Stator and kit-of-parts
Patent Information
- Application Number
- EP2023754133
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-08-29
- Filing Date
- 2023-08-03
- Publication Date
- 2025-07-09
AI Technical Summary
Existing electric machine stators in motor vehicle drive trains face challenges in achieving high power density and efficient cooling, with known cooling methods not adequately addressing the need for improved heat dissipation and fluid flow around conductors.
A cylindrical stator design with twisted, non-circular conductor sections that allow for uniform fluid flow and efficient heat dissipation, utilizing a U-shaped groove geometry and hairpin winding configuration, which can be easily integrated into existing stator designs without altering production processes or slot geometries.
This design enhances cooling performance, prevents fluid stagnation, and maintains high power density by ensuring uniform flow and efficient heat dissipation, while being cost-effective and adaptable to existing stator configurations.
Smart Images
Figure 1.1
Abstract
Description
[0001] Stator und Kit-of-parts
[0002] The present invention relates to a stator for an electrical machine, in particular within a drive train of a motor vehicle, wherein the stator is of cylindrical ring-shaped design and has a plurality of stator teeth, which in the circumferential direction between adjacent stator teeth each define a stator slot which extends in the radial direction and runs axially through the stator, said stator slot having two slot side walls and a slot base, into which a current-carrying winding comprising a plurality of conductors is inserted, wherein the conductors have two conductor sections which run parallel in the axial extent and are arranged in the stator slots, which conductor sections have a contour which deviates from the circular shape in cross section, and which emerge from the stator on an end face of the stator with two free conductor ends each, forming a winding head, wherein a cooling fluid can flow through the stator slots.The invention further relates to a kit of parts.
[0003] 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.
[0004] A detailed description of an electric drive can be found in an article in the magazine ATZ 113th year, 05 / 2011, pages 360-365 by Erik Schneider, Frank Fickl, Bernd Cebulski and Jens Liebold with the title: Highly integrated and flexible electric drive unit for electric vehicles. This article describes a drive unit for one axle of a vehicle which comprises an electric motor which is arranged concentrically and coaxially to a bevel gear differential, with a switchable 2-speed planetary gear set being arranged in the power train between the electric motor and bevel gear differential, which is also positioned coaxially to the electric motor or the bevel gear differential or spur gear differential. The drive unit is very compact and, thanks to the switchable 2-speed planetary gear set, allows a good compromise between climbing ability, acceleration and energy consumption.Such drive units are also referred to as e-axles or electrically operated drive trains.
[0005] In addition to purely electric drivetrains, hybrid drivetrains are also known. Such drivetrains in hybrid vehicles typically comprise a combination of an internal combustion engine and an electric motor, enabling purely electric operation—for example, in urban areas—while maintaining sufficient range and availability, especially for long-distance journeys. Furthermore, in certain operating situations, it is possible to use both the internal combustion engine and the electric motor simultaneously.
[0006] In the development of electric motors intended for electric axles or hybrid modules, there is a continuing need to increase their power densities, making the necessary cooling of the electric motors increasingly important. Due to the necessary cooling performance, hydraulic fluids, such as cooling oils, have become the preferred solution in most concepts for dissipating heat from the thermally stressed areas of an electric motor.
[0007] Jacket cooling and winding head cooling, for example, are known from the state of the art for cooling electrical machines using hydraulic fluids. While jacket cooling transfers the heat generated at the outer surface of the stator core into a cooling circuit, with winding head cooling, the heat is transferred directly to the fluid at the conductors outside the stator core in the area of the winding heads.
[0008] Further improvements are offered by separately designed cooling channels, which are introduced both into the laminated core of the stator (see e.g. EP3157138 A1) and into the slot in addition to the conductors (see e.g. Markus Schiefer: Indirect winding cooling of highly utilized permanent magnet synchronous machines with tooth-wound coil winding, dissertation, Karlsruhe Institute of Technology (KIT), 2017). Concepts are also known in which hydraulic fluid flows directly around the windings in order to increase the power density. Improved cooling with direct contact between hydraulic fluid and conductor in the slot is already known in principle from the prior art. For example, DE102015013018 A1 describes a solution for electrical machines with single-tooth windings, in which the fluid flows directly around the windings wound around the teeth.
