Rotor for a separately excited electrical machine and method for producing a rotor for a separately excited electrical machine

Abstract

The invention relates to a rotor (1) for a separately excited electrical machine (2), comprising a rotor body (4) formed from a plurality of stacked rotor laminations (3), which forms a plurality of slots (5) extending in the axial direction for receiving a winding (6), and rotor poles (7) formed in the radial direction between two of the slots (5), as well as windings (8) running in the slots (5) and enclosing the rotor poles (7), wherein the rotor laminations (3) have a first group of pole arms (9) extending in the radial direction, which are formed monolithically with the rotor laminations (3), and the rotor laminations (3) further have a second group of pole arms (10) extending in the radial direction, which are connected to the rotor laminations (3) in a form-fitting and / or force-fitting and / or material-fitting manner, wherein the second group of pole arms (10) has a tooth width (X),which is smaller than the tooth width (Y) of the first group of pole arms (9).,

Description

The present invention relates to a rotor for a separately excited electric machine, comprising a rotor body formed from a plurality of laminated rotor laminations, which body forms a plurality of slots extending in the axial direction for receiving a winding, and rotor poles which are formed in the radial direction between in each case two of the slots, and windings which run in the slots. The invention further relates to a method for producing a rotor for a separately excited electric machine.In motor vehicles, electric machines are increasingly used for the drive in order to create alternatives to internal combustion engines that require fossil fuels. In order to improve the suitability of electric drives for all days and in addition to be able to offer users the usual riding comfort, considerable efforts have already been made.In the development of electric machines, which are provided in particular for E-axles or hybrid modules, there is a continuing need to increase their power densities and efficiency and at the same time to reduce the production costs. In this context, it is also known to design the electric machines as a separately excited synchronous machine (FSM). A separately excited synchronous machine is a special form of the synchronous machine in which the magnetic field in the rotor is not generated by permanent magnets but by energizable coils. The coils are frequently also referred to as field coils or excitation coils. To energize the coils in the rotating rotor, the current must be supplied via suitable transformer devices.In such rotors for externally excited electric machines, there is a particular technical challenge in the winding of the rotor. As a rule, FSM rotor assemblies produced in full section with small slot openings cannot be wound by means of the very economical (short cycle time) flyer winding method.The flyer winding method is a method known from the prior art for producing coils for the rotors of electric machines. In the flyer winding method, a flyer, a rotating tool, is used to wind the wire around the rotor precisely and uniformly. The rotor is clamped in a device which controls its rotation during the winding process. The wire is fed from a supply roll and passed through the flyer which rotates about the component to be wound. This method is particularly effective for mass production because it provides an automated and fast method of handling. For example, U.S. Pat. No. 6,419,181 B1 describes a method for winding a core having slots with different angular distances from one another and / or different shapes using a wing winder. This method uses different wing winders for slits with equal spacing and includes support members to distribute the wire evenly during winding.A rotor according to the preamble of claim 1 is shown in DE 10 2015 113 840 A1.DE 10 2021 212 003 A1 discloses a machine rotor for a separately excited electric synchronous machine, which comprises a carrier and a machine rotor coil. The carrier has at least one axially open receptacle, into which an associated coil segment of the machine rotor coil is axially inserted. This coil segment contains a winding and fills the receptacle radially and circumferentially. The invention aims to improve the efficiency and mechanical stability of the machine rotor.JP S56-66 146 A discloses a field device for a rotary electric machine which makes it possible to directly wind regular poles even if the number of poles is large. The invention provides that the picture poles are separable and have mounting parts to which the field windings of the adjacent field cores can be mounted. The use of spacers between the field cores does not impair the winding width of the wire, which enables efficient winding around the regular poles. This construction improves flexibility and efficiency in manufacturing rotary electric machines having a large number of poles.JP H08-9 572 A discloses a rotor for a dynamoelectric machine with salient poles, which enables simplified production even in multipolar designs. This is achieved by directly forming some of the magnetic poles in a body with the rotor core, while the remaining magnetic poles are later attached to the rotor core. The rotor core has regularly arranged projections on which coils are directly wound, and fixing grooves for mounting the separately formed magnetic poles. This construction reduces the assembly effort and permits a compact construction.When