Electric axial flux machine with rotor filter

Abstract

An electric axial flux machine comprises a stator (10), a rotor (20) rotatably arranged in an axial direction (A) of the electric axial flux machine with an air gap (30) between them about an axis of rotation (40) of the electric axial flux machine extending in the axial direction (A), an air gap (30) located between the stator (10) and the rotor (20) in the axial direction (A), by means of which the stator (10) and the rotor (20) are spaced apart from each other in the axial direction (A); and a capacitive element (C5) arranged between the rotor (20) and a reference potential of the electric axial flux machine.

Description

Field of TechnologyThe present invention relates to an electric axial flow machine having a rotor filter.Prior ArtFIG. 10 shows a schematic sectional view of an electric axial flow machine in the prior art.In FIG. 10, reference symbol A denotes an axial direction, reference symbol R denotes a radial direction, reference symbol U denotes a circumferential direction, reference symbol 1 denotes a first bearing, reference symbol 2 denotes a second bearing, reference symbol 3 denotes a first region fixed to the housing, reference symbol 4 denotes a second region fixed to the housing, reference symbol 5 denotes a connecting element, reference symbol 10 denotes a stator, reference symbol 20 denotes rotors, reference symbol 30 denotes air gaps, and reference symbol 40 denotes a rotational axis.The axial-flow electric machine shown in FIG. 10 is an axial-flow electric machine in an H-arrangement including the rotors 20 between which the stator 10 is located in the axial direction A. Between the stator 10 and each of the rotors 20, an air gap 30 is formed in the axial direction A, respectively.The rotors 20 are mounted on the second housing-fixed region 4 via the first bearing 1 and the second bearing 2 in such a way that the rotors 20 are rotatable relative to the stator 10 about the axis of rotation 40 during operation of the electric axial flux machine in which a magnetic field having a magnetic flux direction along the axial direction A is formed. The rotors 20 are connected to one another in a rotationally fixed manner by means of the connecting element 5. The stator 10 is connected to the first housing-fixed region 3.By means of the first region 3 fixed to the housing and the second region 4 fixed to the housing, which are each fixedly connected to a housing of the electric axial flow machine, the components respectively connected to the region 3 fixed to the housing and to the region 4 fixed to the housing are fixed to a potential of the housing of the electric axial flow machine as a reference potential. This reference potential can be a ground potential.It is known that in such an electric axial flow machine, very high interference currents frequently occur at a rotor shaft of the electric axial flow machine. These can cause potentially high damage to the rotating machine elements connected to a rotor shaft or arranged in a return flow path, such as the bearings 1, 2, the regions 3, 4 fixed to the housing or even gearwheels.In order to be able to permit electrical devices or vehicles, legal regulations with regard to electromagnetic compatibility (EMC) must be complied with. In the range of E mobility, corresponding legal limit values also apply, which must be complied with. An electric axial-flow machine is often insulated from the housing in the region of the rotor 20 to the extent that electromagnetic emissions are emitted solely via the rotor 20 into an overall system containing the electric axial-flow machine, such as an E-axis or electric axis for a vehicle. This has the result that a rotor shaft functions similar to a rod antenna and the resulting antenna-bound emissions are so high that subsequent vehicle admission is endangered.A wear-free shaft grounding is known from DE19808847C2.A solution is proposed by means of which interference currents (common-mode currents) in the rotor shaft can be derived by means of a grounding element. In this case, the grounding element is designed in such a way that no wear phenomena occur, as in the case of directly contacted shaft grounding rings.SUMMARY OF THE INVENTIONTechnical TaskIt is accordingly the object of the present invention to reduce interference currents at a rotor shaft of an electric axial flow machine and preferably likewise line-bound and antenna-bound emissions of the electric axial flow machine.Technical SolutionThe object is achieved by means of the measures specified in the independent claim.Further advantageous embodiments of the present invention are the subject matter of the dependent claims.According to one aspect, an electric axial flux machine has a stator, a rotor which is arranged in an axial direction of the electric axial flux machine with an air gap located therebetween so as to be rotatable with respect to the stator about a rotation axis of the electric axial flux machine running in the axial direction, an air gap located between the stator and the rotor in the axial direction, by means of which air gap the stator and the rotor are arranged spaced apart from one another in the axial direction; and a capacitive element which is arranged between the rotor and a reference potential of the electric axial flux machine.According to one configuration, the reference potential is a potential of a housing of the electric axial flow machine or