DE10232100A1 - Oil-free compressor for running as a two-step radial compressor, has an electric motor with a rotor connected to a shaft for driving the compressor with a direct drive. - Google Patents

Abstract

An oil-free compressor device has a casing (20) and a shaft (12) to rotate on the casing. A compressor (10) has an impeller (14) connected to the shaft and integral to it. An electric motor (18) has a rotor (16) that connects to the shaft and is integral to it for driving the compressor with a direct drive. A hydrodynamic foil bearing (26,28) for the shaft is free of oil and lubricated by air or processing fluid.

Description

The invention relates generally to compressors and especially on radial compressors.

Radial compressor systems were driven by turbines, as in the U.S. Patent 5,102,305. The turbomachine disclosed there includes a uniform, ceramic rotor structure, which a shaft, a Turbine and a compressor impeller at the opposite ends of the Has wave. The shaft is rotatable through a liquid film foil bearing stored, which is cooled with process fluid or ambient air. The in reason given in this patent for the use of such foil bearings lies in the problem of coking the lubricants oil-lubricated Ball bearings or radial plain bearings in connection with such Kermaikwelle. U.S. Patent 5,899,673 which is a compressor / turbine or pump / turbine with integrated permanent magnet motor / generator disclosed and equipped with conventional ball bearings, may also be of interest.

Radial compressor systems were also operated with electric motors that using gearboxes with the compressor shaft were connected to the desired working speed of the compressor achieve. The gears, as well as the conventional ones equipped with them Oil-lubricated bearings required an oil flow to lubricate them.

Requirements for increasing the power density and effectiveness of small to medium-sized air compressor systems and that these machines become smaller, run quieter and require less maintenance are continuously increasing. It is believed that these requirements are best met using electric motor drives. High speeds are required to achieve the desired effectiveness of the compressor. Efforts to drive compressors directly with high-speed electric motors are discussed in Brondum et al. "High-Speed Direct-Drive Centrifugal Compressors for Commercial HVAC Systems," 1998 International Compressor Conference, Purdue, West Lafayette, Indiana 1417 , 1998 ; Gilon et al. "Experience with High Speed Induction Motors for Direct Driving of Compressors," Proceedings of the Twenty-Seventh Turbomachinery Symposium, Turbomachinery Laboratory, Texas A&M University, College Station, Texas, 1998; Gottschlich et al. "Lubrication Free Centrifugal Compressor," SAE Paper 941148, 1994; Gui et al. "Design and Experimental Study of High-Speed Low-Flow-Rate Centrifugal Compressor," IECEC Paber no. CT-39, ASME, 1995; Soong et al. "Novel High Speed Induction Motor for Commercial Centrifugal Compressor;" Proceedings 34th Annual IEEE Applications Conference, 1, pp 494-501, 1999; and U.S. Patent 5,924,847. These efforts involve the use of magnetic bearings. However, magnetic bearings are expensive, unreliable and require the use of safety bearings with additional complications.

The above goals for the air compressors are also desirable Goals for refrigerant compressors. However, the environmentally safe show alternative refrigerants currently used are low Compatibility with oil contamination. Also complicated the use of oils for lubrication in all applications Construction and functionality, for example due to contamination Need for seals and various maintenance requirements. In addition, the use of gears, seals, pumps etc. lowers effectiveness for this lubrication. Furthermore handle magnetic Bearing two-phase flows (e.g. found in refrigeration systems) are not well as required.

Accordingly, an object of the present invention, a means high-speed electric motor to create an oil-free compressor.

It is also the subject of the present invention, such To create a compressor that is reliable and effective, high Powerful, small, quiet and requires little maintenance.

In order to create such a compressor according to the invention, the Rotor of an electric motor and one or more compressor impellers integrally connected to a shaft, which by at least one oil-free, hydrodynamic film bearing lubricated with air or process fluid is rotatably mounted.

Above and other tasks, features and advantages of the present Invention are set forth in the following detailed description of preferred embodiment recognizable when viewed in conjunction with the attached drawings reads in all different views Identical reference symbols denote identical or similar components.

Brief description of the drawing

Fig. 1 shows a schematic sectional view along an axial plane of a compressor system, which comprises the present invention.

FIG. 2 shows a schematic sectional view along line 2-2 in FIG. 1.

Fig. 3 is a sectional view showing an alternative embodiment of the compressor system along an axial plane.

FIG. 4 shows a sectional view of a further embodiment of the compressor system similar to that from FIG. 3.

