Compressor Assembly

Abstract

The compressor assembly (1) comprises a motor (2) having a motor shaft (7) which drives at least one compressor rotor (5, 6) of a compressor element (3) as well as an oil pump (18, 63), the compressor rotor (6) comprising a compressor rotor portion (35) mounted on a compressor rotor shaft (33) which is coupled to the motor shaft (7) by a direct coupling (40) to form an assembly drive shaft (45), and the oil pump (18) is mounted on the assembly drive shaft (45) or directly on a separate compressor rotor shaft (32).

Description

[Technical Field]

[0001] The present invention relates to a compressor assembly that includes a motor having a motor shaft that drives at least one compressor rotor of a compressor element.

[0002] The motor is typically an electric motor, but could also be an internal combustion engine, or in principle any other type of rotary drive or actuator or combination of devices for generating rotary motion.

[0003] The compressor element of the compressor assembly is intended to compress or pressurize a fluid, typically a gaseous fluid such as air or another gas such as oxygen, carbon dioxide, nitrogen, argon, helium or hydrogen, however, it is not excluded from the present invention that the compressor be used to compress or pressurize denser fluids such as water vapor, etc.

[0004] The present invention is particularly relevant to compressor assemblies in which the compressor elements are oil-free or oil-less compressor elements, meaning that no lubricating oil is injected between the compressor rotors themselves.

[0005] An oil-free compressor element is not a compressor element in which no oil is used at all, but generally includes an oil circulation system for lubrication or cooling purposes. Elements or components of a compressor assembly that require oil lubrication or cooling generally include gears, such as timing gears of the compressor assembly or gears of a geared power transmission between the compressor and the motor; the compressor outlet; compressor element shafts or compressor rotor shaft bearings; motor shaft bearings, etc.

[0006] The reason for using oil-free or oil-less compressor elements is that the fluid being pressurized or compressed within the compressor elements is kept free of or uncontaminated by oil, which is very important in, for example, food processing applications.

[0007] Various techniques can be used to compress or pressurize a fluid in a compressor element. The present invention relates to a compressor assembly, wherein the compressor element is a rotary compressor element having a compressor rotor driven for rotational movement by a motor.

[0008] The present invention particularly relates to a compressor assembly including an oil-free double rotor compressor element that uses oil as a lubricant and / or coolant, although the invention is not limited to this embodiment. The double rotor compressor element may be, for example, a screw compressor element or a tooth compressor element.

[0009] Nevertheless, the present invention is not limited to compressor assemblies with oil-free or oil-less compressor elements, and for example compressor assemblies with oil-injected compressor elements are not excluded from the present invention.

[0010] Additionally, the present invention is not limited to compressor assemblies with rotary compressor elements, as other types of compressor elements may be used.

[0011] In another aspect, the present invention also relates to a compressor assembly including an oil pump for pumping oil through the above-mentioned oil circulation circuit of the compressor assembly, and possible improvements with respect to this oil pump of the compressor assembly, such an oil pump being typically used to pump oil from an oil reservoir or sump to components of the compressor assembly and back to the oil reservoir or sump.

[0012] Furthermore, the present invention relates to a technique in which a motor shaft is connected to a rotor shaft of a compressor rotor of an associated compressor element. [Background technology]

[0013] In a typical conventional compressor assembly, the compressor assembly's motor indirectly drives the compressor rotor shaft of the compressor element of the compressor assembly through an intermediate gearbox or gear transmission, with gears fixedly attached to the motor shaft and compressor rotor shaft interacting with each other directly or through other gears that mesh with associated gears on the motor shaft and compressor rotor shaft.

[0014] Typically, but not necessarily, the motor shaft drives the rotor shaft of the male compressor rotor of the compressor element.

[0015] An intermediate gear transmission or gearbox allows the compressor rotor shaft to be indirectly driven at very high speeds, while the motor shaft rotates at a low, moderate motor speed.

[0016] An intermediate gear transmission or gearbox may be used to indirectly drive multiple stages, i.e., multiple compressor elements, by the same motor, and other rotating components of the compressor assembly, such as the rotor of the oil pump, may also be indirectly driven by the same motor through the intermediation of such a gear transmission or gearbox.

[0017] An obvious drawback of using an intermediate gear transmission or gearbox to interconnect the motor shaft and the compressor rotor shaft is the large space required for the compressor assembly. In particular, such intermediate gear transmissions or gearboxes usually have large bull gears and a surrounding gearbox with non-negligible dimensions. This makes it difficult to design a compact compressor assembly.

[0018] Another drawback of applying such intermediate gear transmissions or gearboxes is that they imply energy losses due to friction losses between the associated gears, etc., which adversely affect the efficiency and overall performance of the compressor assembly.

[0019] As explained above, for cooling and lubrication of the components of the compressor assembly, an oil circulation circuit is usually applied, with oil being pumped by an oil pump, which is often driven by a drive means such as an electric motor.

[0020] Another problem with existing compressor assemblies is that if the oil pump's drive means fails, cooling and lubrication of the compressor assembly components ceases, even if the compressor assembly is still operating at full capacity. Many measures can be taken to prevent this situation, using control means and means to shut down the compressor assembly in the event of a failure of the oil pump or its drive means. Typically, electronic control means are used for this purpose. This is quite complex, and furthermore, the installation of such a system is not practical. Furthermore, the electronics are quite vulnerable under high temperature and pressure conditions. This situation calls for an improved solution.

[0021] Furthermore, the oil pump and its drive means are either located near the compressor assembly or attached to the housing of the compressor assembly, and these components also take up a lot of space, making it difficult to design a compact compressor assembly.

[0022] It is also standard practice in the prior art to provide a multi-stage compressor assembly with a single oil pump and oil circulation circuit to supply oil for lubrication and cooling purposes to the different compressor elements that make up the multi-stage compressor assembly.

[0023] However, a problem with such designs is that oil contamination occurring in one compressor stage of a multi-stage compressor assembly, for example due to malfunction, wear, or abrasion of a particular component of that compressor stage, can easily be transmitted to all other compressor stages and can harm the components of the other compressor stages. In short, this type of design known in the prior art can result in the so-called cross-contamination problem. Summary of the Invention [Problem to be solved by the invention]

[0024] SUMMARY OF THE INVENTION It is an object of the present invention to overcome one or more of the problems mentioned above, and / or possibly further problems.

[0025] In particular, it is an object of the present invention to provide a compressor assembly having a more compact design compared to currently known compressor assembly designs.

