JP2013136960A - Piston for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve lubricity at low cost, while suppressing increase in weight of a piston.SOLUTION: A plurality of striations 24 are formed in a sliding contact surface of a piston skirt 12 of a piston. Each striation 24 is an undulation including a protrusion 26 and a valley 28, wherein a lubrication buildup 30 is selectively provided at only the protrusion 26. In other words, the lubrication buildup 30 forms a line-like shape circulating around the sliding contact surface of the piston skirt 12 along the protrusion 26. The lubrication buildup 30 is made of silver (Ag), silver alloy, copper (Cu), or copper alloy. A convex part 42 made of resin may intervene between the protrusion 26 and the lubrication buildup 30.

Description

  The present invention relates to a piston for an internal combustion engine that reciprocates in a cylinder in the internal combustion engine.

  An automobile travels by converting a driving force generated by an internal combustion engine supplied with fuel into a rotational driving force to rotate a tire. Recently, various attempts have been made to improve the fuel consumption rate (fuel consumption) of an internal combustion engine in an automobile having such a configuration. This is because the amount of fuel consumption is reduced, which can save energy and contribute to the protection of the global environment.

  One such attempt is to reduce the sliding resistance between the inner wall of the cylinder of the internal combustion engine (bore or inner wall of the sleeve) and the piston that reciprocates within the cylinder. When the sliding resistance is small, it is easy for the piston to reciprocate. For this reason, the driving force for reciprocating the piston is reduced, which in turn reduces the fuel consumption.

  In order to reduce sliding resistance, it is known to provide a layer containing a highly lubricious substance on the inner wall or piston skirt of the cylinder, thereby improving the lubricating performance of the inner wall or piston skirt. For example, in the patent document 1, the present applicant forms a streak on the sliding contact surface of the piston skirt, and coats the streak with a lubricious film made of silver, a silver alloy, copper, or a copper alloy. is suggesting.

In Patent Document 2, MoS ₂ , WS ₂ , graphite, polytetrafluoroethylene, boron nitride, cluster diamond, silicon, etc. are dispersed in a dispersion medium to prepare a paint or ink, which is then used for silk printing or pad printing. A technique for forming a convex solid lubricating film having a predetermined pattern by applying to a piston skirt by spraying or the like is disclosed.

International Publication No. 2011/115152 Panfrett JP 2005-320934 A

Silver or silver alloys are generally expensive and heavy. For this reason, if a film made of silver or a silver alloy is formed on the entire sliding contact surface of the piston skirt, the cost increases and the weight of the piston increases. Although copper or copper alloy is relatively inexpensive and lightweight among metals, MoS ₂ , WS ₂ , graphite, polytetrafluoroethylene, boron nitride, cluster diamond, which are the materials of the film described in Patent Document 2, Compared to silicon or the like, it is heavier and it is not easy to avoid an increase in piston weight.

  In order to avoid such problems, it is also conceived to form a film having a predetermined pattern as described in Patent Document 2. In this case, since the coating amount of the paint or ink is reduced, it is considered that the total amount of the formed film is reduced.

  However, even if a film made of silver or a silver alloy is formed in a pattern shape as described in Patent Document 2, the coating amount of paint or ink is not reduced so much. In addition, since silver, silver alloy, copper, and copper alloy are heavier than the above-described materials, it is not easy to largely suppress the increase in the weight of the piston while forming a film made of such a metal.

  The present invention has been made to solve the above-described problems, and it is possible to suppress an increase in the weight of the piston while forming a lubricating portion made of silver, a silver alloy, copper and a copper alloy, and An object of the present invention is to provide a piston for an internal combustion engine that can contribute to an improvement in fuel consumption of the internal combustion engine while avoiding seizure.

To achieve the above object, the present invention provides an internal combustion engine piston that reciprocates in a cylinder of an internal combustion engine.
A plurality of lubricating build-up portions made of at least one of silver, silver alloy, copper, and copper alloy, and having a dotted or linear shape, are provided on the sliding contact surface of the piston skirt. It is characterized by.

