial cross-sectional view schematically showing a part of a low heat conduction portion and the like of a sixth embodiment. FIG. 10 is an axial cross-sectional view schematically showing a part of a low heat conduction portion and the like according to a seventh embodiment. FIG. 10 is an axial cross-sectional view schematically showing a part of a low thermal conductive portion or the like according to an eighth embodiment. FIG. 10 is an axial cross-sectional view schematically showing a part of a low heat conduction portion or the like according to a ninth embodiment. The material heating process of 9th Embodiment is typically shown. FIG. 16 is an axial cross-sectional view schematically showing a part of a low heat conduction portion or the like according to a tenth embodiment. A part of 1st application | coating process of 10th Embodiment is typically shown. A part of 1st application | coating process of 10th Embodiment is typically shown. FIG. 20 is an axial cross-sectional view schematically showing a part of the first coating film immediately after the first application step of the tenth embodiment. FIG. 15 is an axial cross-sectional view schematically showing a part of a first coating film when a certain amount of time has passed since the first application step of the tenth embodiment. FIG. 20 is an axial cross-sectional view schematically showing a part of the first mixed material material applied to the crown surface in the first application process of the eleventh embodiment. FIG. 16 is an axial cross-sectional view schematically showing a part of a low thermal conductive portion or the like according to a twelfth embodiment. The application | coating process of 12th Embodiment is shown typically. A surface treatment process by shot blasting according to a fifteenth embodiment is schematically shown. FIG. 20 is a top view of a piston according to an eighteenth embodiment viewed from the crown side. FIG. 23 is a perspective view of a piston of another example of the 18th embodiment. FIG. 23 is a top view of a piston of another example of the eighteenth embodiment viewed from the crown surface side.

Hereinafter, modes for carrying out the present invention will be described with reference to the drawings.

[First embodiment]
First, the configuration will be described. The internal combustion engine (engine) 100 of the present embodiment shown in FIG. 1 is a 4-stroke gasoline engine. The engine 100 includes a piston 1, a cylinder block 101, a cylinder head 104, a connecting rod (connecting rod) 106, a crankshaft, a valve 107, an ignition device 108, and a combustion chamber 11. The valve 107 has two intake valves and two exhaust valves. The cylinder block 101 includes a cylindrical cylinder liner (cylinder sleeve) 102. The inner peripheral side of the cylinder liner 102 functions as the inner wall of the cylinder 10. The cylinder head 104 is installed in the cylinder block 101 so as to close the opening of the cylinder 10. The cylinder head 104 is provided with a valve 107, a fuel injection nozzle, and an ignition device 108. A crankshaft is rotatably installed on the cylinder block 101. The piston 1 is accommodated in the cylinder 10 so as to be reciprocally movable.

2 and 3, the piston 1 has a piston main body 2 and a low heat conducting portion 3. The piston body 2 is formed of an aluminum alloy (for example, Al—Si AC8A) as a material (raw material). The piston 1 (piston main body 2) has a bottomed cylindrical shape, and includes a piston head (crown portion) 4, a piston boss (apron portion) 5, and a piston skirt (skirt portion) 6. Hereinafter, the direction in which the axial center of the piston 1 extends is referred to as the axial direction. In the axial direction, the side of the piston head 4 with respect to the piston boss 5 and the piston skirt 6 is referred to as one side, and the opposite side is referred to as the other side. The piston head 4 has a crown surface portion 40 and a land portion 41. The crown surface portion 40 is on one side in the axial direction of the piston head 4 and has a crown surface (top surface) 400. The crown surface 400 extends perpendicular to the axis of the piston 1 and has a substantially circular outline when viewed from one axial direction. As shown in FIG. 1 (when the piston 1 is at the top dead center), the combustion chamber 11 is defined between the crown surface 400 and the cylinder head 104. The combustion chamber 11 is a pent roof type. The crown surface 400 is exposed to the combustion gas in the combustion chamber 11. The crown surface portion 40 has a cavity 401. The cavity 401 is a recess formed in the crown surface portion 40 and defines the combustion chamber 11. In other words, the piston head 4 includes the cavity 401 on the combustion chamber 11 side (side facing the combustion chamber 11). The cavity 401 is in the shape of a shallow dish that is substantially at the center of the crown surface 400 and has a flat bottom surface. The crown surface portion 40 has four recesses (inclined valve recesses) 402 along the tip shape of each valve 107 at the peripheral edge of the cavity 401. The land portion 41 extends from the outer peripheral side of the crown surface portion 40 to the other side in the axial direction. There are three annular grooves (ring grooves) 410 on the outer periphery of the land portion 41. A piston ring 7 is installed in the ring groove 410.

The piston boss 5 and the piston skirt 6 extend from the piston head 4 to the other side in the axial direction, and are on the opposite side of the combustion chamber 11 with respect to the piston head 4. The inner peripheral side of the piston skirt 6 and the piston boss 5 is hollow. There are a pair of piston bosses 5 on both sides in the radial direction of the piston 1. Each piston boss 5 has a pin boss 50. Each pin boss 50 has a piston pin hole 51. The piston pin hole 51 extends through the pin boss 50 in the radial direction of the piston 1. There are a pair of piston skirts 6 on both sides in the radial direction of the piston 1. The piston skirt 6 is sandwiched between the piston bosses 5 and 5 in the circumferential direction of the piston 1. Both piston skirts 6 and 6 are connected by a piston boss 5. The piston skirt 6 slides against the inner wall of the cylinder 10. The piston pin end 51 is fitted into the piston pin hole 51. The piston 1 is connected to one end side (small end portion) of the connecting rod 106 via a piston pin. The other end side (large end portion) of the connecting rod 106 is connected to the crankshaft. Cooling water circulates in the passage 103 inside the cylinder liner 102. An oil jet 105 is installed in the cylinder block 101. The heat transferred from the combustion chamber 11 to the piston head 4 is released by being transferred to the cylinder liner 102 and the cooling water therein through the piston ring 7. The heat is also released when oil adheres to the inner peripheral side (back side) of the piston 1 and flows out. The adhesion of the oil is performed by, for example, the injection of oil from the oil jet 105.

The low heat conduction unit 3 is a structure for reducing the thermal conductivity from the combustion chamber 11 to the piston head 4 (piston body 2), and is on the combustion chamber 11 side of the piston head 4 and faces the combustion chamber 11 It is formed all over (crown surface 400). A part of the low heat conducting unit 3 is accommodated in the cavity 401. As shown in FIGS. 4 and 5, the low heat conducting portion 3 has a layer shape that extends along the crown surface 400 (including the bottom surface of the cavity 401) of the piston body 2. The low heat conducting part 3 has a layer 30. The thickness of the layer 30 is arbitrary. Of the materials for forming the low heat conducting section 3, those that are solid (during operation of the engine 100) are hereinafter referred to as solid materials. There are a plurality of voids (hollow portions) 31 inside the low heat conducting portion 3. There is a gas (a gas that is a gas when the engine 100 is operated) in the gap 31. The air gap 31 is a gap between the solid materials or between the solid material and the piston body 2. The air gap 31 is sandwiched and closed by a solid material on both sides of the piston 1 in an arbitrary radial direction. The air gap 31 is closed on the one side (combustion chamber 11 side) in the axial direction (the direction perpendicular to the direction in which the low heat conducting section 3 spreads in layers) (the first air gap 311), and on this one side Some are not closed (second air gap 312). The first gap 311 is a closed space sandwiched between the solid material on both sides in the axial direction or sandwiched between the solid material and the piston body 2. The second gap 312 is an open space opened to the combustion chamber 11 on one side in the axial direction and closed with a solid material or the piston body 2 on the other side in the axial direction. The second air gap 312 is a concave portion of fine irregularities on the surface of the low heat conducting unit 3 on the combustion chamber 11 side, and opens on the combustion chamber 11 side in the low heat conducting unit 3.