[0009] Electrical machines with a hollow cylindrical stator, i.e., internal rotor machines, and configured for use as traction drives in motor vehicles often have a stator winding with a rectangular cross-section to achieve high power density. In electrical machines intended for motor vehicle power, the stator windings are therefore typically designed as coil windings. For example, essentially U-shaped wire segments are inserted into the stator slots from one end face of the stator and then formed on an opposite end face of the stator and connected, for example, by welding.
[0010] The object of the invention is to provide a stator with a winding for an electrical machine that allows for improved cooling performance and higher power outputs, or has improved efficiencies. Furthermore, the object of the invention is to realize a kit of parts for forming a stator winding.
[0011] This object is achieved by a stator for an electrical machine, in particular within a drive train of a motor vehicle, wherein the stator is cylindrical in shape and has a plurality of stator teeth, which in the circumferential direction between adjacent stator teeth each define a stator slot extending in the radial direction and extending in the axial direction through the stator, with two slot side walls and a slot base, into which a current-carrying winding comprising a plurality of conductors is inserted, wherein the conductors have two conductor sections arranged in the stator slots which extend parallel in the axial direction and which have a contour deviating from the circular shape in cross section, and which emerge from the stator on an end face of the stator with two free conductor ends each, forming a winding head, wherein the stator slots can be flowed through by a cooling fluid,wherein in a stator slot at least one of two radially adjacent conductor sections is twisted along its longitudinal extent.
[0012] This provides the advantage that the conductor sections can be centered and / or fixed in the stator slots, thus simultaneously enabling uniform flow around the conductor sections. In particular, a particularly favorable ratio of flow cross-section to electrical conductor cross-section can be achieved in the stator slot. The flow around the twisted conductor sections has also proven to be particularly uniform. Furthermore, the production of the twisted conductor sections is particularly simple and cost-effective. The assembly process for the winding does not need to be changed.
[0013] A key advantage of the invention is that the cross-sections of the conductor sections do not need to be altered, but merely twisted. Furthermore, no adjustment of the stator slot geometry is required, which has a positive impact on stator production and would therefore also make it possible, in principle, to equip an existing stator with the twisted conductors.
[0014] By using a conventional, for example, rectangular wire cross-section and a substantially U-shaped slot geometry with the typically required joint clearances, crossflows in the stator slot can be minimized by alternating constrictions. Furthermore, it has been shown that "dead water areas" (comparable to standing water behind bridge piers in flowing waterways, for example) can be avoided. It has also been shown that the twisted conductor sections can prevent the accumulation of fine abrasion in the stator slots.
[0015] The stator according to the invention is preferably designed for use in a radial flux machine. A stator for a radial flux machine is typically cylindrical and generally consists of electrically insulated, layered, and stacked laminations. Distributed around the circumference, grooves are recessed into the electrical lamination, extending essentially parallel to the rotor shaft. These grooves accommodate the stator winding or parts of the stator winding. The stator grooves preferably have a substantially U-shaped cross-sectional contour. Most preferably, the stator grooves have straight groove walls extending in the radial direction.
[0016] Particularly preferably, a winding with conductors can be embedded in the stator slots of the stator according to the invention. A conductor is in particular an electrically conductive conductor with two parallel conductor sections whose lengths are significantly greater than their diameters. The conductor sections can in principle have any cross-sectional shape other than a circular shape. Rectangular cross-sectional shapes are preferred, as these allow high packing and consequently power densities to be achieved. Most preferably, a conductor is made of copper. Preferably, a conductor has insulation. To insulate the conductors, for example, mica paper, which for mechanical reasons can be reinforced by a glass fabric carrier, can be wound in strip form around one or more windings impregnated with a hardening resin.In principle, it is also possible to use a curable lacquer layer without mica paper to insulate a conductor.
[0017] Most preferably, the winding is designed as a hairpin winding or wave winding. In this context, it is further preferred that the conductors are designed as hairpin conductors.
