Rotor and electric machine

Abstract

The invention relates to a rotor (1) for an electric machine (2), comprising a plurality of magnet elements (3) which are arranged in the rotor (1) in a distributed manner over the circumference, wherein each of the magnet elements (3) is made of magnet segments (4) which are axially fixed together, and at least one first group (11) of the magnet segments (4) and a second group (12) of the magnet segments (4), said second group being arranged at a distance to the first group (11), are separated by a reinforcing layer (6) which runs on a radial plane (5).

Description

[0001] Rotor and electric machine

[0002] The present invention relates to a rotor for an electrical machine comprising a plurality of magnetic elements arranged in the rotor in a manner distributed over the circumference, wherein the magnetic elements are each formed from magnetic segments fixed axially relative to one another. The invention further relates to an electrical machine.

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

[0005] A particular challenge in the manufacture and operation of a rotor of an electrical machine is the design and arrangement of the magnetic elements in a rotor.

[0006] Such rotors of internal rotors with surface magnets, especially in high-speed applications, are provided with a pre-tensioned bandage to prevent the magnets from lifting due to centrifugal force. Direct bonding of the magnets is often not safe and is therefore avoided. Banding is very easy to design and, using modern fiber composite materials, can be made very thin and with little or no eddy current losses. However, the increased magnetic air gap caused by the wall thickness of the bandage always remains a disadvantage of this system.

[0007] It is generally known to circumvent this problem by using form-fitting magnet mounts, as described, for example, in DE102008055893A1. However, this requires replacing the magnet material with structural material, especially near the air gap. Furthermore, due to the resulting high local stresses and the brittle nature of rare-earth magnets, these magnets are only suitable for high to very high speeds to a limited extent.

[0008] Another important aspect in the design of rotors for high-speed electrical machines is the reduction of eddy currents. These currents form in any conductive material in the motor's alternating field, in the normal plane to the magnetic field lines. The larger the surface area and the greater the electrical conductivity of the material, the greater these currents and their resulting losses. Therefore, it is common practice to segment all conductive materials, such as iron or magnets. For this purpose, lamination stacks made of thin laminations, e.g., bonded with self-bonding varnish, are used in iron.

[0009] With permanent magnets, the segmentation doesn't need to be as fine due to their lower conductivity and less fluctuating magnetic field. However, for very demanding applications, segmentations of a few millimeters down to 0.5 mm are used. These segments are then glued together, for example, to form stacks and then magnetized.

[0010] It is therefore the object of the invention to provide a rotor of an electrical machine which is optimized with regard to its production and use in high-speed applications. It is also the object of the invention to realize an improved electrical machine. This object is achieved by a rotor for an electrical machine, comprising a plurality of magnetic elements which are arranged in the rotor in a manner distributed over the circumference, wherein the magnetic elements are each formed from magnetic segments which are fixed axially to one another, wherein a first group of magnetic segments and at least one second group of magnetic segments which is axially spaced from the first group are separated from one another by a reinforcing layer running in a radial plane.

[0011] Preferably, the first group of magnet segments and the second group of magnet segments are axially directly adjacent, so that the reinforcement layer is in contact with both the first group of magnet segments and the second group of magnet segments. However, it would also be conceivable for a further group of magnet segments to be arranged axially between the first and second groups of magnet segments, so that the reinforcement layer is in contact with either only the first group or the second group of magnet segments.

[0012] Most preferably, the magnet segments of the magnet elements are each axially separated from one another by a reinforcing layer running in a radial plane.

[0013] This provides the advantage that the magnetic elements can be securely attached to or in a rotor without further enlarging the magnetic air gap or displacing large portions of the magnetic material. One of the core ideas of the invention is therefore to use the segmentation of the magnetic elements not only to reduce eddy currents, but also to introduce, for example, in the adhesive gap between two adjacent magnetic segments, in addition to an adhesive, a reinforcing layer that dissipates the centrifugal forces preferably radially inward into the rotor shaft and / or, for example, tangentially to a hoop stress. Depending on the application, the reinforcing layers could be introduced into the magnet stack in each segmentation gap or just at intervals. This allows the mechanical fixation of the magnetic segments to be achieved with minimal impact on the magnetic properties of the rotor.Preferably, a radially outer bandage of the rotor can have a very small radial thickness. Most preferably, a radially outer bandage of the rotor can be omitted.

[0014] The reinforcement layers are preferably made of materials with low electrical conductivity and high rigidity and strength, making modern fiber composites such as carbon fiber reinforced plastics particularly suitable. These can be manufactured or incorporated into the rotor structure, for example, by bonding or by direct lamination using a fiber composite process such as prepreg, wet laminate, or RTM.

