Patent Grant
9441620
The present invention relates to a swash plate of a swash plate-type compressor. More particularly, the present invention relates to a swash plate coated with a resin-based sliding material, in which graphite particles are bonded to polyimide and/or polyamide-imide resin.
The prior art is described hereinafter with respect to a swash plate-type compressor, a resin-based coating layer covering the swash plate of a swash plate type compressor, a resin-based sliding material other than the one used for a swash plate-type compressor, spherical carbonaceous material, and then sliding properties of graphite.
Swash Plate Type Compressor
Existing variable-displacement swash plate-type compressors have a structure shown, for example, in FIG. 1. This drawing is from Patent Document No. 1: Japanese Unexamined Patent Publication (kokai) No. 2003-183685. The referential numerals in the drawing indicate the following parts or positions: 10—cylinder block; 12—cylinder bore; 14—single head piston; 16—front housing: 18—rear housing (suction port and supply port are not shown in the drawing); 20—valve plate (valve and port are not shown in the drawing); 21—housing; 22—suction chamber; 24—exhaustion chamber; 50—rotary shaft; 60—swash plate; 61—through hole; 62—rotary plate; 64—thrust bearing; 66—hinge mechanism; 67—arm; 68—guide aperture; 69—guide pin; 70—engagement; 72—head; 76—shoe; 80—guide aperture; 86—swash-plate chamber; 87—compression chamber; 90—schematically shown electro-magnetic valve; 100—exhaust channel; 102—supporting aperture.
Patent Document 1 describes the following operating mechanism of a variable-displacement swash plate-type compressor. An exhausting chamber 24, which is on the high pressure side, and a suction chamber 22, which is on the low pressure side, generate a pressure difference, which is utilized to regulate the pressure within a swash-plate chamber 86. The front and rear sides of a piston 14 are exposed to the pressure in a compression chamber 87 within a cylinder bore 12. The difference between this pressure and the pressure of the swash-plate chamber 86 is regulated to change the inclination angle of a swash plate 60. As a result, the stroke of the piston 14, and hence the exhausting volume of the compressor, is adjusted. Specifically, an electro-magnetic valve 90 is switched on or off to control the pressure in the swash-plate chamber 86, and, in turn, the swash-plate chamber 86 is communicated or disconnected with the exhaustion chamber 24.
The shoe 76 is a sliding member located between the swash plate 60 and the piston 14, as is shown in
Surface Treatment of Swash Plate by Resin-Based Sliding Material
According to the prior art, a sliding coating layer, which is based on polyimide or polyamide-imide, is provided on the swash plate of a swash plate-type compressor. Related prior art documents are: Patent Document 1—Japanese Unexamined Patent Publication (kokai) No. 2003-183685; Patent Document 2—Japanese Unexamined Patent Publication (kokai) No. 2000-265953; Patent Document 3—Japanese Unexamined Patent Publication (kokai) No. 2005-89514; and, Patent Document 4—WO02/075172A1.
The coating layer provided on the surface of a steel-based swash plate in Patent Document 1 is formed of solid lubricant, such as MoS2, PTFE, or graphite, such metallic powder of Ni, Fe, Mn, Cr or Mo having a particle diameter of 20 nm, and a polyamide-imide binder.
A liquid mixture of resin, such as polyamide-imide resin or polyimide resin and a metal or alloy powder having a particle size of 10 to 100 μm are baked on the surface of a swash plate to form a coating layer in Patent Document 2. The metal is for example Sn, Ag, Al, Cu, Zn, Ni, Si, Co, Ti, W, Mo, Mg or Fe. The alloy is of these metals.
