Transformers for separately excited synchronous machines: Integration via bearings

Abstract

Contactless energy transmission device for a rotor of an electric machine, in particular a separately excited synchronous machine within a drive train of a motor vehicle, comprising - a housing part (6) which can be rigidly coupled to a housing of the electric machine and has an inner lateral surface, and - an inductive transformer comprising a primary coil (1) capable of being energized and a secondary coil (2) spaced apart from it, which can be electrically coupled to a winding of the rotor, - a rolling bearing (5) by means of which a rotor shaft (7) is rotatably mounted relative to the housing part (6), wherein the primary coil (1) of the inductive transformer (5) is positioned on the housing part (6) in a rotationally rigid manner relative to it, and the rolling bearing (5) is arranged within the housing part (6) such that the primary coil (1) and the rolling bearing (5) are arranged coaxially, characterized by the fact that the secondary coil (2) of the inductive transformer is arranged inside a transformer housing (8) on the inner outer surface, wherein the housing is connected to the rotor in a rotationally fixed manner and the secondary coil (2) is arranged in axial overlap with the primary coil (1).

Description

[0001] The present invention relates to a contactless energy transmission device for a rotor of an electric machine, in particular a separately excited synchronous machine within a drive train of a motor vehicle.

[0002] Electric motors are increasingly being used for propulsion in motor vehicles to create alternatives to combustion engines that require fossil fuels. Considerable efforts have already been made to improve the everyday usability of electric drives and to offer users the familiar driving comfort.

[0003] A detailed description of an electric drive can be found in an article in the journal ATZ, 113th year, 05 / 2011, pages 360-365, by Erik Schneider, Frank Fickl, Bernd Cebulski, and Jens Liebold, entitled: Highly Integrated and Flexible Electric Drive Unit for E-Vehicles. This article describes a drive unit for a vehicle axle, which includes an electric motor. Such drive units are also referred to as e-axles or electrically powered drivetrains.

[0004] In addition to purely electric powertrains, hybrid powertrains are also known. Such powertrains in hybrid vehicles typically comprise a combination of an internal combustion engine and an electric motor, enabling – for example, in urban areas – purely electric operation while simultaneously providing sufficient range and availability, especially on long-distance journeys. Furthermore, it is possible to operate simultaneously using both the internal combustion engine and the electric motor in certain situations. Depending on the specific design, both purely electric and hybrid powertrains incorporate a transmission, which is used, for example, to adjust the speed and power ranges.

[0005] In the development of electric machines intended for e-axles or hybrid modules, there is a continuing need to increase their power density and efficiency while simultaneously reducing manufacturing costs, as the vehicle's cost and weight are largely determined by the battery size. In this context, it is also known to design the electric machines as separately excited synchronous machines (FSMs). Here, electrical power must be transferred to the rotor of a separately excited synchronous machine to excite the rotor windings. For traction machines, a contact-based transformer is typically used for this purpose. When these windings are energized, a magnetic field is generated, which, in combination with the stator's magnetic field, produces a torque. The strength of the rotor field can be adjusted by varying the current applied.This allows the machine's behavior to be continuously adapted to the respective driving situation in an efficiency-optimized manner.

[0006] The disadvantages of such a contact-based transmitter include mechanical and electrical losses in the contact between stationary and rotating components. Further disadvantages are the wear of the rubbing components and the associated contamination from abrasion, as well as the comparatively large installation space requirement.

[0007] As an alternative to such contact-based transformers, contactless inductive transformers are also known. An inductive transformer is typically a rotationally symmetrical transformer with an air gap, consisting of a primary and a secondary winding. An inductive transformer usually also has a core, for example made of ferrite. Such a core can be made of one or more parts. Examples of such transformers or contactless energy transfer devices can be found in DE 10 2012 021 600 A1, DE 10 2019 212 406 A1, and DE 10 2017 214 766 A1. A contactless energy transfer device according to the preamble of claim 1 can be found in DE 10 2009 014 961 A1.

[0008] For example, all parts of the core can be attached to the stationary side of an electric machine, with the secondary winding rotating inside the core. Alternatively, core parts can be attached to the rotating part of the machine. In this case, the primary and secondary core parts are separated by an air gap. This gap must be large enough to ensure that the core parts do not touch, taking all tolerances and operating conditions into account. The rotating transformer parts are often fitted with a bandage or integrated into another component to support them at higher speeds. An example of such a design can be found in DE 10 2017 214 776 A1 or in DE 10 2012 201 826 A1.

