JP2001271705A - Piston made of aluminum alloy for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piston made of aluminum alloy for an internal combustion engine capable of relieving stress concentration exerted on a pin hole, and of highly setting a bearing resistance. SOLUTION: This piston made of aluminum alloy for an internal combustion engine 10 is provided with a pair of pin holes 21, 31 into which a piston pin 40 is inserted. The pin holes 21, 31 comprise a cylindrical hole 22 coming into contact with the piston pin 40, and conical holes 23, 33 diameters of which expand from ends of cylindrical holes 22, 23 towards the center of the piston 10 so that the conical holes 23, 33 do not come into contact with the piston pin 40. An anode oxide film 50 of electrolyte of mixture of phosphate and fluoride is formed on the conical holes 22, 33 and the cylindrical holes 22, 32, and fine holes of the anode oxide film 50 are impregnated with lubricant.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a piston for an internal combustion engine cast from an aluminum alloy.

[0002]

2. Description of the Related Art In a piston for an internal combustion engine, for example, a combustion pressure of an air-fuel mixture is applied to the piston during an expansion process of the internal combustion engine, and a piston pin is deformed and stress concentrates on a pin boss portion.
In order to cope with this stress concentration, it is necessary to increase the thickness of the pin boss. If the thickness of the pin boss is set to be large, it is difficult to reduce the weight of the piston, and it is difficult to improve the fuel efficiency and engine output of the automobile. Therefore, as a piston for an internal combustion engine that alleviates the stress concentration at the pin boss portion, Japanese Patent Application Laid-Open No. H11-303993 entitled "Piston for Internal Combustion Engine" has been proposed. This technique will be described in detail with reference to the following drawings.

FIG. 15 is a sectional view of a conventional piston for an internal combustion engine. The piston 110 has a pin hole 11 formed in a pair of pin boss portions 111 for inserting a piston pin (not shown).
2 and 112, and chamfered surfaces 113 and 113 are formed in the pin holes 112 and 112 from the connecting rod side.
Conical surface (ie, conical surface) 1 inside 3,113
14, 114 are formed.

A piston pin (not shown) has pin holes 11 at both ends.
Since it is a two-point support beam which is supported by 2,112 and a concentrated load (by pushing and pulling the connecting rod) acts on the center, it bends up and down so that the center has the maximum deflection. For this reason,
By providing the conical portions 114 and 114 so as not to hinder the bending of the piston pin, it is possible to avoid stress concentration expected to occur in the piston pin and the pin boss portions 111 and 111. This is the reason why the conical surfaces 114, 114 are provided.

[0005]

However, the conical surface 1
14 and 114, the piston pin is
The area in contact with 12, 112 is reduced. A load is applied to the small pin holes 112 and 112 in the region from the piston pin as shown by arrows, and the surface pressure increases, which indicates that the piston 10
0 hinders an increase in durability.

Accordingly, an object of the present invention is to provide an aluminum alloy internal combustion engine piston which can reduce stress concentration applied to the pin hole and can set a high surface pressure resistance of the pin hole. is there.

[0007]

According to a first aspect of the present invention, there is provided an aluminum alloy internal combustion engine piston having a pair of pin holes into which piston pins are inserted. A cylindrical hole that comes into contact with the piston pin, and a conical hole that expands in diameter from the end of the cylindrical hole toward the center of the piston so as not to contact the piston pin. In addition, an anodic oxide film is formed with an electrolyte mixed with a fluoride, and a fine pore of the anodic oxide film is impregnated with a lubricant.

[0008] As a result of forming the conical hole in the pin hole to avoid stress concentration, the surface pressure of the cylindrical hole increases. However, a special surface pressure treatment is applied to the cylindrical hole. That is, an anodic oxide film was formed in a cylindrical hole with an electrolytic solution in which a phosphate and a fluoride were mixed, and fine pores of the anodic oxide film were impregnated with a lubricant. Fluoride has the effect of flattening the anodic oxide film, and phosphate has the effect of increasing the diameter of the fine pores in the anodic oxide film. For this reason, the surface resistance of the cylindrical hole is increased by the flat anodic oxide film, and the sliding resistance of the cylindrical hole is reduced by impregnating the fine holes of the flat anodic oxide film with a large amount of lubricant.