In Patent Document 3, a solid lubricant is bonded to at least one binder selected from the group consisting of polyamide-imide, polyimide and epoxy resin. The solid lubricant contains 10 to 40 vol. % of molybdenum disulfide, 10 to 40 vol. % of flake-shaped graphite or scale-shaped graphite, and 1 to 40 vol. % of polytetrafluoroethylene. The total amount of the solid lubricants is 30 to 60 vol. %. In Patent Document 4, the following proposals are made. The swash plate of a swash-plate compressor is coated with a solid-lubricant coating layer produced from polyamide-imide resin and at least one of PTFE and graphite. In addition, concentric grooves and convexities between the neighboring grooves are provided on the sliding surface. It is described that synthetic graphite of high crystallization degree is preferred.
Non-Patent Documents: Tribologist Vol. 55, No. 9 (2010), pages 10-12 illustrates trends of a swash-plate compressor used for automotive air-conditioning. In a compressor in which an alternative fluorocarbon cooling medium HFC1113a is used, seizure is more likely to occur than in a compressor using a fluorocarbon cooling medium CFC12. Therefore, an intermediate layer formed of flame-sprayed copper-based material such as Cu—Pb and Cu—Si is provided on the iron-based swash plate in the variable-displacement type compressor, and the resin-based coating layer containing a solid lubricant is provided on the intermediate layer.
Sliding Material Used in Parts Other than Swash Plate of Swash Plate Compressor
Hitherto, a polyether-ether ketone-based resin bearing has been used as a bearing of a motor for information media such as a hard disc and DVD disc according to Patent Document 5: Japanese Unexamined Patent Publication (kokai) No. 2009-185103. This patent document proposes to replace the conventional motor bearing with a bearing, which contains (a) 100 parts by weight of a thermoplastic resin including polyarylene sulfide resin and aromatic polyamide-imide resin, (b) 1 to 50 parts by weight of such a spherical filler as a ceramic balloon, “sirasu” (a Japanese word) balloon, a glass balloon, a metallic balloon, ceramic particles, silica, glass beads, and metallic powder, and (c) 1 to 50 parts by weight of solid lubricant. It is described that scale-shaped graphite, nodular graphite, flat-sheet-shaped graphite and spherical graphite can be used, but scale-shaped graphite is preferred.
Spherical Carbonaceous Material
In Patent Document 6: Japanese Patent No. 3026269, the present applicant proposed a polyamide-imide resin-based sliding material containing 5 to 80% by weight of heat-treated and dispersed resin particles essentially individually isolated from each other. These particles are formed by heat treating and spheroidizing phenol resin.
Patent Document 7: Japanese Unexamined Patent Publication No. Hei 5-331314 proposes a heat-resistant resin sliding material composed of 40 to 95% by weight of a heat resistant resin such as polyimide resin, and 5 to 60% by weight of spherical graphite having an average particle diameter of 3 to 40 μm, which is obtained by calcining resin-based spherical particles in an inert-gas atmosphere or vacuum. The spherical graphite is described as follows. Preferably, the spherical graphite has a uniform particle diameter, an average-particle diameter of 3 to 40 μm, and geometrically highly spherical shape. Preferably, the starting material of the spherical graphite is at least one of phenol resin, naphthalene resin, furan resin, xylene resin, divinylbenzene polymer, and styrene-divynilbenzene copolymer. A method for producing such spherical graphite comprises subjecting these starting materials to known emulsion polymerization to produce spherical particles, and calcining the resultant spherical particles in an inert gas protective atmosphere or vacuum, thereby carbonizing and/or graphitizing the same.
Spherical carbon particles disclosed in Patent Document 8: Japanese Unexamined Patent Publication (kokai) Hei 7-223809 has a highly oriented, quasi-graphite crystal structure. These spherical fine graphite particles are isotropic. Various resins in which spherical carbon particles are dispersed can be used as the sliding member. These fine carbon particles are meso phase microbeads (mesocarbon microbeads), coal tar, coal tar pitch, asphalt and the like, which are heat-treated at 350 to 450 degrees C. to yield spherical crystals. They are separated from coal tar and the like and is then finely divided, followed by graphitization at 1500 to 3000 degrees C. During this process, spheroidization proceeds according to the description. However, the meso phase microbeads shown in the microscope photograph of that publication are considerably deformed from the geometrically spherical shape.
