BE1029627B1 - COMPRESSOR ASSEMBLY - Google Patents

Abstract

Compressor assembly (1) comprising a motor (2) with a motor shaft (7) driving at least one compressor rotor (5, 6) of a compressor element (3) and an oil pump (18, 63), a compressor rotor (6) compressor rotor section (35) mounted on a compressor rotor shaft (33) connected by direct coupling (40) to the motor shaft (7) to form a compound drive shaft (45) and to which the oil pump (18) is directly mounted on the compound drive shaft (45) or on another compressor rotor shaft (32).

Description

COMPRESSOR ASSEMBLY

TECHNICAL FIELD

The present invention relates to a compressor assembly comprising a motor with a motor shaft driving at least one compressor rotor of a compressor element.

[02] The motor is usually an electric motor, but can also be an internal combustion engine, or in principle can be any other type of rotary drive or activator or combination of rotary motion generating devices.

The compressor element of the compressor assembly is intended to compress or pressurize a fluid, usually 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 invention that the compressor is used for compressing or pressurizing a fluid with a higher density, such as water vapor and the like.

[04] The invention is of particular interest for compressor assemblies where the compressor element is an oil-free or oilless compressor element, which means that no oil is injected for lubrication between the compressor rotors themselves of the compressor element.

[05] An oil-free compressor element is not a compressor element that does not use any oil at all, but usually includes an oil circulation system for lubrication or cooling purposes. Elements or components of the compressor assembly that require oil lubrication or cooling generally include: gears, such as timing gears or gears of a gear transmission between the compressor and the motor of the compressor assembly; a compressor outlet; bearings of a compressor element shaft or compressor rotor shaft; a motor shaft bearing; and so forth.

[06] The reason for using an oil-free or oil-less compressor element is that the fluid to be pressurized or compressed in the compressor element is kept oil-free or uncontaminated by oil. For example, this is very important in food processing applications and so on.

[07] Various techniques can be used to compress or pressurize a fluid in a compressor element. The present invention relates to a compressor assembly in which the compressor element is a rotating compressor element having compressor rotors which are motor driven for rotational movement.

[08] Without limiting the invention to this example, the invention particularly relates to compressor assemblies comprising an oil-free twin-rotor compressor element using oil as a lubricant and/or a refrigerant. For example, a twin-rotor compressor element can be a screw compressor element or a tooth compressor element.

[09] Nevertheless, the invention is not limited to compressor assemblies comprising; an oil-free or oil-less compressor element and its compressor assemblies, for example comprising an oil-injected compressor element, are not excluded from the invention.

[10] The invention is also not limited to compressor assemblies comprising a rotating compressor element, but other types of compressor elements can also be used.

[11] From another point of view, the invention also relates to compressor assemblies comprising an oil pump for pumping oil through an aforesaid oil circulation circuit of the compressor assembly, and to possible improvements with respect to this oil pump in the compressor assembly. Such an oil pump is typically used to pump oil from an oil reservoir or oil sump to components of the compressor assembly and back to the oil reservoir or oil sump.

[12] The invention furthermore relates to techniques in which the motor shaft is coupled to a rotor shaft of a compressor rotor of the relevant compressor element.

Background

[13] In a typical state-of-the-art compressor assembly, the compressor assembly motor indirectly drives a compressor rotor shaft of a compressor element of the compressor assembly through an intermediate gearbox or gear train.

Gears fixed to the motor shaft and compressor rotor shaft interact directly with each other or through other gears meshing with the respective gears on the motor shaft and compressor rotor shaft.

[14] Typically, the motor shaft drives the rotor shaft of a male compressor impeller of the compressor element, but this is not necessarily the case.

[15] The intermediate gear or gearbox allows the compressor rotor shaft to be indirectly driven at a very high speed, while the motor shaft rotates at a reduced moderate engine speed.

[16] An intermediate gear or gearbox can also be used to indirectly drive multiple stages, i.e. multiple compressor elements,

using the same engine. Also, through the intermediary of such a gear transmission or gearbox, other rotating components of the compressor assembly, such as a rotor of an oil pump, can be indirectly driven by the same motor,

[17] An obvious disadvantage of using an intermediate gear or gearbox to interconnect a motor shaft and a compressor rotor shaft is that it takes up a lot of space in the compressor assembly. In particular, such an intermediate gear transmission or gearbox usually comprises a large ring gear and the surrounding gearbox also has a size that is not negligible. This is an inconvenience due to a compact design of the compressor assembly.

[18] Another disadvantage of using such an intermediate gear or gearbox is that it entails energy losses due to friction losses between the gears involved, etc., which has a negative impact on the efficiency and overall performance of the compressor assembly .

[19] As explained, for cooling and lubricating the components of the compressor assembly, an oil circulation circuit is generally used, through which oil is pumped by means of an oil pump. The oil pump is often driven by a driving means, such as an electric motor.

[20] Yet another problem with the existing compressor assemblies is that, in the event of a failure of the oil pump drive means, the cooling and lubrication of the components of the compressor assembly is stopped, even when the compressor assembly is still in operation . Many measures can be taken to prevent such a situation by means of a control means and a means for stopping the compressor assembly in case of failure of the oil pump or its driving means. Usually an electronic control means is used for this purpose. This in itself is all rather complicated and the installation of such a system is also far from practical. Furthermore, electronic equipment is quite vulnerable, especially in high temperatures and under high pressure. This situation cries out for an improved solution.

[21] In addition, the oil pump and its driving means are installed near the compressor assembly or mounted on or in the compressor assembly housing. These components in turn take up a lot of space, which makes a compact design of the compressor assembly difficult.

[22] It is also standard practice in the art to provide a multistage compressor assembly with a single oil pump and oil circulation circuit for supplying oil for lubrication and cooling purposes to the various compressor elements making up the multiple stages of the compressor assembly.

[23] However, a problem with such a design is that oil contamination occurring in one compressor stage of the multistage compressor assembly, for example due to failure, wear or abrasion of a particular component in that compressor stage, can easily be transferred to all others. compressor stages, potentially damaging components in the other compressor stages. In short, with these types of designs, which are known in the art, there is a possible problem of so-called cross-contamination.

