Electric axial flux machine

Abstract

Electric axial flux machine (1), in particular for use within a powertrain of a hybrid or fully electric motor vehicle, wherein the electric axial flux machine (1) has a stator (2) and a rotor (4) separated from the stator (2) by an air gap (3), wherein the rotor (4) has at least a first rotor body (5) with a first group of permanent magnets (6) and a second rotor body (7) with a second group of permanent magnets (8), and the first rotor body (5) and the second rotor body (7) are rotatable relative to each other against the effect of a first torsional stiffness (9) about a common axis of rotation (10) by means of a mechanical field weakening mechanism (11), characterized by the fact that the field weakening mechanism (11) comprises a plurality of toothed planet gears (16) which are rotatably mounted on the first rotor body (5) and are engaged on one side with the rotor shaft (15) and on the other side with the second rotor body (7), so that for a desired adjustment of the mechanical field weakening mechanism (11) the first rotor body (5) and the second rotor body (7) can be rotated relative to each other via the gear coupling of the planet gears (16).

Description

[0001] The present invention relates to an electric axial flux machine, in particular for use within a drive train of a hybrid or fully electric motor vehicle, comprising a stator and a rotor separated from the stator by an air gap.

[0002] Electric motors are increasingly being used to power motor vehicles, creating alternatives to combustion engines that require fossil fuels. Considerable efforts have already been made to improve the everyday suitability of electric drives and also to provide users with the same level of driving comfort they are accustomed to.

[0003] A detailed description of an electric drive can be found in an article in the magazine ATZ, Volume 113, May 2011, pages 360-365, by Erik Schneider, Frank Fickl, Bernd Cebulski, and Jens Liebold, entitled "Highly Integrative and Flexible Electric Drive Unit for E-Vehicles," which arguably represents the closest state of the art. This article describes a drive unit for a vehicle axle that includes an electric motor arranged coaxially with a bevel gear differential. Such drive units are also referred to as e-axles or electrically driven drivetrains.

[0004] Axial flux machines are also increasingly being used in such electric axles. An axial flux machine is a dynamoelectric machine in which the magnetic flux between the rotor and stator runs parallel to the rotor's axis of rotation. Both the stator and rotor are often largely disc-shaped. Axial flux machines are particularly advantageous when the axial space available is limited in a given application. This is often the case, for example, with the electric drive systems for electric vehicles described above. In addition to the shortened axial length, another advantage of the axial flux machine is its comparatively high torque density. The reason for this is the larger air gap area available in a given installation space compared to radial flux machines.Furthermore, a smaller iron volume is required compared to conventional machines, which has a positive effect on the efficiency of the machine.

[0005] Due to its disc-shaped main components, an axial flux machine is particularly well-suited for applications where a very short electric motor length is essential and where a relatively large motor diameter is still acceptable. When developing such axial flux machines, it is therefore generally advisable to strive for the shortest possible design, while keeping the outer diameter of the axial flux machine no larger than absolutely necessary. Axial flux machines for automotive applications also always have to meet the requirements of low weight, high power density, and low cost.

[0006] Electrical machines—including the aforementioned axial flux machines—are subject to losses due to magnetization reversals during operation, which are collectively referred to as iron losses and reduce machine efficiency. In mobile applications, a low efficiency of the electric machine means a reduced vehicle range or increased battery capacity requirements. Therefore, minimizing these iron losses is a constant goal, especially in mobile applications with purely electric drive systems.

[0007] An example of such an electrical machine with iron losses, which can be used within the drivetrain of a hybrid or fully electric motor vehicle, is the so-called permanent-magnet synchronous machine. Due to its high power density compared to other machine types, it is particularly popular in the field of electromobility, where the available installation space is often a limiting factor. The machine's excitation field is usually generated by permanent magnets arranged in the machine's rotor. Slip ring contact, which is necessary in electrically excited synchronous machines to supply current to an excitation coil arranged on the rotor, can be dispensed with in the permanent-magnet synchronous machine.