a ground potential.According to a further configuration, the capacitive element has a part rotating with the rotor, which forms a first electrode, and a fixed part, which forms a second electrode, and a dielectric is arranged between the part rotating with the rotor and the fixed part.According to a further embodiment, an inductive element is electrically connected in parallel with the capacitive element.According to a further embodiment, the inductive element is a ferrite ring.According to a further embodiment, the capacitive element and the inductive element together form an electrical filter.According to a further embodiment, a plurality of capacitive elements and a plurality of inductive elements are provided, which together form a multistage electrical filter.According to a further embodiment, the rotor is rotatably mounted by means of a bearing on a region fixed to the housing, which is fixedly connected to a housing of the electric axial flux machine, and the capacitive element is arranged between the rotor and the region fixed to the housing.According to a further embodiment, the electric axial flux machine has two stators and the rotor is arranged between the two stators in the axial direction.According to a further embodiment, the electric axial flux machine has two rotors, the stator is arranged between the two rotors in the axial direction and each of the two rotors has the capacitive element in each case.Advantageous Effects of the InventionAccording to the preceding aspect or embodiments thereof, a capacitance between the rotor and the housing is increased by means of the capacitive element, which leads to a reduction of interference currents or common-mode currents.Furthermore, an inductive element, such as a ferrite ring, can be integrated, which converts interference currents or common-mode currents into heat. The physical principle works differently from the contactless wave grounding ring in the prior art. On the one hand, the capacitance of the capacitive element is increased by means of a preferably meandering structure of the capacitive element via an increase in the surface area, and on the other hand, the inductance is preferably increased by means of a highly integrated ferrite ring. The common-mode currents are thus largely directly converted into heat in the ferrite ring and are not discharged to a vehicle body via the housing. Therefore, a current return path to the ground of the drive is not of elemental importance. This further leads to an HV-DC filter in an inverter driving the electric axial flow machine being subject to less stress and thus being able to be dimensioned smaller.Brief Description of the DrawingsThe present invention will be described in more detail below by describing embodiments with reference to the accompanying drawings.The drawing shows: FIG. 1 is a schematic sectional view showing a basic structure of an axial flow electric machine; FIG. 2 is a schematic sectional view showing a basic structure of an axial flow electric machine in a so-called I-configuration; FIG. 3 is a schematic sectional view showing a basic structure of an axial flow electric machine in a so-called H-configuration; FIG. 4 is a schematic sectional view of an axial flow electric machine according to an embodiment of the present invention; FIG. 5 is a schematic circuit diagram of the axial flow electric machine according to the embodiment of the present invention; FIG. 6 is a schematic sectional view of an axial flow electric machine according to a first embodiment of the embodiment of the present invention; FIG. 7 is a schematic circuit diagram of the axial flow electric machine according to the first embodiment of the present invention; FIG. 8 is a schematic circuit diagram of an axial flow electric machine according to a second embodiment of the present invention; FIG. 9 is a schematic view of a capacitive element used in the embodiment and its configurations; and FIG. 10 shows a schematic sectional view of an electric axial flow machine in the prior art.DESCRIPTION OF THE EMBODIMENTBefore an embodiment and its configurations are described below in detail with reference to FIGS. 4 to 9, aspects that are equally applicable to the following embodiment and its configurations will be explained with reference to FIGS. 1 to 3.FIG. 1 is a schematic sectional view showing a basic structure of an axial flow electric machine.In FIG. 1, reference numeral 10 denotes a stator, reference numeral 20 denotes a rotor, reference numeral 30 denotes an air gap, reference numeral 40 denotes a rotational axis, reference numeral 50 denotes a magnetic flux direction, reference numeral A denotes an axial direction, and reference numeral R denotes a radial direction.The axial direction is defined as a direction along the direction of the rotation axis 40. The radial direction R is defined as a direction which extends from a center point of the preferably disk-shaped stator 10 or rotor 20, through which the axis of rotation 40 extends, from radially inward to radially outward or vice versa. A circumferential direction, not shown in FIG. 1, is defined as a direction which runs along a circumference of the preferably disk-shaped stator 10 or rotor 20.FIG. 1 is a sectional view taken along a plane in which the rotation axis of the axial flow machine extends.As shown in FIG. 1, in the axial-flow electric machine, the magnetic flux direction 50 between the stator 10 and the rotor 20 is parallel