[0026] Another object of the present invention is to provide a solution that is more efficient from an energy standpoint and cost effective.

[0027] It is yet another object of the present invention to increase the operational reliability and functional safety of the compressor assembly, and in particular to ensure the lubrication and cooling functions of the compressor assembly during operation in an efficient and reliable manner.

[0028] It is also an object of the present invention to provide a compressor assembly design that allows for a more modular construction of multi-stage compressor assemblies, with each "module" or compressor stage functioning as a separate unit that does not substantially impact other "modules" or compressor stages of the compressor assembly.

[0029] It is a further object of the present invention to provide a compressor assembly design that provides improved integration of the means for pumping oil through the compressor assembly. [Means for solving the problem]

[0030] To this end, the present invention relates to a compressor assembly comprising a motor having a motor shaft for driving at least one compressor rotor of a compressor element as well as an oil pump for pumping oil through an oil circulation system of the compressor assembly, said at least one compressor rotor being mounted on a rotor shaft which is coupled to the motor shaft by a direct coupling to form an assembly drive shaft, and the oil pump being mounted directly on the assembly drive shaft or on another rotor shaft of a compressor element of the compressor assembly.

[0031] A first major advantage of such a compressor assembly according to the present invention is that, because the motor shaft is directly connected to the rotor shaft of the compressor assembly, no intermediate gear transmission or gearbox is required to interconnect the motor and the compressor elements driven by the motor.

[0032] In this way, a very compact compressor assembly can be obtained, saving a lot of space.

[0033] An additional benefit associated with the absence of such an intermediate gear transmission or gearbox is that there is no energy loss due to torque transfer from the motor shaft to the coupled compressor rotor shaft, as opposed to the constant losses that occur during torque transfer between gear wheels in gear transmissions. As a result, such a compressor assembly according to the present invention is more energy efficient and has higher overall performance.

[0034] Another important and highly advantageous aspect of the compressor assembly according to the present invention is that the oil pump is mounted either directly to the motor shaft and rotor shaft combination, which are directly interconnected by a direct coupling and which combination form the assembly drive shaft, or to a separate rotor shaft of the compressor element of the compressor assembly.

[0035] The major advantage of this arrangement is that, firstly, the oil pump is driven together with the compressor element by the same motor. This means that if the motor fails, the compressor element stops as well as the oil pump. In this way, a situation where the oil pump fails while the compressor element is still running, which could occur if the oil pump were driven by a separate drive means, does not occur.

[0036] Another major advantage is that the oil pump is fully integrated into the core of the compressor assembly, i.e., close to the drive element of the compressor assembly, more specifically on the assembly drive shaft or on a separate rotor shaft, and since the oil pump is not located at the periphery of the compressor assembly, a very compact design of the compressor assembly is ensured.

[0037] Yet another advantage of such a compressor assembly according to the present invention is that it allows for a more modular construction of multi-stage compressor assemblies, as will be shown in detail herein by way of example.

[0038] It should be appreciated that such a compressor assembly according to the present invention is also more compatible with modern technological trends, where more and more high-speed drives or motors and bearings are being developed and made available. In fact, directly connecting the motor shaft to the compressor rotor shaft without an intermediate gear transmission only makes sense if the motor is able to drive the compressor rotor shaft at the required high speeds necessary to achieve realistic compression of the fluid in the compressor elements.

[0039] However, the selection of a direct coupling between the motor shaft and the compressor rotor shaft is far from obvious and must be designed or constructed with appropriate technology depending on the circumstances. This design may be constrained by many factors.

[0040] For example, large torque pulsations commonly occur not only in tooth compressor elements but also in other compressor elements, resulting in stringent requirements for the rated torque delivered by the direct coupler, which means that there is a large ratio between the rated peak torque delivered by the direct coupler and the rated torque of the direct coupler.

[0041] Another parameter that complicates the design of a reliable direct coupling between the motor shaft and the compressor rotor shaft is the high operating speed required in such compressor applications to achieve actual compression or a sufficiently high compression ratio or fluid flow rate through the compressor elements.

[0042] Additionally, the environment in which direct couplers must operate places severe constraints on their design, which is typically an oil-contaminated, high-temperature environment.

[0043] Furthermore, the motor shaft and compressor motor shaft connected by the direct coupler are often made of different materials and typically have different physical properties, such as different coefficients of thermal expansion, which further complicates the task of designing a reliable direct coupler of the type under consideration.

[0044] Therefore, it is a great challenge to realize and design a direct coupling between the motor shaft and the compressor rotor shaft that has a long service or maintenance free life.

[0045] Another factor preventing the use of a direct coupler on a compressor assembly is its location within the compressor assembly housing, which is rather an inaccessible location with poor visibility between the motor and the compressor elements of the compressor assembly.

[0046] Also, the application of a direct coupler may introduce limitations on the modifications possible on the part of the compressor elements, and therefore this is considered a so-called "frozen design".

[0047] The configuration proposed in this invention is even more challenging because not only is the motor shaft directly connected to the rotor shaft of the compressor assembly, but at the same time the oil pump is integrated into the compressor assembly and driven by the same motor as the compressor elements of the compressor assembly.

[0048] Mounting such an oil pump directly on the compressor assembly drive shaft or another rotor shaft is not obvious, as these shafts rotate at very high rotational speeds that are suitable for the compression process but not necessarily for the pumping process.

[0049] The greater the distance from the central axis of such a rotating shaft, the higher the local speeds experienced by the rotating elements attached to that shaft.

[0050] As a result, as the radial size of the oil pump rotor increases, the velocities experienced at the rotor tip also increase. However, once the rotor tip and pumped oil velocities increase above a certain level, there is an increased risk of cavitation occurring at low ambient pressures (such as at high altitudes).

[0051] Therefore, the radial size of the oil pump must be as small as possible to avoid cavitation. On the other hand, the assembly drive shaft or another rotor shaft must have a size or diameter that exceeds at least a certain minimum value to accommodate the high torque and speeds that are applied to these shafts. These two distinct requirements, namely, keeping the radial size of the oil pump as small as possible under high-speed conditions and having a drive shaft with a diameter or radial size large enough to accommodate high-speed and torque conditions, are clearly in conflict. Therefore, finding the appropriate balance between these two conflicting requirements is very difficult.

