Electric axial flux machine comprising a stator filter

Abstract

The invention relates to an electric axial flux machine comprising: a stator (10); a rotor (20) which is arranged, in an axial direction (A) of the electric axial flux machine, so as to be rotatable relative to the stator (10) about a rotational axis (40) of the electric axial flux machine extending in the axial direction (A), with an air gap (30) located between the rotor and the stator; an air gap (30) which is located between the stator (10) and the rotor (20) in the axial direction (A) and by means of which the stator (10) and the rotor (20) are spaced apart from one another in the axial direction (A); and an element (6) made of a ferrite material which is arranged at a radially outer periphery of the stator (10).

Description

[0001] Title of the invention

[0002] Electric axial flux machine with stator filter

[0003] field of technology

[0004] The present invention relates to an electric axial flux machine with a stator filter.

[0005] State of the art

[0006] Fig. 8 shows a schematic sectional view of an electric axial flux machine in the prior art.

[0007] In Fig. 8, 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 housing-fixed region, reference symbol 4 denotes a second housing-fixed region, 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 an axis of rotation.

[0008] The electric axial flux machine shown in Fig. 8 is an electric axial flux machine in an H-arrangement, which has the rotors 20, between which the stator 10 is located in the axial direction A. An air gap 30 is formed between the stator 10 and each of the rotors 20 in the axial direction A.

[0009] The rotors 20 are mounted on the second housing-fixed region 4 via the first bearing 1 and the second bearing 2 such that, during operation of the electric axial flux machine, in which a magnetic field with a magnetic flux direction along the axial direction A is formed, the rotors 20 are rotatable relative to the stator 10 about the rotation axis 40. 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.

[0010] By means of the first housing-fixed region 3 and the second housing-fixed region 4, which are each fixedly connected to a housing of the electric axial flux machine, the components connected to the housing-fixed region 3 and the housing-fixed region 4 are fixed to a potential of the housing of the electric axial flux machine as a reference potential. This reference potential can be a ground potential.

[0011] It is known that very high interference currents often occur on the rotor shaft of such an axial-flux electric machine. These can potentially cause significant damage to the rotating machine elements connected to the rotor shaft or arranged in a return current path, such as the bearings 1, 2, the housing-fixed areas 3, 4, or even gears.

[0012] Summary of the invention

[0013] Technical task

[0014] It is therefore the object of the present invention to reduce interference currents on a rotor shaft of an electric axial flux machine and preferably also conducted and antenna-bound emissions of the electric axial flux machine.

[0015] Technical solution

[0016] This object is achieved by the measures specified in the independent claim. Further advantageous embodiments of the present invention are the subject of the dependent claims.

[0017] According to one aspect, an axial flux electric machine comprises a stator, a rotor arranged in an axial direction of the axial flux electric machine with an air gap therebetween so as to be rotatable relative to the stator about an axis of rotation of the axial flux electric machine extending in the axial direction, an air gap arranged between the stator and the rotor in the axial direction, by means of which the stator and the rotor are arranged at a distance from one another in the axial direction, and an element made of a ferrite material arranged on a radial outer circumference of the stator.

[0018] According to one embodiment, the element is formed as a nanocrystalline ring ferrite around the radial outer circumference of the stator.

[0019] According to a further embodiment, the element is formed from individual ferrites distributed around the radial outer circumference of the stator and made of a ferritic solid material.

[0020] According to a further embodiment, the element is formed as a ferritic powder coating applied to the stator around the radial outer circumference of the stator.

[0021] According to a further embodiment, the element is arranged overlapping the rotor in the axial direction.

[0022] According to a further embodiment, the element has an inductance which, in conjunction with a capacitance formed between a phase of the stator and a reference potential, forms a stator filter. According to a further embodiment, each phase of the electric axial flux machine contains an inductance and a capacitance, each forming a stator filter for each phase.

[0023] According to a further embodiment, the reference potential is a potential of a housing of the electrical machine or a ground potential.

[0024] According to a further embodiment, the electric axial flux machine has two stators, the rotor is arranged in the axial direction between the two stators, and each of the two stators has the element.

[0025] According to a further embodiment, the electric axial flux machine has two rotors and the stator is arranged in the axial direction between the two rotors.

[0026] Advantageous effects of the invention

[0027] According to the preceding aspect or its embodiments, the element arranged on the radial outer circumference ensures, among other things, that at least a portion of interference currents or common-mode currents in the ferrite material itself is directly converted into heat, thereby relieving the load on an inverter for operating the electric axial flux machine, especially Y-capacitors therein, by reducing reverse currents in the inverter.

