JP2023086759A - Manufacturing method of piston for internal combustion engine - Google Patents

Abstract

To provide a piston for an internal combustion engine capable of further reducing a blow-by gas flow rate and the number of particles of discharged particles, allowing surface roughness of an anodic oxide film to the blow-by gas flow rate to be evaluated accurately, and capable of stably forming the smooth anodic oxide film.SOLUTION: An anodic oxidation treatment device 60 and a piston 10 for an internal combustion engine are brought into close contact with each other through a seal ring 62 disposed in each of a top land 12a and a second land 12b. While sending treatment liquid 63 inside a top ring groove 13 of the piston and to the seal ring 62 of the top land and the second land, a cathode electrode 61 on an anodic oxidation treatment device side is energized with the piston 10 as an anode so that an anodic oxide film 20B is formed over an entire inner surface of the top ring groove and an outer peripheral surface of the piston, which is an outer peripheral surface of a region from the top ring groove to a piston crown surface side, and an outer peripheral surface of a region from the top ring groove to a second ring groove side.SELECTED DRAWING: Figure 8

Description

TECHNICAL FIELD The present invention relates to a method of manufacturing an internal combustion engine piston, and more particularly to a method of manufacturing an internal combustion engine piston having an anodized film formed on the inner surface of a top ring groove.

2. Description of the Related Art A piston ring for an internal combustion engine such as an automobile engine is provided with a piston ring on its outer peripheral surface in order to keep the combustion chamber airtight and to prevent oil from entering the combustion chamber. The piston ring is fitted into a ring groove formed on the outer peripheral surface of the piston. Of the ring grooves, the top ring groove, which is closest to the crown of the piston, is prone to wear and adhesion with the top ring, so the wear resistance and aluminum adhesion resistance of the top ring groove have been improved. Anodizing is applied to the top ring grooves in order to achieve this.

However, when an anodized film is formed in the top ring groove of an aluminum alloy piston that contains silicon (Si), which is a component that contributes to wear resistance and aluminum adhesion resistance, Si contained in the aluminum alloy causes the formation of an anodized film. As a result, an uneven surface is formed on the surface of the anodized film. For this reason, when the engine is running, many small gaps are generated between the top ring groove and the top ring, resulting in problems such as an increase in the flow rate of blow-by gas and a decrease in oil sealing performance. there were.

In Patent Document 1, in a piston body made of an Al—Si alloy-based cast material, the grain size of primary crystal Si and eutectic Si crystallized in the cast material is set to 10 μm or less, thereby improving the piston body. When the top ring groove provided on the outer periphery is anodized, the surface roughness Ra of this anodized film can be smoothed to 1.5 μm or less, and thus the blow-by gas flow rate during engine operation can be reduced. It is stated that it can be reduced.

JP-A-9-159022

However, in the examples described in Patent Document 1, the surface roughness Ra of any of the anodized films remained within the range of 1.1 to 1.5 μm, and the predetermined In the method of making the piston body from an aluminum alloy material and applying an anodizing treatment to it, the lower limit of the surface roughness Ra of the anodized film is 1.1 μm, and it is difficult to further reduce the blow-by gas flow rate. There's a problem.

In addition, the inventors of the present application have found that the surface roughness of the anodized film formed on the top ring groove of the piston, Ra, which is an index of surface roughness measured in Patent Document 1, has a correlation with the blow-by gas flow rate. I have learned that it is not that expensive. For example, there is a measurement result that a piston with an anodized film having a surface roughness Ra of 1.63 has a lower blow-by gas flow rate than a piston with an anodized film with a surface roughness Ra of 1.30. That is, there is a problem that the blow-by gas flow rate cannot be accurately evaluated by the surface roughness index Ra.

Furthermore, in addition to the blow-by gas flow rate, it is also required to reduce the particle number PN (Particulate Number) of discharged fine particles. is difficult to achieve.

