Patent Publication Number: US-2011076167-A1

Title: Electric Motor II

Description:
The present invention relates to an electric motor according to the preamble of patent claim  1 . 
     Electric motors are known in various embodiments. For example, motors are known for conducting media, which comprise a rotor and a stator located around this, wherein the rotor is connected to a media impeller and by way of this may regulate the flow of media. 
     With motors leading media, one strives for a simple construction as well as highest possible integration into an existing housing system. Here, apart from observing the desired simplicity for reasons of repair, one should also take note of the sealedness, in particular with regard to the electrically conducting parts of the electric motor. 
     It is therefore the object of the invention to provide an electric motor which has an extremely simple construction, has a good sealedness with regard to the media to be delivered, and despite this has a high performance and is energy-efficient. 
     This object is achieved by an electric motor according to claim  1 . Here, it is the case of an electric motor for delivering media, wherein this comprises a stator, a rotor with a rotor magnet, as well as a media passage opening between the stator and rotor. In at least one cross section, the ratio of the cross-sectional area of the inlet opening to the cross-sectional area of the rotor magnet (expressed with regard to a formula: V QE =A inlet opening /A rotor magnet ) is between 0.5 and 100, preferably between 0.8 and 50, particularly preferably between 2 and 20. 
     The primary work power of the media gap motor is the delivery of media through the gap between the rotor and stator, or as a generator, the drive by the delivery medium in the media gap. 
     “Cross-sectional area of the inlet opening” is to be understood as the actual open cross section in which air or a fluid may be led. This is therefore the actual “net cross-sectional area of the inlet opening” in this region. For example, with a circularly round inlet opening, it is firstly assumed to be the total circular area, but however the respective cross-sectional area of the blades or the hub (including sheathing, rotor magnet etc.) is subtracted for determining the net cross-sectional area. The measure found here is thus a ratio of the actual rotor magnet (with regard to area) to the actual cross section through which air or another medium may flow. 
     The cross section applied for evaluating V QE  preferably runs through a region in which not only is the rotor magnet present, but also a magnetically or electrically effective section of the stator. Here, the cross section which is used preferably lies perpendicular to the axis of the rotor. 
     Here, basically all substances capable of flowing are to be understood as “media”, e.g. gases, liquids, pastes, dusts or granular substances. 
     One advantageous further formation envisages the smallest diameter of the stator being 1.5-times to 8-times as large as the largest outer diameter of the rotor magnet. In a flanking manner, it is also possible for the smallest inner diameter of the stator to be 1.1- to 1.49-times, preferably 1.25- to 1.49-times as large as the largest outer diameter of the rotor. Likewise, it is possible for the smallest diameter of the stator to be 8.01- to 15-times, preferably 8.01 to 12-times as large as the largest outer diameter of the rotor. 
     The “largest outer diameter” of the rotor magnet is to be understood as the diameter which the actual magnetically effective material actually has (this without sheathing around the rotor magnet). If the rotor magnet does not have a circularly round shape, then the largest outer diameter is to be understood as the largest possible inscribed circle in the respective cross section of the magnet material. 
     The “smallest inner diameter of the stator” is to be understood as the smallest diameter of the electrically or magnetically actually effective stator. A shielding e.g. of a plastic material from the stator towards the rotor, which for example serves for corrosion protection, with this is not to be seen as part of the stator, but only the smallest diameter of the (as a rule metallic) electrically or magnetically effective parts count. With regard to the motor according to the invention, it is the case of a media gap motor, thus of a permanent magnet synchronous motor with the particular characteristic of an excessively large air gap between the stator and the rotor. This large air gap permits the transport of various media between the rotor and the stator in the axial direction. The rotor magnet here may be directly coupled to a delivery device or also integrated into this. 
     With conventional air gap motors, the smallest possible constructional size for the desired torque as well as a high magnetic flux with a lowest application of permanent magnetic material is desired, with a conventional design of the motor without the use of media/throughput function of the air gap. Thus with conventional motors, one thus keeps the air gap small on account of the fact that the magnetic resistance in the air gap is larger than in the ferromagnetic part of the magnetic circuit. 
