Rotor of a permanent magnet excited electric machine

Abstract

The invention relates to a rotor (3) of a permanent magnet electric machine (1) comprising a rotor body (3a) with an outer surface (3b) and with an axis of rotation (D) and with at least one rotor pole (P1), wherein the rotor pole (P1) has a pole axis d and wherein the rotor pole (P1) has separate recesses (5) with inserted permanent magnets (8), wherein the recesses (5) form a V-shaped configuration, and wherein the rotor pole (P1) has flux guides, characterized in that the flux guides are formed by a first group and a second group of flux guides (6, 7), wherein the first group is formed by slot-like flux guides (6) provided on both sides of each permanent magnet (8) of the leg of the V-shaped configuration, and wherein the second group is formed by hole-shaped flux guides (7) separated by a web and located radially outside adjacent to the recesses (5).and that each recess (5) has a radially inward extension to the axis of rotation (D) to form a cooling channel (9).

Description

[0001] The invention relates to a rotor of a permanent magnet excited electrical machine. State of the art

[0002] Permanent magnet electrical machines typically have a rotor that rotates around a rotational axis within a stator. An air gap exists between the stator and rotor. The stator contains energizable windings, and the rotor has permanent magnets that form the rotor poles for generating a magnetic field.

[0003] Rotors for electric machines are available in a wide variety of designs. Electric machines with internal permanent magnets are called IPM machines. IPM machines are often used to power hybrid electric vehicles because they are characterized by good torque density and high overall efficiency.

[0004] A disadvantage of an IPM machine, however, is that the permanent magnetic field is present even when the machine is not supplied with power, which leads to losses induced by the rotating permanent magnetic field of the rotor. Furthermore, the permanent magnetic field induces a voltage ("back EMF") in the stator winding. In a machine with a strong permanent magnet, this back EMF can be quite significant.

[0005] Motor engineers have developed environmentally friendly, high-efficiency motors in response to increased demands for energy efficiency and environmental standards. The simplest way to increase motor efficiency is to use high-energy rare-earth magnets and low-loss electrical steel sheets. However, this approach is expensive. Recently, many novel or hybrid topologies of indoor permanent magnet (IPM) motors have been proposed to increase motor efficiency instead of using expensive materials.

[0006] To reduce manufacturing costs, it is known from DE 10 2014 102 411 A1 to design the rotor core for a mixed assembly of magnets made of different materials. The recesses for accommodating the permanent magnets are arranged in an interleaved V-shape on the inside and an outer V-shape on the outside.

[0007] From the document US 2009 / 0 140 593 A1, for example, a rotor of an IPM motor is known with a rotor body having an axis of rotation and with at least one rotor pole, wherein the rotor pole in a first embodiment has a first pair of V-shaped recesses, into each of which a first set of permanent magnets is inserted.

[0008] This well-known magnet arrangement, consisting of a set of permanent magnets, is based on the so-called single-V rotor topology. The permanent magnets are arranged to form a V-arrangement within a rotor pole. To further optimize the IPM machine, the recesses for accommodating the permanent magnets are designed such that each cavity has a total volume, with each cavity only partially filled with the permanent magnet, thus forming air barriers.

[0009] The aforementioned single-V rotor topology generally exhibits high torque and power density due to the strong magnet and a significant reluctance torque component. However, such high magnetic flux requires a strong flux weakening current when the motor operates at high speeds, which reduces the motor's efficiency, especially at low loads and highway speeds, and reduces the machine's constant power and speed capabilities.

[0010] Another IPM machine with a rotor based on the so-called double-V rotor topology is known from DE 10 2016 212 022 A1. Here, two pairs of permanent magnets are nested in a V-shaped arrangement. To optimize the IPM machine, particularly to increase the base torque and the reluctance torque, the rotor includes, as additional design features, square flux-directing recesses between the radially inner ends of the legs of the permanent magnets of the first V-shaped arrangement.

[0011] CN 1 03 872 819 A shows a permanent magnet machine in which permanent magnets are inserted into slots in the rotor, which are V-shaped relative to a radius of the rotor and installed with different flux guides.

[0012] DE 10 2019 106 721 A1 shows a permanent magnet machine with V-shaped magnets, wherein a pocket is formed which serves as a cooling channel.

[0013] CN 1 17 394 560 A shows an electric machine with permanent magnet rotors, some of which are arranged in a V-shape. In one embodiment, the associated flux guides have a herringbone-like arrangement, but only with permanent magnets that extend radially outward and not with permanent magnets arranged in a V-shape.

[0014] CN 2 10 074 911 U shows a permanent magnet machine with V-shaped magnets. There are flux guides extending from the permanent magnets toward the edge of the rotor. The other openings serve to dissipate heat.