[0052] In conclusion, it can be said that designing a reliable direct coupler for application to a compressor assembly to directly connect the motor shaft to the compressor rotor shaft, and integrating an oil pump into the compressor assembly by directly mounting it on the compressor assembly drive shaft or another rotor, has many advantages, although it is not easy to realize in practice.

[0053] In a preferred embodiment of the compressor assembly according to the invention, the oil pump is mounted on a unitary solid shaft or on a unitary solid section of the shaft.

[0054] This detail of a particular embodiment of a compressor assembly according to the present invention may at first glance appear rather arbitrary, but it has basis in reality as will become more apparent in the text.

[0055] Indeed, to achieve a rigid direct coupling between the motor shaft and the associated rotor shaft of the compressor rotor element, it is advantageous to utilize a hollow shaft and stud arrangement, which is at the same time practical to use, for example for assembling and disassembling the connection, but also for other reasons.

[0056] According to the present invention, it is not practically feasible to mount an oil pump on such a hollow shaft or hollow portion of a shaft, because the diameter of such a shaft would still be too large to allow for mounting a rotor of an oil pump exceeding that diameter, for the reasons mentioned above, such as cavitation problems.

[0057] The proposal of the present invention is to mount the oil pump rotor on a shaft or shaft section that is fully materialized from its central axis to its outer diameter and that is strong enough to withstand high torque loads at very high rotational speeds and the forces required to drive the oil pump rotor. A solid oil pump shaft also has the advantage of being stiffer and stronger. Therefore, the oil pump shaft deflects less under the applied load of the pump outlet pressure. Reducing pump shaft deflection reduces the risk of damage to the oil pump. Such a fully materialized shaft or shaft section can also be implemented in small dimensions that are strong enough to handle all relevant loads.

[0058] A great advantage of such an embodiment of the compressor assembly according to the invention is that it results in a rigid direct coupling between the motor shaft and the rotor shaft, which is very convenient to use and at the same time the oil pump is completely and thoroughly integrated into the compressor assembly, since it remains attached to the drive shaft of the compressor assembly.

[0059] In a preferred embodiment of a compressor assembly according to the present invention, the oil pump is mounted on the non-drive side of the motor or compressor element, opposite the drive side where the motor shaft is connected to the associated rotor shaft of the compressor element by a direct coupler.

[0060] A major advantage of such an embodiment of the compressor assembly according to the invention is that the oil pump is provided outside the compressor assembly, either at the free end of the rotor shaft or at the free end of the motor shaft, and is thus easily accessible, for example for maintenance, to connect oil lines, to assemble or disassemble the oil pump, etc.

[0061] In yet another preferred embodiment of the compressor assembly according to the present invention, the oil pump is a gerotor pump.

[0062] Gerotor pumps are very simple pumps that can be easily implemented in small dimensions and are suitable for use at the high rotational speeds applied to compressor assemblies. The drive force or torque required to operate a gerotor pump is fairly limited. In fact, this is one of the main advantages of integrated oil pumps, and gerotor oil pumps in particular, because they can efficiently deliver a given oil flow rate while consuming little power. Additionally, gerotor pumps have very small clearances to optimize volumetric efficiency. This means that gerotor pumps have a low leakage rate compared to other types of oil pumps.

[0063] In a possible embodiment of the compressor assembly according to the invention, the direct coupler is a flexible coupler.

[0064] Such an embodiment of the compressor assembly according to the present invention is advantageous in that the flexible coupling has damping properties provided by the damping elements of the flexible direct coupling to reduce torsional vibrations present in the driveline formed by the coupling between the motor shaft and the compressor rotor shaft.

[0065] Another advantage of such an embodiment of the compressor assembly according to the invention is that the flexible direct coupling is relatively easy to assemble and design, indeed it does not make high demands as far as the tolerances of the assembly are concerned and can accommodate possible misalignments between the components of the compressor assembly.

[0066] A further advantage of such an embodiment of the compressor assembly according to the present invention is that the oil pump can be easily integrated into the compressor assembly and can be incorporated into any available non-drive side of either the motor shaft or one of the compressor rotors.

[0067] In another possible embodiment of the compressor assembly according to the invention, the direct coupling between the motor shaft and the rotor shaft is a rigid direct coupling.

[0068] Although this may still be a non-obvious choice to directly interconnect the compressor assembly motor shaft and compressor rotor shaft for many of the reasons discussed above, it allows for a more compact drive train for the compressor assembly.

[0069] First, the relatively large flexible coupling is no longer required. Furthermore, by using a rigid direct coupling instead of a flexible direct coupling in the driveline, other components of the compressor assembly can be eliminated. For example, the drive-side motor bearing, its associated oil lubrication passages, and associated seals can be eliminated.

[0070] In fact, when a rigid direct coupler is used, the combination of the motor shaft directly connected to the compressor shaft by the rigid direct coupler can be considered a single assembly drive shaft that is fully rotatably supported within the compressor assembly housing by, on the one hand, a pair of rotor shaft bearings for supporting the rotor shaft end of the assembly drive shaft, and, on the other hand, a single motor shaft bearing on the non-drive side of the motor for supporting the motor shaft portion of the assembly drive shaft.

[0071] In yet another embodiment, it is contemplated that no bearings may be used to support the motor shaft, resulting in a hanging design for the motor.

[0072] In a preferred embodiment of the compressor assembly according to the invention, the rigid direct coupling between the motor shaft and the rotor shaft is a rigid press-fit coupling or a rigid heat-shrink coupling. In yet another embodiment of the compressor assembly according to the invention, the rigid direct coupling between the motor shaft and the rotor shaft is an interference-fit coupling, a press-fit coupling, or a friction-fit coupling.

[0073] A significant advantage of such an embodiment of the compressor assembly according to the present invention is that the motor shaft can be press fit or heat shrunk onto the compressor rotor shaft to form a rigid coupling. These manufacturing methods are highly efficient, relatively easy to perform, and cost effective.

[0074] In yet another preferred embodiment of the compressor assembly according to the invention, in order to form a rigid direct coupling between the motor shaft and the rotor shaft, preferably one of the motor shaft and the rotor shaft is embodied as a hollow shaft with a central axially extending passageway extending through the hollow shaft, in which a connecting stud is provided within the axially extending passageway of the hollow shaft, the connecting stud extending at a first end into the other of the motor shaft and the rotor shaft, which is not embodied as a hollow shaft, the connecting stud being fixedly connected at the first end to the solid shaft, and at an opposite second end of the connecting stud a tensioning means is provided for tensioning the stud with respect to the hollow shaft.