[0018] The stator according to the invention preferably further comprises a stator body. The stator body can be formed in one piece or in multiple pieces, in particular segmented. A one-piece stator body is characterized in that the entire stator body is formed in one piece over its circumference. The stator body is generally formed from a plurality of stacked laminated electrical sheets, each of the electrical sheets being formed to form a closed circular ring. A segmented stator body is characterized in that it is constructed from individual stator segment parts. The stator body can be constructed from individual stator teeth or stator tooth groups, each individual stator tooth or each individual stator tooth group being formed from a plurality of stacked laminated electrical sheets, each of the electrical sheets being designed as a stator segment sheet part.
[0019] The stator body is preferably formed from one or more stator lamination stacks. A stator lamination stack is understood to be a plurality of laminated individual laminations or stator laminations, usually made of electrical steel, which are stacked and stacked together to form a so-called stator lamination stack. The individual laminations can then be held together in the lamination stack, for example, by gluing, welding, or screwing.
[0020] The stator teeth of the stator are preferably formed in the stator body. Stator teeth are components of the stator body that are circumferentially spaced, tooth-like, radially inwardly directed parts of the stator body, with an air gap for the magnetic field formed between their free ends and a rotor body. The air gap is the gap existing between the rotor and the stator. In a radial flux machine, this is a substantially circular gap with a radial width that corresponds to the distance between the rotor body and the stator body.
[0021] The stator is particularly intended for use in an electric machine within a drive train of a motor vehicle. The electric machine is particularly intended 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 of greater than 50 km / h, preferably greater than 80 km / h and in particular greater than 100 km / h can be achieved. The electric machine particularly preferably has an output of greater than 30 kW, preferably greater than 50 kW and in particular greater than 70 kW. It is furthermore preferred that the electric machine provides speeds of greater than 5,000 rpm, particularly preferably greater than 10,000 rpm, very particularly preferably greater than 12,500 rpm.
[0022] According to an advantageous embodiment of the invention, it can be provided that the majority, preferably all, of the electrical conductors have a substantially rectangular cross-section. The advantage of this embodiment is that generally standard electrical conductors can be used to form the stator winding, which is particularly advantageous in terms of stator manufacturing costs.
[0023] The cooling fluid in the stator according to the invention has the function of dissipating heat as efficiently as possible from heating areas of the stator and preventing undesirable overheating of these areas. In addition to this main task, the cooling fluid can also provide lubrication and corrosion protection for moving parts and the metal surfaces of the cooling system of the electric machine. Furthermore, it can also, in particular, dissipate contaminants (e.g., from abrasion), water, and air. The cooling fluid is preferably a liquid. The cooling fluid can, in particular, be an oil. In principle, however, it is also conceivable to use aqueous cooling fluids, for example, emulsions such as water-glycol mixtures.
[0024] The stator's cooling fluid can be connected to a hydraulic cooling system with a hydraulic cooling circuit. Such a hydraulic cooling system serves to dissipate the heat generated within an electrical machine due to electrical losses. Such a cooling system can have cooling channels within the rotor (rotor cooling channel) and / or stator (stator cooling channel) and, in particular, also a flow through the stator slots, through which a corresponding cooling fluid is guided to dissipate the heat.
[0025] The cooling fluid can particularly preferably be pumped through the hydraulic circuit by means of a pump. It is generally conceivable for a plurality of hydraulic circuits to be configured to cool the electric machine. In this case, it is highly preferred for the cooling channels of the stator to be connected to a hydraulic cooling circuit or to various cooling circuits of the cooling system. In particular, by connecting to multiple cooling circuits, it is possible to provide more precise cooling, since, for example, the temperature of the cooling fluid upon entering the cooling channels of the stator, the flow rate of the cooling fluid, or even the type of cooling fluid (oil, emulsion) can be adjusted.
[0026] The stator slots are preferably closed by a slot closure means so that the cooling fluid cannot flow from the stator slots into the air gap between the rotor and stator. The slot closure means is particularly preferably a slot closure wedge.
[0027] It may be advantageous for the conductor sections adjacent in the radial direction to be twisted along their longitudinal extent. It is generally conceivable for each conductor section to be twisted in a stator slot. Furthermore, it is also possible to twist only every other conductor section in the radial direction.
[0028] According to an advantageous embodiment of the invention, it can be provided that the conductor sections adjacent in the radial direction are twisted in the same or opposite directions along their longitudinal extent, whereby the fluidic cross-section within the stator slots can be further influenced. In the case of torsion in the same direction, it is further preferred that the adjacent conductor sections are twisted at different torsion angles.