Therefore, in view of the above problems, the present invention can further reduce the blow-by gas flow rate and the number of discharged fine particles, and can accurately evaluate the surface roughness of the anodized film with respect to the blow-by gas flow rate. It is an object of the present invention to provide a method for manufacturing a piston for an internal combustion engine, capable of forming a smooth anodized film on the surface of the piston.

In order to achieve the above object, the present invention provides a method of manufacturing an internal combustion engine piston having a top ring groove on its outer peripheral surface, the internal combustion engine piston having at least a second groove on the inner surface of the top ring groove. An anodized film is provided on the inner surface of the ring groove side (that is, the lower surface) in the region in which the top ring contacts, and the surface roughness Rpk of the anodized film conforming to JIS B0671-2 is 1.00 μm or less. manufactures pistons for internal combustion engines.

As described above, according to the present invention, the correlation with the blow-by gas flow rate is higher than Ra according to the conventional JIS B0601, and the surface roughness of the anodized film can be accurately evaluated with respect to the blow-by gas flow rate. Further, the airtightness between the anodized film on the lower surface of the top ring groove and the top ring can be further improved, and the flow rate of blow-by gas during actual operation of the engine can be further reduced compared to the conventional art. Also, the particle number PN of the discharged fine particles can be suppressed to a predetermined reference value or less. Furthermore, the area of the top ring groove to be anodized can be reduced, the required power consumption can be suppressed, and the anodization treatment time can be shortened. In addition, it is possible to suppress variations in the amount of heat generated, and to further reduce the surface roughness Rpk.

1 is a cross-sectional view schematically showing the periphery of a top ring groove in an embodiment of an internal combustion engine piston according to the present invention; FIG. FIG. 4 is a cross-sectional view schematically showing the periphery of the top ring groove in another embodiment of the internal combustion engine piston according to the present invention. 1 is a cross-sectional view schematically showing an AC/DC superimposed electrolytic coating that can be used for an internal combustion engine piston according to the present invention; FIG. FIG. 2 is a cross-sectional view schematically showing a conventional DC superimposed electrolytic coating; 1 is a cross-sectional view schematically showing a DC electrolytic coating that can be used for an internal combustion engine piston according to the present invention; FIG. FIG. 4 is a schematic diagram showing a state in which the wettability of the anodized film to oil is low. FIG. 4 is a schematic diagram showing a state in which the wettability of the anodized film to oil is high. FIG. 3 is a schematic cross-sectional view for explaining a method of anodizing the periphery of the top ring groove in order to obtain the internal combustion engine piston shown in FIG. 2 ;

An embodiment of a method for manufacturing an internal combustion engine piston according to the present invention will be described below with reference to the accompanying drawings. The drawings are drawn with priority given to ease of understanding, and are not drawn to scale.

As shown in FIG. 1, a top ring groove 13 is formed in an outer peripheral surface 12 of an internal combustion engine piston 10 according to the present embodiment. As ring grooves, three ring grooves, a top ring groove 13, a second ring groove (not shown), and an oil ring groove (not shown) are formed in order from the piston crown surface 11 side. A top ring 30 is fitted in the top ring groove 13, a second ring (not shown) is fitted in the second ring groove, and an oil ring (not shown) is fitted in the oil ring groove.

The internal combustion engine piston 10 is made of aluminum or an aluminum alloy. The aluminum alloy may contain silicon (Si) as a component that contributes to wear resistance and aluminum adhesion resistance. On the other hand, rings such as the top ring 30 are made of, for example, high carbon steel or martensitic stainless steel. A ring such as the top ring 30 has a substantially C shape with one opening in the circumferential direction, and is inserted into a ring groove such as the top ring groove 13 of the piston 10 in an elastically expanded state. After that, the diameter is reduced by the elastic restoring force, and it is fitted inside the ring groove.

