JP6187545B2 - Piston for internal combustion engine, internal combustion engine including the piston, and method for manufacturing the piston - Google Patents

Description

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

  Conventionally, for example, Patent Document 1 (Japanese Patent Laid-Open No. 2009-243355) discloses a heat shield having a lower thermal conductivity than a piston base material and a heat capacity per unit volume lower than that of the piston base material. A piston for an internal combustion engine in which a film is formed on an upper surface of a land portion is disclosed. According to the thermal barrier film having such thermal characteristics, the temperature of the upper surface of the land portion can be made to follow the temperature of the working gas in the cylinder of the internal combustion engine. That is, the temperature of the upper surface of the land portion can be increased in the combustion stroke of the internal combustion engine, and the temperature of the upper surface can be decreased in the intake stroke. Accordingly, it is possible to reduce the cooling loss in the combustion stroke and improve the fuel consumption, and to suppress the occurrence of knocking or abnormal combustion due to the heating of the working gas in the intake stroke.

  In Patent Document 2 (Japanese Patent Laid-Open No. 11-280545), an iron-based metal material having a smaller thermal diffusivity than the piston base material (specifically, an aluminum alloy) is provided on the side surface of the land portion. An internal combustion engine piston is disclosed. By providing a metal material having such thermal characteristics, the temperature around the metal material can be increased. Accordingly, it is possible to improve the combustion efficiency of the internal combustion engine by promoting the evaporation and vaporization of the liquid fuel adhering to the surface of the metal material and the periphery thereof.

JP 2009-243355 A JP 11-280545 A JP 2014-020300 A Japanese Patent Laid-Open No. 5-079564 JP 2002-332571 A

  By the way, when the thermal barrier film having thermal characteristics as in Patent Document 1 is formed on the upper surface of the land portion, the viscosity of the working gas increases as the temperature of the upper surface increases during the combustion stroke. There is a weak point that the fluidity of the gas is reduced and the combustion worsens easily. If the deterioration of combustion occurs, the flame that would normally have propagated to every corner in the cylinder during the combustion stroke cannot go around the side surface of the land portion. If it does so, the working gas which exists around the side surface of a land part will not be combusted in a combustion stroke, but will stay around the said side surface. Furthermore, in the intake stroke after the combustion stroke, the new working gas flows into the cylinder, so that the working gas remaining around the side surface of the land portion is cooled, and the fuel in the working gas is condensed. Will stick to the side.

  If the metal material of patent document 2 is provided in the side surface of the land part of patent document 1 regarding this problem, it can make it easy to raise the temperature around the said metal material. However, Patent Document 2 specifies the thermal diffusivity of a metal material, and no mention is made of the heat capacity per unit volume of the metal material. Therefore, when the metal material of Patent Document 2 is provided on the side surface of the land portion of Patent Document 1, it is assumed that the surface temperature of the metal material can be increased by the small thermal diffusivity of the metal material in the combustion stroke and the exhaust stroke. However, in the subsequent intake stroke, the temperature of the surface may decrease. Therefore, when the carry-over of the working gas to the intake stroke accompanying the above-described deterioration of combustion occurs, the fuel in the working gas condenses and adheres to the surface of the metal material in the intake stroke.

  Moreover, the metal material of patent document 2 is provided from the upper surface of the said land part to the middle of a second land among the side surfaces of a land part. That is, this metal material is provided not only on the side surface of the top land but also on the side surface of the second land. For this reason, heat transfer from the upper surface of the land portion to the inner wall surface of the cylinder via the piston ring (that is, the top ring) mounted in the groove between the top land and the second land is hindered. As a result, heat can be transferred from the thermal barrier film to the working gas newly flowing into the cylinder during the intake stroke, and the working gas is heated. That is, knocking or abnormal combustion occurs despite the formation of the heat shield film on the upper surface of the land portion.

  The present invention has been made to solve at least one of the above-described problems. That is, in a piston of an internal combustion engine that has a thermal conductivity lower than that of a piston base material and has a heat capacity per unit volume lower than that of the piston base material on the upper surface of the land portion, An object of the present invention is to suppress the fuel adhesion to the side surface of the land portion and to suppress the heating of the working gas in the intake stroke.

