JP2015096633A - Method of forming heat-shielding film for internal engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of forming a heat-shielding film for an internal engine which can prevent deterioration of an internal engine, detachment of a heat-shielding film, etc.SOLUTION: A method of forming a heat-shielding film for an internal engine is based on forming an anodic oxide film on members constituting a wall surface of a combustion chamber of an internal engine and includes a step of surrounding the periphery of a region to be formed with an anodic oxide film in a member 10, with a porous member 28, supplying an electrolytic solution 30 in the region surrounded by the porous member and forming the anodic oxide film.

Description

  The present invention relates to a method for forming a thermal barrier film for an internal combustion engine.

  Conventionally, a technique for forming a thermal barrier film on a member constituting a wall surface of a combustion chamber of an internal combustion engine is known. For example, Patent Document 1 discloses a technique for forming an anodized film made of alumite on a member constituting a wall surface of a combustion chamber whose base material is aluminum or an alloy thereof. By forming a thermal barrier film such as an anodized film on the member constituting the wall surface of the combustion chamber, the heat insulating property on the wall surface of the combustion chamber is improved. As a result, the thermal efficiency of combustion in the internal combustion engine can be improved.

JP 2012-159059 A JP 2012-112332 A

  By the way, when the thermal barrier film is formed by the above technique, a step is generated between the end portion of the thermal barrier film (hereinafter also referred to as the “film end portion”) and a member constituting the wall surface of the combustion chamber. This level | step difference reduces the flow velocity of the gas in a combustion chamber, and causes a performance fall of an internal combustion engine. In addition, when the above steps are exposed to gas, the heat shielding film may peel off. Further, if the above steps are made smooth after the formation of the thermal barrier film, a cost for processing is generated. For this reason, there has been a demand to establish a film forming method that smoothes the film end portion and does not cause the above-described step when forming the thermal barrier film.

  The present invention has been made to solve the above-described problems, and provides a method for forming a heat shield film for an internal combustion engine that can prevent degradation in performance of the internal combustion engine and peeling of the heat shield film. With the goal.

In order to achieve the above object, a first invention is a method for forming a thermal barrier film of an internal combustion engine,
A method for forming a thermal barrier film of an internal combustion engine, wherein an anodized film is formed on a member constituting a wall surface of a combustion chamber of the internal combustion engine,
The method comprises the steps of surrounding a region where an anodic oxide film is formed in the member with a porous member, and supplying an electrolytic solution into the region surrounded by the porous member to form the anodic oxide film. To do.

  According to the first aspect of the present invention, the film end can be smoothly formed without causing a step at the film end. For this reason, it is possible to prevent the deterioration of the performance of the internal combustion engine due to the step at the end of the film and the occurrence of cracks in the members constituting the wall surface of the combustion chamber. Further, since a smooth film edge can be obtained simultaneously with the film forming process, there is no cost for processing the step.

It is sectional drawing of the piston in which the heat shield film was formed by the conventional heat shield film formation method. It is a figure for demonstrating the structure of an anodized film. It is a figure showing the crown surface of the piston after film forming processing was performed by the conventional technology. It is a figure for demonstrating the bad influence to the engine which generate | occur | produces with a level | step difference. 3 is a diagram for explaining a film forming apparatus used in the film forming method in Embodiment 1. FIG. It is a figure for demonstrating a mode that an alumite film is formed on the crown surface of a piston in Embodiment 1. FIG. FIG. 10 is a diagram for explaining how an alumite film is formed on the crown surface of a piston in the second embodiment.

Embodiment 1 FIG.
Hereinafter, a method for forming a thermal barrier film for an internal combustion engine according to Embodiment 1 will be described with reference to FIGS. 1 to 6.

  FIG. 1 is a cross-sectional view of a piston having a heat shield film formed by a conventional heat shield film forming method. FIG. 1 shows a piston 10. An anodized film 12 is formed on the crown surface of the piston 10 as a heat shield film.

