WO2018116753A1

WO2018116753A1 - Piston for internal combustion engine, method for manufacturing piston for internal combustion engine, and structure

Info

Publication number: WO2018116753A1
Application number: PCT/JP2017/042480
Authority: WO
Inventors: 高橋　智一
Original assignee: 日立オートモティブシステムズ株式会社
Priority date: 2016-12-20
Filing date: 2017-11-28
Publication date: 2018-06-28
Also published as: JP2018100625A

Abstract

Provided is a piston for an internal combustion engine enabling an improvement in the controllability of thermal conductivity. The piston for the internal combustion engine is provided with: a body section which is formed from a metal material and provided with a piston head and a skirt part, wherein a holding part is formed in the piston head on the side toward the combustion chamber of the internal combustion engine; and a sintered body which is disposed in the holding part and contains hollow particles and a metal binder, the sintered body being provided with an oxidized binder part where the binder on at least the surface toward the combustion chamber is oxidized.

Description

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

The present invention relates to a piston and other structures of an internal combustion engine.

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

JP 2012-072745 A

The conventional structure has room for improving the controllability of thermal conductivity.

A structure according to an embodiment of the present invention includes a main body formed of a metal material, a holding portion formed in the main body, and a sintered body that is disposed in the holding portion and contains hollow particles and a metal binder. A sintered body in which the binder is oxidized at least on the outer surface.

Therefore, controllability of thermal conductivity can be improved.

1 schematically shows a cross section of a part of an engine taken along a plane passing through the axis of one cylinder of the first embodiment. 1 is a schematic perspective view of a piston according to a first embodiment. 1 schematically shows a cross section (hereinafter referred to as an axial cross section) obtained by cutting a part of a sintered body and a piston head (hereinafter referred to as a sintered body, etc.) according to a first embodiment along a plane parallel to the axis of the piston. 1 schematically shows a partial axial cross section of a sintered body or the like in a material installation step of a first embodiment. 1 schematically shows a sintering process of a first embodiment. FIG. 2 schematically shows a partial axial cross section of a sintered body of a first comparative embodiment in which the sintered body does not contain hollow particles. FIG. 3 schematically shows a partial axial cross section of a sintered body of a second comparative embodiment in which the sintered body does not contain hollow particles. FIG. 6 schematically shows a partial axial cross section of a sintered body of a third comparative embodiment in which the sintered body does not contain hollow particles. The sintering process of 2nd Embodiment is typically shown. A partial axial section of a sintered body or the like of the fourth embodiment is schematically shown.

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 this embodiment is a 4-stroke gasoline engine. As shown in FIG. 1, 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, and an ignition device 108. 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. In the cylinder head 104, a valve 107, a nozzle of a fuel injection valve, and an ignition device 108 are installed. 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. The combustion chamber 11 is defined by the inner wall surface of the cylinder 10, the top surface of the piston, the bottom surface of the cylinder head, and the top surface of the valve. The format of 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.

As shown in FIG. 2, the piston 1 has a main body 2 and a sintered body 3. The main body 2 is formed of an aluminum alloy (for example, Al-Si AC8A) as a material (raw material) for weight reduction or the like. The piston 1 (main body portion 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. The direction in which the axis of the piston 1 extends (the direction along the moving direction of the main body 2 in the cylinder 10) is referred to as the axial direction. The side of the piston head 4 with respect to the piston boss 5 and piston skirt 6 in the axial direction is called one side, and the opposite side is called 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 has a planar shape that extends perpendicular to the axis of the piston 1 and has a substantially circular outline when viewed from one side in the axial direction. As shown in FIG. 1 (when the piston 1 is at 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 directly exposed to the combustion gas in the combustion chamber 11. The main body 2 includes a recess 401 on the combustion chamber 11 side (side facing the combustion chamber 11) of the piston head 4 (crown surface portion 40). The concave portion 401 is substantially at the center of the crown surface 400 in the crown surface portion 40 and has a bottomed cylindrical shape (a shallow dish shape whose bottom surface is a flat surface). The axis of the recess 401 substantially coincides with the axis of the piston 1 (within manufacturing error). 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. Inside the land portion 41 is an annular passage 411. The passage 411 extends in the circumferential direction of the piston 1 and surrounds the recess 401 when viewed from the axial direction. The passage 411 overlaps at least a part of the region where the ring groove 410 is formed in the axial direction.