Sliding Properties of Graphite
Most of the existing compressors used for air-conditioning of an automobile are clutch-less type and are constantly rotated during driving of an automobile. When a compressor for air-conditioning is not driven, cooling medium and lubricating oil are not circulated in the compressor. Therefore, lubrication is liable to become poor. Recently, in order to increase the refrigerating efficiency of a compressor for air-conditioning of an automobile, the amount of pre-charged oil is decreased. Therefore, lubrication is likely to be worsened further. In addition, power of a compressor should be lowered to improve the fuel consumption of an automobile. In order to decrease power of a compressor under poor lubrication, friction between the shoes and swash plate must be decreased.
Generally, when a resin-based coating layer on the swash plate of a swash-plate compressor is worn out, an intermediate layer is exposed to the surface. The intermediate layer has high bonding strength with the upper and lower layers, as well as a certain level of sliding properties. Nevertheless, seizure between the shoe and intermediate layer becomes likely to occur. When the iron-based shoes are brought into direct sliding with an iron-based swash plate without intermediation of an intermediate layer, sliding occurs between the iron-based materials, so that the seizure is highly likely to occur. The present applicant proposed in Patent Document 4 a coating layer, which is formed of PTFE and/or graphite and polyamide-imide resin, for the purpose of mainly enhancing low-friction properties. Improvement in wear resistance is not contemplated in this patent document. It turned out that, when the lubrication conditions become to be extremely deteriorated in a compressor using an alternative cooling medium, wear between the shoe and swash plate is likely to occur. In addition, a flame-sprayed copper intermediate layer is used in swash plate compressors, because the resin-based coating layer is not completely reliable. This intermediate layer makes a compressor expensive, because the price of copper used in the intermediate layer has recently soared.
It is an object of the present invention to improve wear resistance and low-friction property of a resin-based coating layer formed on the swash plate of a swash-plate compressor, particularly, a displacement-variable swash plate compressor, operated under poor lubricating conditions. It is another object of the present invention to provide a resin-based coating layer on a swash plate of a swash-plate compressor, which coating layer can attain improved sliding properties without use of an intermediate layer.
The present invention provides a swash plate of a swash plate-type compressor having shoes and a swash plate which slides thereon, and is characterized in that the swash plate is covered with a coating layer which contains 5 to 60 mass % of spherical graphite particles having an average particle diameter of 5 to 50 μm, with the balance being one or more species selected from polyimide resin and polyamide-imide resin. The spherical graphite particles, excepting minute particles having a particle diameter 0.5 times or smaller than the average particle diameter, have an average shape coefficient (YAvE), as defined below, falling within a range of 1 to 4.70% or more, in number, of the spherical graphite particles have a shape coefficient (Y) within a range of 1 to 1.5.
YAve=total|[PMi2/4πAi]|/i
Y=PM2/4πA
Here, “total” indicates that a value in [ ] is totalized for number “i”, “PM” indicates the circumferential length of one particle, “A” indicates a cross sectional area of one particle, and “i” indicates the measurement number. The present invention is hereinafter described in detail.
Typically, graphite is classified into two types, that is, natural graphite and synthetic graphite. It is however sometimes classified roughly into three types, that is, expanded graphite in addition to the above two types. Natural graphite is classified into scale-shaped graphite, flake-shaped graphite, and graphite having soil appearance. Pulverized synthetic graphite electrode, graphitized petroleum tar or cokes, and meso-phase micro beads are included in the synthetic graphite. The scale-shaped graphite may be referred to as nodular graphite. Not only production methods of these types of graphite are different from each other, but also appearances can be clearly distinguished from each other. Recently, a spheroidizing pulverizing technique has been developed. The produced spheroidized graphite or spherical graphite is commercially available (Technical data of Japan Graphite Industries Co., Ltd., product name CGC-100, 50, 20; Home page of ITO GRAPHITE; http://www graphite.co.jp/seihin.htm). Spherical graphite used in the present invention has a considerably higher particle ratio than any of the commercially available flake-shaped graphite, graphite having soil appearance, or thin-sheet-shaped graphite and the like.