Detailed description of the preferred embodiment

Referring to Figures 1 and 2 of the drawings, generally at 10 there is shown a radial two-stage compressor which includes a shaft 12 to which a pair of compressor impellers 14 are integrally connected at opposite ends of the shaft 12, respectively, and to which a rotor is also connected 16 of a high-speed electric motor 18 (which has a stator 22 ) is integrally connected. Electrical wires 24 are used to provide electrical power to motor 18 from a conventional electrical power source 42 . The rotatable shaft 12 and the compressor impellers 14 and motor rotor 16 integrally connected thereto are suitably rotatably disposed within a housing 20 (as discussed below). The compressor impeller and motor rotor are integrally connected to the shaft to avoid bearings that would undesirably require oil.

The word "integral" as used herein and in the claims with respect to two parts that are joined together does not alone mean that the two parts are made of one piece of material as in Figs. 1 and 2 of the drawings for each of the compressor impellers and the shaft, but also the direct connection of the parts to one another, for example by welding or screw connection and / or interference fit, in order to form a structural unit without intermediate parts such as gears. Thus, the compressor impellers 14 and the motor rotor 16 are each integrally connected to the shaft 12 , so that the compressor impellers 14 are driven directly by the motor 18 (i.e. without an intermediate transmission) and thus rotate at the same speed as the motor rotor 16 . The impellers 14 and the shaft 12 can be made from the same piece of material and the motor rotor 16 can be suitably mounted on the shaft 12 .

Although a two-stage compressor is shown, it will be appreciated that compressor 10 may have only a single stage (a compressor impeller) or more than two stages. The compressor may either have a plurality of stages in series, as seen in FIG. 3 and described later herein, with the exit of each stage being fed to the entrance of the subsequent stage and the last stage forming the outlet of the compressor, or the compressor can have a plurality of parallel stages. It will be appreciated that motor 18 can be a motor / generator.

Have small to medium-sized compressors (in the range from 3 to 100 kW) desirably a high speed range from about 60,000 to 100,000 rpm (revolutions / minute) to achieve the desired effectiveness achieve. Therefore the engine must be a high-speed engine and it must be in be able to reach the required working speed as with oil driven gear cannot be used. High-speed engines, preferably brushless motors with such a compressor can be used are induction motors, permanent magnet Motors and switched reluctance motors.

According to a preferred embodiment of the present invention, the motor 18 is an induction motor since an induction motor is comparatively cheap, easier to assemble, more simple and suitable for larger machines such as pipeline compressors. In addition, permanent magnet motors have great negative stiffness, which complicates the integration (assembly) in a compressor system, ie they lead to zero loads on the foil bearings and can cause instability of the system.

Conventional switched reluctance motors cannot do the same shift quickly, as desired for high speeds. advantageously, an induction motor has no such negative stiffness or Power switching problems. A suitable induction motor could do this for example an EV90 engine element set marketed from Kab Biberach, Germany. A suitable compressor impeller for this for example, one from Concepts ITE, Inc. of White River Junction, Vermont, be displaced.

Since the induction motor or asynchronous motor 18 must be supplied with a voltage the frequency of which corresponds to the desired high speed, a conventional frequency converter 40 is provided to convert the normal 60 Hertz current of the voltage source 42 into the desired high frequency, which of the desired high Speed corresponds to which is fed to the motor 18 through the wires 24 . A suitable frequency converter could, for example, be a drive for high-speed motors, which is marketed by Spindel from Lorton, Virginia.

The elimination of the gears, pumps, seals and the like required for lubrication systems could, in addition to creating the benefits of one. Relief from oil contamination, increased effectiveness. To provide reliable and cost-effective oil-free bearings for the shaft 12 that do not require safety bearings, with the intent to realize small, reliable and efficient oil-free compressors with high power density, quiet running and low maintenance, and to be able to find them in cooling systems To adequately handle two-phase flows, according to the present invention, the radial bearings 26 and axial bearings 28 of the shaft 12 are hydrodynamic film bearings lubricated with air or process fluid.

Examples of suitable hydrodynamic radial and axial foil bearings are closed see U.S. Patents 6,158,893 and 5,961,217 to Heshmat, which are cited in were transferred to the holder of the present application and by Reference is made to the subject of this application. For the purpose of the present patent application describes the term "hydrodynamic" not just dynamic properties of a liquid, but all fluid-mechanical processes in the fluid or fluids within the Camp. Foil bearings combine a flexible construction element with a hydrodynamic lubricated with air or process fluid Component (self-assembling film), which gives the system both rigidity and cushioning is also awarded. The flexible storage can be a have several corrugated foils with protrusions, which are large Offer flexibility by adding dynamic properties for a specific System can be achieved. Additional flexibility is offered by provides either a single or multiple cover films. The compliant construction allows the films with increasing Speed are pushed radially outwards (with radial bearings) and thereby form a converging wedge shape. This converging wedge shape is with increasing speed and load more pronounced, which the Load capacity is increased. The compliant film adapts easily to thermal and centrifugal expansion of the rotor as well as thermal and mechanical Deformations of the bearing housing.