[0028] The formula is: f = 1 / [2TT*sqrt(L*C)] where f is the frequency, TT is the angular frequency, sqrt is the square root function, L is the inductance per phase of the ferrite element, and C is the capacitance between the phase and the reference potential. 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, almost the entire bandwidth of the return currents is converted into heat energy. This creates a so-called "inductive stator filter," which filters out potential interference currents directly at their source.

[0029] By appropriately arranging the element from a ferrite material and designing the capacitance C, eddy current losses in the stator itself can be reduced, thereby increasing the efficiency of the axial flux machine. A further advantage of this arrangement is that the interference currents, which are extracted from the system by the inductive stator filter and converted into heat, are not transmitted as interference currents to a rotor shaft of the axial flux machine, where they can cause damage to rotating machine elements such as bearings, gears, or grounding elements.

[0030] Short description of the drawings

[0031] The present invention will be explained in more detail below by describing embodiments with reference to the accompanying drawings.

[0032] The drawing shows:

[0033] Fig. 1 is a schematic sectional view of a basic structure of an electric axial flux machine;

[0034] Fig. 2 is a schematic sectional view of a basic structure of an electric axial flux machine in a so-called I-arrangement;

[0035] Fig. 3 is a schematic sectional view of a basic structure of an electric axial flux machine in a so-called H-arrangement; Fig. 4 is a schematic sectional view of an electric axial flux machine according to an embodiment of the present invention:

[0036] Fig. 5 is a schematic circuit diagram of the axial flux electric machine according to the embodiment of the present invention;

[0037] Fig. 6 is a schematic view of an axial flux electric machine according to a first embodiment of the present invention;

[0038] Fig. 7 is a schematic view of an axial flux electric machine according to a second embodiment of the present invention; and

[0039] Fig. 8 is a schematic sectional view of an electric axial flux machine in the prior art.

[0040] Description of the embodiment

[0041] Before an embodiment and its configurations are described in detail below with reference to Fig. 4 to Fig. 7, aspects that are equally applicable to the following embodiment and its configurations are explained with reference to Fig. 1 to Fig. 3.

[0042] Fig. 1 shows a schematic sectional view of a basic structure of an electric axial flux machine.

[0043] 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 an axis of rotation, 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 axis of rotation 40. The radial direction R is defined as a direction that runs from a center point of the preferably disc-shaped stator 10 or rotor 20, through which the axis of rotation 40 runs, from radially inside to radially outside, or vice versa. A circumferential direction not shown in Fig. 1 is defined as a direction that runs along a circumference of the preferably disc-shaped stator 10 or rotor 20.

[0044] Fig. 1 shows a sectional view cut along a plane in which the axis of rotation of the axial flux machine runs.

[0045] As shown in Fig. 1, in the electric axial flux machine, the magnetic flux direction 50 between the stator 10 and the rotor 20 runs parallel to the rotational axis 40 of the rotor 20 of the electric axial flux machine, i.e., in the axial direction A of the electric axial flux machine. Often, both the stator 10 and the rotor 20 are largely disk-shaped. Electric axial flux machines are particularly advantageous when the axially available installation space is limited in a given application. In addition to the shortened axial length, another advantage of the electric axial flux machine is its comparatively high torque density.

[0046] An electric axial flux machine can be designed in an I-arrangement or an H-arrangement.

[0047] Fig. 2 shows a schematic view of a basic structure of an electric axial flux machine in a so-called I-arrangement.

[0048] In Fig. 2, the same or corresponding parts as in Fig. 1 are designated by the same or corresponding reference numerals as in Fig. 1, so that with regard to these same or corresponding parts, reference is made to Fig. 1 and its description, and a repeated description 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.

[0049] Fig. 3 shows a schematic view of a basic structure of an electric axial flux machine in a so-called H-arrangement.

[0050] In Fig. 3, the same or corresponding parts as in Fig. 1 and Fig. 2 are designated by the same or corresponding reference numerals, so that with regard to these same or corresponding parts, reference is made to Fig. 1 and Fig. 2 and their description and a repeated description is omitted at this point.

[0051] In the H-arrangement, two rotors 20 are arranged on opposite axial sides of a stator 10.

[0052] The following embodiment and its configurations can be applied to all of the aforementioned arrangements, but are particularly advantageously applicable to an H-arrangement.

[0053] The following is a description of an embodiment.

[0054] Fig. 4 shows a schematic sectional view of an axial flux electric machine according to the embodiment of the present invention.

