Expansible chamber devices – Abutment connection between working member and power...
Reexamination Certificate
2000-03-06
2001-10-30
Ryznic, John E. (Department: 3745)
Expansible chamber devices
Abutment connection between working member and power...
C092S155000, C092S071000, C384S002000
Reexamination Certificate
active
06308615
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to lubrication of moving parts in a compressor. More specifically, the present invention pertains to friction reducing coatings for compressor parts.
To reduce friction between members that form the internal mechanism of a swash plate compressor, various technologies for coating the sliding surfaces of the members have been proposed.
Japanese Unexamined Patent Publication No. 57-146070 describes a double-head-piston-type compressor, the swash plate angle of which is fixed. In the compressor, the spherical surfaces of the shoes for coupling the periphery of the swash plate to the pistons are coated with a lubricant film containing solid lubricant. The coating reduces frictional resistance between the spherical surfaces of the shoes and the corresponding recessed surfaces of the pistons, which reduces power losses.
Japanese Unexamined Patent Publication No. 8-247026 also describes a double-head-piston-type compressor, the swash plate angle of which is fixed. In the compressor, the recessed surfaces of the pistons for receiving the spherical surfaces of the shoes (also known as cam followers) are coated with a film that is mainly made of tin. The tin coating reduces friction between the spherical surfaces of the shoes and the recessed surfaces of the pistons, which prevents damage to the surfaces caused by heat.
These two prior art references relate to fixed swash plate/fixed displacement type compressors, which have fixed swash plate angles. Another type of compressor is known as a variable displacement type. The swash plate of a variable displacement compressor is connected to the drive shaft and is permitted to incline. The swash plate angle &thgr; (the inclination angle of the swash plate with respect to an imaginary plane P perpendicular to the drive shaft) ranges from a minimum inclination angle &thgr;min to a maximum inclination angle &thgr;max, which varies the piston stroke and the displacement of the compressor.
In particular, in the field of air-conditioners for vehicles, variable displacement swash plate compressors that vary the displacement in accordance with the cooling load achieve advantages that cannot be achieved by other types of compressors.
In a typical swash plate compressor, the piston stroke (displacement) is determined in accordance with the swash plate diameter (diameter of an imaginary circle that passes through the centers of the piston couplings) and the swash plate angle. The maximum inclination angle, at which the displacement of the compressor is maximized, is determined in consideration of the permissible limit of friction between the swash plate and the shoes and between the shoes and the pistons during the rotation of the drive shaft and the swash plate. In other words, the permissible limit of friction between the sliding members related to the swash plate is the factor that determines the maximum inclination angle. However, in a swash plate compressor, lubricant oil retained in the compressor is atomized by gas (refrigerant gas such as a chlorofluorocarbon) that circulates in the compressor and is carried to the moving parts. Lubrication and friction in the internal mechanism of a compressor are not problematic as long as the compressor is operating normally.
However, in addition, a coating, as in the prior art mentioned previously, is necessary since there are times when the lubrication by atomized oil is not reliable. That is, there may be a temporary shortage of lubricant oil. For example, when the compressor is started after not operating for a long time, the supply of oil may be inadequate. This is because refrigerant gas is liquefied after the compressor is stopped, and the liquefied refrigerant gas washes away lubricant oil from the moving parts. Accordingly, the parts are not lubricated well when the compressor is started. It takes about one minute until lubricant oil is supplied to the moving parts again by oil atomized by refrigerant gas that enters the compressor. During the one-minute period after the compressor starts, the moving parts that need lubrication are not supplied with oil. Certain parts are coated to provide minimum lubrication in this period. In a conventional variable displacement swash plate compressor (the maximum inclination angle of which is around 19 degrees), the problem of limited lubrication has been solved by taking the prior art measures described previously.
However, in recent years, smaller compressors having larger displacements have been required because of the increasing demand for saving energy and space. Accordingly, it is not acceptable to increase the maximum displacement of a compressor by increasing the swash plate diameter and the housing size. Therefore, it is necessary to increase the piston stroke by increasing the maximum inclination angle of the swash plate. It is empirically known that the maximum inclination angle is limited to around nineteen degrees and cannot be increased more than that with only the prior art coating measures described previously. Therefore, there is a need for a better way to reduce the friction between the spherical surfaces of the shoes and the recessed surfaces of the pistons during the first minute of operation.
SUMMARY OF THE INVENTION
An objective of the present invention is to dramatically reduce friction between two compressor parts and to provide a compressor that has a greater displacement without greater outside dimensions. In other words, the objective of the present invention is to provide compressor parts that can operate for a long period without being damaged by friction or friction heat even if the parts are inadequately lubricated by oil.
To achieve the above objective, the present invention provides a compressor having first and second cooperating parts, which include first and second sliding surfaces. The first sliding surface is on the first part. A solid lubricant film is formed on the first sliding surface, and the solid lubricant film includes a solid lubricant other than a soft metal. The second sliding surface is on the second part. The second sliding surface slides on the first sliding surface, and a soft film that mainly contains soft metal is formed on the second sliding surface.
The present invention is preferably applied to a swash plate compressor, and more preferably applied to a variable displacement swash plate compressor that can vary the inclination angle of the swash plate. In any case, the swash plate compressor includes pistons and shoes. The shoes couple the pistons to the periphery of the swash plate. The shoes include spherical sliding surfaces. The pistons include concave sliding surfaces that slide on the spherical surfaces of the shoes.
Solid lubricant films and soft films are preferably formed on the spherical surfaces and the concavities. In this case, it is possible to increase the maximum inclination angle (&thgr;max) and to dramatically increase the displacement of the compressor without increasing its size.
Generally, two mutually sliding members such as the shoes and the pistons (or shoes and swash plate) are made of different metals to prevent seizure caused by friction between the same metals. For example, when the shoes are made of a bearing steel such as a SUJ2 material (high-carbon chromium bearing steel), each piston (or the swash plate) is made of aluminum or aluminum alloy. In this case, the aluminum alloy includes Al—Si alloys and Al—Si—Cu alloys. Materials such as argil alloys that contain hard particles in the matrix are preferred for the pistons. Argil alloys include 10-30 weight percent silicon, and if the ratio of silicon content is below the eutectic composition, the silicon exists as eutectic silicon in the matrix. Other acceptable piston materials that contain hard particles are Al—Mn inter-metal compound, Al—Si—Mn inter-metal compound, Al—Fe—Mn inter-metal compound, and Al—Cr inter-metal compound.
The cooperating parts are not limited to the shoes and the pistons (or the shoes and the swash plate), however, the basic materials for the coop
Kato Keiichi
Kurakake Hirotaka
Kurita Hajime
Takenaka Kenji
Kabushiki Kaisha Toyoda Jidoshokki Seisakusho
Morgan & Finnegan , LLP
Ryznic John E.
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