[0015] The reinforcement layers preferably overlap the magnet segments across their entire surface to maximize the bonding area. A partial overlap, possibly also through a recess in a magnet segment, to maximize the magnetic material at the air gap would be conceivable, as would a continuous or localized folding of the reinforcement layer at the outer diameter of a magnet segment to generate additional form-fit. Such an embodiment can be particularly advantageous in a rotor configuration with center magnets of a Hallbach array.

[0016] First, the individual elements of the claimed subject matter of the invention are explained in the order in which they appear in the set of claims, and subsequently particularly preferred embodiments of the subject matter of the invention are described.

[0017] A rotor is the rotating part of an electrical machine. The rotor includes, in particular, a rotor shaft. The rotor shaft can be hollow, which reduces weight and allows for the supply of lubricant or coolant to the rotor body.

[0018] For the purposes of the invention, a rotor body is understood to mean the rotor without the rotor shaft. The rotor body can, for example, consist of a rotor core and the permanent magnets inserted into the pockets of the rotor core or fixed circumferentially to the rotor core, as well as any axial cover parts for closing the pockets. It is also conceivable for the permanent magnets to be positioned not in pockets but as surface magnets in the rotor body. A rotor shaft is a rotatably mounted shaft of an electrical machine to which the rotor or rotor body is rotationally coupled.

[0019] The magnetic elements can be designed, for example, as permanent magnets. Preferably, the magnetic elements are designed essentially identically. The permanent magnets can preferably be selected from the group of neodymium-iron-boron (NdFeB) magnets, samarium-cobalt (SmCo) magnets, ferrite magnets, or alnico magnets. NdFeB magnets are among the strongest commercially available permanent magnets currently available and are therefore particularly suitable for high-performance applications requiring high magnetic field strength. SmCo magnets are also powerful permanent magnets with high magnetic energy, which are particularly characterized by their high temperature resistance. Ferrite magnets, also known as ceramic magnets, are cost-effective and have good resistance to corrosion and demagnetization. Alnico magnets consist of an alloy of aluminum, nickel, cobalt, and iron.They are characterized by high remanence (residual magnetization) and good temperature resistance. Alnico magnets are often used in applications where high magnetic stability and good resistance to extreme temperatures are required.

[0020] Preferably, the magnetic elements have the same number of magnetic segments. Furthermore, it is preferred that all magnetic segments are shaped substantially identically. By using identical magnetic segments, a standardized manufacturing process can be applied. This enables mass production of the magnets, resulting in efficient and cost-effective manufacturing. Using identical molds reduces the complexity and the number of different parts that must be manufactured and managed. Furthermore, if all magnetic segments are identical, rotor assembly is also simpler and faster. The segments can be joined together in a repetitive and uniform manner without the need for complicated adjustment or individual alignment. This facilitates automated assembly and reduces labor time and the risk of errors.Identical magnet segments also allow for easier replacement in the event of repair or maintenance. If a magnet segment is damaged, it can be easily replaced with an identical one without requiring specific adjustments or modifications to the rotor's magnetic configuration. This simplifies maintenance and reduces machine downtime. Furthermore, the use of identical magnet segments also allows for more flexible rotor design. The consistent shape of the segments allows for variations in the number of segments or the magnetic arrangement to meet the specific requirements of the application. This enables optimized rotor design and adaptation to different power and application areas.Finally, this also allows for a high degree of consistency in the magnetic properties of the rotor, as all segments undergo the same manufacturing process and therefore have similar magnetic properties, which can help to generate a uniform magnetic field.

[0021] 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 stator extend in a radial direction. The air gap is the gap between the rotor and stator. In a radial flux machine, this is a circular-ring-shaped gap in cross-section with a radial width corresponding to the distance between the rotor body and the rotor body.

[0022] In principle, in connection with this invention, it is also possible for the electrical machine to be designed as an axial flux machine.

[0023] The electric machine may further comprise a control device. A control device, as can be used in the present invention, serves in particular for the electronic control and / or regulation of one or more technical systems of the electric machine.

[0024] The electric machine is intended in particular for use within the drivetrain of a hybrid or fully electric motor vehicle. In particular, the electric machine is dimensioned such that vehicle speeds greater than 50 km / h, preferably greater than 80 km / h, and in particular greater than 100 km / h, can be achieved. The electric motor particularly preferably has an output greater than 30 kW, preferably greater than 50 kW, and in particular greater than 70 kW.

