WO2014083877A1

WO2014083877A1 - Sliding member

Info

Publication number: WO2014083877A1
Application number: PCT/JP2013/068157
Authority: WO
Inventors: 高田亮太郎; 辻井芳孝; 田代尊久; 山中将裕
Original assignee: 本田技研工業株式会社
Priority date: 2012-11-30
Filing date: 2013-07-02
Publication date: 2014-06-05

Abstract

The present invention relates to a sliding member (10) which is provided with a sliding surface (12) which is in sliding contact with a predetermined member. The sliding surface (12) has formed thereon: a protrusion (26) which protrudes toward the predetermined member: and a lubrication coating (32) which covers the protrusion (26). The protrusion (26) and the lubrication coating (32) are formed so that a cross-section of the sliding member (10) cut in the direction in which the protrusion (26) protrudes has a trapezoidal shape. If the length of the top side of the trapezoid is Z and the total length of the lubrication coating (32) in the top side is X, the cross-section coverage expressed by the following formula (1) is 15% or more: Cross-section coverage (%) = (X/Z) × 100 ... (1).

Description

Sliding member

The present invention relates to, for example, a sliding member such as a piston for an internal combustion engine slidingly contacting an inner wall of a cylinder of an internal combustion engine, and more particularly to a sliding member having a convex portion and a lubricating film formed on the sliding contact surface.

In a car, a driving force generated by an internal combustion engine supplied with fuel is converted into a rotational driving force to rotate a tire, thereby traveling. Recently, various attempts have been made to improve the fuel consumption rate (fuel consumption) of internal combustion engines in vehicles having such a configuration. Because the amount of fuel consumption is reduced, energy saving can be achieved, and it can contribute to global environmental protection.

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

In order to reduce the 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 International Publication No. 2011/115152, the applicant forms a streak (protrusion) on a sliding contact portion of a piston for an internal combustion engine made of an aluminum alloy, that is, a piston skirt, and It is proposed to coat with a lubricating film made of silver alloy, copper or copper alloy (in particular, refer to paragraphs [0063] to [0067]).

In the piston for an internal combustion engine configured as described above, the presence of the lubricating film enables the lubricant to be well held between the inner wall of the cylinder (for example, the inner wall of the sleeve) and the piston skirt. Also, the frictional heat is diffused or transmitted quickly. Therefore, the occurrence of adhesion between the piston skirt and the inner wall of the cylinder can be avoided.

The main object of the present invention is to provide a sliding member which is light in weight and capable of sufficiently reducing sliding resistance.

According to an embodiment of the present invention, in a sliding member having a sliding contact surface slidingly contacting a predetermined member,
A convex portion protruding toward the predetermined member and a lubricating film covering the convex portion and having a trapezoidal cross section along the protruding direction of the convex portion are formed on the sliding contact surface,
When the length of the top side of the trapezoid is Z and the total length of the lubricating film in the top side is X, a slide having a cross-sectional coverage of 15% or more represented by the following formula (1) A member is provided.
Cross section coverage [%] = (X / Z) × 100 (1)

That is, in the present invention, the lubricating film is not shaped to cover and swell the entire convex portion (so-called peak shape), but to have a shape in which the top is cut off. The amount of lubricating film can be reduced by this amount. Therefore, weight reduction can be achieved. Moreover, by setting the cross-sectional coverage to 15% or more, the sliding resistance is sufficiently reduced.

When the lubricating film is formed to have a trapezoidal cross-sectional shape from the beginning, the amount of the starting material for obtaining the lubricating film, for example, metal particles can be reduced. Therefore, the cost increase is suppressed.

Once the lubricant film is formed into a mountain shape, the top portion may be polished to obtain a trapezoidal cross-sectional shape. Providing a mountain-shaped lubricating film is easier than providing a lubricating film having a trapezoidal cross-section, and therefore, the time required for forming the lubricating film can be shortened, and thus the production cycle time of the sliding member can be improved. Can be Polishing may be performed, for example, by actually bringing the sliding member into sliding contact with a predetermined member.