∙ Solid material includes carbon and binder. Carbon contains 50% by volume or more of SP2 structure components, that is, graphite (graphite). As a component other than graphite in carbon, for example, carbon black may be included. Carbon particles are agglomerated. The average particle diameter of this lump is 20 μm or more, preferably 100 μm or less, and more preferably 50 μm or less. The binder is a synthetic resin and has a function of bonding carbon particles (lumps) to each other. The binder is an engineering plastic. For example, at least one of polyamide imide, polyamide, and epoxy resin can be used. The low heat conduction part 3 is a layered structure in which carbon blocks (and binders) are deposited. In the layer 30 of the low heat conducting portion 3, carbon lump (particles) and binder are mixed and dispersed. The voids 31 are between a plurality of carbon masses (and binders).

Hereinafter, a method for manufacturing the piston 1 of the present embodiment will be described. The manufacturing method includes a piston body forming step and a low heat conduction portion forming step. The piston body forming process includes a casting process, a heat treatment process, and a machining process. In the casting process, a prototype (intermediate workpiece) of the piston body 2 is cast. Specifically, a molten aluminum alloy is poured into a mold and solidified. At this time, the inner periphery of the piston body 2 is formed, and the basic shape of the cavity 401 is formed. In the heat treatment step, heat treatment is performed. As a result, the properties of the cast prototype are improved and adjusted to appropriate strength and hardness. In the machining process, the heat-treated prototype is machined with a lathe or the like. For example, the piston pin hole 51 and the ring groove 410 are processed, and the outer diameter of the piston body 2 such as the outer periphery of the piston head 4 and the piston skirt 6 is finished. Further, the crown surface 400 (cavity 401) is formed by machining. The entire surface of the piston head 4 on the combustion chamber 11 side (including the cavity 401) is machined.

In the low heat conduction part forming step, the low heat conduction part 3 is formed on the piston head 4 (on the combustion chamber 11 side). The low heat conduction part 3 is formed after the heat treatment process at the earliest (the heat treatment process is performed before the low heat conduction part formation step). In this embodiment, the low heat conduction part 3 is formed after the said machining process. The low heat conduction part forming step includes a material preparation step, a coating step, and a drying step. In the material preparation step, a material (hereinafter referred to as a forming material) for forming the low thermal conductive portion 3 is prepared. The forming material includes a solid material (carbon and binder) and a solvent (solvent). A powder made of carbon particles having an average particle diameter of, for example, 20 μm to 50 μm is prepared. For the measurement of the particle size, for example, a test sieve of JIS Z8801 can be used. The median diameter (d50) can be used as the average diameter. In this case, the “powder having an average particle diameter of x μm” refers to a powder of particles (lumps) classified by the test sieve and having a median diameter of x μm. The solvent is a component that vaporizes in the forming material, and a volatile solvent can be used. Organic solvents such as N-methyl-2-pyrrolidone (NMP) and dimethylacetamide (DMAc) can be used. In the material preparation step, a mixture of carbon and binder powder and a solvent (hereinafter referred to as a mixed material) is prepared. The mixed material contains a solvent, and carbon lump (particles) and binder particles are dispersed in the solvent. In addition, you may mix materials (additive etc.) other than carbon, a binder, and a solvent in mixed material.

In the application process, the piston body 2 is installed in advance (before actual application) so that the piston head 4 is vertically above the piston boss 5 and the piston skirt 6. Specifically, the crown surface 400 is set to face upward in the vertical direction. As shown in FIG. 6, the forming material (mixed material) is applied to the entire combustion chamber 11 side (crown surface 400) of the piston body 2 by the spray gun 90. As a result, a coating film of the forming material is formed on the crown surface 400 (including the surface of the cavity 401). In the drying step, the applied forming material is dried by, for example, infrared irradiation. The solvent in the coating film (mixed material) is vaporized (evaporated). As a result, a plurality of voids 31 are formed between the solid materials.

Next, the function and effect will be described. The low heat conduction unit 3 faces the combustion chamber 11 and constitutes a wall of the combustion chamber 11. Table 1 shows an example of general characteristics of an aluminum alloy (a base metal of the piston body 2) and carbon (graphite or carbon black).

Carbon (graphite or carbon black) in the low heat conducting portion 3 is a low heat conductive material and has a lower thermal conductivity than an aluminum alloy that is a material (base metal) of the piston body 2. Therefore, the low heat conducting portion 3 is located between the combustion chamber 11 and the piston body 2 and functions as a heat insulating layer. The low heat conducting section 3 reduces heat transfer from the gas in the combustion chamber 11 to the piston head 4 (piston body 2), and the heat of the fuel (air mixture) supplied to the combustion chamber 11 is taken away by the piston body 2. To suppress. Therefore, the thermal efficiency of engine 100 can be improved. Carbon has a smaller heat capacity (product of specific heat and density) per unit volume than the aluminum alloy that is the material of the piston body 2, in other words, volume specific heat. In general, the temperature conductivity of a solid is inversely proportional to the volume specific heat. Therefore, the low thermal conductivity portion 3 has a property that the temperature conductivity is less likely to be small (even if the thermal conductivity is low) compared to the piston body 2. If the temperature conductivity of the surface of the piston head 4 in contact with the gas in the combustion chamber 11 (low heat conduction portion 3) is large, the surface temperature easily follows the temperature of the gas in the combustion chamber 11. Thus, the heat loss in the cylinder 10 (combustion chamber 11) can be reduced by reducing the difference between the two temperatures.

The low heat conduction part 3 has a gap 31 inside. The air gap 31 has an extremely low thermal conductivity and an extremely small volume specific heat. Therefore, since the heat conductivity is lower as a whole (on average) in the low heat conduction section 3, heat transfer from the gas in the combustion chamber 11 to the piston head 4 (piston body 2) can be further reduced. . Further, since the specific heat of the volume of the low heat conducting portion 3 as a whole becomes smaller, the temperature conductivity of the low heat conducting portion 3 can be made larger than that of the piston main body 2, thereby the surface temperature of the piston head 4 and the combustion chamber 11. The difference with the gas temperature inside can be made smaller. Note that the size of the gap 31 is arbitrary. The number of voids 31 is arbitrary, and may be one, for example. In this embodiment, since there are a plurality of gaps 31, the above effects can be improved.

The carbon in the low heat conduction part 3 includes graphite. Graphite has a layered crystal structure in which carbons of SP2 hybrid orbitals are bonded to each other, and is excellent in lubricity. That is, graphite is generally used as a solid lubricant because it has an anisotropic layered structure with a low bonding force between crystal planes and is easily sheared by friction. As is clear from this, even if a part of the low heat conducting portion 3 falls into the cylinder 10, the graphite in this part functions as a lubricant, and the cylinder 10 and the piston 1 (piston body) 2) Wear can be suppressed. This is an advantageous effect as compared with the case where the low thermal conductive portion 3 is formed of a high hardness material (for example, ceramic such as zirconia). In addition, the ratio of the graphite in the carbon in the low heat conductive part 3 is arbitrary, for example, may be less than 50 volume%. In the present embodiment, carbon contains 50% by volume or more of graphite. Therefore, the above effect can be improved. Moreover, carbon has high heat resistance represented by melting point and is excellent in durability. Therefore, the durability of the low heat conduction part 3 can be improved.

By the binder, the adhesion between the carbon particles (lumps) and the adhesion between the carbon particles (lumps) and the piston body 2 are improved, and the force for holding these particles (lumps) in the piston body 2 is improved. be able to. By improving the strength of the low heat conduction part 3 and suppressing the chipping and collapse thereof, the function of the low heat conduction part 3 can be maintained for a longer period of time. Engineering plastics have high heat resistance. For this reason, the durability of the low heat conducting portion 3 can be further improved. In addition, the low heat conductive part 3 does not need to contain a binder. Even if the low heat conducting portion 3 is chipped or collapsed and falls into the cylinder 10, wear of the cylinder 10 and the piston 1 (piston body 2) is suppressed as described above.

The gap 31 is between a plurality of carbon chunks (and binders). Since the average particle diameter of the carbon lump is 20 μm or more, a relatively large void 31 is formed. Therefore, since the heat conductivity becomes lower and the volume specific heat becomes smaller as a whole of the low heat conducting portion 3, the above effects can be improved. Since the average particle diameter of the carbon lump is 100 μm or less, the contact area between the solid materials is suppressed from becoming excessively small. Therefore, the strength of the low heat conducting portion 3 can be improved and the chipping or collapse can be more easily suppressed. Since the average particle size of the lump is 50 μm or less, the above effect can be improved.