In order to solve the above-mentioned problem, the first invention is an anode as a heat shielding film having a thermal conductivity lower than that of a piston base material and having a heat capacity per unit volume lower than that of the piston base material. A piston of an internal combustion engine in which an oxide film is formed on the upper surface of the land portion,
The thermal barrier film is not formed on the side surface of the land portion,
Of the land portion , the side surface of the top land, which is a portion above the groove in which the top ring is mounted , has a lower thermal conductivity than the piston base material, and is higher than the thermal barrier film. A heat insulating film having a heat capacity per unit volume , wherein the heat insulating film has a surface roughness smaller than the surface roughness of the heat shielding film, is formed.

According to a second invention, in the first invention,
The heat insulating film is a film thickness that gradually decreases from the lower surface side of the land portion toward the upper surface side of the land portion, or continuously from the lower surface side of the land portion toward the upper surface side of the land portion. The film has a film thickness that decreases, or is formed on the lower surface side of the land portion and is not formed on the upper surface side of the land portion.

According to a third invention, in the first or second invention,
The piston base material is exposed below the groove in the side surface of the land portion.

A fourth invention is an internal combustion engine comprising the piston of any one of the first to third inventions,
A unit volume that is lower than the piston base material and higher than the thermal barrier film at a position facing the side surface of the top land when the piston is located at the bottom dead center of the inner wall surface of the cylinder that houses the piston. A heat-retaining film having a heat capacity per unit is formed.

5th invention is the manufacturing method of the piston in any one of 1st thru | or 3rd invention, Comprising:
And forming the thermal barrier layer on the upper surface of the land portion by anodic oxidation of said piston base material,
After the formation of the thermal barrier film, an insulating material having a lower thermal conductivity than the piston base material and a higher heat capacity per unit volume than the thermal barrier film is formed on the side surface of the top land. and forming the heat retaining film on the side surface of the top land by film,
It is characterized by providing.

According to the first invention, the heat retaining film having a lower thermal conductivity than the piston base material and having a higher heat capacity per unit volume than the heat shielding film is formed on the side surface of the top land . , raising the average temperature of the side surface in one cycle of the internal combustion engine can suppress the temperature of the side surface of the top land is lowered in the intake stroke. Therefore, even if the working gas existing around the side of the top land in a certain cycle remains without being burned in the combustion stroke and is carried over to the intake stroke, it can be burned in the combustion stroke after the intake stroke. It becomes. Therefore, fuel adhesion to the side surface of the top land can be suppressed. According to the first invention, the anodic oxide film as the heat shield film is not formed on the side surface of the land portion, and the surface roughness of the heat insulating film formed on the side surface of the top land is the heat shield film. Since it is smaller than the surface roughness, it is possible to reduce the friction generated between the cylinder and the piston having the heat shield film formed on the side surface of the top land.

When attention is paid to the side surface of the top land , the temperature of the side surface decreases as the distance from the top surface of the land portion increases. Therefore, when the working gas existing around the side of the top land remains without being burned in the combustion stroke and is carried over to the intake stroke, the fuel in the remaining working gas is condensed in the region near the lower surface of the land portion. The probability of doing is increased. In this respect, according to the second invention, the heat retention effect of the side surface of the top land can be enhanced on the lower surface side than the upper surface side of the land portion, so that it is close to the lower surface of the land portion on the side surface of the top land. It is possible to satisfactorily suppress the condensation of fuel in the residual working gas in the region.

  According to the third invention, since the piston base material can be exposed below the groove in which the top ring is mounted, from the upper surface of the land portion to the inside of the land portion and the inner wall surface of the cylinder via the top ring. The amount of heat transfer can be increased. Accordingly, heating of the working gas in the intake stroke can be suppressed.

The temperature of the inner wall surface of the cylinder basically becomes lower as it approaches the crankcase. Therefore, it can be said that the temperature of the heat insulating film formed on the side surface of the top land is lowest at the bottom dead center closest to the crankcase. In this regard, according to the fourth invention, the heat retaining film having a heat capacity per unit volume lower than that of the piston base material and higher than that of the heat shielding film is formed on the side surface of the top land when the piston is located at the bottom dead center. Since it is formed on the inner wall surface of the opposing cylinder, the working gas existing around the side surface is warmed by the heat retaining film formed on the inner wall surface at the position where the temperature of the heat retaining film formed on the side surface is the lowest. Can do. Therefore, fuel adhesion to the side surface of the top land can be suppressed.