to the rotation axis 40 of the rotor 20 of the axial-flow electric machine, that is, in the axial direction A of the axial-flow electric machine. Frequently, both the stator 10 and the rotor 20 are largely disk-shaped. Electric axial-flow machines are advantageous in particular when the axially available installation space is limited in a given application. In addition to the shortened axial structural length, a further advantage of the electric axial flow machine is its comparatively high torque density.An electric axial flow machine can be formed in an I-arrangement or an H-arrangement.FIG. 2 is a schematic view showing a basic configuration of an axial flow electric machine in a so-called I-configuration.In FIG. 2, the same or corresponding parts as in FIG. 1 are denoted by the same or corresponding reference numerals as in FIG. 1, so that reference is made to FIG. 1 and the description thereof with respect to these same or corresponding parts and a description thereof is omitted here.In the I-arrangement, the rotor 20 is arranged axially adjacent to the stator 10 or, as shown in FIG. 2, between two stators 10.FIG. 3 is a schematic view showing a basic structure of an axial flow electric machine in a so-called H-configuration.In FIG. 3, the same or corresponding parts as in FIGS. 1 and 2 are denoted by the same or corresponding reference numerals, so that reference is made to FIGS. 1 and 2 and the description thereof with respect to these same or corresponding parts, and description thereof is omitted here.In the H-arrangement, two rotors 20 are arranged on opposite axial sides of a stator 10.The following embodiment and its configurations can be applied to all of the aforementioned arrangements, but are particularly advantageously applicable to an H-arrangement in particular.The description will be made of an embodiment below.FIG. 4 is a schematic sectional view of an axial flow electric machine according to the embodiment of the present invention.In FIG. 4, reference symbol A denotes an axial direction, reference symbol R denotes a radial direction, reference symbol U denotes a circumferential direction, reference symbol 1 denotes a first bearing, reference symbol 2 denotes a second bearing, reference symbol 3 denotes a first region fixed to the housing, reference symbol 4 denotes a second region fixed to the housing, reference symbol 5 denotes a connecting element, reference symbol 10 denotes a stator, reference symbol 20 denotes rotors, reference symbol 30 denotes air gaps, reference symbol 40 denotes a rotational axis, reference symbol C 5 denotes a capacitive element, and reference symbol GND denotes a reference potential.The axial-flow electric machine shown in FIG. 4 is an axial-flow electric machine in an H-arrangement including the rotors 20 between which the stator 10 is located in the axial direction A. Between the stator 10 and each of the rotors 20, an air gap 30 is formed in the axial direction A, respectively.The rotors 20 are mounted on the second housing-fixed region 4 via the first bearing 1 and the second bearing 2 in such a way that the rotors 20 are rotatable relative to the stator 10 about the axis of rotation 40 during operation of the electric axial flux machine in which a magnetic field having a magnetic flux direction along the axial direction A is formed. The rotors 20 are connected to one another in a rotationally fixed manner by means of the connecting element 5. The stator 10 is connected to the first housing-fixed region 3.By means of the first region 3 fixed to the housing and the second region 4 fixed to the housing, which are each fixedly connected to a housing of the electric axial flow machine, the components respectively connected to the region 3 fixed to the housing and to the region 4 fixed to the housing are fixed to a potential of the housing of the electric axial flow machine as the reference potential GND. This reference potential GND may be a ground potential.FIG. 4 shows in simplified form where the capacitor C 5 is arranged in the electric axial flow machine. The diagram refers to a schematic representation simplified in mechanical engineering and in electrical engineering. It is important here that the capacitor C 5 is placed between a housing or the second region 4 fixed to the housing and the rotor 20 before the actual rotor mounting via the bearings 1, 2, in order to protect the bearings 1, 2 from current breakdowns.FIG. 5 is a schematic circuit diagram of the axial flow electric machine according to the embodiment of the present invention.In FIG. 5, reference numeral GND denotes a reference potential, reference numeral C 1 denotes a capacitance between a phase U and the reference potential, reference numeral C 2 denotes a capacitance between a phase V and the reference potential, reference numeral C 3 denotes a capacitance between a phase W and the reference potential, reference numeral C 4 denotes a capacitance between the rotor 20 and the stator 10, reference numeral C 5 denotes a capacitance between the rotor 20 and the housing, reference numeral L 1 denotes an inductance of a phase U stator winding, reference numeral L 2 denotes an inductance of a phase V stator winding, reference numeral L 3 denotes an inductance of a phase W stator winding, and reference numeral R 1 denotes a resistance between the rotor and the housing.FIG. 5 shows an electrotechnical schematic of the electric axial flux machine with characteristic U, V, W