[0008] A disadvantage of permanent magnet excitation, however, is that the excitation field cannot be easily modified. In principle, a synchronous machine can be operated beyond its rated speed by controlling the so-called field weakening range. In this range, the machine operates at its maximum rated power, with the torque output by the machine reducing as the speed increases. Electrically excited synchronous machines can be operated very easily in the field weakening range by reducing the excitation current. Even with permanent magnet machines, there are known ways of generating an air gap field component by applying a suitable current to the stator of the machine. This air gap field component counteracts the excitation field generated by the permanent magnets and thus weakens it.However, such control of the machine causes increased losses, so that the machine can only be operated with reduced efficiency in this range.

[0009] An effective method for reducing iron losses in electrical machines is the targeted weakening of the magnetic field between the stator and rotor at high-speed operating points, since losses due to high-frequency remagnetization are lower with a weaker magnetic field. In addition to electrical methods, there are also mechanical approaches for targeted field weakening. From the documents US 5 821 171 A, FR 2 831 345 A1, EP 1 085 644 A2, EP 1 867 030 A1, DE 10 2016 103 470 A1, CN 104600929 A and CN 105449969 A, a rotor of a radial flux machine is known which is divided perpendicular to the axis of rotation into several rotor disks equipped with permanent magnets and rotatable relative to one another, which rotor disks, depending on the relative rotation between the rotor disks, provide the full magnetic field in a position with the magnetic poles aligned in the axial direction and a weakened magnetic field in a position rotated relative to that.Active or passive mechanisms are described which claim to be able to switch between these two positions depending on the rotor speed or torque and thus enable more efficient operation of the electric machine across the entire engine characteristic map.

[0010] DE 10 2021 101 898 A1 describes an arrangement in which the rotor of a radial flux machine is divided into two sub-rotors, whose individual rotor disks alternate in the axial direction. One sub-rotor is connected directly to the rotor shaft, while the other sub-rotor is connected to the rotor shaft in a torque-transmitting manner via a torsional stiffness. The torsional stiffness is selected such that at low torques, the sub-rotors are in a torsional position with a weakened magnetic field, and at high torques, the sub-rotors are in a torsional position with a full magnetic field. DE 10 2021 101 904 B3 claims a structurally designed mechanical module that can be inserted into the interior of the permanent magnet-equipped rotor disks, establishes the described connections between the sub-rotors and the rotor shaft, and allows an adjustment characteristic to be defined via the torsional stiffness, which is implemented using springs and roller-equipped cam gears.

[0011] All of the previously mentioned passive solutions, which use a torque as a sensor variable to trigger a relative rotation between two partial rotors against a torsional stiffness, assume that the total electromagnetic torque generated by the stator current supply, in the case of the initially field-weakened position with non-aligned magnetic poles, is simply distributed between the two partial rotors, roughly according to their share of the total length and their respective phase position to the stator field, regardless of the presence of the other partial rotor. Only then could a partial torque proportional to the total torque be readily directed against a torsional stiffness between the partial rotors or one of the partial rotors and the rotor shaft, and cause the desired rotation with increasing torque into the position with full magnetic field and aligned magnetic poles.However, tests and modelling by the applicant have shown that the actual circumstances are far more complicated.

[0012] Even in the de-energized state, interactions occur between the rotor disks of the two sub-rotors in the form of magnetic repulsion moments. The position with the full magnetic field and aligned magnetic poles represents a fragile equilibrium with a vanishing repulsion moment. As rotation begins from this equilibrium position, a repulsion moment arises that increases with increasing rotation until it reaches a maximum, before then decreasing again with further rotation. The progression of the repulsion moment over the angle of rotation within an electrical period, the height of the maximum, and the angle of rotation at which it occurs depend heavily on the chosen arrangement of the permanent magnets within the rotor disks. The progression over an electrical period is fundamentally nonlinear.