The piston boss 5 and the piston skirt 6 extend from the piston head 4 (land portion 41) 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 sides of the piston skirt 6 and the piston boss 5 are hollow. There are a pair of piston bosses 5 on both radial sides 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 radial sides 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 and flows out from the inner peripheral side (back side) of the piston 1 or when oil flows through the passage 411. This adhesion and distribution of oil is performed, for example, by oil injection from the oil jet 105. The passage 411 functions as a cooling passage (cooling channel).

The sintered body 3 is a structure for reducing the thermal conductivity from the combustion chamber 11 to the main body 2 and is located on one side in the axial direction of the piston head 4 (on the combustion chamber 11 side). It is formed on a part of the facing surface (crown surface 400). The sintered body 3 is accommodated in the recess 401. As shown in FIGS. 1 and 2, the sintered body 3 has a planar shape extending along the crown surface 400 (and the bottom surface of the recess 401). The thickness of the sintered body 3 (depth of the recess 401) is arbitrary. There are voids (hollow portions) 33 inside the sintered body 3, and a plurality of voids 33 are dispersed. Gas (air) exists in the gap 33.

The sintered body 3 includes a metal binder 31 and hollow particles 32. The binder 31 includes aluminum. Aluminum may be pure aluminum, an aluminum alloy, or may include both pure aluminum and an aluminum alloy. The binder 31 may contain an additive in addition to aluminum. As shown in FIG. 3, the hollow particle 32 has a spherical outer shell 320 made of metal or ceramics, and its maximum outer dimension is, for example, several tens of μm. There is a gap 33 inside the outer shell 320. As a metal used as the material of the outer shell 320, for example, titanium, a titanium alloy, stainless steel, or the like can be used. As the ceramic used as the material of the outer shell 320, for example, alumina, silica, a composite material of alumina and silica, or the like can be used. A plurality of hollow particles 32 are dispersed inside the sintered body 3 together with the gaps 33. One type of hollow particles 32 having an average particle diameter may be used, or two or more hollow particles 32 having different average particle diameters may be used.

The manufacturing method of the piston 1 includes a casting process, a sintered body forming process, a heat treatment process, a machining process, and an oxidation treatment process. In the casting process, the prototype (intermediate workpiece) of the main body 2 is cast. Specifically, a molten aluminum alloy as a base metal is poured into a mold and solidified. At this time, the inner periphery of the main body 2 is formed, and the recess 401 and the passage 411 are formed. The concave portion 401 may be formed or finished by machining. In the sintered body forming step, the sintered body 3 is formed on the prototype of the main body 2 (on the combustion chamber 11 side). Details will be described later. In the heat treatment step, heat treatment is performed. As a result, the properties of the prototype on which the sintered body 3 is formed are improved and adjusted to appropriate strength and hardness. Note that the heat treatment step may be performed before the sintering step. In the machining process, the heat-treated prototype is machined by a lathe or the like. The side of the piston head 4 facing the combustion chamber 11 is cut to form the crown surface 400. The entire surface of the piston head 4 on the combustion chamber 11 side is machined. Further, for example, the piston pin hole 51 and the ring groove 410 are processed, and the outer diameter of the main body 2 such as the outer periphery of the piston head 4 and the piston skirt 6 is finished. In addition, you may perform a sintered compact formation process after a machining process.

In the oxidation process, the surface of the machined sintered body 3 is anodized. As a specific step of the anodizing treatment, a well-known one may be adopted as appropriate. An anodized film 30 is formed in a region where the binder 31 is anodized. A sintered body 3 having the anodized film 30 is formed on the crown surface 400. In the present embodiment, the anodized film 30 is formed on the entire sintered body 3 (entire range in the radial direction and axial direction of the piston). The anodic oxide film 30 may be formed on a part of the sintered body 3 (a part of the range in the radial direction or the axial direction of the piston). As shown in FIG. 3, the anodized film 30 can be a porous layer having a large number of fine pores (pores) 310. The pore 300 extends in a direction perpendicular to the crown surface between the bottom side (base material side) and the surface of the anodized film 30.

The sintered body forming process includes a material preparation process, a material installation process, and a sintering process. In the material preparation step, a material for forming the sintered body 3 (hereinafter referred to as a forming material) is prepared. The forming material includes metal powder of the binder 31 and hollow particles 32. The metal powder of the binder 31 is aluminum powder. There are various methods for producing the hollow particles 32. For example, mother particles having an average particle diameter of about several tens of μm and formed from a resin (polymer) are prepared. A metal or ceramic child particle having a smaller average particle diameter (for example, submicron or less) is coated on the outer peripheral surface of the mother particle. Coating can be performed by ejecting and driving the child particles on the outer peripheral surface of the mother particles at a high speed, or by rotating a rotating chamber containing the mother particles and the child particles at a high speed. Thereafter, the coated composite particles are heated to dissolve the mother particles or to thermally decompose (gasify) them. As a result, hollow particles 32 having an outer shell 320 made of child particles are formed. By adjusting the particle size of the mother particles, the particle size of the hollow particles 32 can be controlled as desired. A forming material (mixed material) prepared by mixing aluminum powder and hollow particles 32 in a predetermined (weight or volume) ratio is prepared. By stirring, the hollow particles 32 are dispersed in the aluminum powder in the mixed material.

