JP2003013799A - Aluminum alloy-made piston for internal combustion engine and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aluminum alloy-made piston for internal combustion engine capable of uniformly holding an oil film all over a skirt part and capable of restraining surface pressure in contact with a cylinder. SOLUTION: The aluminum alloy-made piston 10 for the internal combustion engine is constituted by forming a streak 22 on an outer surface 21a of the skirt part 20, applying an anodic oxide film 50 on a surface of this streak 22 by using an electrolytic solution mixed with phosphate and fluoride and impregnating a lubricant 54 in fine holes 52 of this anodic oxide film 50. The aluminum alloy-made piston 10 for the internal combustion engine is constituted by forming a portion H1 corresponding to a top part 22a of the streak 22 into a smooth surface on the anodic oxide film 50.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piston for an internal combustion engine in which a piston made of an aluminum alloy is covered with an anodic oxide film, and a method for manufacturing the piston.

[0002]

2. Description of the Related Art A method of reducing sliding resistance of a piston is known in order to improve fuel efficiency and engine output of a vehicle. As an example of this piston, Japanese Patent Laid-Open No. 11-33
Japanese Patent No. 6895 “Piston and Method for Processing Piston” has been proposed. This technique reduces the sliding resistance of the piston by forming an anodized film on the skirt of the piston and forming a chemical conversion treatment film on the anodized film.

On the other hand, there is also known a method of forming a striation on a skirt portion of a piston in order to reduce sliding resistance, and the striation is used in combination with the technique disclosed in the above publication (that is,
The sliding resistance can be further reduced by coating the streaks with a film. Hereinafter, an example in which the streak is covered with a film will be described in detail with reference to the following drawings.

16 (a) and 16 (b) are cross-sectional views of a skirt portion of a conventional piston for an internal combustion engine, FIG. 16 (a) shows an example in which a skirt portion has a ridge, and FIG. 16 (b) shows a ridge. The following shows an example in which a film is covered on. In (a), striations 132 ... (... indicates a plurality) are formed on the skirt portion 131 of the piston 130. The recesses 133 ... of the scratches 132 ... are constantly secured at the depth A1,
By collecting oil in the recesses 133 ...
The oil film can be uniformly held on the entire 31. Therefore, the sliding resistance of the piston 130 can be reduced. In (b), the anodic oxide film 135 is formed on the skirt portion 131 having the streaks 132 ...
A chemical conversion coating 136 is formed on 35.

[0005]

However, the streak 132 ...
By forming the anodic oxide coating 135 and the chemical conversion coating 136 on, it is impossible to form the recesses 137 ... of the chemical conversion coating 136 at a constant pitch in conformity with the recesses 133 of the striations 132. In addition, since the recesses 137 ... of the chemical conversion coating 136 also have a non-uniform depth A2, the skirt portion 13
The oil film cannot be held uniformly over the entire area. Therefore, even if the coatings 135 and 136 are applied to the scratches 132 ...
The sliding resistance of the piston 130 cannot be greatly reduced.

Further, the top portion 138 of the chemical conversion coating 136
Since a and 138b (the other tops are not labeled) project unevenly, when the piston 130 reciprocates in the cylinder, the surface pressure when the top 138a protruding particularly high comes into contact with the cylinder. Get higher Therefore, it is considered that the sliding resistance becomes high.

Therefore, an object of the present invention is to provide an aluminum alloy piston for an internal combustion engine, which can hold an oil film uniformly over the entire area of the skirt, and can suppress the surface pressure at the time of contact with the cylinder, and the manufacture thereof. To provide a method.

[0008]

In order to achieve the above-mentioned object, the first aspect of the present invention is to form a streak on the outer surface of the skirt portion, and to mix the phosphate and the fluoride on the surface of the streak. A piston for an aluminum alloy internal combustion engine, which is coated with an anodic oxide film using the electrolyte solution and impregnated with fine holes in the anodic oxide film with a lubricant, and which corresponds to the top of the streak in the anodic oxide film. It is characterized by being subjected to a process of rounding while cutting.

By mixing phosphate and fluoride in the electrolytic solution, an anodic oxide film is formed flat. Thereby, the anodic oxide film can be formed so as to follow the shape of the streak, and the surface of the anodic oxide film can be made substantially the same shape as the streak. Therefore, the oil film can be uniformly held on the entire surface of the anodized film.

In addition, phosphate has the effect of increasing the pore size of the fine pores in the anodized film. Therefore, a large amount of lubricant can be impregnated in the fine holes, and the lubricant can be reliably fixed in the holes. Further, by performing a rounding treatment while cutting the anodic oxide film corresponding to the top of the streak, that portion can be made a smooth surface. Therefore, it is possible to suppress the surface pressure when the piston contacts the cylinder.

According to a second aspect of the present invention, there is provided a step of processing a streak on the outer surface of the piston skirt portion, and a step of coating the surface of the streak with an anodic oxide film by using an electrolyte mixed with phosphate and fluoride. A step of incorporating a lubricant into the fine pores of the anodic oxide film, and a step of lapping or abrasive grain fluidization processing for cutting and rounding a portion of the anodized film corresponding to the top of the streaks.