The air gap 31 is formed by the vaporization of a substance, that is, a solvent (solvent) mixed in the material for forming the low thermal conductive portion 3. In the drying step, the solvent evaporates and escapes from the coating film, and voids 31 are formed between the deposited carbon blocks (and the binder). The drying process functions as a void forming process. In addition, it is not necessary to provide a drying process in particular (the coating film may be naturally dried). In this manner, the void 31 can be easily formed by mixing the vaporizing component (substance) in the forming material.

Some of the plurality of voids 31 (the first void 311) are closed on the combustion chamber 11 side in the low heat conducting section 3. Air or solvent gas is confined in the first gap 311. Since convection hardly occurs inside the first gap 311, the heat insulating property of the low heat conducting portion 3 is improved. Further, intrusion of unburned fuel from the combustion chamber 11 into the first gap 311 is suppressed. Thereby, deterioration of exhaust gas performance is suppressed.

In the inside of the low heat conducting portion 3, on the other side in the axial direction (on the piston main body 2 side), a layer 303 having relatively few voids 31 in which carbon masses are closely approached by their own weight is formed. On one side in the axial direction (combustion chamber 11 side), a rough layer 304 is formed in which there are relatively many voids 31 between the carbon blocks. In other words, the layer 30 includes a first layer 303 and a second layer 304. Since there are many voids 31 on the combustion chamber 11 side, the heat insulating effect of the low heat conducting section 3 is high.

Note that the format of the engine 100 is arbitrary. For example, the engine 100 may be a two-stroke engine or a diesel engine. The fuel supply method may be an in-cylinder direct injection type that directly injects into the cylinder 10 (combustion chamber 11), or a port injection type that injects into the intake port. The shape of the piston 1 is arbitrary. For example, the shape of the cavity 401 is not limited to the above and is arbitrary. The crown surface 400 may not have a recess such as the cavity 401 or the valve recess 402.

[Second Embodiment]
First, the configuration will be described. Hereinafter, members and structures common to the first embodiment are denoted by the same reference numerals as in the first embodiment, and description thereof is omitted. As shown in FIG. 8, the low heat conducting section 3 has a first layer 301 on the piston body 2 side (inner side) and a second layer 302 on the combustion chamber 11 side (outer side). In general, the difference between layers can be determined by properties, shapes, functions, and the like. The structure of the first layer 301 is the same as that of the layer 30 of the first embodiment. The second layer 302 is a film containing cyanoacrylate. The first layer 301 has a plurality of voids 31 (first voids 311). These voids 31 are covered with the second layer 302 on the combustion chamber 11 side (one side in the axial direction) in the low heat conducting section 3. The second layer 302 closes (seals) the openings of these voids 31 toward the combustion chamber 11 side. Other configurations are the same as those of the first embodiment.

Hereinafter, a method for manufacturing the piston 1 will be described. The low heat conduction part forming step includes a material preparation step, a coating step, a drying step, and a sealing treatment step. The material preparation process, the application process, and the drying process are the same as those in the first embodiment. In the sealing treatment step, sealing treatment is performed on the void 31 (second void 312) formed in the drying step. A liquid adhesive (instant adhesive) containing cyanoacrylate as a main component is prepared. This adhesive is sprayed onto the coating of the mixed material, for example by spraying. Thereafter, the piston main body 2 is installed so that the piston head 4 is on the lower side in the vertical direction, preferably without leaving an excessive interval. Specifically, the crown surface 400 is directed downward in the vertical direction. The adhesive penetrates into the coating film through the opening of the gap 31 (second gap 312), and is cured by moisture in the coating process in the process. Since the piston head 4 is on the lower side in the vertical direction, the adhesive stays on one side in the axial direction of the coating film (on the combustion chamber 11 side) due to gravity and hardens at that position. Adhesive cyanoacrylate is polymerized on the combustion chamber 11 side of the coating film to form a coating film (sealing film) while leaving a gap 31 on the other axial side of the coating film (piston body 2 side). The opening on the combustion chamber 11 side of the gap 31 is closed with the sealing film. In addition, after installing the piston main body 2 so that the piston head 4 may become a vertical direction lower side, you may spray an adhesive agent on a coating film. Other manufacturing steps of the piston 1 are the same as those in the first embodiment.

Next, the function and effect will be described. The air gap 31 is covered with a film (second layer 302) containing cyanoacrylate on the combustion chamber 11 side in the low heat conducting section 3. The opening of the second gap 312 formed in the drying process is closed (sealed) by the second layer 302. As a result, the second gap 312 is converted into the first gap 311. By reducing the second gap 312 and increasing the first gap 311, it is possible to more effectively improve the heat insulation of the low heat conducting section 3 and suppress the deterioration of the exhaust gas performance. With a so-called instantaneous adhesive containing cyanoacrylate, a film for sealing the gap 31 can be easily formed. In particular, when there are many voids 31 (second voids 312), these numerous voids 31 can be easily closed in a short time.

The low heat conduction part 3 has two layers 301 and 302. Thereby, adjustment of the thickness and characteristic (function) of the low thermal conduction part 3 becomes easy. As described above, the second gap 312 can be reduced and the first gap 311 can be increased. Since the gap 31 is on the first layer 301 side, the thermal conductivity of the first layer 301 is lower than that of the second layer 302. In other words, the thermal conductivity on the combustion chamber 11 side (second layer 302) is higher than that on the piston main body 2 side (first layer 301) of the low heat conducting section 3. For this reason, the temperature on the combustion chamber 11 side (second layer 302) in the low heat conducting section 3 can more easily follow the temperature of the gas in the combustion chamber 11. In addition, the temperature distribution on the combustion chamber 11 side (second layer 302) in the low heat conducting section 3 is more easily made uniform, thereby suppressing abnormal combustion (knocking) of fuel. Note that the volume specific heat of the second layer 302 may be made smaller than that of the first layer 301 regardless of the presence or absence of the void 31, and in this case, the above-described effects can be obtained. In addition, the characteristics of each layer may be adjusted so that the first layer 301 in contact with the piston body 2 has higher bonding strength with the piston body 2 than the second layer 302. The number of layers is not limited to two, and may be three. Other functions and effects are the same as those of the first embodiment.

[Third embodiment]
As shown in FIG. 9, the low thermal conductive portion 3 is a thin film and has a layer 30. The thickness of the layer 30 is arbitrary. The low heat conduction part 3 contains carbon and a binder. Carbon includes a plurality of lumps (particles). The average particle size of the lumps is arbitrary. The binder is the same as in the first embodiment. Carbon clumps are dispersed in the binder layer. The plurality of gaps 31 in the low heat conducting unit 3 are mainly the first gaps 311. A carbon lump is embedded in or supported on the wall of the binder constituting each void 31. Other configurations are the same as those of the first embodiment.

Hereinafter, a method for manufacturing the piston 1 will be described. The low heat conduction part forming step includes a material preparation step, a coating step, a material heating step, a spraying step, and a drying step. In the material preparation step, a mixed material 32 containing a binder and a solvent is prepared. The solvent is the same as in the first embodiment. In the mixed material 32, a solvent is mixed in the binder, and the binder (particles thereof) is dispersed in the solvent. In addition, an additive etc. may be mixed with a mixed material and a binder may be abbreviate | omitted. Also, a carbon material (powder) composed of a plurality of carbon masses 33 is prepared. In the application step, the mixed material 32 is applied to the entire crown surface 400 of the piston body 2 by, for example, a spray gun. In the material heating process, the carbon material is heated. In the spraying process, the heated carbon material (powder) is sprayed onto the crown surface 400 (the coated mixed material 32). As shown in FIG. 11, a heat gun 91 can be used in these steps. As a result, the material heating process and the injection process are combined into one process and simplified. The carbon material is heated by the heat gun 91 and sprayed onto the piston head 4 (mixed material 32) together with hot air. In the drying step, the coating film onto which the carbon material has been sprayed is dried. In addition, it is not necessary to provide a drying process in particular (the coating film may be naturally dried). The material heating step and the injection step may be performed (separately) using a tool or apparatus other than the heat gun 91. Other manufacturing steps of the piston 1 are the same as those in the first embodiment.