  When the thermal barrier film is formed by anodic oxidation after the insulating material is formed, the anodic oxidation reaction is hindered and the structure and film thickness of the formed thermal barrier film may vary. In this regard, according to the fifth aspect, since the heat insulating film can be formed by forming the insulating material after the formation of the heat shield film by the anodic oxidation treatment, the heat shield film can be favorably formed.

It is a perspective view of piston 10 concerning an embodiment of the invention. It is a cross-sectional schematic diagram when the piston 10 of FIG. 1 is accommodated in the cylinder of a spark ignition internal combustion engine. It is a figure which shows transition of the temperature of the working gas in a cylinder in the 1 cycle of an internal combustion engine, and the temperature of the upper surface of a land part. It is the figure which showed the relationship between the average temperature in 1 cycle of the internal combustion engine of a ceramic film | membrane, the heat capacity per unit volume of the said ceramic film | membrane, and the reduction effect of unburned HC. It is a figure which shows the heat transfer amount from the upper surface of a land part to the side surface of a piston. It is a figure which shows the heat transfer amount from the upper surface of a land part to the side surface of a piston. It is a figure for demonstrating the modification of the piston which concerns on embodiment of this invention. It is a figure for demonstrating the modification of the piston which concerns on embodiment of this invention. It is a figure for demonstrating the modification of the piston which concerns on embodiment of this invention. It is a cross-sectional schematic diagram when the piston in which the porous alumite film | membrane 32, the ceramic film | membrane 34, and the hard alumite film | membrane 36 were formed was accommodated in the cylinder of a compression ignition internal combustion engine. 1 is a schematic cross-sectional view of an internal combustion engine 50 according to an embodiment of the present invention. It is a flowchart explaining the manufacturing method of the piston which concerns on embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected to the element which is common in each figure, and the overlapping description is abbreviate | omitted. The present invention is not limited to the following embodiments.

[Piston of internal combustion engine]
First, an embodiment of the piston of the present invention will be described with reference to FIG. FIG. 1 is a perspective view of a piston 10 according to an embodiment of the present invention. The piston 10 is formed by casting an aluminum alloy which is a piston base material, like a piston of a general internal combustion engine. As shown in FIG. 1, the piston 10 includes a cylindrical skirt portion 12 whose side surface is in sliding contact with an inner wall surface of a cylinder (not shown), and a land portion 14 having a predetermined thickness formed at the upper end portion of the skirt portion 12. And a pin boss portion 16 that supports a piston pin (not shown). Grooves 18, 20, and 22 for mounting three piston rings (not shown) are formed on the side surface of the land portion. On the upper surface of the land portion 14 (hereinafter also referred to as “piston top surface”), half-moon shaped valve recesses 24, 26, 28, 30 that avoid interference with an intake valve and an exhaust valve (both not shown) are formed. Has been.

  FIG. 2 is a schematic cross-sectional view when the piston 10 of FIG. 1 is accommodated in a cylinder of a spark ignition type internal combustion engine, and corresponds to the AA cross section of FIG. In FIG. 2, it is assumed that the piston 10 is located at the top dead center. As shown in FIG. 2, a porous alumite film 32 is formed on the top surface of the piston. A ceramic film 34 is formed on the side surface of the land portion 14 from the groove 18 to the top surface of the piston, that is, the side surface of the top land. A hard alumite film 36 is formed on the surfaces of the grooves 18, 20, and 22. On the other hand, the piston base material is exposed on the side surface of the land portion 14 from the groove 18 to the lower surface (not shown) of the land portion 14. For example, the piston base material is exposed at the side surface of the land portion 14 between the groove 18 and the groove 20, that is, the side surface of the second land, or the side surface of the land portion 14 between the groove 20 and the groove 22, ie, the side surface of the third land. doing.