phases L 1, L 2, L 3 in a stator winding. Ideally, a sum of the capacitances C 1, C 2, C 3 between the stator winding and a surrounding housing should be very large, in order that common-mode currents or interference currents are derived via these capacitances C 1, C 2, C 3. If the capacitance C4 between the 20 rotor and the stator 10 is greater than the sum of the capacitances of C1, C2, C3, the common-mode currents are substantially derived via a rotor shaft. This may be problematic due to the resulting electromagnetic radiation of the rotor shaft. To reduce this, the capacitance C5 between the rotor 20 and the casing helps to reduce the common-mode currents in the rotor shaft.It is important to derive as much common-mode currents as possible from the overall system in a targeted manner, since excessively high common-mode currents in the rotor shaft may possibly lead to current breakdowns at the bearings 1, 2, a toothing system and also other mechanical elements and may lead to corresponding mechanical failures. Furthermore, very high common-mode currents and also the underlying voltage in the rotor shaft are highly likely to lead to high electromagnetic radiation and thus to poor electromagnetic compatibility (EMC) of the overall system. The rotor shaft is comparable in terms of its properties to a rod antenna which can interfere via its emission with other electrical devices, such as cell phones, radios or even control devices. By means of the capacitance C5, this radiation is eliminated or reduced.The description will be made of a first embodiment of the embodiment.FIG. 6 is a schematic sectional view of an axial flow electric machine according to the first embodiment of the embodiment of the present invention.In FIG. 6, the same reference numerals as in FIG. 4 denote the same or corresponding elements as in FIG. 4, so that with regard to these same or corresponding elements, a new description of these same or corresponding elements is referred to the explanations relating to FIG. 4 and a new description of these same or corresponding elements is omitted at this point. In addition, in FIG. 6, reference numeral L 4 denotes an inductive element between the rotor 20 and the housing. The explanations previously made with respect to FIG. 5 likewise apply analogously likewise to the configuration of FIG. 6.It is important to suppress the rotor shaft in a frequency band as wide as possible, and therefore the inductive element L 4 is provided in addition to the capacitive element C 5.FIG. 6 shows what is known as wear-free wave filtering or wave grounding for the electric axial flow machine, which combines the capacitance C 5 and the inductance L 4 in one element. The integration of the inductance L 4 as a ferrite ring between the rotor shaft and the housing is therefore regarded as particularly advantageous for the function, since interference currents are additionally converted into heat.The capacitor C 5 has mutually engaging meandering lamellae which are led out of the housing and the rotor shaft in a circular manner. The blades are made of a conductive metal. A distance between the plates is selected such that a voltage difference between plate packets rotating relative to one another does not lead to a current breakdown. A dielectric, such as an oil or an additional plastic coating, can be introduced between the plate packs in order to isolate the plate packs from one another.FIG. 7 is a schematic circuit diagram of the axial flow electric machine according to the first embodiment of the present invention.In FIG. 7, the same reference numerals as in FIG. 5 denote the same or corresponding elements as in FIG. 5, so that with regard to these same or corresponding elements, a new description of these same or corresponding elements is referred to the explanations relating to FIG. 5 and a new description of these same or corresponding elements is omitted at this point. In addition, in FIG. 7, reference symbol L 4 denotes the inductive element between the rotor 20 and the housing.FIG. 7 shows the structure of FIG. 5 supplemented by a single-stage filter with the capacitance or the capacitive element C 5 and the inductance or the inductive element L 4 for deriving the interference currents or common-mode currents.The formula applies here: where f is the frequency, π is the number of circles, sqrt is the root function, L is an inductance per phase U, V, W of the element 6 made of the ferrite material, and C is a capacitance between the phase U, V, W and the reference potential GND.The larger the product of L*C, the lower the frequency f of possible return currents that are converted into heat. If the frequency f is very low, then almost the entire bandwidth of the return currents is converted into thermal energy. If the value for the frequency f is very high, only the high-frequency currents are removed, i.e. the filter is not quite as effective.Next, description will be made of a second embodiment of the embodiment.FIG. 8 is a schematic circuit diagram of an axial flow electric machine according to the second embodiment of the present invention.In FIG. 8, the same reference numerals as in FIG. 7 denote the same or corresponding elements as in FIG. 7, so that with regard to these same or corresponding elements, a new description of these same or corresponding elements is referred to the explanations relating to FIG. 7 and a new description of these same or corresponding elements is omitted at