An outer peripheral surface 33 of the top ring 30 protrudes further to the outer peripheral side than the outer peripheral surface 12 of the internal combustion engine piston 10 . On the outer peripheral surface 12 of the piston 10, the area between the piston crown surface 11 and the top ring groove 13 is called a top land 12a, and the area between the top ring groove 13 and a second ring groove (not shown) is called a second land 12b. A space between the ring groove and the oil ring groove (not shown) is called a third land (not shown). Since the outer peripheral surface of each ring such as the top ring 30 protrudes outward from the outer peripheral surface 12 of the internal combustion engine piston 10, the internal combustion engine piston to which each ring such as the top ring 30 is attached When inserting 10 into the cylinder 40, each ring such as the top ring 30 is inserted into the cylinder 40 in a state in which the diameter thereof is elastically reduced. Therefore, when the internal combustion engine piston 10 is inserted into the cylinder 40, each ring such as the top ring 30 is pressed against the inner wall surface 41 of the cylinder 40 by its elastic force, and the top ring 30 and the second ring are burned. The oil ring has the function of keeping the chamber airtight, and the oil ring has the function of scraping off oil remaining on the inner wall surface 41 of the cylinder 40 .

Of the inner surfaces of the top ring groove 13 formed in the outer peripheral surface 12 of the internal combustion engine piston 10, the inner surface on the piston crown surface 11 side is called a lower surface 13a, and the inner surface on the second ring groove (not shown) side is called a lower surface 13c. , is called a bottom surface 13b. In the present embodiment, an anodized film 20A is formed on at least a region of the lower surface 13c of the top ring groove 13 with which the top ring 30 is in contact. Although this region varies depending on the design of the piston, for example, if the length (groove width) from the outer peripheral surface 12 of the internal combustion engine piston 10 to the bottom surface 13b of the top ring groove 13 is 100%, then the outer peripheral surface 12 side It is preferable to have a region with a length of at least 90% from the side of the outer peripheral surface 12, more preferably a region with a length of at least 80% from the side of the outer peripheral surface 12, and a length of at least 70% from the side of the outer peripheral surface 12. Regions are more preferred.

The reason why the anodized film 20A is formed on the lower surface 13c of the top ring groove 13 in this manner is that, as shown in FIG. Due to the high pressure, the bottom surface 32 of the top ring 30 strongly contacts the bottom surface 13 c of the top ring groove 13 . On the other hand, although not shown, in the intake process, the upper surface 31 of the top ring 30 of the internal combustion engine piston 10 is brought into close contact with the upper surface 13a of the top ring groove 13, and each time these processes are repeated, the internal combustion engine piston 10 moves toward the top ring groove. 13 moves between an upper surface 13a and a lower surface 13c. Therefore, since the lower surface 13c of the top ring groove 13 is likely to be worn or adhered to the top ring 30, the anodized film 20A is formed in order to improve wear resistance and aluminum adhesion resistance. There is a need.

The surface roughness of the anodized film 20A is 1.00 μm or less using the surface roughness Rpk according to JIS B0671-2 as an index. Such an anodized film 20 having a surface roughness Rpk of 1.00 μm or less can be formed, for example, by an AC/DC superposition electrolysis method. The AC/DC superposition electrolysis method is a method of anodizing an aluminum alloy member to be electrolyzed by repeating a step of applying a positive voltage and a step of removing electric charges. As shown in FIG. 3, the anodized film (AC/DC superimposed electrolytic film) 21 formed by the AC/DC superimposed electrolysis method grows in random directions and has no orientation. The anodized film 21 grows while encapsulating the silicon 16 contained in the silicon 15, so that the anodized film 21 with a dense and smooth surface can be formed.

On the other hand, it is difficult to form the anodized film 20 having a surface roughness Rpk of 1.00 μm or less only by direct current electrolysis. The DC electrolysis method is a method of anodizing an aluminum alloy member to be electrolyzed by applying a constant DC voltage. As shown in FIG. 4, the anodized film (DC electrolytic film) 22 formed by the DC electrolysis method grows in one direction, so that the silicon 16 contained in the aluminum alloy member 15 to be electrolytically treated acts as an anode. The growth of the oxide film 22 is inhibited and a plurality of large pores 23 are generated on the surface. With the anodized film 22 having such a highly uneven surface, it is difficult to achieve a surface roughness Rpk of 1.00 μm or less.