  In other words, in the present invention, the lubricating build-up portion is selectively provided only in the portion involved in the sliding contact. For this reason, the amount of metal (silver, silver alloy, copper or copper alloy) used to obtain the lubricous build-up portion is greatly reduced as compared with the case where the lubrication build-up portion is provided over the entire piston skirt. be able to.

  And since the usage-amount of a metal reduces, cost can be reduced. In addition, since the lubricating build-up portion is selectively provided only on the convex portion, it is possible to avoid a significant increase in the weight of the piston for the internal combustion engine.

  In addition, providing a lubricous build-up part made of silver, silver alloy, copper or copper alloy keeps the lubricating oil well between the inner wall of the cylinder and the piston skirt, and adhesion between the two. What happens is avoided. This effectively avoids the occurrence of seizure. This effect is particularly remarkable when the piston for the internal combustion engine is in sliding contact with the inner wall of the FC sleeve or the Al sleeve.

  Furthermore, since the sliding contact portion is constituted by the lubricated build-up portion, it is not particularly necessary to form streaks on the sliding contact surface of the piston skirt. In this case, the processing operation for forming the streak becomes unnecessary.

  An intermediate layer may be interposed between the slidable contact surface of the piston skirt and each of the lubricating build-up portions. And it is preferable to provide this intermediate | middle layer as a convex part, and to provide a lubricous buildup part only on this convex part.

  In this case, the lubricating build-up portion is in a state in which the convex portion has entered therein. For this reason, the amount of metal used is further reduced.

  The intermediate layer may cover the entire sliding contact surface of the piston skirt. In this case, the sliding contact surface of the piston skirt may be a smooth surface, and an intermediate layer may be formed on the smooth sliding contact surface. Furthermore, it is possible to provide a convex portion by raising a part of the intermediate layer. Of course, a striation may be formed on the sliding contact surface of the piston skirt, and an intermediate layer as a convex portion may be provided by covering the protrusion (convex portion) of the striation with a resin.

  Such an intermediate layer can be formed using a resin. In particular, when a convex portion is provided from polyimide resin, polyamideimide resin, epoxy resin, nylon-6 resin, nylon-6,6 resin, etc., the bonding force between the piston skirt and the lubricated build-up portion becomes strong. Therefore, it is preferable.

The intermediate layer may contain various solid lubricants such as molybdenum disulfide (MoS ₂ ), boron nitride (BN), and graphite in addition to the above-described resin. In this case, even if the intermediate layer is exposed, the lubricating performance is maintained by the solid lubricant contained in the intermediate layer.

The entire sliding contact surface of the piston skirt is covered with resin, and a part of the resin is raised so as to be provided with a convex portion, and a lubricating overlay is provided on the convex portion.

  According to the present invention, a plurality of lubricated built-up portions made of at least one of silver, silver alloy, copper, and copper alloy are provided in a slidable contact surface of the piston skirt as a dotted shape or a linear shape. Therefore, the amount of metal (silver, silver alloy, copper, or copper alloy) used to obtain the lubricated build-up portion can be reduced. Along with this, the cost for providing the lubricated built-up portion is reduced. Further, since the weight of the piston for the internal combustion engine is avoided from being greatly increased, it is possible to avoid an increase in the driving force for reciprocating the piston for the internal combustion engine. This can contribute to an improvement in fuel consumption of the internal combustion engine.

  In addition, since the lubricating build-up portion is made of at least one of silver, silver alloy, copper, and copper alloy, the lubricating oil is well held between the piston skirt and the inner wall of the cylinder, and between the two. It is avoided that adhesion occurs. For this reason, it is possible to avoid seizure.