In the material setting step, the mixed forming material is filled into the original concave portion 401 as shown in FIG. Specifically, the forming material is put up to the upper end of the recess 401. Note that the position of the forming material into the concave portion 401 is arbitrary. Alternatively, the aluminum powder and the hollow particles 32 may be separately put in the recess 401 and then mixed in the recess 401. In the sintering process, the filled forming material (specifically, aluminum powder) is sintered. In this embodiment, the discharge plasma sintering method is used, and sintering is performed by mechanical pressurization and pulse current heating. As shown in FIG. 5,

carbon electrodes

81 and 82 are brought into contact with both sides of the original in the axial direction. A pulse voltage (current) is applied from the power supply 80 in a state where the forming material is pressurized (pressure in the axial direction is indicated by an arrow). The forming material is sintered by heat generation of each aluminum powder by energization, discharge plasma energy generated between the particles, and the like. A sintered body 3 having a volume reduced from the beginning is formed inside the recess 401. The sintered body 3 is a sintered layer that spreads in a direction perpendicular to the crown surface 400. As a result, a prototype of the piston head 4 having the recess 401 for accommodating the sintered body 3 is formed. In the machining process performed thereafter, a part of the sintered body 3 is cut together with a part of the piston head 4, and the crown surface 400 including the sintered body 3 on the surface is finished into a flat surface.

Next, the function and effect will be described. In the casting process, the main body 2 having the piston head 4 and the skirt 6 is formed of a metal material (aluminum alloy). Therefore, the piston 1 includes the main body 2. The main body 2 is made of a metal material and has a piston head 4 and a skirt 6. In the sintered body forming step, a sintered body 3 made of a material (forming material) containing a metal binder 31 is provided on the combustion chamber 11 side of the piston head 4. Therefore, the piston 1 includes the sintered body 3. The sintered body 3 is on the combustion chamber 11 side of the piston head 4 and includes a metal binder 31. The sintered body 3 faces the combustion chamber 11 and constitutes a part of the inner wall of the combustion chamber 11. The sintered body 3 includes more minute voids (holes) than the main body portion 2 formed by casting. The void has a lower thermal conductivity than the solid. Therefore, the sintered body 3 as a whole can have a lower thermal conductivity than the main body 2. The sintered body 3 is located between the combustion chamber 11 and the main body 2 and functions as a low heat conductive layer (heat insulating layer). The sintered body 3 reduces the heat transfer from the gas inside the combustion chamber 11 to the piston head 4 (main body portion 2), and the heat of the fuel (air mixture) supplied to the combustion chamber 11 is taken to the main body portion 2. Suppress it. Therefore, a reduction in combustion efficiency can be suppressed and the thermal efficiency of engine 100 can be improved. In addition, since the heat absorption to the main body 2 is suppressed by the sintered body 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. Note that the material of the main body 2 is not limited to an aluminum alloy, and may include, for example, iron. The metal of the binder 31 is not limited to aluminum, but may be a titanium alloy, magnesium, or the like, but a metal (low thermal conductivity material) whose thermal conductivity is equal to or lower than the material (base metal) of the main body 2. preferable. Moreover, it is preferable that it is a metal with high heat resistance and durability.

In the oxidation treatment step, the binder 31 is oxidized at least on the surface (crown surface 400) of the sintered body 3 on the combustion chamber 11 side. Therefore, the binder 31 is oxidized at least on the surface of the sintered body 3 on the combustion chamber 11 side. The portion where the binder 31 is oxidized (oxidized binder portion) has a lower thermal conductivity due to metal oxidation. The oxidized binder portion improves the heat insulating effect of the sintered body 3. The thermal conductivity can be lowered at least on the surface of the sintered body 3 on the combustion chamber 11 side (oxidized binder portion). Note that the oxidation method of the binder 31 is not limited to the anodizing treatment. In the present embodiment, the binder 31 is oxidized by anodizing treatment in the oxidation treatment step. Therefore, the binder 31 is anodized, and the oxidized binder portion is the anodized film 30. Unlike mere oxidation treatment, the anodized film (anodized film 30) can be porous with many pores 300. Due to the pores 300, the thermal conductivity of the sintered body 3 is lower than before the anodizing treatment. By forming a large number of pores 300 by the anodic oxidation treatment, the heat insulating property of the oxidized binder portion is improved as compared with the case of simple oxidation treatment.

