Electric machine

Abstract

An electric machine (12) characterized by: • a ferromagnetic or ferrimagnetic rotor (14) of at least approximately circular cylindrical shape and an iron-containing stator (16) of at least approximately circular cylindrical shape, wherein the rotor (14) and the stator (16) each have two spaced-apart end faces (14a, 14b; 16a, 16b), wherein: • the stator (16) has on at least one of its end faces (16a, 16b) a plurality of stator poles (16c) arranged circumferentially at least sectionally regularly, which face an air gap (18), and on one or both sides of a stator pole support (16d) a ring of the stator poles (16c) and an annular return without individual poles and with a radial air gap are arranged, • the rotor (14) has on both of its end faces (14a, 14b) a plurality of rotor poles (14c) arranged circumferentially regularly,which on one side face the air gap (18) and on the other side are coupled to an iron-containing rotor return (14d), wherein the rotor poles (14c) on one of the end faces (14a, 14b) are arranged circumferentially offset by 1 / m * B relative to the rotor poles (14c) on the other side of the rotor pole support (14d), where m is the number of phases of the electrical machine and B is the circumferential width of the rotor pole (14c), • the stator (16) has at least one stator coil (20, U, U*, V, V*, W, W*) which is configured to induce a magnetic field in at least a part of the stator poles (16c),

Description

IntroductionAn electric machine is described below which is suitable and provided, for example, for use in a land vehicle, as a drive in a robot arm or for positioning, for example, workpieces, tools, machine parts, conveyor baskets and the like. This can also be an electric machine which is suitable and provided exclusively or additionally to an internal combustion engine or as an auxiliary unit in the vehicle (automobile or bicycle).BackgroundElectric machines are used in a variety of industrial and mobility applications. In most of these applications, the highest possible efficiency and long service life of the machine are required, without the maintenance requirements or the risk of failure thereby increasing. There is a further need for small, light-weight electric machines that can be operated at low to medium speeds or high torque, so that in many cases mechanical force transmission components such as transmissions can be dispensed with. Thus, the electric machine can be easily integrated into the driven equipment. A further requirement is that the electrical machine be well suited for operation with a frequency converter.Neodymium permanent magnet materials (NdFeB) and the resulting new permanent magnet machine technology are increasingly being used for servomotors. Permanent magnet machines are becoming increasingly prevalent in many industrial special applications such as gearless, slow running torque machines. However, the rare earth materials required for the permanent magnets are relatively expensive and may be available only to a limited extent.US 2008 / 0258572 A1 discloses a reluctance rotary machine.JP 2010-263718 A relates to an axial gap motor in which stator magnetic poles excited by a winding exciting coil are arranged on a magnetic pole face in the circumferential direction. Here, as many poles are arranged on an outer circumferential side as an inner circumferential side of the magnetic pole face. The stator magnetic pole on an inner circumferential side of the stator is excited with a certain polarity, while the stator magnetic pole on the outer circumferential side of the stator is excited with the reverse polarity. Opposite the stator is a rotor with poles arranged in the same way.Furthermore, the document JP 2005-318 792 A discloses an electric machine having a circular-cylindrical stator and a circular-cylindrical rotor, wherein the stator has, on at least one of its end faces, a multiplicity of stator poles which are arranged at least in sections in a regular manner in the circumferential direction and face an air gap. Furthermore, the rotor also has, on at least one of its end faces, a multiplicity of rotor poles which are arranged regularly in the circumferential direction and which likewise face the air gap.Document JP 2007-236 130 A discloses an electric machine in which a rotor to which a permanent magnet is attached and a stator to which an armature winding is attached are opposed to each other in the axial direction, wherein the magnetic path formed via the rotor and the stator consists of a flux along the direction of the rotating shaft and a flux along the radial direction of an end surface perpendicularly intersecting the rotating shaft, and extends in the radial direction of the end surface perpendicularly intersecting the rotating shaft.Underlying ProblemThe object to be achieved is an electric machine with a cost-effective design, simple production and efficient, reliable operation.Summary of the Solution Presented hereAn electric machine has a ferromagnetic or ferrimagnetic, at least approximately circular-cylindrical rotor and an at least approximately circular-cylindrical iron-containing stator. The rotor and the stator each have two end faces spaced apart from one another. The stator has on at least one of its end faces a plurality of stator poles which are arranged at least in sections regularly in the circumferential direction and face an air gap, wherein a ring of stator poles and an annular return path which is not structured with individual poles and has a radial air