1 is a schematic overall perspective view of a piston according to a first embodiment of the present invention. It is a side view of the piston shown in FIG. It is a cross-sectional schematic diagram which expands and shows the surface layer part vicinity of the piston skirt which comprises the said piston. It is a cross-sectional schematic diagram which expands and shows the surface layer part vicinity of the piston skirt which comprises the piston which concerns on the modification of 1st Embodiment. It is a side view of the piston which concerns on 2nd Embodiment of this invention. It is a cross-sectional schematic diagram which expands and shows the surface layer part vicinity of the piston skirt which comprises the piston of FIG. It is a cross-sectional schematic diagram which expands and shows the surface layer vicinity vicinity of the piston skirt which comprises the piston which concerns on the modification of 2nd Embodiment.

  Hereinafter, preferred embodiments of a piston for an internal combustion engine according to the present invention (hereinafter sometimes simply referred to as “piston”) will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic overall perspective view of a piston 10 according to the first embodiment of the present invention, and FIG. 2 is a side view thereof. The piston 10 has a pair of piston skirts 12 and 12 at a lower portion thereof, and wall portions 14 and 14 extending along a substantially vertical direction are interposed between the piston skirts 12 and 12. Each of the wall portions 14 and 14 is provided with pin boss portions 16 and 16 so as to protrude in the horizontal direction, and a piston pin for inserting a piston pin (not shown) into each of the pin boss portions 16 and 16. Holes 17 are formed through. The piston pin is passed through a through hole formed in a small end portion of a connecting rod (connecting rod) (not shown), thereby supporting the connecting rod.

  An oil ring groove 18, a first piston ring groove 20, and a second piston ring groove 22 are formed in this order in the upper part of the piston skirts 12 and 12 from the bottom to the top. Of course, the oil ring groove 18, the first piston ring groove 20, and the second piston ring groove 22 are formed so as to go around the head of the piston 10 along the circumferential direction.

  The piston 10 configured as described above is made of AC2A, AC2B, AC4B, AC4C, AC4D, AC8H, A1100 (all aluminum alloys defined in JIS), or an aluminum alloy such as an Al—Cu alloy.

  As shown in an enlarged view in FIG. 3, in the first embodiment, a streak 24 is provided on the sliding contact surface of the piston skirt 12. Here, the arrow X direction in FIG. 3 corresponds to the arrow X direction in FIGS. 1 and 2, and the same applies to the subsequent drawings.

  The streak 24 is a swell having a raised protrusion 26 and a recessed valley 28, and is formed by machining the piston skirt 12 along its circumferential direction. The height H of the protrusions 26 (convex parts) is in the range of 0.001 to 0.1 mm, and the interval between the adjacent protrusions 26 and 26, that is, the pitch P is in the range of 0.1 to 0.5 mm. It is preferable to be within. A more preferable range of the height H is 0.008 to 0.012 mm, and a more preferable range of the pitch P is 0.25 to 0.3 mm.

  Here, in the first embodiment, the lubricating build-up portion 30 is provided only on the protrusion 26 in the streak 24. That is, the lubricous build-up portion 30 is not provided in the valley portion 28 constituting the streak 24, and extends linearly along the circumferential direction of the piston skirt 12 according to the locus of the protrusion portion 26.

  The lubricity build-up portion 30 is made of any of silver, silver alloy, copper, or copper alloy. Both of these show excellent lubrication performance when the piston skirt 12 is in sliding contact with the inner wall of the bore of the cylinder block or the inner wall of the cylinder sleeve. Note that preferable examples of the silver alloy include an Ag—Sn alloy and an Ag—Cu alloy, and preferable examples of the copper alloy include a Cu—Sn alloy, a Cu—Zn alloy, and a Cu—P alloy.

  When the lubricating build-up part 30 is made of silver or a silver alloy, the purity of silver is preferably 60% by weight or more. If it is less than 60% by weight, the thermal conductivity of the lubricated built-up portion 30 is slightly low, and therefore it is not easy to form a smooth wear surface, thereby reducing the friction loss (Psf) of the internal combustion engine. It tends to be less effective. The purity of silver is more preferably 80% by weight or more.

  On the other hand, when the lubricating build-up part 30 is made of copper or a copper alloy, the purity of copper is preferably 70% by weight or more, particularly preferably 80% by weight or more for the same reason as described above.