The structure of the swash plate of a swash plate-type compressor according to the present invention is first described. Copper or aluminum can be used instead of iron of the iron-based substrate 110. In one embodiment, where sliding of materials of the same type occurs between the iron-based substrate and shoe, advantages of the present invention will be demonstrated. An intermediate layer is not necessary but a sintered copper intermediate layer, a flame-sprayed Cu, Al, Cu—Al intermediate layer or the like may cover the surface of iron-based substrate 110.
Spherical graphite particles 115b, excepting minute particles having a particle diameter 0.5 times or smaller than the average particle diameter, have an average shape coefficient (YAVE), as defined below, falling within a range of 1 to 4, preferably 1 to 2.5. In addition, 70% or more, in number, of the spherical graphite particles 115b have a shape coefficient (Y) of 1 to 1.5.
YAVE=total|[PMi2/4πAi]|/i
Y=PM2/4πA
Here, “total” indicates that a value in [ ] is totalized for number “i”, “PM” indicates the circumferential length of one particle, “A” indicates a cross sectional area of one particle, and “i” indicates the measurement number. The circle-equivalent diameter and shape coefficient of a graphite particle are measured as follows.
A swash plate is cut at an arbitrary position. A visual field of 0.37 mm×0.44 mm on a cut surface is photographed at a magnification of 200 times. The image of the resin coating layer is converted to binary image by means of, for example, LUZEX-FS produced by Nicolet Co., Ltd. The binary image is measured to obtain the circle-equivalent diameter and the shape of each graphite particle.
The average diameter D of spherical graphite particles 115b and the thickness t of the resin-based coating layer 112 preferably have a relation of 0.1 t<D<1.0 t, more preferably 0.25 t<D<0.67 t. The resin-based coating layer 112 preferably has a thickness t of 5 to 50 μm, more preferably 10 to 40 μm.
Spherical graphite particles 115 according to the present invention have a degree of graphitization of 0.6 or more, with the proviso that the degree of graphitization of perfect graphite crystal is 1. The spherical graphite particles 115 may be natural graphite or close to natural graphite, and therefore have improved lubrication property and compatibility. The spherical graphite particles 115b preferably have a degree of graphitization of 0.8 or more. The degree of graphitization is defined by C. R. Houska's equation stated in Non-Patent Document 2: Tribologist Vol. 49, No. 7 (2004), page 561, “Method for Using Carbon Material”. The spherical graphite particles 115b are blended in the resin-based coating layer 112 at a proportion of preferably 5 to 60 mass %, more preferably 10 to 50 mass % based on the total.
Balance of the above-mentioned spherical graphite particles 115b is a resin-based binder 113 composed of polyimide (PI) resin and/or polyamide-imide (PAI) resin. Polyester imide, aromatic polyimide, polyether imide, bismaleic imide in liquid form or solid powder form can be used as the polyimide. Aromatic polyamide-imide resin can be used as the polyamide-imide resin. Improved heat resistance and low coefficient of friction are characteristic features provided by these resins.
Referring to
The resin-based coating layer 112 according to the present invention may further contain one or more species of MoS2, PTFE, WS2, h-BN, and CF (fluorinated graphite), which are common solid lubricants, in an amount of 1 to 70 mass %, with the proviso that the total content of the solid lubricant and spherical graphite is 10 to 80 mass %. A total amount of spherical graphite and solid lubricant at less than 10 mass % is not very effective. When the solid lubricant alone exceeds 70 mass %, or when the total content of spherical carbon and solid lubricant exceeds 80 mass %, drawbacks such as reduction in heat resistance or strength of the resin-based coating layer 112 become apparent. The particle diameter of a solid lubricant is preferably 0.5 to 50 μm, more preferably 1 to 20 μm.