gap are arranged on one or both sides of a stator pole carrier. The rotor has on both of its end sides a plurality of rotor poles arranged regularly in the circumferential direction, which poles face the air gap on the one hand and are coupled to a ferrous rotor return circuit on the other hand. The rotor poles on one of the end sides are arranged offset by 1 / m*B in the circumferential direction relative to the rotor poles on the other side of the rotor pole carrier, wherein m is the number of phases of the electric machine and B is the width of the rotor pole in the circumferential direction. The stator has at least one stator coil which is configured to induce a magnetic field in at least a part of the stator poles. Arrangements with this construction provide very good ratios of force to weight and force to (electrical and mechanical) losses with efficient use of installation space.Advantageous Configurations, Variants and PropertiesThe electric machine designed as a reluctance machine has a simple rotor construction made of ferromagnetic or ferromagnetic material without conductors (squirrel cage, field exciter winding or the like) or permanent magnets. The stator is also formed from soft magnetic iron and has one or more corresponding stator coils. A reluctance machine generates in its rotor, due to its function--similar to the rotor losses of a permanently excited machine--only a very small waste heat. Waste heat occurring in the stator can likewise be dissipated relatively easily also externally.The stator coil of the stator can be distributed over different planes or disks. (A "disc" has a stator pole support with the stator poles and one or more stator coils and one or two rotors on one or both end faces of the stator.)In an electric machine of the type presented here, which works according to the principle of magnetic reluctance, the rotor has as low a magnetic resistance as possible in one direction and a high magnetic reluctance in another direction. The torque in motor operation arises because the rotor tends to align the magnetically conductive direction on the stator field. The magnitude of the torque generated is directly proportional to the ratio of the inductances of the two magnetic directions of the rotor. A disadvantage of reluctance machines, that they do not start up automatically in the direct mains connection, can easily be overcome by frequency converters. A further disadvantage of reluctance machines is the higher current requirement for the same torque compared to permanent magnet excited machines, since the rotor must be magnetized by the stator. However, the power factor viewed from the mains is determined by the converter and is close to one even in reluctance machines. Reluctance machines of the type presented here have a rotor structure which is very simple to produce without magnets and a squirrel cage, so that they are very robust. In addition, in reluctance machines of the type presented here, the risk of permanent power loss due to demagnetization in the event of failure or overheating is dispensed with. Reluctance machines of the type presented here are intrinsically safe in operation, since no counter electromotive voltage is induced by the missing permanent magnets. Overvoltage protection of the converter is therefore not required.The substantial elimination of rotor losses and rotor structure provides a number of advantages to these electric machines and equipment containing them. A machine with this technology may have a low operating temperature. This low operating temperature extends the life of the machine insulation and the life or lubrication intervals of the bearings. Especially machine bearings require regular maintenance. The lower bearing temperature is immediately noticeable by longer lubrication intervals, a lower maintenance effort and a higher reliability. Even a bearing exchange is very simple due to the non-existing magnetic forces, as occur in permanent magnet machines. Since losses at the rotor are difficult to cool compared to stator losses, the thermal insensitivity of the rotor is highly advantageous because of the lack of permanent magnets. A further advantage is the low heat emission to adjacent parts, especially in closed housings. Since less heat is dissipated through the machine shaft, the bearing temperature decreases particularly on the drive side. Finally, the rotors have less inertia due to the absence of the squirrel cage and permanent magnets.In addition, in contrast to conventional arrangements in which the air gap is formed on the (inner or outer) lateral surface between the rotor and the stator, the front-side formation of the air gap between the rotor and the stator allows a significantly more efficient use of installation space. The extent of the generation of force in the electric machine depends on the area of the air gap. The end face A S of the stator / rotor depends quadratically on the radius r (A S= pi*r 2), while the lateral surface A M of the stator / rotor depends only linearly on the radius and the cylinder length Z L( A M= Z L* 2* r*pi). Thus and because of the small overall height in the axial direction, the installation space of the machine is utilized significantly better, which predominates in the influence of the radial dimension on the torque formation. Therefore, the surface area of the air gap can be relatively larger when arranged on the end side than when the air gap is arranged on the circumference as otherwise customary. Moreover, when the air gap is arranged at