  Here, the purity of silver is defined as “% by weight of silver contained in the lubricating buildup 30”. When the lubricating build-up part 30 is formed by plating, the component contained in the lubricous build-up part 30 is approximately silver, and therefore the purity of silver is approximately 100%. Moreover, when the lubricous build-up part 30 made of a silver alloy is formed, the purity of silver is obtained as the weight percentage of silver contained in the lubricous build-up part 30. Furthermore, when obtaining the lubricity build-up part 30 which consists of a sintered compact after apply | coating a silver particle, the purity of silver is defined as a ratio of the silver particle in a paste. The same applies to the purity of copper.

  In addition, it is not particularly necessary to provide all of the lubricating build-up portion 30 from the same metal. For example, the protruding portion 26 of one streak 24 is covered with a lubricating buildup portion 30 made of silver, and the protruding portion 26 of another streak 24 adjacent to the streak 24 is made of a copper alloy. You may make it provide from another kind of metal, such as coat | covering with the build-up part 30. FIG.

  In addition, the thickness of the lubricating build-up portion 30 is not particularly limited, but if it is too small, the lubricous build-up portion 30 will be worn in a relatively short period of time, and the protrusion 26 that is the base is exposed. Will do. On the other hand, if it is excessively large, the lubricating build-up portion 30 becomes heavy, so that the driving force for reciprocating the piston 10 becomes large. In order to avoid the occurrence of the above inconveniences, it is preferable to set the thickness of the lubricating build-up portion 30 to 0.5 to 100 μm.

  The lubricity build-up part 30 is formed by, for example, subjecting the piston 10 before being incorporated into the internal combustion engine to etching with an alkaline solution, acid cleaning, and two zinc replacement treatments, followed by plating. Can do. As the plating bath, a silver cyanide plating bath or a copper cyanide plating bath may be employed. Of course, when a silver alloy plating film or a copper alloy plating film is formed, the plating conditions may be changed so as to obtain such an alloy film.

  Thus, when performing a plating process, the trough part 28 of the stripe 24 is coat | covered with a mask. Thereby, the lubricating build-up part 30 can be selectively provided with respect to the projection part 26 which is a convex part.

  Or you may make it form the lubricous buildup part 30 which consists of a sintered compact obtained by using microparticles as a starting material. As the fine particles, so-called nanoparticles having an average particle diameter of 1 to 80 nm, more preferably 30 to 80 nm are suitable. The lubricating build-up portion 30 formed from such nanoparticles has a strong bonding force with respect to the piston skirt 12, and eventually becomes difficult to drop off from the piston skirt 12.

  Then, the nanoparticles are dispersed in an appropriate dispersion medium (preferably a polar dispersion medium) such as terpineol, nonanol, ethylene glycol, propylene glycol monomethyl ether acetate, or methyl ethyl ketone to prepare a paste having a viscosity of about 10 cp. .

  Next, the paste is applied to the piston skirt 12. For application, a known application method such as screen printing or pad printing can be employed.

  At this time, the valley portion 28 of the streak 24 is covered with a screen. As a result, the paste is prevented from being applied to the troughs 28, and the paste is selectively applied only to the protrusions 26 that are convex portions.

  Next, the paste is heated together with the piston 10. The suitable heating temperature in this case is 160-240 degreeC. Thereby, the dispersion medium in the paste is volatilized and the nanoparticles are fused. That is, sintering occurs, and the lubricating build-up part 30 made of a sintered body of nanoparticles is obtained. Since the paste is applied only to the protrusions 26, the lubricating build-up part 30 is also selectively formed only on the protrusions 26.

  When nanoparticles are used, it is possible to sinter in a relatively low temperature range of 160 to 240 ° C. to form the lubricous built-up portion 30 as described above. Therefore, the piston skirt 12 made of an aluminum alloy is avoided from becoming high temperature, and therefore, it is possible to avoid affecting the mechanical strength and the like of the piston skirt 12.

