JP2014227859A - Piston of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a novel piston of an internal combustion engine, capable of utilizing the characteristics of an anodic oxide film to the maximum while securing a region for a stamp.SOLUTION: A tapered part 24b is designed so that its size a in the direction of the outer periphery of a crestal plane is greater than a target film thickness b of an anodic oxide film 36. The tapered part 24b is also designed so that its size h in the direction of the depth is greater than a size e between a contact point of each of valve recesses 26, 28 with the tapered part 24b and the crestal plane. On the tapered part 24b, the anodic oxide film 36 is designed so that its size c in the direction of the outer periphery of the crestal plane is smaller than the size a. The anodic oxide film 36 is also designed so that its size f in the direction of the depth is smaller than the size h. A region where the anodic oxide film 36 is not formed is a seal surface (a size d in the direction of the outer periphery of the crestal plane and a size g in the direction of the slope of the tapered part 24b).

Description

  The present invention relates to a piston for an internal combustion engine, and more particularly to a piston for an internal combustion engine in which a heat insulating film is formed.

  Conventionally, it is known to form a heat insulating film on a wall surface of a combustion chamber of an internal combustion engine. For example, in the example of Patent Document 1, when a heat insulating film (anodized film) having a film thickness of 50 to 500 μm and a porosity of 30% or more is formed on an aluminum foil, in addition to low thermal conductivity and low heat capacity, peeling -It has been shown that excellent durability with no detachment was obtained. In the said Example, aluminum foil imitates the wall surface of a combustion chamber, this aluminum foil is immersed in electrolyte solution (aqueous solution, such as an oxalic acid and a sulfuric acid), and the voltage of 25-40V is applied for 2 to 15 hours. The heat insulation film is formed by electrolysis.

JP 2010-249008 A

  In view of the above characteristics, it is desirable to form the heat insulating film on the entire wall surface of the combustion chamber. For example, in the case of a piston, it is desirable to form a heat insulating film over the entire area of the upper surface of the crown. On the other hand, it is necessary to mark an identification symbol such as a dimension rank of the piston on the upper surface. Since this stamp is necessary not only at the time of shipment of the piston but also at the time of maintenance, it is not desirable to attach it to a heat insulating film that may disappear due to combustion gas or the like. Therefore, it is required to secure an area for marking on the upper surface of the piston crown, in addition to the area for forming the heat insulating film. However, based on such a viewpoint, there is no conventional piston having a heat insulating film.

  The present invention has been made in view of the above-described problems. That is, an object of the present invention is to provide a new piston for an internal combustion engine capable of maximizing the characteristics of a heat insulating film while securing a region for marking.

In order to achieve the above object, a first invention is a piston of an internal combustion engine in which a heat insulating film is formed,
The piston includes an inclined portion that is connected to an upper surface of the crown portion and is inclined downward as it is separated from the center of the upper surface in the horizontal direction and connected to a side surface of the crown portion.
The heat insulating film is formed in the upper region on the upper surface side and the upper surface of the inclined portion,
A region where the heat insulating film is not formed is provided in a lower region on the side surface side and the side surface of the inclined portion.

The second invention is the first invention, wherein
The inclined portion is formed in an annular shape along the outer periphery of the upper surface, and the diameter increases from the upper surface toward the side surface.

The third invention is the first or second invention, wherein
The piston further includes a valve recess that is partially formed on the outer periphery of the crown and connected to the upper surface, and is further inclined to the horizontal direction away from the center of the upper surface and connected to the side surface. ,
The heat insulating film is formed in the valve recess.

Moreover, 4th invention is set in 3rd invention,
An outer edge of the valve recess formed on the side surface extends over both the upper region and the lower region.

According to a fifth invention, in any one of the first to fourth inventions,
The heat insulating film is an anodized film having a thermal conductivity lower than the thermal conductivity of the piston base material and a heat capacity per unit volume lower than the heat capacity per unit volume of the piston base material.

  According to the present invention, a heat insulating film can be formed on the upper region and the upper surface of the crown portion, and a region where no heat insulating film can be formed on the lower region and the upper surface of the crown portion can be provided. Therefore, it is possible to provide a piston capable of making the most of the characteristics of the heat insulating film while ensuring the lower region and the upper surface of the crown as a region for engraving.