A second aspect of the present invention is characterized in that the thickness of the anodic oxide film is reduced in the cylindrical hole, and the thin anodic oxide film and the thick anodic oxide film in the cylindrical hole are connected by a taper. A conical hole is formed by connecting a thin anodic oxide film and a thick anodic oxide film of a cylindrical hole with a taper. Thus, when forming the anodic oxide film on the pin hole, a conical hole is formed at the same time, and the step of cutting the conical hole with a tool is omitted.

[0010]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a perspective view of an aluminum alloy internal combustion engine piston (first embodiment) according to the present invention. The aluminum alloy internal combustion engine piston 10 is a member formed of a Si (silicon) -based aluminum alloy,
Piston ring grooves 13 and 14 and an oil ring groove 15 are formed in the piston head 12, and a pair of skirt portions 17 and 17 are formed below the oil ring groove 15, and left and right between the pair of skirt portions 17 and 17. The pin boss portions 20 and 30 (the pin boss portions 30 on the back side are shown in FIG. 2) are formed, and the pin holes 2 for inserting the piston pins 40 into the pin boss portions 20 and 30 are formed.
1, 31 (the pin holes 31 are shown in FIG. 2). 42 is a connecting rod.

FIG. 2 is a sectional view taken along line 2-2 of FIG. The aluminum alloy internal combustion engine piston 10 has cylindrical holes 22 and 32 for contacting the pin holes 21 and 31 of the left and right pin bosses 20 and 30 with the piston pin 40, and cylindrical holes for preventing contact with the piston pin 40. Piston 1 from the ends of 22, 32
And conical holes 23 and 33 which expand toward the center 11 of the zero (ie, toward the connecting rod 42).
A special anodic oxide film 50 is formed in the electrolytic solution containing phosphate and fluoride in the cylindrical holes 3, 33 and the cylindrical holes 22, 32, and the fine pores of the anodic oxide film 50 are impregnated with a lubricant. is there. The special anodic oxide film 50 and the lubricant will be described in more detail with reference to FIG.

FIG. 3 is an enlarged view of part 3 of FIG.
1 shows a state in which a cylindrical hole 32 and a conical hole 33 are provided, and a chamfered surface 36 is provided between the conical hole 33 and the end portion 35 of the pin boss 30. Cylindrical hole 32, conical hole 33 and chamfer surface 36
In this example, a special anodic oxide film 50 is uniformly formed on the surface, and fine pores of the anodic oxide film 50 are impregnated with a lubricant. In this figure, the cylindrical hole 32 and the piston pin 4
Although the gap between 0 and 0 is shown large, there is practically no gap between the cylindrical hole 32 and the piston pin 40.

The conical hole 33 has an axial length L of 1 to 5 m.
m and the height H in the radial direction is 1 to 30 μm
(0.001 to 0.03 mm). Length L is 1
By setting it to be equal to or greater than mm, sufficient relief is ensured when the piston pin 40 is elastically deformed. Also,
By setting the length L to 5 mm or less, a predetermined amount of the area of the cylindrical hole 32 is secured, and the piston pin 40 can be supported by the cylindrical hole 32.

By setting the height H to 1 μm or more, sufficient relief is provided when the piston pin 40 is elastically deformed. Further, by setting the height H to 30 μm or less, the inclination angle θ of the conical hole 33 is kept small, and the non-contact start point 3 where the piston pin 40 comes into non-contact with the pin hole 31.
7 (that is, the boundary point between the cylindrical hole 32 and the conical hole 33) is alleviated.

As described above, by reducing the stress concentration, the thickness t of the pin boss portion 30 can be reduced, and the weight of the piston can be reduced. The region E is a region where the piston pin 40 does not contact the pin hole 31 when the piston pin 40 is elastically deformed (the conical hole 33).
And the area of the chamfered surface 36).

FIG. 4 is an enlarged view of a part 4 of FIG. 3. In this figure, the film surface 50a of the special anodic oxide film 50 is directed upward for easy understanding. The lubricant 54
An example using a thermosetting resin will be described. The special anodic oxide film 50 has a film surface 50a having a substantially constant thickness t1 and a flat film surface 50a, and has fine holes 52... is there. The holes 52 are holes having a relatively large hole diameter d1. Therefore, a sufficient amount of lubricant (thermosetting resin) 54 can be impregnated in the holes 52..., And the impregnated thermosetting resin 54 can be securely fixed in the holes 52. it can.