  As described above, according to the first embodiment, the lubricity build-up portion 30 is selectively provided only on the projecting portion 26 that is a convex portion, so that the metal (silver, silver) for obtaining the lubricity build-up portion 30 is obtained. Alloy, copper or copper alloy). Therefore, the cost is reduced. In addition, since the lubricating build-up portion 30 exists only in the protrusion 26, it is possible to avoid a significant increase in the weight of the piston 10.

  When the internal combustion engine is assembled and operated, substantially only the projections 26 are in sliding contact with the inner wall of the cylinder (the inner wall of the cylinder bore or the inner wall of the cylinder sleeve) via the lubricating oil. As described above, the protruding portion 26 is provided with the lubricating built-up portion 30, and the lubricating built-up portion 30 exhibits a sufficient lubricating action between the inner wall of the cylinder and the piston skirt 12.

  That is, in the internal combustion engine, the slidable contact surface of the piston skirt 12 slidably contacts, for example, an inner wall of an FC (gray cast iron) sleeve or an Al sleeve in the cylinder. In the internal combustion engine having such a configuration, the sum of the thermal conductivity of the lubricity build-up portion 30 and the thermal conductivity of the FC sleeve or the Al sleeve is 350 W / m · K or more, and the lubrication build-up is achieved. The absolute value of the difference in Young's modulus with respect to the FC sleeve or the Al sleeve of the portion 30 is 10 GPa or more. According to the earnest study by the present inventors, in this case, the lubricating oil is satisfactorily held in the minute clearance between the sleeve and the piston skirt 12, and adhesion occurs between the sleeve and the piston skirt 12. Is avoided. For this reason, the occurrence of seizure can be effectively avoided, and the friction loss of the internal combustion engine can be greatly reduced.

  As described above, the lubricating build-up portion 30 is selectively provided only on the protruding portion 26, thereby reducing the cost and suppressing the increase in the weight of the piston 10 and exhibiting a sufficient lubricating action. Can do.

  Instead of providing the protrusions with the protrusions 26 of the streak 24, the protrusions may be provided with resin. This will be described as a modification of the first embodiment.

  In this modification, as shown in an enlarged cross-sectional view in FIG. 4, the sliding contact surface of the piston skirt 12 is formed as a smooth surface, and the resin layer 40 (intermediate layer) is fixed to the smooth sliding contact surface. ing. The resin layer 40 is formed with protruding portions 42 so as to form a plurality of linear shapes that circulate around the sliding contact surface. In this case, the convex portion 42 is wide on the bottom side close to the piston skirt 12 and narrow on the top side away from the piston skirt 12. For this reason, a streak shape similar to the streak 24 is formed by the plurality of linear-shaped convex portions 42.

  The resin constituting the resin layer 40 (convex portion 42) is preferably of a type that improves the bonding force between the lubricated built-up portion 30 and the piston skirt 12. Preferable examples of such materials include polyimide resin, polyamideimide resin, epoxy resin, nylon-6 resin, nylon-6,6 resin and the like. It may further contain a solid lubricant described later.

  In this modified example, since the convex portion 42 made of resin is interposed between the sliding contact surface of the piston skirt 12 and the lubricating buildup portion 30, the lubrication buildup portion 30 is formed. The amount of silver, silver alloy, copper or copper alloy used is reduced. As a result, the cost can be reduced and the weight of the piston 10 can be prevented from greatly increasing.

  In addition, in this modification, when forming the lubricating buildup portion 30 using nanoparticles as a starting material, a dispersion medium for obtaining a paste is provided between the sliding contact surface of the piston skirt 12 and the lubricating buildup portion 30. It is preferable to select one that can swell the intervening convex portions 42 (resin). Specific examples thereof include N-methylpyrrolidone, polyvinylpyrrolylone, trichloroethylene, carbon tetrachloride and the like.

  In this case, when a paste is applied on the convex portion 42 in order to form the lubricous build-up portion 30, the resin swells under the action of the dispersion medium. As a result, an intermixing layer in which silver particles are diffused is formed at the interface between the resin and the paste. The mutual mixing layer causes a so-called anchor effect between the convex portion 42 and the lubricous build-up portion 30, so that the bonding force of the lubricous build-up portion 30 to the convex portion 42 is further strengthened.