It is a perspective view of the piston which concerns on embodiment. It is an expansion schematic diagram of the X part of FIG. It is a figure explaining the formation area of the anodic oxide film 36 in the taper part 24b. 4 is a diagram for explaining the structure of an anodized film 36. FIG. It is an expansion schematic diagram of the taper part 24b periphery during an anodizing process. It is a figure for demonstrating the conventional method of an anodizing process. It is a figure for demonstrating the conventional method of an anodizing process. It is a figure for demonstrating the conventional method of an anodizing process. It is a figure for demonstrating the problem at the time of attaching a mark before anodizing treatment. It is a figure for demonstrating the other example of the formation method of a sealing surface.

  Hereinafter, an embodiment of a piston according to the present invention will be described with reference to FIGS. 1 to 10. The piston according to the present invention can be applied to either a diesel engine or a gasoline engine.

[Piston configuration]
FIG. 1 is a perspective view of a piston according to the embodiment. As shown in FIG. 1, the piston 10 includes a cylindrical skirt portion 12 whose side surface is in sliding contact with an inner surface of a cylinder block (not shown), and a crown portion 14 having a predetermined thickness formed at the upper end portion of the skirt portion 12. And pin boss portions 16 and 18 that support piston pins (not shown).

  Three piston ring grooves 18, 20, and 22 are formed on the side surface of the crown portion 14. The crown portion 14 above the piston ring groove 18 constitutes a top land portion 24. Valve recesses 26 and 28 for avoiding interference with a valve (not shown) are formed on the upper surface (hereinafter also referred to as “crown surface”) of the top land portion 24. The depths of the valve recesses 26 and 28 are formed so as to gradually increase from the center of the top land portion 24 toward the side surface. Squish areas 30 and 32 are formed between the valve recesses 26 and 28. A cavity 34 is recessed in the center of the top surface of the top land portion 24.

  The side surface of the top land portion 24 includes a parallel portion 24a parallel to the central axis direction of the piston 10 and a tapered portion 24b formed above the parallel portion 24a. The diameter of the tapered portion 24b increases as it goes downward from the crown surface side.

  An anodized film 36 is formed on a part of the tapered portion 24b and the crown surface. FIG. 2 is an enlarged schematic view of a portion X in FIG. As shown in FIG. 2, the anodized film 36 is formed on the entire crown surface, that is, the valve recess 28, the squish area 32, and the cavity 34. Moreover, the anodic oxide film 36 is formed in the area | region of the crown side of the taper part 24b.

  FIG. 3 is a diagram for explaining a region where the anodized film 36 is formed in the tapered portion 24b. As shown in FIG. 3, the dimension “a” in the outer peripheral direction of the crown surface of the tapered portion 24 b is designed to be larger than the target film thickness “b” (10 to 500 μm) of the anodized film 36. The dimension h (about 1 to 3 mm) in the depth direction of the taper portion 24b is designed to be larger than the dimension e from the contact point of the valve recesses 26 and 28 with the taper portion 24b to the crown surface. In the taper portion 24b, the dimension c of the anodized film 36 in the crown surface outer circumferential direction is designed to be smaller than the dimension a. The dimension f in the depth direction of the anodized film 36 is designed to be smaller than the dimension h. In addition, the area | region in which the anodic oxide film 36 is not formed is a sealing surface (dimension d in the outer peripheral direction of the crown surface, and dimension g (about 2 to 4 mm) in the inclined direction of the tapered portion 24b).

  FIG. 4 is a view for explaining the structure of the anodized film 36. As shown in FIG. 4, the anodic oxide film 36 is composed of an alumite film 36a and a sealing material 36b. The alumite film 36 a is a porous film formed by anodizing an aluminum alloy that is a base material of the piston 10. The sealing material 36b is provided for the purpose of sealing the crack 36c formed on the upper surface of the anodized film 36a and the communication hole 36d formed therein to suppress thermal fatigue of the anodized film 36a. As the sealing material 36b, a material (preferably polysilazane) in which a heat-resistant material such as silica acts as a main component after coating and curing is used.