[0075] A great advantage of such an embodiment of the compressor assembly according to the invention is that the motor shaft and the associated compressor rotor shaft are rigidly connected to each other at their end faces by means of connecting studs, either by axial or conical clamping, and tensioning means provide an axial force pressing the end faces of the motor shaft and compressor rotor shaft together, generating a clamping force between the end faces.

[0076] The result is a rigid interconnection between the motor shaft and the compressor rotor shaft, transferring torque between these shafts without energy loss.

[0077] Another advantage of such interconnections by rigid direct couplers, in which connecting studs are used to generate the axial clamping force, is that the couplers can be fastened or loosened from the non-drive side of the associated hollow shaft, which in some cases is the motor shaft or compressor rotor shaft. In this way, disassembly can be initiated without opening the entire compressor assembly housing.

[0078] Also, if a radial press fit is applied to realize the rigid coupling, a connecting stud may be required for easy disassembly of the rigid direct coupling.

[0079] Indeed, when a radial press fit (or shrink fit) is used for the rigid connector, the outer shaft is heated and brought onto the inner shaft, and the rigid connector is obtained after the outer shaft has cooled and contracted.

[0080] When such press-fit or shrink-fit rigid connectors need to be disassembled, oil under pressure is usually applied between the two interconnected shafts. Furthermore, the shaft being removed is simultaneously subjected to a pulling force, which is generated by applying a pushing force on the other shaft. This pushing force on the other shaft can be realized in a practical manner by the connecting stud of the above-mentioned configuration.

[0081] In a preferred embodiment of the compressor assembly according to the invention, the clamping force required to ensure proper torque transmission on the coupler and for the proper functioning of the rigid direct coupler is reduced by using friction shims or so-called Hirth couplings or serrations between the end faces of the motor shaft and the compressor rotor shaft.

[0082] Friction shims increase the friction between the end faces of associated shafts, thereby preventing rotational movement between those end faces with a smaller axial clamping force than would be required if such friction shims were not used and the end face friction were not increased. The objective, of course, is to transmit torque from one shaft to another without slippage between the shaft end faces under a given applied axial clamping force.

[0083] In fact, it is known that flat surfaces in contact with each other can be moved relative to each other by applying at least a minimum force directed tangentially or parallel to the surfaces. The minimum tangential force required depends on (is proportional to) the normal force applied to press the surfaces together. For the same applied normal force, this required tangential force will be lower if the friction between the surfaces is low than if the friction between the surfaces is high.

[0084] The application of such friction shims also allows the size or diameter of the connecting stud to be reduced.

[0085] When Hirth couplings or serrations are used, there is no significant or even any risk of slippage occurring between the end faces of the rotor shaft and motor shaft during torque transmission, because such couplers or serrations have teeth on their respective end faces that are complementary when brought together from the mechanical interlocking of the shafts.

[0086] The invention will be further explained with reference to the drawings. [Brief explanation of the drawings]

[0087] [Figure 1] 1 is a schematic diagram illustrating an embodiment of a compressor assembly according to the prior art. [Figure 2] 1 is a schematic diagram illustrating an embodiment of a compressor assembly according to the prior art. [Figure 3] 1 and 2, an embodiment of a compressor assembly with a flexible direct coupler according to the invention is shown. [Figure 4] 1 and 2, an embodiment of a compressor assembly with a rigid direct coupler according to the invention is shown. [Figure 5] FIG. 5 is a schematic diagram of a two-stage compressor assembly formed from two of the compressor assemblies shown in FIG. [Figure 6] 1 is a simplified diagram of a cross section through a gerotor pump. [Figure 7]5 shows an embodiment of a compressor assembly according to the present invention that is a preferred alternative to the embodiment shown in FIG. [Figure 8] The part designated F08 in FIG. 7 is shown in greater detail on a larger scale. [Figure 9] A larger scale detail of the part designated F09 in Figure 7. [Figure 10] Similar to FIG. 9, but on a larger scale, the relevant components for an alternative interconnection at the end faces of the rotor shaft and motor shaft are shown. [Figure 11] Similar to FIG. 9, but on a larger scale, the relevant components for an alternative interconnection at the end faces of the rotor shaft and motor shaft are shown. [Figure 12] 11 is an enlarged perspective view of the part indicated by F12 in FIG. [Figure 13] 11. The part designated by F13 in FIG. 11 is shown in an enlarged front view. [Figure 14] 7 shows yet another embodiment of a compressor assembly according to the present invention, which is an alternative to the embodiment shown in FIG. [Figure 15] 7 shows yet another embodiment of a compressor assembly according to the present invention, which is an alternative to the embodiment shown in FIG. [Figure 16] 7 shows yet another embodiment of a compressor assembly according to the present invention, which is an alternative to the embodiment shown in FIG. [Figure 17] 7 shows yet another embodiment of a compressor assembly according to the present invention, which is an alternative to the embodiment shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0088] 1 shows a prior art compressor assembly 1. The compressor assembly 1 includes a motor 2 that drives a compressor element 3. The compressor assembly 1 includes an intermediate gear transmission 4 disposed between the motor 2 and the compressor element 3 to interconnect the motor 2 and the compressor element 3.

[0089] As explained at the beginning, a major advantage of such an arrangement is that the rotational speed of the motor 2 can be kept relatively low. This relatively low rotational speed is converted to a higher rotational speed by the intermediate gear transmission 4 required to drive the compressor rotors 5 and 6 of the compressor element 3.

[0090] The motor has a motor shaft 7 connected at one end 8 to a gear transmission shaft 10 on the drive side 9, which is rotatably supported within an intermediate gear transmission housing 11 by a pair of bearings 12 and 13.

[0091] The connection between the motor shaft 7 and the gear transmission shaft 10 is realized by an intermediate coupler 14 .

[0092] A drive gear 15 is fixedly mounted on the gear transmission shaft 10 and meshes with a driven pinion wheel 16 which is fixedly mounted on one compressor rotor shaft 17 of the compressor rotor 6 of the compressor element 3.

[0093] The compressor assembly 1 also includes an oil pump 18 which is not integrated into the compressor assembly 1 and is driven by a separate electric motor 19 to pump oil through an oil circulation system 20 from an oil reservoir 21 to the compressor assembly 1 and back to the oil reservoir 21.

