JP2022074388A - Piston for internal combustion engine and method for manufacturing the same - Google Patents

Abstract

To provide a piston for an internal combustion engine including an anode oxide film capable of improving abrasion resistance and providing good adhesion with a piston ring on an inner surface of a piston ring groove, and a method for manufacturing the same.SOLUTION: A method for manufacturing a piston 10 for an internal combustion engine of aluminum alloy 15 seals an anode oxide film 21 formed on an inner surface 13c of a piston ring groove of the piston for the internal combustion engine with a sealing liquid containing lithium ions. A softening anode oxide film 20 formed in the piston for the internal combustion engine comprises: a porous part 21 of the anode oxide film; and a sealing unit 22 in which a hole of a surface portion of the anode oxide film is blocked and a chemical compound of lithium, aluminum, and oxygen exists. Vickers hardness HV on a surface of the softening anode oxide film 20 is less than 320.SELECTED DRAWING: Figure 2

Description

The present invention relates to a piston for an internal combustion engine and a method for manufacturing the same, and more particularly to a piston for an internal combustion engine having an anodic oxide film on the inner surface of a piston ring groove and a method for manufacturing the piston.

In recent years, the internal combustion engine of an automobile has been increasing in output, and the heat load of the piston tends to increase. A piston ring is attached to the outer peripheral surface of the piston in order to maintain the airtightness of the combustion chamber. The piston ring is fitted in a ring groove formed on the outer peripheral surface of the piston. The inner surface of the ring groove is struck by the piston ring and wears, and the sealing property is easily impaired. Therefore, in order to improve the wear resistance of the inner surface of the ring groove, the inner surface of the ring groove is anodized.

However, the aluminum alloy used as the piston material contains silicon in order to improve castability and wear resistance, and the silicon has a crystallized metal structure. Since silicon is partially exposed on the inner surface of the ring groove, the formation of the anodic oxide film formed by oxidizing aluminum by the anodic oxidation treatment is also partially inhibited, resulting in a non-uniform film with irregularities on the surface. It ends up. In such an anodized film, a gap is created between the anodic oxide film and the piston ring, and as the sealing property deteriorates, the flow rate of blow-by gas increases and the oil rises, resulting in deterioration of fuel efficiency and PM (Particulate Matter: particles). There is a problem that it becomes a factor of the generation of substances subject to European environmental regulations such as (particulate matter) and an increase in the number of substances such as PN (Particulate Number).

On the other hand, Patent Document 1 describes the surface of the anodic oxide film formed on the surface of the aluminum alloy as a treatment method capable of improving the corrosion resistance of the anodic oxide film formed on the surface of the aluminum alloy and in a short time. , 0.02 to 20 g / L of lithium ion, a pH value of 10.5 or more, and a sealing treatment liquid having a temperature of 65 ° C. or less are described for sealing treatment.

Japanese Unexamined Patent Publication No. 2010-77532

It is difficult to mechanically smooth the surface of the anodic oxide film formed on the inner surface of the piston ring groove of the piston for internal combustion engine made of aluminum alloy by post-treatment because the width of the piston ring groove is several mm. be.

Therefore, in view of the above problems, the present invention has an internal combustion engine provided with an anodic oxide film on the inner surface of the piston ring groove, which can improve wear resistance and also have good adhesion to the piston ring. It is an object of the present invention to provide a piston for use and a method for manufacturing the same.

In order to achieve the above object, the present invention is, as one aspect, a method for manufacturing a piston for an internal combustion engine, in which the method anodizes the inner surface of the piston ring groove of the piston for an internal combustion engine made of an aluminum alloy. It includes a step of forming a film and a step of sealing the anodic oxide film with a sealing liquid containing lithium ions so that the Vickers hardness HV of the surface of the anodic oxide film after the sealing treatment is less than 320. ..