     The present media gap motor is basically constructed as a conventional permanent magnet synchronous motor, but with the particularity of a stator inner diameter which is overdimesionally large compared to the outer diameter of the rotor or of the permanent magnet. 
     In order to produce the required magnetic flux despite the large gap between the rotor and the stator, and the high magnetic resistance which this entails, as well as the high scatter share at the pole transitions, it requires the application of magnets which have a very high remanence and a very high energy density. In particular, rare-earth magnet materials are suitable for this. The magnet height simultaneously needs to be adapted accordingly. A high motor efficiency with respect to the diameter of the rotor or magnet may be achieved despite the relatively low flux, since a relatively large winding area is available due to the large outer diameter of the stator. 
     It is particularly amazing for the man skilled in the art, that one may design a well functioning motor despite the unusually large air gap. 
     Here, the large gap between the rotor and stator even permits to rotor magnet to be displaced somewhat in the axial direction (direction of the rotation axis) without the characteristic values noticeably worsening by way of this. 
     The rotor of the electric motor preferably has a rotor magnet which is surrounded by a sheathing. The rotor magnet is mechanically protected by way of this. One may also have an influence on the type of magnetic field in this manner. For example here, a “beaker-like design” may be envisaged, into which the rotor magnet is inserted, in order to give a rotor magnet which at the end-side would otherwise be exposed to media, the best possible protection. The sheathing of the rotor magnet here (just as preferably the rotor magnet itself), is designed in an essentially cylinder-like manner. 
     The electric motor preferably contains a stator which has an essentially hollow-cylindrical shape and which surrounds the rotor in a concentric manner. Here, it is advantageous that the stator may be designed as part of the inner wall of the compressor housing, for example of a compressor housing of a turbocharger. The stator may for example also be applied as an insert into a corresponding opening of the compressor housing. The advantage with these embodiments is the fact that only an as small as possible design change of conventional mechanical turbochargers is necessary, so that cost- and competitive advantages may be realised by way of this, in particular with large-scale production. 
     Apart from the variants mentioned above, which focus on the outer surrounding of the stator, the stator may yet also be provided with a shielding towards the rotor. This serves for the protection of the stator, in particular for corrosion protection. The shielding may preferably be given in the form of a thin tube or flexible tubing, wherein this shielding is preferably designed of electrically and magnetically not-conductive material. 
     Thus as a whole, the hollow-cylindrical design of the stator is advantageous but not absolutely necessary. 
     The rotor may be designed in different manners. The motor preferably has a rotor shaft, wherein this rotor shaft is mounted in a simple or in a multiple manner over its length. In a particularly advantageous embodiment, the rotor shaft is essentially mounted on one side and projects out essentially freely on the other side. Thus the necessity of a further bearing location and, as the case may be, struts between the rotor and stator which could further increase the throughput resistance, may be done away with by way of this. A further embodiment envisages the rotor magnet in the inside being hollow in regions, for placing on a common shaft connected to a medium impeller or a medium conveyor worm. An even better integration of the rotor shaft or the drive shaft with the rotor magnet and even a part delivering medium (medium impeller medium conveyor worm) may be effected in this manner. It is advantageous on integrating the rotor magnet into the rotor shaft or the medium impeller/medium delivery worm, for the components adjacent to the rotor magnet to be of a material which is not magnetically conductive or very poorly magnetically conductive, preferably of reinforced or non-reinforced plastic, as well as of metal which is not magnetically conductive. 
     A further advantages formation envisages the mounting of the rotor shaft being non-lubricated or being lubricated by the medium to be delivered itself (this is advantageous for example with hydrodynamic bearings). As a whole, practically any media may be considered for the delivery with the electric motor according to the invention, specifically all gases (in particular air) as well as liquid media (in particular aqueous, explosive, volatile, sterile or highly pure media). 