Therefore, as shown in FIG. 5, in order to obtain an anodized film 26 having a surface roughness Rpk of 1.00 μm or less by using the anodized film 22 formed by the DC electrolysis method, the surface portion 24 of the anodized film 22 is is scraped off by processing, and the surface of the anodized film 22 is sealed with the powder of the film thus generated. As a result, the anodized film 26 is provided with the sealing portions 25 in which the pores of the DC electrolytic film are filled with the film powder, which makes the surface smooth and allows the surface roughness Rpk to be 1.00 μm or less. can. Such processing can be performed, for example, by cutting using a cutting tool such as a bite or a knife, or by mechanical processing such as a whetstone with a shaft or barrel polishing.

It is presumed that the surface of the anodized film 26 obtained by such DC electrolysis and processing has a structure called a plateau structure. The term "plateau structure" is also used in JIS-B0671, and refers to a structure in which a surface is formed by a plateau portion (flat portion) and a valley portion. As stipulated in JIS B0671-2, Rpk, an index of surface roughness, can evaluate the characteristics of the plateau structure surface. On the other hand, as standardized in the conventional JIS B0601, the index of surface roughness Ra relates to the characteristics of the arithmetic mean roughness of contour curves. Therefore, it is presumed that the surface roughness Rpk can more accurately evaluate the surface roughness of the anodized film 26 with respect to the blow-by gas flow rate than the surface roughness Ra. Blow-by gas is gas that leaks from the combustion chamber to the crank chamber through the gap between the piston and the cylinder wall during the compression/expansion process, and is closely related to the airtightness of the piston ring and ring groove. In addition, although the surface of the anodized film (AC/DC superimposed electrolytic film) 21 formed by the AC/DC superimposed electrolysis method cannot be said to have a plateau structure, the surface is very smooth, so Rpk It is presumed that the index of surface roughness can be evaluated almost accurately.

By forming the anodized films 21 and 26 having a surface roughness Rpk of 1.00 μm or less in a predetermined region of the lower surface 13c of the top ring groove 13 of the internal combustion engine piston 10 as the anodized film 20A, 1, when the top ring 30 is in close contact with the bottom surface 13c of the top ring groove 13 in the compression process and the expansion process, the airtightness between the top ring 30 and the anodized film 20A on the bottom surface 13c of the top ring groove 13 is is extremely high, the flow rate of blow-by gas that leaks from the combustion chamber to the crank chamber through the gap between the internal combustion engine piston 10 and the cylinder 40 can be reduced. In particular, by forming the surface of the anodized film 20A into a plateau structure, the airtightness between the anodized film 20A on the lower surface 13c of the top ring groove 13 and the top ring 30 can be further improved. The flow rate can be further reduced.

The surface roughness Rpk of the anodized film 20A is preferably 0.90 μm or less, more preferably 0.60 μm or less. The lower limit of the surface roughness Rpk of the anodized film 20A is not particularly limited, but is preferably 0.01 μm or more, more preferably 0.10 μm or more, and even more preferably 0.20 μm or more. Thus, by setting the surface roughness Rpk of the anodized film 20A to 0.90 μm or less, and further to 0.60 μm or less, the anodized film 20A on the lower surface 13c of the top ring groove 13 and the top ring 30 Since the airtightness of the engine can be further improved, the blow-by gas flow rate during actual engine operation can be further reduced.

The thickness of the anodized film 20A is not particularly limited, but the upper limit is preferably 15 μm or less, more preferably 10 μm or less. Moreover, the lower limit is preferably 3 μm or more, more preferably 5 μm or more.

Further, in the internal combustion engine piston 10, in addition to the blow-by gas flow rate, reduction in the particle number PN of the discharged fine particles is also required. PN is considered to be caused by a phenomenon in which engine oil enters the combustion chamber through the gap between the piston 10 and the cylinder 40 (called oil rise). It is considered that the contribution of wettability to oil is also large.