  A cavity 14 is recessed in the center of the crown surface of the piston 10. In the piston 10 described in the first embodiment, the anodized film 12 is not formed on the surface of the cavity 14. For this reason, the formation region of the anodized film 12 is only the crown surface of the piston 10.

  Next, the structure of the anodic oxide film 12 will be described with reference to FIG. 2 which is a schematic diagram in which the portion X in FIG. 1 is enlarged.

  FIG. 2 is a diagram for explaining the structure of the anodized film 12. As shown in FIG. 2, the anodic oxide film 12 includes an alumite film 12a and a sealing material 12b. The alumite film 12 a is a porous film formed by anodizing an aluminum alloy that is a base material of the piston 10. The sealing material 12b is provided for the purpose of suppressing thermal fatigue of the anodized film 12a by sealing the crack 12c formed on the upper surface of the anodized film 12a and the communication hole 12d formed therein. As the sealing material 12b, a material (preferably polysilazane or polysiloxane) in which a heat-resistant material such as silica acts as a main component after coating and curing is used.

  The anodic oxide film 12 having the structure shown in FIG. 2 has a lower thermal conductivity and a lower heat capacity than an aluminum alloy, and has a lower heat conductivity and a lower heat capacity than a conventional ceramic heat shield film. Therefore, the wall surface of the combustion chamber is not always kept at a high temperature as in the case of a ceramic heat shield film, but it is possible to follow the gas temperature in the combustion chamber that varies between engine cycles. That is, the wall surface temperature of the combustion chamber can be made low during the intake to compression stroke (up stroke in the case of a two-cycle engine) and high during the expansion to exhaust stroke (down stroke in the case of a two-cycle engine). Therefore, according to the piston 10 on which the anodized film 12 is formed, not only the thermal efficiency of the engine but also the intake efficiency can be improved, so that it is possible to obtain effects such as improved fuel consumption and reduced NOx emission.

  By the way, when the anodized film 12 is formed by the conventional technique, a step is generated between the piston 10 and the end of the anodized film 12. This step can have various adverse effects on the engine. Hereinafter, with reference to FIG. 3 and FIG. 4, an adverse effect on the engine caused by this step will be described.

  FIG. 3 is a view showing the crown surface of the piston 10 after the film forming process is performed by the conventional technique. FIG. 3 shows a state in which a step A is generated between the piston 10 and the film end of the alumite film 12a. In the conventional technique, the sealing material 12b is applied to the alumite film 12a while the step A is generated.

FIG. 4 is a diagram for explaining an adverse effect on the engine caused by the step A. FIG. In FIG. 4, the flow of the combustion gas in the combustion chamber of the engine is indicated by an arrow S. Further, in FIG. 4, a state where the flow of the combustion gas is disturbed by the combustion gas hitting the step A is indicated by an arrow T. Disturbances in the flow of the combustion gas due to the step A reduce the flow velocity of the combustion gas. For this reason, a combustion delay occurs in the engine. As a result, reduction in fuel consumption, reduction in engine performance such as reduction of exhaust performance due to the increase of the NO _X and HC is caused.

  Further, in FIG. 4, a state in which the film end portion of the anodic oxide film 12 is exposed to the combustion gas so that the film end portion is chipped is represented by a broken line U. When the chip | tip shown with the broken line U arises, the sealing material 12b in the chip | tip part lose | disappears. Thereby, peeling of the anodic oxide film 12 occurs from the lacked portion. Here, the boundary between the anodized film 12 and the aluminum of the base material of the piston 10 is a place where stress is concentrated. For this reason, thermal fatigue of the piston 10 occurs at this location, and the piston 10 may crack.

  In order not to cause an adverse effect due to these steps A, it is necessary to form a smooth film end. However, in order to process the step A smoothly after the formation of the anodized film 12, a cost corresponding to the processing cost is required.