SUMMARY OF THE INVENTION

[24] It is an object of the invention to solve one or more of the aforementioned problems and/or possibly other problems.

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

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

[27] Yet another object of the invention is to increase the operational reliability and functional safety of the compressor assembly and in particular it is an object to efficiently perform the lubrication and cooling functions during operation of the compressor assembly. and reliable manner.

[28] It is also an object of the present invention to provide a compressor assembly design that allows for a more modular configuration of multi-stage compressor assemblies, where each "module" or compressor stage functions as a separate unit that separates other "modules" or compressor stages from not materially affect the compressor assembly.

[29] A further object of the invention is to realize a design of a compressor assembly with an improved integration of the means for pumping oil through the compressor assembly.

[30] To this end, the present invention relates to a compressor assembly comprising a motor with a motor shaft driving at least one compressor rotor of a compressor element, and an oil pump for pumping oil through an oil circulation system of the compressor assembly and wherein the aforesaid at least one compressor

sorotor is mounted on a rotor shaft which is connected by direct coupling to the motor shaft to form a compound drive shaft and the oil pump is mounted directly on the compound drive shaft or on another rotor shaft of a compressor element of the compressor assembly. 5 [31] A first major advantage of such a compressor assembly according to the invention is that the motor shaft is directly connected to a rotor shaft of the compressor assembly, so that no intermediate gear transmission or gearbox is required to drive the motor and the respective motor driven by the motor. compressor element together.

[32] In this way a much more compact compressor assembly can be obtained and a lot of space is saved.

[33] An additional advantage associated with the absence of such an intermediate gear train or gearbox is that no energy is lost in transmitting torque from the motor shaft to the respective compressor rotor shaft, which is not the case with gear trains where there is a certain loss occurs during the transmission of torque between gears. As a result, such a compressor assembly according to the invention is more energy efficient and generally has a higher performance.

[34] Another important and very advantageous aspect of a compressor assembly according to the invention is that the oil pump is mounted directly on the combination of the motor shaft and the rotor shaft, which are directly connected to each other by means of the direct coupling and which combination forms a compound drive shaft, or on another rotor shaft of a compressor element of the compressor assembly.

[35] A major advantage of such a configuration is first of all that the oil pump is driven by the same motor together with the compressor element. This means that when the engine fails, both the compressor element and the oil pump are stopped. In this way there can be no situation in which the oil pump does not function while the compressor element is still in operation, which may be the case when the oil pump is driven by a separate driving means.

[36] Another major advantage is that the oil pump is fully integrated in the core of the compressor assembly, i.e. close to the drive elements of the compressor assembly and more specifically on the assembled drive shaft or on another rotor shaft. It is not positioned at a peripheral position of the compressor assembly, which ensures a very compact design of the compressor assembly.

[37] Yet another advantage of such a compressor assembly according to the invention is that it allows a more modular assembly of multi-stage compressor assemblies, as will be shown further in the text by means of an example.

[38] It should be understood that such a compressor assembly according to the invention is also more in line with the trends in modern technology, with more and more high speed drives or motors and bearings being developed and made available. Indeed, it only makes sense to couple a motor shaft directly to a compressor rotor shaft, without intermediate gearing, if the motor is capable of driving the compressor rotor shaft at the high speed required to achieve realistic fluid compression. in the relevant compressor element.

[39] However, the choice of a direct coupling between the motor shaft and compressor rotor shaft is far from obvious and the direct coupling between the motor shaft and the compressor rotor shaft has to be designed or assembled with suitable technology, depending on the case . This design can be limited by many factors.

[40] For example, large torque pulsations often occur in tandem compressor elements, but this also occurs in other compressor elements, resulting in high demands on the nominal torque to be transmitted by the direct coupling.

This means that there is a large ratio between the rated peak torque to be transmitted by the direct coupling and the rated torque of the direct coupling.

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

[42] The environment in which the direct link must operate also places high demands on the design. This environment is usually a hot environment that is contaminated with oil.

[43] In addition, the motor shaft and the compressor motor shaft to be coupled by the direct coupling are often made of different materials, usually with different physical properties, such as different coefficients of thermal expansion, for example. This further complicates the task of designing a reliable direct coupling of the type discussed here.

[44] Therefore, it is a great challenge to realize and design such a direct coupling between a motor shaft and a compressor rotor shaft, with a considerable life without the need for service or maintenance.

[45] Another factor against the use of a direct coupling in a compressor assembly is its location in the compressor assembly housing, which is rather a blind, inaccessible location between the motor and a compressor element of the compressor assembly.

[46] The application of a direct coupling can also introduce limitations for possible adjustments on the compressor element side and can therefore be considered as a so-called “frozen design”. : [47] The configuration as proposed in the present invention is even more challenging, since not only is the motor shaft directly coupled to a rotor shaft of the compressor assembly, but at the same time the oil pump is integrated in the compressor assembly and driven by the same motor when the compressor element of the compressor assembly is driven.

[48] It is not obvious to mount such an oil pump directly on the drive shaft assembly or on another rotor shaft of the compressor assembly, as these shafts rotate at a very high speed suitable for compression processes, but not necessarily for pumping processes.

[49] The greater the distance from the central axis of such a rotating shaft, the higher the local velocity experienced by a rotating element mounted on that shaft.

[50] As a result, as the radial size of a rotor of the oil pump is increased, the speed experienced at the tips of the rotor also increases. However, when the speed of the rotor tips and the pumped oil increase above a certain level, there is a high risk of cavitation occurring, especially at low ambient pressures (e.g. at high altitudes).

[51] For this reason, the radial dimension of the oil pump should be kept as small as possible to prevent cavitation. On the other hand, the compound drive shaft or other rotor shaft has a size or diameter at least above a certain minimum to be able to cope with the high torques and speeds applied to those shafts. These two different requirements, i.e. the requirement to minimize the radial dimensions of the oil pump at those high speeds and the requirement to have a drive shaft of sufficient diameter or radial size to be able to handle the high speed conditions and high torque are clearly contradictory. It is therefore quite a challenge to find the right balance between these two conflicting requirements.