Next, the function and effect will be described. As shown in FIG. 12, in the spraying process, a plurality of heated carbon masses 33 are embedded in the coating film of the binder (mixed with the solvent). Around each embedded mass 33 of carbon, the solvent in the coating is vaporized and expanded by the heat of the mass 33. Thereby, a plurality of voids 31 are formed in the coating film. The injection process functions as a gap forming process. Thus, the shape of the void 31 is formed by the vaporization (expansion) of the solvent. The void 31 formed by the vaporization / expansion of the solvent is relatively large. Therefore, the porosity (ratio of the volume of the void 31 in the low heat conduction part 3) can be improved, and the heat insulating property of the low heat conduction part 3 can be improved. Further, even if the coating film (binder layer) is a thin film, voids 31 are easily formed therein. In other words, the layer 30 of the low heat conducting portion 3 having the void 31 can be thinned. In the injection process, a carbon material may be embedded mainly on the combustion chamber 11 side of the coating film. In this case, the air gap 31 is easily formed on the combustion chamber 11 side in the low heat conduction section 3, and a layer having low thermal conductivity is formed on the side facing the combustion chamber 11. For this reason, the heat insulation effect can be improved. In the spraying process, a carbon material may be embedded mainly on the piston body 2 side of the coating film. In this case, the number of the second gaps 312 can be easily reduced because the gaps 31 are difficult to open to the combustion chamber 11 side. Other functions and effects are the same as those of the first embodiment.

[Fourth embodiment]
The other configurations of the low heat conducting unit 3 are the same as those of the third embodiment. The low heat conduction part forming step is the same as that of the third embodiment except for the sealing treatment step. The sealing treatment process may be performed before or after the drying process. In the sealing treatment step, among the plurality of voids 31 formed in the injection step, the one opened to the combustion chamber 11 side (second void 312) is closed with the sealing film 35. As a result, the second gap 312 is converted into the first gap 311. The material used for the closing may be a mixed material prepared in the material preparation step, or may be an adhesive as in the second embodiment. Other manufacturing steps of the piston 1 are the same as those in the first embodiment. Similar to the second embodiment, the second gap 312 can be reduced and the first gap 311 can be increased. Other functions and effects are the same as those of the third embodiment.

[Fifth Embodiment]
As shown in FIG. 14 and FIG. 15, carbon lump and binder are mixed and dispersed in the layer 30 of the low heat conducting portion 3. The air gap 31 is on the other axial side in the layer 30 (on the piston body 2 side). The air gap 31 is closed by a solid material on one side in the axial direction (combustion chamber 11 side), and is closed by the piston body 2 and the solid material on the other side in the axial direction. Other configurations are the same as those of the third embodiment. The low heat conduction part forming step includes a material preparation step, a piston body heating step, and an application step. In the material preparation step, a mixed material containing carbon, a binder, and a solvent is prepared. The solvent is the same as in the first embodiment. In the mixed material, a solvent is mixed in the carbon and the binder, and the lump of carbon and the binder (particles thereof) are dispersed in the solvent. In addition, an additive etc. may be mixed with a mixed material and a binder may be abbreviate | omitted. The piston body 2 is heated in the piston body heating step. The application process is the same as in the first embodiment, and the mixed material is applied to the entire crown surface 400 of the heated piston body 2 by, for example, a spray gun. In addition, you may provide a drying process after an application | coating process. Other manufacturing steps of the piston 1 are the same as those in the first embodiment.

Next, the function and effect will be described. When the mixed material is applied to the piston head 4 of the piston body 2 that has been preheated (preheated) in the coating process, the solvent in the mixed material is removed from the piston body on the back side of the coating film (the side facing the crown surface 400). Evaporates (boils) by the heat of 2 and expands. As a result, a plurality of voids 31 are formed in the layer 30. The coating process functions as a void forming process. The piston body heating step may be a step of heating only the combustion chamber 11 side (piston head 4) of the piston body 2. In this case, for example, compared with the case where the piston boss 5 side is also heated, the amount of heat (energy) required for heating can be suppressed. On the surface side of the coating film (side facing the combustion chamber 11), the heat of the piston body 2 is less transmitted than the back surface side and is at a low temperature. Therefore, the opening of the gap 31 to the combustion chamber 11 is suppressed, and the first gap 311 is formed. In the low heat conducting section 3, the gap 31 (first gap 311) is formed on the piston body 2 side, so that the thermal conductivity on the combustion chamber 11 side is increased, and the same effect as in the second embodiment is obtained. . Since the shape of the void 31 is formed by the vaporization (expansion) of the solvent, the same effect as in the third embodiment can be obtained. Other functions and effects are the same as those of the first embodiment.

[Sixth embodiment]
As shown in FIG. 16, as in the second embodiment, the low heat conducting unit 3 includes layers 301 and 302. The first layer 301 is the same as the layer 30 of the fifth embodiment. The second layer 302 is a film containing cyanoacrylate. There is a void 31 in the first layer 301. The second layer 302 closes (seals) the opening of the gap 31 toward the combustion chamber 11. Other configurations are the same as those of the fifth embodiment. The low thermal conductive portion forming step is the same as that of the fifth embodiment except for the sealing treatment step. The sealing treatment step is performed after the coating step, and the pore 31 is sealed. An adhesive similar to that of the second embodiment is prepared and sprayed on the coating film. If the number (or area) of openings of the gap 31 to be sealed is smaller than that in the second embodiment, the piston head 4 does not have to be on the lower side in the vertical direction as in the second embodiment. Other manufacturing steps of the piston 1 are the same as those in the first embodiment.

Even when the gap 31 formed in the coating process opens to the combustion chamber 11 side, it is blocked (sealed) by the second layer 302. Therefore, the same effect as the second embodiment can be obtained. The material of the second layer 302 may be a mixed material prepared in the material preparation step. That is, the opening of the void 31 toward the combustion chamber 11 may be closed (sealed) by further applying a mixed material to the first layer 301 formed including the void 31 in the application step. At this time, if the solvent of the mixed material of the second layer 302 is less likely to evaporate than the solvent of the mixed material of the first layer 301, the first layer 301 and the second layer 302 are excessively separated. It becomes easy to apply without a time lag (in the same process). Other functions and effects are the same as those of the fifth embodiment.

[Seventh embodiment]
As shown in FIG. 17, the low heat conducting section 3 has a plurality of mountain-shaped protrusions (convex sections) 34 that spread from the combustion chamber 11 side toward the piston body 2 side. The first gap 311 is a space inside each protrusion 34, and is closed by a solid material on one side in the axial direction (combustion chamber 11 side) and closed by the piston body 2 or the solid material on the other side in the axial direction. Yes. The second gap 312 is a space between the adjacent protrusions 34 (a recess between the protrusions). Other configurations are the same as those of the fifth embodiment. The low heat conduction part forming step includes a material preparation step, a piston body heating step, a coating step, and a peeling step. The material preparation process and the piston body heating process are the same as in the fifth embodiment. In the application process, the mixed material is applied to the entire crown surface 400 of the heated piston body 2 by a stamp. The stamp includes, for example, a porous member (rubber, sponge, etc.), and this member is impregnated with a mixture. Press this stamp against the crown 400. In the peeling step, the stamp is peeled off from the piston head 4. The stamp is a roller for painting. By using a roller, the coating process and the peeling process can be performed in one operation, and the processes can be simplified together. Other manufacturing steps of the piston 1 are the same as those in the first embodiment.

