JP5390761B2 - piston - Google Patents

Description

  The present invention relates to a piston, for example, a piston made of FCD (Ferrum Casting Ductile: also called ductile cast iron, spheroidal graphite cast iron, nodular cast iron, etc.) or other cast iron used for internal combustion engines or the like.

  In the case of a piston made of a general aluminum alloy or the like, a piston 10 (see FIG. 5) used for an internal combustion engine or the like, and a cylinder liner (bore) 20 into which the piston 10 is inserted (a cylinder block in the case of a linerless) ( In order to suppress scuffing (scratching generated by locally melting the piston skirt) and seizure, which is a kind of damage caused as a result of sliding between the piston and the piston, as shown in FIG. There is a fact that the surface roughness of the sliding surface 11A that slides with respect to the cylinder liner 20 of the 10 skirt portions 11 must be set to, for example, around 10-point average roughness (RzJIS) = 15 μm.

  For this reason, as shown in FIG. 6, the lubrication state of the sliding surface 11A of the skirt portion 11 is a so-called mixed lubrication state (a state in which fluid lubrication and solid contact (contact between metals) are mixed). The fact is that the frictional force is relatively large.

By the way, in recent years, an FCD piston made of, for example, ductile cast iron or the like instead of an aluminum alloy or the like has been proposed in Patent Document 1 or the like.
JP 2006-112309 A

  The FCD piston as described in Patent Document 1 has excellent heat insulation properties with respect to aluminum alloys and the like, and can improve combustion of an internal combustion engine. For example, it can reduce exhaust harmful substances and fuel consumption. Therefore, there is an advantage that it is excellent in terms of environmental protection and economy.

  However, demands such as environmental protection and economic efficiency should be demanded, and further improvement is required for the FCD piston in order to contribute to the realization thereof.

  The present invention has been made in view of such circumstances, and provides a piston made of cast iron, which has a simple and inexpensive configuration, and which is further excellent in fuel efficiency and can contribute to improvements in environmental protection, economy, and the like. The purpose is to do.

For this reason, the piston according to the present invention is
The piston is made of cast iron and used in the presence of a lubricating substance, and the surface roughness of the base material of the sliding surface of the skirt portion of the piston is in a range of RzJIS = 5.5 μm to 0.5 μm. It is formed.

In the present invention, the sliding surface of the skirt portion of the piston may be subjected to a surface treatment accompanied by a corrosion reaction.
In the present invention, the surface treatment may be a phosphate film treatment.
In the present invention, the cast iron may be spheroidal graphite cast iron.

  ADVANTAGE OF THE INVENTION According to this invention, although it is a simple and cheap structure, it can provide the piston which uses cast iron as a material which is further excellent in fuel-consumption performance and can contribute to improvement of environmental protection, economical efficiency, etc.

  Hereinafter, embodiments according to the present invention will be described with reference to the accompanying drawings. The present invention is not limited to the examples described below.

  The piston 10 made of cast iron such as FCD according to the first embodiment of the present invention will be described in detail with reference to FIGS. 1 to 4.

  Here, as described above, in the case of a piston made of a general aluminum alloy or the like, a slide between the piston 10 and a cylinder liner (bore) 20 (see FIG. 6) into which the piston 10 is inserted is inserted. In order to suppress scuffing or seizure, which is a kind of damage caused as a result of movement, as shown in FIG. 5, the surface roughness of the sliding surface 11A that slides against the cylinder liner 20 of the skirt portion 11 of the piston 10 is reduced. For example, there is a fact that the ten-point average roughness (RzJIS) must be set to around 15 μm.

  The lubrication state of the sliding surface 11A sliding with respect to the cylinder liner (bore) 20 of the skirt portion 11 having such a relatively large surface roughness (for example, a value of around RzJIS = 15 μm) is as shown in FIG. In addition, the boundary lubrication state (or mixed lubrication state) is obtained, and the friction coefficient is extended and the frictional force is relatively large. RzJIS is described in Annex 1 of JIS B0601 (2001).

  If such a boundary lubrication state can be made, for example, a fluid lubrication state with a small friction coefficient, the frictional force generated on the sliding surface 11A of the skirt portion 11 can be reduced, thereby reducing the fuel consumption. As a result, it can contribute effectively in terms of environmental protection and economic efficiency.

  However, in actuality, in the case of a piston made of aluminum alloy, steel, or the like, the surface roughness of the sliding surface 11A of the skirt portion 11, which is an effective means for shifting the boundary lubrication state to the fluid lubrication state, is reduced. As a result, there is a high risk that scuffing or seizure will occur on the sliding surface 11A of the skirt portion 11, and the surface roughness of the sliding surface 11A of the skirt portion 11 cannot be sufficiently reduced. That is the situation.

  On the other hand, in the case of a piston made of cast iron that is superior in slidability and scuff resistance compared to aluminum alloy, steel, etc., while suppressing the occurrence of scuffing and seizure, the skirt portion 11 It is considered possible to reduce the surface roughness of the sliding surface 11A to bring the lubrication state closer to the fluid lubrication state from the boundary lubrication state.