After the streaks were covered with the anodic oxide film, the anodic oxide film corresponding to the tops of the streaks was subjected to lapping treatment or abrasive grain flow processing so that the anodic oxide film was cut and rounded. For this reason, the anodic oxide film corresponding to the tops of the scratches can be finished into a smooth surface only by lapping or abrasive grain flow processing, and the surface pressure when the piston contacts the cylinder can be suppressed.

According to a third aspect of the present invention, a step of forming a streak on the outer surface of the piston skirt, a step of rounding while cutting the top of the streak, and a phosphate and a fluoride are mixed on the surface of the streak. The process of covering the anodized film with an electrolytic solution, the process of including a lubricant in the fine holes of this anodized film, and the lapping process or abrasive grain flow processing on the part of the anodized film corresponding to the rounded scratches. And the step of applying.

Before covering the striations with the anodic oxide coating, the tops of the striations may be cut and rounded to cover the striations with the anodized film rolled. Therefore, the anodized film can be finished into a smooth surface by only slightly polishing the anodized film, so that the time for performing the lapping process and the abrasive grain fluidizing process can be shortened.

According to a fourth aspect of the present invention, the lapping process is performed by using a soft lapping machine such as a buff lapping machine. A soft lapping machine can be polished by following the irregularities of the surface to be wrapped. Therefore, by performing the lapping process with a soft lapping machine, it is possible to appropriately cut and round the portion corresponding to the top of the striation.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION 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,
The piston head grooves 12 and 14 and the oil ring groove 15 are formed on the piston head 12, and the pair of skirt portions 20 and 25 are formed below the oil ring groove 15.
The ridges 22 are formed on the outer surfaces 21a of the skirt portions 0, 25 (the outer surface of the skirt portion 25 is not shown).
This is a member in which a pair of pin boss portions 35, 37 (see FIG. 2 for the pin boss portion 37) are formed between 0 and 25.

The skirt portions 20 and 25 are anodized film (special anodized film) 5 made of an electrolyte solution in which phosphate and fluoride are mixed on each outer surface 21a having the scratches 22 formed thereon.
0, 50 (the anodic oxide film 50 of the skirt portion 25 is shown in FIG. 2), respectively, to form a special anodic oxide film 50, 50.
Is a member in which the lubricant 54 (shown in FIG. 4) is impregnated. The area covered with the anodic oxide film 50 is indicated by "mesh".

FIG. 2 is a view taken in the direction of arrow 2 in FIG. 1, in which the shape of the aluminum alloy piston for an internal combustion engine will be described in detail. When viewed from the connecting rod (not shown) side, the piston 10 for an internal combustion engine made of an aluminum alloy comprises a pair of skirt portions 20 and 25 that face each other, and end portions of the pair of skirt portions 20 and 25 that face each other. (One end) 20a, 25
By connecting a with each other by the wall portion 30 and connecting opposite ends (other ends) 20b, 25b of the skirt portions 20, 25 with the wall portion 32, the wall portions 30, 32 and the skirt portion 2 are connected.
It is a member in which a substantially rectangular shape is formed with 0 and 25, and pin boss portions 35 and 37 are bulged in the centers of the wall portions 30 and 32.

In addition, in the piston 10 for an aluminum alloy internal combustion engine, the portion where the wall portions 30 and 32 intersect the skirt portions 20 and 25 (that is, one end 20 of the skirt portions 20 and 25).
a, 25a and the other ends 20b, 25b), the inner walls 40 to 43 of these portions are formed in an arc shape, and the wall thickness t1 of the skirt portions 20 and 25 is set to be thinner than the wall thickness t2 of the wall portions 30 and 32. .

Opposing ends 20 of the skirt portions 20, 25
By connecting a and 25a with the wall portion 30 and connecting the other ends 20b and 25b with the wall portion 32, the wall portions 30 and 32 and the skirt portions 20 and 25 form a substantially rectangular shape. Therefore, the width W of the skirt portions 20 and 25 is set to the width W1 of the pin boss portions 35 and 37.
Can be smaller. Therefore, the skirt portion 2
By narrowing the width of 0 and 25, the weight of the aluminum alloy piston 10 for the internal combustion engine can be reduced. Further, since the wall thickness t1 of the skirt portions 20 and 25 is set to be smaller than the wall thickness t2 of the wall portions 30 and 32, the weight of the aluminum alloy internal combustion engine piston 10 can be reduced.

On the other hand, the skirt portions 20 and 25 and the wall portion 3
By forming a substantially rectangular shape with 0 and 32, the skirt portion 2
The walls 0 and 25 can be reinforced by the walls 30 and 32. Therefore, the rigidity of the skirt portions 20 and 25 can be increased. In addition, one end 20a, 25a and the other end 20b of the skirt where the walls 30, 32 intersect the skirt 20, 25,
Since the inner walls 40 to 43 of 25b are formed in an arc shape, it is possible to prevent stress from being concentrated on the one ends 20a, 25a and the other ends 20b, 25b of the skirt portion. Therefore, the rigidity of the skirt portions 20 and 25 can be further increased.