     One particular advantage of the medium gap motor according to the invention lies in the fact that the axial centre of the stator and the axial centre of the rotor may be displaced in the axial direction, and specifically by tenth up to a 1.5 times, preferably a tenth to a fifth of the largest axial extension of the rotor magnet. The electric motor according to the invention is particularly suitable for the use in an electrically supported turbocharger with a freely projecting electric motor, for the transport of explosive gases, dusts, vapours, sticking substances, pastes, liquids such as water or oil; decomposing products, such as foodstuffs; in ventilation devices, in pumps, in particular in pumps for aggressive media, such as salt water, chemical solutions (in particular in the orthodontic field); in disinfectable or sterilisable pumps, canned pumps (medium transport in the axial direction), metering pumps, micro-pumps, disposable pumps, multi-stage pump systems; for use in turbines, generators, delivery worms for example for granular media, fluids or pastes; in gas-, water- and steam turbines; in devices for measuring the media flow via a generator voltage. 
     One advantageous further design envisages the rotor magnet having a remanence between 0.3 Teslas and 0.8 Teslas, preferably larger than 0.8 Teslas, particularly preferably larger than 1.2 Teslas. The flux density in the media gap here is between 0.05 Teslas and 0.5 Teslas, preferably more than 0.5 Teslas. 
     The present motor is thus fundamentally different to previous developments. What is important here, is that an intended leading of fluid or even a delivery of fluid through the gap between the rotor and the stator is effected in a targeted manner, and this is basically possible over the whole media gap. 
     Another particularity is that the media gap/air gap between the rotor and the stator is designed in a relatively large manner, as is clarified by the area relations or diameter relations. This goes against common practice with regard to common electric motors, with which a high magnetic flux with a low magnetic magnitude is the main concern, or a large power density and therefore a compact arrangement. 
     With regard to the present electric motor, it is to be ascertained that the inner diameter and outer diameter of the stator increase proportionally to the enlarged air gap. An increase of the winding area results by way of this, thus also an increased application of high-quality copper wire The specific resistance of the stator winding reduces on account of the increased ratio of copper wire to power. 
     In order to keep the demagnetisation factor as low as possible, it is advantageous for the magnet to consist of solid material, for example in the form of a solid cylinder. This solid cylinder may be provided with an as small as possible bore for mounting purposes. A division of the rotor magnet into segments is thus not necessarily advantageous, but is also not ruled out, however the single-piece design of the rotor magnet here appears to be the most advantageous. 
     In order not to negatively influence the magnetic flux within the media gap/rotor gap, no or only very weakly magnetically conductive material should be installed in the over-dimensioned gap. Likewise, the medium located in the gap should have no or only weak magnetic characteristics. The relatively large media gap/rotor gap when required, permits a complete insulation of the stator with respect to the rotor. A shaft sealing of the rotating shaft with respect to the stator is thus advantageously done away with. Thus a medium accelerator which is secure against leakage arises. 
     The motor is to be designed as a synchronous motor. By way of this, the rotational speed may be determined also electrically in an exact manner, (which is different to the case with asynchronous motors with slip), and thus a throughput control, metering control or throughput measurement given a known delivery quantity per rotor revolution are simultaneously possible. 
     A further advantageous design envisages that in at least one cross section, the ratio of the cross-sectional area of the stator to the cross-sectional area of the rotor magnet (expressed with regard to a formula: V QS =A stator /A rotor magnet ) is between 2 and 100, preferably between 10 and 50. Here, it is in each case the “net cross-sectional areas” of the electrically effective components of the stator or rotor magnet which are to be specified. Insulating components or components which are not electrically/magnetically effective, are not taken into account. Thus with a stator, a metal base body (including copper windings for example) is taken into account in the cross-section, but not a surrounding insulating plastic. Accordingly, with regard to the rotor magnet, it is also only the actually magnetically effective areas which are taken into account, even if the rotor consists of different parts (the individual areas are then to be added accordingly, so that one may evaluate a total area of the rotor magnet). The mentioned cross section preferably lies perpendicular to the axis of the rotor. 
     Further advantageous formations are specified in the remaining dependent claims. 
    
    
     
       The invention is now explained by way of several figures. There are shown in 
         FIGS. 1   a  to  1   d : views of a turbocharger, with which the electric motor according to the invention is applied, 
         FIGS. 2   a  and  2   b : an illustratory picture of the magnetic flux or cross-sectional views of an electric motor according to the invention, 
         FIGS. 3 to 6 : views or sections of further application examples for the electric motor according to the invention. 