[0094] FIG. 2 shows another compressor assembly 1 according to the prior art, which is a two-stage compressor assembly 1 and comprises a first compressor element 3 and a second compressor element 22 similar to those described above.

[0095] The two compressor elements 3 and 22 are driven by the same motor 2 and motor shaft 7 , again via an intermediate gear transmission 4 .

[0096] At this time, the drive gear 15 of the intermediate gear power transmission device 4 is engaged with a driven pinion wheel 16 for driving the first stage formed by the first compressor element 3, and a similar driven pinion wheel 23 for driving the second stage formed by the second compressor element 22.

[0097] This is clearly a practical way to drive two compressor stages simultaneously with one motor 2. On the other hand, there is no flexibility to control the rotational speed of the two compressor stages 3 and 22 independently of each other.

[0098] An oil pump 18 supplies oil to the two compressor stages 3, 16, which, as explained at the beginning, implies a high risk of so-called cross-contamination.

[0099] 3 shows a compressor assembly 1 according to the present invention. The compressor assembly 1 comprises a motor 2, in this case an electric motor, mounted in a motor housing 24 and comprising a motor shaft 7 extending axially in the direction XX' through the motor housing 3. The motor shaft 7 comprises a motor rotor 25 which rotates together with the motor shaft 7 within a motor stator winding 26 fixedly mounted within the motor housing 24.

[0100] On the drive side 9 of the motor 2, a compressor element 3 is connected to the motor 2.

[0101] As explained at the beginning, the present invention is particularly relevant to a compressor assembly 1 in which this compressor element 3 is an oil-free or oil-less compressor element 3 .

[0102] According to the present invention, the compressor element 3 of the compressor assembly 1 is preferably a double rotor compressor element 3, more particularly, the compressor element 3 of the compressor assembly 1 is preferably a tooth compressor element 3 or a screw compressor element 3.

[0103] The compressor element 3 comprises compressor rotors 5 and 6 mounted in a compressor element housing 27 and operable to cooperate with one another to compress a fluid 28 supplied to the compressor element 3 at a compressor inlet 29. The compressed or pressurized fluid 30 is discharged at a compressor outlet 31 for supply to a consumer or consumer network of the pressurized or compressed fluid 30.

[0104] In this case, the fluid is air drawn from the surroundings of the compressor element 3, but this does not necessarily have to be the case.

[0105] Each of the compressor rotors 5 and 6 has a compressor rotor shaft, a compressor rotor shaft 32 and a compressor rotor shaft 33, and is provided with a compressor rotor portion, a compressor rotor portion 34 and a compressor rotor portion 35, respectively, in the center.

[0106] The compressor rotor portion 34 may be a female rotor portion 34 cooperating with a male rotor portion 35 to form another compressor rotor portion 35, or vice versa. In practice, each of the compressor rotor portions 34 and 35 may be, for example, a screw rotor of a screw compressor element or a tooth rotor of a tooth compressor element, although other types are not excluded from the present invention.

[0107] Compressor element shafts 32 and 33 are each rotatably supported within compressor element housing 27 by a pair of compressor rotor shaft bearings, a pair of compressor rotor shaft bearings 36 and 37 and a pair of compressor rotor shaft bearings 38 and 39, respectively.

[0108] In order for the electric motor 2 to drive the compressor element 3, and more precisely the compressor rotors 5 and 6 of the compressor element 3, the motor shaft 7 is, according to the invention, directly connected to the compressor rotor shaft 33 of the compressor rotor 6 by a direct coupler 40 of the associated shafts 7 and 33. The direct coupler 40 is provided between a free end 41 of the motor shaft 7 and a free end 42 of the compressor rotor shaft 33, and is arranged in an intermediate housing section 43 provided between the motor housing 24 and the compressor element housing 27.

[0109] The motor housing 24 , compressor housing 27 and intermediate housing section 43 cooperate to form a compressor assembly housing 44 .

[0110] The combination of the interconnected motor shaft 7 and compressor rotor shaft 33 and direct coupler 40 can be considered to form a composed drive shaft 45 .

[0111] 3, the direct coupling 40 between the motor shaft 7 and the compressor rotor shaft 33 is a flexible direct coupling 46. Typically, such a flexible direct coupling 46 may include one or more damping elements that contribute to driveline vibration damping and can accommodate minor misalignments between the associated shafts 7 and 33.

[0112] In this case, a flexible direct coupling 46 is used so that the rotor shaft 7 is rotatably supported within the motor housing 24 by a pair of motor shaft bearings 47 and 48 .

[0113] As a result, compressor rotor 6 of compressor element 3 is directly driven by motor shaft 7. The other compressor rotor 5 is indirectly driven by interaction between two timing gears 49 and 50 attached to non-drive ends 51 of compressor rotor shafts 32 and 33, respectively.

[0114] Finally, on the non-drive side 52 of the motor 2, i.e., opposite the drive side 9 where the motor 2 is connected to the compressor element 3, the compressor assembly 1 further comprises an oil pump 18. This oil pump 18 is in turn integrated into the motor housing 24 or mounted on the motor housing 24 or on a motor housing cover of the motor housing 24.

[0115] Important for the invention is the feature that this oil pump 18 is mounted directly on the motor shaft 7 of the electric motor 2, or more generally on the assembly drive shaft 45 or on a separate compressor rotor shaft 32 of the compressor element 3. In this way, a thorough integration of the oil pump 18 of the compressor assembly 1 is obtained, which makes it possible to realize a very compact design of the compressor assembly.

[0116] As explained at the beginning, the choice of mounting the oil pump 18 directly on one of the above-mentioned shafts 7, 32 or 45 is not obvious, since these shafts 7, 32 or 45 rotate at very high rotational speeds.

[0117] Of course, the oil pump 18 is intended to provide the driving force for circulating the oil 53 within the oil circulation system 20 of the compressor assembly 1. The oil circulation system 20 is intended to supply the oil 53 to the components of the compressor assembly 1 for lubrication and / or cooling purposes.

[0118] Oil 53 is drawn into oil pump inlet 54 through suction line 55 from oil reservoir 21 or sump 21, which is preferably also integrated into compressor assembly housing 44, for example by being mounted directly below motor housing 24. Oil is further pumped through oil pump pressure line 56 to the relevant components of compressor assembly 1 and returned to oil reservoir or sump 21. Oil circulation system 20 typically also includes an oil cooler and an oil filter, although these are not shown.