  Therefore, in the first embodiment, when the anodic oxide film 12 is formed on the piston 10, a film forming method is performed in which the film end is smooth. Hereinafter, the film forming method will be described in detail with reference to FIGS.

  FIG. 5 is a diagram for explaining a film forming apparatus used in the film forming method in the first embodiment. FIG. 5 shows a film forming apparatus 20 for forming the anodic oxide film 12 on the crown surface of the piston 10. The film forming apparatus 20 is provided with a piston 10. The piston 10 is held such that its bottom is supported by the electrode 24. The piston 10 is held with its side surface surrounded by the cooling device 26.

  As shown in FIG. 5, the outer peripheral portion of the crown surface of the piston 10 is sealed by a porous member 28 made of a porous elastic body. Similarly, the boundary between the crown surface of the piston 10 and the cavity 14 is sealed by a porous member 28. Here, the porous elastic body is a substance through which a liquid permeates, for example, a sponge.

  An acidic electrolyte solution 30 is injected into a space formed by the crown surface of the piston 10 and the porous member 28. Thereby, the acidic electrolyte solution 30 contacts the crown surface of the piston 10. The acidic electrolytic solution 30 is provided with an electrode 22. In addition, as shown by the arrow in FIG. 5, the acidic electrolyte 30 is injected from one end and discharged from the other end.

  When electrolysis is performed by applying a voltage between the electrodes 22 and 24 in the state in which the acidic electrolyte 30 is injected in the film forming apparatus 20, the crown surface of the piston 10 as the anode is oxidized, and the alumite film 12a is formed. It is formed. The porosity of the alumite film 12a is adjusted to a desired value by the applied voltage, and the thickness of the alumite film 12a is adjusted by the application time. During the film forming process, the piston 10 is cooled by the cooling device 26 in order to remove the oxidation reaction heat.

  FIG. 6 is a view for explaining a state in which the alumite film 12a is formed on the crown surface of the piston 10 in the first embodiment. FIG. 6 is an enlarged schematic diagram of a Y portion in FIG.

  FIG. 6A is a diagram illustrating the porous member 28 before the film forming process. In FIG. 6A, the state in which the acidic electrolyte 30 permeates the porous member 28 is indicated by an arrow D. Here, the porous member 28 used in the first embodiment is partially different in density in the porous member 28. Here, the density is the number of holes into which liquid enters per unit volume. In the porous member 28, a portion having a relatively large number of holes is expressed as a rough portion, and a portion having a relatively small number of holes is expressed as a dense portion.

  The porous member 28 in the first embodiment is a portion where the acidic electrolyte solution 30 side and the crown surface side portion of the piston 10 are rough. Since moisture easily penetrates into the rough portion, the acidic electrolytic solution 30 preferentially penetrates into the rough portion. The difference in permeability in the porous member 28 is indicated by an arrow E in FIG. Specifically, the penetration rate increases in the direction indicated by the arrow E.

  FIG. 6B is a diagram illustrating the porous member 28 after the film forming process. FIG. 6B shows a state in which the alumite film 12a is formed by the film forming process. The formed anodized film 12a forms a smooth film end. Thus, by providing a difference in the permeability of the acidic electrolytic solution 30 in the porous member 28, a smooth film end can be formed without causing a step in the alumite film 12a.

  FIG. 6C is a diagram illustrating the porous member 28 during seal regeneration. FIG. 6C shows a state in which the permeated acidic electrolyte solution 30 is discharged when the porous member 28 is crushed. After discharging the acidic electrolyte 30, the film forming region in the piston 10 is washed and dried. Thereafter, a sealing process is performed on the film forming region to form the anodic oxide film 12.

According to the method for forming the anodic oxide film 12 according to the first embodiment, the film end can be smoothly formed without causing a step in the film end. Therefore, reduction in engine performance such as reduction of exhaust performance due to the increase in the reduction and NO _X and HC fuel consumption which occurs in the step is generated, the piston 10 due to peeling of the anodized film 12 cracks occur such as Can be prevented. Furthermore, since a smooth film edge can be obtained simultaneously with the film forming process, the cost for processing the step is not required.