  Here, the surface roughness of the sliding surface 11A of the skirt portion 11 of the FCD piston 10 shown in FIG. 1 is determined so that the skirt portion 11 of the piston 10 and the piston 10 can slide freely with a predetermined gap as shown in FIG. When the thickness of the lubricating material film such as lubricating oil (hereinafter referred to as oil film thickness) X generated between the cylinder liner (bore) 20 to be inserted is made smaller than the sliding surface 11A of the skirt portion 11. The lubrication state becomes a fluid lubrication state, and the friction coefficient can be made small.

  Therefore, in order to reduce the friction coefficient by changing the lubrication state of the sliding surface 11A of the skirt portion 11 to the fluid lubrication state, the surface roughness of the sliding surface 11A of the skirt portion 11 is set to the skirt portion 11 and the cylinder liner (bore). It is considered effective and desirable to set it smaller than the oil film thickness X generated between 20 and 20.

  The oil film thickness X is determined by the sliding surface shape (piston skirt profile), sliding speed, load (load), lubricating oil viscosity, and the like.

  On the other hand, from the viewpoint of scuffing resistance, seizure resistance, etc., in order to cool the frictional heat generated between the sliding surface 11A of the skirt portion 11 and the cylinder liner 20, there is plenty of water in the vicinity of the frictional heat generating portion. It is preferable that lubricating oil be present in

  However, in the case of a piston made of aluminum alloy, steel, or the like, if the surface roughness of the sliding surface 11A of the skirt portion 11 is reduced, the lubrication retained in the portion of the roughness valley (oil sump: see FIG. 6). The amount of oil is insufficient, the frictional heat described above cannot be sufficiently cooled, and scuffing or seizure is likely to occur.

  On the other hand, in the case of a piston made of cast iron, such as an FCD piston, the base material has a structure having a large number of holes (pits or pores), and carbon particles excellent in lubricity are deposited on the surface. Therefore, even if the surface roughness is reduced, the pits function as an oil sump and the lubricating oil is retained in the pits, so that the frictional heat described above can be effectively cooled and the carbon particles are used for friction. Since the coefficient is lowered, the generation of frictional heat can be suppressed, and since the melting point is higher than that of aluminum alloys, the occurrence of scuffing and seizure can be suppressed, and wear and friction can be reduced. It will be possible.

  That is, in the case of a piston made of cast iron, such as an FCD piston, the surface roughness can be reduced while suppressing the occurrence of scuffing and seizure, so that the sliding surface 11A of the skirt portion 11 can be reduced. When the lubrication state is set to the fluid lubrication state, the friction coefficient can be extended and the friction can be reduced. Therefore, the fuel consumption performance is excellent, and the environmental protection and the economic efficiency can be effectively contributed.

  Here, FIG. 3 and FIG. 4 show some of the findings obtained by various research experiments by the present inventors.

  FIG. 3 shows the relationship between the “surface roughness of the skirt portion” and the “friction loss”. From FIG. 3, as the surface roughness of the skirt portion is reduced from the current RzJIS = 15 μm, the friction increases. It is understood that the loss is reduced, the polarity is changed in the vicinity of RzJIS = 5 μm, the friction loss gradually increases as the surface roughness is further reduced, and the possibility of scuffing near RzJIS = 0.5 μm increases. The

  FIG. 4 shows the relationship between “friction coefficient” and “oil film thickness / surface roughness of skirt part”. From FIG. 4, “oil film thickness / surface roughness of skirt part” is 1. The friction coefficient gradually decreases as it approaches 1 from a smaller state (“oil film thickness” <“surface roughness of the skirt portion, where the boundary-lubricated hue is strong)”, and 1 (“oil film thickness” ”=“ Surface roughness of the skirt portion, where the fluid-lubricating hue is strong ”and bends near (“ oil film thickness ”>“ surface roughness of the skirt portion ”). Thus, it is understood that although the coefficient of friction gradually increases, it is maintained at a small value as the lubricating oil retention capacity in the valley portion decreases).

  Therefore, from FIG. 3 and FIG. 4, in the piston made of cast iron, the surface roughness of the sliding surface 11A of the skirt portion 11 is in a range from a value around RzJIS = 5.5 μm to a value around RzJIS = 0.5 μm. It is considered desirable to set to. In consideration of manufacturing variations and the like, the surface roughness of the sliding surface 11A of the skirt portion 11 can be set, for example, to a value in the vicinity of RzJIS = 3 μm to 1 μm. When priority is given to reducing friction, the surface roughness of the sliding surface 11A can be set to a value in the vicinity of RzJIS = 2 μm to 0.5 μm, for example.

  In the piston made of cast iron, the surface roughness of the sliding surface 11A of the skirt portion 11 is smaller than the oil film thickness generated between the sliding surface 11A and the cylinder liner 20, and the surface roughness. It is considered desirable to set the thickness (RzJIS) within a range not smaller than 0.5 μm.