The pair of skirt portions 20 and 25 form a ridge 22 (shown in FIG. 1) on the outer surface 21a shown by a mesh having a width W and a length L (shown in FIG. 1) to form a skirt. Part 20,
A special anodic oxide coating 50, 50 on each outer surface 21a of 25
And the fine pores of the special anodic oxide coatings 50, 50 are impregnated with a lubricant. The special anodic oxide film and the lubricant will be described in more detail with reference to FIG.

FIG. 3 is a view from the arrow 3 of FIG. 1, and the lower ends 23 and 28 of the skirt portions 20 and 25 (see also FIG. 1 for the lower end 28).
Shows a state in which is extended downward from the lower ends 36 and 38 of the pin boss portions 35 and 37. Lower ends 23,2 of the skirts 20,25
8 is extended downward from the lower ends 36 and 38 of the pin boss portions 35 and 37, so that the aluminum alloy internal combustion engine piston 10
While moving in the cylinder, the skirts 20, 2
By bringing 5 into contact with the cylinder, the posture of the piston 10 can be easily maintained in a normal state.

FIG. 4 is an enlarged cross-sectional view of the surface of the special anodic oxide coating of the aluminum alloy internal combustion engine piston according to the present invention. An example in which a thermosetting resin is used as the lubricant 54 will be described. The special anodic oxide film 50 has a film thickness t
3, the coating surface 21 is formed flat and the coating surface 21 is provided with fine holes 52 ... (... indicates a plurality of holes. The same applies hereinafter). The holes 52 ... Are holes having a relatively large hole diameter d1. Therefore, the holes 52 ... Can be impregnated with a sufficient amount of the lubricant (thermosetting resin) 54, and the impregnated thermosetting resin 54 can be reliably fixed in the holes 52. it can.

As described above, by fixing the thermosetting resin 54 to the fine holes 52 ... Of the anodic oxide film 50, the wear resistance of the anodic oxide film 50 is enhanced and the lubricant 54 is also added.
The sliding resistance can be reduced with. In addition, the special anodic oxide coating 50 can further reduce the sliding resistance by making the coating surface 21 flat.

FIG. 5 is a sectional view taken along line 5-5 of FIG. The special anodic oxide film 50 can be formed flat by dissolving Si by mixing phosphate and fluoride in the electrolytic solution. The anodic oxide film 50 is now applied to the skirt 2
It is possible to form the surface of the anodic oxide film 50 to have substantially the same shape as that of the scratches 22 ...

Further, the anodic oxide film 50 is provided with streaks 22 ...
The oil film can be uniformly held over the entire surface of the anodized film 50 by forming the oil film so as to follow the shape of the above. Also,
As described with reference to FIG. 4, by enlarging the diameter of the fine holes of the anodized film, a large amount of the lubricant 54 is added to the fine holes 52.
Can be impregnated and the lubricant 54 can be reliably fixed in the hole 52.

In addition, the special anodic oxide coating 50 is formed by cutting and rounding the anodic oxide coating on the flat portion 50a corresponding to the top portion 22a of the streak 22 (particularly the corner portions 50b, 5).
0b is rounded) so that the flat portion 50a
Also, the portion H1 of the corner portions 50b, 50b (that is, the portion corresponding to the top portion 22a of the streak 22) can be a smooth surface.

Therefore, the surface pressure when the piston 10 contacts a cylinder (not shown) can be suppressed. In this way, the oil film is uniformly held on the entire surface of the anodized film 50, the lubricant 54 can be firmly fixed, and the surface pressure can be suppressed. Therefore, the piston 10 can be slid smoothly. .

Hereinafter, a method for forming an ordinary anodic oxide film will be described as a comparative example with reference to FIG. FIGS. 6A to 6C are explanatory views showing a comparative example in which a normal anodic oxide film is formed on the skirt portion of a piston for an internal combustion engine. (A) shows an ordinary anodic oxide film formed with a sulfuric acid electrolyte. Si particles 111 ... Are distributed in the skirt portion 100 of the piston for an internal combustion engine made of an aluminum alloy as a base material, of which Si near the surface is
.. have a bad influence on the anodic oxide coating 113, so that the anodic oxide coating 113 is uneven as a whole.

(B) is an enlarged view of (a), in which the anodic oxide film could not be formed on the portions of the Si particles 115 that happened to appear on the surface, resulting in a large depression D1 and Si very close to the surface. Although the anodic oxide film 117 could be formed on the portion of the grain 116, the film thickness was smaller than that of the surrounding anodic oxide film 113, and a depression D2 was formed. That is, S
Even if the aluminum alloy piston 100 containing i is anodized with a sulfuric acid electrolyte, a flat anodized film 113 is formed.
I found that I could not get. Also, with sulfuric acid electrolyte,
It was found that when the diameter of the fine holes 118 ... Is d2, 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 118 ... And the impregnated liquid thermosetting resin is heated to be changed into the cured resin 119. . Since the resin has a small frictional resistance, the anodic oxide coating 113, 117
By impregnating the cured resin 119 ... With, the sliding resistance when the Si-based aluminum alloy piston reciprocates in the cylinder at a high speed becomes relatively small.