[0119] Typically, components of compressor assembly 1 that require lubrication are, for example, bearings such as motor shaft bearings 47 and 48, or compressor rotor shaft bearings 36-39, or gears such as timing gears 32 and 33. Components that require cooling are, for example, electric motor 2, compressed fluid 30 at outlet 31 of compressor element 3, compressor element 3 itself, or other elements of compressor assembly 1.

[0120] Such an embodiment of the compressor assembly 1 according to the invention proves to be very interesting in that a very sophisticated integration of the components within the compressor assembly is achieved.

[0121] However, FIG. 4 shows another embodiment of a compressor assembly according to the present invention in which, compared to the embodiment of FIG. 3, more elements are integrated or some elements are removed.

[0122] In this case, the motor shaft 7 and the compressor rotor shaft 33 are still interconnected by a direct coupler 40 , but the direct coupler 40 is now a rigid direct coupler 57 .

[0123] In the example of FIG. 4, this rigid direct coupling 57 between the motor shaft 7 and the compressor rotor shaft 33 is a rigid press-fit coupling or a rigid heat-shrink coupling 57 .

[0124] In the first step to achieving this rigid direct coupler 57, the end 8 of the motor shaft 7 is heated to increase its radial size. This heated end 8, now with its increased radial size, is then brought over the end 42 of the compressor rotor shaft 33. After cooling, the motor shaft end 8 shrinks, resulting in a strong, rigid interconnection between the motor shaft 7 and the compressor rotor shaft 33.

[0125] Another difference from the embodiment of the compressor assembly according to the present invention shown in Figure 3 is that in the embodiment of Figure 4, the motor shaft 7 is rotatably supported within the motor housing 24 by only a single motor shaft bearing 58. In effect, the combination of the motor shaft 7 and the compressor rotor shaft 33, rigidly interconnected by the rigid direct coupler 57, can be considered to be a rigid assembly drive shaft 45, which is rotatably supported by a pair of bearings 38 and 39 (for the compressor rotor 6) within the compressor element housing 27 and a single motor shaft bearing 58 within the motor housing 24.

[0126] Of course, other configurations of bearing arrangements can be used to support the rigid assembly drive shaft 45.

[0127] FIG. 5 shows one embodiment of a compressor assembly 1 according to the present invention, which is a multi-stage compressor assembly 59, in particular a two-stage compressor assembly 59 comprising a first compressor stage 60 and a second compressor stage 61.

[0128] Each of the first compressor stage 60 and the second compressor stage 61 is implemented as a compressor assembly 1 that is an exact copy of the embodiment shown in FIG.

[0129] The stages 60 and 61 are connected in series, where the compressor outlet 31 of the compressor element 3 of the first stage 60 is interconnected with the compressor inlet 29 of the compressor element 3 of the second stage 61 by a fluid duct 62. In this way, the compressed fluid 30 compressed in the first stage 60 is supplied to the inlet 29 of the second stage 61, where it is further compressed and discharged at the compressor outlet 30 of the compressor element 3 of the second stage 61.

[0130] Each compressor stage 60 or 61 comprises a motor 2 having a motor shaft 7, as well as a compressor element 33 and an oil pump 18, both of which are driven by the motor shaft 7. The motor shaft 7 of each compressor stage 60 or 61 is coupled by a direct coupling 40 to the rotor shaft 33 of the associated compressor element 3 so as to form an assembly drive shaft 45. The oil pump 18 of each compressor stage 60 or 61 is in this case mounted directly on the assembly drive shaft 45, although these oil pumps 18 could equally well be mounted on another rotor shaft 32 of the associated compressor element 3 of such compressor stage 60 or 61.

[0131] Each compressor stage 60 or 61 is provided with a separate oil circulation system 20 with its associated oil pump 18 such that oil 53 is not exchanged between the oil circulation systems 20 of the different compressor stages 60 or 61 of the multi-stage compressor assembly 59. In this way, cross-contamination is clearly avoided.

[0132] As in the example of FIG. 4, the motor shaft 7 of each compressor stage 60 or 61 of the multi-stage compressor assembly 59 is supported by a single bearing 58 .

[0133] In accordance with the present invention, the oil pump 18 of the compressor assembly 1 is preferably a gerotor pump 63. Such a type of oil pump 18 is shown in Figure 6. The gerotor pump 63 is a positive displacement pump comprising an inner rotor 64 and an outer rotor 65. The inner rotor 64 has n teeth 66, i.e., seven teeth in the illustrated case, and the outer rotor 65 has n+1 teeth 67, i.e., eight teeth 67 in this case.

[0134] Rotors 64 and 65 rotate about their respective central axes, A and B, which are not coincident but are spaced apart from one another by a small distance. During rotation, the volume 68 between the teeth 66 of the inner rotor 64 and the teeth 67 of the outer rotor 65 permanently increases or decreases, resulting in a pumping action.

[0135] A major advantage of such a gerotor pump 63 is that it can be made in relatively small dimensions and is a very robust and reliable pump with excellent cavitation characteristics.

[0136] FIG. 7 shows another embodiment of a compressor assembly 1 according to the present invention, in which again a rigid direct coupler 57 is applied to interconnect the motor shaft 7 of the motor 2 of the compressor assembly 1 and the compressor rotor shaft 33 of the compressor element 3 of the compressor assembly 1.

[0137] In the embodiment shown in FIG. 7, to form a rigid coupling 57 between the motor shaft 7 and the compressor rotor shaft 33, one of the motor shaft 7 and the compressor rotor shaft 33 is implemented as a hollow shaft 69 that includes a central, axially extending passageway 70 extending therethrough.

[0138] In the case of Figure 7, the motor shaft 7 is embodied as a hollow shaft 69. An axially extending passage 70 of the hollow shaft 69 is provided with a connecting stud 71 which extends at a first end 72 on the other side of the motor shaft 7 into a compressor rotor shaft 33 which is not embodied as a hollow shaft 69 or into a solid shaft 73. This solid shaft 73 is the compressor rotor shaft 33 in the example described here.

[0139] The connecting stud 71 is fixedly connected at its first end 72 to a solid shaft 73. In the embodiment of FIG. 7, this fixed connection is realized in particular at the free end 42 of the compressor rotor shaft 33.

[0140] The interconnection between the first end 72 of the connecting stud 71 and the free end 42 of the compressor rotor shaft 33 is shown in more detail in Figure 8. For that reason, the solid shaft 73 is provided with an internally threaded bore 74 for receiving the first end 72 of the connecting stud 71, and the first end 72 of the connecting stud 71 is provided with an external thread 75 that can cooperate with the internal thread 74 of the solid shaft 73.