the end face, its dimension is significantly less temperature-dependent, since the radius of the rotor and of the stator is usually greater than its axial length. In conjunction with a lower heat output in any case than in other types of machines, this has the consequence that the air gap can have a substantially smaller transverse dimension (distance between the magnetic field line exit / entry surfaces of the rotor and of the stator), which in turn improves the force formation of the electric machine.The rotor may be formed of solid iron for low speed machines and of laminated soft magnetic steel sheets or of powdered iron fixed to the rotor shaft for high speed machines.In reluctance machines of the type presented here, the stator has a plurality of teeth facing the rotor, which are wound around by coils that can be excited individually (or in groups). In motor operation, the individual windings of the stator are energized independently of one another with current. In principle, each of the stator teeth can only pull a rotor tooth approximately opposite it into the aligned position at all times. In this aligned position, the rotor tooth is fully aligned with the stator tooth. By providing the current pulses in a correspondingly time-controlled manner, a circulating, averagely directed force is thus generated.In motor operation, when passing the aligned position, the previously switched-on current pulse is switched off, while in generator operation a voltage is induced in the coil that has not been energized until then. In reluctance machines of the type described above, the stator teeth, but also the rotor teeth, are permanently remagnetized at the alternating pole frequency. The material is magnetized only in one direction, so that, in contrast to other types of machines, only a part of the hysteresis loop is passed through in operation. This results in significantly lower remagnetization losses. In addition, it is possible not to reduce the magnetization down to zero, which further reduces hysteresis losses. This is possible since residual magnetization has only a slight influence on the operating behavior because of the quadratic dependence during the torque formation. At high rotational speeds, high magnetic reversal losses occur in the rotor. These magnetic reversal losses are essentially composed of an eddy current component and a hysteresis component. While at least some of the eddy current losses are to be limited by a stack-up of sufficiently thin metal sheets, the hysteresis losses are to be limited to a somewhat low value only by using so-called electric sheets of special alloys and special crystalline construction. In this case, a lower specific conductivity due to alloying of the soft magnetic material with silicon is also desirable.Reluctance machines of the type presented here can have a stator pole pitch which is smaller than the rotor pole pitch. The stator winding is not constructed from individual windings which are each assigned to a stator pole, but can be designed as a rotating field winding. For this purpose, corresponding to the number of phases (for example three) with respect to one another by 360° / 2* number of phases (in the case of three phases, that is to say 60°), windings which are spatially offset on the circumference are accommodated in the slots between the stator poles. The winding width of the windings corresponds approximately to the pole pitch of the rotor. If these stator windings are supplied with approximately sinusoidal currents which are in turn shifted in time according to the number of phases (i.e. 120° in the case of three phases) (three-phase system), the stator generates a magnetic rotating field. This rotating field has an approximately sinusoidal variation of the intensity of the stator excitation. This intensity rotates with respect to the stator, but the field substantially retains its shape.Rotating field systems of this type can also be realized with other phase numbers such as 2, 4, 5, 6 and more. A 6-phase system consists of 6 stator windings which are fed with 6 currents which are offset with respect to one another by in each case 60°. With a larger number of phases, the remaining field modulation described above is reduced even further.Furthermore, winding systems and their current supply can be realized for generating non-sinusoidal fields, which nevertheless rotate with unchanged form.The stator poles can be arranged on one or on both sides of a stator pole carrier in at least two rings concentric to one another. Between each two adjacent rings of one side of the stator pole carrier at least a part of at least one of the stator coils can be accommodated.In the rotor and the stator, in one variant rotor poles or stator poles located radially further inwards have at least approximately the same surface area oriented towards the respective air gap. In addition, variants with a structured and an unstructured air gap are possible.In a variant of the electric machine, the stator coils do not project beyond the stator poles in the direction of the air gap. However, it is also possible to let the coil at least partially enter the opposite gap of the rotor, so that the latter is directly magnetized by the stator coils (in motor operation). This provides more space for the stator coils. The course of the magnetic field is not influenced by this.The stator coils with the same phase can be assigned to pitch circular coils only to a part of the stator poles on the respective side of the stator pole carrier, or