However, as shown in (b), the depressions D1 and D2 are generated in the anodized film 113, and the anodized film 1 is formed.
13 is difficult to generate flat, and the hole diameter d2 of the fine holes 118 ...
Therefore, the resin 119 cannot be sufficiently contained in the anodized film 113. Therefore, the anodized film 11
Even if 3 is impregnated with resin 119, the frictional resistance cannot be reduced to a desired value.

The method for forming the special anodic oxide film shown in the enlarged cross-sectional view of FIG. 4, that is, the method for manufacturing the aluminum alloy piston for the internal combustion engine will be described below. FIG. 7 shows an aluminum alloy internal combustion engine piston according to the present invention (first embodiment).
3 is a flow chart for explaining the special anodic oxide film treatment method, and shows a method for manufacturing an aluminum alloy piston for an internal combustion engine. In the figure, STXX indicates a step number. ST10: A streak is formed on the outer surface of the skirt portion of the aluminum alloy internal combustion engine piston (that is, the AC8C aluminum alloy piston as the Si-based aluminum alloy).

ST11: Degrease the outer surface of the skirt portion having the striations. ST12: 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 the outer surface of the skirt. Fine pores are generated on the surface of this anodized film. ST13: A liquid thermosetting resin (fluorine-based resin) containing a fluororesin is prepared, and the liquid thermosetting resin is impregnated into the fine pores of the anodized film.

ST14: The liquid thermosetting resin impregnated in the fine pores is heated to be cured. This completes the anodic oxidation treatment of the aluminum alloy piston according to the present invention. ST15: Lapping treatment or abrasive grain fluidization processing is applied to the portion corresponding to the streaks of the anodizing treatment, so that the portion is rounded while being cut. Hereinafter, S of the method of anodizing the Si-based aluminum alloy
T10 to ST15 will be described in detail with reference to FIGS.

FIG. 8 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, showing ST10. A striation 22 is formed on an outer surface 21a of a skirt portion 20 of an aluminum alloy internal combustion engine piston (that is, an AC8C aluminum alloy piston as a Si-based aluminum alloy).

9 (a) and 9 (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. In addition, in order to facilitate understanding, the description will be given with the outer surface of the skirt portion 20 arranged laterally. (A) is a figure which shows the state after ST11 (degreasing), and has shown the state which degreased the outer surface 21a of the skirt part 20 of the piston for aluminum alloy internal combustion engines. In the vicinity of the outer surface 21a of the skirt portion 20, Si particles 55, 56, 57 are dispersed in aluminum.

(B) is a diagram showing a state after ST12 (special anodic oxide film treatment), which was electrolyzed in a mixed aqueous solution of trisodium phosphate and potassium fluoride to form an anodic oxide film 50. Indicates the status. Due to the corrosive action of trisodium phosphate, the outer surface 21a (shown in (a)) of the skirt portion 20 is dissolved and the Si grains 55, 56, 57 are exposed. The exposed Si particles 55, 56, 57 are dissolved and become smaller by the action of potassium fluoride.

Therefore, the outer surface 21a of the skirt portion 20 is
Despite the presence of Si grains 55, 56, 57, the anodic oxide film 50 grows well. As a result, the film surfaces 21 of the anodic oxide film 50 are aligned, so that the surface roughness becomes small,
The film thickness t3 becomes almost constant. Also, phosphoric acid 3
Since it contains sodium, the pore diameter d1 of the fine pores 52 ...
It is sufficiently large as 0 nm.

FIGS. 10 (a) and 10 (b) are third explanatory views of a special anodic oxide film treatment method for an aluminum alloy internal combustion engine piston (first embodiment) according to the present invention. (A) is
It is a figure which shows the state after ST13 (resin impregnation process), The liquid thermosetting resin 53 containing a fluororesin was prepared,
This liquid thermosetting resin 53 is applied to the holes 5 of the anodized film 50.
2 shows the impregnated state. The hole diameter d1 of the holes 52 ... Is 1
Since it is as large as 00 nm, a large amount of thermosetting resin 53 is formed in the holes 5.
2 ... Can be impregnated into the inside. The thermosetting resin 53 is a resin that is in a liquid state without being diluted with a solvent.

(B) is a diagram showing a state after ST14 (resin curing treatment), showing a state of heating the liquid thermosetting resin 53 by transmitting heat from the coil 58 of the oven as shown by an arrow. The liquid thermosetting resin 53 cures to become a thermosetting resin (lubricant) 54. As a result, the special anodic oxide coating 50 shown in FIG. 4 is impregnated with the thermosetting resin 54.

FIGS. 11 (a) and 11 (b) are fourth explanatory views of a special anodic oxide film treatment method for an aluminum alloy internal combustion engine piston (first embodiment) according to the present invention. (A) is
The state where the anodic oxide film 50 is covered on the scratches 22 of the skirt portion 20 is shown. Since the film surfaces 21 of the anodic oxide film 50 are uniform, the surface roughness is small and the film thickness t3 is substantially constant.

(B) is a diagram showing a state after ST15, which is the same diagram as FIG. In the anodized film 50,
The flat portion 50a corresponding to the top portion 22a of the streak 22 is cut and rounded (in particular, the corner portions 50b and 50b are rounded).
The flat portion 50a is made into a smooth surface by performing lapping treatment or abrasive grain flow processing. Therefore, the surface pressure when the piston 10 contacts the cylinder can be suppressed.