Such dynamic film bearings can advantageously handle two-phase flows (liquid / gas mixtures, including liquid gushes occurring in a gas) and are therefore ideal bearings for coolant compressors. Such hydrodynamic film bearings can advantageously use coolants or other process fluids or air for lubrication and are therefore oil-free. They have been found to work very effectively at high speeds (from 30,000 to well over 100,000 rpm) and under various environmental conditions ranging from cryogenic to high temperatures. They have little power loss, perform well under impact (Hehmat et al. "Compliant Foil Bearing Technology and Their Application to Highspeed Turbomachinery," 19 ^th Leeds-Lyon Symposium on Thin Film in Tribology - From Micro Meters to Nano Meters, Leeds , UK. Dowsen et al. Eds, Elsivier, pp 559-575, 1992) and have shown very long lifetimes in commercial applications. Such bearings can have a surface load capacity above 689 mPa (Heshmat et al. "Structural Damping of Self-acting Compliant Foil Journal Bearings," ASME Journal of Tribology, v. 116, pp 76-82, 1994) and the damping properties are considered sufficient considered to enable successful operation above the first system-critical speed (Heshmat, "Operation of Foil Bearings Beyond the Bending Critical Mode," ASME Preprint No. 99-TRIB-48, 1999). This enables the compressor to work with a supercritical rotor. In order to provide the desired reliability, effectiveness, high power density, small size, quiet operation and low maintenance for compressors in refrigeration machines and other compressors, according to the present invention, the hydrodynamic film bearing lubricated with air or process fluid is used in a compressor driven by a high-speed motor used.

The individual components of the compressor, in accordance with the present invention, can be arranged differently than shown in the drawings. For example, an alternator / motor may be attached to one end of the shaft and one or more stages of the compressor (one or more compressor impellers) may be located at the other end of the shaft, as shown in FIG. 4 and described in more detail below.

In Fig. 3, 100 generally designates an alternative embodiment of the compressor, which has a shaft 112 , a pair of compressor impellers 114 at the opposite ends of the shaft 112 , a motor 118 with rotor 116 and stator 122 and radial bearing 126, and axial bearing 128 , which are arranged together within a housing 120 . These components are similar to shaft 12 , compressor impellers 14 , motor 18 , bearings 26 and 28 and housing 20 of the embodiment of FIGS. 1 and 2, except in the cases shown or described differently below. Although shaft 112 and compressor impellers 114 , unlike the compressor in FIGS. 1 and 2, are separate components that are interconnected as described below, they are nevertheless integrally connected as defined above for that term , As seen in FIG. 3, the left end portion of the shaft 112 has an enlarged diameter. At its end is a protrusion 150 of reduced diameter, which corresponds to the diameter of the other end of the shaft, so that compressor impellers of the same size can be mounted on each end. A threaded bore 152 along with a counterbore 154 is centrally located in the left or enlarged end of the shaft 112 . A similar threaded bore 152 is made in the other end of the shaft 112 . Each of the compressor impellers 114 has a bore 156 that extends axially in the center of the impeller along with a counterbore 158 at the outer end of the impeller and a counterbore 166 at the inner end of the impeller for radial alignment. The protrusion 150 is received in the counterbore 166 in one compressor impeller 114 and the other end of the shaft 112 is received in the counterbore 166 in the other compressor impeller 114 . In between, press fitments are provided to maintain the radial positions with centrifugal expansion and to avoid the separation of the parts at high speeds.

Connecting bolts or bolts 160 and 162 are each received in the compressor impeller bore 156 and screwably received in the threaded bores 152 of the shaft. The inner portion 164 (which is screwed into the shaft 112 ) of the connecting bolt 160 has a reduced diameter, which forms a shoulder which bears against another shoulder which is formed by the associated countersunk bore 154 in order to precisely align the shaft 112 axially , A guided nut 168 (along with a washer 172 ) is received at the outer end of each connecting bolt 160 and 162 to create an axial preload, with a portion 172 of the reduced diameter nut 168 being received in the associated counterbore 158 .

Compressor system 100 is shown connected in series to maximize pressure so that the outlet or high pressure outlet 130 of one compressor stage with low pressure inlet 129 is fed to inlet 131 of the other compressor stage, as shown by pipe or line 133 , the outlet or Outlet 132 of the other compressor stage is fed to a suitable location for performing useful work. If desired, the compressor stages of the system 100 can be connected in parallel to maximize the volume dispensed, that is, each stage is powered by a source and the output thereof is directed to an appropriate location for useful work. Likewise, the compressors in Fig. 4, discussed below, can be connected either in series or in parallel.