For this reason, by fixing the thermosetting resin 54 to the fine holes 52 of the anodized film 50, the abrasion resistance is enhanced by the special anodized film 50 and the sliding resistance is increased by the lubricant. Can be reduced. In addition, the special anodic oxide film 50 can increase the surface pressure resistance by flattening the film surface 50a.

Hereinafter, a method for forming an ordinary anodic oxide film will be described with reference to FIG. 5 as a comparative example. FIGS. 5A to 5C show a comparative example in which a common anodic oxide film is formed in a pin hole of a piston for an internal combustion engine. (A) shows a normal anodic oxide film formed with a sulfuric acid electrolytic solution. The Si grains 101 are distributed in the pin holes 100 of the piston for the internal combustion engine made of an aluminum alloy as a base material, and the Si grains 102 in the vicinity of the surface have an adverse effect on the anodic oxide film 103, resulting in anodic oxidation. Film 103
Are uneven as a whole.

(B) is an enlarged view of (a), in which a large dent D1 is formed at the portion of the Si grain 105 that has happened to appear on the surface, without forming an anodic oxide film. Although the anodic oxide film 107 was formed on the portion of the grain 106, the film thickness was smaller than that of the surrounding anodic oxide film 103, and a depression D2 was formed. That is, S
It was found that even when the pin hole 100 of the aluminum alloy piston containing i was anodized with a sulfuric acid electrolyte, a flat anodic oxide film could not be obtained. Also, in the sulfuric acid electrolyte, if the pore diameter of the fine pores 108 is d2, it was found that d2 is generally as small as about 15 nm.

(C) shows a state in which the liquid thermosetting resin is impregnated into the fine holes 108, and the impregnated liquid thermosetting resin is heated to be changed into the cured resin 109. . Since the resin has low frictional resistance, the anodic oxide films 103, 107
Impregnated with the cured resin 109, the sliding resistance of the pin hole 100 with respect to the piston pin becomes relatively small.

However, as shown in FIG. 2B, depressions D1 and D2 are formed in the anodic oxide film 103 and
03 is difficult to generate flat. Therefore, the surface pressure resistance of the pin hole cannot be sufficiently increased. Also, the pore diameter d of the fine pores 108 formed in the anodic oxide film 103
2 is too small to allow the anodic oxide film 103 to contain the resin 109 sufficiently. Therefore, the anodic oxide film 10
Even if the resin 3 is impregnated with the resin 109, the frictional resistance cannot be reduced to a desired value.

Hereinafter, a method for forming the special anodic oxide film shown in the enlarged sectional view of FIG. 4 will be described. FIG. 6 is a flowchart for explaining a special anodic oxide film treatment method for an aluminum alloy internal combustion engine piston (first embodiment) according to the present invention. In the drawing, STxx indicates a step number. ST10: The pin hole of the pin boss of the aluminum alloy internal combustion engine piston (that is, the AC8C aluminum alloy piston as a Si-based aluminum alloy) is degreased. Mask other than the pin holes of the pin boss. When an anodic oxide film is formed on the entire surface of the aluminum alloy piston for an internal combustion engine, no mask is used. ST11: Electrolyze in a mixed aqueous solution of trisodium phosphate as a phosphate and potassium fluoride as a fluoride to form a special anodic oxide film on pin holes. Fine pores are formed on the surface of the anodic oxide film.

ST12: A liquid thermosetting resin containing a fluororesin is prepared, and the liquid thermosetting resin is impregnated into fine pores of the anodic oxide film. ST13: The liquid thermosetting resin impregnated in the fine pores is cured by heating. This completes the anodizing treatment of the aluminum alloy piston according to the present invention.
Hereinafter, S of the anodizing treatment method for Si-based aluminum alloy
T10 to ST13 will be described in detail with reference to FIGS.

FIGS. 7 (a) and 7 (b) are first explanatory views of a method for treating a special anodic oxide film on an aluminum alloy internal combustion engine piston (first embodiment) according to the present invention. (A)
It is a figure which shows the state after ST10 (degreasing), and shows the state which removed the pin hole 31 of the pin boss | hub part 30 of the piston for aluminum alloy internal combustion engines. In the vicinity of the pin hole 31 of the pin boss 30, Si grains 55, 56, 57 are dispersed in aluminum.