  Both the porous anodized film 32 and the hard anodized film 36 are formed by anodizing the piston base material (that is, aluminum alloy). However, the porous anodized film 32 and the hard anodized film 36 are different in anodized characteristics and film thickness (thickness in the direction perpendicular to the cylinder axis direction; the same applies hereinafter). Specifically, the porous alumite film 32 has a thermal conductivity lower than that of the piston base material, and also has a heat capacity per unit volume lower than that of the piston base material. Moreover, the film thickness of the porous alumite film | membrane 32 is 100-500 micrometers. Since the porous alumite film 32 is excellent in swing characteristics (referring to the temperature followability of the film forming surface with respect to changes in the temperature of the working gas in the cylinder, the same applies hereinafter), various effects can be obtained (details are described later). .

The porous alumite film 32 may have a film configuration including heat insulating particles (for example, particles of silica (SiO ₂ ), alumina (Al ₂ O ₃ ), zirconia (ZrO ₂ ), titania (TiO ₂ )). . In addition, regarding the configuration of the porous alumite film and its thermal characteristics (that is, thermal conductivity and heat capacity per unit volume), for example, JP 2010-249008 A and JP 2013-14830 A can be referred to. .

  Like the porous anodized film 32, the hard anodized film 36 also has a lower thermal conductivity than the piston base material, and also has a lower heat capacity per unit volume than the piston base material. However, the thickness of the hard anodized film 36 is several μm and the porosity is small, and compared with the porous anodized film 32, the thermal conductivity of the hard anodized film 36 and the heat capacity per unit volume are much higher. For this reason, the hard alumite film 36 has almost no swing characteristics, and instead has excellent film hardness and wear resistance. According to the hard anodized film 36, friction due to contact between the grooves 18, 20, 22 and the piston ring can be prevented.

The ceramic film 34 is made of ceramics such as zirconia (ZrO ₂ ), silica (SiO ₂ ), silicon nitride (Si ₃ N ₄ ), yttria (Y ₂ O ₃ ), titania (TiO ₂ ), and cermet (TiC / TiN). , mullite _{(3Al 2 O 3 · 2SiO 2} ), cordierite _{(2MgO · 2Al 2 O 3 ·} 5SiO 2), composite ceramics such as steatite (MgO · SiO ₂₎ (hereinafter simply referred to as "ceramic material". The film is formed by thermal spraying or cold spraying. The ceramic film 34 has a lower thermal conductivity than the piston base material and a higher heat capacity per unit volume than the porous alumite film 32. The film thickness of the ceramic film 34 is 50 to 3000 μm.

As an example, the thermal conductivity λ ₃₂ of the porous anodized film 32 is λ ₃₂ ≦ 0.5 W / m · K, and the heat capacity C ₃₂ per unit volume of the porous anodized film ₃₂ is C ₃₂ ≦ 1500 × 10 ³ J / M ³ · K. The thermal conductivity lambda ₃₄ of the ceramic film 34 is <a 0.5~30W / m · K, the heat capacity _{C 34} per unit volume of the ceramic film 34 ^{_{C 34> λ 34 1500 × 10}} 3 J / m 3 -K. The thermal conductivity λ _Al of the aluminum alloy is λ _Al = 96.2 W / m · K, and the heat capacity C _Al is C _Al = 2639 × 10 ³ J / m ³ · K.

The porous alumite film 32 and the ceramic film 34 differ in film density and film surface roughness Ra (an arithmetic average roughness measured in accordance with JIS B601 (2001); the same applies hereinafter). Specifically, the porous alumite film 32 has a lower density than the ceramic film 34. The reason why the density of the porous alumite film 32 is low is that the pores formed in the process of anodizing increase the porosity of the porous alumite film 32. The porous alumite film 32 has a surface roughness Ra that is greater than the surface roughness Ra of the ceramic film 34. The reason why the surface roughness Ra of the porous alumite film 32 is large is that the addition of the piston base material prevents the formation of the alumite so that the height of the film surface is not uniform. As an example, the surface roughness Ra ₃₂ of the porous alumite film 32 is 1.0 μm ≦ Ra ₃₂ ≦ 3.0 μm, and the surface roughness Ra ₃₄ of the ceramic film ₃₄ is Ra ₃₄ <1.0 μm.