Here, the lapping process is carried out by using a soft lapping machine such as a buff wrap (buff wrap as an example). A soft lapping machine such as a raised buff flap can be polished by following the irregularities of the surface to be wrapped to some extent. Therefore, by performing the lapping process with the soft lapping machine, the portion corresponding to the top of the striation can be cut and rounded. It should be noted that similar effects can be obtained by adopting abrasive grain fluidization processing instead of the raised buff flap. Abrasive grain flow processing is a semi-solid viscoelastic material prepared by kneading an abrasive, and mechanically pushing this material into the processing area to move it under pressure to move the desired surface with this material. The method of processing.

According to the present invention, trisodium phosphate has the effect of increasing the pore size of the fine pores 52 ... Therefore, the fine holes 52 ... Of the anodized film 50 can have a large hole diameter d1. Therefore, the anodized film 50
It is possible to impregnate a large amount of the thermosetting resin 54, and it is possible to securely fix the impregnated thermosetting resin 54 in the holes 52. As a result, sliding resistance can be reduced and durability can be improved. On the other hand, potassium fluoride has the function of dissolving Si and the function of increasing the film thickness.
Therefore, the coating surface 21 of the anodic oxide coating 50 can be made flat, so that the sliding resistance can be further reduced.

Further, the fluororesin contained in the thermosetting resin 54 has excellent wear resistance and heat resistance, and the thermosetting resin 54 can be made a resin having excellent wear resistance and heat resistance. Therefore, the thermosetting resin 54, for example, 100 ℃ ~
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.

In addition, after covering the scratches 22 with the anodic oxide film 50, a flat portion 50 corresponding to the top 22a of the scratches 22 is formed.
The flat portion 50a and the corner portion 50a are formed by lapping or abrasive grain fluidizing processing on the a and the corner portion 50b, 50b.
b and 50b were cut and rounded. Therefore, the scratches 22 can be formed only by the lapping process or the abrasive grain fluidizing process.
Finish the part corresponding to the top 22a of the to a smooth surface,
It is possible to suppress the surface pressure when the piston 10 contacts the cylinder.

As an example, assuming that the thickness of the anodic oxide coating 50 is 6 μm, the polishing amount of the anodic oxide coating is 1 to 5 μm.
It is preferable to suppress This is because if the polishing amount is less than 1 μm, it becomes difficult to suppress the surface pressure, and if the polishing amount exceeds 5 μm, the thickness of the anodic oxide film 50 becomes too thin.

[0050]

[Examples] Tables 1 and 2 show examples and comparative examples according to the present invention.
And it demonstrates based on FIG. Common conditions: Specimen material AC8C (JIS H 5202 aluminum alloy casting) The composition is shown in Table 1, but is a casting containing about 10% Si.

[0051]

[Table 1]

[0052]

[Table 2]

Example: After degreasing the outer surface of the skirt of a piston for an internal combustion engine made of an aluminum alloy, with a mixed electrolyte of 0.4 mol / l trisodium phosphate and 0.125 mol / l potassium fluoride, Electrolyte temperature 22 ℃, voltage 70V
As a result, electrolysis was performed for 30 minutes to form a special anodic oxide film on the outer surface of the skirt. The fine pores of the special anodic oxide film have a large pore diameter d1 (see FIG. 10 (a)) of 100 nm, and the maximum surface roughness Rmax of the anodic oxide film is 2-3.
It is as flat as μm. In addition, Rmax is JIS B 06
Although it is the maximum height of the surface roughness defined by 01, "maximum surface roughness Rmax" is shown for convenience.

Next, the produced anodic oxide film is coated with 10 mmH.
After being dipped in a perfluorooctylethylmethacrylate (thermosetting resin) liquid for 5 minutes under a reduced pressure of g, the atmosphere was opened to dipping in hot water at 98 ° C. for 10 minutes. After taking out from warm water, it was heated in an oven for 5 minutes to cure the perfluorooctylethylmethacrylate.

Then, a portion corresponding to the top of the streak was subjected to lapping treatment or abrasive grain flow processing so that the portion was cut and rounded. As a result, the portion corresponding to the top of the streak can be finished into a smooth surface. This piston was incorporated into the engine to perform break-in operation, and the engine output characteristics at that time were measured. As a result, it was found that the desired engine output characteristics could be obtained from the beginning of the break-in operation. The reason is that the surface pressure when the piston contacts the cylinder can be suppressed and the initial sliding resistance can be reduced by finishing the portion corresponding to the top of the striations into a smooth surface. The chemical formula of perfluorooctylethylmethacrylate is as follows.

[0056]

[Chemical 1]

Comparative Example: Similar to the example, after degreasing the outer surface of the skirt portion of the aluminum alloy internal combustion engine piston,
A mixed electrolyte solution of 0.4 mol / l trisodium phosphate and 0.125 mol / l potassium fluoride was used and the electrolyte temperature was adjusted to 22
Electrolysis was carried out for 30 minutes at a voltage of 70 V at 70 ° C. to form a special anodic oxide film on the outer surface of the skirt. The fine pores of the special anodic oxide coating have a large pore diameter d1 (see FIG. 10 (a)) of 100 nm, and the maximum surface roughness Rmax of the anodic oxide coating is as flat as 2-3 μm. Note that Rmax
Is the maximum height of the surface roughness defined by JIS B 0601, but for convenience, "surface maximum roughness Rmax" is shown.