(B) is a view showing a state after ST11 (special anodic oxide film treatment), in which an anodized film 50 is formed by electrolysis in a mixed aqueous solution of trisodium phosphate and potassium fluoride. Indicates the status. The pin hole 31 (shown in (a)) is dissolved by the corrosive action of trisodium phosphate,
The Si grains 55, 56, 57 are exposed. Exposed Si grains 5
5, 56, 57 are dissolved and reduced by the action of potassium fluoride.

Therefore, the Si grains 55, 5
The anodic oxide film 50 grows well despite the presence of 6,57. As a result, the film surface 5 of the anodic oxide film 50
Since 0a is aligned, the surface roughness is reduced, and the film thickness t1 is substantially constant. In addition, since the electrolyte contains trisodium phosphate, the pore diameter d1 of the fine pores 52 is sufficiently increased to approximately 100 nm by the action of increasing the pore diameter of trisodium phosphate.

FIGS. 8 (a) and 8 (b) are second explanatory views of a special anodic oxide film treatment method for the aluminum alloy internal combustion engine piston (first embodiment) according to the present invention. (A)
FIG. 11 is a view showing a state after ST12 (resin impregnation processing), in which a liquid thermosetting resin 53 containing a fluororesin is prepared,
This liquid thermosetting resin 53 is applied to the holes 5 of the anodic oxide film 50.
2 show the impregnated state. The hole diameter d1 of the holes 52 is 1
00 nm, a large amount of thermosetting resin 53
2 ... can be impregnated. Note that the thermosetting resin 53 is a resin that is in a liquid state without being diluted with a solvent.

FIG. 4B is a view showing a state after ST13 (resin curing processing), in which the liquid thermosetting resin 53 is heated by transmitting heat as indicated by an arrow from a coil 58 of an oven. The liquid thermosetting resin 53 is cured to form a thermosetting resin 54. Thus, the special anodic oxide film 50 shown in FIG. 4 is impregnated with the thermosetting resin 53.

According to the present invention, potassium fluoride contains Si
Has a dissolving effect and a film increasing effect. For this reason, since the film surface 50a of the anodic oxide film 50 can be flattened, the withstand pressure can be sufficiently increased. On the other hand, trisodium phosphate has the effect of increasing the diameter of the fine holes 52. Therefore, the fine holes 5 of the anodic oxide film 50
2 can be set to a large hole diameter d1. Therefore,
Since the anodic oxide film 50 can be impregnated with a large amount of the thermosetting resin 54, the sliding resistance can be reduced.

Further, the fluororesin contained in the thermosetting resin 54 is excellent in abrasion resistance and heat resistance, and the thermosetting resin 54 can be a resin excellent in abrasion resistance and heat resistance. Therefore, the thermosetting resin 54 is heated to, for example, 100 ° C.
Since it can be used at a high temperature of 300 ° C. or higher, it is suitable for a member used in a high temperature state such as a piston.

[0031]

Examples Examples and comparative examples according to the present invention are shown in Tables 1 and 2 below.
A description will be given based on FIG. Common conditions: Test material AC8C (JIS H5202 aluminum alloy casting) The components are shown in Table 1, and are castings containing about 10% Si.

[0032]

[Table 1]

[0033]

[Table 2]

Example: A pin hole of a pin boss of an aluminum alloy internal combustion engine piston was degreased and then mixed with a mixed electrolyte of 0.4 mol / l trisodium phosphate and 0.125 mol / l potassium fluoride. Electrolyte temperature 22 ℃, voltage 70V
For 30 minutes to form a special anodic oxide film in the pin holes. The fine pores of the special anodic oxide film have a large hole diameter d1 (see FIG. 8A) of 100 nm, and the surface maximum roughness Rmax of the anodic oxide film is as flat as 2 to 3 μm. Note that Rmax is the maximum height of the surface roughness defined in JIS B 0601.
max ".

