JP5885531B2 - Piston of internal combustion engine - Google Patents

Description

  The present invention relates to a piston for an internal combustion engine applied to, for example, an internal combustion engine of an automobile and a method for manufacturing the same, and mainly relates to a multilayer solid lubricant film formed on the surface of a skirt portion.

  As a piston of a conventional internal combustion engine on which a multilayer solid lubricant film is formed, for example, one described in Patent Document 1 below is known.

  That is, conventionally, the first solid lubricant film having a composition with a small amount of wear is formed in the lower layer, and the second solid lubricant film having a composition with a large amount of wear is formed in the upper layer, whereby the streaks remaining in the skirt portion. As a result, the friction is reduced.

JP 2010-216362 A

  However, since the conventional pistons are formed by overlapping different solid lubricant films, the bonding force between the layers cannot be sufficiently ensured, and there is a possibility that peeling is likely to occur.

  Therefore, the present invention has been devised in view of the technical problem of the piston of the conventional internal combustion engine, and has a characteristic that the upper layer is easily worn and the lower layer is hard to be worn, and has sufficient connectivity. An object of the present invention is to provide a piston or the like for an internal combustion engine provided with a solid lubricant film having the following.

  The present invention relates to a piston of an internal combustion engine in which a solid lubricant film is formed on a skirt portion, and in particular, the solid lubricant film contains a resin that is a binding resin and a solid lubricant having a specific gravity greater than that of the resin. The interface that contacts the skirt portion is set so that the content of the solid lubricant is 50 wt% or less, while the surface that is in sliding contact with the cylinder wall of the engine contains the solid lubricant. The amount of the solid lubricant is set so as to be 50 to 95 wt%, and the solid lubricant content is continuously changed between the interface contacting the skirt portion and the surface slidingly contacting the cylinder wall. It is characterized by having.

  In addition, as a composition of the said solid lubricating film, it is desirable to include at least 1 sort (s) of polyamideimide resin, a polyimide resin, or an epoxy resin as a binder resin, and to include at least molybdenum disulfide as a solid lubricant.

  The solid lubricant film is formed by applying a coating composition containing a step of molding and processing the piston and a resin as a binder and a solid lubricant having a specific gravity greater than that of the resin to the skirt portion. It can be formed by a step, a step of rotating the piston around an axis before the solid lubricant is dried, and a step of baking the coating composition.

  Furthermore, the solid lubricant film includes a first film composition having a solid lubricant content of 50 wt% or less and a second film having a solid lubricant content of 50 to 95 wt% on the surface of the skirt portion. It can also be formed by applying the composition simultaneously with a plurality of sprays.

  According to the present invention, the distribution of the components of a single coating composition is adjusted so that the coating interface has less solid lubricant and the coating surface has more solid lubricant to form the coating. Thus, it is possible to achieve both the property that the upper layer is easily worn and the lower layer is hard to be worn, and sufficient bondability. As a result, it is possible to obtain a piston having a solid lubricating film having characteristics that the upper layer is easily worn and the lower layer is hard to be worn, and that has sufficient bondability.

  In manufacturing this piston, by utilizing the method of adjusting the distribution of the contained component by centrifugal force using the specific gravity difference of the contained component of the coating composition, it is possible to simply rotate the piston. A solid lubricating coating having a desired configuration is obtained. This provides good productivity and low manufacturing costs.

  Further, when manufacturing the piston, when a method of forming a solid lubricating film by simultaneously applying the plurality of coating compositions is employed, in particular, the concentration distribution of the solid lubricant in the coating is arbitrarily set. It becomes possible to change, and it is used for the formation of a film with higher versatility.

It is a principal part longitudinal cross-sectional view which shows the state which applied the piston which concerns on this invention to the internal combustion engine. It is a half sectional view of the piston. It is a principal part enlarged view of the skirt part shown in FIG. It is process drawing showing the process order of the manufacturing process of the piston which concerns on 1st Embodiment of this invention. It is the schematic showing the application aspect of the film formation coating material which concerns on the same embodiment. It is the schematic showing the process aspect of the centrifugation process process shown in FIG. It is the graph showing the relationship between the rotation speed of a centrifugation process, and a rotation speed. The distribution of the content component in a solid lubricating film is shown, (a) is the schematic before a centrifugation process, (b) is the schematic showing the state after a centrifugation process. It is the schematic showing the process order of the piston manufacturing process which concerns on the modification of the embodiment. It is the schematic showing the application aspect of the film formation coating material which concerns on the modification. It is process drawing showing the process order of the manufacturing process of the piston which concerns on 2nd Embodiment of this invention. It is the schematic showing the application aspect of each film formation coating material concerning the embodiment, its application amount, etc. It is the graph showing the relationship between the film thickness position when changing the rotational speed of a piston at the time of application | coating of a film formation coating material, and the density | concentration of a solid lubricant.