In the oxidation treatment step, the binder 31 is oxidized from the surface (crown surface 400) of the sintered body 3 to a predetermined depth. Therefore, the oxidized binder portion is from the surface of the sintered body 3 to a predetermined depth. The predetermined depth is such a depth that the pores 300 of the anodized film 30 are formed. In other words, the range in which the anodic oxide film 30 grows and the pores 300 are formed from the surface to the inside of the sintered body 3 functions as an oxidation binder part. The heat insulation effect can be exerted by the pores 300 of the anodized film 30 against heat transferred to the inside of the sintered body 3.

From the viewpoint of reducing thermal conductivity and ensuring strength, it is conceivable that the volume ratio of the pores 300 as a whole in the anodized film 30 (the porosity of the anodized film 30) is set to an appropriate value. However, the growth of the pores 300 depends on various conditions of the anodizing treatment. For this reason, it is difficult to accurately control the proportion of the volume occupied by the pores 300 in the anodized film 30. The pore 300 is fine (for example, several tens of nm) and has a small diameter. Therefore, the effect of increasing the porosity in the anodized film 30 by increasing the pores 300 is small.

On the other hand, in the present embodiment, the sintered body 3 of the material (forming material) including the hollow particles 32 is provided on the side of the combustion chamber 11 in the piston head 4 in the sintered body forming step. Therefore, the sintered body 3 includes the hollow particles 32. Due to the hollow particles 32, the porosity in the sintered body 3 increases. The sintered body 3 has a plurality of relatively large voids 33 in each hollow particle 32 formed therein. These voids 33 have extremely low thermal conductivity, and the hollow particles 32 function as a heat insulating material. Therefore, the sintered body 3 as a whole (on average) has a lower thermal conductivity than the main body 2. If a material having a lower thermal conductivity than the main body 2 or the binder 31 (low thermal conductivity material) is used as the material of the hollow particles 32 (outer shell 320), the thermal conductivity of the sintered body 3 is further reduced. it can. The shape of the hollow particles 32 is not limited to a spherical shape, and may be a columnar shape. In the present embodiment, the hollow particles 32 (outer shell 320) are spherical. Therefore, the arrangement (direction) of the hollow particles 32 in the sintered body 3 does not need to be particularly taken into consideration, so that the handling is simple and the production of the sintered body 3 can be facilitated.

Here, the ratio of the volume occupied by the voids 33 in the individual hollow particles 32 can be controlled as desired by adjusting the particle size of the mother particles as the raw material, for example. Therefore, the overall porosity of the sintered body 3 including the plurality of hollow particles 32 can be accurately controlled by adjusting the type and number of the hollow particles 32. Further, the volume of the void 33 in the hollow particle 32 is relatively large. Therefore, in the sintered body 3, the effect of increasing the porosity by increasing the hollow particles 32 is greater than the effect of increasing the porosity by increasing the pores 300 of the anodized film 30. For example, it is easy to control the porosity of the sintered body 3 including the hollow particles 32 to be preferably 30% by volume or more and 70% by volume or less, more preferably 50% by volume or in the vicinity thereof. By controlling the porosity in such a range, it is possible to achieve both a reduction in the thermal conductivity and strength of the sintered body 3 at a high level.

Note that, as a means for improving the porosity of the sintered body 3, it is also conceivable to adjust the voids around the crystallized material in the anodized film 30. That is, as shown in FIG. 6, inside the main body 2 is a crystallized product 20 (a material such as silicon in the material of the main body 2 crystallized) in the solidification process of the base metal. The crystallized product 20 is dissolved by the anodizing treatment, and the crystallized product 20 and the vicinity 21 can be formed in the vicinity of the crystallized product 20 within the anodized film 30 (sintered body 3). As shown in FIG. 7, it is conceivable to increase the amount of the crystallized material 20 by increasing the amount of the crystallized material 20 (for example, silicon) in the base metal. Since the number of the voids 21 in the crystallized product 20 and the vicinity thereof increases, the volume of the voids 21 as a whole inside the anodized film 30 (sintered body 3) increases. However, there is a limit to increasing the porosity of the anodic oxide film 30 by increasing the number of crystallized substances 20, and there is a possibility that the effect of reducing the thermal conductivity of the sintered body 3 cannot be sufficiently obtained. . Further, as shown in FIG. 8, it is conceivable to increase the solidification time of the base metal and increase the grain size of the crystallized product 20. Since the crystallized substance 20 and the void 21 in the vicinity thereof become large, the volume of the void 21 as a whole inside the anodized film 30 increases. However, there is a limit to increasing the porosity of the anodic oxide film 30 by increasing the particle size of the crystallized product 20, and there is a possibility that the effect of reducing the thermal conductivity of the sintered body 3 cannot be sufficiently obtained. is there. On the other hand, in the present embodiment, the porosity of the sintered body 3 is increased not by the voids 21 around the crystallized product 20 but by the hollow particles 32, so that the heat of the sintered body 3 can be obtained without the above-mentioned limit. Conductivity can be reduced. Further, the controllability of the porosity in the sintered body 3 is good.