         FIG. 7 : the distribution of the magnetic field in the rotor, stator and air gap; 
         FIGS. 8   a  to  8   d  courses of voltage, current, torque as well as power loss over the time axis; 
         FIGS. 9   a  and  9   b  views or sections of a further embodiment of an application of an electric motor according to the invention; 
         FIG. 10   a  an explanation of the proportions and arrangement of rotor magnet, stator and a compressor wheel; 
         FIG. 10   b  one embodiment of a compressor wheel with an inclined rotor and an inclined stator; 
         FIG. 11  one explanation of geometric details with electric motors according to the invention. 
     
    
    
     One application example of the invention is firstly shown by way of the  FIGS. 1   a  to  1   d , by way of example. 
       FIGS. 1   a  to  1   d  show a turbocharger  1  which may be coupled to a turbine housing  5  on an internal combustion engine. After the combustion, the exhaust gas is collected by way of the exhaust gas fans shown in  FIG. 1   a  and is used for driving a turbine wheel  2 . The turbine wheel  2  is surrounded by the turbine housing  5  and is essentially deduced from a conventional mechanical turbocharger. A bearing housing  7  connects to the turbine housing  5 , and then a compressor housing  6 . A compressor wheel is attached in this compressor housing  6 , and compresses the air fed through an inlet opening (this inlet opening is in particular easily seen in  FIG. 1   c ) and leads it to the combustion space of the internal combustion engine in a manner which is not shown here. The compressor wheel  3  on the left side in  FIG. 1   a  shows a continuation, to which a rotor  4   a  of an electric motor is given. The rotor  4   a  is attached centrally in the inlet air opening  4   e.    
     A stator  4   b  which has an essentially hollow-cylindrical shape and is represented as part of the inner wall of the compressor housing in the region of the inlet air opening, is provided around the rotor  4   a . Here, the stator  4   b  is even provided as an insert into a suitable opening, so that this may be assembled very easily. Here therefore in  FIG. 1   a , the rotor gap between the rotor  4   a  and the stator  4   b  is the inlet air opening  4   e  for the compressor wheel. With this, the inlet air opening  4   e  is free of struts between the rotor and the stator also according to  FIG. 1   a . The smallest inner diameter of the stator (see “d s ” in  FIG. 1   d ) is 1.5 times larger than the largest outer diameter d R  of the rotor. 
     The rotor  4   a  of the electric motor  4  comprises a rotor magnet  4   c  which here is surrounded by an sheathing (see e.g.  FIG. 1   d ). With this, the sheathing is designed in an essentially “beaker-shaped” manner, wherein the base of the beaker is almost completely closed towards the compressor wheel (disregarding a centric assembly bore). 
     The compressor wheel may (but need not) be of a non-metallic material, here with one embodiment, for example of a plastic, and the influence on the electromagnetic field of the electric motor is minimised. The rotor magnet  4   c  in turn is hollow in regions for placing on a common shaft with the compressor wheel. Here, a bore  4   c  of the rotor magnet is to be accordingly seen in  FIG. 1   d . Furthermore, it may be seen that a sequence of elements is shown in the sequence of the rotor (consisting of the rotor magnet  4   c  and sheathing  4   d ), the compressor wheel  3 , shaft  8 , turbine wheel  2 , which minimises a thermal loading of the electric motor. The shaft  8  here in the present embodiment is designed such that the turbine wheel  2 , compressor wheel  3  as well as rotor  4   a  are firmly (rotationally fixedly) connected to one another, thus may not be separated by a rotation clutch or free-wheel. 
     However, it is basically possible to provide such a clutch within the framework of the present invention, if it is the case for example that the turbine wheel  2  is very high, but however the design effort would in turn also be increased by way of this. 
     The nominal voltage of the electric motor  4  in  FIG. 1   a  here is 12 V, but other voltages (for example 48V for hybrid vehicles) are also possible. 
     The electric motor may be operated in motor operation (for accelerating and avoiding a “turbolag”), as well as in generator operation (for recovering energy). If the charging pressure (in the turbine housing) reaches a certain nominal value, then additional energy is produced by way of using a converter capable of return feed. Ideally, one may do away with a wastegate/pressure dose for blowing out excess exhaust gas pressure, as is represented in  FIG. 1   b , numeral  9 , by way of this energetic conversion of the braking energy in generator operation. 