  Hereinafter, embodiments of a piston and the like of an internal combustion engine according to the present invention will be described in detail based on the drawings. In the following embodiments, description will be made based on an example in which the piston or the like is applied to a piston of an automobile engine.

  As shown in FIG. 1, the piston 1 according to the present invention is slidably provided with respect to a substantially cylindrical cylinder wall 3 formed in a cylinder block 2, and the cylinder wall 3 and a cylinder head (not shown) are connected to each other. A combustion chamber C is formed therebetween, and is linked to a crankshaft (not shown) via a connecting rod 5 connected to a piston pin 4 inserted substantially along the radial direction.

  The entire piston 1 is integrally cast in a substantially cylindrical shape with an Al—Si based aluminum alloy material such as AC8A, for example, and as shown in FIGS. 1 and 2, the combustion chamber C is defined on the crown surface 6a. A crown portion 6, a pair of thrust side skirt portions 7 and an anti-thrust side skirt portion 8 provided integrally on the outer periphery of the lower end side of the crown portion 6, and both circumferential ends of the skirt portions 7, 8. A pair of apron portions 9 and 9 to be connected are provided.

  The crown portion 6 has a disk shape formed relatively thick, and a valve recess (not shown) for avoiding interference with an intake / exhaust valve (not shown) is formed in the crown surface 6a. Further, ring grooves 6b to 6d for holding three piston rings PL1 to PL3 such as a pressure ring and an oil ring are formed in the outer peripheral portion of the crown portion 6 in a notch.

  Each of the skirt portions 7 and 8 is disposed symmetrically about the axis of the piston 1 and is formed to have a substantially arcuate cross section with a relatively thin thickness width. The thrust side skirt portion 7 is pressed against the cylinder wall 3 while being inclined with respect to the angle of the connecting rod 5 when the piston 1 moves down during the expansion stroke or the like, while the anti-thrust side skirt portion 8 Is in pressure contact with the cylinder wall 3 while inclining in the opposite direction when the piston 1 moves upward during the compression stroke or the like. Note that the thrust load on the cylinder wall 3 of the skirt portions 7 and 8 is larger in the thrust side skirt portion 7 that receives the combustion pressure and presses against the cylinder wall 3.

  Further, as shown in FIGS. 1 and 3, well-known stripes 7a and 8a are provided on the surfaces of the skirt portions 7 and 8, and the skirts provided with the respective stripes 7a and 8a are provided. A solid lubricant film 10 made of a predetermined film composition is formed on the surfaces of the portions 7 and 8. The coating composition of the solid lubricating coating 10 is mainly composed of a binding resin (binder) 11 and a solid lubricant 12 having a specific gravity greater than that of the binding resin 11.

Here, as shown in FIG. 3, the solid lubricating coating 10 refers to an interface that contacts the surface of each skirt portion 7, 8 (in the range of thickness t = 1 μm from the surface of each skirt portion 7, 8; In 10a, the solid lubricant 12 content is set to 50 wt% or less (the binding resin 11 content is 50 wt% or more), while the cylinder wall 3 In the surface that is in sliding contact with the surface (referred to as the “coating surface” hereinafter), the content of the solid lubricant 12 is 50 to 95 wt% (the content of the binding resin 11). Is set to 5 to 50 wt %) . The binder resin 11 includes at least one of an epoxy resin, a polyimide resin, or a polyamideimide resin (PAI) that is excellent in heat resistance, wear resistance, and adhesion, and the solid lubricant 12 includes at least Molybdenum disulfide (MoS ₂ ) is included.

  The reason why the content of the solid lubricant 12 is set to 50 wt% or less at the coating interface 10a is as described in the conventional patent publication (Japanese Patent Laid-Open No. 2010-216362). This is because the adhesion can be improved by increasing the content of the resin 11. On the other hand, the solid lubricant 12 is set so that the content of the solid lubricant 12 is 50 to 95 wt% on the coating surface 10 b. When the content of the lubricant exceeds 95 wt%, that is, when the content of the binder resin is less than 5 wt%, the adhesiveness decreases due to a decrease in the binding force, and conversely, when the content of the solid lubricant 12 is less than 50 wt% This is because the familiarity is lowered.