The cross-sectional coverage is more preferably 20% or more. This is because the friction loss is further reduced.

Preferred examples of the lubricating film include those composed of at least one of silver, a silver alloy, copper or a copper alloy. In this case, since it becomes easy to dissipate the frictional heat generated with the sliding contact, the seizure can be avoided.

On the other hand, the convex portion can be formed of a metal material or a resin material. When the convex portion is made of a metal material, it is preferable to interpose an intermediate layer made of a resin material between the convex portion and the lubricating film. Thereby, the bonding strength of the lubricating film to the convex portion is improved. That is, the lubricating film is less likely to come off from the projections.

As a suitable example of the sliding member in which the above lubricating films are provided, the piston for internal combustion engines which carries out reciprocating operation in the cylinder of an internal combustion engine is mentioned. In this case, the sliding contact surface on which the lubricating film is provided is a piston skirt.

According to the present invention, the lubricating film is not shaped to cover the whole of the convex portion and bulged, but is shaped to cut off the top, so the amount of the lubricating film is reduced by this amount. Can. This reduces the amount of starting material used to obtain the lubricious coating, such as metal particles. For this reason, it is possible to suppress the cost increase while providing the lubricating film, and to reduce the weight.

FIG. 1 is a schematic overall perspective view of a piston for an internal combustion engine as a sliding member according to an embodiment of the present invention. FIG. 2 is a side view of the piston for an internal combustion engine shown in FIG. FIG. 3 is an enlarged schematic cross-sectional view showing the vicinity of a surface layer portion of a piston skirt that constitutes the piston. FIG. 4 is an enlarged schematic cross-sectional view showing the vicinity of the surface layer portion of the piston skirt in the previous stage when the state of FIG. 3 is reached. FIG. 5 is a graph showing the relationship between the cross-sectional coverage of the lubricating coating and the friction loss of the internal combustion engine. FIG. 6 is an enlarged schematic cross-sectional view showing the vicinity of the surface layer portion of the piston skirt in which the cross-sectional coverage of the lubricating film is different from that in FIG. FIG. 7 is an enlarged schematic cross-sectional view showing the vicinity of the surface layer portion of the piston skirt in which the cross-sectional coverage of the lubricating film is different from that in FIGS. 3 and 6.

Hereinafter, preferred embodiments of the sliding member according to the present invention will be described in detail with reference to the accompanying drawings. In this embodiment, as the sliding member, a piston for an internal combustion engine (hereinafter, may be simply referred to as "piston") is exemplified.

FIG. 1 is a schematic overall perspective view of a piston 10 (sliding member) according to the present embodiment, and FIG. 2 is a side view thereof. The piston 10 has a pair of

piston skirts

12, 12 at its lower part, and between the

piston skirts

12, 12,

wall portions

14, 14 extending along a substantially vertical direction intervene.

Pin bosses

16, 16 are provided on each of the

walls

14, 14 so as to protrude in a horizontal direction, and piston pins (not shown) for inserting piston pins (not shown) in each of the

pin bosses

16, 16

Holes

17, 17 are formed through. The piston pin is passed through a through hole formed at a small end of a connecting rod (connecting rod) not shown, thereby pivotally supporting the connecting rod.

The piston skirt 12 is a sliding contact surface in sliding contact with the inner wall of the bore (cylinder bore) of the cylinder block or the inner wall of the cylinder sleeve. An oil ring groove 18, a first piston ring groove 20, and a second piston ring groove 22 are formed in this order on the upper portion of the piston skirt 12 from the lower side to the upper side. Of course, the oil ring groove 18, the first piston ring groove 20, and the second piston ring groove 22 are formed to go around the head of the piston 10 in the circumferential direction.