[0015] It is therefore an object of the invention to propose a further optimized rotor of a permanent magnet excited electrical machine, wherein in an IPM machine provided with the optimized rotor, in particular field-related losses are to be reduced, while a back EMF is to be minimized.

[0016] This object is achieved by a rotor having the features of claim 1.

[0017] The rotor of a permanent-magnet electric machine comprises a rotor body with an outer surface and a rotational axis D, and with at least one rotor pole P1. The rotor pole P1 has a pole axis d, and the rotor pole P1 has separate recesses with inserted permanent magnets. The recesses form a V-shaped configuration, and the rotor pole has flux guides. The rotor is designed with the following rotor features according to the invention.

[0018] Flux guides are incorporated into the rotor, forming a first group and a second group. The first group of flux guides is formed by slot-like flux guides inserted on both sides of each permanent magnet of the leg of the V-shaped configuration.

[0019] Depending on their design and arrangement, these flux guides can serve both as barriers to the q-axis flux and as flux conductors for the d-axis flux. The slot-like recesses can be thick enough to reverse the rotor salience (limb polarization) (referred to in the technical literature as flux-enhanced or inverse salience or normal salience IPM), or thin enough to improve the magnetic behavior of the machine (in terms of MTPA or demagnetization resistance, etc.). The flux guides, as air pockets of the first group, act as a barrier to the permanent magnets and reduce the magnetic flux, thus reducing the back EMF of the electric machine and the losses induced by the permanent magnet.

[0020] The slot-shaped recesses of the first group of flow guides reduce the “floating” steel mass that is exposed to the centrifugal load from the ribs.

[0021] According to the invention, the second group is formed by hole-shaped flux guides located radially outwardly adjacent to the recesses, separated by a web. This provides lateral support for the associated permanent magnet.

[0022] Another advantage of these hole-shaped, radially outer flux guides is that they form a flux bypass. The flux bypass shares a common magnetic "bridge" with the adjacent rotor pole, over which the magnetic flux is redirected instead of reconnecting to the same permanent magnet via the radially aligned rib. These can be saturated / desaturated during operation by applying a q-axis current.

[0023] According to the invention, each receptacle of the permanent magnets has a radially inwardly extending extension.

[0024] Preferably, the radially inwardly extending extensions are designed as cooling channels. The cooling channels extend longitudinally through the rotor and run parallel.

[0025] The cooling channels allow the flow of coolant such as oil from the rotor shaft and achieve direct cooling of the permanent magnets through centrifugal action.

[0026] The rotor designed according to the invention with the described rotor features allows for high torque (magnetic torque and reluctance torque) of the electric machine to be achieved while reducing the rotor weight. The no-load magnetic flux passing through the air gap can be reduced, resulting in higher efficiency at low loads and high speeds. Furthermore, a reduction in the short-circuit current and a wider speed range at constant power can be achieved by reducing the power drop at high speeds.

[0027] The d and q directions of the rotor correspond to the respective axes of the coordinate system defined by the D / q transformation. The d axis is referred to as the polar axis.

[0028] Flux guides are understood to be air pockets that form magnetically non-conductive spaces in the rotor that are kept free of rotor material and permanent magnets. Description of the characters

[0029] Fig. 1 shows a cross-section through a rotor segment of an electrical machine.

[0030] In Fig. 1 schematically shows a rotor segment 3a of an electrical machine 1 whose rotor 3 rotates about the axis of rotation D in a stator 2. The rotor segment 3a forms a rotor pole P1. The pole axis of the rotor pole P1 is indicated by d. In this exemplary embodiment, the rotor 3 consists of six circular segments, which are referred to below as rotor segments and which allow 6-pole operation. The rotor 3 rotates within the stator 2, with only a narrow air gap 4 separating the two components. The rotor 3 comprises a cylindrical rotor body formed from a rotor laminated core with an outer surface 3b. In an embodiment not shown, the outer surface 3b of the rotor can have notches and / or recesses.

[0031] A rotor core is understood to be a multitude of laminated individual laminations, generally made of electrical steel, stacked together. The individual laminations can be held together by gluing, welding, or screwing. The basic structure of the electrical machine is known to those skilled in the art and will therefore not be explained in detail.

[0032] The rotor 3 has two recesses 5 for each rotor segment 3a or rotor pole P1 for receiving permanent magnets 8. The illustrated rotor pole P1 comprises a total of two permanent magnets 8, which are identically designed.

[0033] The two recesses 5 form a V-shaped configuration 6, which are arranged symmetrically to the pole axis d. As can be seen from the drawing, the recesses 5 are formed by two separate rectangular recesses 5, which are positioned in a V-shape relative to each other. The tip of the V-shaped configuration points radially inward. A web 3d is provided radially inward between the recesses 5, so that a central rib 10 is formed in the rotor pole P1 along the pole axis d.