  It goes without saying that the anodic oxide film 36 having the structure shown in FIG. 4 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 insulating 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 insulating 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 36 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.

  As described with reference to FIGS. 1 to 3, the anodized film 36 is formed not only on the crown surface but also on a part of the tapered portion 24b. By forming the anodic oxide film 36 over such a wide range, the above-described effects can be obtained to the maximum. In addition, the piston 10 can be smoothly slid in the cylinder by designing the dimensions of the anodized film 36 formed on the tapered portion 24b as described above. At the same time, the tapered portion 24b where the anodized film 36 is not formed can be used as a region for marking. The engraving includes maintenance information (pin diameter, bore diameter dimension rank, front mark) and manufacturing information (manufacturing date, bar code, QR code (registered trademark)) of the piston 10 and the like.

[Piston manufacturing method]
The outline of the manufacturing method of the piston 10 is as follows. That is, first, a piston in which the tapered portion 24b, the valve recesses 26 and 28, the squish areas 30 and 32, the cavity 34, and the like are formed is cast from an aluminum alloy. The dimensional size of the casting piston is that the diameter of the crown portion 14 is φA and the diameter of the crown surface is φB (<φA). Subsequently, the cast piston is anodized to form an alumite film 36a on a part of the tapered portion 24b and the crown surface. Subsequently, the sealing material 36b is sprayed to cover the alumite film 36a. Thereby, the piston 10 in which the anodized film 36 is formed is obtained.

  An anodizing process in the manufacturing process of the piston 10 will be described with reference to FIGS. FIG. 5 is an enlarged schematic view of the periphery of the tapered portion 24b during the anodizing process. In the anodizing treatment, a masking material 40 having a circular cross section in the horizontal direction and an inner diameter φC satisfying φA> φC> φB is used. When a casting piston is inserted into such a masking material 40, the top land portion 24 is fastened by the masking material 40, and a sealing surface is formed on the tapered portion 24b. As shown in FIG. 5, when the inside of the masking material 40 is filled with an electrolytic solution (aqueous solution of oxalic acid, sulfuric acid, etc.) and electrolysis is performed using the piston 10 as an anode, it is above the sealing surface (shown in the figure). An alumite film 36a is formed on the taper portion 24b (above the film forming end). In addition, in the taper part 24b connected to the valve recesses 26 and 28, a seal surface is formed below the connection point between the valve recesses 26 and 28 and the taper part 24b. That is, the connection point is the film forming end.

  Here, FIG. 6 to FIG. 8 are diagrams for explaining a conventional method of anodizing treatment. As shown in FIG. 6, an alumite film can be formed on the entire top surface of the crown portion by anodizing with a masking material in contact with the side surface of the piston. However, after the formation of the alumite film, it is necessary to cut the alumite film or the like in order to give the above-mentioned marking. That is, in the conventional method, the number of steps increases and the productivity is likely to decrease.

  In addition, as shown in FIG. 6, when the masking material is worn or deteriorated, there is a possibility that the electrolyte enters from between the masking material and the side surface of the piston during the anodizing process. In particular, when an alumite film having a thickness of 100 μm or more is formed, the voltage application time takes several hours, so that the electrolytic solution easily enters. As a result, the thickness of the anodized film becomes insufficient, or an anodized film is formed on the side surface of the piston. If an alumite film is formed on the side surface of the piston, the cylinder bore surface may be damaged by the anodized film formed on the side surface when the piston slides in the cylinder.

  The same applies when an O-ring seal material is used instead of the masking material. As shown in FIGS. 7 to 8, there is a possibility that the electrolyte enters from between the O-ring seal material and the side surface of the piston during the anodizing process. In addition, during the anodizing process, the electrolyte may leak through the valve recess to the side of the piston (FIG. 7), or the electrolyte may enter the side of the piston from above the O-ring seal (FIG. 8). There is.