In the sintered body 3, the strength of the hollow particles 32 and the vicinity thereof is lowered due to the voids 33 inside the hollow particles 32. For this reason, insufficient strength of the sintered body 3 can be a problem. The binder 31 improves the bonding strength (hardness) inside the sintered body 3 including the voids 33, and suppresses chipping and collapse thereof. In addition, the strength of joining the sintered body 3 and the main body 2 is improved, and the force for holding the sintered body 3 in the piston head 4 (concave portion 401) is improved. Therefore, the function of the sintered body 3 can be maintained for a longer period. In addition to the hollow particles 32 and the binder 31, additives (sintering aid and the like) may be mixed in the forming material. The binder 31 is a metal. Therefore, even if a relatively large gap 33 is formed, the strength of the sintered body 3 can be improved and the chipping and collapse can be more easily suppressed.

In the sintered body forming step, the mixed material (forming material) containing the hollow particles 32 and the binder 31 is sintered. The binder 31 includes a metal powder. Therefore, the sintered body 3 is obtained by sintering a mixed material containing the hollow particles 32 and the metal powder. Since the binder 31 before solidification is a metal powder, the specific gravity of the binder 31 can be prevented from being biased in the sintered body 3, and the hollow particles 32 are dispersed as uniformly as possible inside the sintered body 3. Can be made. By sintering the mixed material in which the metal powder and the hollow particles 32 are stirred, the metal powder and the hollow particles 32 can be dispersed in the sintered body 3 as uniformly as possible. Therefore, the heat insulating performance can be homogenized between the respective parts in the sintered body 3.

The metal powder is aluminum powder. The aluminum powder functions as a binder 31 that adheres to each other or the main body 2 and holds the hollow particles 32 in the sintered body 3 by being sintered. Since the binder 31 is made of aluminum powder, the bonding force between the main body 2 and the sintered body 3 formed of an aluminum alloy can be improved. The aluminum powder may be a pure aluminum powder or an aluminum alloy powder (for example, AC8A, which is the same as the base metal of the main body 2). The aluminum powder may be granular aluminum powder.

The anodizing treatment not only improves the heat insulating performance of the binder 31 as described above, but also improves the strength of the binder 31. Therefore, the strength of the binder 31 in the vicinity of the hollow particles 32 can be improved, and the chipping of the sintered body 3 and the falling off from the main body 2 can be suppressed. Further, since the anodic oxide film 30 is formed by an anodic oxidation treatment, the bonding strength with the base material is strong. In the casting process, the main body 2 having the recess 401 on the combustion chamber 11 side in the piston head 4 is formed. Therefore, the piston 1 includes the recess 401. The recess 401 is on the combustion chamber 11 side in the piston head 4. In the sintered body forming step, the sintered body 3 is provided in the recess 401. Therefore, the sintered body 3 is in the recess 401 and is held by the piston head 4 by the recess 401. The concave portion 401 functions as a holding portion. As a result, it is possible to prevent the sintered body 3 from falling off the main body 2. In addition, even when sintering is performed by mechanical pressurization and pulse current heating using the discharge plasma sintering method in the sintering process, pressure is applied to the piston head 4 while holding the forming material. This is advantageous.

In the sintered body forming process, the forming material is filled in the recess 401 in the material setting process, and the (filled) forming material is sintered in the sintering process. In the sintering process, a discharge plasma sintering method is used. Since energization is used for heating or the like and friction is not used, there is little possibility that the hollow particles 32 are crushed during sintering. Note that a preform obtained by pressure-molding the forming material may be prepared, and this may be placed in the recess 401 and sintered. In this case, it is possible to improve manufacturing efficiency and quality. Alternatively, the sintered body 3 may be formed in a disc shape separately from the main body 2 and the sintered body 3 may be cast into a base metal such as an aluminum alloy of the piston 1.