According to the present invention, oxides such as alumina and silica, nitrides such as SiN, carbides such as SiC, and sulfides such as ZnS may further be blended as hard particles in the resin-based coating layer 112. The blending amount of these hard particles is preferably 0.2 to 7 mass %, more preferably 1 to 5 mass %. The particle diameter of the hard particles is preferably 0.01 to 3 μm, more preferably 0.01 to 1 μm.
A plurality of concentric circumferential grooves 140 (
The resin-based coating layer according to the present invention can be formed by a method of blending the spherical graphite particles, polyamide-imide resin and other additives, and applying the mixture by roll coating, spraying coating, spin coating, pad printing and the like. The resin-based coating layer according to the present invention may be subjected to surface-roughness adjustment by means of mechanical working such as machining, polishing and the like. Preferably, a plurality of concentric grooves or a single or plural spiral grooves are formed on the surface of the resin-based coating layer, and a ridge is formed between the adjacent grooves. Since the spherical graphite particles hardly separate from the surface, fine surface roughness can be maintained, thereby enhancing seizure resistance. The grooves and convexities further enhance seizure resistance.
Generally, cleavage of the graphite particles having larger particle diameter is more likely to occur on the sliding surface. In this case, decrease of friction can be expected.
(a) Orientation
Since the flake-shaped graphite particles 115a are in sheet form, cleavage planes are parallel to the sheet plane of the graphite particles. Among the flake-shaped graphite particles 115a present in the resin-based binder 113, few particles (115a′) are oriented in parallel in the sliding direction. Most of the graphite particles are aligned in a direction perpendicular to the surface of the iron-based substrate 110 or aligned aslant. Among the aligned flake-shaped graphite particles 115a′, those present on the very surface of a coating layer cleave and wear out, while most of the other particles held in the coating layer subsequently cleave. Low friction property is exhibited during the repeated cleavage process mentioned above. Meanwhile, the cleavage direction of the other, perpendicularly or obliquely oriented flake-shaped graphite particles is not coincident with the machining direction or sliding direction.
(b) Surface Roughening
The depth of recesses 116 (
(c) Generation of Cracks
Flake-shaped graphite particles 115a are likely to separate from the sliding surface. The separated potion of the sliding surface becomes a defect 116′ (
(d) Summary of Flake-shaped Graphite Particles
Flake-shaped graphite particles 115a are soft and are likely to cleave. Low friction is expected, because cleavage of graphite takes place on the sliding surface. However, since the flake-shaped graphite particles separate from the sliding surface, wear resistance and low-friction property are not achieved together. In order to avoid such problems, the flake-shaped graphite particles 115a must have a small particle diameter.
By contrast, the spherical graphite particles 115b (
Orientation tendency of spherical graphite particles 115 in a particular direction is not appreciable. That is, these particles are oriented in all directions. Mutual contact of spherical graphite particles are point contact. As a result, the resin-based coating layer 113 is difficult to peel, thereby making it unnecessary to provide an intermediate layer, leading to a considerable cost reduction. Consequently, the polyamide-imide based coating layer according to the present invention exhibits wear resistance and low-friction property in combination, and improves seizure resistance.
As is described hereinabove,
The present invention is described in detail with reference to the following examples.
The following starting materials were used to produce a resin-based coating layer.
The above mentioned starting materials was blended as follows to prepare a paint composition. The paint was pressed and applied on the iron-based substrate. Baking was then carried out at a curing temperature of the resin-based coating to form coating.
A machining test of the resin-based coating layer was carried out under the following conditions.