winding FSM rotor packages produced in full section, a needle winding method is therefore usually used, which entails a substantially higher cycle time and thus also higher process costs compared to a flyer winding method. Furthermore, a considerable free space must be provided in the rotor for the needle itself for this process, which negatively influences the copper fill factor in the rotor winding windows and thus also the efficiency of the overall motor via the resistance of the rotor winding.It is therefore the object of the invention to provide a rotor for a separately excited electrical machine and a method for producing a rotor for a separately excited electrical machine, which avoid or at least reduce the problems known from the prior art.This object is achieved by a rotor for a separately excited electric machine, comprising a rotor body formed from a plurality of laminated rotor laminations, which body forms a plurality of slots extending in the axial direction for receiving windings, and the rotor laminations have a first group of pole arms extending in the radial direction, which are monolithically formed with the rotor laminations, and the windings extending in the slots enclose the pole arms of the first group, so that when the windings are energized, rotor poles are formed, wherein the rotor laminations furthermore have a second group of pole arms extending in the radial direction, which are connected in a positive-locking and / or force-locking and / or firmly bonded manner to the rotor laminations of the first group.The solution according to the invention thus consists in dividing the laminated core of the rotor body into at least two different parts, the basic structure formed from the rotor laminations and the first pole arms monolithically formed with them, and the group of second pole arms which are initially separate therefrom and can be connected to the basic structure. The first group of pole arms can thereby be wound by means of a flyer winding method, whereby (apart from a necessary joining tolerance) almost the complete winding window can be filled with the winding. Only after the winding is the second group of pole arms connected to the basic structure, for example by an axial insertion and subsequent fixing.Furthermore, only the pole arms of the first group are wound around with a winding. The pole arms of the second group have no winding. In other words, only the pole arms of the first group are wound around, but not the pole arms of the wide group. The windings surrounding the pole arms of the first group form a magnetic field which is rectified in the radial direction with regard to the magnetic pole alignment, so that all pole arms of the first group form an equally n-shaped magnetic pole on their respective radial outer sides. The pole arms of the second group thus respectively form the corresponding opposite magnetic pole on their radial outer side. Thus, the number of windings is equal to the number of pole pairs of the rotor or the number of windings corresponds to half the number of poles.In order to make this possible, the rotor body preferably consists of two different types of sheet metal sections, namely the rotor sheet with the first group of pole arms (also referred to as a basic structure) monolithically formed therewith and the second group of rotor poles likewise formed from a rotor sheet.It is understood that the rotor body can also be formed from more than two groups of pole arms. In particular, it is conceivable for a third group of pole arms to be present, which, like the second group of pole arms, is connected to the rotor lamination. This embodiment is particularly preferred for forming a six-pole electric machine.The rotor lamination with the first group of pole arms further preferably has a yoke from which the first group of pole arms extends radially outwards. The yoke is preferably of annular design, in particular of circular ring-shaped design. Furthermore, it is preferred that the rotor sheet with the first group of pole arms (basic structure) has a first form-fit element in each case in the circumferential direction between two of these pole arms, into which a corresponding second form-fit means, which is formed on a polar of the second group of pole arms, can be inserted in a form-fit manner.In this context, it has proven to be particularly advantageous for the first form-fitting element or the second form-fitting element to be configured as a dovetail-like groove. Dovetail grooves offer a comparatively large contact surface and thus an improved force transmission between the connected parts, which can contribute to increasing the strength and stability of the form-fit connection. Furthermore, the typical shape of the dovetail groove also leads to a self-locking of the form-fit connection, since the counterpart wedges itself in the groove under load. Finally, a dovetail shape also allows simple assembly, since the positive locking can usually be effected by inserting the positive locking partners in the longitudinal extension of the dovetail-like groove. This has proven particularly favorable in particular in connection with the rotor according to the invention.In order to enable optimized winding by flyer winding, it has furthermore proven to be particularly advantageous for the rotor lamination to have three or four pole arms of the first group of pole arms. Accordingly, it is preferred that the electric machine is designed as a 6- or 8-pole electric machine, in particular as a separately excited synchronous machine, whereby a broad field of