  Further, the sliding contact surface of the piston skirt 12 is a smooth surface, and a plurality of linear lubricated build-up portions 30 are provided on the smooth sliding contact surface directly or through the smooth resin layer 40 without the convex portion 42. You may do it.

  In addition, the resin layer 40 may be provided as a linear shape only in a portion where the lubricous build-up portion 30 is provided.

  Next, a second embodiment will be described. In addition, the same referential mark is attached | subjected to the same component as the component shown by FIGS. 1-4, and the detailed description is abbreviate | omitted.

  FIG. 5 is a side view of the piston 50 according to the second embodiment. In this case, the lubricated build-up part 52 is provided on the sliding contact surface of the piston skirt 12 as a plurality of dot-like shapes. In addition, the lubricous buildup part 52 consists of silver, a silver alloy, copper, or a copper alloy similarly to 1st Embodiment.

  Although not shown in FIG. 5 for easy understanding, as shown in an enlarged view in FIG. 6, in the second embodiment, the streak 24 is formed in the piston skirt 12. On the other hand, the lubricating build-up portion 52 is randomly arranged regardless of whether it is the convex portion (projection portion 26) or the valley portion 28 of the streak 24. That is, in the second embodiment, the formation position of the lubricous build-up portion 52 is not limited to the protrusion 26 (convex portion).

  However, in the second embodiment, since the lubricous build-up portion 52 is provided in a dot shape, the volume of each lubricous build-up portion 52 is small. That is, in the first embodiment, the amount of metal (silver, silver alloy, copper, or copper alloy) used is reduced by providing the lubricated build-up portion 30 only at positions that are involved in actual sliding contact. However, in the second embodiment, the amount of metal used is reduced by reducing the volume of each lubricous build-up part 52, and hence the sum of the volumes of all the lubrication build-up parts 52. .

  For this reason, also in 2nd Embodiment, while the cost can be reduced similarly to 1st Embodiment, the effect that it can avoid that the weight of piston 50 increases greatly is acquired.

  In addition, as a method of forming the lubricous build-up portion 52 in a dot shape, a known coating method such as the above-described plating treatment, screen printing, or pad printing can be used. When the plating process is performed, the piston skirt 12 is covered with a mask, and when screen printing or pad printing is performed, the lubricating build-up portion 52 can be provided in a dot shape.

  Further, it is not essential to form the streak 24. That is, the slidable contact surface of the piston skirt 12 may be a smooth surface, and the point-like lubricating buildup portion 52 may be provided on the smooth slidable contact surface. In this case, the recessed part formed between the lubricity build-up parts 52 and 52 plays the role which hold | maintains lubricating oil.

  Furthermore, an intermediate layer may be interposed between the sliding contact surface of the piston skirt 12 and the lubricated build-up portion 52. This will be described as a modification of the second embodiment.

  In this modification, as shown in an enlarged cross-sectional view in FIG. 7, the smooth sliding contact surface of the piston skirt 12 is entirely covered with the intermediate layer 54, and a point-shaped lubricating meat is formed on the intermediate layer 54. A raised portion 52 is provided.

The intermediate layer 54 may be formed of an inorganic substance exhibiting good lubricity, such as MoS ₂ or graphite, but may be polyimide resin, polyamideimide resin, epoxy resin, nylon-6 resin, nylon-6,6 resin. You may make it form from resin, such as. In the former case, the lubricating performance is maintained by the intermediate layer 54 even if the lubricating build-up portion 52 should fall off (peel) from the intermediate layer 54. Further, in the latter case, an advantage is obtained that the joining force between the lubricating build-up portion 52 and the piston skirt 12 is improved.

  The intermediate layer 54 may further contain a solid lubricant in addition to the resin material. In other words, the intermediate layer 54 may be a mixed layer of an inorganic substance exhibiting lubricity and the resin as described above.