[0029] According to a further preferred development of the invention, it can also be provided that the conductor sections accommodated in a stator slot develop a spring elasticity acting in the radial direction. This makes it possible to compensate for tolerances in the radial direction and also to fix the conductor sections in the radial direction within the stator slot.
[0030] Furthermore, according to a similarly advantageous embodiment of the invention, it can be provided that conductor sections accommodated in a stator slot and adjacent in the radial direction have a corrugation extending axially in phase in the circumferential direction. The advantageous effect of this embodiment is based on the fact that the winding can thus also be fixed in the slots in the circumferential direction by spring force.
[0031] According to a further particularly preferred embodiment of the invention, it can be provided that conductor sections accommodated in a stator slot and adjacent in the radial direction have an axially phase-shifted, in particular anti-phase, corrugation in the circumferential direction.
[0032] In particular, this makes it possible to achieve the effect that, when a spring force is provided that also acts in the circumferential direction, an improved, because more uniform, cooling performance can be achieved in the axial extension of the groove.
[0033] In principle, the elasticity of the corrugation can compensate for tolerances and thermal expansion of the conductor sections relative to the stator slots.
[0034] The torsion of the conductor sections and their corrugation can thus create a type of elongated wave spring, the properties of which can be varied according to a given application. For example, the torsion and corrugation can be configured so that the conductor sections mutually support each other on the opposite slot walls of a stator slot. The conductor sections can also be designed so that the conductor sections mutually support each other in the radial direction. Furthermore, it is also possible for the conductor sections to be subject to play, free of play, or specifically preloaded in both spatial directions.
[0035] It is also preferred that the conductor sections accommodated in a stator slot and adjacent in the radial direction contact each other in the radial direction. Furthermore, by appropriately selecting the torsion and corrugation of the conductor sections, it is possible to form only point and / or line contacts between the conductor sections of the conductors and with the slot walls. In the case of line contacts, these are in the direction of flow, so that only in the line contact does no fluid flow, but no "dead water areas" are created, so that no or only very limited fine abrasion can accumulate in front of or behind the contact in the direction of flow. Furthermore, the flow cross-section per hairpin side then fluctuates only slightly, which leads to only minimal crossflows and thus promotes uniform flow velocities, uniform heat dissipation, and low flow resistance.
[0036] Furthermore, the invention can also be further developed in such a way that the winding has a first group of conductors, wherein the first group of conductors has two parallel conductor sections positioned in different stator slots of the stator, wherein at least one of the conductor sections is twisted along its longitudinal extent.
[0037] The advantage of this design is that a stator slot through which cooling fluid can flow can be formed by only one group of conductors, in that the conductors, in particular the Hairp conductors, are inserted into the stator slots alternately rotated by 180° around their longitudinal axis, for example.
[0038] In a likewise preferred embodiment of the invention, it can also be provided that the first group of conductors has two parallel conductor sections positioned in different stator slots of the stator, wherein both conductor sections are twisted in opposite directions along their longitudinal extent, for example. This can, for example, prevent assembly errors when inserting the conductors into the stator slots.
[0039] It may also be advantageous to further develop the invention in such a way that the winding of the stator is formed from the first group of conductors, which promotes cost-effective production due to the high degree of uniformity.
[0040] In principle, however, it would also be possible to provide a second group of conductors with a twisting of the conductor sections that differs from the first group of conductors, which can create additional degrees of freedom in the design of the flow-through cross-section in a stator slot.
[0041] Finally, the object of the invention can also be achieved by a kit of parts for forming a stator winding comprising a first group of conductors, wherein the first group of conductors has two parallel conductor sections that can be positioned in different stator slots of the stator, wherein at least one of the conductor sections is twisted along its longitudinal extent. The kit of parts can, for example, be a packaging unit.
[0042] The invention will be explained in more detail below with reference to figures without limiting the general inventive concept.