[0013] In the case of the desired efficient stator current supply for different speeds, these magnetic repulsion moments increase in different ways, sometimes several times over, depending on the speed. Overall, the resulting partial moments are in no way suitable for simply counteracting the torsional stiffness between the partial rotors or one of the partial rotors and the rotor shaft, causing the partial rotors to rotate into the position with full magnetic field, since they are not directed in the right direction due to the high proportion of magnetic repulsion moments.

[0014] From US 5 245 238 A an electric axial flux machine according to the preamble of claim 1 is known.

[0015] For further prior art, reference is made to DE 60 2006 000 650 T2 and DE 10 2018 127360 A1.

[0016] In order to represent a functional arrangement in the sense of the aforementioned passive solutions for the torque-adaptive field weakening of the rotor of an electric axial flux machine, the object of the present invention is to provide an electric axial flux machine with improved mechanical field weakening, which in particular also effectively converts the partial moments actually occurring on rotor bodies for a desired adjustment and transmits them to the rotor shaft.

[0017] This object is achieved by an electric axial flux machine, in particular for use within a drive train of a hybrid or fully electric motor vehicle, comprising a stator and a rotor separated from the stator by an air gap, wherein the rotor has at least a first rotor body with a first group of permanent magnets and a second rotor body with a second group of permanent magnets, wherein the first rotor body and the second rotor body are rotatable relative to one another against the effect of a first torsional stiffness about a common axis of rotation by means of a mechanical field weakening mechanism.

[0018] This provides the advantage that an electrical machine can be realized with a purely mechanical field weakening device, which reliably and cost-effectively adjusts the positions of permanent magnets within the rotor required for demand-based field weakening depending on the operating conditions of torque and speed. In principle, the invention thus also avoids the need for actuators that intervene externally on or in the rotor. Among other things, the invention divides the previously single-piece rotor in the I-arrangement into at least two rotor bodies, with each rotor body containing a certain proportion of the permanent magnets. A suitable mechanical connection allows a change in orientation, i.e. rotation of the partial rotors relative to one another, depending on the torque.

[0019] First, the individual elements of the claimed subject matter of the invention are explained in the order in which they appear in the set of claims, and subsequently particularly preferred embodiments of the subject matter of the invention are described.

[0020] The magnetic flux in an electric axial flux machine (AFM), such as an electric drive machine of a motor vehicle designed as an axial flux machine, is directed axially to a direction of rotation of the rotor of the axial flux machine in the air gap between stator and rotor.

[0021] Depending on the application, it may be advantageous to design an axial flux machine in an I-arrangement or an H-arrangement. In an I-arrangement, the rotor is arranged axially next to a stator or between two stators. In an H-arrangement, two rotors are arranged on opposite axial sides of a stator. The axial flux machine according to the invention is preferably configured in an I-arrangement.

[0022] In principle, it is also possible for a plurality of I-type and / or H-type rotor-stator configurations to be arranged axially adjacent to one another. In this context, it would also be possible to arrange several I-type rotor-stator configurations axially adjacent to one another. In particular, it is also preferable for the H-type and / or I-type rotor-stator configurations to be essentially identical in design, so that they can be combined in a modular manner to form an overall configuration. Such rotor-stator configurations can, in particular, be arranged coaxially to one another and connected to a common rotor shaft or to multiple rotor shafts.

[0023] The stator of the electric axial flux machine according to the invention preferably has a stator body with a plurality of stator windings arranged in the circumferential direction. The stator body can be formed as a single piece or segmented in the circumferential direction. The stator body can be formed from a stator core with a plurality of laminated electrical sheets. Alternatively, the stator body can also be formed from a pressed soft magnetic material, such as the so-called SMC material (Soft Magnetic Compound).