  And the said coating composition comprised as mentioned above is diluted with the organic solvent, and is apply | coated to the piston 1 as a coating material. That is, the coating composition is applied to the outer peripheral surface of the piston 1 (both the skirt portions 7 and 8), and the solid lubricating coating 10 is formed by baking and curing the coating composition.

  In order to adjust the coating composition, for example, an organic solvent is blended into the binding resin 11, a solid lubricant 12 is added to the resin solution, and hard particles are further added as necessary. It may be used and mixed and dispersed. In this case, the combined amount of the binder resin 11, the solid lubricant 12, and the hard particles is adjusted so as to be 100 wt%.

  Hereinafter, the manufacturing method of the piston 1 will be described with reference to FIGS.

  First, the piston 1 is formed by a predetermined manufacturing method such as casting, and then the streaks 7a and 8a are formed on the skirt portions 7 and 8 by cutting (processing step S1 shown in FIG. 4). Subsequently, the piston 1 is washed with water by steam cleaning to remove the processing lubricant and the like adhering to the surface, and then dried (cleaning step S2 shown in FIG. 4).

  Next, a film-forming paint 10x obtained by dissolving the film composition in a predetermined organic solvent is applied to the surfaces of the skirt portions 7 and 8 of the cleaned and dried piston 1 by air spray (shown in FIG. 4). Film formation process S3). Specifically, as shown in FIG. 5, the washed piston 1 is placed on a turntable 21, and the film forming paint 10 x injected into the tank 20 a while turning the turntable 21 is sprayed by the spray gun 20. By spraying, the film-forming coating material 10x is applied to the surfaces of the skirt portions 7 and 8 on which the strips 7a and 8a are formed.

  Subsequently, the coating composition is centrifuged by rotating the piston 1 to which the coating film forming paint 10x is applied under predetermined conditions described later (centrifugation processing step S4 shown in FIG. 4). Note that the centrifugal treatment here is extremely low so that the paint 10x does not scatter (separate), unlike so-called normal centrifugal separation performed by generating thousands or tens of thousands × g (gravity acceleration), for example. A process performed at the number of rotations. Specifically, as shown in FIG. 6, the piston 1 after application of the paint 10x is fixed to a jig 30 attached to a rotating device (not shown) such as a so-called centrifuge, and the jig 30 is passed through the jig 30. The piston 1 is rotated around its axis O with the rotational force transmitted in this manner.

Then, before the rotation (treatment), as shown in FIG. 7A, in the film-forming coating material 10x in which the binding resin 11 and the solid lubricant 12 have a substantially uniform distribution, the binding resin 11 ( PAI specific gravity: 1.49) and solid lubricant 12 having a large specific gravity (MoS ₂ specific gravity: 4.80) are separated by centrifugal force. That is, as shown in FIG. 7B, the binding resin 11 is biased at the coating interface 10a and the solid lubricant 12 is biased at the coating surface 10b.

  As a result, the content of the binding resin 11 is large at the coating interface 10a, the content of the binding resin 11 decreases from the coating interface to the coating surface 10b, and the content of the solid lubricant 12 increases, so that the coating surface 10b In such a configuration, the content of the solid lubricant 12 is increased. In other words, the coating film forming paint 10x has a small content of the solid lubricant 12 at the coating interface 10a (50 wt% or less), and a large content of the solid lubricant 12 at the coating surface 10b (50 to 95 wt%). And it will be comprised so that content of the binding resin 11 and the solid lubricant 12 may change continuously from the film interface 10a to the film surface 10b.

  Here, the conditions for the centrifugation process are determined by a curve P shown in FIG. 8 obtained by a predetermined formula. That is, this curve P represents the relationship between the rotation speed R of the piston 1 and the rotation time T when the thickness t of the coating interface 10a is set to be 1 μm. The reason why the range of the curve P is set to 200 to 1000 rpm is that the rotation time t becomes too long at 200 rpm or less, and conversely, the paint 10a itself applied to the piston 1 at 1000 rpm or more. This is because they will leave.

  From this point of view, it is considered that 300 to 500 rpm is optimal as the rotation speed R that does not increase the rotation time t and does not involve the risk of the paint 10x itself being detached. This is because the rotation time t can be greatly shortened from 300 rpm, and at 600 rpm or more, the amount of shortening of the rotation time t obtained with respect to the increased risk of the paint 10a being detached is small.