Further, another aspect of the present invention is an internal combustion engine piston having a piston ring groove on the outer peripheral surface, wherein the internal combustion engine piston is provided with an anodic oxide film on the inner surface of the piston ring groove, and the anodic oxidation is performed. The pores on the surface of the film are closed, and compounds of lithium, aluminum, and oxygen are present on the surface where the holes are closed, and the Vickers hardness HV on the surface of the anodized film is It is less than 320.

As described above, according to the present invention, the anodic oxide film formed on the inner surface of the piston ring groove of the piston for an internal combustion engine made of an aluminum alloy is sealed with a sealing liquid containing lithium ions, and after the sealing treatment. By setting the Vickers hardness HV of the surface of the anodic oxide film to less than 320, even if the surface of the anodic oxide film after the sealing treatment is uneven and uneven, the vertical pressure of the piston ring at the time of starting the engine The unevenness is smoothed out, and the adhesion with the piston ring is improved. Therefore, by improving the sealing performance of the piston ring groove of the piston for internal combustion engine, it is possible to reduce the flow rate of blow-by gas and suppress the rise of oil, which contributes to the improvement of fuel efficiency and the compliance with environmental regulations of PM and PN. be able to.

It is one embodiment of the piston for an internal combustion engine which concerns on this invention, and is sectional drawing which shows typically the periphery of the 1st piston ring groove. It is sectional drawing which shows typically the periphery of the lower surface of the 1st piston ring groove of the piston for an internal combustion engine shown in FIG. 1. It is a graph which shows the measurement result of the hardness of the anodic oxide film of Test Example 1. It is a graph which shows the measurement result of the hardness of the anodic oxide film of Test Example 2. It is a graph which shows the measurement result of the hardness of the anodic oxide film of Test Example 3. It is a graph which shows the measurement result of the hardness of the anodic oxide film of Test Example 4.

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

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

The piston 10 for an internal combustion engine is made of an aluminum alloy. The aluminum alloy generally contains silicon (Si) as a component that contributes to wear resistance and aluminum adhesion resistance. Examples of such an aluminum alloy include AC materials such as AC4, AC8, AC8A, and AC9 as pistons, ADC materials such as ADC10 to ADC14, and A4000. On the other hand, the ring such as the first piston ring 30 is made of, for example, high carbon steel, martensitic stainless steel, or the like. The ring such as the first piston ring 30 has a substantially C-shape with one opening in the circumferential direction, and is a ring such as the first piston ring groove 13 of the piston 10 in a state where the diameter is elastically expanded. After being placed in the groove, the diameter is reduced by the elastic restoring force and fitted into the ring groove.

The outer peripheral surface 33 of the first piston ring 30 is in a state of protruding toward the outer peripheral side of the outer peripheral surface 12 of the piston 10 for an internal combustion engine. The outer peripheral surface 12 of the piston 10 is referred to as a first land 12a between the piston crown surface 11 and the first piston ring groove 13, and between the first piston ring groove 13 and the second piston ring groove (not shown). The second land 12b is referred to, and the space between the second piston ring groove and the oil ring groove (not shown) is referred to as a third land (not shown). Since the outer peripheral surface of each ring such as the first piston ring 30 is in a state of protruding outward from the outer peripheral surface 12 of the piston 10 for an internal combustion engine, each ring such as the first piston ring 30 is attached. When the piston 10 for an internal combustion engine is inserted into the cylinder 40, each ring such as the first piston ring 30 is inserted into the cylinder 40 in a state of being elastically reduced in diameter. Therefore, when the piston 10 for an internal combustion engine is inserted into the cylinder 40, each ring such as the first piston ring 30 is pressed against the inner wall surface 41 of the cylinder 40 by its elastic force, and the first piston ring 30 and the first piston ring 30 and the like are in a state of being pressed against the inner wall surface 41 of the cylinder 40. The second ring functions to maintain the airtightness of the combustion chamber, and the oil ring functions to scrape off the oil remaining on the inner wall surface 41 of the cylinder 40.