[0025] It is further preferred that the electric machine provides rotational speeds greater than 5,000 rpm, particularly preferably greater than 10,000 rpm, very particularly preferably greater than 12,500 rpm, most preferably greater than 25,000 rpm.

[0026] The electric machine can preferably also be installed in an electrically operated axle drive train. An electric axle drive train of a motor vehicle comprises an electric machine and a transmission, wherein the electric machine and the transmission form a structural unit. In particular, it can be provided that the electric machine and the transmission are arranged in a common drive train housing. Particularly preferably, such a drive train housing can also form a connection structure for the electric machine. Alternatively, it would of course also be possible for the electric machine to have a motor housing and the transmission to have a transmission housing, wherein the structural unit can then be effected by fixing the transmission relative to the electric machine. This structural unit is occasionally also referred to as an e-axle.

[0027] It is preferred that the reinforcement layers and the magnet segments are integrally bonded to one another. According to an advantageous embodiment of the invention, it can also be provided in this context that the respective reinforcement layers are bonded to the magnet segments by means of an adhesive bond, which has proven particularly advantageous in terms of manufacturing technology. Adhesives suitable for bonding reinforcement layers and magnet segments can, for example, be selected from the group of epoxy resins, polyurethanes, or acrylates. Both the reinforcement layer and the magnet segments can be ground or sandblasted, or otherwise activated, prior to bonding to ensure better adhesion of the adhesive. The adhesive can be applied to one or both sides, depending on the design requirements.The adhesive can be cured preferably at room temperature or by heat treatment. It would also be possible to bond the reinforcement layers and the magnetic elements using hot-melt bonding. The reinforcement layer can also be directly impregnated with a resin. This can be done as a prepreg, wet laminate, or using the RTM injection process.

[0028] In principle, it would also be conceivable for the reinforcement layers and the magnet segments to be bonded by sintering. This involves applying pressure and heat to create a solid bond between the reinforcement layers and the magnet segments. It is advantageous for the corresponding surface of the reinforcement layer to be made of a metallic material.

[0029] According to a further preferred development of the invention, the reinforcement layers can also be made of a fiber-reinforced material. Particularly preferably, the reinforcement layers are made of a fiber-reinforced plastic.

[0030] The reinforcement layers preferably have a layer thickness between 0.005-1 mm, preferably between 0.0075-0.5, most preferably between 0.02-0.2 mm. The use of thin reinforcement layers can improve the magnetic flux density of the machine, as this allows a higher magnetic fill factor to be achieved. A low layer thickness of the reinforcement layers enables a higher degree of lamination of the magnets with a good fill factor. This also reduces eddy current losses, as it reduces the cross-section for the eddy current paths, which leads to lower losses and improved energy efficiency. A thinner reinforcement layer also results in less material being used and thus a lower weight for both the rotor and the stator. Furthermore, installation in applications with limited space is also facilitated.Finally, by using thinner reinforcement layers, the rotor can also have a lower inertia, enabling higher speeds. This is particularly advantageous in applications where high speeds are required, such as electric vehicles or high-speed machinery.

[0031] The reinforcement layers are preferably essentially identical. The reinforcement layers can be designed as segments or rings, or a combination of both. The individual reinforcement layers can overlap or be tangentially offset from one another.

[0032] Since the fiber orientation of the reinforcement layers is preferably radial and / or tangential, only very low circular currents (eddy currents) develop. Thus, unlike in a bandage, fibers with a low electrical conductivity can also be used.

[0033] It is also conceivable that the reinforcement layers are made of non-magnetic or non-conductive material, which is generally preferred. However, it is also possible for the reinforcement layers to be made of magnetic or non-conductive material, since the reinforcement layers in a permanently excited rotor configured for a radial flux machine are not located in the radial magnetic flux direction and therefore do not impede it.

[0034] Furthermore, it is preferred that the rotor does not have an outer band. The absence of an outer band minimizes eddy current losses in the machine. In a machine with an outer band, eddy currents can occur in the band, which can lead to losses and heating. Eliminating the outer band reduces these losses and improves the efficiency of the machine. Eliminating the outer band also simplifies the manufacturing and assembly of the rotor. It eliminates the need to manufacture, machine, and assemble the band separately. This can lead to cost and time savings in production.

[0035] Eliminating the bandage makes it possible to reduce the magnetic air gap, resulting in an increase in torque yield. Eliminating the bandage, which acts as a thermal barrier, enables significantly improved heat dissipation from the rotor via the stator cooling system, as rotor losses can be transferred directly to the stator core.

[0036] Particularly preferably, the rotor is configured as a permanently excited rotor for a radial flux machine.