[0024] The rotor of an electric axial flux machine can be designed, at least in part, as a laminated rotor. A laminated rotor is designed with layers in the axial direction. Alternatively, the rotor of an axial flux machine can also have a rotor carrier, which is equipped with magnetic laminations and / or SMC material and with magnetic elements designed as permanent magnets.

[0025] The permanent magnets can preferably be incorporated into the pockets of the rotor core. A single larger rotor magnet designed as a bar magnet or several smaller permanent magnet elements can be provided per pocket.

[0026] The rotor preferably has a plurality of rotor bodies. Particularly preferably, the rotor bodies are formed from essentially the same parts, in particular essentially identical. It is most preferred for the rotor bodies to be formed from identical, in particular essentially identical rotor laminations. The rotor bodies are therefore particularly preferably formed from a rotor lamination stack, which is composed of a plurality of laminated individual laminations or rotor laminations, generally made of electrical steel sheet, which are layered and packaged one above the other to form a stack, the so-called rotor lamination stack. The individual laminations can be held together in the rotor lamination stack by gluing, welding, or screwing. A rotor lamination stack can, in particular, also have permanent magnets introduced into the pockets of the rotor lamination stack or fixed circumferentially to the rotor lamination stack.

[0027] A rotor shaft is a rotatably mounted shaft of an electrical machine to which the rotor or rotor body is non-rotatably coupled.

[0028] The electric axial flux machine may further comprise a control device. A control device, as can be used in the present invention, serves in particular for the electronic control and / or regulation of one or more technical systems of the electric axial flux machine.

[0029] The electric axial flux machine is intended in particular for use within a drive train of a hybrid or fully electric motor vehicle. In particular, the electric machine is dimensioned such that vehicle speeds greater than 50 km / h, preferably greater than 80 km / h, and in particular greater than 100 km / h can be achieved. The electric motor particularly preferably has an output greater than 30 kW, preferably greater than 50 kW, and in particular greater than 70 kW. It is further preferred that the electric machine provides speeds greater than 5,000 rpm, particularly preferably greater than 10,000 rpm, and most particularly preferably greater than 12,500 rpm.

[0030] The electric axial flux machine can preferably also be installed in an electrically operated axle drive train. An electric axle drive train of a motor vehicle comprises an electric axial flux machine and a transmission, wherein the electric axial flux machine and the transmission form a structural unit. In particular, it can be provided that the electric axial flux machine and the transmission are arranged in a common drive train housing. Particularly preferably, such a drive train housing can also form a connection structure for the axial flux machine. Alternatively, it would of course also be possible for the electric axial flux machine to have a motor housing and the transmission to have a transmission housing, wherein the structural unit can then be effected by fixing the transmission relative to the electric axial flux machine. This structural unit is occasionally also referred to as an electric axle.

[0031] Furthermore, according to a likewise advantageous embodiment of the invention, it can be provided that the field weakening mechanism comprises a plurality of toothed planetary gears which are rotatably mounted on the first rotor body and engage, on the one hand, with the rotor shaft and, on the other hand, with the second rotor body, so that for a desired adjustment of the mechanical field weakening mechanism, the first rotor body and the second rotor body can be rotated relative to one another via the gear coupling of the planetary gears. According to a further particularly preferred embodiment of the invention, it can be provided that the planetary gears each have an external toothing which meshes with an internal toothing of the second rotor body and an external toothing of the rotor shaft.

[0032] Furthermore, the invention can also be further developed in such a way that the first rotor body has bolts extending in the axial direction, on which the planetary gears are rotatably mounted, which can contribute to improved system integration.

[0033] In a likewise preferred embodiment variant of the invention, it can also be provided that at least three planetary gears are arranged equidistantly distributed over the circumference on the first rotor body, which has proven to be particularly advantageous with regard to friction, manufacturing costs and operational reliability.