Next, the produced anodic oxide film is treated with 10 mmH.
After being dipped in a perfluorooctylethylmethacrylate (thermosetting resin) liquid for 5 minutes under a reduced pressure of g, the atmosphere was opened to dipping in hot water at 98 ° C. for 10 minutes. After taking out from warm water, it was heated in an oven for 5 minutes to cure the perfluorooctylethylmethacrylate.

This piston was incorporated into an engine to perform a break-in operation, and the engine output characteristics at that time were measured. As a result, it has been found that it is necessary to carry out the break-in operation for a relatively long time before the desired engine output characteristic is obtained. The reason is that in the anodized film, there is a portion corresponding to the top of the streak as the top,
This is because the surface pressure when the piston comes into contact with the cylinder becomes high and the initial sliding resistance becomes high.

12 (a) to 12 (c) are sectional views for explaining a special anodic oxide film of the aluminum alloy internal combustion engine piston according to the present invention, and FIGS. 12 (a) to 12 (b) are comparisons of Table 1. Example,
(C) shows an example of Table 1. (A) shows a scratch 1 on the skirt 121 of the piston 120 for an internal combustion engine made of an aluminum alloy.
22 shows a state in which 22 is formed, a special anodic oxide film 50 is formed on the scratches 122, and the fine holes of the anodic oxide film 50 are impregnated with a lubricant.

The special anodic oxide film 50 can be covered with the anodic oxide film 50 with a uniform thickness (t3) along the scratches 122.
A portion 50c corresponding to the top portion 122a of the ridge 122 protrudes similarly to the top portion 122a of the streak 122. Therefore, the piston 12
When 0 reciprocates in the cylinder 59 as shown by the arrow,
A large surface pressure is applied to the top portion 50c of the anodized film 50.

In (b), the top 50c of the anodic oxide film 50 and the top 122a (shown in (a)) of the scratch 122 are worn over the portion H2. As a result, the part 122b of the streak 122 is exposed, and this part 122b cannot be protected by the anodized film 50.

In (c), a striation 22 is formed on the skirt portion 20 of the piston 10 for an internal combustion engine made of an aluminum alloy, a special anodic oxide film 50 is formed on the striation 22, and fine holes in the anodic oxide film 50 are formed. Was impregnated with lubricant. In this state, the special anodic oxide film 50 can be covered with a uniform thickness (t3) along the streak 22. As in the comparative example, the anodic oxide film 50 has a streak. Part 50c corresponding to the top 22a of 22 (see (a))
But protrudes in the same manner as the top portion 22a of the streak 22. Next, the portion 50c of the anodic oxide film 50 is subjected to lapping or abrasive grain flow so that the portion 50c is cut and rounded to make the portion H1 flat and corner portions 50a and corner portions 50a.
It was formed on a smooth surface composed of b and 50b.

Therefore, when the piston 10 reciprocates in the cylinder 59 as shown by the arrow, the smooth surface of the anodized film 50 (that is, the flat portion 50a and the corner portion 50).
It is possible to prevent a large surface pressure from being applied to b, 50b). Therefore, the sliding resistance of the piston can be reduced and the piston can be smoothly moved.

Next, the second to fourth embodiments will be described with reference to FIGS.
It will be described based on 5. The same members as those in the first embodiment are designated by the same reference numerals and the description thereof will be omitted. FIG. 13 is a side view of an aluminum alloy internal combustion engine piston (second embodiment) according to the present invention. In the piston 60 for an internal combustion engine made of an aluminum alloy, the lower ends 63 of a pair of skirts 62 (the skirts on the inner side are not shown) are moved upward from the lower end 36 of the pin boss portion 35 and the lower end 38 of the pin boss portion 37 by a δ dimension. It is a thing. Therefore, the pair of skirts 62 are
It can be made smaller than the skirt portions 20 and 25 of the first embodiment. Therefore, the aluminum alloy internal combustion engine piston 60 can be made lighter than the aluminum alloy internal combustion engine piston 10.

FIG. 14 is a side view of an aluminum alloy internal combustion engine piston (third embodiment) according to the present invention. In the piston 70 for an internal combustion engine made of an aluminum alloy, the skirt portion 72 has a substantially inverted trapezoidal shape, that is, the skirt width gradually increases from W3 to W4 from the lower end 73 toward the piston head 74. By forming the skirt portion 72 into a substantially inverted trapezoidal shape, the rigidity of the skirt portion 72 can be increased.

FIGS. 15 (a) to 15 (d) are sectional views of an aluminum alloy internal combustion engine piston (fourth embodiment) according to the present invention. In (a), a striation 22 is formed in the skirt portion 20 of the aluminum alloy internal combustion engine piston 80.
In (b), the top 22a (shown in (a)) of the streak 22 is rounded while being cut by lapping or abrasive grain flow processing, so that the top 22a of the streak 22 is flattened 22b and corners 22c, A smooth surface is formed over the portion H3 of 22c.