  Then, finally, baking is performed about the film formation coating material 10x which finished the above-mentioned centrifugation process (baking process S5 shown in FIG. 4). Specifically, the piston 1 after completion of the centrifugal separation treatment is put into a drying furnace and heated under conditions such as 180 ° C. for 30 minutes or 200 ° C. for 20 minutes. The solid composition 10 is formed by curing the coating composition while volatilizing the solvent.

  As described above, in the present embodiment, for the single coating composition, the solid lubricating coating 10 is formed by performing the centrifugal separation process using the specific gravity difference of the components contained therein. In the solid lubricant coating 10, the coating interface 10a has a large content of the binding resin 11 (the content of the solid lubricant 12 is 50 wt% or less (the content of the binding resin 11 is 50 wt% or more)), and the coating surface 10b Can obtain a distribution in which the content of the solid lubricant 12 is increased (the content of the solid lubricant 12 is 50 to 95 wt%). As a result, it is possible to obtain a piston having a solid lubricant film that combines the characteristics that the upper layer is easily worn and the lower layer is less likely to be worn, and sufficient bondability.

  In addition, since the distribution of the contained components is adjusted by the centrifugal separation process in forming the solid lubricating coating 10, the piston 1 to which the coating composition (the coating forming coating 10x) is applied is simply rotated. It is possible to form a desired solid lubricant film by this extremely simple method. Thereby, it will be used also for favorable productivity and reduction of manufacturing cost.

  9 and 10 show a modification of the first embodiment of the present invention, in which the coating method of the film-forming paint 10x in the first embodiment is changed.

  That is, in this modification, in the manufacturing process of the piston 1 in the first embodiment, the piston 1 is molded and processed (molding process S1 shown in FIG. 9), and this is washed and dried (see FIG. 9). In the cleaning step S2), the film forming paint 10x is applied to the surfaces of the skirt portions 7 and 8 not by the air spray but by so-called screen printing (film forming step S3 shown in FIG. 9).

  Specifically, as shown in FIG. 10, a film forming paint 10 x is placed on a screen 26 stretched on a predetermined frame member 25, and a squeegee 27 is pressed against the screen 26 so as to rub the screen 26. By moving the film, the film-forming paint 10x is transferred to the surfaces of the skirt portions 7 and 8 through the screen 26.

  Thereafter, similarly to the first embodiment, after the centrifugal treatment is performed on the coating composition by rotating the piston 1 (centrifugal treatment step S4 shown in FIG. 9), the piston 1 is dried in a drying furnace. And firing under the same conditions as in the first embodiment (firing step S5 shown in FIG. 9).

  As described above, in this modified example, the application of the film-forming coating material 10x is performed by the screen printing, so that the same operational effects as those of the first embodiment can be obtained. It is also used to improve the yield of the paint 10x.

  In other words, since the air spray is applied by spraying, the air spray is applied to a coating that is not applied to the surfaces of the skirt portions 7 and 8 (for example, applied to the masking portions applied to the ring grooves 6b to 6d, etc.). However, in the case of the screen printing, since all of the coating is applied to the surfaces of the skirt portions 7 and 8, the yield of the coating film-forming coating 10x is improved. It becomes possible.

  FIGS. 11-13 shows 2nd Embodiment, such as a piston of the internal combustion engine which concerns on this invention, and changes the formation method of the solid lubricating film 10 in the said 1st Embodiment.

  That is, in this embodiment, the solid lubricating coating 10 in the first embodiment is not a single coating composition, but a first coating composition containing a large amount of binding resin 11 (binding resin: 50 wt. % (Solid lubricant: 50 wt% or less)) and a second coating composition containing a large amount of solid lubricant 12 (solid lubricant: 50-95 wt% (binding resin: 5-50 wt%)). To do.

  This is because each skirt portion of the piston 1 in which the molding and the like (processing step S1 shown in FIG. 11) and the cleaning and the like (cleaning step S2 shown in FIG. 11) are performed in the piston manufacturing process of the first embodiment. Two types of the first film forming paint 10y and the second film forming paint 10z are simultaneously applied to the surfaces 7 and 8 using the two spray guns 31 and 32 (film forming step S3 shown in FIG. 11). This is formed by firing (firing step S5 shown in FIG. 11).