Next, the formed anodic oxide film is
After immersion in a perfluorooctylethyl methacrylate (thermosetting resin) solution for 5 minutes under reduced pressure of g, the film was opened to the atmosphere and immersed in 98 ° C. hot water for 10 minutes. After removal from the warm water, the mixture was heated in an oven for 5 minutes to cure perfluorooctylethyl methacrylate. As a result, the surface pressure 30k
The coefficient of friction μ was reduced to 0.006 at gf / cm ² . The coefficient of friction μ will be described in detail with reference to the graph of FIG. The chemical formula of perfluorooctylethyl methacrylate is as follows.

[0036]

Embedded image

Comparative Example: After the pin holes of the pin boss portion of an aluminum alloy piston for an internal combustion engine made of aluminum alloy were degreased, they were electrolyzed with an electrolyte of 15% sulfuric acid at an electrolyte temperature of 0 ° C. and a voltage of 15 V for 20 minutes. An ordinary anodic oxide film was formed on the surface of the aluminum alloy piston. The fine pores of an ordinary anodic oxide film have a small hole diameter d2 (see FIG. 5 (b)) of 15 nm, and the maximum surface roughness Rmax of the anodic oxide film is 12-13.
μm and unevenness.

Next, the formed anodic oxide film was
After immersion in perfluorooctylethyl methacrylate solution for 5 minutes under reduced pressure of g, the vessel was opened to the atmosphere and immersed in 98 ° C warm water for 10 minutes. After removal from the warm water, the mixture was heated in an oven for 5 minutes to cure perfluorooctylethyl methacrylate. As a result, the friction coefficient μ was 0.07 at a surface pressure of 30 kgf / cm ² . This friction coefficient μ is larger than that of the example of 0.006. The coefficient of friction μ will be described in detail with reference to the graph of FIG.

FIG. 9 is a graph showing the friction coefficient of a special anodic oxide film of the piston for an aluminum alloy internal combustion engine (first embodiment) according to the present invention. Indicates a surface pressure kgf / cm ² . The solid line shows the graph of the example, and the broken line shows the graph of the comparative example. Keep embodiment, the μ friction coefficient 0.013 when the surface pressure 10 kgf / cm ^2, when the surface pressure 20 kgf / cm ² 0.00
8, 0.006 when the contact pressure is 30 kgf / cm ² , 4 contact pressure
0.008 at 0 kgf / cm ² , surface pressure 50 kgf /
It is 0.006 at cm ² . According to the embodiment, when the surface pressure is in the range of 10 to 50 kgf / cm ² , the friction coefficient μ is set to 0.1.
013 or less. Therefore, the sliding resistance can be sufficiently reduced.

On the other hand, in the comparative example, the friction coefficient μ was 0.06 when the surface pressure was 10 kgf / cm ² , and was 20 kgf / cm ^2.
When / cm ² 0.069, 0.069 when the surface pressure of 30kgf / cm ^2, 0.06 when the surface pressure of 40kgf / cm ²
2, 0.054 when the surface pressure is 50 kgf / cm ² .
According to the comparative example, when the surface pressure is in the range of 10 to 50 kgf / cm ² , the friction coefficient μ is 0.054 or more, which is larger than the friction coefficient μ0.013 of the example. Therefore, the sliding resistance cannot be sufficiently reduced.

Next, an aluminum alloy internal combustion engine piston 1
The operation of 0 will be described. FIGS. 10A and 10B are explanatory diagrams of the operation of the aluminum alloy internal combustion engine piston (first embodiment) according to the present invention. In the compression step (a),
The lifting force F1 of the connecting rod 42 acts on the center of the piston pin 40, and the center of the piston pin 40 is elastically deformed upward while both ends are supported. At this time, since the region E does not come into contact with the piston pin 40, when the piston pin 40 is elastically deformed, the elastic deformation of the piston pin 40 is released in the region E and the stress concentration on the pin holes 21 and 31 is reduced.

In addition, the anodic oxide film 5 is formed in the cylindrical holes 22 and 32.
The surface resistance is increased by flattening the anodic oxide film 50, and the sliding resistance is reduced by impregnating the fine holes of the flat anodic oxide film with a large amount of lubricant. As described above, the thickness t of the pin boss portions 20, 30 is reduced by reducing the stress concentration applied to the pin holes 21, 31 and increasing the surface pressure of the cylindrical holes 22, 32 and reducing the sliding resistance. The weight of the piston 10 is reduced.