application for such an electric machine, in particular also in the field of traction motors for motor vehicles, can be established.As already described at the beginning, the pole arms of the second group have second form-fitting elements, with which they can be joined, for example by being pushed axially, into the first form-fitting elements of the basic structure.This allows, on the one hand, the economically particularly attractive flyer winding method to be used and, furthermore, high fill factors of winding material in the rotor grooves between two circumferentially adjacent pole arms to be achieved. A higher fill factor means that more copper or other conductive material can be placed in the grooves, leading to lower electrical losses and increased efficiency of the electric machine. Furthermore, with more winding material in the slots, the electric machine can also generate a higher power with the same size.The electrical sheets with the first group of pole arms (basic structure) are preferably arranged stacked one on top of the other in a stacked manner. The electrical sheets can be stacked by means of various methods. For example, the electric sheets can be designed as stack stacking, in which the individual sheet metal sheets are simply stacked one above the other. This is the simplest and most cost effective way of packaging, but it may result in increased magnetic loss. A lamination stack assembly may also be configured as a lamination stack in which the laminations are arranged in layers, each layer being rotated through a certain angle. Thereby, anisotropic magnetic properties can be better compensated. It is also conceivable to pack the laminations by means of a segment lamination, in which the laminations are divided into segmented parts, which are then assembled to form a complete pack, which can contribute to precise control of the magnetic properties and to a reduction in the eddy current losses. It would also be possible to design the electrical laminations as a cross-cut or skew lamination, in which the lamination laminations are cross-cut and then reassembled into a stack, whereby undesired noises and vibrations can be reduced. Finally, it would also be possible to configure the laminated core arrangement as a step-lap lamination, in which the laminated cores are then arranged such that their ends overlap, whereby the mechanical stability can be increased and magnetic losses can be reduced. It is also possible to process electrical laminations into a rotor body by a die-cutting lamination process. In this process, the electrical sheets are stamped and the stamped parts are not simply stacked, but instead they are already connected to one another in the stamping press. This is done by forming certain areas of the sheets out of the plane of the sheets to join the closest sheet in the direction of the punching operation.The electrical sheets having the first group of pole arms (basic structure) can furthermore be impregnated by means of a baking lacquer. When manufacturing the rotor of the electric machines, it is therefore advantageous that the individual sheet metal layers of the laminated core provided for the rotor body are insulated and stabilized. A frequently used method for achieving this is the dipping method (also known as vacuum pressure impregnation), in which a baking lacquer is applied to the laminated electrical core. The prepared laminated core is first immersed in a container with liquid baking lacquer, which has the property that it cures at elevated temperatures. A vacuum and pressure phase then follows, wherein the vacuum phase initially helps to remove air bubbles and moisture from the laminated core and to ensure that the paint penetrates into the intermediate spaces between the laminated layers. A hydraulic pressure is then built up in order to press the lacquer deeper into the laminated core and to ensure good penetration. After the dipping process, the laminated core is heated in order to allow the lacquer to cure. The curing process varies depending on the type of baking lacquer used, but it leads to the lacquer becoming solid and forming an insulating and stabilizing layer. Post-processing of the cured baking lacquer may be necessary in order to remove excess lacquer or to perform smaller shape corrections.The application of the baking lacquer to the electrical sheets can also be effected by means of a method selected from the group of the spraying methods, roller methods, impregnation methods and / or powder coating methods.According to an advantageous embodiment of the invention, it can be provided that the number of polarames of the first group corresponds to the number of pole arms of the second group. If the number of pole arms in both groups is equal, a symmetric magnetic field is generated, which may contribute to more uniform torque production and avoid or reduce imbalance that could lead to vibrations or inefficient operation of the electric machine.According to a further preferred development of the invention, it can also be provided that the pole arms of the first group and the pole arms of the second group are arranged in each case alternately in the circumferential direction of the rotor body. An alternating arrangement of the two groups of pole arms can lead to a more uniform torque profile, since the magnetic forces act more uniformly on the rotor, which contributes to a reduction of vibrations and an increase of the running smoothness of the electric machine.Furthermore, according to a likewise advantageous embodiment of the invention, it can