     The turbocharger according to the invention is used in a drive system according to the invention for motor vehicles which contain an internal combustion engine connected to the turbocharger, as well as a storage device for electrical energy. The electric motor of the turbocharger  1  here is connected to the storage device for electric energy for taking electrical energy in a motor operation of the turbocharger  1 , and for feeding in electrical energy in a generator operation of the turbocharger. In a particularly preferred embodiment, the electric motor of the turbocharger is connected to an electrical storage device, wherein this electrical storage device is additionally connectable to an electromotoric drive of a motor vehicle. This may be a “hub motor” of a motor vehicle or another electric motor, which is provided in the drive train of a motor vehicle (for example in the region of the gear). This connection of the electrical turbocharger to a hybrid vehicle is particularly energy efficient. 
     Control electronics for determining the rotational speed of the turbine wheel  2  or the compressor wheel  3 , actual values of pressure conditions on the turbine housing side and compressor housing side, as well as further values relevant to the torque for the internal combustion engine are provided for the efficient control of the drive system or the turbocharger. 
       FIG. 2   a  shows a field line representation of the magnetic flux between the rotor  4   a  and the stator  4   b.    
       FIG. 2   b  once again shows the geometric particulars of the electric motor according to the invention. Here one may see a solid-cylindrical rotor magnet which has a largest diameter d RM . A sheathing  4   d  is attached around this rotor magnet  4   c . In turn, a medium impeller  10   a  is attached on this sheathing. A medium passage opening  4   e  is given around the media impeller  10   a  and this is surrounded radially outwardly by a shielding  11 . The actual stator  4   b , whose outer diameter is specified at d s , is then given around the shielding  11 . 
     With the exemplary electric motor, the remanence is 1.28 Teslas, the energy density  315  kJ/m 3  and the rotor magnet consists of NdFeB. 
     Here then, an electric motor  4  for the delivery of media is shown, wherein this comprises a stator  4   b , a rotor  4   a  with a rotor magnet  4   c , as well as a media passage opening  4   e  between the stator and rotor. The smallest inner diameter d s  of the stator, here is 1.5-times to 8-times, preferably 2-times to 4-times as much as the largest outer diameter of the rotor magnet itself (d RM ), in the present case d s =2×d RM . 
     The rotor magnet is preferably surrounded with a sheathing for the protection from media or damage or for the protection from centrifugal force at greater peripheral speeds. This may be designed in a beaker-like manner. The stator is preferably designed as an insert into a corresponding opening of a surrounding housing. A shielding  11  is preferably provided to the inside, thus towards the media passage opening, and this protects the stator from corrosion and improves the flux characteristics. 
     This is preferably designed in the shape of a tube, wherein the tube is of an electrically and magnetically non-conductive or poorly conductive plastic e.g. glass fibres, alternatively e.g. of glass, cast epoxy resin or rubber. The rotor particularly preferably has a rotor shaft, wherein this rotor shaft is mounted in a simple or multiple manner over its length. The rotor shaft here is preferably mounted on one side and thus in a “projecting” manner. 
     The flow resistance through the rotor is further reduced by way of this. The rotor magnet is preferably placed on a common shaft with a media impeller or a media conveyor worm or is integrated in the inside and thus centred straight away. One may again attach a media impeller or a media conveyor worm around the motor magnet (these have recesses for receiving the rotor magnet), so that an as large as possible integration of the components is possible. 
       FIG. 3  shows a use of an electric motor which comprises a media impeller  10   a  of a plastic material. A rotor magnet  4   c  is attached on the end-side of this media impeller  10   a . Bearing locations  12  mount a rotor shaft  8  which is screwed in the medium impeller. A stator  4   b  is accommodated in an inner wall of a housing  6 . The flow of a medium  13  is introduced from the left, and is conveyed towards the right by the media impeller  10   a . Preferably, in the present case, again there is a large gap width not only radially about the axis  14 , but also axially in the direction of the axis  14 . This is also due to the fact that the axial centre of the stator AZS and the axial centre of the rotor AZR are displaced in the axial direction, and specifically by a tenth to a fifth of the largest axial extension GAAR of the rotor magnet. 