  In the first embodiment, the density of the porous member 28 has a partial difference, but the method of making the permeability in the porous member 28 different is not limited to this. For example, the permeation rate into the porous member 28 may be made different by controlling the acidic electrolyte 30 with a pressure difference from the outside air. Further, a partial difference in density may be provided in the porous member 28 and the pressure of the acidic electrolyte solution 30 may be controlled. This modification can be similarly applied to Embodiment 2 described later.

  Moreover, although Embodiment 1 demonstrated using the piston 10 in which the cavity 14 was provided in the crown surface, it is not limited to this. Even in a piston in which the cavity 14 is not provided, the thermal barrier film forming method of the first embodiment may be used for the purpose of smoothing the film end portion in the outer peripheral portion of the crown surface. This modification can be similarly applied to Embodiment 2 described later.

  In the first embodiment, the piston 10 is used as a specific example of the member constituting the wall surface of the combustion chamber, but the present invention is not limited to this. In the present invention, an intake valve, an exhaust valve, a cylinder head, or the like may be used as a member constituting the wall surface of the combustion chamber on which the anodized film is formed. This modification can be similarly applied to Embodiment 2 described later.

Embodiment 2. FIG.
Next, Embodiment 2 of the present invention will be described with reference to FIG. In the method for forming a thermal barrier film for an internal combustion engine according to the second embodiment, in the same configuration as in the first embodiment, the porous member 28 on the opposite side to the portion in contact with the acidic electrolyte 30 is immersed in cooling water. And it is characterized by obtaining a smooth film | membrane edge part by controlling the easiness of the acidic electrolyte solution 30 to permeate by applying pressure to this cooling water.

  FIG. 7 is a view for explaining a state in which the alumite film 12a is formed on the crown surface of the piston 10 in the second embodiment. FIG. 7A is a diagram illustrating the porous member 28 before film formation. FIG. 7A shows a state in which the cooling water 36 is in contact with the opposite side of the acidic electrolyte 30 in the porous member 28. Furthermore, the ease of penetration of the cooling water 36 into the porous member 28 is controlled.

  Specifically, the cooling water 36 is controlled in the porous member 28 so that the crown surface side of the piston 10 is less likely to permeate and becomes more likely to permeate toward the opposite side of the crown surface of the piston 10. As a result, the acidic electrolytic solution 30 soaked into the porous member 28 is diluted with the cooling water 36. For this reason, as shown to Fig.7 (a), the acidic electrolyte solution 30 becomes easy to osmose | permeate the crown surface side of the piston 10. FIG.

  Two complete seal portions 32 and 34 are provided in the porous member 28 shown in FIG. The complete seal portion 32 is provided in order to prevent the cooling water 36 from penetrating to the region where the acidic electrolyte solution 30 is injected beyond the porous member 28. Conversely, the complete seal portion 34 is provided in order to prevent the acidic electrolyte 30 from penetrating to the region where the cooling water 36 is injected beyond the porous member 28.

  FIG. 7B is a diagram showing the porous member after the film forming process. In FIG. 7B, an alumite film 12a is formed on the crown surface of the piston 10, and the film end is smoothly formed. Thus, according to the formation method of the anodic oxide film 12 of Embodiment 2, the film edge part can be formed smoothly.

DESCRIPTION OF SYMBOLS 10 Piston 12 Anodized film 20 Film forming apparatus 28 Porous member 30 Acidic electrolyte

Claims (1)

A method for forming a thermal barrier film of an internal combustion engine, wherein an anodized film is formed on a member constituting a wall surface of a combustion chamber of the internal combustion engine,
The method comprises the steps of surrounding a region where an anodic oxide film is formed in the member with a porous member and supplying an electrolytic solution into the region surrounded by the porous member to form the anodic oxide film. A method for forming a thermal barrier film for an internal combustion engine.

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