[0037] Furthermore, it is preferable for the magnetic elements to be designed as surface magnets on the rotor. The magnetic elements are therefore preferably not arranged in pockets of the rotor body. Further preferably, the surface magnets, with their radially outer surface, are in direct contact with the air gap between the stator and the rotor of a radial flux machine. Surface magnets are frequently used in permanently excited rotors of electrical machines, such as permanent magnet synchronous machines (PMSM) or permanent magnet direct current machines (PMDC). These magnets can be made, for example, from neodymium iron boron (NdFeB) or samarium cobalt (SmCo), since these materials exhibit high magnetic energy and good magnetic properties.

[0038] The construction of surface magnets in a permanently excited rotor consists of several steps. First, the magnets are formed into the desired shape, which can vary depending on the application. They are preferably manufactured in rectangular or trapezoidal shapes to ensure optimal magnetic utilization. The magnets can then be attached to a metal or plastic surface, such as an inner ring, with a special adhesive or resin. This surface can either be part of the rotor or applied to the rotor. One advantage of surface magnets is their high magnetic field strength and efficiency compared to other excitation methods. They offer improved power density, lower weight and inertia, higher speeds, and better responsiveness to load changes. These advantages are particularly evident with surface magnets in the "Halbach arrangement."In addition, they enable a compact design of the machine and reduce the energy loss associated with excitation.

[0039] Furthermore, according to a likewise advantageous embodiment of the invention, it can be provided that the magnetic elements each have a first end face and a second end face, and the reinforcing layers cover the end faces, at least partially, preferably completely. Complete coverage, for example, has the advantage of a particularly good adhesive bond and thus a good force transmission from a magnetic segment to a reinforcing layer.

[0040] According to another particularly preferred embodiment of the invention, at least two axially spaced reinforcement layers can be connected to one another. This can achieve, in particular, the effect of a reinforcement layer being able to be placed around the rotor magnet segments, which can provide manufacturing advantages. Furthermore, such a connection of reinforcement layers can lead to improved power transmission.

[0041] Furthermore, the invention can also be further developed such that the rotor is designed from laminated material and that a reinforcement layer runs between at least one group of rotor laminates. It would therefore also be conceivable to additionally reinforce laminated rotors for high-speed applications with fiber composite layers. Such reinforcement layers can preferably also overlap with inner rings introduced on the inner diameter of the magnet segments, which absorb the forces of the magnet segments and further transmit the torque. In a likewise preferred embodiment of the invention, it can also be provided that the reinforcement layers are designed in the shape of an annular disk. This basically allows forces occurring during operation to be transmitted in both the circumferential and radial directions. In principle, however, reinforcement layer shapes other than the annular disk are also possible.For example, it would also be conceivable for the reinforcement layers to be designed as radially extending web-like elements that run like sunbeams from the radial inside to the outside, but are not connected in the circumferential direction.

[0042] It may also be advantageous to further develop the invention such that the rotor has a plurality of inner rings, against which the magnet segments rest radially and to which the reinforcement layers are fixed. These inner rings can also be made of fiber composite material. The inner rings can also ensure the correct positioning of the magnet segments during rotor assembly. The inner rings advantageously also ensure the transmission of force and torque to the rotor shaft by means of a force-fit or form-fit connection.

[0043] According to a further preferred embodiment of the subject matter of the invention, it can be provided that the number of inner rings corresponds to the number of magnet segments per magnet element, which can contribute to a particularly uniform power transmission and a particularly high speed stability of the rotor.

[0044] Finally, the object of the invention can also be achieved by an electrical machine comprising a rotor according to one of claims 1-9.

[0045] Such an electric machine with a permanently excited rotor can contribute to creating powerful and efficient electric drives that can be used in various applications such as electric vehicles, industrial robots, wind turbines, and other areas. The invention will be explained in more detail below with reference to figures, without limiting the general inventive concept.

[0046] It shows:

[0047] Figure 1 shows a radial flow machine in an axial section view,

[0048] Figure 2 shows a rotor section in an exploded view,

[0049] Figure 3 shows a first embodiment of a magnet segment reinforcement layer configuration in a schematic axial sectional view,

[0050] Figure 4 shows a second embodiment of a magnet segment reinforcement layer configuration in a schematic axial sectional view,

[0051] Figure 5 shows a third embodiment of a magnet segment reinforcement layer configuration in a schematic axial sectional view.