[0141] At the opposite second end 76 of the connection stud 71 there is provided tensioning means 77 for tensioning the connection stud 71 with respect to the hollow shaft 69. This is shown in more detail in Figure 9. The second end 76 of the connection stud 71 is provided with an external thread 78 which is cooperable with a nut 79 having an internal thread in order to tighten the connection stud 71 by applying a force against the hollow shaft 69, in this case the motor shaft 7.

[0142] 10 and 12 show an embodiment in which the rigid direct interconnection 57 between the motor shaft 7 and the compressor rotor shaft 33 is improved compared to when the torque is transmitted by preloading the motor shaft 7 and the compressor rotor shaft 17 in order to realize the rigid direct interconnection 57 and generate a clamping force F by means of a connecting stud 71 and a tensioning means 77. In particular, the clamping force F required to ensure proper torque transmission on the interconnection 57 and for the proper functioning of the rigid direct interconnection 57 is reduced using a so-called Hirth coupling or serrations 81 at or between the end faces 82 and 83 of the motor shaft 7 and the compressor rotor shaft 33.

[0143] 12, such hearth serrations 81 are achieved by providing end faces 82 and 83 of the motor shaft 7 and compressor rotor shaft 33 with complementary interlocking teeth 84 that prevent the end faces 82 and 83 from rotating relative to one another when interlocked. It is clear that the axial clamping force F required to prevent rotational slip of the end faces 82 and 83 relative to one another is not very large.

[0144] Another alternative solution, in which the rigid direct coupler 57 is also an interconnected coupler, can be realized by implementing the rigid direct coupler 57 as a splined coupler. In that case, one of the ends of the motor shaft 7 and the compressor rotor shaft 33 is provided with axially extending teeth that are provided on the outer periphery and complementary to axially extending grooves provided on the interior of the other of the ends of the motor shaft 7 and the compressor rotor shaft 33. The teeth are inserted into the axially extending groove to rigidly and directly connect the motor shaft 7 and the compressor rotor shaft 33 and transmit torque between the shafts 7 and 33. With this configuration, there is obviously no risk of slippage between the end faces of the motor shaft 7 and the compressor rotor shaft 33.

[0145] In further embodiments of the compressor assembly 1 according to the invention, the rigid direct coupling 57 between the motor shaft 7 and the compressor rotor shaft 33 can be realized in other complementary shapes that ensure reliable transmission of torque.

[0146] 11 and 13 show another embodiment in which the friction between the end faces 82 and 83 of the associated shafts 7 and 33 is made less extreme by means of a friction shim 85, which is a kind of flat disc-shaped ring 85 having a roughened side surface 86 and which is mounted between the associated end faces 82 and 83. The side surface 86 is roughened, for example, by embedding particles such as diamond crystals or other particles into the associated side surface 86 or by giving the side surface 86 a cross-sectional shape that is not flat or smooth.

[0147] FIG. 14 shows an alternative and improved embodiment of a compressor assembly 1 according to the invention with respect to the embodiment shown in FIG.

[0148] In fact, in the embodiment shown in FIG. 7, the oil pump 18 is mounted on the assembled drive shaft 45 on the motor shaft section 7, which is implemented as a hollow shaft 69. This can be problematic in that the hollow shaft 69 needs to have a sufficiently large wall thickness T or outer diameter D. The increased outer diameter of the motor shaft 7 also affects the oil pump 18 mounted on it. Particularly in the case of the high rotational speeds applied in compressor applications, the increased size of the oil pump 18 is problematic, leading to high rotational speeds of the rotor tips 64 / 66 of the oil pump 18 and cavitation of the pumped oil 53, even when a gerotor pump 63 is used.

[0149] To prevent this situation, in the embodiment shown in FIG. 14 , the oil pump 18 is mounted on a free end 87 of the non-drive side 52 of the compressor rotor shaft 33, which in this embodiment still forms the solid shaft portion 73 of the assembled drive shaft 45. This free end 87 extends outward from the compressor element housing 27. In this way, it is ensured that the oil pump is mounted on a one-piece, fully solid, solid hollow or solid shaft 73 or on a one-piece, solid, solid portion 88 of such shaft 73. This shaft 73 or shaft portion 88 can therefore be implemented with an outer diameter that is smaller than the outer diameter of the hollow shaft portion 69 of the assembled drive shaft 45, as the case may be.

[0150] Additionally, the solidity of the compressor rotor shaft 33 implemented as a solid shaft 73 leads to increased stiffness.

[0151] On the other hand, the inner and / or outer diameter of the hollow shaft 69 (which is the motor shaft 7) can be increased, since the constraints imposed by the limited dimensional requirements of the oil pump 18 to avoid cavitation no longer exist on that side of the assembled drive shaft 45. As a result, the connecting stud 71 can be implemented with a larger radial dimension, allowing for a larger preload to be applied between the motor shaft 7 and the compressor rotor shaft 33. This also leads to a larger safety margin.

[0152] 15 to 17 show yet another embodiment of a compressor assembly 1 according to the invention, to which the same principles apply.

[0153] In the embodiment of FIG. 15, the oil pump is mounted on the free end 89 of the other compressor rotor shaft 32 of the compressor element 3, which is not part of the assembly drive shaft 45 but is nevertheless made by the interconnection of the compressor rotor shaft 33 with the motor shaft 7 by means of a rigid direct coupling 57. The motor shaft 7 is still embodied as a hollow shaft 69 with a connecting stud 71. The oil pump 18 is mounted on the integral solid part 88 of the compressor rotor shaft 31, as in the example of FIG. 14, but this shaft is embodied entirely as a solid shaft 73.

[0154] The embodiment of the compressor assembly 1 according to the invention shown in FIG. 16 differs from the above-described embodiment shown in FIG. 15 in that the assembly drive shaft 45 is now made up of a hollow shaft 69, the compressor rotor shaft 33, and a solid shaft 73, the motor shaft 7, interconnected by a rigid direct coupling 57. The compressor rotor shaft 33 has an axially extending passage 70 that extends through the hollow shaft 69. A connecting stud 71 is provided in the axially extending passage 70 of the hollow shaft 69 formed by the compressor rotor shaft 33. At a first end 72, the connecting stud 71 extends into the motor shaft 7, which is now a solid shaft 73. At its first end 72, the connecting stud 71 is fixedly connected to the solid shaft 73 in a manner similar to that described above. At its opposite second end 76, the connecting stud 71 is provided with tensioning means 77 for tensioning the connecting stud 71 with respect to the hollow shaft 69.

