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Plunger piston compressor for refrigerantsRelated Patent Categories: Pumps, Motor Driven, Electric Or Magnetic Motor, Reciprocating Rigid Pumping MemberPlunger piston compressor for refrigerants description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070110599, Plunger piston compressor for refrigerants. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS REFERENCE TO RELATED APPLICATIONS [0001] This application is entitled to the benefit of and incorporates by reference essential subject matter disclosed in International Patent Application No. PCT/DK2004/000591 filed on Sep. 9, 2004 and German Patent Application No. 103 42 421.0 filed Sep. 13, 2003. FIELD OF THE INVENTION [0002] The invention concerns a plunger piston compressor for refrigerants, particularly for CO.sub.2, with a case-like housing, having a compressor block with a compression section comprising a cylinder as first housing element and a bottom part as second housing element, the compressor block and the bottom part being connected with each other and delimiting a closed inner chamber, and with a motor with a drive shaft located in the inner chamber. BACKGROUND OF THE INVENTION [0003] Such a refrigerant compressor is known from U.S. Pat. No. 2,583,583. The motor is grip-held in the bottom part. The drive shaft of the motor is supported in both the bottom part and in the compressor block. On the compressor block is fixed a cylinder, in which a piston is arranged to be reciprocating. The piston is driven by the drive shaft via a connecting rod. [0004] Another refrigerant compressor is known from DE 195 16 811 C2. This compressor is enclosed by a relatively thin-walled case. The involved compressive strength merely permits the use of traditional refrigerants, for example, partially halo-genated fluorohydrocarbons, for example R134a, or hydrocarbons, like propane or isobutene, which have even less greenhouse potential. Such refrigerant compressors have relatively low working pressures, which, on the suction side, are for example lower than 5 bar. In order to decouple the vibrations, which occur because of the oscillating movement of the piston mass, from the housing and thus from the environment, the compressor itself is supported in the housing via a spring arrangement. [0005] Lately, carbon dioxide (CO.sub.2) has become more and more used as refrigerant. CO.sub.2 has the advantage of a better environmental compatibility, particularly with regard to ozone and greenhouse potential. Next to the incombustibility, an additional advantage is that also thermodynamically it is more favourable. Further, CO.sub.2 has a substantially higher volumetric refrigerating capacity. This substantially reduces the refrigerant volume, which is required to produce a certain refrigerating capacity, in relation to refrigerants, which are based on hydrocarbons. [0006] However, with CO.sub.2-systems, much higher working pressures occur. On the suction side they can be up to 70 bar and on the pressure side up to 160 bar. Accordingly, a pressure-proof design of the compressor is necessary, which requires an accordingly stable housing. This requirement requires great efforts and involves relatively high costs. [0007] An oil-free, semi-hermetical piston compressor for small refrigerating capacities is known from the publication "Small Oil Free Piston Type Compressor for CO.sub.2" by Heinz Baumann, published under "Proceedings of the International Purdue Compressor Technology Conference 2002, Purdue, USA, C25-3". Further to the compressor block with a first shaft bearing, the compressor housing comprises a cylindrical tube element, in which the stator of the drive motor is fixed, a second bearing element for the drive shaft, and a motor-side housing cover. The individual parts of the housing bear on each other with flange surfaces and are fixed to each other by several screw bolts distributed on the circumference. [0008] A corresponding compressor, as known from EP 0 378 967, comprises a compressor block with four cylinders, each offset by 90.degree.. The compressor has a so-called Scotch-Yoke drive, in which each two pistons facing each other are connected by means of a yoke, which again is connected with a crank pin of a drive shaft via a sliding piece. The movement directions of the two sliding pieces or yokes, respectively, are here perpendicular to each other. During the rotation of the drive shaft, each piston pair performs a common reciprocating movement. [0009] A further semi-hermetical two-cylinder piston compressor with a similar design is shown in "CO.sub.2-Verdichter und-Ausrustungen", Die Kalte-und Klimatech-nik 10/2002, pages 116 to 123. Also here, the motor housing is flanged onto the compressor block. A cover is fixed on the compressor block by means of several screws distributed in the circumferential direction. [0010] The CO.sub.2-compressors known from the state of the art are characterised by the design characteristics of the traditional several-cylinder, semi-hermetical compressors, which are dimensioned for large refrigerating capacitiess and accordingly have a higher mechanical stability. The pistons of the individual cylinders are moved by a drive shaft, which is supported in at least two main bearings. These bearings, which are located in different housing parts, must be oriented accurately in relation to each other during mounting, which involves relatively large efforts. BRIEF SUMMARY OF THE INVENTION [0011] The invention is based on the task of providing a high-pressure refrigerant compressor with a simple design and cheap in manufacturing. [0012] With a plunger piston compressor as mentioned