[0055] 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 housing-fixed region, reference symbol 4 denotes a second housing-fixed region, 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 an axis of rotation. The electrical axial flux machine shown in Fig. 4 is an electrical axial flux machine in an H-arrangement having the rotors 20, between which the stator 10 is located in the axial direction A. An air gap 30 is formed between the stator 10 and each of the rotors 20 in the axial direction A.

[0056] The rotors 20 are mounted on the second housing-fixed region 4 via the first bearing 1 and the second bearing 2 such that, during operation of the electric axial flux machine, in which a magnetic field with a magnetic flux direction along the axial direction A is formed, the rotors 20 are rotatable relative to the stator 10 about the rotation axis 40. 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.

[0057] By means of the first housing-fixed region 3 and the second housing-fixed region 4, which are each fixedly connected to a housing of the electric axial flux machine, the components connected to the housing-fixed region 3 and the housing-fixed region 4 are fixed to a potential of the housing of the electric axial flux machine as a reference potential. This reference potential can be a ground potential.

[0058] To reduce high interference currents on a rotor shaft of the electric axial flux machine, element 6 is made of a ferrite material. Element 6 is arranged between the stator 10 and the first housing-fixed region 3.

[0059] Fig. 5 shows a schematic circuit diagram of the axial flux electric machine according to the embodiment of the present invention.

[0060] In Fig. 5, reference symbol GND denotes a reference potential, reference symbol C1 denotes a capacitance between a phase U and the reference potential, reference symbol C2 denotes a capacitance between a phase V and the reference potential, reference symbol C3 denotes a capacitance between a phase W and the reference potential, reference symbol C4 denotes a capacitance between the rotor 20 and the stator 10, reference symbol C5 denotes a capacitance between the rotor 20 and the housing, reference symbol L1 denotes an inductance of a stator winding of phase U, reference symbol L2 denotes an inductance of a stator winding of phase V, reference symbol L3 denotes an inductance of a stator winding of phase W, reference symbol L6 denotes an inductance of the element 6 for phase W,the reference symbol L7 denotes an inductance of the element 6 for the phase V and the reference symbol L8 denotes an inductance of the element 6 for the phase U.,

[0061] The inductances L6 to L8 are implemented by the element 6 made of a remote material on the radial outer circumference of the stator 10 in Fig. 4. The capacitances C1 to C3 are formed between the phases U, V, and W in the stator 10 and the housing, which is fixed to the reference potential GND, such as ground potential. For example, the stator 10 can be grounded via a ground strap.

[0062] According to the preceding embodiment, the element 6 arranged on the radial outer circumference ensures, among other things, that at least a portion of interference currents or common-mode currents in the ferrite material itself is converted directly into heat, thereby relieving the load on an inverter for operating the electric axial flux machine, especially Y-capacitors therein, by reducing reverse currents in the inverter.

[0063] The formula is: f = 1 / [2TT*sqrt(L*C)] where f is the frequency, TT is the angular number, sqrt is the root function, L is an inductance per phase U, V, W of element 6 made of the remote material and C is a capacitance between the phase U, V, W and the reference potential GND.

[0064] 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, almost the entire range of return currents is converted into heat energy. This creates a so-called "inductive stator filter," which filters out potential interference currents directly at their source.

[0065] By appropriately arranging element 6 from a ferrite material and designing the respective capacitance C, eddy current losses in the stator 10 itself can be reduced, thereby increasing the efficiency of the electric axial flux machine. A further advantage of this arrangement is that the interference currents, which are extracted from the system by the inductive stator filter and converted into heat, are not transmitted as interference currents to a rotor shaft of the electric axial flux machine, where they could cause damage to rotating machine elements such as bearings, gears, or grounding elements.

[0066] The following is a description of a first embodiment of the embodiment

[0067] Fig. 6 shows a schematic view of an axial flux electric machine according to the first aspect of the embodiment of the present invention.

[0068] In Fig. 6, the same reference numerals as in Fig. 4 designate identical or corresponding elements as in Fig. 4, so that with regard to these identical or corresponding elements, reference is made to the explanations for Fig. 4 for a repeated description of these identical or corresponding elements, and a repeated description of these identical or corresponding elements is omitted here. Likewise, the explanations previously made with regard to Fig. 5 apply analogously to the embodiment of Fig. 6.

[0069] In Fig. 6, on the right side of Fig. 6, a half-section is shown along a sectional plane S shown on the left side of Fig. 6. The sectional plane S is a plane extending in the radial direction R and perpendicular to the axial direction A. In Fig. 6, the element 6 is formed from a ferrite material as a preferably nanocrystalline ring ferrite, which is wound, for example, between the stator 10 and the housing.