[0155] The oil pump 18 is still mounted on the integral, fully solidified compressor rotor shaft 31 of the other rotor 5 .

[0156] The embodiment of the compressor assembly 1 according to the invention shown in Figure 17 is similar to the embodiments of Figures 7 and 16. The similarity with the embodiment of Figure 7 is that the oil pump 18 is attached to the motor shaft 7 on the non-drive side 52 of the motor 2. The similarity with the embodiment of Figure 16 is that the motor shaft 7 is embodied as a solid shaft 73 and is coupled to the compressor rotor shaft 33, which is again a hollow shaft 69 with a central passage 70 and a connecting stud 71, and which is directly connected to the motor shaft 7 by means of a rigid direct coupling 57. The oil pump 18 is therefore again attached to the integral solid part 88 of the shaft 7.

[0157] The present invention is not limited to the embodiment of the compressor assembly 1 as described above, and such compressor assembly 1 can be applied and implemented in many different ways without departing from the scope of the present invention.

Claims

1. A compressor assembly (1) comprising a motor (2) having a motor shaft (7) for driving at least one compressor rotor (5, 6) of a compressor element (3) and an oil pump (18, 63) for pumping oil (53) through an oil circulation system (20) of the compressor assembly (1); the at least one compressor rotor (6) comprises a compressor rotor portion (35) attached to a compressor rotor shaft (33), the compressor rotor shaft (33) being connected to the motor shaft (7) by a direct coupling (40) to form an assembly drive shaft (45); the oil pump (18) is mounted directly on the assembly drive shaft (45), the oil pump (18) being mounted on an integral solid shaft (73) or an integral solid portion (88) of a shaft (7, 32, 33), the oil pump (18) being a gerotor pump (63), and the direct coupling (40) between the motor shaft (7) and the compressor rotor shaft (33) is a rigid coupling (57).

2. 2. The compressor assembly (1) of claim 1, wherein the oil pump (18) is mounted on a non-drive side (51, 52) of the motor (2) or the compressor element (3) opposite a drive side (9) at which the motor shaft (7) is coupled to the associated compressor rotor shaft (33) of the compressor element (3) by the direct coupler (40).

3. 2. The compressor assembly (1) of claim 1, wherein the rigid coupling (57) between the motor shaft (7) and the compressor rotor shaft (33) is a rigid press-fit coupling or a rigid heat-shrink coupling.

4. To form the rigid coupling (57) between the motor shaft (7) and the compressor rotor shaft (33), one of the motor shaft (7) and the compressor rotor shaft (33) is implemented as a hollow shaft (69) with a central axially extending passage (70), the passage (70) extending through the hollow shaft (69), and a connecting stud (71) is provided in the axially extending passage (70) of the hollow shaft (69), the connecting stud (71) being 2. The compressor assembly (1) according to claim 1, wherein the connecting stud (71) extends at one end (72) into the other of the motor shaft (7) and the compressor rotor shaft (33), which are embodied as a solid shaft (73), the connecting stud (71) being fixedly connected to the solid shaft (73) at the first end (72), and wherein an opposite second end (76) of the connecting stud (71) is provided with tensioning means (77) for tensioning the connecting stud (71) with respect to the hollow shaft (69).

5. 5. The compressor assembly (1) of claim 4, wherein the solid shaft (73) comprises an internally threaded hole (74) for receiving the first end (72) of the connecting stud (71), and the first end (72) of the connecting stud (71) comprises an external thread (75) capable of cooperating with the internal thread (74) of the solid shaft (73).

6. 5. The compressor assembly (1) of claim 4, wherein the second end (76) of the connection stud (71) comprises an external thread (78) capable of cooperating with a nut (79) having an internal thread (80) to apply a force against the hollow shaft (69) to tighten the connection stud (71).

7. 2. The compressor assembly (1) according to claim 1, wherein the compressor rotors (5, 6) of the compressor element (3) of the compressor assembly (1) each comprise a compressor rotor portion (34, 35) attached to a compressor rotor shaft (32, 33), and each of the compressor rotor shafts (32, 33) is supported by a pair of bearings (36-39).

8. 2. The compressor assembly (1) of claim 1, wherein the motor shaft (7) is supported only by a single bearing (58) or by a pair of bearings (38, 39) of the compressor rotor shaft (33) to which the motor shaft (7) is directly coupled by the direct coupler (40).

9. The compressor assembly (1) according to claim 1, wherein the compressor element (3) of the compressor assembly (1) is an oil-free or oil-less compressor (3).

10. The compressor assembly (1) of claim 1, wherein the compressor element (3) of the compressor assembly (1) is a double rotor compressor element (3).

11. The compressor assembly (1) according to claim 1, wherein the compressor element (3) of the compressor assembly (1) is a tooth or screw compressor element (3).

12. 2. The compressor assembly (1) according to claim 1, wherein the motor (2) of the compressor assembly (1) is an electric motor (2) including a motor stator (26) inserted into a motor housing (24) and a motor rotor (25) mounted on the motor shaft (7) extending through the motor stator (26).

13. A multi-stage compressor assembly (59) comprising at least a first compressor stage (60) and a second compressor stage (61), each of said compressor stages (60, 61) being formed by a compressor assembly (1) according to any one of claims 1 to 12, each of said compressor stages (60, 61) comprising a motor (2) having a motor shaft (7), and a compressor element (3) and an oil pump (18), said motor shaft (7) driving both said compressor element (3) and said oil pump (18), said motor shaft (7) being connected by a direct coupler (40) to form an assembly drive shaft (45). a rotor shaft (33) of a compressor element (3) and the oil pump (18) is mounted on the assembly drive shaft (45) or directly on another rotor shaft (32) of the compressor element (3) associated with the compressor stage (60, 61), each of the compressor stages (60, 61) having a separate oil circulation system (20) including the oil pump (18) associated with the compressor stage (60, 61), such that oil (53) is not exchanged between the oil circulation systems (20) of the different compressor stages (60, 61) of the multi-stage compressor assembly (59).

14. 14. The multi-stage compressor assembly (59) of claim 13, wherein the motor shaft (7) of each of the compressor stages (60, 61) of the multi-stage compressor assembly (59) is supported by a single bearing (58).

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