can be assigned to the entirety of the stator poles on the respective side as ring coils on one or both sides of the stator pole carrier.The electric machine of the type presented here can have a number of phases of 2, 3, 4, 5, 6 or more.The stator poles on one side of the stator pole carrier may have the same or a larger or smaller pole pitch than the rotor poles facing them, depending on whether the polyphaseity of the electric machine is generated in one or more disks. With the same pole pitch, the number of stator poles can be less than the number of rotor poles facing them.In the stator in the embodiment with stator poles on its two end sides, arrangement can be made such that the stator poles on one side of the stator pole carrier have no offset in the circumferential direction relative to the stator poles on the other side of the stator pole carrier.In the rotor and the stator, rotor poles or stator poles located radially further inward can have end faces which have at least approximately the same surface area oriented toward the respective air gap. An embodiment with an unstructured air gap in the case of the poles located radially further inward is also possible. This variant offers further design freedom, in particular for optimizing the coils and effective surfaces.Each air gap between the rotor and the stator may have a cross dimension of approximately 400-100 μm, preferably approximately 200 μm, on average, and each rotor and stator may have a run-flat tolerance of approximately 40-10 μm, preferably approximately 20 μm.In slow-running variants, each air gap can preferably contain a ferrous or a thin non-magnetic disk, which preferably has a friction-reducing coating. The ferrous variant allows the air gap to be further reduced to increase torque.For each phase, a circular-ring-cylindrical stator coil can be accommodated on each of the two sides of the respective stator pole carrier between two mutually concentric rings of stator poles. On each side of the respective stator pole carrier, at least a part of at least one of the stator coils can be accommodated between in each case two adjacent rings of one side of the stator pole carrier.The cross sections of the stator poles and / or of the rotor poles can be reduced continuously or in stages towards the air gap.Further features, characteristics, advantages and possible modifications of this electric machine will become apparent from the following description, in which reference is made to the attached drawings.Brief Description of the FiguresFIG. 1 shows a stator of an electric machine designed as a reluctance machine in a schematic plan view. FIG. 1 ashows the stand from FIG. 1 in a schematic side view. FIG. 2 shows a rotor of an electric machine designed as a reluctance machine in a schematic plan view. FIG. 2 ashows the rotor from FIG. 2 in a schematic side view. FIG. 3 shows a second variant of an electric machine designed as a reluctance machine in a schematic lateral sectional view. FIG. 4 shows a third variant of an electric machine designed as a reluctance machine in a schematic plan view, wherein the rotor is shown radially outside the stator for better clarity of the phase offset. FIG. 5 shows a variant of the configuration of the rotor poles of the reluctance machine in a perspective lateral partial view.Detailed Description of Several Variants of the Electric MachineIn the figures, an electric machine is shown which is arranged in a closed housing 10. The electric machine 12 in the form of a reluctance machine with an approximately circular-cylindrical rotor 14 and an approximately circular-cylindrical stator 16 is accommodated in the housing 10. The details of the reluctance machine are explained further below. The stator 16 is separated from the rotor 14 by an air gap 18 and has a plurality of stator coils 20.The rotor 14 and the stator 16 are here formed from pressed powder iron or from solid iron; they can also be formed (for higher rotational speed requirements) from a stack of thin iron sheet layers.The rotor 14 and the stator 16 each have two end faces 14 a, 14 b; 16 a, 16 b, which are spaced apart from one another. The stator carries on one of its end faces 16 a, 16 b a plurality of stator poles 16 cwhich are arranged regularly in the circumferential direction and which face the air gap 18. The rotor 14 also has on one of its end faces 14 a, 14 b, a plurality of rotor poles 14 cwhich are arranged regularly in the circumferential direction and which on the one hand face the air gap 18 and on the other hand are coupled to a ferrous rotor return 14 d. The stator 16 has a plurality of stator coils 20, U, U*, V, V*, W, W* which are configured to induce a magnetic field in the respective stator poles 16 c.During a rotary movement of the rotor 14, the self-inductance of a stator coil 20 changes periodically between a smallest value and a largest value. The torque at the rotor is proportional to the square of the current through the stator coils 20, i.e. the direction of the torque is independent of the direction of the current in the stator coils 20. A large change in inductance as a function of rotor position causes a large torque. During a rotary movement of the rotor 14, a shaft 14' is set in rotation.At low speed, the iron losses of the electric machine 12 play only a minor role. This can be used to increase the effective currents in the pole windings and thus leads to a high permissible continuous torque in the lower rotational speed range. Furthermore, during operation at low speeds, only