       FIG. 4  shows a representation corresponding essentially to  FIG. 3 , wherein here a shielding  11  is additionally provided, which protects the stator from the medium  13 . 
       FIG. 5  shows a further embodiment of a pump according to the invention or of a throughput meter according to the invention, with which three propellers  10   a  are mounted on a rotor shaft  8 . With this, the bearings are attached on the left, as well as on the right side of the three media impellers  10   a . The stator  4   b  is attached in the axial direction with respect to the axis  14  centred about the rotor magnet  4   c . The media impellers have an inner cavity which accommodates the rotor shaft  8  or the rotor magnets  4   c  located therein. A particularly simple and securely mounted device is given in this manner, and by way of suitable webs, on the one hand the retention of the rotor shaft  8  is ensured, and also an adequate throughput of media  13  is achieved on account of the relatively small web cross sections. 
       FIG. 6  shows an embodiment example which is quite similar to  FIG. 5 . However, here a media conveyor worm  10   b  is provided instead of the three individual impellers  10 , and this seals media towards the shielding  11  in a particularly good manner. 
       FIG. 7  shows a representation of the distribution of the magnetic field in the region of the stator  4   b , the rotor  4   a  or rotor magnet  4   c , as well as the media gap/inlet opening. The chambers shown in the stator are hollow inclusions of the surrounding sheet-metal inlay, and these are wrapped around with copper wire. 
     One may recognise in  FIG. 7  that the field lines at the pole transitions are short circuited without flooding the stator. Since the magnetic field is provided by the permanent magnets without losses, this has no negative influence on the efficiency of the motor. 
       FIGS. 8   a  to  8   d  show courses of voltage, current, torque as well as power losses over the time axis. 
     The figures do not show any special characteristics, but despite the large air gap, the characteristic lines are typical of a synchronous motor. 
       FIGS. 9   a  and  9   b  show a further embodiment of an application for an electric motor according to the invention. 
     Here, a possibility is shown of leading tubes or conduits through the air gap. These tubes serve for leading through media (e.g. fluids, pastes, granulates or gases) and are thus suitable for painting installations or for blasting treatment (e.g. sand blasting, glass pearl blasting etc.) of workpieces. Different types of media may be led through different tubes (e.g. various colours). 
     One should take care that these tubes should have no or only weakly magnetic characteristics. Electrical current may be led through these conduits, but influences the magnetic flux and thus the power (torque/rotational speed/true running) of the motor and is therefore to be accordingly taken into account on designing the total arrangement. 
       FIG. 9   a  shows a plan view in which tubes  15  (3 pieces, for example painting tubes) are arranged parallel to a middle axis  10 . The rotor  4   a  or rotor magnet  4   c  is arranged centrally in the middle axis  10 . The stator  4   b  is attached separated by a tube or a shielding/sheathing  11 . 
       FIG. 9   b  shows a cross section according to B-B. On this, one may see medium flows from the left to the right in the picture through the tube  15 , and hits an acceleration disk  16 , by which means a dispersion of the medium is effected and subsequently a painting, for example of a vehicle. The acceleration disk  16  is connected to the rotor  4   a  which comprises a rotor magnet  4   c . The rotor magnet  4   c  together with the rotor  4   a  is mounted on bearings L 1  and L 2  and the drive is effected via the stator  4   b  lying outside the shielding/sheathing. 
       FIG. 10   a  shows a schematic representation of the compressor wheel  3 , the stator  4   b  as well as the rotor  4   c  for illustrating the geometric conditions. What is shown is the compressor wheel which is mounted on a shaft  10  on one or on both sides, and is subjected to flow in an air inlet flow direction LES. The air flow which flows in, is accelerated by the compressor wheel  3  which comprises a conveyor structure F. The front edge of the conveyor structure is indicated at VF, and the rear edge of the delivery structure is indicated at HF. The front edge of the rotor magnet  4   c  is indicated at VR and the rear edge of the rotor magnet  4   c  is indicated at HR. The front edge of the stator is indicated at VS, and the rear edge of the stator is indicated at HS (the stator here is rotationally symmetrical, but here the upper stator section has been shown for reasons of a better overview). The compressor wheel  3  thus has a conveyor structure F in the form of blades, wherein the front edges VF of the conveyor structure, in the air inlet flow direction, lie downstream with respect to a magnetically effective front edge of the rotor magnet  4   c  and a magnetically effective front edge VS of the stator. The compressor wheel with its rear edge HF in contrast, in the air inlet flow direction, lie upstream with respect to the rear edge HR of the rotor magnet  4   c  as well as the rear edge of the stator  4   b.    