[52] In conclusion, designing a reliable, direct coupling for use in a compressor assembly for directly coupling a motor shaft to a compressor rotor shaft and integrating an oil pump into the compressor assembly by direct connection to an assembly drive shaft or another rotor of the compressor assembly is not easy to realize in practice, but has many advantages,

[53] In a preferred embodiment of a compressor assembly according to the invention, the oil pump is mounted on a monolithic, non-hollow shaft or a monolithic, non-hollow part of a shaft.

[54] This specification of a particular embodiment of a compressor assembly according to the invention may seem somewhat arbitrary at first glance, but it is based on a reality that will become clearer later in the text.

[55] In order to realize a rigid, direct coupling between the motor shaft and the respective rotor shaft of the compressor rotor element, which is at the same time practical to use, for example for mounting and dismounting the connection, but also for other reasons, it is it is convenient to use a hollow shaft and stud configuration.

[56] According to the invention it is practically not feasible to mount the oil pump on such a hollow shaft or hollow part of a shaft, since the diameter of such a shaft would be too large to be acceptable for mounting a rotor of an oil pump over that diameter, for the aforementioned reasons of cavitation problems and so on.

[57] A proposal according to the invention is to install the oil pump impeller on a shaft or shaft part which is completely materialized from its center shaft to its outside diameter and which is strong enough to withstand the high torque load at the very high speeds. and to additionally absorb the forces required to drive the oil pump rotor. A solid oil pump shaft also has the advantage of being stiffer or stronger. Therefore, under the working load of the pump outlet pressure, the deflection of the oil pump shaft will be smaller. Reducing the pump shaft deflection reduces the risk of damage to the oil pump. Such a fully materialized shaft or shaft part can also be designed with reduced dimensions, but sufficiently strong to withstand all relevant loads,

[58] The great advantage of such an embodiment of a compressor assembly according to the invention is therefore that a rigid, direct coupling between the motor shaft and the rotor shaft can be realized, which direct coupling is also very convenient to use, and that at the same time the oil pump is still mounted on a drive shaft of the compressor assembly, so that it is fully, deeply integrated into the compressor assembly.

[59] In a preferred embodiment of a compressor assembly according to the invention, the oil pump is mounted on a non-driven side of the motor or compressor element, opposite a driven side where the motor shaft, by means of direct coupling with the relevant rotor shaft, is mounted. the compressor element is connected.

[60] A great advantage of such an embodiment of a compressor assembly according to the invention is that the oil pump is provided on an outside of the compressor assembly, either at a free end of a rotor shaft or at a free end of the motor shaft. In this way the oil pump is easily accessible, for instance for maintenance or for connecting oil pipes, for mounting and dismounting the oil pump, etc.

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

[62] A gerotor pump is a very simple pump that can be easily produced in small dimensions and is suitable for use at the high speeds used in compressor assemblies. The required driving force or torque to drive the gerotor oil pump is quite limited. This is in fact one of the main advantages of an integrated oil pump and in particular of a gerotor oil pump, as it is an efficient way to provide an oil flow with low power consumption. The clearances in a gerotor pump are also very small to optimize volumetric efficiency. This means that there is a lower leakage rate in the gerotor oil pump than in other types of oil pumps.

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

[64] Such an embodiment of a compressor assembly according to the invention has the advantage that the flexible coupling has damping properties provided by damping elements of the flexible, direct coupling, which reduce torsional vibrations present in the drive train passing through the coupling. between the motor shaft and the rotor shaft of the compressor.

[65] Another advantage of such an embodiment of a compressor assembly according to the invention is that the flexible, direct coupling is relatively easy to assemble and design. This is because a flexible, direct coupling does not impose high requirements in terms of tolerances in the assembly and can compensate for possible misalignment between components of the compressor assembly.

[65] Yet another advantage of such an embodiment of a compressor assembly according to the invention is that an oil pump can be easily integrated into the compressor assembly and installed on any available non-drive side of either the motor shaft or one of the compressor rotors can become.

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

[68] This may be an even less obvious choice for connecting the motor shaft and a compressor rotor shaft of a compressor assembly in a direct manner, for a variety of reasons as explained earlier, but it ensures that the drive train of the compressor assembly can be even more compact.

[69] Firstly, there is no longer a need for a relatively large flexible coupling.

Furthermore, other components of the compressor assembly can be eliminated by using a rigid direct coupling instead of a flexible direct coupling in the drive train. In such a case, a motor bearing on the drive side and the associated oil lubrication channels to this bearing and the associated seals can be eliminated, for example.

[70] When a rigid direct coupling is used, the combination of the ; motor shaft directly coupled to the compressor shaft by means of a rigid direct coupling can of course be regarded as a single compound drive shaft. This compound drive shaft is supported for sufficient rotation within the compressor assembly housing by means of, on the one hand, a pair of rotor shaft bearings for supporting the rotor shaft side of the compound shaft and, on the other hand, a single motor shaft bearing mounted on the non-drive side of the motor is provided for supporting the motor shaft part of the assembled shaft.

[71] In yet another embodiment, it is even conceivable not to use bearings at all to support the motor shaft, so that a suspended design of the motor is obtained.

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

[73] A major advantage of such an embodiment of a compressor assembly according to the invention is that the motor shaft can be pressed or heat-shrinked onto the rotor shaft of the compressor into a rigid coupling. These manufacturing methods are highly efficient, relatively simple to perform and cost effective.

[74] Yet another preferred aspect of a compressor assembly according to the invention is that for forming the rigid, direct coupling between the motor shaft and the rotor shaft: preferably one of the motor shaft and the rotor shaft is constructed as a hollow shaft which is centrally comprises an axially extending channel extending through the hollow shaft, the axially extending channel of the hollow shaft having a connecting bolt provided with a first end extending into the other of the motor shaft and the rotor shaft not acting as a hollow shaft and which connecting bolt is fixedly connected to said non-hollow shaft at said first end and wherein a tensioning means is provided at the opposite second end of the connecting bolt for tensioning the connecting bolt relative to the hollow shaft .