slight iron losses occur in the rotor-the heating of the rotor remains low.The electric machine 12 is designed as a reluctance machine, the rotor 14 and stator 16 of which are provided with slots 17. This electric machine has a very simple rotor which is robust to implement and which causes low magnetic losses. The stator 16 and the rotor 14 are strongly grooved on their respective end faces 16 a, 14 afacing each other. For this purpose, the stator 16 and the rotor 14 have in the variant illustrated in FIG. 1 in each case an identical number of stator poles 16 cand rotor poles 14 c, respectively. In the illustrated example of the reluctance machine, these are six stator poles 16c and two rotor poles 14c. For each of two diametrically opposite stator poles, associated stator coils 20, U, U*, V, V*, W, W* are provided. The coils 20 are located exclusively on the stator 16 and have the winding shape shown in the illustrated three-phase system. Here, a variant of the winding shape drawn in dashed lines is also illustrated for the stator coil W*.It can be seen that in reluctance machines of the type shown here, stator poles 16c are arranged on one or both sides of a stator pole carrier 16d in two (or more) mutually concentric rings 16e', 16e". In the variants of FIGS. 1 and 3, one of the stator coils 20 is accommodated between each two adjacent rings 16e', 16e" of one side of the stator pole carrier 16d. As can be seen, the stator coils 20 do not project beyond the stator poles 16 cin the direction of the respective air gap 18. Rather, they are completely accommodated in the slots formed by adjacent stator poles 16c.The variant of FIG. 3 has, as can be seen, three stators with stator poles on both sides of the respective stator pole carrier, wherein a rotor with rotor poles is arranged in each case between the three stators on both sides. On both outer ends of the overall arrangement from FIG. 3, a rotor disk is arranged in each case, which rotor disk is equipped with rotor poles only on its inner end face.In the variant of FIGS. 1, 1 a, 2, 2 a, the stator coils of the same phase U, U*, V, V*, W, W* are assigned to the respective stator poles 16 cin the form of pitch-circle coils on one side of the stator pole carrier 16 d. In the variant of FIG. 3, the stator coils 20 U, U*, V, V*, W, W* are assigned to the respective stator poles 16 cin the form of ring coils on both sides of the stator pole carrier 16 d. In this case, the two ring coils assigned to a stator pole carrier 16 dare assigned to a different phase.The electric machine has three phases in the variants shown here. However, the number of phases may be 2, 3, 4, 5, 6 or more.For mounting the components of the electric machine, a spacer bushing (not shown) with a clamping set is mounted between the posts. These absorb the torque via holes in the spacer bushes with fitting pins (not shown) and transmit it to the shaft 14'. The posts are thus not mechanically prestressed and deformation is avoided. For the stator windings, connecting lines (not shown) are led outwards by the clamping set via the holes in the spacer bushes, wherein every second hole is provided for the locating pins. The two coils of each phase are connected in series, resulting in six coil connections. The lead-through of the connecting lines through the bearing (not shown) is effected by 12 corresponding grooves in the shaft. Here, too, every second groove is provided for the connection lines (not shown). The remaining grooves serve for transmitting torque to a torque support. An ordered cable guide and a cable connection can also be integrated into the torque support.For the construction, the stator 16 is mounted with loose rotor disks 14 on the central shaft 14' with the addition of spacer plates, so that the transverse dimension of the air gap 18 is fixed. The housing 10 is then pushed on, bearings (not shown) are inserted and the housing 10 is welded to the stator at points. The axial tolerance is measured by spacer disks in the bearing seat.A further variant is shown in FIG. 4. Here, for better understanding, the rotor 14 is shown radially outside the stator 16. The phase offset of the stator teeth can thus be better recognized. In a machine realized according to this principle, the rotor 14 and the stator 16 would face each other at the end face (as in FIGS. 1, 2 and 3 ). It can be seen here, too, that the stator poles are divided into three phases X Y Z, each of which has its own phase winding (not illustrated in any more detail here), of which one is energized at each time.In a right-handed rotor, (i) the stator poles 16 cof the phase X would be aligned with the rotor poles 14 cand thus free of force, (ii) the stator poles 16 cof the phase Y would be aligned with the rotor poles 14 cin an ascending traction phase in which the associated stator coil is energized, and (iii) the stator poles 16 cof the phase Z would be aligned with the rotor poles 14 cin an ascending phase in which the associated stator coil is de-energized.The stator coils are here likewise arranged between the inner and the outer pole ring. The return of the stator coils can be accommodated in an adjacent plane of the stator carriers (as described above) in this variant.In this variant, the phase offset is realized in that ten rotor poles 14 c(a total of 31) are provided on the rotor 14 for each phase, which poles are distributed equally along the entire circumference of the rotor (on its end face) and are of equal width. In the case of the stator 16, stator poles 16 