The anodized film (AC/C superimposed electrolytic film) 21 formed by the direct superimposition electrolysis method is oriented in random directions as described above, so that the surface is densely formed, and the oil is applied to the inside of the anodized film. Therefore, as shown in FIG. 6, wettability to the oil 50a is low. In the anodized film 26 obtained by DC electrolysis and machining, the surface of the DC electrolysis film is scraped off and the surface is sealed with the resulting powder. low sex. On the other hand, as shown in FIG. 4, the direct-current electrolytic coating 22 having a plurality of large pores 23 on the surface is easy for oil to penetrate into these pores 23. Therefore, as shown in FIG. is high.

By forming the anodized films 21 and 26 having surfaces with low wettability to oil as the anodized films 20A on predetermined regions of the lower surface 13c of the top ring groove 13 of the internal combustion engine piston 10, the crank chamber is When the oil coming up along the outer peripheral surface 12 of the internal combustion engine piston 10 from the top ring groove 13 permeates inward from the outer peripheral portion of the hole of the porous anodized film 20A on the lower surface 13c of the top ring groove 13, the anodized film Since the oil does not easily spread in 20A and the oil stagnates, it is possible to suppress the oil rise, thereby suppressing the particle number PN of the discharged fine particles to a predetermined reference value or less.

In addition, the portion of the bottom surface 13c of the top ring groove 13 that is not in contact with the top ring 30 is made of an aluminum alloy with low surface roughness, thereby further preventing oil from entering the combustion chamber. . Further, of the bottom surface 13c of the top ring groove 13, only the area in contact with the top ring 30, which is an important part to be reinforced with wear resistance and aluminum adhesion resistance, is subjected to anodizing treatment to improve the top ring groove. The anodizing treatment area can be reduced, the necessary power consumption can be suppressed, and the anodizing treatment time can be shortened. In addition, it is possible to suppress variations in the amount of generated heat, and to further reduce the surface roughness Rpk of the anodized film 20 . The anodized film may be formed not only on the area where the top ring 30 contacts but also on the entire bottom surface 13c of the top ring groove 13. FIG.

The present invention is not limited to the embodiment described above. For example, as another embodiment, as shown in FIG. an upper surface 13a, a bottom surface 13b, and a lower surface 13c), and an outer peripheral surface 12 of the internal combustion engine piston 10 in the region from the top ring groove 13 to the piston crown surface 11 side (that is, the top land 12a) and the top ring It has an anodized film 20B extending from the groove 13 to the outer peripheral surface of the region (that is, the second land 12b) toward the second ring groove (not shown) side. The anodized film 20B may be integrally formed. The anodized film 20B may be formed over the entire surface of the top land 12a and the second land 12b, or may be formed partially. In some cases, for example, the anodized film 20B is formed in an area extending from the edge of the top ring groove 13 toward the piston crown surface 11 side or the second ring groove (not shown) to at least 4 mm, preferably up to 2 mm. .

Since the anodized film 20B is also formed on the top land 12a and the second land 12b in this manner, the oil is stagnated not only on the inner surface of the top ring groove 13 but also on the top land 12a and the second land 12b, and the oil rises significantly. can be suppressed, and the effect of reducing PN can be further enhanced.

Next, a method for manufacturing an internal combustion engine piston according to the present invention, that is, a method for forming an anodized film in a predetermined region of a top ring groove provided on an outer peripheral portion of an internal combustion engine piston will be described.

As shown in FIG. 8 , first, an anodizing device 60 is arranged so as to surround the outer peripheral side of the top ring groove 13 of the internal combustion engine piston 10 . The anodizing device 60 and the internal combustion engine piston 10 are brought into close contact with each other via sealing rings 62a and 62b which are arranged substantially in the center positions of the top land 12a and the second land 12b, respectively. Then, while feeding the treatment liquid 63 into the inside of the top ring groove 13 of the internal combustion engine piston 10 and the portion up to the sealing rings 62a and 62b of the top land 12a and the second land 12b, the internal combustion engine piston 10 is used as the anode. Anodized film 20B is formed on the surface of the aluminum alloy in the portion to which the treatment liquid 63 is sent by energizing between the cathode electrode 61 on the oxidation treatment device 60 side.