[Effects of piston]
According to the piston 10 in which the porous alumite film 32 and the ceramic film 34 are formed, the following effects can be obtained. First, the effect of the porous alumite film 32 will be described with reference to FIG. FIG. 3 is a graph showing changes in the temperature of the working gas in the cylinder and the temperature of the upper surface of the land portion in one cycle of the internal combustion engine. In this figure, “conventional wall temperature” represents the temperature of the upper surface when a general ceramic film is formed on the upper surface of the land portion. The “wall temperature in the embodiment” represents the temperature of the upper surface when the porous alumite film (that is, the porous alumite film 32) is formed on the upper surface of the land portion. The “base (Al) wall temperature” represents the temperature of the upper surface when the piston base material is exposed on the upper surface of the land portion.

  As shown in FIG. 3, when a general ceramic film is formed (conventional wall temperature), the heat shielding property on the upper surface of the land portion is higher than when the piston base material is exposed (base (Al) wall temperature). Since it can improve, the cooling loss in a combustion stroke can be reduced. However, the temperature of the upper surface of the land portion remains high even in the intake stroke. Therefore, in this intake stroke, heat moves from the upper surface of the land portion toward the working gas. Accordingly, the working gas is heated, and knocking and abnormal combustion are likely to occur.

  On the other hand, when a porous alumite film is formed (wall temperature in the embodiment), the temperature of the upper surface of the land portion in the intake stroke is lowered by the swing characteristic to suppress heating of the working gas in the intake stroke. (See the down arrow). Therefore, the occurrence of knocking or abnormal combustion can be suppressed. Further, according to this swing characteristic, the temperature of the upper surface of the land portion can be greatly increased in the combustion stroke (see the upward arrow). Therefore, the fuel consumption can be improved by greatly reducing the cooling loss in the combustion stroke, compared with the case where a general ceramic film is formed.

  Next, the effect of the ceramic film 34 will be described. Since the ceramic film 34 has a density higher than that of the porous anodized film 32, the piston 10 is moved up and down as compared with the case where a porous anodized film similar to the porous anodized film 32 is formed on the side surface of the top land. It is possible to suppress film damage. In addition, since the ceramic film 34 has a surface roughness Ra smaller than the surface roughness Ra of the porous anodized film 32, the porous anodized film similar to the porous anodized film 32 is formed on the side surface of the top land. In comparison, the friction generated between the piston 10 and the cylinder can be reduced.

  Further, since the ceramic film 34 has a lower thermal conductivity than the piston base material and has a higher heat capacity per unit volume than the porous alumite film 32, the ceramic film 34 in one cycle of the internal combustion engine. The average temperature of the film can be increased. FIG. 4 is a graph showing the relationship between the average temperature of the ceramic film in one cycle of the internal combustion engine, the heat capacity per unit volume of the ceramic film, and the effect of reducing unburned HC. It is assumed that the thermal conductivity of the ceramic film in FIG. 4 is lower than that of the piston base material, as is the thermal conductivity of the ceramic film 34. As shown in FIG. 4, if the heat capacity per unit volume of the ceramic film is increased, the average temperature in one cycle of the ceramic film can be increased. This is because the heat retention effect of the ceramic film is enhanced by increasing the heat capacity per unit volume of the ceramic film having a lower thermal conductivity than the piston base material.

  If the average temperature in one cycle of the ceramic film can be increased, the following effects can be expected. That is, when the porous alumite film 32 is formed on the upper surface of the land portion, the temperature of the upper surface can be increased in the combustion stroke (see FIG. 3). However, since the viscosity of the working gas increases with this temperature rise, there is a weak point that the fluidity of the working gas is lowered and combustion deterioration is likely to occur. As described above, when the combustion worsens, the working gas present around the side surface of the top land cannot be burned in the combustion stroke and remains around the side surface. In addition, the working gas remaining around the side surface of the top land is cooled, and the fuel in the working gas is condensed and adheres to the side surface.