Of the inner surfaces of the first piston ring groove 13 formed on the outer peripheral surface 12 of the piston 10 for an internal combustion engine, the inner surface on the piston crown surface 11 side is called the upper surface 13a, and the inner surface on the second ring groove (not shown) side is the lower surface 13c. The inner surface on the bottom side of the groove between them is called the side surface 13b. Then, in the present embodiment, the upper surface 13a, the side surface 13b, and the lower surface 13c of the first piston ring groove 13 have an anodic oxide film 20 whose hardness has been reduced by the sealing treatment according to the present invention (hereinafter, “softened anodic oxide film”). ") Is formed. The softened anodic oxide film 20 may be provided only on the lower surface 13c of the inner surface of the first piston ring groove 13.

As shown in FIG. 1, the softened anodic oxide film 20 is formed on the lower surface 13c of the first piston ring groove 13 in the internal combustion engine piston 10 on the piston crown surface 11 side in the compression step and the expansion step. Since the pressure inside the combustion chamber becomes high, the lower surface 32 of the first piston ring 30 strongly adheres to the lower surface 13c of the first piston ring groove 13. On the other hand, although not shown, in the suction step, in the internal combustion engine piston 10, the upper surface 31 of the first piston ring 30 is in close contact with the upper surface 13a of the first piston ring groove 13, and the piston 10 for the internal combustion engine 10 is repeated every time these steps are repeated. Moves between the upper surface 13a and the lower surface 13c of the first piston ring groove 13. Therefore, since the lower surface 13c of the first piston ring groove 13 is likely to be worn from the first piston ring 30, it is necessary to form the softened anodic oxide film 20 in order to improve the wear resistance and the sealing property. There is.

Of course, the softened anodic oxide film 20 may also be formed on the upper surface 13a of the first piston ring groove 13. Further, since the first piston ring 30 is also in close contact with the cylinder 40 due to its tension, it does not come into contact with the side surface 13b of the first piston ring groove 13, and is therefore softened to the side surface 13b of the first piston ring groove 13. It is not essential to form the anodic oxide film 20, but of course, the softened anodic oxide film 20 may be formed on the side surface 13b of the first piston ring groove 13.

As shown in FIG. 2, the softened anodic oxide film 20 of the present embodiment has a porous portion 21 of the anodic oxide film produced by anodizing the aluminum alloy 15 on the lower surface 13c of the first piston ring groove 13. It has a structure including a sealing processing portion 22 in which the pores on the surface portion of the anodic oxide film are closed by sealing the anodic oxide film with a sealing treatment liquid containing lithium ions.

Since the anodizing film formed by the anodizing treatment usually grows in the direction perpendicular to the surface of the aluminum alloy 15 to be anodized, silicon 16 and the like are crystallized on the surface layer of the aluminum alloy 15. At the present location, the growth of the anodized film is inhibited, and a large number of irregularities are generated on the surface. The unevenness on the surface of this anodic oxide film cannot be smoothed by the pore-sealing treatment. INDUSTRIAL APPLICABILITY According to the present invention, the surface hardness of the anodic oxide film can be softened while maintaining the excellent wear resistance of the anodic oxide film by sealing the anodic oxide film with a sealing liquid containing lithium ions. It is based on the knowledge.

The pore-sealing portion 22 in which the holes on the surface portion of the anodic oxide film are closed by the pore-sealing treatment has a lower hardness than the anodic oxide film and is excellent in initial compatibility with the piston ring 30. That is, even if the surface of the softened anodic oxide film 20 after the hole sealing treatment is uneven and non-uniform, the unevenness is smoothed by the vertical pressure of the piston ring 30 at the time of starting the engine, and as shown in FIG. 2, it is smooth. To become. Therefore, the adhesion between the lower surface 13c of the piston ring groove and the piston ring 30 is improved, the flow rate of blow-by gas can be reduced, and fuel efficiency can be improved. In addition, the sealing property is improved and the oil rise can be suppressed, so that PM and PN can be suppressed within the required values.