Next, the function and effect will be described. In the application process, the mixed material is applied to the piston head 4 by a stamp. When the stamp is peeled off from the piston head 4 (piston body 2) in the peeling process, for example, a plurality of protrusions (convex portions) 34 corresponding to a plurality of unevenness (pores) on the surface of the porous member are formed. Formed with mixed material. A plurality of second gaps 312 are formed between the adjacent protrusions 34. Each protrusion 34 is dried and solidified by heat from the piston body 2. At that time, the heat of the piston main body 2 promotes the vaporization (expansion) of the solvent in the mixed material on the piston main body 2 side in the protrusion 34, and a cavity is generated. As a result, a first gap 311 is formed in the protrusion 34. Since the air gap 31 (first air gap 311) is formed not only outside but also inside the protrusion 34, the air gap 31 is efficiently provided (increase the porosity) in the low heat conducting section 3, and the low heat conducting section 3 Can be prevented from becoming thick in the axial direction as a whole. The stamp may not be a roller. A sealing process similar to that in the second embodiment may be applied. That is, a second layer that seals the second gap 312 (the recess between the protrusions 34) and converts it into the first gap 311 may be provided. Other functions and effects are the same as those of the fifth embodiment.

[Eighth embodiment]
As shown in FIG. 18, as in the second embodiment, the low heat conducting unit 3 includes layers 301 and 302. In each of the layers 301 and 302, carbon lump and binder are mixed and dispersed. The thickness of each layer 301, 302 is arbitrary. The first layer 301 has a plurality of voids 31 (first voids 311). The air gap 31 is biased toward the combustion chamber 11 side (second layer 302 side) in the first layer 301. The second layer 302 closes the opening of the gap 31 toward the combustion chamber 11 side. Other configurations are the same as those of the fifth embodiment. The low heat conduction part forming step includes a material preparation step, a coating step, a drying step, and a heating step. The material preparation process is the same as in the fifth embodiment. The application process is the same as in the fifth embodiment, and the mixed material is applied to the crown surface 400 of the piston body 2 by, for example, a spray gun. In the drying step, the surface of the applied forming material (coating film) (surface layer facing the combustion chamber 11) is dried by, for example, infrared irradiation. In the heating step, the inside (deep layer) of the coating film whose surface has been dried is heated. By heating the piston body 2, the coating film (forming material) is heated from the back side (piston body 2 side). Other manufacturing steps of the piston 1 are the same as those in the first embodiment.

Next, the function and effect will be described. In the drying step, the surface of the coating film is dried. That is, the solvent of the forming material is evaporated from the surface. As a result, the surface of the coating is solidified and a coating (second layer 302) is formed. On the inner side (piston main body 2 side) of the coating film than the second layer 302 is a fluid first layer 301 in which the solvent remains in the forming material. In the heating step, the back surface of the coating film is heated. A plurality of voids 31 are formed on the piston body 2 side in the first layer 301 as the solvent evaporates (boils) in this portion and expands. The heating process functions as a void forming process. The heating step may be a step of heating only the combustion chamber 11 side (piston head 4) of the piston main body 2 as in the piston main body heating step of the fifth embodiment. Further, instead of heating the piston main body 2, the coating film (with the surface dried) may be directly heated by infrared rays or the like. The coating film (dried surface) may be heated not from the back side but from the front side (combustion chamber 11 side). Since the shape of the void 31 is formed by the vaporization (expansion) of the solvent, the same effect as in the third embodiment can be obtained.

Since the piston body 2 is installed so that the piston head 4 is on the upper side in the vertical direction, the air gap 31 will move from the piston body 2 side in the first layer 301 to the combustion chamber 11 side (second layer 302 side). And However, the air gap 31 is blocked by the solidified second layer 302 and does not open on the surface of the low thermal conductive portion 3 (the surface of the second layer 302). In other words, the second layer 302 functions as a sealing film that closes the opening of the gap 31. As described above, it is easy to form a sealing film on the surface of the low thermal conductive portion 3, and the sealed void 311 (first void 311) can be easily formed. On the other hand, since the plurality of voids 31 gather on the combustion chamber 11 side in the first layer 301, the heat insulation effect is improved. Other functions and effects are the same as those of the second embodiment. Note that the formation material of the first layer 301 and the second layer 302 is the same, and only the presence or absence of the void 31 is different. Therefore, both layers 301 and 302 can be collectively regarded as one layer if the presence or absence of the void 31 and the sealing function is not taken into consideration.

[Ninth Embodiment]
As shown in FIG. 19, the air gap 31 is present not only on the combustion chamber 11 side (second layer 302 side) but also on the piston body 2 side in the first layer 301. Other configurations are the same as those in the eighth embodiment. The low heat conduction part forming step includes a material preparation step, a coating step, and a material heating step. The material preparation process and the application process are the same as in the eighth embodiment. As shown in FIG. 20, in the material heating step, the applied forming material (coating film 36) is heated by, for example, irradiating infrared rays 92 only from the combustion chamber 11 side. Other manufacturing steps of the piston 1 are the same as those in the first embodiment.

Next, the function and effect will be described. In the material heating step, the coating film 36 is heated from the surface (surface layer facing the combustion chamber 11) side. Thereby, the surface of the coating film 36 is dried, and a solidified film (second layer 302) is formed on the surface side, and on the inner side (first layer 301) of the second layer 302 in the coating film, The solvent is vaporized by heat and expands, and a plurality of voids 31 are formed. The material heating process functions as a void forming process. Similar to the eighth embodiment, even if the air gap 31 tries to move to the combustion chamber 11 side in the first layer 301, it is stopped by the solidified second layer 302 and does not open on the surface. Thus, since the surface side of the coating film 36 is first dried and solidified, the void 31 formed in the coating film 36 is easily sealed. In the same material heating process, the void 31 and the film (second layer 302) that seals the gap 31 are formed, so the drying process and heating process of the eighth embodiment are combined into one process and simplified. It becomes. In the material heating step, the coating film 36 is first heated rapidly (for example, from the vicinity of the coating film 36), and then slowly (from a distance from the coating film 36), so that the air gap 31 is sealed. The hole 302 may be effectively formed. This material heating step may also be interrupted (may be discontinuous). In the material heating step, the forming material may be heated not only from the combustion chamber 11 side but also from the piston body 2 side, for example. By heating the forming material only from the combustion chamber 11 side, the amount of heat required for heating can be suppressed as compared to the case of heating from the other side. Other functions and effects are the same as those of the eighth embodiment.

[Tenth embodiment]
As shown in FIG. 21, as in the second embodiment, the low heat conducting unit 3 includes two layers 301 and 302. The first layer 301 has a plurality of mountain-shaped protrusions (convex portions) 37 that spread from the combustion chamber 11 side toward the piston body 2 side. The air gap 31 is a space between adjacent projections 37 (a recess between the projections 37), is closed by the second layer 302 on one side in the axial direction (combustion chamber 11 side), and on the other side in the axial direction, the piston body 2 Or solid material. Other configurations are the same as those of the fifth embodiment. The low heat conduction part forming step includes a material preparation step, a first application step, a first drying step, a second application step, and a second drying step. The material preparation process is the same as in the fifth embodiment. In the first application step, a mesh-like member (mesh) 93 is installed on the entire crown surface 400 of the piston body 2. The forming material (mixed material) 370 is applied through the mesh 93. FIG. 22 is a schematic view of the forming material 370 together with the mesh 93 as viewed from the combustion chamber 11 side. A forming material 370 is applied to the crown surface 400 through the mesh 93. FIG. 23 is a schematic view of the forming material 370 (first coating film) after the mesh 93 is removed as viewed from the combustion chamber 11 side. In the first drying step, the first coating film is dried by, for example, infrared irradiation. In the second application step, a forming material (mixed material) 370 is further applied on the dried first coating film. For application, the mesh 93 may be used again, or a stamp may be used. In the second drying step, the forming material 370 (second coating film) applied in the second application step is dried by, for example, infrared irradiation. Other manufacturing steps of the piston 1 are the same as those in the first embodiment.