The piston skirt 12 is further provided with a plurality of streaks 24. Each streak 24 is an undulation having a protrusion (protrusion) 26 raised toward the inner wall of the cylinder bore or the inner wall of the cylinder sleeve and a depressed valley 28, and the piston skirt 12 is provided with the ridge 24. It is formed by machining along the circumferential direction. It is preferable that the height of the protrusions 26 be in the range of 0.001 to 0.1 mm, and the distance between adjacent protrusions 26, that is, the pitch be in the range of 0.1 to 0.5 mm. It is. The more preferable range of the height of the protrusions 26 is 0.008 to 0.012 mm, and the more preferable range of the pitch is 0.25 to 0.3 mm.

The piston 10 configured as described above is made of, for example, an aluminum alloy such as AC2A, AC2B, AC4B, AC4C, AC4D, AC8H, A1100 (all are aluminum alloys defined in JIS), or Al-Cu alloy. Since the projection 26 is formed by machining the piston skirt 12 as described above, it is made of the same metal material as the piston 10.

As shown in an enlarged manner in FIG. 3, the cross section of the projection 26 is approximated to a trapezoidal shape and is covered with the intermediate layer 30. Here, the arrow X direction in FIG. 3 corresponds to the arrow X direction in FIGS. 1 and 2. The same applies to the subsequent drawings.

The intermediate layer 30 linearly extending along the circumferential direction of the piston skirt 12 improves the bonding strength between the lubricant film 32 and the piston skirt 12 described later, and contains a resin material exhibiting heat resistance. As preferable examples of this type of resin material, polyimide resin, polyamide imide resin, epoxy resin, nylon-6 resin, nylon-6,6 resin and the like can be mentioned.

The intermediate layer 30 may be made of only the above-described resin material, but may be a resin material to which a solid lubricant is added. As the solid lubricant, known ones may be blended, and preferred examples thereof include molybdenum disulfide (MoS ₂ ), boron nitride (BN), graphite (C) and the like. When the mid layer 30 contains a solid lubricant, the compounding ratio of the resin material and the solid lubricant may be such that the ratio by weight of resin material: solid lubricant is 1: 9 to 9: 1.

The intermediate layer 30 is coated with a lubricious coating 32 extending linearly along the circumferential direction of the piston skirt 12.

In this case, the lubricant film 32 is made of silver, a silver alloy, copper, or a copper alloy. These all exhibit excellent lubricating 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. Preferred examples of silver alloys include Ag-Sn alloys and Ag-Cu alloys, and preferred examples of copper alloys include Cu-Sn alloys, Cu-Zn alloys, Cu-P alloys and the like.

When the lubricating film 32 is made of silver or a silver alloy, the purity of silver is preferably 60% by weight or more. If the amount is less than 60% by weight, the thermal conductivity of the lubricating coating 32 is slightly low, which makes it difficult to form a smooth wear surface, and hence the effect of reducing the friction loss (Psf) of the internal combustion engine is It tends to be scarce. More preferably, the purity of silver is 80% by weight or more.

On the other hand, when the lubricating film 32 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 film 32". For example, in the case where the lubricant film 32 made of a sintered body is obtained after applying silver particles, the purity of silver is defined as the ratio of silver particles in the paste. In addition, when the lubricating film 32 made of a silver alloy is formed, the purity of silver is determined as the weight percentage of silver contained in the lubricating film 32. The same applies to the purity of copper.

In addition, it is not necessary to provide all of the lubricating film 32 from the same metal material in particular. For example, while forming the lubricating film 32 which covers one arbitrary protrusion part 26 with silver, the lubricating film 32 which covers another protrusion part 26 adjacent to the said protrusion part 26 is formed with a copper alloy etc. It may be provided from another kind of metal material.

The thickness of the lubricating coating 32 shown as T in FIG. 3 is not particularly limited, but if the thickness is too small, the lubricating coating 32 wears in a relatively short time. On the other hand, if it is excessively large, the weight of the lubricating coating 32 will be large, and the driving force for reciprocating the piston 10 will be large. In order to avoid the occurrence of the above-mentioned problems, it is preferable to set the thickness of the lubricating film 32 to 0.5 to 100 μm.