  In this regard, if the average temperature in one cycle of the ceramic film can be increased, even if the working gas existing around the ceramic film in a certain cycle remains without being burned in the combustion stroke and is carried over to the intake stroke, It becomes possible to burn in the subsequent combustion stroke. Therefore, fuel adhesion to the side surface of the top land can be suppressed. That is, the effect of reducing unburned HC can be enhanced (see FIG. 4).

  Here, the reason why the ceramic film 34 is formed only on the side surface of the top land in relation to the effect of the ceramic film 34 will be described with reference to FIGS. 5 to 6 are views showing the heat transfer amount from the upper surface of the land portion to the side surface of the piston. In view of the above-described effect of reducing unburned HC, an option of forming the ceramic film 34 on the side surfaces of the second land and the third land is not limited to the side surface of the top land. However, the decrease in the temperature of the upper surface of the land portion in the intake stroke described with reference to FIG. 3 causes a large heat transfer from the side surface of the piston to the inner wall surface of the cylinder from the latter half of the previous exhaust stroke to the first half of the intake stroke. Has contributed. Therefore, when a ceramic film similar to the ceramic film 34 is formed on the side surface of the second land or the third land, the amount of heat transferred from the side surface to the inner wall surface decreases (see the arrow in FIG. 5). Then, the working gas sucked into the cylinder is warmed by the heat remaining on the top surface of the piston after the middle of the intake stroke, and knocking and abnormal combustion occur.

  In this respect, the ceramic film 34 is formed on the side surface of the top land, and the piston base material is exposed without forming the ceramic film 34 on the side surface of the second land or the third land. The amount of heat transfer from the side surface of the piston through the piston ring to the inner wall surface of the cylinder can be increased (see the arrow in FIG. 6). Accordingly, heating of the working gas in the intake stroke can be suppressed. As described above, the ceramic film 34 is formed on the side surface of the top land, and the piston base material is exposed on the side surface of the second land or the third land, so that the effect of reducing the unburned HC is enhanced and the working gas in the intake stroke is increased. Heating can be suppressed.

In the above embodiment, the porous alumite film 32 corresponds to the “heat shield film” of the first invention, and the ceramic film 34 corresponds to the “heat insulating film” of the invention. When the multi-hard anodized film 32 includes porous particles, the porous anodized film 32 including porous particles corresponds to the “heat shielding film” of the first invention.

[Piston variants]
By the way, in the said embodiment, the ceramic film 34 with constant film thickness was formed in the whole region of the side surface of a top land. However, the thickness of the ceramic film 34 may be changed stepwise or continuously, or the ceramic film 34 may be formed on a part of the side surface of the top land. 7 to 9 are views for explaining modifications of the piston according to the embodiment of the present invention. These drawings correspond to the schematic sectional views of the cylinder of the spark ignition type internal combustion engine, as in FIG.

  In the example of FIG. 7, the thickness of the ceramic film 34 is changed in two stages. Specifically, the thickness of the ceramic film 34b on the piston top surface side is made thinner than the thickness (50 to 3000 μm) of the ceramic film 34a on the groove 18 side. In the example of FIG. 8, the film thickness on the groove 18 side is the largest (50 to 3000 μm), and the film thickness is reduced toward the piston top surface from the groove 18. In the example of FIG. 9, although the film thickness of the ceramic film 34 is constant (50 to 3000 μm), the ceramic film 34 is formed from the middle of the top land to the groove 18, and from the middle of the top land to the top surface of the piston. The piston base material is exposed.

  When attention is paid to the side surface of the top land, the temperature of the side surface decreases as the distance from the top surface of the piston increases. Therefore, when the working gas existing on the side surface of the top land remains without being burned in the combustion stroke and is carried over to the intake stroke, the probability that the fuel in the residual working gas is condensed in a region near the side surface becomes high. In this regard, as shown in FIGS. 7 to 9, if the ceramic film 34 is formed in a region near the groove 18 on the side surface of the top land, the heat retaining effect in the region can be enhanced. Therefore, the condensation of fuel in the residual working gas can be satisfactorily suppressed.