care arranged (on its end face) along the circumference 30. These stator poles 16 care all of the same width. In each case in the region of one of the three phases X Y Z, the stator poles 16 care equally distributed. As illustrated in FIG. 4, in one position, ten rotor poles 14 care aligned with the ten stator poles 16 cof one phase (in FIG. 4, those of phase X). Since one less stator pole 16 cis provided along the circumference of the stator 16, the ten phase Y stator poles 16 cand the ten phase Z stator poles 16 cmay be offset by one third and two thirds of a width of a stator pole 16 cin the circumferential direction of the stator 16, respectively. This arrangement results in a rotational movement of the rotor 14 when current is continuously supplied to the stator windings of the individual phases.It can be seen that in this variant the stator poles 16 con one side of the stator pole carrier 16 dhave the same pole pitch as the rotor poles 14 cfacing them. The number of stator poles 16 cis smaller by one than the number of rotor poles 14 cfacing them.In this variant, too, the stator 16 can be equipped with stator poles 16 con its two end sides 16 a, 16 b. In this case, the stator poles 16 con one side of the stator pole support 16 ddo not have any circumferential offset relative to the stator poles 16 con the other side of the stator pole support 16 d; i.e., they are aligned with each other in the axial direction of the stator.In the case of the rotor 14, which is equipped with rotor poles 14 con its two end sides 14 a, 14 b, the rotor poles 14 con one of the end sides 14 a, 14 bare arranged offset by 1 / m*B in the circumferential direction relative to the rotor poles 14 con the other side of the rotor pole carrier 14 d. In this case, m is the number of phases of the electric machine and B is the width of the rotor pole 14 cin the circumferential direction U of the rotor.Even if this is not held in this way throughout the figures for reasons of better clarity, there are variants of the machine presented here in which rotor poles 14 cor stator poles 16 c, respectively, located radially further inward on the rotor 14 and the stator 16 have at least approximately the same surface area oriented toward the respective common air gap 18.Each air gap 18 between the rotor 14 and the stator 16 has a transverse dimension of approximately 200 μm on average in operation in the variants shown. For this purpose, each rotor 14 and stator 16 has a face running tolerance of approximately 20 μm.In order to further reduce the transverse dimension of the air gap, in a further variant of the electric machine, not illustrated in detail, a ferrous disc is accommodated in each air gap 18 between the rotor and the stator, which disc can also have a friction-reducing coating (polytetrafluoroethylene, silicon carbide or the like).The stator windings for each phase on both sides of the respective stator pole carrier 16 dmay be configured, for example in the variant of FIG. 3, between the two mutually concentric rings 16 e', 16 e" of stator poles 16 cin the form of a respective circular-ring-cylindrical stator coil 20.Moreover, for example, in the variants of FIGS. 1, 2 and 4, at least a part of at least one of the stator coils can be accommodated on each side of the respective stator pole carrier 16 dbetween in each case two adjacent rings 16 e', 16 e" of one side of the stator pole carrier 16 d.For better utilization / concentration of the magnetic flux, in a further variant the cross sections of the stator poles 16 cand / or of the rotor poles 14 care reduced toward the air gap 18. This can be done by reducing the cross section of the stator poles 16 cand / or of the rotor poles 14 cin a continuous or stepped manner towards the air gap 18. In the stepped variant shown in FIG. 5, each individual rotor pole 14 cis reduced on its radially oriented sides on one or both sides in the circumferential direction U of the rotor 14 by approximately 2% to approximately 8% of its width. This step has a height of about 2 to 20 times the transverse dimension of the air gap 18.The variants of electric machines described above and their functional and operating aspects serve merely for better understanding of their structure, mode of operation and properties; they do not restrict the disclosure, for example, to the exemplary embodiments. The figures are partially schematic, wherein essential properties and effects are in part shown in a clearly enlarged manner in order to clarify the functions, principles of action, technical configurations and features. In this case, each mode of operation, each principle, each technical configuration and each feature which is / are disclosed in the figures or in the text can be freely and arbitrarily combined with all claims, each feature in the text and in the other figures, other modes of operation, principles, technical configurations and features which are contained in this disclosure or result therefrom, with the result that all conceivable combinations are to be assigned to the described apparatuses. Combinations between all individual embodiments in the text, i.e. in each section of the description, in the claims and also combinations between different variants in the text, in the claims and in the figures, are also included here. The claims also do not limit the disclosure and thus the possible combinations of all features shown with one another. All disclosed features are explicitly also disclosed individually and in combination with all other features here.