The cross section of the intermediate layer 30 and the lubricating coating 32 along the projecting direction of the projection 26 has a trapezoidal shape along with the cross section of the projection 26. For this reason, in plan view, as shown in the lower part of FIG. 3, a concentric circle is formed by the projection 26, the intermediate layer 30 and the lubricating film 32. The cross-sectional shape shown in FIG. 3 is formed, for example, by polishing the top side from the state shown in FIG.

In FIG. 3, extension lines of the oblique sides of the protrusion 26, the intermediate layer 30, and the lubricating film 32 are shown together in phantom lines. As can be understood from this imaginary line and FIG. 4, when the oblique side of the protrusion 26 is extended, the cross section along the projecting direction of the protrusion 26 (direction toward the cylinder sleeve or the inner wall of the cylinder bore) is an isosceles triangle. It is approximated to In the following, the state shown in FIG. 4 (that is, the state shown by the phantom line in FIG. 3) is referred to as the “initial state”.

Assuming that the length of the top side of the trapezoidal shape shown in FIG. 3 is Z, Z is expressed by the following equation (2).
Z = X1 + Y1 + L + Y2 + X2 (2)

Here, X1 and X2 are the total length of the lubricating coating 32 in the top side, Y1 and Y2 are the total length of the intermediate layer 30 in the top side, and L is the length of the top side of the protrusion.

On the other hand, the cross-sectional coverage of the lubricating film 32 is determined by the above equation (1). In addition, X in Formula (1) can be calculated as X1 + X2. Accordingly, the equation (1) can be transformed into the following equation (3).
Cross-sectional coverage = 100 x (X1 + X2) / (X1 + Y1 + L + Y + X2)
... (3)

The lubricant film 32 is provided so that the cross-sectional coverage thus obtained is 15% or more, more preferably 20% or more. By providing the lubricating film 32 with such a cross-sectional coverage, the amount of use of silver, a silver alloy, copper, or a copper alloy can be reduced. In addition, in FIG. 3, the state whose cross-sectional coverage is 20% is shown.

FIG. 5 is a graph showing the relationship between the cross-sectional coverage of the lubricating coating 32 and the friction loss (Psf) of the internal combustion engine. From FIG. 5, it can be seen that Psf can be reduced by setting the cross-sectional coverage to 15% or more, and Psf can be further reduced by setting the cross-section coverage to 20% or more.

When the internal combustion engine including the piston 10 configured as described above is operated, the lubricating film 32 substantially penetrates the lubricating oil to the inner wall of the cylinder (the inner wall of the cylinder bore or the inner wall of the cylinder sleeve). Touch. For example, in the case where the lubricating film 32 is in sliding contact with the inner wall of FC (grey cast iron) sleeve or Al sleeve, the sum of the thermal conductivity of the lubricating film 32 and the thermal conductivity of the FC sleeve or Al sleeve is determined And the absolute value of the difference in Young's modulus of the lubricating coating 32 with respect to the FC sleeve or the Al sleeve is 10 GPa or more. According to the intensive studies of the present inventors, in this case, the lubricating oil is well retained in the minute clearance between the sleeve and the piston skirt 12 and adhesion between the sleeve and the piston skirt 12 occurs. Is avoided. For this reason, it is possible to effectively avoid the occurrence of seizure and to significantly reduce the friction loss (Psf) of the internal combustion engine.

Moreover, in the present embodiment, the lubricating film 32 is firmly joined to the piston skirt 12 via the intermediate layer 30. For this reason, the lubricant film 32 is less likely to come off the intermediate layer 30 and hence the piston skirt 12. In other words, the lubricious coating 32 is held on the piston skirt 12 for a long period of time. For this reason, in the piston 10, the above-described effect obtained by the presence of the lubricating coating 32 is continued for a long time. Further, both the solid lubricant and the resin material as described above are inexpensive and lightweight.

Further, since the lubricant film 32 is hard to come off, for example, the above effect can be obtained under the action of the lubricant film 32 even when the piston 10 is vigorously reciprocated in the cylinder. That is, even a car such as a racing car that is operated under a severe environment can be provided as an internal combustion engine having excellent durability.