be provided that the second group of pole arms is formed from a plurality of stacked electric sheets. The lamination of the laminations reduces eddy current losses in the second group of pole arms.In principle, it would be possible for the pole arms of the second group to be formed from a material which differs from the material of the first group and is adapted to the specific function of the second group of pole arms.According to a further particularly preferred embodiment of the invention, it can be provided that the first group of pole arms and the second group of pole arms are formed from a metal sheet with an identical material thickness and material composition. This can achieve in particular the effect that the basic structure and the second group of pole arms are manufactured from an identical sheet metal, which allows a correspondingly economical production of the rotor body.The object of the invention can also be achieved by a method for producing a rotor for a separately excited electrical machine, comprising the following steps:providing a rotor body formed from a plurality of laminated rotor laminations, which body forms a plurality of slots extending in the axial direction for receiving a winding, wherein the rotor laminations have a first group of pole arms extending in the radial direction, which are formed monolithically with the rotor laminations;providing a second group of pole arms which can be connected to the rotor laminations in a positive-locking and / or non-positive-locking and / or firmly bonded manner and wherein the pole arms of the first group and the pole arms of the second group can each be positioned alternately in the circumferential direction of the rotor body;winding the first group of pole arms with windings,connecting the pole arms of the second group to the rotor laminations.This procedure permits, on the one hand, the use of the economically advantageous flyer winding method and, on the other hand, the achievement of high filling factors of winding material in the rotor grooves between two adjacent pole arms. An increased fill factor implies that a larger volume of copper or other conductive material may be accommodated in the grooves, resulting in reduced electrical losses and increased efficiency of the electric machine. With an increased volume of winding material in the slots, it is also possible for the electric machine to produce a higher power with unchanged size, which contributes to an improved power density. In a likewise preferred embodiment variant of the invention, it can therefore also be provided that the first group of pole arms is wound by means of a flyer winding method.It can also be advantageous to further develop the invention to the effect that the rotor laminations and the second group of pole arms are formed from a common lamination, whereby in particular cost savings can be achieved, since on the one hand less material waste arises and on the other hand the complexity in the semi-finished logistics for producing the rotor body is reduced. The second group of pole arms can preferably be separated, preferably stamped, from a sheet or coil.Furthermore, it can also be preferred that the second group of pole arms is manufactured from a grain-oriented sheet metal.According to the invention, the second group of pole arms has a tooth width which is smaller than the tooth width of the first group of pole arms, which can contribute to higher filling degrees in the rotor grooves. In particular, the second group of pole arms may have narrower pole arms if it is stamped from a material with a higher saturation flux density, such as a grain-oriented sheet metal.According to a further preferred embodiment of the subject matter of the invention, it can be provided that the longitudinal extension of the second group of pole arms is oriented parallel to the rolling direction of the sheet metal from which the second group of pole arms is formed. Since the rotor laminations and the second group of pole arms can be stamped individually, they can be stamped out in the lamination in a positioned manner in the rolling direction. This makes it possible to realize further advantages by using grain-oriented sheet metal, such as, for example, lower iron losses in the second group of pole arms and / or higher saturation flux densities. Due to a higher saturation flux density, the pole arms of the second group can also be narrower in the circumferential direction than the pole arms of the first group. This mechanically produces an asymmetry between the pole types (depending on the current direction, for example, all north poles part of the basic structure, all south poles in the second group of pole arms), but not in the magnetic circuit itself. If the pole arms of the second group are now made narrower than the pole arms of the first group, this can contribute to a low dead weight of the pole arms of the second group, as a result of which the centrifugal force caused by the dead weight and the material load associated therewith can also be lowered. Furthermore, a larger winding window can also be provided by narrower pole arms of the second group, which in turn optimizes the winding process and the fill factor achievable therewith.Finally, the invention can also be advantageously embodied to the effect that after the connecting of the pole arms of the second group to the rotor laminations, a bandage is arranged on the outer jacket of the rotor. This allows an increased rotational speed stability of the rotor to be achieved. The bandage also contributes to the rotor