  Specifically, as shown in FIG. 12, the first film forming paint 10y sprayed by the first spray gun 31, which is one of the spray guns, is disposed adjacent to the first spray gun 31 at a predetermined interval. The piston 1 placed on the turntable (not shown) is placed in a range where the second coating gun 10z sprayed by the second spray gun 32, which is the other spray gun, overlaps, and the turntable is rotated. By doing so, the first and second coating forming paints 10y and 10z are applied to the surfaces of the skirt portions 7 and 8, respectively.

  Then, as shown in the figure, the spray amount of the paint 10y by the first spray gun 31 becomes a curve Y, while the spray amount of the paint 10z by the second spray gun 32 becomes a curve Z. As represented by the curve X obtained by polymerization, the total spray amount in which the spray amounts of both the paints 10y and 10z are combined is constant in the overlap section L of the both paints 10y and 10z. The fixed both paints 10y and 10z are applied to the surfaces of the skirt portions 7 and 8, respectively.

  At this time, the piston 1 is rotated and moved from the left side to the right side in FIG. That is, at the time of the rotation, the second coating film forming paint 10z is sprayed from the first spray gun 31 side where the front end in the rotation direction of the skirt portions 7 and 8 sprays the first coating forming paint 10y with respect to the overlap section L. The piston 1 is rotationally moved so as to enter the second spray gun 32 side. As a result, in the coating film formed by applying both the paints 10y and 10z, the content (concentration) of the solid lubricant 12 from the coating interface 10a to the coating surface as shown by the curve Q shown in FIG. It will increase continuously over 10b. As a result, it is possible to obtain a piston including the solid lubricant film 10 having a distribution in which the content of the binding resin 11 is large in the film interface 10a and the content of the solid lubricant 12 is increased in the film surface 10b.

  Further, at this time, by changing the feed speed of the piston 1, different characteristics as shown in FIG. 13 can be obtained for the solid lubricant film 10. This figure shows the increase characteristic of the concentration d of the solid lubricant 12 as the film thickness t increases, with the state of the film thickness t = 0 being the surface position (interface position) of each skirt portion 7 and 8. If the feed rate is constant, the concentration d of the solid lubricating film 10 also increases proportionally (see the straight line A in the figure). On the other hand, when the feed rate is gradually increased, the concentration d of the solid lubricating coating 10 increases so that the amount of change decreases from the coating interface 10a to the coating surface 10b (see curve B in the figure). When the feed rate is gradually reduced, the concentration d of the solid lubricating coating 10 increases so that the amount of change increases from the coating interface 10a to the coating surface 10b (see curve C in the figure).

  From the above, by adjusting the coating amount of the plurality of first and second coating compositions as in this embodiment, even without using a single coating composition as in the first embodiment, The coating interface 10a has a high content of the binding resin 11 (the content of the solid lubricant 12 is 50 wt% or less (the content of the binding resin 11 is 50 wt% or more)), and the coating surface 10b contains the solid lubricant 12 The solid lubricant film 10 having a distribution in which the amount increases (the content of the solid lubricant 12 is 50 to 95 wt%) can be formed, and the upper layer easily wears and the lower layer does not easily wear, and has sufficient bonding properties. A piston with a solid lubricating coating is obtained.

  In the case of the present embodiment, the solid lubricating film 10 is formed by simultaneously applying a plurality of first and second coating compositions at the same time. It is possible to arbitrarily change the concentration d of the lubricant 12, which is also used for forming a more versatile solid lubricant film 10.

Next, a modified example of the second embodiment of the present invention will be described . The application amount of the first and second coating compositions (first and second coating forming paints 10y and 10z) in the second embodiment. The adjustment means is changed.

  That is, in this modification, when the first and second coating forming paints 10y and 10z are simultaneously applied in the coating forming step S3 of the second embodiment, the spray amount itself of the first and second spray guns 31 and 32 is itself. By adjusting the above, the first and second coating forming paints 10y and 10z are applied to the skirt portions 7 and 8 of the piston 1.

  Specifically, the piston 1 that has been subjected to the above-described cleaning or the like is placed on the turntable 21 as in the first embodiment, and first the first spray as shown by both curves Y and Z shown in FIG. Both the paints 10y and 10z are applied in a state where the spray amount of the first film-forming paint 10y by the gun 31 is increased and the spray amount of the second film-forming paint 10z by the second spray gun 32 is reduced. As the time elapses, the spray amount ratio of both the spray guns 31 and 32 is reversed, that is, the spray amount of the second film forming paint 10y by the first spray gun 31 is small and the second film by the second spray gun 32 is used. The spray amount of both the spray guns 31 and 32 is adjusted so that the spray amount of the forming paint 10z increases.