Furthermore, since the lubricant film 32 has a trapezoidal cross section, the weight of the piston 10 can be reduced as compared with the case where the lubricant film 32 is provided in a mountain shape. In addition, when the lubricating coating 32 is initially formed to have a trapezoidal cross section, the amount of starting material (particles of silver, silver alloy, copper, or copper alloy) for providing the lubricating coating 32 is reduced. For this reason, the increase in cost can be suppressed while providing the lubricating film 32.

Furthermore, even if the lubricant film 32 falls off from the intermediate layer 30 and the intermediate layer 30 comes into sliding contact with the inner wall of the cylinder, if the intermediate layer 30 contains a solid lubricant, The solid lubricant can maintain lubricating performance.

The mid layer 30 and the lubricious coating 32 can be provided on the piston skirt 12 as follows, for example. In the following, the case of polishing is described as an example.

First, the above-described resin material to be the intermediate layer 30 is prepared and melted. A solid lubricant as described above may be blended with this melt. In this case, resin material: solid lubricant = 1: 9 to 9: 1 (weight ratio).

The melt is then supplied onto the protrusions 26 of the streaks 24. For this purpose, for example, a melt may be applied to the protrusions 26. By cooling and solidifying the melt supplied in this manner, an intermediate layer 30 is formed on the protrusion 26.

On the other hand, fine particles of silver, silver alloy, copper or copper alloy, preferably, so-called nanoparticles having an average particle diameter of 1 to 80 nm are dispersed in a dispersion medium such as polyhydric alcohol such as benzyl alcohol, ethylene glycol or glycerin. The paste is prepared by dispersing in A dispersant is added to this paste.

As a preferable dispersing agent, carboxylic-ester type polymer dispersing agent is mentioned. In particular, polymers of fatty acid esters are suitable. The fatty acid ester may be an unsaturated fatty acid ester such as butene acid or a saturated fatty acid ester. Furthermore, it is preferable that it is a polymer of higher carboxylic acid ester.

As a specific example of such a carboxylic acid ester-based polymer dispersant, the main chain is a polyester, and an unsaturated hydrocarbon chain is bonded as a side chain, and an amide bond is added to either the main chain or the side chain Include. The presence of the above-mentioned side chain or amide bond can be confirmed by performing FT-IR (Fourier transform infrared spectroscopy) analysis or nuclear magnetic resonance (NMR) analysis.

The proportion of the carboxylic acid ester-based polymer dispersant is preferably 6 to 11% by weight when the total weight of particles of silver, silver alloy, copper or copper alloy in the paste is 100% by weight. The remainder of the paste, that is, the components other than the particles and the dispersant is a dispersion medium.

In order to form the lubricating film 32, the above-described paste is applied onto the intermediate layer 30 by a known application method such as screen printing or pad printing, for example. Thereafter, the paste is heated together with the piston 10, preferably at 160 to 240.degree. As a result, the dispersion medium in the paste is volatilized and the nanoparticles are fused. That is, sintering takes place, and the lubricating film 32 made of a sintered body of nanoparticles is obtained.

When nanoparticles are used, it is possible to form a film by sintering at a relatively low temperature of 160 to 240 ° C. as described above. Accordingly, the piston skirt 12 made of an aluminum alloy is prevented from becoming high in temperature, which can prevent the mechanical strength and the like of the piston skirt 12 from being affected.

At this point (in the initial state), the cross sections along the projecting direction of the protrusions 26, the intermediate layer 30, and the lubricating coating 32 approximate the shape shown in FIG. Next, the piston skirt 12 is subjected to polishing processing to polish the projection 26, the intermediate layer 30 and the lubricating film 32.

Polishing is completed from the initial state shown in FIG. 4 before the cross-sectional coverage of the lubricating coating 32 becomes less than 15%, more preferably less than 20%. Thereby, for example, the protrusion 26, the intermediate layer 30, and the lubricating film 32 having the cross-sectional shape shown in FIG. 3 can be obtained.