[0009] The object of the invention is now to provide a contactless energy transmission device for a rotor of an electric machine, in particular a separately excited synchronous machine within a drive train of a motor vehicle, which also has a compact design and high operational reliability even at high electrical powers to be transmitted.

[0010] This problem is solved by the measures specified in the independent claims. Advantageous embodiments can be found in the dependent claims.

[0011] The primary coil of the energy transmission device—hereinafter referred to as the transformer—of an electric machine, comprising a ferrite core and windings, is arranged coaxially around a rolling bearing, hereinafter also called a rotor bearing, comprising a bearing outer ring. The bearing outer ring is integrated into a housing part, on the outer diameter of which the primary coil is placed. The housing part is an integral component of a bearing shield or connected to it. This arrangement can be implemented on either the side of the electric machine facing a gearbox or the side facing away from the gearbox. The housing part is preferably designed as a substantially rotationally symmetric body, which can be divided into two cylindrical ring sections. The second cylindrical ring section extends radially outward from an outer surface of the first cylindrical ring section.

[0012] The coaxial arrangement of the rotor bearing and transformer allows for saving axial installation space and keeping the machine's external dimensions compact. Furthermore, this enables the use of a design for the electric machine with a radial air gap and a flat but axially long coil cross-section, which is electromagnetically advantageous.

[0013] The primary coil is thermally connected to the housing part on which it is arranged, so that heat from the primary coil can be dissipated via the housing part, in particular to a machine housing of the electric machine, and thermal overload can be avoided.

[0014] Inverter electronics for supplying the primary side are integrated between the housing and the primary coil and thermally connected to the housing, which is designed primarily as a bearing shield. This allows heat from the inverter electronics to be dissipated, particularly to the machine housing, thus preventing thermal overload.

[0015] The assembly consisting of the primary coil, inverter electronics, and housing component constitutes a self-contained, manufacturable, and testable unit, thereby increasing machine quality and reducing scrap. In other words, the primary coil, inverter electronics, and housing component form a modular structural unit.

[0016] In one embodiment, at least one channel, extending at least partially radially or tangentially, for guiding a coolant is integrated into the housing part, which is particularly designed as a bearing shield, thereby improving heat dissipation. The channel is particularly arranged as a through-opening inside the housing part. Heat transfer thus occurs from the inverter electronics via the housing part to the coolant. The inverter electronics are arranged on an axial surface of the housing part. This axial surface preferably faces the electric machine.

[0017] In a further embodiment, at least one groove is formed in the bearing shield, which is covered by the inverter electronics and thus forms a channel for guiding a coolant. Elements such as ribs or pins can be formed within the groove to increase the surface area facing the coolant. This further improves heat dissipation from the primary coil and inverter electronics.

[0018] In one embodiment, the primary coil and the inverter electronics are potted on the housing part with an epoxy compound or overmolded with plastic, thereby improving protection against environmental influences, thermal coupling and electrical insulation of the components.

[0019] The secondary coil comprises a ferrite core and a winding, and is enclosed in a substantially pot-shaped housing, which is hereinafter also referred to as the transformer housing. In other words, the transformer housing is designed as a hollow cylinder, which preferably has a connection at one distal end for mounting, in particular, to or on the rotor, especially a rotor shaft. The rectifier electronics are also located within the housing and are thermally connected to it. The housing is preferably mounted axially to the rotor housing or rotor body. The housing has openings for the passage of electrical conductors. The housing can be made, for example, of aluminum or glass-fiber reinforced plastic. The housing can be constructed of multiple parts. Alternatively, the housing can be integrally connected to the rotor housing or rotor body, or be made of one of the aforementioned materials.

[0020] This arrangement provides fixed support for the rectifier electronics and secondary coil at varying speeds and thermally couples them to the rotor housing, allowing heat to be dissipated. Additionally, heat can be dissipated convectively via the radial outer surfaces of the transformer housing.

[0021] The secondary-side assembly comprises the secondary coil, rectifier electronics, and transformer housing. It represents a self-contained, manufacturable, and testable unit, thereby increasing machine quality and reducing scrap. In other words, the secondary coil, rectifier electronics, and transformer housing form a modular structural unit.

[0022] In one embodiment, the outer surfaces of the transmitter housing are provided with tangential ribs, thereby improving speed stability and convective heat dissipation.

[0023] In one embodiment, the rectifier electronics and secondary coil are potted in the transformer housing with an epoxy compound or overmolded with plastic, thereby improving protection against environmental influences, thermal coupling and electrical insulation of the components.