[0043] It shows:
[0044] Figure 1 shows an electric radial flux machine in a cross-sectional view,
[0045] Figure 2 shows an electric radial flux machine in an axial section view,
[0046] Figure 3 is an axial sectional view through a stator slot with twisted conductor sections of the conductors,
[0047] Figure 4 is a cross-sectional view of a first embodiment of conductor sections in a stator slot at different axial positions,
[0048] Figure 5 is a cross-sectional view of a second embodiment of conductor sections in a stator slot at different axial positions,
[0049] Figure 6 is a plan view of a stator slot with conductor sections in different corrugations,
[0050] Figure 7 shows a kit of parts for forming a winding of a stator in a schematic representation,
[0051] Figure 8 shows a motor vehicle with an electric drive train in a schematic block diagram. Figures 1 and 2 show a stator 1 for an electric machine 2, in particular within a drive train 3 of a motor vehicle 4, as also sketched in Figure 8. The stator 1 is cylindrical in shape and has a plurality of stator teeth 5, which each define a stator slot 6 extending in the radial direction between adjacent stator teeth 5 and running axially through the stator 1, with two slot side walls 15 and a slot base 16, into which a current-carrying winding 7 comprising a plurality of conductors 8 is inserted. In the exemplary embodiment shown, the winding 7 is designed as a hairpin winding and the conductors 8 as hairpin conductors.
[0052] The conductors 8 have two conductor sections 9a, 9b that run parallel in axial extension and are arranged in the stator slots 6. These conductor sections have a non-circular cross-sectional contour. In the illustrated embodiments, the conductor sections 9a, 9b have a rectangular cross-sectional contour. The conductor sections 9a, 9b each emerge from the stator 1 at an end face 14 of the stator 1 with two free conductor ends 10, forming a winding head 11. The conductor sections 9a, 9b have a substantially rectangular cross-sectional contour.
[0053] The stator slots 6 of the stator 1 can be flowed through by a cooling fluid 12, which will be explained in more detail below with reference to Figures 3-5.
[0054] As can be seen from a synopsis of Figures 3-5, in a stator slot 6 at least one of two conductor sections 9a, 9b adjacent in the radial direction is twisted along its longitudinal extent.
[0055] It is also apparent from the figure that the conductor sections 9a, 9b adjacent in the radial direction are twisted in the same or opposite directions along their longitudinal extent. It is also clearly evident from Figures 4-5 that the conductor sections 9a, 9b accommodated in a stator slot 6 form a spring elasticity acting in the radial direction.
[0056] As shown in Figure 5, in this embodiment, the conductor sections 9a, 9b, which are accommodated in a stator slot 6 and are adjacent in the radial direction, have an axially phase-shifted, or more precisely, antiphase, corrugation 13 in the circumferential direction, which can also be clearly seen from the alternating radial contact of the conductor sections 9a, 9b with the slot side walls 15. In contrast, the embodiment shown in Figure 4 does not have a corrugation 13.
[0057] The hairpin winding 7 has a first group of hairpin conductors 21, which has two parallel conductor sections 9a, 9b positioned in different stator slots 6 of the stator 1, wherein at least one of the conductor sections 9a, 9b is twisted along its longitudinal extent. It is also conceivable in principle for the first group of conductors 21 to have two parallel conductor sections 9a, 9b positioned in different stator slots 6 of the stator 1, wherein both conductor sections 9a, 9b are twisted along their longitudinal extent. In the embodiments shown, the hairpin winding 7 of the stator 1 is formed exclusively from a first group of hairpin conductors 21.
[0058] Figure 6 particularly clearly shows the various possibilities for providing the conductor sections 9a, 9b with a corrugation 13. In the top image of Figure 6, the conductor sections 9a, 9b arranged radially one above the other in a stator slot 6 are provided with an in-phase corrugation 13. In other words, the conductor sections 9a, 9b are congruent when viewed from above onto the stator slot 6. The middle image shows an embodiment in which the conductor sections 9a, 9b have an anti-phase corrugation 13. In the embodiment shown, the corrugations 13 are essentially sinusoidal, so that with an anti-phase design, one conductor section 9a follows a sine curve and another conductor section 9b follows a cosine curve. The lower image in Figure 6 shows two conductor sections 9a, 9b that have a phase offset from one another.Even if in the exemplary embodiments the conductor sections 9a, 9b have a sinusoidal corrugation 13, it is of course conceivable that the corrugation 13 can also have a different wave-like shape, such as a zigzag or sawtooth-like course.