In the expansion step (b), the combustion pressure F 2 of the air-fuel mixture acts on both ends of the piston pin 40. Since the connecting rod 42 is attached to the center of the piston pin 40, only the both ends of the piston pin 40 are elastically deformed downward. At this time, since the region E does not contact the piston pin 40 as described in (a), when the piston pin 40 is elastically deformed, the elastic deformation of the piston pin 40 is released in the region E and the pin holes 21 and 31 are released. The stress concentration is reduced.

In addition, anodized film 5 is formed in cylindrical holes 22 and 32.
The surface resistance is increased by flattening the anodic oxide film 50, and the sliding resistance is reduced by impregnating a large amount of lubricant into the fine pores of the flat anodic oxide film. As described above, the thickness t of the pin boss portions 20, 30 is reduced by reducing the stress concentration applied to the pin holes 21, 31 and increasing the surface pressure of the cylindrical holes 22, 32 and reducing the sliding resistance. Reduce the weight of the piston.

Next, a second embodiment and a third embodiment will be described. The same members as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted. FIG. 11 is a cross-sectional view of an aluminum alloy internal combustion engine piston (second embodiment) according to the present invention. The piston 60 for an aluminum alloy internal combustion engine is formed by reducing the thickness of the anodic oxide film 50 on the chamfered surface 63 of the pin hole 62 and by reducing the thickness of the anodic oxide film 50 on the cylindrical portion 64.
Thick anodic oxide film 50 and thick anodic oxide film 5
The conical holes 65 are formed in the anodic oxide film 50 by connecting 0 with a taper.

When the anodic oxide film 50 is formed in the pin hole 62, the conical hole 65 can be formed at the same time, so that the step of cutting the conical hole 65 with a tool can be omitted. The fine holes of the anodic oxide film 50 are impregnated with a lubricant (thermosetting resin) as in the first embodiment. As in the first embodiment, the conical hole 65 has an axial length L of 1 to 5 mm and a radial height H of 1 to 30 μm (0.001 to 0.03 mm). did. Thereby, the same effect as in the first embodiment can be obtained.

Next, the operation of the second embodiment will be described.
FIGS. 12 (a) and 12 (b) are illustrations of an anodic oxide film processing step of an aluminum alloy internal combustion engine piston (second embodiment) according to the present invention. In (a), the pin hole 62 of the pin boss 61 is degreased. Next, the insulating cylinder 68 is fitted into the cathode cylinder 67, and the cathode cylinder 67 is inserted into the pin hole 62. Thus, the insulating cylinder 68 is arranged in the region E1,
The cathode cylinder 67 is arranged in the area E2. In this state, the pin hole 62 is immersed in an electrolytic solution containing a mixture of phosphate and fluoride, and the pin boss 61 is connected to the anode.

A current flows between the pin boss 61 and the cathode cylinder 67. A large amount of current flows from the cathode cylinder 67 toward the region E2 of the pin hole 62 as indicated by the arrow. On the other hand, the flow of current to the region E1 is blocked by the insulating cylinder 68, and only the current that has avoided the insulating cylinder 68 flows toward the region E1 as shown by the arrow.

In FIG. 6B, the anodic oxide film 50 is thickened in the region E2 to form a cylindrical hole 64. On the other hand, area E
No. 1 shows that the anodic oxide film 50 is tapered and the anodic oxide film 5
0 forms a conical hole 65. For this reason, since it is not necessary to cut the conical hole 65 with a tool, the piston 60 can be manufactured without trouble.

FIG. 13 is a cross-sectional view of an aluminum alloy internal combustion engine piston (third embodiment) according to the present invention. The aluminum alloy internal combustion engine piston 70 changes the amount of Si particles 73 deposited on the surface of the pin hole 72,
The conical hole 74 is formed in the anodic oxide film 50 by adjusting the thickness of the anodic oxide film 50.

That is, since the Si particles 73 do not conduct an electric current, the anodic oxide film 50 becomes thinner when the amount of the Si particles 73... Is large, and becomes small when the amount of the Si particles 73. 50 becomes thicker. Using this, the thickness of the anodic oxide film 50 on the chamfered surface 75 of the pin hole 72 is reduced, the anodic oxide film 50 on the cylindrical portion 76 is made thicker, and the thin anodic oxide film 50 and the thick anodic oxide film 50 are tapered. To form a conical hole 74 in the anodic oxide film 50.