this point. In addition, in FIG. 8, reference numeral L 5 denotes another inductive element between the rotor 20 and the housing, and reference numeral C 6 denotes another capacitive element between the rotor and the housing.FIG. 8 shows the structure of FIG. 7 supplemented by a two-stage filter with the capacitances or the capacitive elements C 5, C 6 and the inductances or the inductive elements L 4, L 5 for deriving the interference currents or common-mode currents. However, the filter can also be extended in "multistage", i.e. an n-stage filter is likewise possible.The following describes a capacitive element used in the embodiment and the configurations thereof.FIG. 9 is a schematic view of a capacitive element used in the embodiment and its configurations.In FIG. 9, reference numeral 101 denotes a case of the capacitive element, reference numeral 102 denotes a protection layer, reference numeral 103 denotes electrodes, reference numeral 104 denotes a dielectric, reference numeral 105 denotes contact layers, and reference numeral 106 denotes terminals.FIG. 9 shows that a structure of the capacitive element C 5 is modeled on a so-called layered capacitor, wherein the electrodes 102 rotate with respect to one another. In addition to the axial arrangement shown here, a radial arrangement of the electrodes 102 with respect to one another can also be implemented, wherein the electrodes 102 arranged on the housing side and on the rotor side are then not pushed into one another, but rather are mounted into one another.Although the present invention has been described above by way of embodiments, it is to be understood that various configurations and changes may be made without departing from the scope of the present invention as defined in the appended claims.With regard to further features and advantages of the present invention, express reference is made to the disclosure of the drawing.List of Reference NumeralsA axial direction R radial direction U circumferential direction GND reference potential C 1, C 2, C 3 capacitance between phase and reference potential C 4 capacitance between rotor and stator C 5, C 6 capacitive element between rotor and housing L 1, L 2, L 3 inductance of stator winding L 4, L 5 inductive element between rotor and housing R 1 resistance between rotor and housing 1 first bearing 2 second bearing 3 first housing-fixed region 4 second housing-fixed region 5 connecting element 10 stator 20 rotor 30 air gap 40 rotational axis 50 magnetic flux direction 101 housing of capacitive element 102 protective layer 103 electrode 104 dielectric 105 contact layer 106 terminalReferences included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedDE 19808847C2

[0009]

Claims

An axial-flux electric machine, comprising: a stator (10); a rotor (20) arranged rotatably with respect to the stator (10) in an axial direction (A) of the axial-flux electric machine with an air gap (30) located therebetween about a rotation axis (40) of the axial-flux electric machine running in the axial direction (A); an air gap (30) located between the stator (10) and the rotor (20) in the axial direction (A), by means of which the stator (10) and the rotor (20) are arranged spaced apart from each other in the axial direction (A); and a capacitive element (C5) arranged between the rotor (20) and a reference potential of the axial-flux electric machine.The axial flow electric machine according to claim 1, wherein the reference potential is a potential of a housing of the axial flow electric machine or a ground potential.The axial flow electric machine according to claim 1 or 2, wherein the capacitive element (C5) includes a part rotating with the rotor (20) forming a first electrode and a fixed part forming a second electrode, and a dielectric is disposed between the part rotating with the rotor (20) and the fixed part.The axial flow electric machine according to any one of claims 1 to 3, wherein an inductive element (L4) is electrically connected in parallel with the capacitive element (C5).The axial flow electric machine according to claim 4, wherein the inductive element (L4) is a ferrite ring.Axial flow electric machine according to claim 4 or 5, wherein the capacitive element (C5) and the inductive element (L4) in cooperation form an electric filter.The axial flow electric machine according to any one of claims 4 to 6, wherein a plurality of capacitive elements (C5, C6) and a plurality of inductive elements (L4, L5) are provided, which together form a multistage electric filter.The electric axial flow machine according to any one of claims 1 to 7, wherein the rotor (20) is rotatably mounted by means of a bearing (1, 2) on a housing-fixed region (4) which is fixedly connected to a housing of the electric axial flow machine, and the capacitive element (C5) is arranged between the rotor (20) and the housing-fixed region (4).The axial-flux electric machine according to any one of claims 1 to 8, wherein the axial-flux electric machine includes two stators (10), and the rotor (20) is disposed between the two stators (10) in the axial direction (A).The axial-flow electric machine according to any one of claims 1 to 8, wherein the axial-flow electric machine includes two rotors (20), the stator (10) is disposed between the two rotors (20) in the axial direction (A), and each of the two rotors (10) includes the capacitive element (C5), respectively.

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