The hardness of the sealing portion 22, that is, the hardness of the surface of the softened anodic oxide film 20 is the Vickers hardness HV, and if it is less than 320, the piston is driven by the vertical pressure of the piston ring 30 at the time of starting the engine. The unevenness of the surface can be smoothed to the extent that the adhesion to the ring is good. The surface hardness of the preferred softened anodic oxide film 20 is Vickers hardness HV, preferably 130 or more and less than 320, and more preferably 150 or more and less than 320. The lower limit of the surface hardness of the softened anodic oxide film 20 is the Vickers hardness HV, preferably 130 or more, which is the hardness of the aluminum alloy. If it is less than 130, it may affect the wear resistance which is the purpose of forming the anodic oxide film.

As a method for manufacturing a piston for an internal combustion engine having such a softened anodic oxide film, an anodic oxidation treatment step of forming an anodic oxide film on the inner surface of the piston ring groove of the piston for an internal combustion engine made of an aluminum alloy is performed, and then the anodic oxidation treatment step is performed. , Including performing a sealing treatment step of sealing an anodized film with a sealing treatment liquid containing lithium ions. Each process will be described below.

In the anodizing treatment step, a conventional anodizing treatment capable of forming an anodizing film on the surface of an aluminum alloy can be widely adopted. For example, in an acidic treatment bath such as sulfuric acid, oxalic acid, phosphoric acid, chromic acid, or a basic treatment bath such as sodium hydroxide, sodium phosphate, sodium fluoride, and an electrode plate such as titanium or carbon as a cathode. By immersing the piston for an internal combustion engine as an anode and performing electrolysis, the aluminum alloy on the inner surface of the piston ring groove of the piston for an internal combustion engine can be oxidized to form an anodized film. As the electrolysis method, any of DC electrolysis, AC electrolysis, AC / DC superimposition electrolysis and the like may be used. The anodizing film to be treated for the pores of the present invention is not limited to the specific anodizing treatment.

The film thickness of the anodic oxide film formed in the anodic oxidation treatment step is not particularly limited, but is preferably 5 to 20 μm, more preferably 5 to 10 μm, for example.

In the sealing process, the surface portion of the anodic oxide film is applied or sprayed on the piston for an internal combustion engine on which the anodic oxide film is formed, or immersed in the sealing solution. The hole is closed. More specifically, the surface portion of the anodic oxide film is melted by the pore-sealing treatment liquid and then reprecipitated to form a sealing-treated portion in which the pores are closed on the surface portion of the anodic oxide film. In addition to aluminum oxide, compounds of lithium, aluminum, and oxygen are present in this sealing treatment portion. This sealing processing unit is not disassembled to release the sealing state even in a high temperature environment where the piston for the internal combustion engine is exposed.

The sealing liquid is an aqueous solution containing lithium ions, and lithium sulfate, lithium chloride, lithium silicate, lithium nitrate, lithium carbonate, lithium phosphate, lithium hydroxide and the like are used as compounds that serve as lithium ion sources. be able to. Of these, lithium hydroxide, lithium carbonate, and lithium silicate are preferable as the aqueous solution exhibits basicity. However, lithium silicate is not practical because it is highly toxic and difficult to dissolve in water. Therefore, lithium carbonate and lithium hydroxide are more preferable.

The lithium ion concentration of the pore-sealing treatment liquid is preferably 1 to 15 g / L, more preferably 1 to 12 g / L. With lithium ions having a concentration of 1 g / L or more, the reaction of the sealing treatment is promoted, and a sealing treatment portion having a sufficiently reduced hardness can be obtained. The upper limit of the lithium ion concentration is not particularly limited, but is preferably 15 g / L or less. When the lithium ion concentration exceeds 15 g / L, the reaction proceeds rapidly, which is not preferable.