[75] A great advantage of such an embodiment of a compressor assembly according to the invention is that the motor shaft and the relevant compressor rotor shaft are rigidly rigid by means of the axial or conical clamping of the shaft end faces against each other by means of the connecting bolt. are connected. The tension means provides an axial force that presses the end faces of the motor shaft and compressor rotor shaft together to create a clamping force between both end faces.

[76] As a result, a tight interconnection of the motor shaft and the compressor rotor shaft is obtained, and torque is transferred between those shafts without any energy loss.

[77] Another advantage of such an interconnection by means of a rigid, direct coupling using a connecting bolt to create an axial clamping force is that the coupling can be engaged and disengaged from a non-drive side of the respective hollow shaft. which is, depending on the case, the motor shaft or the compressor rotor shaft. In this way disassembly can be started without having to open the entire compressor assembly housing.

[78] Also in case a radial press fit is used to realize the rigid coupling, a connecting bolt may be necessary to easily dismantle the rigid direct coupling.

[79] Indeed, when a radial press-fit (or shrink-fit) is used for the rigid coupling, the outer shaft is heated and brought over the inner shaft.The rigid coupling is obtained after cooling, and thus shrinking the outer shaft .

[80] When such a rigid press-fit or shrink-fit coupling has to be dismantled, oil under pressure applied between the two interconnected shafts is usually used. Furthermore, the shaft to be removed is simultaneously exposed to a pulling force, which force is created by exerting a pushing force on the other shaft. This pushing force on the other axle can be realized in a practical way by means of 9! of the connecting bolt in the above configuration.

[81] In a preferred embodiment of a compressor assembly according to the invention, the clamping force required to ensure a good torque transmission over the clutch and for a good operation of the rigid, direct coupling is reduced by means of friction discs or a so-called Hirth clutch. coupling or gearing between the end faces of the motor shaft and the compressor rotor shaft.

[82] Friction discs increase the friction between the end faces of the respective shafts so that rotational movement between these end surfaces can be prevented by means of a lower axial clamping force, compared to the axial clamping force that would be required if such friction discs were not used, and the friction of the end faces would not be increased. The goal, of course, is to transfer torque under a given applied axial clamping force from one shaft to the other without slippage between the end faces of the shafts.

[83] Indeed, it is known that plane surfaces in contact can be displaced relative to each other by applying at least a minimal force directed tangentially or parallel to the plane surfaces. The required minimum tangential force depends on (proportional to) the normal force exerted to push the surfaces against each other. For the same applied normal force, this required tangential force will be lower when the friction between the surfaces is low compared to a case where the friction between the surfaces is higher.

[84] By using such friction discs, the size or diameter of the connecting bolt can also be reduced.

[85] In case a Hirth coupling or gearing is used, there is no great chance or no chance at all of slip between the end faces of the rotor shaft and the motor shaft during torque transmission, since such coupling or gearing includes teeth that each are provided with the end faces which are complementary and brought together by a mechanical locking of the shafts.

BRIEF DESCRIPTION OF THE DRAWINGS

[86] The invention is further illustrated with reference to the drawings, in which: ; figures 1 and 2 are schematic drawings which illustrate two different embodiments of a compressor assembly known in the art: figures 3 and 4, similar to figures 1 and 2, each illustrate an embodiment of a compressor assembly according to the invention , respectively comprising a direct flexible coupling and a rigid direct coupling; figure 5 shows a schematic drawing of a two-stage compressor assembly illustrated in figure 4 formed with two compressor assemblies; figure 6 is a simplified drawing of a cross-section through a gerotor pump; figure 7 illustrates an embodiment for a compressor assembly according to the invention, which is a preferred alternative to the embodiment shown in figure 4; figures 8 and 9 show in more detail on a larger scale the parts indicated by FO8 and FO9 in figure 7; Figures 10 and 11, similarly to Figure 9, illustrate the part in question on a larger scale for an alternative connection at the end faces of the rotor shaft and motor shaft; figures 12 and 13 represent on a larger scale the parts indicated by F12 and F13 in figure 10 and figure 11, respectively in perspective view and in front view; and, figures 14 and 17 show still other embodiments of a compressor assembly according to the invention, which are an alternative to the embodiment shown in figure 7.

DETAILED DESCRIPTION OF EMBODIMENT(S)

[87] Figure 1 illustrates a compressor assembly 1 according to the state of the art. The compressor assembly 1 comprises a motor 2 which drives a compressor element 3 .

For mutually connecting the motor 2 and the compressor element 3, the compressor assembly 1 is provided with an intermediate gear transmission 4, which is positioned between the motor 2 and the compressor element 3.

[88] As explained in the introduction, a major advantage of such a configuration is that the speed of the motor 2 can be kept relatively low. 6, the intermediate gear transmission 4 required by the compressor element 3 is converted to a higher speed.

[89] The motor has a motor shaft 7 coupled with one end 8 at a drive side 9 to a gear transmission shaft 10 rotatably supported in the intermediate gear transmission housing 11 by means of a pair of bearings 12 and 13.

[90] The connection between the motor shaft 7 and the gear transmission shaft 10 is realized by means of an intermediate coupling 14.

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

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

[93] Figure 2 illustrates another compressor assembly 1 known in the art, which is a two-stage compressor assembly 1 comprising a first compressor element 3 as in the previous case, as well as a second compressor element 22.

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

[95] This time, the drive gear 15 of the intermediate gear train 4 meshes with the driven pinion 16 for driving the first stage formed by the first compressor element 3, as well as with a similar driven pinion 23 for driving the second stage formed by the second compressor element 22 .

[96] This is clearly a practical way to drive two compressor stages simultaneously from a single motor 2 . On the other hand, there is no flexibility in independently controlling the rotational speed of two compressor stages 3 and 22,

[97] The oil pump 18 supplies oil to the two compressor stages 3 and 15, which entails a high risk of so-called cross-contamination, as explained in the introduction.