Here, as an example, if the depth A3 (shown in (a)) from the top 22a to the valley of the scratch is 20 μm, the polishing amount needs to be suppressed to 5 to 15 μm, especially 9 μm.
It is preferable to suppress it to μm. When the polishing amount is less than 5 μm, it is difficult to reduce the surface pressure, and when the polishing amount exceeds 15 μm, it cannot serve as a scratch.

In (c), a special anodic oxide film 50 is formed on the scratches 22, and the fine holes of the anodic oxide film 50 are impregnated with a lubricant. Since the special anodic oxide coating 50 has the same coating surface 21, the surface roughness is small and the film thickness t3 is substantially constant. Therefore, the flat portion 51a and the corner portions 51b and 51b of the anodic oxide film 50 can be formed to be smooth to some extent along the flat portion 22b of the streak 22 and the portion H3 of the corner portions 22c and 22c.

In (d), the flat portion 51a and the corner portions 51b and 51b of the anodic oxide coating 50 are subjected to lapping treatment or flow of grindstones, so that the flat portion 51a and the corner portions 51b and 51b of the anodic oxide coating 50 have a portion H4. (That is, the anodic oxide film 50 corresponding to the portion H3 of the rounded streak
Can be formed into a sufficiently smooth surface.
Therefore, it is possible to suppress the surface pressure when the piston 10 contacts the cylinder 59.

As an example, if the thickness of the anodic oxide film 50 is 6 μm, the polishing amount of the anodic oxide film is 1 to 5 μm.
It is necessary to suppress the thickness to 1 μm, and it is particularly preferable to suppress the thickness to 1 μm. If the polishing amount is less than 1 μm, it becomes difficult to round the corners, and if the polishing amount exceeds 5 μm, the anodized film 5
The film thickness of 0 becomes too thin.

Here, the lapping process is carried out by using a soft lapping machine such as a buff wrap (buff wrap as an example). A soft lapping machine can be polished by following the irregularities of the surface to be wrapped to some extent. Therefore, by performing a lapping process with a soft lapping machine, the portion corresponding to the top of the striation can be cut and rounded.

By using the raised buff flap, it is possible to grind not only the portion corresponding to the top of the striation but also the portion corresponding to the trough of the striation. Therefore, the corner portion of the flat portion can be polished so as to have roundness. It should be noted that similar effects can be obtained by adopting abrasive grain fluidization processing instead of the raised buff flap. Abrasive grain flow processing is a semi-solid viscoelastic material prepared by kneading an abrasive, and mechanically pushing this material into the processing area to move it under pressure to move the desired surface with this material. The method of processing.

According to the fourth embodiment, the top portion 22a of the scratch 22 is cut and rounded before the scratch 22 is covered with the anodic oxide film 50, whereby the rounded portions 22a, 22b, 2 are formed.
It is possible to cover the 2b with the anodized film 50 in a rolled state. Therefore, even if the anodic oxide coating 50 is slightly polished, the flat portion 51a and the corner portion 5 of the anodic oxide coating 50 can be formed.
Since the surfaces 1b and 51b can be finished to have a smooth surface, the time required for the lapping process or the abrasive grain fluidizing process can be shortened. Therefore, a piston that can obtain a desired engine output characteristic in a short run-in operation can be manufactured relatively easily.

In the above embodiment, the example in which trisodium phosphate is used as the phosphate is shown, but sodium phosphate or the like may be used instead. Although an example using potassium fluoride as the fluoride is shown, sodium fluoride may be used in addition to the above, and alkali metal fluorides have the same action and effect.

Further, the example in which the perfluorooctylethylmethacrylate liquid is used as the liquid thermosetting resin has been described, but other thermosetting resins containing fluorine may be used. Further, although the example in which the thermosetting resin is used as the lubricant has been described, the same effect can be obtained by using another resin such as a photocurable resin. The photocurable resin is, for example, an ultraviolet curable resin or a visible light curable resin. Furthermore, in the above-described embodiment, an example in which the concave portion of the striation 22 is formed in a curved shape has been described, but the concave portion of the striation may be formed in a substantially trapezoidal shape, and the shape of the concave portion is arbitrary.

[0077]

The present invention has the following effects due to the above configuration. A first aspect of the present invention forms a flat anodic oxide film by mixing phosphate and fluoride in the electrolytic solution. Thereby, the anodic oxide film can be formed so as to follow the shape of the streak, and the surface of the anodic oxide film can be made substantially the same shape as the streak. Therefore, the oil film can be uniformly held on the entire surface of the anodized film. In addition, the phosphate has the effect of increasing the pore size of the fine pores in the anodized film.
Therefore, a large amount of lubricant can be impregnated in the fine holes, and the lubricant can be reliably fixed in the holes.

Furthermore, by performing a process of cutting and rolling the anodic oxide film corresponding to the top of the streaks, that part can be made a smooth surface. Therefore, it is possible to suppress the surface pressure when the piston contacts the cylinder. In this way, the oil film can be held uniformly, the lubricant can be reliably fixed, and the surface pressure can be suppressed, so that the desired engine output characteristics can be obtained in a short run-in operation.

