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Piston compressorRelated Patent Categories: Pumps, Three Or More Cylinders Arranged In Parallel, Radial, Or Conical Relationship With Rotary Transmission AxisPiston compressor description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070134102, Piston compressor. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001] The present invention relates to a piston compressor in which sealing members are interposed between a valve plate and a cylinder block, and between a valve plate and a housing member. [0002] In general, in a piston compressor configuring a refrigeration circuit of a vehicle air conditioner device, an entire housing includes: a cylinder block; a front housing member fixed on a front end face of the cylinder block; and a rear housing member fixed onto a rear end face of the cylinder block with a valve plate in between. In addition, the entire housing is integrated by tightening and fixing the front housing member, the cylinder block, the valve plate, and the rear housing member to one another by means of a plurality of through bolts. In the cylinder block, a plurality of cylinder bores are arranged around a shaft, and a piston is housed so as to be able to reciprocate in each cylinder bore. Moreover, in each cylinder bore, a compression chamber, whose volume is changed by a reciprocal movement of the piston, is defined. Compression of a refrigerant gas is carried out within the compression chamber. [0003] A partition wall is formed in the rear housing member to define a discharge chamber and a suction chamber between the valve plate and the rear housing member. The valve plate has discharge ports and suction ports. The discharge ports each connect one of the cylinder bores with the discharge chamber. The suction ports each connect one of the cylinder bores with the suction chamber. The partition wall is arranged at positions that correspond to cylinder bores so as to enable each chamber to communicate with the cylinder bores, while at the same time, preventing communication between the discharge chamber and the suction chamber. [0004] In the piston compressor, gaskets that serve as sealing members are interposed between a rear end face of the cylinder block and a front face of the valve plate. The gaskets inhibit leakage of the refrigerant from between a valve plate and a member adjacent to the valve plate. [0005] In recent years, from the viewpoint of environmental issues, as the refrigerant used in the refrigeration circuit, carbon dioxide has been preferred to chlorofluorocarbon. In circumstances in which carbon dioxide is used, a discharge pressure is at a much higher level than a suction pressure, and then, in contrast to cases in which chlorofluorocarbon is used, the difference in pressure between the discharge chamber and the suction chamber increases. Thus, in cases in which carbon dioxide is used, in the piston compressor, the inhibition of the leakage of the refrigerant from a discharge chamber to a suction chamber by means of the gasket is required to be highly effectively. [0006] On the other hand, in the piston compressor, in order for the valve plate to bear a compression reaction force of the compression chamber, a predetermined degree of rigidity is required. Moreover, it has been disclosed in the Prior Art section of Japanese Laid-Open Patent Publication No. 9-4563 that, by increasing the thickness of the valve plate, the degree of rigidity of the valve plate can be reinforced in such a way that, even if the valve plate is subjected to a compression reaction force, the valve plate is not easily deformed. A diameter of a cylinder bore of a general piston compressor which uses chlorofluorocarbon as a refrigerant is about 30 mm. A thickness of a valve plate of the general compressor is about 2 mm. [0007] A graph of FIG. 4 illustrates the thickness of a valve plate on the horizontal axis and an extent of the leakage of a refrigerant from the discharge chamber to the suction chamber in the piston compressor (or dead volume) on the vertical axis. The performance of the piston compressor is expressed in accordance with a balance between the extent of the leakage of the refrigerant and the dead volume from the discharge chamber to the suction chamber. The dead volume depends on the size of a volume of a discharge port, i.e., a volume in a region in which the gas is not compressed. In the graph of FIG. 4, as the value on the vertical axis approaches zero, the extent of the leakage of the refrigerant is reduced, and the dead volume is reduced. This demonstrates that the performance of the piston compressor is enhanced. On the other hand, in the graph of FIG. 4, as a value on the vertical axis moves away from zero, the extent of the leakage of the refrigerant increases, and the dead volume increases. This demonstrates that the performance of the piston compressor is diminished. [0008] In the graph of FIG. 4, a curve K1 is a curve that represents an extent of the leakage of a refrigerant in the piston compressor in a case where carbon dioxide is used as a refrigerant in the refrigeration circuit; and a curve K2 is a curve that represents an extent of the leakage of a refrigerant in the piston compressor in a case where chlorofluorocarbon is used as a refrigerant. As can be evidenced by curve K1 and curve K2 in FIG. 4, in a case where valve plates of an identical thickness are used, a larger extent of the leakage of the refrigerant occurs in cases where carbon dioxide is used as the refrigerant. It