[98] Figure 3 illustrates a compressor assembly 1 according to the invention. The compressor assembly 1 comprises a motor 2, which in this case is an electric motor, mounted in a motor housing 24 and comprising a motor shaft 7 extending through the motor housing 3 in an axial direction XX'. The motor shaft 7 is provided with a motor rotor 25 which rotates with the motor shaft 7 in motor stator windings 26 fixedly mounted in the motor housing 24 .

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

[100] As explained in the introduction, the invention is of particular importance for compressor assemblies 1, where this compressor element 3 is an oil-free or oil-less compressor element 3.

According to the invention, the compressor element 3 of the compressor assembly 1 is preferably a twin-rotor compressor element 3, and more specifically, the compressor element 3 of the compressor assembly 1 is preferably a tooth compressor element 3 or a screw compressor element 3.

[102] The compressor element 3 is mounted in a compressor element housing 27 and comprises compressor rotors 5 and 6 which can cooperate to compress fluid 28 which is supplied to the compressor element 3 at a compressor inlet 29 . Compressed or pressurized fluid 30 is discharged at a compressor outlet 31 for delivery to a pressurized or compressed fluid 30 consumer or network of consumers.

[103] The fluid in this case is air taken from the environment of the compressor element 3, but this is not necessarily the case.

[104] The compressor rotors 5 and 6 each comprise a compressor rotor shaft, respectively compressor rotor shaft 32 and compressor rotor shaft 33, on which a compressor rotor part is provided in a central part, respectively compressor rotor part 34 and compressor rotor part 35.

[105] The compressor rotor part 34 may be a female rotor part 34 cooperating with a male rotor part 35 forming the other compressor rotor part 35, or vice versa. in practice, the compressor rotor parts 34 and 35 can each be, for example, a screw rotor of a screw compressor element, or a toothed rotor of a toothed compressor element, but other types are not excluded from the invention.

[106] The compressor element shafts 32 and 33 are each rotatably supported in the compressor element housing 27 by a pair of compressor rotor bearings, a pair of compressor rotor bearings 36 and 37 and a pair of compressor rotor bearings 38 and 39, respectively.

[107] In order to drive the compressor element 3, or more precisely the compressor rotors 5 and 6 of the compressor element 3, by means of the electric motor 2, the motor shaft 7, according to the invention, is directly connected to the compressor rotor shaft 33 of the compressor rotor 6 coupled, by means of a direct coupling 40 of the respective shafts 7 and 33. The direct coupling 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 located in an intermediate housing compartment 43 provided between the motor housing 24 and the compressor element housing 27.

[108] The motor housing 24, the compressor housing 27 and the intermediate housing compartment 43 together form the compressor assembly housing 44.

[109] The combination of the interconnected motor shaft 7 and compressor rotor shaft 33 and the direct coupling 40 can be regarded as a compound drive shaft 45.

[110] In the embodiment of Figure 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 will comprise one or more damping elements connected to a damping of vibrations in the drive train and can compensate for small misalignments between the respective shafts 7 and 33.

[111] Since a flexible direct coupling 46 is used in this case, the rotor shaft 7 is rotatably supported in the motor housing 24 by means of a pair of motor shaft bearings 47 and 48.

[112] As a result, the compressor rotor 6 of the compressor element 3 is directly driven by the motor shaft 7. The other compressor rotor 5 is indirectly driven through the interaction between a plurality of timing gears 49 and 50 mounted on a non-drive end 51 of the compressor rotor shaft 32 and the compressor rotor shaft 33, respectively.

[113] Finally, on a non-drive side 52 of the motor 2, i.e. the side opposite the drive side 9 where the motor 2 is coupled to the compressor element 3, the compressor assembly 1 is further provided with an oil pump 18. This oil pump 18 is this time integrated in the motor housing 24 or is mounted on the motor housing 24 or on a motor housing cover of said motor housing 24 .

[114] An important feature of the invention is that this oil pump 18 is mounted directly on the motor shaft 7 of the electric motor 2 or more generally on the compound drive shaft 45 or on another compressor rotor shaft 32 of the compressor element 3. In this way a very thorough integration of the oil pump 18 in the compressor assembly 1 is obtained and a very compact design of the compressor assembly can be realized.

[115] As explained in the introduction, the choice is to connect the oil pump 18 directly to one of ; mounting the aforementioned shafts 7, 32 or 45 is far from self-evident, since these shafts 7, 32 or 45 rotate at very high speeds.

[116] The oil pump 18 is, of course, intended to provide a driving force for circulating oil 53 in an oil circulation system 20 of the compressor assembly 1. This oil circulation system 20 is intended to supply oil 53 to components of the compressor assembly 1 for lubrication purposes or for cooling purposes, or both.

[117] Oil 53 is drawn at the oil pump inlet 54 through a suction line 55 from an oil reservoir 21 or oil sump 21 which is preferably also integrated into the compressor assembly housing 44, for example by being mounted directly below the motor housing 24 . The oil is further pumped through an oil pump pressure line 56 to the appropriate components of the compressor assembly 1 and returned to the oil reservoir or sump 21 . In the oil circulation system 20 there is usually also an oil cooler and oil filter, which are shown in the figures.

[118] Components of the compressor assembly 1 that typically require lubrication are, for example, bearings, such as motor shaft bearings 47 and 48 or compressor rotor bearings 36 to 39, or its gears, such as timing gears 32 and 33. A component that needs cooling is, for example, the electric motor 2, compressed fluid 30 at an outlet 31 of the compressor element 3, the compressor element 3 itself or other elements of the compressor assembly 1. {119] It is clear that such an embodiment of a compressor assembly 1 according to the invention is very interesting because a very extensive integration of components in the compressor assembly is achieved.

[120] However, Figure 4 illustrates another embodiment of a compressor assembly according to the invention where elements are even more integrated or where some elements are eliminated compared to the embodiment of Figure 3.

[121] In this case, the motor shaft 7 and the compressor rotor shaft 33 are again connected by a direct coupling 40, but the direct coupling 40 is this time a rigid direct coupling 57.