A machining process is performed after the sintered body forming process. After the sintered body 3 is formed on the piston head 4, the side facing the combustion chamber 11 of the piston head 4 is cut to form the crown surface 400. That is, the sintered body 3 is formed before the crown surface 400 is formed by cutting. Therefore, in the sintered body forming step, there are few restrictions due to the shape of the crown surface 400, and thus the work of forming the sintered body 3 is facilitated. In other words, even when the crown surface 400 has a complicated shape, the sintered body 3 can be easily formed on the crown surface 400. Further, when machining is performed after the formation of the oxidized binder portion (anodized film 30), the oxidized binder portion may be unnecessarily removed by machining. On the other hand, an oxidation treatment process is performed after the machining process. In other words, the oxidized binder portion is in a portion formed by machining in the main body portion 2. Thus, by forming the oxidized binder portion after machining, the oxidized binder portion can be sufficiently provided without unnecessary cutting. Further, the anodic oxide film 30 has a high hardness and is relatively difficult to machine. Machining can be facilitated by performing machining prior to the anodizing treatment.

When the sintered body 3 (oxidation binder part) is provided over the entire crown surface 400 of the piston head 4, the temperature of the crown surface 400 increases excessively, abnormal fuel combustion (knocking) occurs, and intake efficiency decreases. Cause it. On the other hand, the sintered body 3 (oxidized binder portion) is in a part of the crown surface 400. Therefore, it is possible to suppress an excessive increase in the temperature of the crown surface 400 and achieve both improvement in heat insulation and suppression of knocking and the like. Specifically, in the in-cylinder direct injection type engine 100, the sintered body 3 is located on the crown surface 400 at a location corresponding to at least a fuel injection region (a location where the temperature or pressure is highest when the fuel collides or explodes. And its periphery). By forming the sintered body 3 at this location, heat transfer from the gas inside the combustion chamber 11 to the piston head 4 (main body 2) can be more effectively reduced. Note that a relatively large number of hollow particles 32 may be arranged at locations where fuel is directly injected to enhance the heat insulation effect.

[Second Embodiment]
In the present embodiment, in the sintering process, as shown in FIG. 9, the principle of friction stir welding (joining) is used and sintering is performed using a rotating tool 9. The tool 9 has a cylindrical shape, and the diameter D2 of the axial end 90 thereof is not less than the diameter D1 of the recess 401, and is preferably slightly larger than the diameter D1. The axis of the tool 9 and the axis of the recess 401 are aligned. With the tool 9 rotated around its axis (rotation around the axis is indicated by arrow A), the end 90 of the tool 9 is pressed against the forming material (the axial pressing force is indicated by arrow B). . Alternatively, the tool 9 is rotated with the end 90 pressed against the forming material. Thereby, the forming material is mixed while being pressed and heated by frictional heat. The aluminum powder as the material of the binder 31 plastically flows, the oxide film on the surface of each powder is broken, and the sintered body 3 whose volume is reduced from the beginning is formed. When the sintering is completed, the tool 9 is pulled up from the inside of the recess 401. Other configurations are the same as those of the first embodiment.

The piston head 4 has a recess 401. Therefore, even when sintering is performed by rotating the tool 9 in the sintering process, it is advantageous because the forming material is held on the piston head 4 and can be agitated by applying pressure thereto. The diameter D2 of the end 90 is not less than the diameter D1 of the recess 401. Therefore, the formation material can be prevented from jumping out from the radial gap between the rotating end 90 and the recess 401. Diameter D2 is larger than diameter D1. Therefore, since the sintered body 3 is formed while a part of the outer edge of the recess 401 is wound around the rotating end 90, the bonding force between the sintered body 3 and the recess 401 can be improved. Other functions and effects are the same as those of the first embodiment.

[Third embodiment]
In the present embodiment, the pores 300 in the anodized film 30 (oxidized binder portion) of the sintered body 3 are sealed at the site on the side opened to the crown surface 400 (combustion chamber 11). Specifically, the opening is blocked or narrowed at this portion. Or the pore 300 is chemically inactive. This part is called a sealing part. The method for manufacturing the piston 1 includes a sealing treatment process. In the sealing treatment step, as a surface treatment of the anodized sintered body 3, the pores 300 are sealed by boiling the formed anodized film 30 in boiling water. In addition to pure water boiling water, a high temperature aqueous solution to which a chemical is added may be used. Further, the anodized film 30 may be treated with high-temperature pressurized steam. By boiling, hydroxide grows on the anodic oxide film 30 and seals the pores 300 (a sealed part is formed). The sealing portion of each pore 300 functions as a sealing layer that spreads in a direction perpendicular to the crown surface 400 as a whole. Other configurations are the same as those of the first embodiment.