[0059] It is understood that the corrugation 13 and the torsion of the conductor sections 9 can be combined with each other as desired in order to form a defined flow of cooling fluid 12 through a stator slot 6.
[0060] Figure 7 shows a kit of parts 20 for forming a hairpin winding 7 of a stator 1 comprising a first group of hairpin conductors 21, wherein the first group of hairpin conductors 21 has two parallel conductor sections 9a, 9b that can be positioned in different stator slots 6 of the stator 1, wherein at least one of the conductor sections 9a, 9b is twisted along its longitudinal extent.
[0061] 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.
[0062] List of reference symbols
[0063] 1 stator
[0064] 2 electric machine
[0065] 3 Drivetrain
[0066] 4 Motor vehicle
[0067] 5 stator teeth
[0068] 6 Stator slot
[0069] 7 winding
[0070] 8 conductors
[0071] 9 ladder sections
[0072] 10 conductor ends
[0073] 11 winding head
[0074] 12 Cooling fluid
[0075] 13 Corrugation
[0076] 14 Front side
[0077] 15 groove side walls
[0078] 16 Groove base
[0079] 20 kits of parts
[0080] 21 first group of leaders
Claims
Claims 1 . Stator (1) for an electrical machine (2), in particular within a drive train (3) of a motor vehicle (4), wherein the stator (1) is cylindrically ring-shaped and has a plurality of stator teeth (5), which in the circumferential direction between adjacent stator teeth (5) each define a stator slot (6) extending in the radial direction and extending in the axial direction through the stator (1), with two slot side walls (15) and a slot base (16), into which a current-carrying winding (7) comprising a plurality of conductors (8) is inserted, wherein the conductors (8) have two conductor sections (9a, 9b) extending parallel in the axial direction and arranged in the stator slots (6), which have a contour deviating from the circular shape in cross section, and which are connected to an end face (14) of the stator (1) with two free conductor ends (10) each, forming a winding head (11) from the stator (1 ) leave,wherein the stator slots (6) can be flowed through by a cooling fluid (12), characterized in that in a stator slot (6) at least one of two conductor sections (9a, 9b) adjacent in the radial direction is twisted along its longitudinal extent.
2. Stator (1) according to claim 1, characterized in that the conductor sections (9a, 9b) adjacent in the radial direction are twisted in the same direction or in opposite directions along their longitudinal extent 3. Stator (1) according to one of the preceding claims, characterized in that the conductor sections (9a, 9b) accommodated in a stator groove (6) form a spring elasticity acting in the radial direction. Stator (1) according to one of the preceding claims, characterized in that conductor sections (9a, 9b) accommodated in a stator slot (6) and adjacent in the radial direction have a corrugation (13) extending axially in phase in the circumferential direction. Stator (1) according to one of the preceding claims, characterized in that conductor sections (9a, 9b) accommodated in a stator slot (6) and adjacent in the radial direction have a corrugation (13) extending axially out of phase, in particular in antiphase, in the circumferential direction. Stator (1) according to one of the preceding claims, characterized in that the winding (7) has a first group of conductors (21), wherein the first group of conductors (21) has two parallel conductor sections (9a, 9b) positioned in different stator slots (6) of the stator (1), wherein at least one of the conductor sections (9a, 9b) is twisted along its longitudinal extent.Stator (1) according to claim 6, characterized in that the first group of conductors (21) has two parallel conductor sections (9a, 9b) positioned in different stator slots (6) of the stator (1), wherein both conductor sections (9a, 9b) are twisted along their longitudinal extent. Stator (1) according to one of the preceding claims, characterized in that the winding (7) of the stator (1) is formed from the first group of conductors (21). Stator (1) according to one of the preceding claims, characterized in that the conductor sections (9a, 9b) have a substantially rectangular cross-sectional contour. Kit-of-parts (20) for forming a winding (7) of a stator (1), comprising a first group of conductors (21), wherein the first group of conductors (21) has two parallel conductor sections (9a, 9b) positionable in different stator slots (6) of the stator (1), wherein at least one of the conductor sections (9a, 9b) is twisted along its longitudinal extent.