[122] In the example of Figure 4, this rigid direct coupling 57 between the motor shaft 7 and the compressor rotor shaft 33 is a rigid pressed coupling or a rigid heat-shrinked coupling 57.

[123] In a first step in realizing this rigid, direct coupling 57: the end 8 of the motor shaft 7 is heated to increase its radial size. Subsequently, this heated end 8 of enlarged radial dimension is brought over the end 42 of the compressor rotor shaft 33 . After cooling, the end 8 of the motor shaft is shrinked and a firm rigid interconnection between the motor shaft 7 and the compressor rotor shaft 33 is obtained.

[124] Another difference from the embodiment of a compressor assembly according to the invention shown in Figure 3 is that in the embodiment of Figure 4 the motor shaft 7 is rotatably supported in the motor housing 24 by only a single motor shaft bearing 58 . In fact, the combination of the motor shaft 7 and the compressor rotor shaft 33, which are rigidly connected by the rigid direct coupling 57, should be regarded as a rigid compound drive shaft 45, which is connected by the pair of bearings 38 and 39 (of the compressor rotor). 6) is rotatably supported in the compressor element housing 27 and by the single motor shaft bearing 58 in the motor housing 24.

[125] Of course, other configurations of bearing assemblies could be used to support the rigid assembly drive shaft 45.

Figure 5 shows an embodiment of a compressor assembly 1 according to the invention, wherein the compressor assembly 1 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.

[127] The first compressor stage 60 and the second compressor stage 61 are each designed as a compressor assembly 1, each being an exact copy of the embodiment shown in Figure 4.

[128] Stages 60 and 61 are connected in series. To this end, the compressor outlet 31 of the compressor element 3 of the first stage 60 is connected to the compressor inlet 29 of the compressor element 3 of the second stage 61 by means of a fluid channel 62 .

In this way, compressed fluid 30, which has been 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 .

[129] Each compressor stage 60 or 61 comprises a motor 2 with a motor shaft 7 and a compressor element 33, as well as 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 connected by means of a direct coupling 40 to a rotor shaft 33 of the respective compressor element 3 to form a compound drive shaft 45 . In this case, the oil pump 18 of each compressor stage 60 or 61 is mounted directly on the assembled drive shaft 45, but these oil pumps 18 may just as well be mounted on another rotor shaft 32 of the relevant compressor element 3 of such a compressor stage 60 or 61.

[130] Each compressor stage 60 or 61 includes a separate oil circulation system 20 that includes the respective oil pump 18 of that compressor stage 60 or 61, so that no oil 53 is exchanged between the oil circulation systems 20 of the different compressor stages 60 or 61 of the multistage compressor assembly 59 is becoming. In this way, cross-contamination is clearly avoided.

[131] As in the example of Figure 4, the motor shafts 7 of each compressor stage 60 or 61 of the multistage compressor assembly 59 are supported by a single bearing 58.

[132] According to the invention an oil pump 18 of the compressor assembly 1 is preferably a gerotor pump 63. Such type of oil pump 18 is illustrated in Figure 6 . A 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. in the case shown 7 teeth, while the outer rotor 65 has n+1 teeth 67, in this case 8 teeth 87.

[133] The rotors 64 and 65 rotate about their central axis, respectively central axis A and central axis B, which do not coincide, but are spaced apart from each other. During the rotation, the volumes 68 between the teeth 66 of the inner rotor 64 and the teeth 67 of the outer rotor 65 decrease and decrease permanently, resulting in the pumping action.

[134] 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 properties.

[135] Figure 7 illustrates another embodiment of a compressor assembly 1 according to the invention in which again a rigid, direct coupling 57 is used for connecting the motor shaft 7 of the motor 2 of the compressor assembly 1 to a compressor rotor shaft 33 of a compressor element. 3 of the compressor assembly 1.

[136] In the illustrated example of Figure 7, 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 formed as a hollow shaft 69 centrally comprising an axially extending channel 70 extending through the hollow shaft 69,

[137] In the case of Figure 7, the motor shaft 7 is constructed as a hollow shaft 69. In the axially extending channel 70 of the hollow shaft 69, a connecting bolt 71 is provided, which extends with a first end 72 into the other of the motor shaft 7 and compressor rotor shaft 33, which is not constructed as a hollow shaft 69 or non-hollow shaft 73 . This non-hollow shaft 73 is the compressor rotor shaft 33 in the example discussed here.

[138] The connecting bolt 71 is fixedly connected with its first end 72 to said non-hollow shaft 73. In the illustrated example of Figure 7, this fixed connection is particularly realized at the free end 42 of the compressor rotor shaft 33.

[139] The interconnection between the first end 72 of the connecting bolt 71 and the free end 42 of the rotor shaft 33 of the compressor is illustrated in more detail in FIG. Therefore, the non-hollow shaft 73 is provided with an internal threaded hole 74 for receiving the first end 72 of the connecting bolt 71, which first end 72 of the connecting bolt 71 is provided with an external thread 75 that is connected to the internal thread 74 in the non-hollow shaft 73 can cooperate.

[140] At the opposite second end 76 of the connecting bolt 71 a tensioning means 77 is provided for tensioning the connecting bolt 71 relative to the hollow shaft 69. In figure 9 this is illustrated in more detail. The second end 76 of the connecting bolt 71 is provided with an external thread 78 which can cooperate with a nut 79 having an internal thread 80, for tightening the connecting bolt 71 by exerting a force against the hollow shaft 69, which in in this case the motor shaft is 7.

[141] Figures 10 and 12 illustrate an embodiment in which the rigid, direct connection 57 between the motor shaft 7 and the compressor rotor shaft 33 is improved, compared to the case where a rigid, direct coupling 57 is realized and torque is transmitted by the preloading the motor shaft 7 and compressor rotor shaft 17 to create a clamping force F by means of a connecting bolt 71 and a tensioning means 77. In particular, the necessary clamping force F to ensure good torque transfer across the coupling 57 and for proper operation of the rigid, direct coupling 57 lowered using a so-called Hirth coupling or gearing 81 between or near the end faces 82 and 83 of the motor shaft 7 and the compressor rotor shaft 33.