being able to be operated reliably at particularly high rotational speeds. A main function of such a bandage is thus in particular to mechanically stabilize the windings of the rotor. At high speeds, large forces can act on the windings due to centrifugal forces. The bandage absorbs these forces and prevents the coils from coming out or slipping out. Furthermore, a bandage also protects the rotor windings from external influences such as dust, moisture or mechanical damage. A bandage is preferably formed from a high-strength material, in particular selected from the group of the fiber composites, glass fiber materials, carbon fiber materials or special metal alloys. These materials provide high tensile strength and at the same time are lightweight so as not to adversely affect rotor dynamics. Preferably, a bandage is constructed in the form of a ring or a plurality of rings lying one inside the other, which engage around the outer casing of the rotor. An insulating layer may be provided between the rotor and the casing to ensure electrical insulation and to compensate for thermal expansion differences.In summary, the invention thus offers significant advantages with respect to the formed winding windows, on the one hand the possible copper fill factor which is very large due to the type of winding and, on the other hand, the size of the winding window which is higher due to grain-oriented sheet metal and thus narrower pole arms of the second group.Furthermore, depending on the specific geometry and mechanical utilization (stresses in the sheet metal), it may also be useful to change from a copper winding to an aluminum winding, which may likewise contribute to the realization of a cost-optimized rotor.The invention will be explained in more detail below with reference to figures without limiting the general concept of the invention.It shows: FIG. 1 shows a separately excited electric machine in a schematic axial sectional representation, FIG. 2 shows a rotor of a separately excited electric machine in a cross-sectional illustration, FIG. 3 shows a rotor with a bandage in a cross-sectional illustration, FIG. 4 shows the rotor known from FIG. 2 in a perspective view, FIG. 5 shows the wound rotor without the second group of pole arms in a perspective and a cross-sectional illustration, FIG. 6 shows the second group of pole arms in an assembled state and an unmounted state in a cross-sectional illustration in each case, FIG. 7 shows three different sheet metal section configurations for producing the rotor body in each case in a plan view.FIG. 1 first shows a energizable rotor 1 which is rotatably mounted in a hollow cylindrical stator 19 of the externally excited electric machine 2. It can be seen well from the hatching that the rotor body 4 of the rotor is formed from a plurality of laminated rotor laminations 3.It can be clearly seen in FIGS. 2 to 4 that a plurality of slots 5 are provided in the rotor body 4 distributed in the circumferential direction and extending in the axial direction for receiving a winding 6. When the winding is energized accordingly, the rotor poles 7 are formed, which are formed in the radial direction between two of the slots 5. These are denoted in the figures by N and S for a magnetic north pole and south pole. The rotor laminations 3 have a first group of pole arms 9 extending in the radial direction, which are formed monolithically with the rotor laminations 3. The rotor laminations 3 further include the annular yoke 15. The windings 6 extend in the slots 5 and enclose the pole arms 9 of the first group of pole arms 9.The rotor laminations 3 also have a second group of pole arms 10 extending in the radial direction, which are connected in a positive-locking manner via the yoke 15 to the rotor laminations 3. It can also be easily seen from the figure that the pole arms 9 of the first group and the pole arms 10 of the second group are arranged in each case alternately in the circumferential direction of the rotor body 4. The number of pole arms 9 of the first group corresponds in the exemplary embodiment shown to the number of pole arms 10 of the second group.The second group of pole arms 10 is likewise formed from a plurality of stacked electric sheets 11, wherein the first group of pole arms 9 and the second group of pole arms 10 are formed from a sheet 12 having an identical material thickness and material composition.As is clearly evident from FIG. 3, a bandage 18 can be arranged on the outer casing 13 of the rotor 1.The rotor known from FIGS. 2-4 can be manufactured by means of a method described in more detail below for producing a rotor 1 for an externally excited electric machine 2. First, a rotor body 4 is provided which is formed from a plurality of laminated rotor laminations 3 and forms a plurality of slots 5 extending in the axial direction for receiving a winding 6, wherein the rotor laminations 3 have a first group of pole arms 9 extending in the radial direction, which are formed monolithically with the rotor laminations 3. Furthermore, a second group of pole arms 10 is provided, which can be connected with the rotor laminations 3 in a form-fitting manner, and wherein the pole arms 9 of the first group and the pole arms 10 of the second group can be positioned in each case alternately in the circumferential direction of the rotor body 4.First, the winding of the first group of pole arms 9 with the windings 6, as can also be seen in FIG. 5, takes place by means of a flyer winding method. After the winding, the pole arms 10 of the second group are connected to the