  Thus, also by adjusting the spray amount itself of both the spray guns 31 and 32, the coating interface 10a has a large content of the binding resin 11 (the content of the solid lubricant 12 is 50 wt% or less (the binding resin). 11), and the coating surface 10b has a distribution in which the content of the solid lubricant 12 increases (the content of the solid lubricant 12 is 50 to 95 wt%). It is possible to obtain the same effects as those of the second embodiment.

  The present invention is not limited to the configuration of each of the embodiments and the like. For example, regarding a specific aspect of the centrifugation process, in addition to the aspect disclosed in the first embodiment, the process such as the rotation speed is performed. Any mode can be adopted as long as the conditions are satisfied, and can be arbitrarily set according to the capacity of the equipment.

  Moreover, also about the said baking process S5, about concrete conditions, it is arbitrary and can be changed freely according to the specification etc. of a solid lubricating film.

  Further, the washing step S2 before the film forming step S3 is not necessarily limited to the washing with water. For example, when a lubricating oil is used in the processing step S1, a degreasing treatment and a chemical conversion treatment are performed. Also good.

  The technical ideas other than the invention described in the scope of the claims ascertained from the respective embodiments will be described below.

(A) The piston of the internal combustion engine according to claim 1,
The piston of the internal combustion engine, wherein the solid lubricant content in the solid lubricant film is proportionally increased from the interface contacting the skirt portion to the surface.

(B) The piston of the internal combustion engine according to claim 1,
The piston of an internal combustion engine, wherein the content of the solid lubricant in the solid lubricant film increases so as to decrease from the interface contacting the skirt portion to the surface.

(C) The piston of the internal combustion engine according to claim 1,
The content of the solid lubricant in the solid lubricating coating, a piston for an internal combustion engine, characterized in that it is increased as from the interface in contact with the skirt portion ing large variation over the said surface.

(D) A method of manufacturing a piston for an internal combustion engine according to claim 3,
A method of manufacturing a piston for an internal combustion engine, comprising: cleaning the piston after cutting, and then applying the coating composition.

1 ... Piston 7 ... Thrust side skirt (skirt)
7a ... streak 8 ... anti-thrust side skirt part (skirt part)
8a ... streak 10 ... solid lubricating coating 10a ... coating interface (interface contacting the skirt)
10b ... coating surface (surface in sliding contact with cylinder wall)
10x: Film-forming paint (film composition)
10y ... 1st film formation coating material (1st film composition)
10z Second coating film-forming paint (second coating composition)
DESCRIPTION OF SYMBOLS 11 ... Binding resin 12 ... Solid lubricant S1 ... Processing process S2 ... Cleaning process S3 ... Film formation process S4 ... Centrifugation process S5 ... Firing process

Claims (2)

A piston of an internal combustion engine having a solid lubricating film on a skirt portion where streaks are formed,
The solid lubricating coating is
At least one of a polyamide-imide resin, a polyimide resin or an epoxy resin as a binding resin;
A solid lubricant comprising at least molybdenum disulfide;
Containing
While the interface contacting the skirt portion is set so that the content of the solid lubricant is 50 wt% or less,
For the surface that is in sliding contact with the cylinder wall of the engine, the solid lubricant content is set to 50 to 95 wt%,
Between the interface in contact with the skirt portion and the surface in sliding contact with the cylinder wall, the amount of change in the solid lubricant content is small on the interface side in contact with the skirt portion, and the surface in sliding contact with the cylinder wall A piston for an internal combustion engine configured to continuously change from an interface in contact with the skirt portion to a surface in sliding contact with the cylinder wall so that the amount of change increases on the side . A piston of an internal combustion engine in which a solid lubricating film is formed on a skirt,
The solid lubricating coating is
Containing a resin that is a binding resin and a solid lubricant having a specific gravity greater than that of the resin;
While the interface contacting the skirt portion is set so that the content of the solid lubricant is 50 wt% or less,
For the surface that is in sliding contact with the cylinder wall of the engine, the solid lubricant content is set to 50 to 95 wt%,
Between the interface in contact with the skirt portion and the surface in sliding contact with the cylinder wall, the amount of change in the solid lubricant content is small on the interface side in contact with the skirt portion, and the surface in sliding contact with the cylinder wall A piston for an internal combustion engine configured to continuously change from an interface in contact with the skirt portion to a surface in sliding contact with the cylinder wall so that the amount of change increases on the side .

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