[0070] A second embodiment of the present invention will be described below.

[0071] Fig. 7 shows a schematic view of an axial flux electric machine according to the second embodiment of the present invention; and

[0072] In Fig. 7, the same reference numerals as in Fig. 4 and Fig. 6 designate identical or corresponding elements as in Fig. 4 and Fig. 6, so that with regard to these identical or corresponding elements, reference is made to the explanations for Fig. 4 and Fig. 6 for a repeated description of these identical or corresponding elements, and a repeated description of these identical or corresponding elements is omitted here. Likewise, the explanations previously made with regard to Fig. 5 apply analogously to the embodiment of Fig. 7.

[0073] In Fig. 7, on the right side of Fig. 7, a half-section is shown along a section plane S shown on the left side of Fig. 7. The section plane S is a plane running in the radial direction R and perpendicular to the axial direction A.

[0074] In Fig. 7, element 6 is formed from a ferrite material consisting of individual ferrite segments arranged circumferentially between the stator 10 and the housing. The individual segments can be formed from a solid material or, alternatively, can be introduced in powder form into corresponding chambers in the stator or housing. The shape and composition of the ferrite material can be freely selected.

[0075] Likewise, the ferritic material can also be applied directly as a powder coating to the radial outer circumference of the stator 10. Finally, the previously described different variants of the element 6 made of a ferrite material can be combined with one another in any technically feasible manner. Although the present invention has been described above with reference to embodiments, it is understood that various configurations and modifications can be made without departing from the scope of the present invention as defined in the appended claims. For further features and advantages of the present invention, express reference is made to the disclosure of the drawings.

[0076] List of reference symbols

[0077] A axial direction

[0078] R Radial direction

[0079] S cutting plane

[0080] U circumferential direction

[0081] GND reference potential

[0082] C1, 02, 03 Capacitance between phase and reference potential

[0083] 04 Capacitance between rotor and stator

[0084] 05 Capacitance between rotor and housing

[0085] L1, L2, L3 inductance of the stator winding

[0086] L6, L7, L8 Inductance of the element made of ferrite material

[0087] 1 First camp

[0088] 2 Second camp

[0089] 3 First housing-fixed area

[0090] 4 Second housing-fixed area

[0091] 5 Connecting element

[0092] 6 Element made of ferrite material

[0093] 10 Stator

[0094] 20 rotors

[0095] 30 air gap

[0096] 40 axis of rotation

[0097] 50 Magnetic flux direction

Claims

Patent claims 1. An axial flux electric machine, comprising: a stator (10); a rotor (20) arranged in an axial direction (A) of the axial flux electric machine with an air gap (30) therebetween, rotatable relative to the stator (10) 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 at a distance from one another in the axial direction (A); and an element (6) made of a ferrite material, which is arranged on a radial outer circumference of the stator (10).

2. Electric axial flux machine according to claim 1, wherein the element (6) is formed as a nanocrystalline ring ferrite around the radial outer circumference of the stator (10).

3. Electric axial flux machine according to claim 1, wherein the element (6) is formed from individual ferrites made of a ferritic solid material and arranged distributed around the radial outer circumference of the stator (10).

4. Electric axial flux machine according to claim 1, wherein the element (6) is formed as a ferritic powder coating applied to the stator (10) around the radial outer circumference of the stator (10).

5. Electric axial flux machine according to one of claims 1 to 4, wherein the element (6) is arranged overlapping the rotor (20) in the axial direction (A).

6. Electrical axial flux machine according to one of claims 1 to 5, wherein the element (6) has an inductance (L6, L7, L8) which, in cooperation with an intermediate see a phase of the stator (10) and a reference potential (3) formed capacitance (C1, C2, C3) forms a stator filter.

7. Electric axial flux machine according to claim 6, wherein for each phase of the electric axial flux machine there is an inductance (L6, L7, L8) and a capacitor (C1, C2, C3), which form a stator filter for each phase.

8. Electric axial flux machine according to claim 6 or 7, wherein the reference potential is a potential of a housing of the electric machine or a ground potential.

9. An axial flux electric machine according to any one of claims 1 to 8, wherein the axial flux electric machine comprises two stators (10), the rotor (20) is arranged between the two stators (10) in the axial direction (A), and each of the two stators (10) comprises the element (6).

10. An axial flux electric machine according to any one of claims 1 to 8, wherein the axial flux electric machine comprises two rotors (20), and the stator (10) is arranged between the two rotors (20) in the axial direction (A).

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