Claims

Electric machine (12), characterized by • a ferromagnetic or ferromagnetic at least approximately circular-cylindrical rotor (14) and an at least approximately circular-cylindrical iron-containing stator (16), wherein the rotor (14) and the stator (16) each have two end faces (14a, 14b; 16a, 16b) spaced apart from one another, wherein • the stator (16) has, on at least one of its end faces (16a, 16b), a multiplicity of stator poles (16c) which are arranged at least in sections regularly in the circumferential direction and face an air gap (18), and, on one or both sides of a stator pole carrier (16d), a ring comprising the stator poles (16c) and an annular return path which is not structured with individual poles and has a radial air gap are arranged, • the rotor (14) is arranged on its two end faces (14a, 14b) has a plurality of rotor poles (14c) which are arranged regularly in the circumferential direction and which on the one hand face the air gap (18) and on the other hand are coupled to a ferrous rotor return (14d), wherein the rotor poles (14c) are arranged on one of the end sides (14a, 14b) offset by 1 / m*B in the circumferential direction relative to the rotor poles (14c) on the other side of the rotor pole carrier (14d), wherein m is the number of phases of the electric machine and B is the width of the rotor pole (14c) in the circumferential direction, • the stator (16) has at least one stator coil (20, U, U*, V, V*, W, W*) which is configured to induce a magnetic field in at least one part of the stator poles (16c)Electric machine (12) according to Claim 1, characterized in that • the stator coils (20, U, U*, V, V*, W, W*) do not project or project beyond the stator poles (16c) in the direction of the air gap (18).Electric machine (12) according to one of the preceding claims, characterized in that • the stator coils of the same phase (20, U, U*, V, V*, W, W*) are assigned to the respective stator poles (16c) as pitch-circle coils or as ring coils on one or both sides of the stator pole carrier (16d).The electric machine (12) according to any one of the preceding claims, having as the phase number 2, 3, 4, 5, 6 or more.Electric machine (12) according to one of the preceding claims, characterized in that • the stator poles (16c) on one side of the stator pole carrier (16d) have an identical, dissimilar or greater pole pitch than the rotor poles (14c) facing them, and, with the same pole pitch, the number of stator poles (16c) is less than the number of rotor poles (14c) facing them.Electric machine (12) according to one of the preceding claims, characterized in that • in the case of the stator (16) in the embodiment with stator poles (16c) on its two end faces (16a, 16b), the stator poles (16c) on one side of the stator pole carrier (16d) have no offset in the circumferential direction relative to the stator poles (16c) on the other side of the stator pole carrier (16d).Electric machine (12) according to any one of the preceding claims, characterized in that • each air gap (18) between the rotor (14) and the stator (16) has, on average, a transverse dimension of approximately 400 - 100 μm, preferably approximately 200 μm, during operation, and • each rotor (14) and stator (16) has a run-flat tolerance of approximately 40 - 10 μm, preferably approximately 20 μm.Electric machine (12) according to one of the preceding claims, characterized in that • a thin disc (22) containing iron or non-magnetic material is accommodated in each air gap (18), said thin disc preferably having a friction-reducing coating.Electric machine (12) according to one of the preceding claims, characterized in that • the cross sections of the stator poles (16c) and / or of the rotor poles (14c) are reduced continuously or in a stepped manner towards the air gap.

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