Known solid lubricants may be blended, and suitable examples thereof include molybdenum disulfide (MoS ₂ ), boron nitride (BN), and graphite (C). In this case, the joining force between the lubricating buildup portion 52 and the piston skirt 12 is improved, and even if the intermediate layer 54 comes into sliding contact with the inner wall of the cylinder, the lubricating performance is maintained by the solid lubricant. The

  As described above, the metal for obtaining the lubricating buildup portion 52 while maintaining the lubricity by the intermediate layer 54 or improving the bonding force between the lubrication buildup portion 52 and the piston skirt 12. The amount of use can be reduced. As a result, the cost can be reduced and the weight of the piston 50 can be prevented from greatly increasing.

  Any of the inorganic substances and resins as described above is inexpensive and lightweight. For this reason, even if the entire sliding contact surface of the piston skirt 12 is covered with the intermediate layer 54, the cost increases significantly, and the piston 50 It is avoided that the weight of is excessively large. Moreover, when the entire sliding contact surface of the piston skirt 12 is covered with the intermediate layer 54, the operation is easier and simpler than when the intermediate layer 54 is selectively provided on a part of the sliding contact surface of the piston skirt 12. The advantage is obtained.

  Note that the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the invention.

  For example, also in the second embodiment, the lubricating build-up portion 52 may be formed in a dot shape only on the protrusion portion 26 of the streak 24. In other words, in this case, a part of the protrusion 26 that circulates around the sliding contact surface of the piston skirt 12 is covered in a dot shape by the lubricating overlay 52.

  Moreover, you may make it form the intermediate | middle layer 54 in a stripe shape similarly to the modification of 1st Embodiment. In this case, what is necessary is just to form the lubricous buildup part 52 in the shape of a dot in the top part of a streak shape.

  Further, in the second embodiment, as in the first embodiment, the sliding contact surface of the piston skirt 12 is a smooth surface, and the smooth sliding contact surface is provided directly on the smooth sliding contact surface or only at the portion where the lubricated buildup portion 52 is provided. A plurality of lubricated build-up portions 52 may be provided through the intermediate layer 54 provided as a dot shape.

  Furthermore, in the modification of the second embodiment, the entire sliding contact surface of the piston skirt 12 is covered with the intermediate layer 54. However, the intermediate layer 54 is selectively formed on a part of the sliding contact surface of the piston skirt 12. It may be provided in a dot shape or a line shape, and the lubricating build-up portion 52 may be selectively provided only on the intermediate layer 54.

DESCRIPTION OF SYMBOLS 10, 50 ... Piston for internal combustion engines 12 ... Piston skirt 24 ... Streaks 26 ... Projection part 28 ... Valley part 30, 52 ... Lubrication build-up part 40 ... Resin layer 42 ... Convex part 54 ... Intermediate layer

Claims (7)

In an internal combustion engine piston that reciprocates in a cylinder of the internal combustion engine,
A plurality of lubricating build-up portions made of at least one of silver, silver alloy, copper, and copper alloy, and having a dotted or linear shape, are provided on the sliding contact surface of the piston skirt. A piston for an internal combustion engine.   The piston for an internal combustion engine according to claim 1, wherein an intermediate layer is interposed between the sliding contact surface of the piston skirt and each of the plurality of lubricated build-up portions.   3. The piston according to claim 2, wherein the intermediate layer is provided as a convex portion on a sliding contact surface of the piston skirt, and the plurality of lubricous build-up portions are provided only on the convex portion. A piston for an internal combustion engine.   3. The internal combustion engine according to claim 2, wherein the intermediate layer covers the entire sliding contact surface of the piston skirt and is interposed between the sliding contact surface and the lubricating build-up portion. Piston.   The piston according to any one of claims 2 to 4, wherein the intermediate layer contains at least a resin.   The piston for an internal combustion engine according to claim 5, wherein the intermediate layer further includes a solid lubricant.   The piston for an internal combustion engine according to claim 6, wherein the solid lubricant is at least one selected from the group consisting of molybdenum disulfide, boron nitride, and graphite.

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