  Moreover, in the said embodiment, it demonstrated that the piston 10 was applied to a spark ignition type internal combustion engine. However, a piston on which three types of films (a porous anodized film 32, a ceramic film 34, and a hard anodized film 36 are indicated; the same applies hereinafter) may be applied to a compression ignition type internal combustion engine. FIG. 10 is a schematic cross-sectional view when a piston on which three types of films are formed is housed in a cylinder of a compression ignition type internal combustion engine. In FIG. 10, it is assumed that the piston 40 is located at the top dead center. The piston 40 and the piston 10 shown in FIG. 10 are basically the same except for the point that the cavity 42 is formed at the center of the upper surface of the land portion 14. Therefore, according to the piston 40, the effect similar to the effect by the piston 10 can be acquired.

[Internal combustion engine]
Next, an embodiment of the internal combustion engine of the present invention will be described with reference to FIG.
The internal combustion engine according to the present embodiment corresponds to a spark ignition type internal combustion engine in which the piston 10 is incorporated. Therefore, the description of the piston 10 and the three types of films is omitted.

  FIG. 11 is a schematic cross-sectional view of the internal combustion engine 50 according to the embodiment of the present invention. In FIG. 11, it is assumed that the piston 10 is located at the bottom dead center. As shown in FIG. 11, a ceramic film 54 is formed on the inner wall surface of the cylinder 52 of the internal combustion engine 50. Of the inner wall surface, the piston base material is exposed in a region other than the region where the ceramic film 54 is formed.

The thermal characteristics and the like of the ceramic film 54 are basically the same as those of the ceramic film 34. That is, the ceramic film 54 is formed by thermal spraying or cold spraying of a ceramic material. The ceramic film 54 has a lower thermal conductivity than that of the piston base material, and has a higher heat capacity per unit volume than that of the porous alumite film 32. The thickness of the ceramic film 54 is 50 to 3000 μm. The film width of the ceramic film 54 (referred to as the film thickness in the direction parallel to the cylinder axis direction; hereinafter the same) is the same as the film width of the ceramic film 34.

  As shown in FIG. 11, the ceramic film 54 is formed at a position facing the side surface of the top land (that is, the surface on which the ceramic film 34 is formed) when the piston 10 is located at the bottom dead center. The temperature of the inner wall surface of the cylinder 52 basically becomes lower as it approaches the crankcase. Therefore, it can be said that the temperature of the ceramic film 34 is lowest at the bottom dead center closest to the crankcase. In this regard, if the ceramic film 54 is formed as shown in FIG. 11, the ceramic film 54 formed on the inner wall surface of the cylinder 52 exists around the side surface of the top land at the position where the temperature of the ceramic film 34 is lowest. The working gas can be warmed. Therefore, fuel adhesion to the side surface of the top land can be suppressed.

  In the above embodiment, the ceramic film 54 corresponds to the “heat retaining film” of the fourth invention.

[Piston manufacturing method]
Next, a piston manufacturing method according to an embodiment of the present invention will be described with reference to FIG.
The manufacturing method according to the present embodiment corresponds to a method for manufacturing the piston 10.

  FIG. 12 is a flowchart for explaining a manufacturing method of the piston according to the embodiment of the present invention. As shown in FIG. 12, in the present embodiment, first, hard alumite is formed on the surfaces of the grooves 18, 20, and 22 by anodizing (step S1). Specifically, in this step S1, masking is performed on the surface of the land portion of the piston in which the grooves 18, 20, 22 and the valve recesses 24, 26, 28, 30 and the like are formed, in which hard alumite is not required to be formed. Apply. Subsequently, this piston is installed in an electrolysis apparatus including an electrolytic cell, a cathode, and a power source. Then, electrolysis conditions (electrolyte temperature, current density and electrolysis time, which are the same hereinafter) suitable for film formation of hard alumite are set, and electricity is supplied between the piston as the anode and the cathode. By passing through this step S1, the hard alumite film | membrane 36 is formed.