The temperature of the sealing liquid is preferably 10 to 70 ° C, more preferably 10 to 60 ° C. When the sealing treatment is performed at a high temperature of 10 ° C. or higher, a sealing treatment portion having high activity and reactivity and sufficiently reduced hardness can be obtained even in a short time. On the other hand, at a temperature higher than 70 ° C., the dissolution of the film from the surface of the anodic oxide film proceeds rapidly, which is not preferable.

The treatment time for the sealing treatment is preferably 0.5 to 4 minutes, more preferably 0.5 to 2 minutes. By setting the treatment time to 0.5 minutes or more, the surface of the anodic oxide film is melted, and the sealing treated portion having a sufficiently reduced hardness can be reprecipitated. On the other hand, if the time exceeds 4 minutes, the dissolution of the film from the surface of the anodic oxide film proceeds rapidly, which is not preferable.

In the sealing treatment step, it is preferable to perform the sealing treatment with the sealing treatment liquid, then wash with water and dry.

Although the formation of the softened anodic oxide film 20 in the first piston ring groove 13 has been described, the present invention is not limited to the first piston ring groove 13, but other piston ring grooves and the like. A softened anodic oxide film 20 may be formed in the piston ring groove. By improving the adhesion with the piston ring, it is possible to reduce the flow rate of blow-by gas and the rise of oil, which contributes to improved fuel efficiency and compliance with environmental regulations. Further, by improving the wear resistance, the sealing property with the piston ring can be kept good. Further, by forming the softened anodic oxide film 20 in the first piston ring groove 13 of the piston ring grooves, the fuel consumption is improved by suppressing the heat escape below the first piston ring groove 13. This can be said to be a reduction in cooling loss.

Hereinafter, examples and comparative examples of the present invention will be described.

[Test Example 1]
A test piece of aluminum material A1050 simulating a piston for an internal combustion engine made of an aluminum alloy is subjected to anodic oxidation treatment of a sulfuric acid bath (electrolysis conditions: 0.5A, 10 min) to form an anodic oxide film of about 20 μm on the surface. bottom. This test piece was immersed in a sealing liquid having a lithium ion concentration of 10 g / L to seal the anodic oxide film. The temperature of the sealing liquid was 30 ° C., and the treatment time was 1 minute. Then, the hardness of the anodic oxide film after the pore sealing treatment was measured with a dynamic ultrafine hardness tester DUH-211 manufactured by Shimadzu Corporation. The measurement conditions were a load of 100 mN. The hardness was evaluated by Vickers hardness HV. The hardness of the anodic oxide film after the sealing treatment of the five test pieces was measured, and the average value thereof is shown in FIG. 3 (Example). As a comparative example, the hardness of the anodic oxide film before the sealing treatment was measured in the same manner as described above. The results are shown in FIG.

As shown in FIG. 3, the hardness of the anodic oxide film (comparative example) without the sealing treatment was 320 in Vickers hardness HV, but the anodic oxide film after the sealing treatment (example). The hardness of Vickers hardness HV was significantly reduced to 270. By softening the hardness of the anodic oxide film to a significantly low value of 270 with Vickers hardness HV in this way, even if the surface of the anodic oxide film is uneven and uneven, the piston at the time of engine start The unevenness can be smoothed by the pressure in the vertical direction of the ring.

[Test Example 2]
The test piece was anodized and sealed in the same manner as in Test Example 1 except that the lithium ion concentration of the sealing solution was changed from 10 g / L to 1, 20, 30 g / L to seal the holes. The hardness of the anodic oxide film after the treatment was measured. The results are shown in FIG.

As shown in FIG. 4, the hardness of the anodic oxide film (Example) after the pore-sealing treatment is the same as that of the anodic oxide film without the pore-sealing treatment (Comparative Example) regardless of the lithium ion concentration of the pore-sealing treatment liquid. ) Could be significantly lower than the hardness. In particular, when the lithium ion concentration was 1 g / L and 10 g / L, the hardness of the anodic oxide film after the sealing treatment decreased only to about 200 at the Vickers hardness HV, but the lithium ion concentration was 20 g. In the case of / L and 30 g / L, the hardness of the anodic oxide film after the sealing treatment was reduced to 100 or less in Vickers hardness HV. Therefore, since 130, which is the lower limit of the preferable range of Vickers hardness HV, has a lithium ion concentration of 10 to 20 g / L, the preferred lithium ion concentration range is 1 to 15 g / L, which is more preferable. It can be seen that the concentration range is 1 to 12 g / L.