[0024] In a further embodiment, at least one cavity between the rotor housing and the transferor housing forms a channel for guiding a cooling medium, thereby improving heat dissipation from the secondary-side arrangement.

[0025] The individual elements of the claimed invention are explained below.

[0026] A rotor is the rotating part of an electric machine. The rotor includes, in particular, a rotor shaft. The rotor shaft can be hollow, which reduces weight and allows the supply of lubricant or coolant to the rotor body. Preferably, the hollow shaft of the contactless energy transmission device is a rotor shaft of an electric machine that is at least partially hollow.

[0027] The electric machine can be designed, in particular, as a rotary machine. The rotary machine can be configured, in particular, as a radial flux machine. A radial flux machine is characterized by the fact that the magnetic field lines in the air gap formed between the rotor and the stator extend in a radial direction. The air gap is the gap existing between the rotor and the stator. In a radial flux machine, this is an annular gap with a radial width corresponding to the distance between the rotor body and the stator body.

[0028] The electric machine is intended for use within the powertrain of a hybrid or fully electric motor vehicle. In particular, the electric machine is dimensioned to enable vehicle speeds greater than 50 km / h, preferably greater than 80 km / h, and especially greater than 100 km / h. The electric motor preferably has a power output greater than 50 kW, preferably greater than 80 kW, and especially greater than 150 kW. It is further preferred that the electric machine provides rotational speeds greater than 8,000 rpm, particularly preferably greater than 12,000 rpm, and most preferably greater than 1,500 rpm.

[0029] For the purposes of this application, motor vehicles are defined as land vehicles that are moved by mechanical power and are not bound to railway tracks. A motor vehicle may, for example, be selected from the groups of passenger cars, trucks, mopeds, light vehicles, motorcycles, buses, or tractors.

[0030] The inductive transformer is configured such that electrical power levels preferably greater than 1 kW and particularly preferably greater than 2 kW can be transmitted, at least for short periods, without electrically or thermally overloading the transformer. Most preferably, the inductive transformer is configured to transmit electrical power levels between 0.5 kW and 10 kW, more preferably between 1 kW and 5 kW, and most preferably between 2 kW and 4 kW.

[0031] The transformer windings are made of an electrically conductive but non-ferromagnetic material, such as copper or aluminum, and are electrically insulated from each other. Preferably, the windings are oriented tangentially around the hollow shaft, resulting in a cylindrical ring-shaped winding body with a diameter and a longitudinal extent in the axial direction. Most preferably, the windings are wound around and / or within a core made of a ferromagnetic material.

[0032] The windings can be formed from one or more electrical conductors with a circular cross-section. It is also conceivable that the electrical conductors forming the winding have a cross-sectional shape other than circular, in particular a rectangular shape. Particularly preferably, the windings can be formed from insulated copper foils, which can be wound around each other similarly to a toilet paper roll.

[0033] According to an advantageous further development of the invention, the primary winding can have a higher number of turns than the secondary winding. This allows for a voltage conversion from the comparatively high battery voltage to the lower rotor voltage during the transfer of electrical energy between the primary and secondary windings.

[0034] In this context, it is further preferred that an electrical voltage of 40-1500V, preferably 100-1000V, most preferably 300-850V, is applied to the primary winding. Furthermore, it is preferred that a voltage of 70-500V is applied to the secondary winding.

[0035] The primary core and / or the secondary core are / are made of a ferromagnetic material, preferably a ferrite material. The primary core and / or secondary core may be made of multiple parts. The respective core parts are preferably substantially rotationally symmetrical, but may contain elements and recesses for fixing or passing through further components.

[0036] The primary core and / or the secondary core are particularly preferably ring-shaped. Most preferably, the primary core and / or the secondary core have a U-shaped cross-sectional contour with a circumferential groove. Preferably, the grooves of the U-shaped cross-sectional contours of the primary core and the secondary core are oriented towards each other. It is also particularly preferred that the primary winding runs in the groove of the primary core and / or the secondary winding in the groove of the secondary core.

[0037] The invention and its technical context are explained in more detail below with reference to the figures. It should be noted that the invention is not limited to the embodiments shown. In particular, unless explicitly stated otherwise, it is also possible to extract aspects of the concepts illustrated in the figures and combine them with other elements and findings from the present description and / or figures. It should be emphasized that the figures, and especially the depicted dimensions, are only schematic. Identical reference numerals denote the same objects, so that explanations from other figures may be consulted for further clarification. Terms such as "radial," "axial," or similar refer to the axis of rotation of the electrical machine, unless a different reference is explicitly used.Furthermore, for the sake of better readability of the figures, only individual or a few identical elements of a reference symbol may be provided.