When the anodic oxide film 50 is formed in the pin hole 72, the conical hole 74 can be formed at the same time, so that the step of cutting the conical hole 74 with a tool can be omitted. The fine holes of the anodic oxide film 50 are impregnated with a lubricant (thermosetting resin) as in the first embodiment. As in the first embodiment, the conical hole 74 has an axial length L of 1 to 5 mm and a radial height H of 1 to 30 μm (0.001 to 0.03 mm). did. Thereby, the same effect as in the first embodiment can be obtained.

Here, a method of adjusting the deposition amount of the Si particles 73 will be described. It is known that when casting a cast made of an aluminum alloy, if the surface of the molten metal is rapidly cooled, Si particles 73 are unlikely to precipitate on the surface. Therefore, when casting the piston 70 for an internal combustion engine made of an aluminum alloy, for example, by cooling a cast pin for forming the pin hole 72, the Si particles 73 are formed in the region E2 of the pin hole 72. Precipitation on the surface can be suppressed.

Next, the operation of the third embodiment will be described.
FIGS. 14 (a) and 14 (b) are explanatory views of an anodic oxide film processing step of an aluminum alloy internal combustion engine piston (third embodiment) according to the present invention. In (a), first, S in the area E2
An aluminum alloy internal combustion engine piston 70 having a reduced amount of i-particles 73... is prepared. Next, after the pin hole 72 of the pin boss 71 is degreased, the cathode cylinder 78 is inserted into the pin hole 72. In this state, the pin hole 72 is immersed in an electrolytic solution in which phosphate and fluoride are mixed, and the pin boss 71 is connected to the anode.

An electric current flows between the pin boss 71 and the cathode cylinder 78. Pin hole 7 with small amount of Si particles 73...
A large amount of current flows as indicated by an arrow toward the second region E2.
On the other hand, a small amount of current flows as shown by the arrow toward the region E1 where the amount of the Si particles 73.

In FIG. 5B, the anodic oxide film 50 becomes thicker in the region E2, and a cylindrical hole 64 is formed. On the other hand, area E
In 1, the anodic oxide film 50 becomes thinner at the chamfered surface 75, becomes a tapered surface from the cylindrical hole 76 to the chamfered surface 75, and forms a conical hole 74 with the anodic oxide film 50. For this reason, the conical hole 7
Since it is not necessary to cut 4 with a tool, the piston 70 can be manufactured without any trouble.

In the above-described embodiment, an example in which trisodium phosphate is used as the phosphate is described. However, sodium phosphate or the like may be used. Further, although an example in which potassium fluoride is used as the fluoride has been described, sodium fluoride or the like may be used in addition to the above, and an alkali metal-based fluoride has the same effect.

Further, an example has been described in which a perfluorooctylethyl methacrylate liquid is used as the liquid thermosetting resin, but other thermosetting resins containing fluorine may be used. Although an example in which a thermosetting resin is used as the lubricant has been described, similar effects can be obtained by using another resin such as a photocurable resin. In addition, the photocurable resin corresponds to, for example, an ultraviolet curable resin or a visible light curable resin.

In the above embodiment, an example in which a conical hole is formed on the entire circumference of the pin hole has been described.
As shown in (b), the center of the piston pin is elastically deformed upward (to the side of the piston head), so that the entire region of the pin hole on the piston head side (for example, in a range of 120 °).
Even if a conical hole is formed only in the hole, the same effect as in the above embodiment can be obtained.

[0060]

According to the present invention, the following effects are exhibited by the above configuration. According to the first aspect, by forming a conical hole in which the piston pin does not come into contact with the pin hole, it is possible to secure a relief when the piston pin is elastically deformed. For this reason, it is possible to prevent the elastically deformed piston pin from being strongly pressed against the pin hole, and to alleviate the stress concentration applied to the pin hole.

As a result of forming the conical hole in the pin hole in order to reduce the stress concentration, the surface pressure of the cylindrical hole increases. That is, an anodic oxide film was formed in a cylindrical hole with an electrolytic solution in which a phosphate and a fluoride were mixed, and fine pores of the anodic oxide film were impregnated with a lubricant. Fluoride has the effect of flattening the anodic oxide film, and phosphate has the effect of increasing the diameter of the fine pores in the anodic oxide film. Therefore, the flat anodic oxide film can increase the surface pressure resistance of the cylindrical hole, and the sliding resistance of the cylindrical hole can be reduced by impregnating a large amount of lubricant into the fine holes of the flat anodic oxide film. it can. Thus, by reducing the stress concentration of the pin hole, and increasing the surface pressure of the cylindrical hole and reducing the sliding resistance, the thickness of the pin boss portion is reduced,
The weight of the piston can be reduced.