  Subsequent to step S1, porous alumite is formed on the upper surface of the land portion by anodizing (step S2). This step S2 is basically the same as step S1. That is, masking is performed on the area of the land portion where it is not necessary to form a porous alumite film. Subsequently, this piston is installed in an electrolysis apparatus in an inverted state, and electrolysis is performed. Specifically, electrolysis conditions suitable for the film formation of the porous alumite are set, and electricity is supplied between the piston as the anode and the cathode. Thereby, a porous alumite film is formed. After film formation, the film formation surface is polished as necessary. When the heat insulating particles are used in combination with porous alumite, a solution containing the heat insulating particles (for example, a polysilazane solution or a polysiloxane solution) is applied to the surface of the porous alumite after the porous alumite film is formed. Work. By passing through this step S2, the porous alumite film | membrane 32 is formed.

  Subsequent to step S2, a ceramic material is deposited on the side surface of the top land (step S3). In this step S3, first, the side surface of the top land is cut by the thickness of the ceramic material. The reason for cutting is to prevent the clearance between the side surface of the top land and the inner wall surface of the cylinder from being reduced by the film formation of the ceramic material. Subsequently, the cut surface is blasted. The reason for blasting is to intentionally deteriorate the surface roughness of the machined surface and improve the adhesion of the ceramic film formed on the machined surface to the piston base material by the anchor effect. Subsequently, thermal spraying or cold spraying of the ceramic material is performed on the blasted surface. Thereby, a ceramic material is deposited. After film formation, the film formation surface is polished as necessary. By passing through this step S3, the ceramic film 34 is formed.

  Since the ceramic material basically exhibits insulating properties, the anodic oxidation reaction is hindered when step S1 or step S2 is performed after step S3. In this regard, according to the present embodiment, steps S1 and S2 are processed before the processing of step S3, so that variations in the structure and film thickness of the three types of films can be suppressed.

  In the above embodiment, step S2 corresponds to the “heat shield film forming step” of the fifth invention, and step S3 corresponds to the “heat insulation film forming step” of the invention.

[Modification of manufacturing method]
By the way, in the said embodiment, step S2 was processed after the process of step S1. However, step S2 may be processed before the process of step S1.
In the above embodiment, the ceramic material is formed by thermal spraying or cold spraying in step S3. However, a ring-shaped molded body may be separately manufactured from a ceramic material, and the molded body may be press-fitted into the side surface of the top land.

10, 40 Piston 14 Land portion 18, 20, 22 Groove 32 Porous anodized film 34, 54 Ceramic film 36 Hard anodized film 50 Internal combustion engine 52 Cylinder

Claims (5)

An internal combustion engine in which an anodic oxide film as a thermal barrier film having a thermal conductivity lower than that of a piston base material and having a heat capacity per unit volume lower than that of the piston base material is formed on an upper surface of a land portion. A piston,
The thermal barrier film is not formed on the side surface of the land portion,
Of the land portion , the side surface of the top land, which is a portion above the groove in which the top ring is mounted , has a lower thermal conductivity than the piston base material, and is higher than the thermal barrier film. A piston for an internal combustion engine , wherein a heat retaining film having a heat capacity per unit volume and having a surface roughness smaller than the surface roughness of the heat shielding film is formed. The heat insulating film is a film thickness that gradually decreases from the lower surface side of the land portion toward the upper surface side of the land portion, or continuously from the lower surface side of the land portion toward the upper surface side of the land portion. 2. The piston of the internal combustion engine according to claim 1, wherein the piston has a film thickness that decreases, or is formed on a lower surface side of the land portion and is not formed on an upper surface side of the land portion. In lower than the grooves of the side surface of the land portion, a piston for an internal combustion engine according to claim 1 or 2, characterized in that the piston base material is exposed. An internal combustion engine comprising the piston according to any one of claims 1 to 3,
A unit volume that is lower than the piston base material and higher than the thermal barrier film at a position facing the side surface of the top land when the piston is located at the bottom dead center of the inner wall surface of the cylinder that houses the piston. An internal combustion engine, wherein a heat retaining film having a heat capacity per unit is formed. A method for manufacturing a piston according to any one of claims 1 to 3,
And forming the thermal barrier layer on the upper surface of the land portion by anodic oxidation of said piston base material,
After the formation of the thermal barrier film, an insulating material having a lower thermal conductivity than the piston base material and a higher heat capacity per unit volume than the thermal barrier film is formed on the side surface of the top land. and forming the heat retaining film on the side surface of the top land by film,
The manufacturing method of the piston characterized by comprising.

Images