Pumps – Three or more cylinders arranged in parallel – radial – or...
Reexamination Certificate
1999-12-13
2001-08-21
Freay, Charles G. (Department: 3746)
Pumps
Three or more cylinders arranged in parallel, radial, or...
C074S060000, C092S071000
Reexamination Certificate
active
06276905
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a swash-plate type compressor and, more particularly, to an engagement structure of a piston and a shoe which are included in the swash-plate type compressor.
Conventional swash-plate type compressors are disclosed in each of Japanese Patent Application Laid-Open Nos. 135990/1986, 65509/1974, and 138474/1981. Each of the swash-plate type compressors comprises a rotatable shaft driven to cause a rotation thereof, a swash plate connected to the rotatable shaft to rotate together with the rotatable shaft, a piston having a concave part facing the swash plate, and a shoe having a spherical convex part inserted in the concave part. When the rotatable shaft rotates, the shoe slides along the swash plate and converts the rotation of the rotatable shaft to a reciprocating movement of the piston in cooperation with the awash plate.
Among these conventional swash-plate type compressors, the compressor using a double-head piston is called a double swash-plate type compressor. The compressor using a piston provided with a compression head only on one end is called a single swash-plate type compressor. In the single swash-plate type compressor, the concave part of the piston is usually made along a single spherical surface having a radius of curvature which is substantially equal to that of the spherical convex part.
During operation of each of the conventional swash-plate type compressors, the shoe performs wobbling movement thereof in the concave part in accordance with the rotating movement of the swash plate. Therefore, the maintaining of excellent lubricating properties is demanded between the spherical convex part of the shoe and the concave part of the piston.
However, the swash-plate type compressor in previous technique has disadvantages in that lubricant oil cannot easily enter between the concave part of the piston and the spherical convex part of the shoe. This is because the concave part of the piston substantially coincides with the spherical convex part of the shoe, there is little clearance between both sliding surfaces.
Therefore, a large force acts on the concave part of the piston, thereby generating wear by sliding movement with the shoe. Particularly in the initial stage of operation of the swash-plate type compressor, since the concave part does not sufficiently fit with the spherical convex surface of the shoe, wear amount is considerable. Moreover, an abnormal wear is sometimes generated in the concave part of the piston.
To prevent this, it is described, for example, in U.S. Pat. No. 4,734,014 that the convex curved surface of the shoe is formed into a spherical surface having a smaller curvature radius than that of the spherical surface of the concave part and that the vertex of the spherical curved surface is formed into a flat part. In the compressor described in this U.S. patent, an oil reservoir is formed between the flat part of the shoe and the accomodation concave part, which is advantage for the lubricating properties.
However, when the end of the flat surface of the shoe slides on the inner surface of the concave part, the local wear of the concave part is more promoted. Therefore, a clearance is generated in a part different from the clearance disposed beforehand. In addition, the load of the local force causes partial deformation in the concave part. So that, the life of the compressor is shortened. Additionally, as a result of reinforcement of relative vibration of the shoe, the generation of noise during the operation is also promoted.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a swash-plate type compressor in which local wear or partial deformation is not caused in the concave portion although lubricant oil is readily introduced between a concave portion of a piston and a spherical convex portion of a shoe in an initial stage of the compressor and which.
It is another object of the present invention to provide an engagement structure between the piston and the shoe in the swash-plate type compressor, in which wear is promoted without dragging or tearing to thereby make the concave part of the piston fit to the spherical convex portion of the shoe.
Other objects of the present invention will become clear as the description proceeds.
According to an aspect of the present invention, there is provided a swash-plate type compressor which comprises a rotatable shaft driven to cause a rotation thereof, a swash plate connected to the rotatable shaft to rotate together with the rotatable shaft, a piston having a concave part facing the swash plate, and a shoe having a spherical convex part inserted in the concave part. The shoe is slidable along the awash plate for converting the rotation of the rotatable shaft to a reciprocating movement of the piston in cooperation with the swash plate. The piston further has a protrusion formed in the concave part to leave a clearance between the concave part and the spherical convex part.
It may be arranged that the protrusion is formed at a bottom of the concave part.
It may be arranged that the concave part has at least two spherical surfaces which partially superpose to each other to form the protrusion between adjacent ones of the spherical surfaces.
It may be arranged that the piston has a pair of opposite surfaces defining a groove therebetween, the concave part being formed in one of the opposite surfaces, the awash plate having a peripheral portion inserted in the groove.
It may be arranged that another of the opposite surfaces is formed with an additional concave part, the compressor further comprising an additional shoe having a spherical convex part inserted in the additional concave part, the additional shoe being slidable along the swash plate for converting the rotation of the rotatable shaft to the reciprocating movement of the piston in cooperation with the swash plate and the first-mentioned shoe.
It may be arranged that the piston further has an additional protrusion formed in the additional concave part to leave a clearance between the additional concave part and the spherical convex part of the additional shoe.
It may be arranged that the additional protrusion is formed at a bottom of the additional concave part.
It may be arranged that the additional concave part has at least two spherical surfaces which partially superpose to each other to form the protrusion between adjacent ones of the spherical surfaces.
According to another aspect of the present invention, there is provided a piston and shoe engagement structure of a swash-plate type compressor provided with a swash plate for rotating around a rotatable shaft and performing reciprocating movement along the rotatable shaft, and a piston having a groove for passing the swash plate to convert the movement of the swash plate to the reciprocating movement via a shoe, wherein end surfaces of the groove are provided with concave parts having circular surface shapes to hold a spherical surface part of the shoe, the each of concave parts having a bottom part provided with a convex part.
It may be arranged that, by superposing at least two spherical surfaces different in central position, the convex part is formed in a boundary part between the spherical surfaces.
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Baker & Botts L.L.P.
Freay Charles G.
Sanden Corporation
Tyler Cheryl J.
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