As described above, since the anodic oxide film 30 has a sealed portion in which the pores 300 are sealed, it is possible to prevent the unburned gas from entering the pores 300 and deteriorating the exhaust gas characteristics of the engine 100. Other functions and effects are the same as those of the first embodiment.

[Fourth embodiment]
In the present embodiment, as shown in FIG. 10, the surface of the anodized film 30 (oxidized binder portion) of the sintered body 3 facing the combustion chamber 11 is covered with a film 34. The film 34 is a silica film containing silica. The method for manufacturing the piston 1 includes a sealing treatment process. In the sealing treatment step, as the surface treatment of the anodized sintered body 3, the surface of the anodized film 30 is covered with a film. As a result, the pores 300 in the anodized film 30 are sealed. The membrane 34 functions as a sealing layer. The pore 300 is sealed with silica at the sealing portion. Other configurations are the same as those of the first embodiment.

On the surface of the sintered body 3 (anodized film 30) facing the combustion chamber 11, a part of the plurality of voids 33 can be opened. The film 34 uniformly covers the surface of the anodized film 30. For this reason, the crown surface 400 can be smoothed. Further, not only the pore 300 but also the opening of the gap 33 can be closed with the film 34. Therefore, it is possible to prevent the unburned gas from entering the gap 33 and deteriorating the exhaust gas characteristics of the engine 100. The material of the film 34 may contain subcomponents other than silica. Further, the film may be formed using a material other than silica. In the present embodiment, the film 34 is a silica film containing silica as a main component. Since silica is excellent in heat resistance, the durability of the sealing layer can be improved. Other functions and effects are the same as those of the third 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. For example, even if it is not an engine piston, a main body made of a metal material, and a sintered body containing hollow particles and a metal binder, wherein the binder is oxidized at least on the outer surface. If it is a structure provided, it functions as a heat insulating structure and can obtain the above-mentioned effect (heat insulating effect) as well as the piston. For example, the structure may be applied to each member (cylinder, valve, etc.) exposed to the high temperature gas facing the combustion chamber of the engine and the inner wall of the intake port or the exhaust port in order to suppress heat transfer. Providing the structure on each member facing the combustion chamber is advantageous for improving the thermal efficiency of the engine. If the structure is applied to the inner wall of the intake port, it is possible to suppress the intake air from being heated before being sucked into the cylinder, which is advantageous for suppressing abnormal combustion. If the structure is applied to the inner wall of the exhaust port, the exhaust gas can be discharged at a high temperature, which is advantageous for recovering exhaust energy. In addition, the above structure can be applied to various uses as long as it has a wall surface that requires heat insulation, such as a wall surface that constitutes a turbine blade, an outer wall of a housing that houses an internal combustion engine, a house, a boiler, or the like. . Here, the metal material of the main body may be aluminum, steel, titanium, nickel, copper, or an alloy thereof.