According to a second aspect of the present invention, after the streaks are covered with an anodic oxide film, the anodic oxide film corresponding to the top of the streaks is subjected to lapping treatment or abrasive grain fluidization processing, thereby cutting and rolling the anodic oxide film. I did it. For this reason, the anodic oxide film corresponding to the tops of the scratches can be finished into a smooth surface only by lapping or abrasive grain flow processing, and the surface pressure when the piston contacts the cylinder can be suppressed. Therefore, a piston that can obtain a desired engine output characteristic in a short run-in operation can be manufactured relatively easily.

According to the third aspect of the present invention, the anodic oxide film can be covered in a rolled state by cutting and rolling the top of the ridge before covering the ridge with the anodized film. Therefore, the anodized film can be finished into a smooth surface by only slightly polishing the anodized film, so that the time for performing the lapping process and the abrasive grain fluidizing process can be shortened. Therefore, a piston that can obtain a desired engine output characteristic in a short run-in operation can be manufactured relatively easily.

According to the present invention, the soft lapping machine can be polished by following the irregularities of the surface to be lapped. Therefore, by performing the lapping process with a soft lapping machine, it is possible to appropriately cut and round the portion corresponding to the top of the striation. Therefore, by using a soft lapping machine, it is possible to relatively easily form a smooth surface at the portion corresponding to the top of the striation.

[Brief description of drawings]

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

FIG. 2 is a view on arrow 2 of FIG.

FIG. 3 is a view taken in the direction of arrow 3 in FIG.

FIG. 4 is an enlarged cross-sectional view of the surface of a special anodic oxide coating on the aluminum alloy internal combustion engine piston according to the present invention.

5 is a sectional view taken along line 5-5 of FIG.

FIG. 6 is an explanatory view showing a comparative example in which a normal anodic oxide film is formed on a skirt portion of a piston for an internal combustion engine.

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

FIG. 9 is a second special anodic oxide film treatment method for an aluminum alloy internal combustion engine piston (first embodiment) according to the present invention.
Illustration

FIG. 10 is a third 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. 11 is a fourth explanatory diagram of a special anodic oxide film treatment method for an aluminum alloy internal combustion engine piston (first embodiment) according to the present invention.

FIG. 12 is a cross-sectional view for explaining a special anodic oxide film of the aluminum alloy internal combustion engine piston according to the present invention.

FIG. 13 is a side view of an aluminum alloy internal combustion engine piston according to the present invention (second embodiment).

FIG. 14 is a side view of an aluminum alloy internal combustion engine piston (third embodiment) according to the present invention.

FIG. 15 is a sectional view of an aluminum alloy internal combustion engine piston (fourth embodiment) according to the present invention.

FIG. 16 is a sectional view of a skirt portion of a conventional piston for an internal combustion engine.

[Explanation of symbols]

10, 60, 70, 80 ... Aluminum alloy internal combustion engine piston, 20, 25, 62, 72 ... Skirt portion, 21a ...
Outer surface of skirt part, 22 ... streak, 22a ... Streak top part, 22b ... Flat part, 22c ... Corner part, 50 ... Anodized film, 50a ... Flat part, 50b ... Corner part, 51a ...
Flat parts, 51b ... Corner parts, 52 ... Fine holes, 54 ... Lubricant, H1, H4 ... Parts, H3 ... Rounded streak parts.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F02F 3/10 F02F 3/10 B F16J 1/00 F16J 1/00 1/01 1/01 1/08 1 / 08 (72) Inventor Koji Kobayashi 1-10-1 Shin-Sayama, Sayama City, Saitama Prefecture F-term in Honda Engineering Co., Ltd. (reference) 3J044 AA12 AA18 BA04 BB05 BB12 BB39 BC04 CA14 DA09 EA02

Claims (4)

[Claims] 1. A streak is formed on the outer surface of a skirt, and an anodic oxide film is coated on the surface of the streak with an electrolyte solution containing a mixture of phosphate and fluoride. An aluminum alloy piston for an internal combustion engine, the hole of which is impregnated with a lubricant, characterized in that the anodized film is subjected to a rounding treatment while cutting the portion corresponding to the top of the striation. Alloy pistons for internal combustion engines. 2. A step of forming a streak on the outer surface of the piston skirt portion, a step of covering the surface of the streak with an anodic oxide film by using an electrolyte mixed with phosphate and fluoride, Made of an aluminum alloy, which comprises a step of containing a lubricant in the fine holes of the acid film, and a step of performing lapping or abrasive fluidizing processing for rounding while cutting the portion corresponding to the top of the streaks in the anodized film. Manufacturing method of piston for internal combustion engine. 3. A step of processing a streak on the outer surface of the piston skirt, a step of rounding while cutting the top of the streak, and an electrolytic solution in which phosphate and fluoride are mixed on the surface of the streak. A step of applying an anodic oxide film by using it, a step of including a lubricant in the fine holes of this anodic acid film, and a lapping process or abrasive grain flow processing on the part of the anodic oxide film corresponding to the rounded streaks A process for producing a piston for an internal combustion engine made of an aluminum alloy, which comprises: 4. The method for manufacturing an aluminum alloy piston for an internal combustion engine according to claim 2 or 3, wherein the lapping process is performed with a soft lapping machine such as a buff lapping machine.