[142] As shown more clearly in Figure 12, such Hirth gearing 81 is achieved by designing the end faces 82 and 83 of the motor shaft 7 and the compressor rotor shaft 33 with complementary meshing teeth 84, which prevent the end faces 82 and 83 rotate relative to each other in the interlocked state. It will be appreciated that no very large axially directed clamping force F is required to prevent such rotational slippage of the end faces 82 and 83 relative to each other.

[143] Another alternative solution where the rigid direct coupling 57 is an even more interlocked coupling could be realized by designing the rigid direct coupling 57 as a splined coupling. In that case, one of the ends of the motor shaft 7 and the compressor rotor shaft 33 is provided with axially extending teeth arranged on the outer periphery, which are complementary to axially extending grooves internally formed in the other ends of the motor shaft 7 and the compressor rotor shaft 33 are installed. For rigidly and directly coupling the motor shaft 7 and compressor rotor shaft 33 and for transmitting torque between the shafts 7 and 33, said teeth are inserted in the axially extending grooves. In this configuration, there is clearly no risk of slip between the end faces of the motor shaft 7 and the compressor rotor shaft 33.

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

[145] Figures 11 and 13 illustrate another embodiment in which the friction between the end faces 82 and 83 of the respective shafts 7 and 33 is reduced by means of a friction disc 85 which is a kind of flat disc-shaped ring 85 with roughened side surfaces 86 and which is mounted between the respective end faces 82 and 83. For example, the side surfaces 86 are roughened by embedding particles such as diamond crystals or other particles into the respective side surfaces 86 or by providing the side surfaces 86 with a cross-sectional profile that is not flat or smooth.

[146] Figure 14 shows an alternative and improved embodiment of a compressor assembly 1 according to the invention for the embodiment shown in Figure 7.

Namely, in the embodiment shown in Fig. 7, the oil pump 18 is mounted on the compound drive shaft 45 on the motor shaft part 7, which is formed as a hollow shaft 69. This can be problematic because the hollow shaft 69 must be provided with a sufficiently large wall thickness T or outside diameter D. When the outer dimensions of the motor shaft 7 are increased, this also has consequences for an oil pump 18 which is mounted over said motor shaft 7. Particularly in the case of the high speeds used in compressor applications, increasing the size of the oil pump 18 is problematic and results in high speeds at the rotor tips 64 / 66 of the oil pump 18, which can occur even when a gerotor pump 63 is used, and results in cavitation in the pumped oil 53.

[148] To avoid such a situation, the embodiment of the oil pump 18 shown in Figure 14 is mounted over a free end 87 at the non-drive side 52 of the compressor rotor shaft 33, which in this embodiment is still the non-driving end. hollow shaft portion 73 of the assembled drive shaft 45 . This free end 87 extends out of the housing of the compressor element 27 . In this way it is ensured that the oil pump is mounted over a monolithic, fully materialized, non-hollow or solid shaft 73 or monolithic, non-hollow, solid part 88 of such shaft 73. This shaft 73 or this shaft part 88 can therefore possibly be designed with smaller outer dimensions, which are smaller than the outer dimensions of the hollow shaft part 69 of the assembled drive shaft 45.

[149] The rigidity of the compressor rotor shaft 33, which is constructed as a non-hollow shaft 73, also results in improved rigidity.

[150] On the other hand, the inner diameter and/or outer diameter of the hollow shaft 69 (which is the motor shaft 7) can be increased, since there are no more restrictions imposed on that side of the compound drive shaft 45 by the reduced size requirements of the oil pump 18 to prevent cavitation. As a result, the connecting bolt 71 can be made with a larger radial dimension and a higher preload between the motor shaft 7 and the compressor rotor shaft 33 can be applied. This also results in greater safety margins.

[151] Figures 15 and 17 illustrate yet other embodiments of a compressor assembly 1 according to the invention, applying the same principle.

[152] In the embodiment of Figure 15, the oil pump is mounted over a free end 89 of the other compressor rotor shaft 32 of the compressor element 3, which compressor rotor shaft 32 is not part of the assembled drive shaft 45, which still consists of a mutual connection of the compressor rotor shaft 33 and the motor shaft 7 is composed by means of a rigid direct coupling 57. The motor shaft 7 is still as hollow shaft 69 with connection

bolt 71 performed. The oil pump 18 is mounted again, as in the example of figure 14, over a monolithic, non-hollow part 88 of the compressor rotor shaft 31, which shaft is otherwise completely designed as a non-hollow shaft 73.

[153] The embodiment of a compressor assembly 1 according to the invention illustrated in Figure 16 differs from the previous embodiment shown in Figure 15 in that this time the assembled drive shaft 45 is composed of a hollow shaft 69 which is the compressor rotor shaft 33 and a non hollow shaft 73, which is the motor shaft 7, which are interconnected by means of a rigid direct coupling 57. The compressor rotor shaft 33 is provided with an axially extending channel 70 extending through the hollow shaft 69 . In the axially extending channel 70 of the hollow shaft 69 formed by this compressor rotor shaft 33, a connecting bolt 71 is provided. This connecting bolt 71 extends with a first end 72 into the motor shaft 7, which is the non-hollow shaft 73 this time. The connecting bolt 71 is fixedly connected to the non-hollow shaft 73 at this first end 72 in a similar manner as in the previous cases. At the opposite second end 76 of the connecting bolt 71, a tensioning means 77 is provided for tensioning the connecting bolt 71 relative to the hollow shaft 69.

[154] The oil pump 18 is still mounted on the monolithic, fully materialized, non-hollow compressor rotor shaft 31 of the other rotor 5.

[155] The embodiment of a compressor assembly 1 according to the invention shown in Figure 17 is similar to the embodiments of Figures 7 and 16. The correspondence with the embodiment of Figure 7 is that the oil pump 18 at a non-drive side 52 of the motor 2 is mounted on the motor shaft 7. The similarity with the embodiment of figure 16 is that the motor shaft 7 is designed as a non-hollow shaft 73, which is connected to the compressor rotor shaft 33 . This compressor rotor shaft 33 is again a hollow shaft 69 with a central channel 70 and connecting bolt 71, which is directly connected to the motor shaft 7 by means of a rigid, direct connection 57 . The oil pump 18 is therefore again mounted on a monolithic, non-hollow part 88 of a shaft 7 .