Other aspects 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, the piston is a main body portion that is formed of a metal material and includes a piston head and a skirt portion, and a holding portion is provided on the combustion chamber side of the internal combustion engine in the piston head. A formed main body,
A sintered body that is disposed in the holding portion and contains hollow particles and a metal binder, and includes a sintered body that includes an oxidized binder portion in which the binder is oxidized at least on the surface on the combustion chamber side. .
(2) In a more preferred embodiment, in the above embodiment,
The oxidized binder portion is an anodized film.
(3) In another preferred embodiment, in any of the above embodiments,
The oxidized binder portion includes a sealed portion in which pores of the anodized film are sealed.
(4) In still another preferred embodiment, in any of the above embodiments,
The pores are sealed by boiling at the sealing portion.
(5) In still another preferred embodiment, in any of the above embodiments,
The pores are sealed with silica at the sealing portion.
(6) In still another preferred embodiment, in any of the above embodiments,
The oxidized binder portion is in a portion formed by machining in the main body portion.
(7) In still another preferred embodiment, in any of the above embodiments,
The oxidized binder part is located at a part of the crown surface of the piston head.
(8) In still another preferred embodiment, in any of the above embodiments,
The oxidized binder portion is disposed from the surface of the sintered body to a predetermined depth.
(9) In still another preferred embodiment, in any of the above embodiments,
The sintered body is formed by sintering a mixed material containing the hollow particles and the metal powder.
(10) In still another preferred embodiment, in any of the above embodiments,
The metal material of the main body portion contains an aluminum alloy, and the binder contains aluminum.
(11) A method for manufacturing a piston of an internal combustion engine, in one embodiment thereof,
A main body comprising a piston head and a skirt, the main body of the piston head having a holding part formed on the combustion chamber side of the internal combustion engine, formed of a metal material;
Providing a sintered body formed of a material containing hollow particles and a metal binder in the holding portion;
And oxidizing the binder on at least the combustion chamber side surface of the sintered body.
(12) In a more preferred embodiment, in the above embodiment,
The step of oxidizing the binder includes a step of oxidizing the binder by anodization.
(13) In another preferred embodiment, in any of the above embodiments,
A step of sealing the pores of the film formed by the anodizing treatment by boiling.
(14) In still another preferred embodiment, in any of the above embodiments,
The step of oxidizing the binder includes a step of oxidizing the binder from the surface of the sintered body to a predetermined depth by the anodizing treatment.
(15) In still another preferred embodiment, in any of the above embodiments,
The binder contains the metal powder,
The step of providing the sintered body includes a step of sintering the mixed material containing the hollow particles and the binder.
(16) In one embodiment of the structure,
A main body formed from a metal material;
A holding part formed in the main body part;
A sintered body that is disposed in the holding portion and contains hollow particles and a metal binder, wherein the binder is oxidized at least on the outer surface.

This application claims priority based on Japanese Patent Application No. 2016-247018 filed on Dec. 20, 2016. The entire disclosure including the specification, claims, drawings, and abstract of Japanese Patent Application No. 2016-247018 filed on December 20, 2016 is incorporated herein by reference in its entirety.

100 engine (internal combustion engine), 11 combustion chamber, 1 piston, 2 body part, 3 sintered body, 30 anodized film (oxidized binder part), 31 binder, 32 hollow particles, 4 piston head, 401 recess (holding part) , 6 Piston skirt (skirt part)

Claims

A piston of an internal combustion engine,
A main body portion formed of a metal material and having a piston head and a skirt portion, wherein the piston head has a holding portion formed on the combustion chamber side of the internal combustion engine,
A sintered body that is disposed in the holding portion and contains hollow particles and a metal binder, and includes a sintered body that includes an oxidized binder portion in which the binder is oxidized at least on the surface on the combustion chamber side. Piston for internal combustion engine.
The piston of the internal combustion engine according to claim 1,
The oxidation binder part is an anodized film. A piston for an internal combustion engine.
The piston of the internal combustion engine according to claim 2,
The said oxidation binder part is provided with the sealing part by which the pore of the said anodic oxide film was sealed, The piston of an internal combustion engine.
The piston of the internal combustion engine according to claim 2,
The oxidation binder part is a piston of an internal combustion engine located at a part of a crown surface of the piston head.
The piston of the internal combustion engine according to claim 2,
The oxidation binder portion is disposed from the surface of the sintered body to a predetermined depth. A piston of an internal combustion engine.
The piston of the internal combustion engine according to claim 1,
The sintered body is formed by sintering a mixed material containing the hollow particles and the metal powder.
A method of manufacturing a piston for an internal combustion engine,
A main body comprising a piston head and a skirt, the main body of the piston head having a holding part formed on the combustion chamber side of the internal combustion engine, formed of a metal material;
Providing a sintered body formed of a material containing hollow particles and a metal binder in the holding portion;
And a step of oxidizing the binder on at least the surface of the sintered body on the combustion chamber side.
In the manufacturing method of the piston of an internal-combustion engine according to claim 7,
The step of oxidizing the binder includes a step of oxidizing the binder by anodizing treatment.
The method for manufacturing a piston of an internal combustion engine according to claim 8,
The manufacturing method of the piston of an internal combustion engine provided with the process of sealing the pore of the membrane | film | coat formed by the said anodizing process by boiling.
The method for manufacturing a piston of an internal combustion engine according to claim 8,
The step of oxidizing the binder includes a step of oxidizing the binder from the surface of the sintered body to a predetermined depth by the anodizing treatment.
In the manufacturing method of the piston of an internal-combustion engine according to claim 7,
The binder contains the metal powder,
The step of providing the sintered body includes a step of sintering a mixed material containing the hollow particles and the binder.
A structure,
A main body formed from a metal material;
A holding part formed in the main body part;
A sintered body that is disposed in the holding portion and contains hollow particles and a metal binder, and the sintered body is oxidized at least on the outer surface.