At this time, hydrogen bubbles 64 are generated from the cathode electrode 61 side during the anodizing process. When the hydrogen bubbles 64 come into contact with the inner surface of the top ring groove 13, the anodization of that portion does not progress, so there is a problem that the surface roughness of the formed anodized film 20B increases. Therefore, as shown in FIG. 8, by adopting a configuration in which the treatment liquid 63 is sent to the top land 12a and the second land 12b, most of the generated hydrogen bubbles 64 are generated in the top land 12a and the second land 12b, which have low pressure. Since it flows to the side, it is possible to prevent the hydrogen bubbles 64 from entering the inside of the top ring groove 13 . Therefore, a smooth anodized film 20B having a small surface roughness can be obtained.

This anodizing treatment method can be used for both the AC/DC superposition electrolysis method and the DC electrolysis method. Further, as shown in FIG. 1, when the anodized film 20A is formed on a partial region of the lower surface 13c of the inner surface of the top ring groove 13, the other inner surfaces of the top ring groove 13, the top land 12a and the second By masking the surface of the land 12b with a resin or metal spring, spray coating, or the like, the anodized film 20A can be formed only on a desired region.

Examples of the present invention and comparative examples are described below.

[Anodizing treatment]
As Examples 1 to 3, an anodized film was formed on the inner surface of the top ring groove of an internal combustion engine piston made of an aluminum alloy by the following procedure. First, an internal combustion engine piston was cast using an aluminum alloy containing 12% Si, and after a predetermined heat treatment, a ring groove was formed by machining. The processing of the top ring groove was finished so that the surface roughness Rpk was about 0.01 μm. Then, the inner surface of the top ring groove was subjected to anodization treatment by an AC/DC superposition electrolysis method using a sulfuric acid treatment solution under the conditions of 20 to 30 μs of energization time for one positive voltage application and a frequency of 10 to 12 kHz. . Then, the surface roughness Ra and the surface roughness Rpk of the anodized film (AC/C superimposed electrolytic film) formed on the lower surface of the top ring groove were measured according to JIS B0601 and JIS B0671-2, respectively. Table 1 shows the results.

In addition, as Examples 4 to 6, the surface of the anodized film (direct current electrolytic film) was subjected to surface processing treatment with a cutting tool after the anodizing treatment was performed by the DC electrolysis method instead of the AC/DC superimposition electrolysis method. , an anodized film was formed on the inner surface of the top ring groove in the same manner as in Examples 1 to 3. The conditions of the DC electrolysis method were a current density of 4 to 10 A/dm ² and a treatment time of 0.2 to 1.5 minutes. Table 1 shows the results.

Furthermore, as Comparative Examples 1 to 3, an anodized film was formed on the inner surface of the top ring groove in the same manner as in Examples 1 to 3, except that the anodizing treatment was performed by a DC electrolysis method instead of the AC/DC superposition electrolysis method. The conditions of the DC electrolysis method were a current density of 4 to 10 A/dm ² and a treatment time of 0.2 to 1.5 minutes. Table 1 shows the results.

[Measurement of flow rate of blow-by gas]
Using the internal combustion engine pistons of Examples 1 to 6 and Comparative Examples 1 to 3, on which the anodized film was formed in this manner, an experiment was conducted to measure the flow rate of blow-by gas in an actual engine. As experimental conditions, an in-line 4-cylinder 1200 cc engine was used, the engine speed was 6400 rpm WOT, the water temperature was 90°C, and the oil temperature was 135°C. Table 1 shows the results. The blow-by gas flow rate shown in Table 1 was obtained by calculating the average value of the measured values of the blow-by gas flow rate (unit: L/min) for 30 hours from the start of engine operation, and taking the average value of Comparative Example 1 as 100. It is shown as a ratio of cases.