[0034] It may also be advantageous to further develop the invention in such a way that the torsional rigidity is configured as a spring element, in particular as a compression spring or arc spring. According to a further preferred embodiment of the subject matter of the invention, the characteristic curve of the torsional rigidity can be selected such that, upon exceeding a specified minimum torque, the first rotor body and the second rotor body begin to rotate relative to each other from a position with maximally weakened magnetic field, and upon reaching and / or exceeding a specified maximum torque, they have completed a rotation relative to each other into a position with full magnetic field.

[0035] Finally, the invention can also be advantageously implemented in such a way that the axial flow machine is designed in I-configuration.

[0036] The invention will be explained in more detail below with reference to figures without limiting the general inventive concept.

[0037] It shows: Fig. 1 an axial flow machine in I-design in a schematic axial section, Fig. 2 which from the Fig. 1 known axial flow machine in a development, Fig. 3 shows a first embodiment of a field weakening mechanism not according to the invention in a schematic cross-sectional view, Fig. 4 a second embodiment of a field weakening mechanism according to the invention in a schematic cross-sectional view

[0038] The Fig. 1 shows an electric axial flux machine 1, particularly for use within a drive train of a hybrid or fully electric motor vehicle, comprising a stator 2 with two axially spaced-apart disc-shaped stator bodies 18, 19, between which the likewise disc-shaped rotor 4 is rotatably mounted. An air gap 3 is formed between each of the stator bodies 18, 19 and the rotor 4. The axial flux machine 1 shown is thus designed in an I-configuration.

[0039] The rotor 4 has a first rotor body 5 with a first group of permanent magnets 6 and a second rotor body 7 with a second group of permanent magnets 8, wherein the first rotor body 5 and the second rotor body 7 are rotatable relative to each other against the effect of a first torsional stiffness 9 about a common axis of rotation 10 by means of a mechanical field weakening mechanism 11. This is also shown by the synopsis of the Fig. 1-4 can be seen.

[0040] The Fig. Figure 2 shows a developed view of the stator 2 and the rotor 4, in which the two rotor bodies 5, 7 are shown in a rotated position and thus in a field-weakened operating state. The stator teeth 21 formed on the stator bodies 18, 19, which are wound by the stator coils 20, can be seen. The torsional stiffness 9 is designed as a spring element, in particular as a compression spring or arc spring. The characteristic curve of the torsional stiffness 9 is selected such that when a specified minimum torque is exceeded, the first rotor body 5 and the second rotor body 7 begin to rotate relative to one another from a position with maximum field-weakening, and when a specified maximum torque is reached and / or exceeded, they have completed a rotation relative to one another into a position with full magnetic field.

[0041] In the Fig. 3 shows a first embodiment of a field weakening mechanism 11, which is not according to the invention and effects the torque-dependent relative rotation of the two rotor bodies 5, 7 with respect to one another. The field weakening mechanism 11 shown here comprises a lever element 12 that can be pivoted about a pivot point, wherein the first rotor body 5 can be coupled to a first lever section 13 and the second rotor body 7 can be coupled to a second lever section 14 of the lever element 12, and the first lever section 13 and the second lever section 14 are arranged on opposite sides of the lever element 12, so that for a desired adjustment of the mechanical field weakening mechanism 11, the first rotor body 5 and the second rotor body 7 can be rotated relative to one another by tilting the lever element 12. For this purpose, the lever element 12 is pivotally arranged on a rotor shaft 15 of the rotor 4.

[0042] The lever element 12, designed as a single lever, is thus arranged such that the radially inner end of the lever element 12 with respect to the rotor 4 engages with the rotor shaft 15, and the two rotor bodies 5, 7 are rotated relative to one another via two further, spaced-apart, radially further outward lever sections 13, 14, counteracting the torsional rigidity 9 acting in the circumferential direction. The state at small moments is defined such that the opposing partial magnets in the rotor bodies 5, 7 are rotated relative to one another, resulting in a "normally field-weakened" arrangement.