Next, the function and effect will be described. When the mesh 93 is removed in the first application step, the forming material 370 remains in a mesh shape (a plurality of dots or grains). That is, the forming material 370 is applied in a fine uneven shape. Each convex part made of the forming material 370 maintains its shape immediately after application as shown in FIG. 24, but after a certain amount of time, it is scooped by its own weight, and as shown in FIG. 25, the piston body with the combustion chamber 11 side as the apex It becomes the mountain-shaped protrusion 37 which spreads toward 2 side. The first layer 301 is formed by these protrusions 37. That is, the gap 31 is derived from the unevenness formed during the first application process. The first application process functions as a void forming process. In the first drying step, each protrusion 37 is solidified by drying. In the second application step, the forming material 370 is overcoated at a position that overlaps the apex of each protrusion 37 in the direction in which the axis of the piston 1 extends. The opening of the recess between the protrusions 37 is closed by the second coating film, and a first gap 311 is formed. The second coating film (second layer 302) that solidifies in the second drying step functions as a sealing film for the recesses (voids 31). The second application process functions as a sealing treatment process. Note that the first and second drying steps are not particularly required (the coating film may be naturally dried). The piston body 2 may be heated, and the coating film may be dried by heat from the piston body 2. In the second application step, the same adhesive as in the second embodiment may be used instead of the mixed material. The second coating step may not be provided (the second layer 302 may not be formed). In this case, the recess between the protrusions 37 functions as the gap 31 (second gap 312). In the present embodiment, since the second coating step is provided (the second layer 302 is formed), the second gap 312 is converted into the first gap 311 and the same effect as in the second embodiment is obtained. The size of the gap 31 can be adjusted by changing the mesh roughness of the mesh 93. Thereby, the porosity can be adjusted. Other functions and effects are the same as those of the first embodiment.

[Eleventh embodiment]
The configuration is substantially the same as in the tenth embodiment. The low heat conduction part forming step includes a material preparation step, a pretreatment step, a first application step, a first drying step, a second application step, and a second drying step. In the material preparation step, the water-repellent paint 373, the first mixed material 371, and the second mixed material are prepared. The first mixed material 371 includes a solid material (carbon and binder) and water. Carbon includes a plurality of lumps (particles). The average particle size of the lumps is arbitrary. The binder is a water-soluble binder for adhering carbon particles, and is a chemical glue such as carboxymethyl cellulose (CMC) or polyvinyl alcohol (PVA). Water is a solvent (solvent) for chemical glue. In the first mixed material 371, carbon lump and binder particles are dispersed in water. An additive or the like may be mixed in the first mixed material 371. The second mixed material is the same as the mixed material of the fifth embodiment. In the pretreatment step, the water repellent paint 373 is applied to the entire crown surface 400 of the piston body 2. In the first application step, the first mixed material 371 is applied on the applied water-repellent paint 373. For application, a spray may be used, or a mesh or a stamp may be used. In the first drying step, the coating film of the first mixed material 371 is dried by, for example, infrared irradiation. In the second application step, the second mixed material is repeatedly applied to the dried coating film of the first mixed material 371 as in the tenth embodiment. In the second drying step, the applied second mixed material is dried as in the tenth embodiment. Other manufacturing steps of the piston 1 are the same as those in the first embodiment.

Next, the function and effect will be described. In the first application step, the first mixed material 371 is repelled without getting wet in the region where the water repellent paint 373 is applied. As a result, as shown in FIG. 26, the first mixed material 371 remains on the crown surface 400 in a plurality of dots or grains. That is, the first mixed material 371 is applied in a fine uneven shape. The first layer 301 is formed by a plurality of convex portions of the first mixed material 371. In the first drying step, each convex portion (first mixed material 371) is solidified by drying. The first application process functions as a void formation process, the second application process functions as a sealing treatment process, the drying process and the second application process may be omitted, and an adhesive instead of the second mixed material As in the tenth embodiment, may be used. By changing the composition of the first mixed material 371, the size of the protrusions formed in the first application step (that is, the size of the gap 31) can be adjusted. Thereby, the porosity of the low heat conductive part 3 can be adjusted. By using chemical glue as the binder of the first mixed material 371, the application of the first mixed material 371 is easy. In addition, the binder is easily burned by heat from the combustion chamber 11 and the like. The voids 31 can be formed more efficiently by burning out the binder. Other functions and effects are the same as those of the first and second embodiments.

[Twelfth embodiment]
As shown in FIG. 27, the plurality of voids 31 (first voids 311) are adjacent to each other across a thin film-like wall 38 made of a solid material. Other configurations are the same as those of the fifth embodiment. The low heat conduction part forming step includes a material preparation step, a foaming step, a coating step, and a drying step. The material preparation process is the same as in the fifth embodiment. In the foaming step, the forming material (mixed material) 370 is bubbled by bubbling, stirring, or using a foaming agent. As shown in FIG. 28, the forming material 370 in a foamed state is applied to the crown surface 400 of the piston body 2 in the application process. In the drying step, the applied forming material 370 (coating film) is dried by, for example, infrared irradiation. Other manufacturing steps of the piston 1 are the same as those in the first embodiment.

Next, the function and effect will be described. The air gap 31 of the low heat conducting portion 3 is formed by foaming the forming material 370. The foaming process and the coating process function as a void forming process. When the coating film is dried and solidified by the drying process, the solid material remains in the form of foam and forms a film-like wall 38 that defines the gap 31. In addition, it is not necessary to provide a drying process in particular (the coating film may be naturally dried). Further, the foaming step and the coating step may be combined as one step. That is, the forming material (mixed material) 370 may be applied while foaming, or may be foamed while being applied. By forming the gap 31 by foaming the forming material 370, the low heat conduction portion 3 having a relatively high porosity can be formed. Moreover, the porosity of the low heat conductive part 3 can be adjusted by adjusting a foaming degree. Other functions and effects are the same as those of the first and second embodiments.

[Thirteenth embodiment]
In the solid material of the low heat conducting section 3, any of the following (1) to (5) is used instead of carbon. (1) Boron nitride (2) Molybdenum disulfide (3) Carbon and boron nitride (4) Boron nitride and molybdenum disulfide (5) Carbon, boron nitride and molybdenum disulfide Above, boron nitride is an atmospheric pressure h- BN. The binder adheres the particles (1) to (5). Other configurations and the manufacturing process of the piston 1 are the same as those in any of the first to twelfth embodiments.

Table 2 shows an example of general characteristics of the base metal and molybdenum disulfide and boron nitride.

Like carbon, boron nitride and molybdenum disulfide have lower thermal conductivity than the aluminum alloy that is the material of the piston body 2. Like carbon (graphite), boron nitride (h-BN) and molybdenum disulfide have a layered structure with a low bonding force between crystal faces, and are generally used as solid lubricants. Further, boron nitride and molybdenum disulfide have high heat resistance and excellent durability. Therefore, the same effect as that of the first to twelfth embodiments can be obtained.

[14th Embodiment]
The entire crown surface 400 (including the surface of the cavity 401) in the piston body 2 is a casting surface when the piston body 2 is cast. The other configuration and the manufacturing process of the piston 1 are the same as those in any of the first to thirteenth embodiments. Therefore, the site | part in which the low heat conductive part 3 in the piston head 4 is formed becomes a casting surface. Since the casting surface has fine irregularities, the irregularities exhibit a function (anchor effect) for holding a solid material, and can prevent the low heat conduction portion 3 from falling off the piston body 2. Further, since the casting surface that is formed when the piston body 2 is cast is utilized as it is, no special surface treatment is required. In the crown surface 400, only a part of the crown surface 400 may be a casting surface, and the other part may not be a casting surface. For example, only the cavity 401 may be a casting surface, and other parts may be machined. In addition, the same effects as those of the first to thirteenth embodiments can be obtained.

[Fifteenth embodiment]
In the piston main body 2, the entire crown surface 400 (including the surface of the cavity 401) is subjected to a surface treatment that improves the bonding force with the low heat conducting unit 3. The piston body forming step includes a surface treatment step. The surface treatment process is performed, for example, after the machining process. The other configuration and the manufacturing process of the piston 1 are the same as those in any of the first to thirteenth embodiments. As shown in FIG. 29, a shot (projection material) 94 is sprayed to roughen the surface of the crown surface 400 to provide fine irregularities. This unevenness increases the degree of adhesion (anchor effect) of the solid material to the surface. Therefore, it is possible to suppress the dropout of the low heat conducting unit 3. Here, it is also conceivable that the projection material 94 adheres to the surface. If molybdenum disulfide is used as the projection material 94 (molybdenum disulfide shot), even if the fixed projection material 94 falls into the cylinder 10, it functions as a lubricant, and the cylinder 10 and the piston 1 Wear can be suppressed. Note that surface treatment for providing fine unevenness may be performed by a method other than shot blasting (for example, a photoetching method). In the crown surface 400, only a part of the surface treatment is performed, and other portions may not be subjected to the surface treatment. For example, the surface treatment may be performed only on the cavity 401, and the surface treatment may not be performed on other portions. In addition, the same effects as those of the first to thirteenth embodiments can be obtained.