[Evaluation of wettability to oil]
Regarding the aluminum alloy substrates on which an anodized film was formed under the same conditions as in Examples 1, 4, and Comparative Example 1 described above, and the aluminum alloy substrates that were not subjected to such anodization treatment, An oil wettability test was conducted. The oil used was 5W-30, each test object was placed on a hot plate, a predetermined amount of oil was dropped at a predetermined temperature, and the longest width (unit: mm) of the oil was measured. bottom. Table 2 shows the results. The wettability results shown in Table 2 are shown as a ratio when the width of the oil in the aluminum alloy substrate at 30°C is set to 1.0.

As can be seen from the results in Table 1, while there is a correlation between the surface roughness Rpk and the blow-by gas flow rate, the surface roughness Ra is within a narrow range of about 0.8 to 1.1 μm. No correlation with flow rate was found. Thus, it can be seen that the index of surface roughness Ra cannot accurately evaluate the surface roughness of the anodized film with respect to the blow-by gas flow rate. In addition, the blow-by gas flow rate of Examples 1 to 6 is 31% or more lower than that of Comparative Example 1. can be reliably reduced.

Moreover, as can be seen from the results in Table 2, the higher the temperature, the wider the oil width. In addition, since the direct-current electrolytic coating of Comparative Example 1 is porous, the oil width was wider than that of the aluminum alloy substrate in the low temperature range. On the other hand, since the AC/DC superimposed electrolytic coating of Example 1 has a dense surface, the oil width is narrower than that of the aluminum alloy substrate, and even if the temperature rises, compared to the aluminum alloy substrate, The rate at which the oil width spreads was remarkably small. In addition, the direct-current electrolytic coating surface-treated in Example 4 had a narrower oil width and maintained a narrow oil width even when the temperature increased. As described above, the anodized films of Examples 1 and 4 have low wettability to oil, and the difference from the aluminum alloy substrate and Comparative Example 1 is remarkable especially in a high temperature range. By providing such an anodized film with low wettability to oil in such a high temperature range, it is possible to effectively suppress oil discharge, thereby greatly contributing to the reduction of the particle number PN of discharged fine particles.

REFERENCE SIGNS LIST 10 internal combustion engine piston 11 piston crown surface 12a top land 12b second land 13 top ring groove 13c lower surface of top ring groove 15 aluminum alloy member 16 silicon 20, 21, 22, 26 anodized film 23 hole 25 sealing portion 30 top Ring 40 Cylinder 50 Oil 60 Anodizing device 61 Cathode electrode 62 Sealing ring 63 Treatment liquid 64 Hydrogen bubbles

Claims (3)

A method for manufacturing a piston for an internal combustion engine having a top ring groove on its outer peripheral surface, comprising:
The internal combustion engine piston has an anodized film on at least the inner surface of the second ring groove side of the inner surface of the top ring groove and the inner surface of the region in contact with the top ring,
The anodized film has a surface roughness Rpk of 1.00 μm or less according to JIS B0671-2,
The manufacturing method is
bringing the anodizing device and the piston for an internal combustion engine into close contact with each other via seal rings arranged in the top land and the second land;
While feeding the treatment liquid into the inside of the top ring groove of the internal combustion engine piston and the top land and the second land up to the sealing ring, the internal combustion engine piston is used as the anode, and the cathode electrode on the anodizing device side. By energizing between
The entire inner surface of the top ring groove, the outer peripheral surface of the internal combustion engine piston, the outer peripheral surface of the region from the top ring groove to the piston crown side, and the region from the top ring groove to the second ring groove side. A method of manufacturing a piston for an internal combustion engine, wherein the anodized film is formed over the outer peripheral surface. 2. The piston for an internal combustion engine according to claim 1, wherein the treatment liquid is supplied from one side of the anodizing apparatus with the cathode electrode interposed therebetween and the treatment liquid is discharged from the other side when the treatment liquid is fed. manufacturing method. forming a region between the anodizing device and the top and second lands where the pressure is lower than that inside the top ring groove of the piston for an internal combustion engine when the treatment liquid is supplied; Item 3. A method for manufacturing an internal combustion engine piston according to Item 1 or 2.

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