[0043] As in the Fig.4, in a second embodiment according to the invention, the field weakening mechanism 11 can also comprise a plurality of toothed planet gears 16, which are rotatably mounted on the first rotor body 5 and engage with the rotor shaft 15 on the one hand and with the second rotor body 7 on the other hand, so that for a desired adjustment of the mechanical field weakening mechanism 11, the first rotor body 5 and the second rotor body 7 can be rotated relative to one another via the gear coupling of the planet gears 16. The planet gears 16 each have an external toothing which meshes with an internal toothing of the second rotor body 7 and an external toothing of the rotor shaft 15. The first rotor body 5 has bolts 17 extending in the axial direction, on which bolts the planet gears 16 are rotatably mounted.Due to the gear coupling, this arrangement can also achieve a torque-induced rotation of the rotor bodies 5,7 against each other.

[0044] The invention is not limited to the embodiments illustrated in the figures. The above description is therefore not to be considered restrictive, but rather explanatory. The following claims are to be understood in such a way that a stated feature is present in at least one embodiment of the invention. This does not exclude the presence of further features. Where the claims and the above description define 'first' and 'second' features, this designation serves to distinguish between two similar features without establishing a priority. List of reference symbols 1 axial flux machine 2 Stator 3 Air gap 4 Rotor 5 first rotor body 6 permanent magnets 7 second rotor body 8 permanent magnets 9 Torsional stiffness 10 axis of rotation 11 Field weakening mechanism 12 Lever element 13 Lever section 14 Lever section 15 Rotor shaft 16 planetary gears 17 bolts 18 first stator body 19 second stator body 20 stator coils 21 stator teeth

Claims

[1] Electric axial flux machine (1), in particular for use within a drive train of a hybrid or fully electric motor vehicle, wherein the electric axial flux machine (1) has a stator (2) and a rotor (4) separated from the stator (2) by an air gap (3), wherein the rotor (4) has at least a first rotor body (5) with a first group of permanent magnets (6) and a second rotor body (7) with a second group of permanent magnets (8), and the first rotor body (5) and the second rotor body (7) are rotatable relative to one another against the effect of a first torsional stiffness (9) about a common axis of rotation (10) by means of a mechanical field weakening mechanism (11), characterized by , that the field weakening mechanism (11) comprises a plurality of toothed planetary gears (16) which are rotatably mounted on the first rotor body (5) and are in engagement with the rotor shaft (15) on the one hand and with the second rotor body (7) on the other hand, so that for a desired adjustment of the mechanical field weakening mechanism (11), the first rotor body (5) and the second rotor body (7) can be rotated relative to one another via the gear coupling of the planetary gears (16). [2] Axial flow machine (1) according to claim 1, characterized by that the planet gears (16) each have an external toothing which meshes with an internal toothing of the second rotor body (7) and an external toothing of the rotor shaft (15). [3] Axial flow machine (1) according to claim 1 or 2, characterized by that the first rotor body (5) has bolts (17) extending in the axial direction, on which the planet gears (16) are rotatably mounted. [4] Axial flow machine (1) according to one of claims 1 to 3, characterized by that at least three planetary gears (16) are arranged equidistantly distributed over the circumference on the first rotor body (5). [5] Axial flow machine (1) according to one of claims 1 to 4, characterized by that the torsional stiffness (9) is designed as a spring element, in particular as a compression spring or arc spring. [6] Axial flow machine (1) according to claim 5, characterized by that the characteristic curve of the torsional rigidity (9) is selected such that when a specified minimum torque is exceeded, the first rotor body (5) and the second rotor body (7) begin to rotate relative to one another from a position with maximum field weakening and when a specified maximum torque is reached and / or exceeded, they have completed a rotation relative to one another into a position with full magnetic field. [7] Axial flow machine (1) according to one of claims 1 to 6, characterized bythat the axial flux machine (1) is designed in I-configuration.

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