Alternatively, the projection 26 of the piston skirt 12 may be polished before the intermediate layer 30 is formed, and then the intermediate layer 30 and the lubricating film 32 may be provided.

Here, the cross-sectional coverage of the lubricating film 32 decreases as the polishing process on the protrusions 26 increases. For this reason, it is originally desirable to increase the polishing rate, but in this case, it takes a long time for the polishing process and it is complicated. Therefore, the intermediate layer 30 and the lubricant film 32 having the cross-sectional shape as shown in FIG. 6 may be formed without polishing the projection 26. As shown in FIG. The intermediate layer 30 and the lubricating film 32 may be formed after some polishing process is performed on the surface 26.

6 and 7, the cross-sectional coverage of the lubricating coating 32 is 70% and 45%, respectively. Therefore, also in the cases shown in FIGS. 6 and 7, it is possible to reduce Psf of the internal combustion engine while reducing the amount of use of silver, silver alloy, copper, or copper alloy.

In the above, polishing can be performed, for example, by incorporating the piston 10 provided with the lubricating film 32 in a cylinder block and sliding the piston skirt 12 on the inner surface of the cylinder bore or cylinder sleeve.

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

For example, in this embodiment, the piston skirt 12 itself is machined to provide the streaks 24 (protrusions 26), but the smooth piston skirt 12 is directed to the inner wall of the cylinder bore or cylinder sleeve. It is also possible to form an intermediate layer 30 having a projecting shape and use it as a projection. That is, in this case, the convex portion made of the resin material is covered with the lubricating film 32.

Alternatively, the protrusion 26 may be directly coated with the lubricating film 32 without providing the intermediate layer 30. In this case, the lubricant film 32 can also be formed by plating, for example.

Then, the lubricating film 32 having a trapezoidal cross-sectional shape may be formed from the beginning without polishing. Polishing of the lubricating coating 32 can also be performed using a suitable polishing machine before the piston 10 is incorporated into the cylinder block.

Furthermore, the present invention is not particularly limited to the piston 10, and can be applied to a member that slides on a mating member (predetermined member). As such a member, for example, a piston of a fluid pressure cylinder or the like can be mentioned.

The sliding member may be made of aluminum. Of course, other metal materials may be used.

Claims

In a sliding member (10) provided with a sliding contact surface (12) in sliding contact with a predetermined member,
The sliding contact surface (12) is provided with a convex portion (26) projecting toward the predetermined member and a lubricating film (32) covering the convex portion (26).
In both of the convex portion (26) and the lubricating film (32), the cross section along the projecting direction of the convex portion (26) has a trapezoidal shape.
When the length of the top side of the trapezoid is Z and the total length of the lubricating film (32) in the top side is X, the cross-sectional coverage represented by the following formula (1) is 15% or more A sliding member (10) characterized in that
Cross section coverage [%] = (X / Z) × 100 (1)
The sliding member (10) according to claim 1, wherein the cross-sectional coverage is 20% or more.
The sliding member (10) according to claim 1 or 2, wherein the lubricating film (32) is made of at least one of silver, silver alloy, copper or copper alloy. ).
A sliding member (10) according to any one of the preceding claims, characterized in that the projection (26) is made of metal or resin.
The sliding member (10) according to any one of claims 1 to 4, wherein the convex portion (26) is made of a metal material, and the convex portion (26) and the lubricating film (32) A sliding member (10) characterized in that an intermediate layer (30) made of a resin material is interposed therebetween.
The sliding member (10) according to claim 5, wherein the intermediate layer (30) is made of a polyimide resin, a polyamideimide resin, an epoxy resin, a nylon-6 resin, a nylon-6,6 resin. Moving member (10).
A sliding member (10) according to claim 5 or 6, characterized in that the intermediate layer (30) contains a solid lubricant.
The sliding member (10) according to any one of claims 1 to 7, characterized in that the sliding member (10) is a piston for an internal combustion engine that reciprocates in a cylinder of the internal combustion engine. Sliding member (10).
A sliding member (10) according to any one of the preceding claims, characterized in that it consists of aluminum or an aluminum alloy.