is demonstrated that in the case of both of the refrigerants, as the thickness of a valve plate increases, the extent of the leakage of the refrigerant decreases, and the performance of the piston compressors is enhanced. [0009] A straight line M is a straight line that represents the size of a dead volume. As demonstrated by the straight line M, as the thickness of the valve plate increases, a route length of the discharge port increases. In this manner, the volume of the discharge port increases, and the dead volume increases. In other words, in the graph of FIG. 4, it is demonstrated that, as the thickness of a valve plate increases, the volume efficiency of the piston compressor diminishes, and the performance of the piston compressor is diminished. [0010] As described above, in a case where carbon dioxide is used as a refrigerant, it is essential that the leakage of the refrigerant from the discharge chamber to the suction chamber be effectively inhibited. Thus, consideration has been given to intensifying a tightening force by means of the through bolts, thereby enhancing a sealing force while increasing a pressure contacting force of the gasket relative to the cylinder block, the valve plate, and the rear housing member. When the pressure contacting force is intensified, the rear housing member is brought into close pressure contact with the gasket and the valve plate. At this time, regions of the valve plate compressed by the partition wall of the rear housing member may be deformed into the cylinder bores. If the valve plate is deformed, a pressure contacting state of the cylinder block and the valve plate relative to the gasket is degraded at a peripheral edge of each cylinder bore, whose edge supports the valve plate. As a result, the degree of sealing force between the cylinder block and the valve plate is reduced, and such a situation is not desirable. [0011] Therefore, as described in Japanese Laid-Open Patent Publication No. 9-4563, consideration has been given to increasing the thickness of a valve plate, and then, enhancing the level of rigidity of the valve plate, thereby preventing deformation of the valve plate that results from an increase in the compression force, and enhancing the sealing force created by the gasket. However, as demonstrated by the straight line M of FIG. 4, increasing the thickness of the valve plate results in an increase in dead volume and thus reduces the volume efficiency of the compressor. SUMMARY OF THE INVENTION [0012] It is an objective of the present invention to provide a piston compressor that is capable of preventing a reduction in volume efficiency while inhibiting leakage of the refrigerant. [0013] In accordance with one aspect of the present invention, a piston compressor in which carbon dioxide is used as a refrigerant is provided. The compressor includes a cylinder block, reciprocating pistons, a valve plate, a housing member, and sealing members. The cylinder block has an end face and a plurality of cylinder bores. The pistons are housed in the individual cylinder bores. The valve plate has a plurality of discharge ports. The housing member is fixed to the end face of the cylinder block with the valve plate in between. The housing member has a partition wall. The housing member and the valve plate define a suction chamber and a discharge chamber. The discharge chamber is connected to the cylinder bores through the corresponding discharge ports. The suction chamber and the discharge chamber are partitioned by the partition wall. The sealing members each are interposed between the valve plate and the cylinder block, and between the valve plate and the housing. A value of a ratio of the thickness of the valve plate relative to a diameter of each cylinder bore is between 0.13 and 0.4, inclusive. [0014] Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings that illustrate by way of example the principles of the invention. BRIEF DESCRIPTION OF THE DRAWINGS [0015] The invention, together with the objects and the advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments, together with the accompanying drawings in which: [0016] FIG. 1 is a longitudinal cross-sectional view illustrating a piston compressor according to an embodiment; [0017] FIG. 2 is a partially enlarged cross-sectional view illustrating the vicinity of a valve plate and a cylinder bore; [0018] FIG. 3 is a graph depicting a relationship between the performance of the piston compressor and the value of a ratio in thickness of a valve plate relative to a diameter of a cylinder bore; and [0019] FIG. 4 is a graph depicting a relationship between the performance of the piston compressor and the thickness of the valve plate. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [0020] The present invention will now be described with reference to FIG. 1 to FIG. 3 and to an embodiment of a piston compressor for use in a refrigeration circuit in which carbon dioxide is used as a refrigerant. In the following description, with respect to the "upward" and "downward" directions of the piston compressor, the direction of arrow Y1 appearing in FIG. 1 is defined as a vertical direction, and the "frontward" and "rearward" directions of the piston compressor are each defined as a direction of arrow Y2. Continue reading about Piston compressor... Full patent description for Piston compressor Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Piston compressor patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. 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