  Assume that a method is adopted in which a stamp such as maintenance information is given before the anodizing treatment and the stamp is exposed after the anodizing treatment. However, the anodized film has a property of forming in a direction perpendicular to the base material surface. Therefore, as shown in FIG. 9, the cells of the anodic oxide film may be concentrated at the center of the stamped portion (groove portion), and cracks may be generated on the outer periphery of the groove. As described above, when the properties of the anodized film are taken into consideration, it is not desirable to mark in advance because it leads to defects such as film defects.

  In this regard, according to the anodizing treatment shown in FIG. 5, a sealing surface can be formed on the tapered portion 24 b by the masking material 40. Therefore, it is possible to prevent the electrolyte from entering the side surface of the piston during the anodizing process by sealing the electrolyte above and inside the seal surface. Moreover, this sealing surface can be made into the area | region which does not form the anodized film 36a. Therefore, the seal surface can be marked after the anodizing treatment.

  By the way, in the said embodiment, the inclined surface of the taper part 24b may bulge in convex shape. That is, as long as the sealing surface can be secured by the masking material 40 when inserted into the masking material 40, the shape of the tapered portion 24b can be variously modified.

  Moreover, in the said embodiment, although the dimension f of the depth direction of the anodic oxide film 36 was designed smaller than the dimension e from the contact with the taper part 24b of the valve recesses 26 and 28 to a crown surface, it is larger than the dimension e. You may design large. As long as the taper portion 24b is designed to be smaller than the dimension h in the depth direction, the magnitude relationship between the dimension e and the dimension f can be changed as appropriate.

  Moreover, in the said anodizing process, although the sealing surface was formed in the taper part 24b using the masking material 40, the formation method of this sealing surface is not restricted to said example. FIG. 10 is a diagram for explaining another example of a method for forming a seal surface. As shown in FIG. 10, a sealing surface may be formed on the tapered portion 24b using an O-ring sealing material. However, when an O-ring sealing material is used, it is necessary to consider the inner diameter of the holding member that holds the sealing material. In this regard, if the inner diameter φ of the holding member above the sealing material is C, a sealing surface can be formed on the tapered portion 24b as in the masking material 40 as long as the holding member satisfies φA> φC ≧ φB. When an O-ring seal material is used, the contact points of the valve recesses 26 and 28 and the taper portion 24b are located above the seal surface in order to prevent leakage of the electrolyte solution via the valve recess described in FIG. It is necessary to manage the position of the O-ring seal material. In this case, the dimension f is larger than the dimension e.

In the above embodiment, the upper surface of the top land portion 24 is the “top surface of the crown portion” of the first invention, the parallel portion 24a is the “side surface of the crown portion” of the invention, and the tapered portion 24b is the same invention. The “anodized film” 36 corresponds to the “heat insulating film” of the present invention.
The valve recesses 26 and 28 correspond to the “valve recess” in the third aspect of the invention.

10 Piston 24 Top land portion 24a Parallel portion 24b Taper portion 26, 28 Valve recess 36 Anodized film

Claims (5)

A piston of an internal combustion engine in which a heat insulating film is formed,
The piston includes an inclined portion that is connected to an upper surface of the crown portion and is inclined downward as it is separated from the center of the upper surface in the horizontal direction and connected to a side surface of the crown portion.
The heat insulating film is formed in the upper region on the upper surface side and the upper surface of the inclined portion,
The piston of the internal combustion engine, wherein a region where the heat insulating film is not formed is provided in a lower region on the side surface side and the side surface of the inclined portion.   2. The piston of the internal combustion engine according to claim 1, wherein the inclined portion is formed in an annular shape along an outer periphery of the upper surface, and has a diameter that increases from the upper surface toward the side surface. The piston further includes a valve recess that is partially formed on the outer periphery of the crown and connected to the upper surface, and is further inclined to the horizontal direction away from the center of the upper surface and connected to the side surface. ,
The piston of the internal combustion engine according to claim 1 or 2, wherein the heat insulating film is formed in the valve recess.   The piston of the internal combustion engine according to claim 3, wherein an outer edge of the valve recess formed on the side surface extends over both the upper region and the lower region.   The heat insulating film is an anodized film having a thermal conductivity lower than that of a piston base material and a heat capacity per unit volume lower than a heat capacity per unit volume of the piston base material. The piston of the internal combustion engine according to any one of 1 to 4.

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