Working Machine: general purpose turning machine (dry)
Nose R of Cutting Tool: 0.4 mm R
Working Pitch: 0.025 mm/rev
The machined surface was observed under a scanning type electron microscope.
In these drawings, white portions are edges of the concavities. It is apparent from these drawings that the number of the separated portions of the graphite in inventive examples (
Composition of the resin-based coating layer produced in Example 1 was changed as follows, and solid lubricant was used. Wear resistance and coefficient of friction was measured under the following condition.
Number of Revolution—9500 rpm
Load—519—1735 N (successive increase)
Environment—mixture of cooling medium/ice machine oil, suction environment of compressor
Opposite Material Shoe (SUJ2)
As is described hereinabove, the present invention enhances reliability of a swash plate of a swash plate-type compressor and attains cost reduction.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-269650 | Dec 2010 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2011/077964 | 12/2/2011 | WO | 00 | 6/4/2013 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2012/074107 | 6/7/2012 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 6378415 | Sugiura et al. | Apr 2002 | B1 |
| 20030111511 | Kanayama et al. | Jun 2003 | A1 |
| 20040255775 | Pitla | Dec 2004 | A1 |
| Number | Date | Country |
|---|---|---|
| 0 450 847 | Oct 1991 | EP |
| 2 557 125 | Feb 2013 | EP |
| 62-010232 | Jan 1987 | JP |
| 3-281991 | Dec 1991 | JP |
| 5-331314 | Dec 1993 | JP |
| 7-223809 | Aug 1995 | JP |
| 3026269 | Mar 2000 | JP |
| 2000-265953 | Sep 2000 | JP |
| 2003-183685 | Jul 2003 | JP |
| 2005-089514 | Apr 2005 | JP |
| 2008-122619 | May 2008 | JP |
| 2009-029884 | Feb 2009 | JP |
| 2009-185103 | Aug 2009 | JP |
| 02075172 | Sep 2002 | WO |
| 2011126078 | Oct 2011 | WO |
| Entry |
|---|
| Second and Supplementary Notice Informing the Applicant of the Communication of the International Application (To Designated Offices Which Apply to 30 Month Time Limit Under Article 22(1)); dated Apr. 4, 2013, issued in International Application No. PCT/JP2011/077964 (Form PCT/IB/308) (1 page). |
| Communication in Cases for Which No Other Form Is Applicable dated Apr. 22, 2013, issued in International Application No. PCT/JP2011/077964 (Form PCT/IB/345) (1 page), (PCT/ISA/217) (1 page), attachment (9 pages). |
| Translation of the International Preliminary Report on Patentability (PCT/IB/338) (1 page), (PCT/IB/373) (1 page) of International Application No. PCT/JP2011/077964 mailed Jun. 13, 2013 (Form PCT/ISA/237) (7 pages). |
| Notification Concerning Transmittal of International Preliminary Report on Patentability (Chapter I of the Patent Cooperation Treaty) dated Jun. 13, 2013, issued in International Application No. PCT/JP2011/077964 (Form PCT/IB/326) (1 page), (Form PCT/IB/373) (1 page) and (Form PCT/ISA/237) (6 pages) (Partial translation). |
| WrittenOpinion of PCT/JP2011/077964, mailing date of Feb. 28, 2012. |
| International Search Report for PCT/JP2011/077964, mailing date of Feb. 28, 2012. |
| “Special Issue on Tribology in Automotive Auxiliaries and Electrical Components”, Journal of Japanese Society of Tribologists, vol. 55, No. 9, pp. 10-12, (2010), Cited in Specification; With English partial Translation. |
| “Special Issue on Characteristics and Application of Various Types of Tribo-Materials”, Journal of Japanese Society of Tribologists, vol. 49, No. 7, p. 561, (2004), Cited in Specification; With English partial translation. |
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| Number | Date | Country | |
|---|---|---|---|
| 20130247699 A1 | Sep 2013 | US |