[0052] Figure 1 shows a rotor 1 for an electric radial flux machine 2 comprising a plurality of magnetic elements 3 arranged distributed over the circumference in the rotor 1, wherein the magnetic elements 3 are each formed from magnetic segments 4 fixed axially to one another. In the embodiment shown, the individual magnetic elements 3 abut one another in the circumferential direction, which can be clearly seen from Figure 2. The individual magnetic segments 4 are essentially identical. The rotor 1 constructed in this way is arranged between the cylindrical ring-like stator 10 of the radial flux machine 2. Even though Figure 1 shows a radial flux machine 2, it is of course understood that a rotor 1 according to the invention can also be used for an axial flux machine.

[0053] The magnet segments 4 are each separated from one another by a reinforcement layer 6 extending in a radial plane 5, which can be clearly seen from the comparison of Figure 1 and Figure 2. The respective reinforcement layers 6 are bonded to the magnet elements 4 by means of an adhesive.

[0054] In the illustrated embodiment, the reinforcement layers 6 are made of a fiber-reinforced material. The magnetic elements 3 each have a first end face 7 and a second end face 8, with the annular disc-like reinforcement layers 6 completely covering the end faces 7, 8.

[0055] The rotor 1 further comprises a plurality of inner rings 9, against which the magnet segments 4 radially abut and to which the reinforcement layers 6 are fixed. The number of inner rings 9 preferably corresponds to the number of magnet segments 9 per magnet element 3.

[0056] As can be seen in Figures 3-5, the rotor 1 can also have a first group 11 of magnet segments 4 and a second group 12 of magnet segments 4 axially spaced from the first group 11, wherein one or more reinforcement layers 6 can be arranged in various ways between these groups 11, 12.

[0057] In the embodiment of Figure 3, only one reinforcement layer 6 is present between a first group 11 and a second group 12 in the rotor 1, which results in a rotor 1 that is particularly compact in axial terms.

[0058] In the embodiment of Figure 4, two reinforcement layers 6 are arranged in the rotor 1, but between the two reinforcement layers 6, a magnet segment from the first group 11 and the second group 12 lies axially directly adjacent to one another. This allows, for example, a rotor 2 to be configured in which only every second rotor segment 4 is connected to a reinforcement layer 6, which still results in good radial fixation while still maintaining a very compact axial structure of the rotor 1.

[0059] Figure 5 shows a further preferred embodiment of the rotor 1, in which a reinforcement layer 6 is present between all magnet segments of the groups 11, 12, which leads to a particularly good and secure radial fixation of the magnet segments 4, in particular in high-speed applications.

[0060] 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.

[0061] List of reference symbols

[0062] 1 rotor

[0063] 2 Electric machine 3 Magnetic elements

[0064] 4 magnet segments

[0065] 5 Radial plane

[0066] 6 reinforcement layer

[0067] 7 Frontal surface 8 Frontal surface

[0068] 9 inner rings

[0069] 10 Stator

[0070] 11 first group

[0071] 12 second group

Claims

Claims 1. Rotor (1) for an electrical machine (2), comprising a plurality of magnetic elements (3) which are arranged distributed over the circumference in the rotor (1), wherein the magnetic elements (3) are each formed from magnetic segments (4) which are fixed axially to one another, characterized in that a first group (11) of the magnetic segments (4) and at least one second group (12) of the magnetic segments (4) which is spaced axially from the first group (11) are separated from one another by a reinforcing layer (6) running in a radial plane (5).

2. Rotor (1) according to claim 1, characterized in that the respective reinforcing layers (6) are connected to the magnet segments (4) by means of an adhesive connection.

3. Rotor (1) according to claim 1 or 2, characterized in that the reinforcing layers (6) are made of a fiber-reinforced material.

4. Rotor (1) according to one of the preceding claims, characterized in that the magnet segments (4) each have a first end face (7) and a second end face (8) and the reinforcing layers (6) cover the end faces (7, 8) at least in sections, preferably completely.

5. Rotor (1) according to one of the preceding claims, characterized in that at least two axially spaced reinforcement layers (6) are connected to one another.

6. Rotor (1) according to one of the preceding claims, characterized in that the rotor (1) is laminated and that a reinforcing layer (6) runs between at least one group of the rotor laminations.

7. Rotor (1) according to one of the preceding claims, characterized in that the reinforcing layers (6) are designed in the manner of an annular disc.

8. Rotor (1) according to one of the preceding claims, characterized in that the rotor (1) has a plurality of inner rings (9) against which the magnet segments (4) bear radially and to which the reinforcing layers (6) are fixed.

9. Rotor (1) according to claim 8, characterized in that the number of inner rings (9) corresponds to the number of magnet segments (9) per magnet element (3).

10. Electrical machine (2) comprising a rotor (1) according to one of the preceding claims.

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