[Sixteenth embodiment]
In the mixed material used in the low heat conduction part forming step, the solvent is water. The other structure and the manufacturing process of the piston 1 are the same as those in any of the first to tenth and twelfth embodiments. The same effects as the first to tenth and twelfth embodiments can be obtained.

[17th embodiment]
In the mixed material used in the low heat conduction part forming step, the binder is chemical glue (CMC or PVA). The other configuration and the manufacturing process of the piston 1 are the same as those of any of the first to tenth and twelfth embodiments. The same effects as those of the first to tenth and twelfth embodiments can be obtained. Further, by using chemical glue as the binder, the same effects as those of the eleventh embodiment can be obtained.

[Eighteenth embodiment]
The low heat conducting portion 3 is partially formed on the crown surface 400 of the piston body 2. The other configuration and the manufacturing process of the piston 1 are the same as those in any of the first to 17th embodiments. The same effect as that of the first to 17th embodiments can be obtained at the site where the low heat conducting section 3 is formed. In this case, in the in-cylinder direct injection type engine 100, the low heat conduction unit 3 is provided on the crown surface 400 at least a part corresponding to the fuel injection region (the part where the fuel collides / explodes and the temperature or pressure becomes highest) It is preferable to be formed on the periphery. By forming the low heat conduction portion 3 at this location, heat transfer from the gas in the combustion chamber 11 to the piston head 4 (piston body 2) can be more effectively reduced. Moreover, since the heat absorption to the piston main body 2 is suppressed by the low heat conductive layer 3, the location where the fuel adheres on the crown surface 400 quickly becomes high temperature and maintains a high temperature state. Therefore, the adhering fuel is quickly vaporized and burned, so that deterioration of exhaust gas characteristics can be suppressed.

Further, the low heat conducting portion 3 may be formed only on the surface of the cavity 401 or other concave portion on the crown surface 400. By forming the low heat conduction part 3 in this way, the low heat conduction part 3 is accommodated in the recess, and thus it is possible to suppress the crown surface 400 from rising to the combustion chamber 11 side by the low heat conduction part 3. FIG. 30 shows an example in which the low heat conducting portion 3 is formed only on the surface of a part of the recess (valve recess 402). 31 and 32 show an example of the piston 1 in which the shape of the piston body 2 is different from that of the first to 17th embodiments. The low heat conduction part 3 is formed only on the surface of a part of the recess (valve recess 403). The portion where the low heat conductive portion 3 is formed on the surface of the recesses 401 to 403 may be a cast surface as in the fourteenth embodiment, or may be subjected to a surface treatment as in the fifteenth embodiment. .

[Other Embodiments]
As mentioned above, although the form for implementing this invention was demonstrated based on drawing, the specific structure of this invention is not limited to embodiment, The design change etc. of the range which does not deviate from the summary of invention are included. Even if it exists, it is included in this invention. In addition, any combination or omission of each constituent element described in the claims and the specification is possible within a range where at least a part of the above-described problems can be solved or a range where at least a part of the effect is achieved. It is.

[Other aspects that can be grasped from the embodiment]
Other aspects (or technical solutions, the same applies hereinafter) that can be understood from the embodiment described above will be described below.
(1) In one aspect of the piston of the internal combustion engine,
A body comprising an aluminum alloy and facing a combustion chamber of an internal combustion engine; and a piston boss and a piston skirt disposed on the opposite side of the combustion chamber with respect to the piston head;
The piston head is located on the combustion chamber side and is made of a material containing at least one of carbon, boron nitride, and molybdenum disulfide, and has a low heat conduction portion having a void inside.
(2) In a more preferred embodiment, in the above embodiment,
The material includes carbon, and the carbon includes 50% by volume or more of a component having an SP2 structure.
(3) In another preferred embodiment, in any of the above embodiments,
The voids are formed by the vaporization of the solvent mixed in the material.
(4) In still another preferred embodiment, in any of the above embodiments,
The material is a synthetic resin and includes a binder that bonds the particles of the carbon, the boron nitride, or the molybdenum disulfide.
(5) In still another preferred embodiment, in any of the above embodiments,
The binder is an engineering plastic.
(6) In still another preferred embodiment, in any of the above embodiments,
The gap is closed on the combustion chamber side in the low heat conduction portion.
(7) In still another preferred embodiment, in any of the above embodiments,
The air gap is covered with a film containing cyanoacrylate on the combustion chamber side in the low heat conduction portion.
(8) In still another preferred embodiment, in any of the above embodiments,
The voids are formed by vaporizing substances mixed in the material.
(9) In still another preferred embodiment, in any of the above embodiments,
The low heat conduction part has a plurality of layers.
(10) In still another preferred embodiment, in any of the above embodiments,
The main body includes a concave portion that accommodates the low heat conduction portion on the combustion chamber side,
A surface treatment is performed on the surface of the concave portion to improve the bonding force with the low thermal conductive portion.
(11) In still another preferred embodiment, in any of the above embodiments,
The main body includes a concave portion that accommodates the low heat conduction portion on the combustion chamber side,
The surface of the said recessed part is a casting surface at the time of casting the said main body.
(12) In still another preferred embodiment, in any of the above embodiments,
The material includes a plurality of carbon chunks having an average particle size of 20 μm or more,
The voids are between the plurality of carbon chunks.
(13) In still another preferred embodiment, in any of the above embodiments,
The gap is formed by foaming the material.
(14) In one aspect of the method for producing a piston of an internal combustion engine,
Forming a body having a piston head facing a combustion chamber of an internal combustion engine and a piston boss and a piston skirt disposed on the opposite side of the combustion chamber with respect to the piston head from an aluminum alloy;
Forming a low thermal conduction part having a void inside on the combustion chamber side of the piston head with a material containing at least one of carbon, boron nitride, and molybdenum disulfide.
(15) In a more preferred embodiment, in the above embodiment,
The material includes a vaporizing component;
The step of forming the low thermal conductive portion includes the step of forming the voids by the vaporization of the components.
(16) In another preferred embodiment, in any of the above embodiments,
The component is a solvent,
In the step of forming the voids, the solvent is vaporized and expanded to form the voids.
(17) In still another preferred embodiment, in any of the above embodiments,
The material is a synthetic resin, and includes a binder that bonds particles of the carbon, the boron nitride, or the molybdenum disulfide, and a solvent as the component to be vaporized,
The step of forming the low thermal conduction part includes
Applying the binder mixed with the solvent to the combustion chamber side of the piston head;
Heating a powder comprising at least one of the carbon, the boron nitride, and the molybdenum disulfide;
Injecting the heated powder to the combustion chamber side of the piston head.
(18) In still another preferred embodiment, in any of the above embodiments,
The material is a synthetic resin, and includes a binder that bonds particles of the carbon, the boron nitride, or the molybdenum disulfide, and a solvent as the component to be vaporized,
The step of forming the low thermal conduction part includes
Heating the body;
Applying the material to the combustion chamber side of the piston head of the heated body.
(19) In still another preferred embodiment, in any of the above embodiments,
The material is a synthetic resin, and includes a binder that bonds particles of the carbon, the boron nitride, or the molybdenum disulfide, and a solvent as the component to be vaporized,
The step of forming the low thermal conduction part includes
Applying the material to the combustion chamber side of the piston head;
Drying the surface of the applied material;
Heating the material whose surface has been dried.
(20) In still another preferred embodiment, in any of the above embodiments,
The material includes a vaporizing component;
The step of forming the low thermal conduction part includes
Applying the material to the combustion chamber side of the piston head;
Heating the applied material from the combustion chamber side.
(21) In still another preferred embodiment, in any of the above embodiments,
In the step of heating the material, the material is heated only from the combustion chamber side.
(22) In still another preferred embodiment, in any of the above embodiments,
The material is a synthetic resin and includes a binder that bonds particles of the carbon, the boron nitride, or the molybdenum disulfide,
The step of forming the low thermal conduction part includes
Applying the material to the combustion chamber side of the piston head through a mesh member;
Applying the material on the applied material.
(23) In still another preferred embodiment, in any of the above embodiments,
The material includes water, a water-soluble binder that bonds the particles of the carbon, the boron nitride, or the molybdenum disulfide, and water.
The step of forming the low thermal conduction part includes
Applying a water repellent coating to the combustion chamber side surface of the piston head;
Applying the material onto the applied water-repellent paint.
(24) In still another preferred embodiment, in any of the above embodiments,
The material is a synthetic resin and includes a binder that bonds particles of the carbon, the boron nitride, or the molybdenum disulfide, and a solvent.
The step of forming the low thermal conduction part includes
Pressing the stamp containing the material against the combustion chamber side of the piston head;
Peeling the stamp from the piston head.