[Test Example 3]
The test piece was anodized and sealed in the same manner as in Test Example 1 except that the temperature of the sealing liquid was changed from 30 ° C to 10, 50, 70 ° C, and the anode after the sealing treatment was performed. The hardness of the oxide film was measured. The results are shown in FIG.

As shown in FIG. 5, the hardness of the anodic oxide film (Example) after the pore-sealing treatment is the same as that of the anodic oxide film (Comparative Example) without the pore-sealing treatment, regardless of the temperature of the pore-sealing treatment liquid. It was possible to reduce the hardness significantly. Therefore, it can be seen that the treatment temperature is preferably 10 to 70 ° C, more preferably 10 to 60 ° C.

[Test Example 4]
The test piece was anodized and sealed in the same manner as in Test Example 1 except that the sealing treatment time was changed from 1 minute to 0.5, 5 and 10 minutes. The hardness of the anodized film was measured. The results are shown in FIG.

As shown in FIG. 6, the hardness of the anodic oxide film (Example) after the pore-sealing treatment is the same as that of the anodic oxide film (Comparative Example) without the pore-sealing treatment, regardless of the sealing treatment time. It was possible to reduce the hardness significantly. In particular, when the treatment time was 1 minute, the hardness of the anodic oxide film after the pore-sealing treatment decreased only to about 180 in Vickers hardness HV, but when the treatment time was 4 minutes or more, the sealing was performed. The hardness of the anodic oxide film after the pore treatment was reduced to 100 or less in Vickers hardness HV. Therefore, it can be seen that the processing time for the sealing treatment is preferably 0.5 to 4 minutes, more preferably 0.5 to 2 minutes.

10 Piston for internal combustion engine 11 Piston crown surface 12a 1st land 12b 2nd land 13 1st piston ring groove 13c Lower surface of 1st piston ring groove 15 Aluminum alloy 16 Silicon 20 Anodized film after sealing treatment (softened anodized film) )
21 Porous part 22 Sealing part 30 Top ring 40 Cylinder

Claims (6)

The process of forming an anodic oxide film on the inner surface of the piston ring groove of an aluminum alloy piston for an internal combustion engine,
A method for manufacturing a piston for an internal combustion engine, which comprises a step of sealing the anodic oxide film with a sealing liquid containing lithium ions so that the Vickers hardness HV of the surface of the anodic oxide film after the sealing treatment is less than 320. .. The method for manufacturing a piston for an internal combustion engine according to claim 1, wherein the lithium ion concentration of the sealing liquid is in the range of 1 to 15 g / L, and the temperature of the sealing liquid is in the range of 10 to 70 ° C. The method for manufacturing a piston for an internal combustion engine according to claim 1, wherein the lithium ion concentration of the sealing liquid is in the range of 1 to 12 g / L, and the temperature of the sealing liquid is in the range of 10 to 70 ° C. The method for manufacturing a piston for an internal combustion engine according to any one of claims 1 to 3, wherein the processing time for the sealing process is in the range of 0.5 to 4 minutes. The method for manufacturing a piston for an internal combustion engine according to any one of claims 1 to 3, wherein the processing time for the sealing process is in the range of 0.5 to 2 minutes. A piston for an internal combustion engine having a piston ring groove on the outer peripheral surface.
An anodic oxide film is provided on the inner surface of the piston ring groove.
The pores on the surface of the anodic oxide film are closed, and compounds of lithium, aluminum, and oxygen are present on the surface portion where the pores are closed, and the Vickers hardness of the surface of the anodic oxide film is present. A piston for an internal combustion engine having an HV of less than 320.

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