  By forming the surface roughness of the sliding surface 11A of the skirt portion 11 within the range as described above (for example, cutting), the sliding of the skirt portion 11 is suppressed while suppressing the occurrence of scuffing and seizure. It is possible to provide an FCD piston that can reduce the friction coefficient by extending the friction coefficient of the surface 11A to a fluid lubrication state, and thus has excellent fuel efficiency and is effective in improving environmental protection and economy. It will be possible.

  In the second embodiment of the present invention, an example in which the FCD piston described in the first embodiment is further improved will be described.

  In the second embodiment, the surface roughness (RzJIS) of the sliding surface 11A of the skirt portion 11 of the piston 10 is, for example, a value substantially equal to the generated oil film thickness, or RzJIS = 5, as described in the first embodiment. After performing cutting or the like so as to be in the range of about 5 μm to RzJIS = 0.5 μm, so-called phosphate film treatment (Parkerizing (registered trademark) treatment) is performed.

  Phosphate film treatment generates phosphate on the surface of the base material, and while sacrificing wear while preventing direct contact between metals, it creates a flatter sliding surface and its crystal Combined with a porous structure that can hold a sufficient amount of lubricating oil, friction can be reduced, frictional heat generation can be kept low, and initial conformability of the sliding surface can be improved. .

  Therefore, when the surface roughness of the sliding surface 11A of the skirt portion 11 is reduced in the piston made of the FCD or the like of the present embodiment, the initial conformability can be improved. Is advantageous.

  Further, since the process of the phosphate film treatment involves a corrosion reaction, holes (pits or porous) on the surface of the base material that have an important influence on the lubrication characteristics of the sliding surface 11A of the skirt portion 11 of the piston 10 and the like. The number will be increased or the size will be expanded.

  Therefore, when the phosphate film treatment is performed, the function as an oil sump by the porous portion can be promoted with respect to the base material (cast iron) itself, compared with the case where it is not applied, so the base material (cast iron) As described above, the frictional heat can be cooled more effectively, and the precipitation of carbon grains on the surface of the base metal is expanded and the friction coefficient is further lowered. It is possible to suppress the occurrence of seizure and seizure, and to reduce wear and friction.

  For this reason, even when the surface roughness (RzJIS) of the sliding surface 11A of the skirt portion 11 of the piston 10 is reduced, the phosphate film treatment is performed as in this embodiment as compared with the case where it is not performed. In addition to the fact that the initial conformability can be further increased, even when the phosphate film disappears due to wear or the like, the presence or absence of the porous portion of the base material increased or expanded, Generation | occurrence | production of seizure etc. can be suppressed more effectively, and abrasion reduction and friction reduction can be made more effective.

In each of the above-described embodiments, the FCD piston is representatively described among pistons made of cast iron. However, the present invention is not limited to this, and various cast irons such as malleable cast iron are used as materials. It can be applied to the piston.
Further, the surface treatment applied to the piston according to the present invention is not limited to the above-described phosphate film treatment, and other surface treatments involving corrosion reactions may be appropriately employed as required. Is possible.
Furthermore, the piston according to the present invention is not limited to use in an internal combustion engine. In addition to an external combustion engine, a machine that does not extract power (such as a compressor), or various actuators, etc., is present in the presence of a lubricating substance. It can be applied to a piston reciprocated by
In addition, although lubricating oil is assumed as a lubrication substance, it is not limited to this, For example, in addition to Newtonian fluids, such as light oil and gasoline, even fluids, such as ER fluid and MR fluid, predetermined lubrication The present invention is applicable to any fluid having characteristics.

  Each embodiment described above is merely an example for explaining the present invention, and various modifications can be made without departing from the gist of the present invention.

It is a figure which shows an example of the surface roughness of the skirt part of the FCD piston which concerns on Example 1 of this invention. It is explanatory drawing which shows typically the lubrication state (fluid lubrication state) between the skirt part of the FCD piston which concerns on an Example same as the above, and a cylinder liner (bore). It is a figure which shows an example of the relationship between the surface roughness of the skirt part of a piston, and a fuel consumption. It is a figure which shows an example of the relationship between a friction coefficient and the surface roughness of the skirt part of a piston. It is a figure which shows an example of the surface roughness of the skirt part of the conventional aluminum piston. It is explanatory drawing which shows typically the lubrication state (boundary lubrication state) between the skirt part and cylinder liner (bore) of the conventional aluminum piston.

Explanation of symbols

10 Piston 11 Skirt 11A Sliding surface 20 Cylinder liner (bore)

Claims (4)

The piston is made of cast iron and used in the presence of a lubricating substance, and the surface roughness of the base material of the sliding surface of the skirt portion of the piston is in a range of RzJIS = 5.5 μm to 0.5 μm. Piston characterized by being formed.   The piston according to claim 1, wherein the sliding surface of the skirt portion of the piston is subjected to a surface treatment accompanied by a corrosion reaction.   The piston according to claim 2, wherein the surface treatment is a phosphate film treatment. The piston according to any one of claims 1 to 3, wherein the cast iron is spheroidal graphite cast iron.