in the introduction, this task is solved in that the drive shaft is only supported on one side of the motor. [0013] An alignment of different bearings to the same drive shaft can thus be avoided. This simplifies the embodiment. A one-sided bearing has until now not been regarded as an option for high-pressure refrigerant compressors, as the high pressures result in a corresponding load of the shaft and thus of the bearing. Surprisingly, it has turned out, however, that also with high-pressure refrigerants a one sided bearing is sufficient. [0014] Preferably, the drive shaft is supported on the side of the motor, which is adjacent to the compression section. Thus, the drive shaft is, in a manner of speaking, "symmetrically" loaded on both sides of the bearing. On one side, the motor is engaging. On the other side, the crankshaft drive is engaging. In both cases, the length of the drive shaft between the force contact points and the bearing is relatively short, so that the load on the bearing remains small, also when the individual forces are not exactly the same. [0015] Preferably, the drive shaft has a counterweight, and a connecting rod bearing is located between the counterweight and the bearing. Also this measure contributes to reducing the load on the bearing. The contact point of the connecting rod is as closely adjacent to the bearing as possible. [0016] It is also advantageous that, in the area of their connection parallel to the drive shaft, the compressor block and the bottom part overlap axially on their whole circumference and that the connection is formed in the overlapping area. Thus, in principle, it is possible to transfer the basic design known from domestic refrigerant compressors, comprising a compressor block, a crankshaft drive and a drive motor, to the requirements of a high-pressure refrigerant compressor, thus achieving a simplified compressor embodiment. As CO.sub.2 used as refrigerant has a higher volumetric refrigerating capacity than refrigerants on the basis of hydrocarbons, a predetermined performance will permit a reduction of the cylinder volume and the piston diameter. The reduced oscillating masses in connection with the increased total mass of the compressor caused by the correspondingly stably formed housing lead to a compressor design, in which the compression section no longer has to be mechanically decoupled from the housing by means of springs. To the outside, the whole compressor works with relatively little vibration. Accordingly, it is no longer required to enclose the compressor block in a casing, on the contrary, the compressor block can be used as a housing element, which surrounds the inner chamber together with the bottom part. This again causes that the bottom part must have a relatively stable design. It can, for example, be made as a thick-walled deep-drawn part by cold forming of a steel plate with a thickness of approximately 8 mm. However, such a design makes it difficult to make radial flanges, as known from the state of the art, for connecting the compressor block and the bottom part with each other by means of several clamp bolts distributed on the circumference. A hermetical and undetachable welding connection, which would satisfy the stability requirements in itself, would bring so much heat into the design that the high temperatures occurring would damage parts of the compressor. These problems are reduced in a simple manner in that one housing element is inserted into the other, the two housing elements being connected with each other in the resulting overlapping area. This connection is so stable that the pressure ruling in the inner chamber cannot push the housing elements apart in the axial direction. Further, it has to be so tight that the gas available in the inner chamber cannot flow off in an uncontrolled manner. These are in fact the only requirements for the connection in the overlapping area. As will be described below, such a connection can be made in a relatively simple manner, also when both the compressor block and the bottom part are made to be relatively stable, that is, have relatively large wall thicknesses. [0017] Preferably, the connection is free of auxiliary joining parts. This simplifies the mounting. [0018] In a particularly advantageous embodiment, one of the two housing elements has an outer thread and the other housing element has an inner thread in the overlapping area, the outer thread and the inner thread engaging in each other. In order to make the connection between the compressor block and the bottom part, the two housing elements are put together and turned in relation to each other. The engagement between the outer thread and the inner thread is sufficient for preventing an axial disassembling of the two housing elements, also with high pressures in the inner chamber. [0019] In an alternative embodiment, it is ensured that in the overlapping area, the two housing elements are clamped to each other radially. Thus, the connection merely exists in the form of a frictional connection between the compressor block and the bottom part. When, however, a sufficient force causes this frictional connection, the resulting connection is sufficient to fix the bottom part reliably on the compressor block. [0020] It is preferred that the radially outer housing element in the overlapping area is shrunk-fit or pressed onto the radially inner housing element. Thus, sufficient tension force can be achieved, so that the outer housing element can exert sufficiently large pressure forces on the inner housing element. Continue reading about Plunger piston compressor for refrigerants... 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