[0038] It shows: Fig. 1 an electric machine with a contactless energy transfer device in a schematic axial section view in a first embodiment, Fig. 2 an electric machine with a contactless energy transfer device in a schematic axial section view in a second embodiment, Fig. 3 an electric machine with a contactless energy transfer device in a schematic axial section view in a third embodiment, Fig. 4 an electrical machine with a contactless energy transfer device in a schematic axial section view in a fourth embodiment.

[0039] Fig. Figure 1 shows a schematic axial section view of an electric machine with a contactless energy transfer device in a first embodiment. The electric machine is a so-called separately excited synchronous machine. The rotor 110 comprises a rotor shaft 7 designed as a hollow shaft and a rotor body in which windings for generating a magnetic field are arranged. The rotor body is enclosed in the axial direction by a rotor housing 13. The rotor shaft 7 is rotatably mounted in a housing part 6 designed as a bearing shield via a rolling bearing 7. The housing part is designed as a body of revolution, which has a first cylindrical ring section with an inner surface and an outer surface. The rolling bearing is arranged with its outer ring on the inner surface. A primary coil 1 of an inductive transformer of an energy transfer device is arranged on the outer surface.The primary coil 1 and the rolling bearing 5 have at least partial axial overlap. Furthermore, the rolling bearing 5 and the primary coil 1 are arranged coaxially. The primary coil 1 comprises a ferrite core 9 and a winding 10. A second cylindrical ring section of the housing part 6 extends radially from the outer surface of the first cylindrical ring section. Thus, the first and second cylindrical ring sections form an L-shaped cross-section, with one leg oriented parallel to an axis of rotation of the rotor and the other leg extending radially outwards. Inverter electronics 3 are arranged on a first axial surface of the second cylindrical ring section. The first axial surface of the second cylindrical ring section faces the rotor 110.In the illustrated embodiment, the primary coil 1 and the inverter electronics 3 are encapsulated with an epoxy compound for protection against environmental influences, as well as for improving thermal coupling and electrical insulation of the components. The primary coil 1, the inverter electronics 3, and the housing part 6 thus form a modular structural unit.

[0040] An adapter housing 8 is arranged axially on the rotor housing 13 and connected to it in a rotationally fixed manner. A secondary coil 2 is arranged on an inner surface of the adapter housing. The secondary coil 2 comprises a ferrite core 11 and a winding 12. The secondary coil 2 is arranged coaxially with the primary coil 1 and is axially aligned with it. The adapter housing 8 has an axial surface facing away from the rotor, on which a rectifier electronics 4 is arranged. The secondary coil 2 is electrically connected to the rotor windings via the rectifier electronics 4, although this is not shown in the illustration. In the illustrated embodiment, the secondary coil 2 and the rectifier electronics 4 are encapsulated with an epoxy compound for protection against environmental influences, as well as to improve thermal coupling and electrical insulation of the components.The secondary coil 2, the rectifier electronics 4 and the transformer housing 8 thus form a modular structural unit.

[0041] Fig. Figure 2 shows a schematic axial section view of an electric machine with a contactless energy transfer device in a second embodiment. The second embodiment differs from the first embodiment. Fig. 1 only through channels 16 in the second cylindrical ring section of the housing part 6. The channels are designed to carry a coolant and are connected to a cooling system (not shown). The cooling channels run section by section in radial and tangential directions within the housing part 6, thus forming a meandering structure. The channels 16 are arranged radially in the area of ​​the inverter electronics 3 to achieve the best possible heat dissipation. The channels 16 are designed as closed conduits within the housing part 6, so the coolant is not in direct contact with the inverter electronics 3.

[0042] Fig. Figure 3 shows a schematic axial section view of an electric machine with a contactless energy transfer device in a third embodiment. This third embodiment allows for direct cooling and heat dissipation of the inverter electronics 3. In the second cylindrical ring section, a groove 17 is formed in the first axial surface. This groove is closed by the inverter electronics 3, thus forming a channel 16 for guiding a coolant. Ribs (18) are formed in the groove to increase the cooling surface area, thereby improving heat dissipation. Although the second and third embodiments are shown as alternatives, a combination of the closed channels of the second embodiment with the channel of the third embodiment is possible.