In Fig. 4, 200 generally designates an alternative embodiment of the compressor, which includes a shaft 212 , a two-stage compressor impeller 214 , a motor 218 with rotor 216 and stator 222 and radial bearing 226 and axial bearing 228 . All components are suitably arranged within a housing 220 and are similar to shaft 112 , compressor impellers 114 , motor 118 , bearings 126 and 128 and housing 120 of the embodiment from FIG. 3, except in the cases shown or described differently below. In this embodiment, both compressor stages are attached to the same end of shaft 212 and have a single impeller that is suitably shaped to form both stages, which are therefore integrally connected to one another. It is noted that, if desired, both stages can be formed from a pair of compressor impellers which are suitably connected together, e.g. B. are screwed or welded. The housing 220 is suitably shaped to form the exits 230 and 232 of the two stages, ie a first housing section 280 is provided for the shaft, the motor, the bearings and the inner stage and a second housing section 282 is provided for the outer stage provided, the sections 280 and 282 being connected to one another by suitable means, for example screws or welding.

The shaft, like the compressor in FIG. 3, has an enlarged end portion that has a reduced diameter protrusion 250 , with a threaded bore 252 along with a counterbore 254 being provided centrally in the end of the shaft. The single compressor impeller 214 has a bore 256 axially extending axially through the impeller, a counterbore 258 at its outer end for radial alignment, and a counterbore 266 at its inner end. As with the compressor 100 in FIG. 2, the protrusion 250 is received in the counterbore 266 with a compression fit therebetween to maintain the radial position with centrifugal expansion and to avoid separating parts at high speeds.

A connecting bolt or screw bolt 260 is received in the bore of the compressor impeller 256 and screwed into the threaded bore 252 . The inner portion 264 (which is screwed into the shaft 212 ) of the connecting pin 260 has a reduced diameter, thereby forming a shoulder that abuts a shoulder formed by the associated counterbore 254 to precisely axially align the shaft 212 . A guided nut 268 (along with a washer 270 ) is disposed at the outer end of the connecting bolt 260 to create an axial preload, with a reduced diameter portion 272 of the nut 268 received in the counterbore 258 . A connecting bolt 284 is screwed centrally into the other end of the shaft 212 , and a nut 286 and washer 288 mounted on the bolt serve to maintain the position of the rotor 216 and create an axial preload.

It is noted that although the present invention is detailed herein has been described, the invention can be carried out without thereby deviate from the principles of the invention, and that such Embodiments are intended to be within the scope of the present invention as defined in the appended claims is.

Claims (9)

1. Oil-free compressor device with a housing ( 20 , 120 , 220 ), a shaft ( 12 , 112 , 212 ) rotatably arranged in the housing ( 20 , 120 , 220 ), a compressor ( 10 , 100 , 200 ) with at least one compressor impeller ( 14 , 114 , 214 ), which is integrally connected to the shaft ( 12 , 112 , 212 ), an electric motor ( 18 , 118 , 218 ) with a rotor ( 16 , 116 , 216 ) which is used to drive the compressor ( 10 , 100 , 200 ) is integrally connected to the shaft ( 12 , 112 , 212 ) and has at least one oil-free, hydrodynamic film bearing ( 26 , 28 ; 126 , 128 ; 226 ; 228 ) lubricated with air or process fluid for the shaft ( 12 , 112 , 212 ). 2. Compressor device according to claim 1, characterized in that said compressor ( 10 , 100 , 200 ) is a coolant compressor. 3. Compressor device according to claim 1 or 2, characterized in that said electric motor ( 18 , 118 , 218 ) is an induction motor or asynchronous motor. 4. Compressor device according to at least one of the preceding claims, further characterized by a frequency converter ( 40 ) for supplying said motor ( 18 ) with electrical voltage at a high frequency. 5. Compressor device according to at least one of the preceding claims, characterized in that said compressor ( 10 , 100 ) has a pair of said compressor impellers ( 14 , 114 ), which are respectively attached to the opposite ends of said shaft ( 12 , 112 ) , 6. Compressor device according to at least one of the preceding claims, characterized in that said compressor ( 200 ) has at least one compressor impeller ( 214 ) which is shaped such that it forms a plurality of compressor stages. 7. Compressor device according to at least one of the preceding claims, characterized in that a compression fitment is provided between said compressor impeller ( 114 , 214 ) and said shaft ( 112 , 212 ) and the compressor device has at least one connecting element ( 160 , 162 , 168 ; 260 , 268 ) for connecting said compressor impeller ( 114 , 214 ) to said shaft ( 112 , 212 ). 8. Compressor device according to claim 7, characterized in that said connecting element comprises a connecting bolt ( 160 , 162 ; 260 ) and a guided nut ( 168 ; 268 ). 9. Compressor device according to at least one of the preceding claims, characterized in that it has both an axial film bearing ( 28 , 128 , 228 ) and a radial film bearing ( 26 , 126 , 226 ).