rotor laminations 3, so that the rotor 1 shown in FIGS. 2-4 is formed. The openings 8 can be clearly seen, into which the second group of pole arms 10 is then subsequently inserted.In the exemplary embodiments, the connecting of the pole arms 10 of the second group is effected by means of a form-fit connection which has in the rotor sheet a dovetail groove 14 in which the dovetail contour 16, which is formed at the radially inner end of the pole arms 10 of the second group, can engage in a form-fit manner. The positive locking can be effected by axially inserting the second group of pole arms 10 into the respective dovetail grooves 14, which can be seen particularly well from FIG. 6. The second group of pole arms 10 has a tooth width X which may be smaller than the tooth width Y of the first group of pole arms 9, which may provide additional space for winding material in the slots 5.As can be seen from FIG. 7, the rotor laminations 3 and the second group of pole arms 10 can be formed from a common lamination 12.In this case, it can also be advantageous if the longitudinal extent of the second group of pole arms 10 is oriented parallel to the rolling direction 17 of the sheet metal 12 from which the second group of pole arms 10 is formed.The invention is not limited to the embodiments shown in the figures. The foregoing description is, therefore, not to be considered as limiting, but illustrative. The following claims should be understood to mean that a said feature is present in at least one embodiment of the invention. This does not exclude the presence of further features. If the patent claims and the above description define "first" and "second" features, this designation serves to distinguish two features of the same type without specifying a ranking.List of reference characters1 Rotor 2 Electric machine 3 Rotor plate 4 Rotor body 5 Slots 6 Winding 7 Rotor poles 8 Openings 9 Pole arms 10 Pole arms 11 Electric plate 12 Plate 13 Casing 14 Dovetail slot 15 Yoke 16 Dovetail contour 17 Rolling direction 18 Bandage 19 Stator X Tooth width Y Tooth width

Claims

Rotor (1) for a separately excited electric machine (2), comprising • a rotor body (4) formed from a plurality of laminated rotor laminations (3) and forming a plurality of slots (5) extending in the axial direction for receiving windings (6), and • the rotor laminations (3) having a first group of pole arms (9) extending in the radial direction, which are monolithically formed with the rotor laminations (3), and • the windings (6) extending in the slots (5) enclose the pole arms (9) of the first group, • so that when the windings (6) are energized, rotor poles (7) are formed, the rotor laminations (3) further having a second group of pole arms (10) extending in the radial direction, which are connected in a positive-locking and / or force-locking and / or firmly bonded manner to the rotor laminations (3) of the first group, characterized in that, the second group of pole arms (10) having a tooth width (X) which is smaller than the tooth width (Y) of the first group of pole arms (9).Rotor (1) according to Claim 1, characterized in that the number of pole arms (9) of the first group corresponds to the number of pole arms (10) of the second group.Rotor (1) according to Claim 1 or 2, characterized in that the pole arms (9) of the first group and the pole arms (10) of the second group are arranged in each case alternately in the circumferential direction of the rotor body (4).Rotor (1) according to one of the preceding claims, characterized in that the second group of pole arms (10) is formed from a plurality of stacked electric sheets (11).Method for producing a rotor (1) for a separately excited electric machine (2), comprising the following steps: - providing a rotor body (4) which is formed from a plurality of laminated rotor laminations (3) and forms a plurality of slots (5) which extend in the axial direction for receiving a winding (6), wherein the rotor laminations (3) have a first group of pole arms (9) which extend in the radial direction and are formed monolithically with the rotor laminations (3); providing a second group of pole arms (10), which can be connected to the rotor laminations (3) in a positive-locking and / or non-positive-locking and / or firmly bonded manner, and wherein the pole arms (9) of the first group and the pole arms (10) of the second group can each be positioned alternately in the circumferential direction of the rotor body (4), wherein the second group of pole arms (10) has a tooth width (X) which is smaller than the tooth width (Y) of the first group of pole arms (9); winding the first group of pole arms (9) with windings (6), connecting the pole arms (10) of the second group to the rotor laminations (3).Method according to claim 5, characterised in that the winding of the first group of pole arms (9) takes place by means of a flyer winding method.Method according to claim 5 or 6, characterised in that the rotor laminations (3) and the second group of pole arms (10) are formed from a common lamination.Method according to one of Claims 5 - 7, characterized in that the longitudinal extent of the second group of pole arms (10) is oriented parallel to the rolling direction of the sheet metal from which the second group of pole arms (10) is formed.Method according to one of Claims 5 - 8, characterized in that, after the connection of the pole arms (10) of the second group to the rotor laminations (3), a bandage is arranged on the outer casing (13) of the rotor (1).

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