[0043] Fig.Figure 4 shows a schematic axial section view of an electric machine with a contactless energy transfer device in a fourth embodiment. The fourth embodiment differs from the first embodiment by the elements shown below. The fourth embodiment can be combined with both the second and third embodiments. In the fourth embodiment, a radial outer surface of the transferor housing 8 has ribs 17, which run essentially tangentially. This results in improved rotational speed stability and improved convective heat dissipation due to the increased surface area of ​​the radial outer surface. Furthermore, a cavity 20 is arranged between the rotor housing and the transferor housing, which forms a channel 16 for guiding a cooling medium and is connected to a cooling system (not shown).This improves heat dissipation, particularly in the area of ​​the rectifier electronics 4 and the secondary coil 2.

[0044] The invention is not limited to the embodiments illustrated in the figures. The foregoing description is therefore not to be considered limiting, but rather explanatory. The following claims are to be understood as meaning that a named feature is present in at least one embodiment of the invention. This does not preclude the presence of further features. Insofar as the claims and the foregoing description define 'first' and 'second' features, this designation serves to distinguish between two similar features without establishing any hierarchy. Reference symbol list 1 Primary coil 2 Secondary coil 3 Inverter electronics 4 rectifier electronics on 5 rolling bearings / rotor bearings 6 Housing part / Bearing shield 7 Rotor shaft 8 transformer housings 9 Ferrite core of the primary coil 10. Winding of the primary coil 11 Ferrite core of the secondary coil 12. Secondary coil winding 13 Rotor housings 14 Potting or plastic overmolding 15 Potting or plastic overmolding 16 Cooling channel 17 Nut 18 ribs 20 cavity 100 electric machine 110 Rotor

Claims

[1] Contactless energy transfer device for a rotor of an electric machine, in particular a separately excited synchronous machine within a drive train of a motor vehicle, comprising - a housing part (6) which can be rigidly coupled to a housing of the electric machine and has an inner lateral surface, and - an inductive transformer comprising a primary coil (1) capable of being energized and a secondary coil (2) spaced apart from it, which can be electrically coupled to a winding of the rotor, - a rolling bearing (5) by means of which a rotor shaft (7) is rotatably mounted relative to the housing part (6), wherein the primary coil (1) of the inductive transformer (5) is positioned on the housing part (6) in a rotationally rigid manner relative to it, and the rolling bearing (5) is arranged within the housing part (6) such that the primary coil (1) and the rolling bearing (5) are arranged coaxially, characterized by , that the secondary coil (2) of the inductive transformer is arranged inside a transformer housing (8) on the inner outer surface, wherein the latter is connected to the rotor in a rotationally fixed manner and the secondary coil (2) is arranged in axial overlap with the primary coil (1). [2] Contactless energy transfer device (1) according to claim 1, wherein the primary coil (1) and the secondary coil (2) of the inductive transformer (5) are arranged coaxially to each other within the transformer housing (8). [3] Contactless energy transmission device (1) according to claim 1 or 2, wherein the rolling bearing (5) has an inner ring and an outer ring, between which a plurality of rolling elements (28) are accommodated, wherein the inner ring is non-rotatably connected to the rotor shaft (7) and the outer ring is non-rotatably connected to the housing part (6). [4] Contactless energy transfer device according to claim 3, wherein the housing part (6) has a first cylindrical ring section, on the outer surface of which the primary coil (1) is arranged, and on the inner surface of which the outer ring of the rolling bearing (5) is arranged such that the rolling bearing and the primary coil are at least partially overlapping. [5] Contactless energy transfer device according to claim 4, wherein the housing part (6) has a second cylindrical ring section which extends radially outwards from the outer surface of the first cylindrical ring section, wherein the inverter electronics (3) are arranged on a first axial surface of the second cylindrical ring section which faces the rotor. [6] Contactless energy transfer device according to one of the preceding claims, wherein the housing part (6) is a bearing shield of the electric machine. [7] Contactless energy transfer device according to one of the preceding claims, wherein the housing part has a channel (16) for guiding a cooling fluid. [8] Contactless energy transfer device according to claim 6, wherein the channel (16) in the second cylindrical ring section is formed by a groove in the first axial surface and by the inverter electronics (3) covering the groove. [9] Contactless energy transfer device (1) according to any one of claims 1 to 5, wherein the primary coil (1), the inverter electronics (3) and the housing part (6) form a modular structural unit. [10] Contactless energy transfer device (1) according to one of claims 1 to 6, wherein the secondary coil (2), the rectifier electronics (4) and the transformer housing (8) form a modular structural unit.

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