According to the second aspect, a conical hole can be formed by connecting a thin anodic oxide film having a cylindrical hole and a thick anodic oxide film with a taper. When the anodic oxide film is formed on the pin hole, a conical hole is formed at the same time, and the step of cutting the conical hole with a tool can be omitted. Therefore, the piston can be easily manufactured without trouble.

[Brief description of the drawings]

FIG. 1 is a perspective view of an aluminum alloy internal combustion engine piston according to the present invention (first embodiment).

FIG. 2 is a sectional view taken along line 2-2 of FIG.

FIG. 3 is an enlarged view of a part of FIG. 2;

FIG. 4 is an enlarged view of a part of FIG. 3;

FIG. 5 is a comparative example in which an ordinary anodic oxide film is formed in a pin hole of a piston for an internal combustion engine.

FIG. 6 is a flowchart illustrating a method for treating a special anodic oxide film of an aluminum alloy internal combustion engine piston (first embodiment) according to the present invention.

FIG. 7 is a first explanatory view of a special anodic oxide film treatment method for an aluminum alloy internal combustion engine piston (first embodiment) according to the present invention.

FIG. 8 is a second explanatory view of a special anodic oxide film treatment method for the aluminum alloy internal combustion engine piston (first embodiment) according to the present invention.

FIG. 9 is a graph showing a friction coefficient of a special anodic oxide film of an aluminum alloy internal combustion engine piston according to the present invention (first embodiment).

FIG. 10 is a diagram illustrating the operation of an aluminum alloy internal combustion engine piston according to the present invention (first embodiment).

FIG. 11 is a sectional view of an aluminum alloy internal combustion engine piston according to the present invention (second embodiment).

FIG. 12 is an explanatory view of an anodized film treatment step of an aluminum alloy internal combustion engine piston according to the present invention (second embodiment).

FIG. 13 is a cross-sectional view of an aluminum alloy internal combustion engine piston according to the present invention (third embodiment).

FIG. 14 is an explanatory view of an anodized film treatment step of an aluminum alloy internal combustion engine piston (third embodiment) according to the present invention.

FIG. 15 is a sectional view of a conventional piston for an internal combustion engine.

[Explanation of symbols]

10, 60, 70 ... piston for internal combustion engine made of aluminum alloy,
11: Center of piston, 21, 31, 62, 72: Pin hole, 22, 32, 64, 76: Cylindrical hole, 23, 33, 6
5, 74: conical hole, 40: piston pin, 42: connecting rod, 50: anodized film, 52: fine hole, 54: lubricant (thermosetting resin).

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02F 3/10 F02F 3/10 B F16J 1/02 F16J 1/02 (72) Inventor Ryotaro Takada Saitama 1-10-1 Shin-Sayama, Sayama-shi Honda Engineering Co., Ltd. (72) Inventor Yuji Marui 1-4-1 Chuo, Wako-shi, Saitama F-term in Honda R & D Co., Ltd. (Reference) 3J044 AA01 AA06 AA18 BA04 BB11 BB12 BB40 BC01 CA25 DA09

Claims (2)

[Claims] 1. An aluminum alloy internal combustion engine piston having a pair of pin holes into which piston pins are inserted, wherein each of the pin holes is a cylindrical hole that contacts a piston pin;
The piston pin has a conical hole whose diameter increases toward the center of the piston from the end of the cylindrical hole so as not to come into contact with the piston pin, and the conical hole and the cylindrical hole are anodic with an electrolyte mixed with phosphate and fluoride. An aluminum alloy piston for an internal combustion engine, characterized in that an oxide film is formed and fine holes in the anodized film are impregnated with a lubricant. 2. The aluminum alloy internal combustion engine according to claim 1, wherein the thickness of the anodic oxide film is reduced in the cylindrical hole, and the thin anodic oxide film and the thick anodic oxide film of the cylindrical hole are tapered. Engine piston.