This application claims priority based on Japanese Patent Application No. 2016-164279 filed on August 25, 2016. The entire disclosure including the specification, claims, drawings, and abstract of Japanese Patent Application No. 2016-164279 filed on August 25, 2016 is incorporated herein by reference in its entirety.

100 engine (internal combustion engine), 11 combustion chamber, 1 piston, 2 piston body, 3 low heat conduction part, 31 gap, 4 piston head, 5 piston boss, 6 piston skirt

Claims (24)

1. A piston of an internal combustion engine,
   A main body formed of an aluminum alloy, the main body having a piston head, and a piston boss and a piston skirt provided on a side opposite to the combustion chamber of the internal combustion engine with respect to the piston head When,
   A low heat conduction part provided on the combustion chamber side of the internal combustion engine of the piston head, formed of a low heat conduction part forming material containing carbon, boron nitride, or molybdenum disulfide, and having a void inside;
   With a piston.
2. The piston according to claim 1,
   The low heat conduction part forming material includes a piston containing 50% by volume or more of a component of SP2 structure.
3. The piston according to claim 2,
   The air gap of the low thermal conduction part is formed by volatilization of a volatile solvent mixed in the low thermal conduction part forming material.
4. The piston according to claim 3,
   The low heat conduction portion forming material is a binder formed of a synthetic resin, and includes a binder that bonds the carbon, the boron nitride, or the molybdenum disulfide together.
5. The piston according to claim 4, wherein
   The binder is an engineering plastic piston.
6. The piston according to claim 1,
   The air gap of the low heat conduction part is closed on the crown side of the piston head.
7. The piston according to claim 6,
   The air gap of the low heat conduction part is covered with a coating of acryl acetate on the crown surface side of the piston head.
8. The piston according to claim 1,
   The air gap of the low thermal conduction part is formed by vaporizing a substance mixed in the low thermal conduction part forming material.
9. The piston according to claim 1,
   The low heat conduction part has a multilayer structure.
10. The piston according to claim 1,
    The main body is a housing recess provided on the combustion chamber side of the main body, and includes a housing recess that houses the low heat conduction unit,
    The accommodation recess is subjected to a surface treatment that improves the binding force with the low thermal conductivity portion.
11. The piston according to claim 1,
    The said accommodating recessed part was formed by the casting surface at the time of casting the said main-body part.
12. The piston according to claim 1,
    The low heat conduction part forming material is a lump of carbon having an average particle size of 20 μm or more,
    The air gap is formed between the plurality of carbon chunks.
13. The piston according to claim 1,
    The air gap of the low heat conduction part is formed by firing a substance mixed in the low heat conduction part forming material.
14. A method of manufacturing a piston for an internal combustion engine,
    A main body portion forming step of forming a main body portion made of an aluminum alloy with a piston head portion, a piston boss portion provided on the opposite side of the combustion chamber of the internal combustion engine with respect to the piston head portion, and a piston skirt portion; ,
    A low heat conduction part formed of a low heat conduction part forming material containing carbon, boron nitride, or molybdenum disulfide is formed on the combustion chamber side of the internal combustion engine of the piston head, and a low heat conduction part having a void inside is formed. The manufacturing method of a piston provided with the low heat conductive part formation process.
15. The method for manufacturing a piston according to claim 14,
    The low heat conduction part forming material includes a vaporizing component,
    The low thermal conduction part forming step includes a gap forming step of forming the gap by vaporizing the vaporized component.
16. A method of manufacturing a piston according to claim 15,
    The vaporizing component is a volatile solvent,
    The said space | gap formation process is a process of forming the said space | gap by volatilizing, after the said volatile solvent expand | swells The manufacturing method of a piston.
17. A method of manufacturing a piston according to claim 15,
    The low heat conduction part forming material is a binder formed of a synthetic resin, and includes a binder that bonds the carbon, the boron nitride, or the molybdenum disulfide, and a volatile solvent.
    The low thermal conduction part forming step includes:
    A low heat conduction part forming material heating step for heating the low heat conduction part forming material;
    An injection step of injecting the low thermal conductive portion forming material heated by the low thermal conductive portion forming material heating step onto the main body portion;
    A method for manufacturing a piston.
18. A method of manufacturing a piston according to claim 15,
    The low heat conduction part forming material is a binder formed of a synthetic resin, and includes a binder that bonds the carbon, the boron nitride, or the molybdenum disulfide, and a volatile solvent.
    The low thermal conduction part forming step includes:
    A body heating step for heating the body,
    An application step of applying the low thermal conduction part forming material to the main body part;
    A method for manufacturing a piston.
19. A method of manufacturing a piston according to claim 15,
    The low heat conduction part forming material is a binder formed of a synthetic resin, and includes a binder that bonds the carbon, the boron nitride, or the molybdenum disulfide, and a volatile solvent.
    The low thermal conduction part forming step includes:
    An application step of applying the low thermal conduction part forming material to the main body part;
    A drying step of drying the surface of the low thermal conductive portion forming material applied by the application step;
    After the drying step, a heating step for heating the low thermal conduction part forming material,
    A method for manufacturing a piston.
20. The method for manufacturing a piston according to claim 14,
    The low heat conduction part forming material includes a vaporizing component,
    The low thermal conduction part forming step includes:
    An application step of applying the low thermal conduction part forming material to the main body part;
    After the application step, a low heat conduction part heating step of heating the low heat conduction part forming material from the crown side of the main body part,
    A method for manufacturing a piston.
21. A method of manufacturing a piston according to claim 20,
    The said low heat conductive part heating process is a process of heating the said low heat conductive part formation material only from the crown side of the said main-body part The manufacturing method of a piston.
22. The method for manufacturing a piston according to claim 14,
    The low heat conduction part forming material is a binder formed of a synthetic resin, and includes a binder that bonds the carbon, the boron nitride, or the molybdenum disulfide, and a volatile solvent.
    In the low heat part forming step, the low heat part forming material is applied to the main body part via a mesh, and then the low heat part forming material is further applied to the low heat part forming material applied to the main body part via the mesh. The manufacturing method of a piston provided with the process of apply | coating.
23. The method for manufacturing a piston according to claim 14,
    The low heat conduction part forming material is a binder formed of a synthetic resin, and includes a binder that bonds the carbon, the boron nitride, or the molybdenum disulfide together, and a water-soluble solvent.
    The low heat part forming step includes a step of applying the water repellent paint so as to be dispersed on the surface of the main body, and then applying the low heat part forming material on the water repellent paint applied to the main body. Piston manufacturing method.
24. The method for manufacturing a piston according to claim 14,
    The low heat conduction part forming material is a binder formed of a synthetic resin, and includes a binder that bonds the carbon, the boron nitride, or the molybdenum disulfide, and a volatile solvent.
    The low heat portion forming step includes a step of applying the low heat portion forming material to the main body portion by a stamp and then peeling the stamp from the main body portion.

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