     However, other arrangements are also possible here, with which the rotor magnet or stator only project beyond one edge of the compressor wheel, and it is also possible for the rotor magnet to lie completely within the compressor wheel, and thus to be laterally enclosed by the edges of the conveyor structure. 
       FIG. 10   b  shows a further embodiment, with which the stator  4   b  (this is rotationally symmetrical with respect to the axis  10 ), is inclined with respect to the axis  10 . The stator thus here has essentially the shape of a hollow truncated cone. The same also applies to the rotor  4   a  or the respective rotor magnets, and this too with its sections, is inclined with respect to the axis  10  (thus these are not parallel/co-linear, but would intersect in their extensions). 
     The compressor wheel shown in  FIG. 10   b  is mounted on both sides (see indicated bearing locations L 1  and L 2 ). However, the embodiment forms of the further figures may basically also be mounted on both sides (even if this, under certain circumstances, means more constructional effort). 
     With regard to  FIG. 10   b , it is the case that the rotor magnet  4   c  is arranged radially outside the hub of the compressor wheel with respect to the axis  10  of the compressor wheel  3 . The compressor wheel here is designed such that air may be led radially within, as well as radially outside the rotor magnet. Here, the compressor wheel is also designed such that at least 70% of the supplied air mass (or of the supplied air mass flow), is led radially outside the rotor magnet. 
       FIG. 11  once again shows a cross section through a stator  4   b  and rotor  4   a , according to the invention. Here one may see a rotor magnet  4   c  which consists of individual segments (four distributed over the periphery). Alternatively to this, one may also imagine e.g. a cylindrical single magnet for example. A sheathing  4   d  is attached around this rotor magnet  4   c . In turn, a conveyor structure F (here in section, therefore hatched) is shown on this sheathing. An air passage or media passage opening  4   e  is given around the conveyor structure and is surrounded radially to the outside by a shielding  11  (this is of plastic and is magnetically/electrically insulating). The electrically effective part of the stator  4   b  is given around the shielding  11 . 
     In the cross section shown in  FIG. 11 , the cross-sectional area of the media passage opening or the air passage or the inlet opening  4   e , to the cross-sectional area of the four segments of the rotor magnet (defined as V QE =A inlet opening /A rotor magnet )=4:1. 
     Here, the inlet opening  4   e  is defined as the opening which may indeed be subjected to through-flow, thus the area content within the sheathing  11 , but minus the areas of the hatched conveyor structure, as well as the hub of the rotor (the hub includes the sheathing  4   d  as well as everything located therein). What is meant here is the “net cross-sectional area” of the inlet opening. The cross section in  FIG. 5   c  visibly runs through the electrically and magnetically effective section of the stator  4   b . In this cross section, the ratio of the cross-sectional area of the stator to the cross-sectional area of the rotor magnet (defined as V QS =A stator /A rotor magnet )=13:1. 
     Here, only the electrically or magnetically effective part (thus core metal+copper wire, however minus copper wire coating as well as possible “hollow areas”) is to be understood as the cross-sectional area of the stator. Accordingly, it behaves as with the rotor magnet, and here only the cross sections of the pure rotor magnet segments in this cross section are applied. 
     The above-mentioned ratios for the relation of the smallest inner diameter of the stator to the largest outer diameter of the rotor, supplementary to 1.5 to 8-fold, may also lie in other intervals, specifically 1.1- to 1.49-fold, preferably 1.25- to 1.49-fold. Accordingly however, at the other end of the scale, the smallest inner diameter of the stator may also be 8.01- to 15-fold, preferably 8.01- to 12-fold the size of the largest outer diameter of the rotor.