The present invention is by no means limited to the embodiments of a compressor assembly 1 as described above, but such a compressor assembly 1 can be used and implemented in many different ways without departing from the scope of the invention.

Claims (18)

CONCLUSIONS Compressor assembly (1) comprising a motor (2) with a motor shaft (7) 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}, characterized in that said at least one compressor rotor (6) comprises a compressor rotor part (35) mounted on a compressor rotor shaft (33) passing through is connected to the motor shaft (7) by a direct coupling (40) to form a compound drive shaft (45) and that the oil pump (18) is directly connected to the compound drive shaft (45) or to another compressor rotor shaft (32) of a compressor element (3) of the compressor assembly (1) is mounted. Compressor assembly (1} according to claim 1, characterized in that the oil pump (18) is mounted on a monolithic, non-hollow shaft (73) or monolithic, non-hollow part (88) of a shaft (7, 32, 33). } is mounted. A compressor assembly (1) according to claim 2, characterized in that the oil pump (18) is mounted on a non-driven side (51, 52) of the motor (2) or the compressor element (3), opposite a driven side (9) through which the motor shaft (7) passes! of the direct coupling (40) is connected to the relevant compressor rotor shaft (33) of the compressor element (3). Compressor assembly (1} according to claim 2 or 3, characterized in that the oil pump (18) is a gerotor pump (63). Compressor assembly (1) according to one or more of the preceding claims, characterized in that the direct coupling (40) is a flexible coupling (46). Compressor assembly {1} according to one or more of claims 1 to 5, characterized in that the direct coupling (40) between the motor shaft (7) and the compressor rotor shaft (33) is a rigid coupling (57). Compressor assembly (1} according to claim 6, characterized in that the rigid coupling (57) between the motor shaft (7) and the compressor rotor shaft (33) is a rigid pressed coupling or a rigid heat-shrinked coupling. Compressor assembly (1) according to claim 6 or 7, characterized in that to form the rigid, direct 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 constructed as a hollow shaft (69) which centrally comprises an axially extending channel (70) extending through the hollow shaft (69), wherein in the axially extending channel (70) of the hollow shaft (69) a connecting bolt (71) is provided extending with a first end (72) into the other of the motor shaft (7) and compressor rotor shaft (33) which cannot be regarded as a hollow shaft or a non-hollow shaft (73 ) is designed and which connecting bolt (71) is fixedly connected to said non-hollow shaft (73) at said first end (72) and wherein at the opposite second end (76) of the connecting bolt (71} a tensioning means (77 ) is provided for tensioning the connecting bolt {71} in relation to the hollow shaft (69). Compressor assembly {1} according to claim 8, characterized in that the non-hollow shaft (73) is provided with an internal threaded hole (74) for receiving the first end {72} of the connecting bolt (71), which first end (72) of the connecting bolt {71} is provided with an external thread (75) that can cooperate with the internal thread (74) in the non-hollow shaft (73). Compressor assembly {1} according to claim 8 or 5, characterized in that the second end (76) of the connecting bolt (71) is provided with an external thread (78) which can be fitted with a nut (79) with an internal thread {80}. cooperate, for tightening the connecting bolt (71) by exerting a force against the hollow shaft (69). Compressor assembly (1) according to one or more of the preceding claims, characterized in that the compressor rotors (5, 6) of the compressor elements (3) of the compressor assembly {1} comprise compressor rotor parts (34, 35) each mounted on a compressor rotor shafts (32, 33} are mounted and that each of these compressor rotor shafts (32, 33} is supported by a pair of bearings (36-39). Compressor assembly (1) according to one or more of the preceding claims, characterized in that the motor shaft (7) is supported by a single bearing (58) or exclusively by the pair of bearings (38, 39) of the compressor rotor shaft (33). ) to which the motor shaft (7) is directly connected by means of the direct coupling (40). Compressor assembly (1) according to one or more of the preceding claims, characterized in that the compressor element (3} of the compressor assembly (1) is an oil-free or oil-less compressor (3). Compressor assembly (1) according to one or more of the preceding claims, characterized in that the compressor element (3) of the compressor assembly {1} is a double-rotor compressor element (3). Compressor assembly (1} according to one or more of the preceding claims, characterized in that the compressor element (3) of the compressor assembly (1) is a tooth or screw compressor element {3}. Compressor assembly (1} according to one or more of the preceding claims, characterized in that the motor (2) of the compressor assembly (1} is an electric motor {2} comprising a motor stator (26} mounted in a motor housing (24). ) is inserted and a motor rotor (25) mounted on the motor shaft (7} extending through the motor stator (26). A compressor assembly (1) according to one or more of the preceding claims, characterized in that the compressor assembly (1} is a multi-stage compressor assembly (59) comprising at least a first compressor stage (60) and a second compressor stage (61) vessel, each stage (60, 61) being formed by a compressor assembly (1) according to one or more of claims 1 to 16, each compressor stage (60, 61) comprising a motor (2} with a motor shaft (7) and a compressor element (3) and an oil pump (18), both of which are driven by the motor shaft (7), the motor shaft (7) being directly coupled (40) to a rotor shaft (33) of the respective compressor element { 3} is connected to form a compound drive shaft (45) and the oil pump (18) is connected directly to the compound drive shaft (45) or to another rotor shaft (32) of the relevant compressor element (3} of the compressor stage (60, 61 } mounted, and each compressor stage (60, 61) comprises a separate oil circulation system {20} that includes the respective oil pump (18) of that compressor stage (60, 61}, in such a way that no oil (53) is left between oil circulation systems (20) of different compressor stages (60, 61} of the multistage compressor assembly (59} is exchanged. A compressor assembly {1} according to claim 17, characterized in that the motor shaft {7} of each compressor stage {60, 61} of the multi-stage compressor assembly {59} is supported by a single bearing {58}.