[0034] A permanent magnet 8 is inserted and fixed in each rectangular recess 5.

[0035] In an embodiment not shown, the two recesses 5 which form a V-shaped configuration 6 can also be arranged asymmetrically to the pole axis d.

[0036] As can be seen from the drawing, the V-shaped recesses 5 are designed such that a cooling channel 9 is directly connected to the receptacles radially inward. The two cooling channels 9 extend inward and run parallel in the longitudinal direction along the rotational axis D through the rotor 3. The permanent magnets 8 are directly cooled by the cooling channels 9.

[0037] The recesses 5 are preferably created by punching. The web-shaped section 3d remains between the two recesses 5.

[0038] As it is from the Fig. 1, the rotor 3 has further rotor features which are formed by a first and a second group of flux guides 6, 7. The number, size and position of the first and second groups of flux guides 6, 7 can be designed during the design process. For dimensioning the flux guides and their positioning in the rotor 3, two different procedures are generally used in the prior art. Firstly, the dimensions of the flux guides are determined directly by specific parameters or ratios which are either taken from the literature or originate from a parameter variation. Secondly, the rotor geometry is described using various parameters and optimized using algorithms with regard to specified target variables. The direct methods are often faster and have proven themselves in research and practice over the years.They are based on analytical or numerical approaches designed for previously defined objectives.

[0039] In the exemplary embodiment shown, slot-like flux guides 6 are introduced as a first group on both sides of each permanent magnet 8 of the leg of the V-shaped configuration, which are arranged in a herringbone pattern with respect to the longitudinal extent of the permanent magnet 8. The slot-like flux guides 6 on each side of the associated permanent magnet 8 are equidistant from one another and are at an obtuse angle W to one another. The flux guides 6 begin adjacent to the recess 5 and run in a straight line on one side adjacent to the outer surface 3b. On the opposite side of the herringbone-like arrangement, the flux guides 6 begin adjacent to the recess 5 and run in a straight line to the side surface of the circular segment of the rotor pole P1.

[0040] In an alternative embodiment, the flow guides 6 can also have a different shape, for example, circular or wedge-shaped. The flow guides 6 on each side can also be arranged at different distances from each other.

[0041] Due to the rotor layout, it is possible to arrange the flux guides 6 symmetrically on both sides of the recesses 5 (illustration of the Fig. 1) or asymmetrically (not shown), where the flux guides 6 on the left and right side of the permanent magnets 8 are not identical.

[0042] In the illustrated embodiment, further flux guides 7 are introduced radially outwardly adjacent to the recesses 5, separated by a web. These flux guides are designed as hole-shaped recesses, with each leg of the V-shaped arrangement being assigned a hole-shaped recess. In the illustrated embodiment, the hole-shaped recess has a pentagonal cross-section, but can also be designed with any other cross-section, such as round, oval, etc.

[0043] In an alternative embodiment not shown, further hole-shaped recesses can be introduced radially outwardly adjacent to the permanent magnets 8 as flux guides 7, which redirect the magnetic flux in the radial direction.

[0044] Furthermore, as a design variant, a central flux barrier aligned along the polar axis d can be provided.

[0045] The number of rotor segments 3a, and thus rotor poles, is advantageously between 2 and 14 poles. Each rotor segment 3a forms a rotor pole.

[0046] During the manufacture of the rotor 3, the permanent magnets 8 are inserted into the recesses, which form axially aligned pockets due to the laminated sheet stack, and extend in the axial direction through the rotor body.

[0047] The rotor 3 of the electric machine 1 can be implemented with or without oil cooling.

[0048] The rotor 3 is installed into an electrical machine by means of a stator 2 while maintaining an air gap 4. List of reference symbols 1 electric machine 2 Stator 3 Rotor 3a Rotor segment 3b outer peripheral surface 3c web-shaped section 3D bridge 4 Air gap 5 recesses 6 river tours 7 river tours 8 permanent magnet 9 Cooling channel D axis of rotation W angle P1 rotor pole d polar axis

Claims

[1] Rotor (3) of a permanent-magnet electrical machine (1) comprising a rotor body (3a) with an outer circumferential surface (3b) and with a rotational axis (D) and with at least one rotor pole (P1), wherein the rotor pole (P1) has a pole axis d and wherein the rotor pole (P1) has separate recesses (5) with inserted permanent magnets (8), wherein the recesses (5) form a V-shaped configuration, and wherein the rotor pole (P1) has flux guides, wherein the flux guides are formed by a first group and a second group of flux guides (6, 7), wherein the first group is formed by slot-like flux guides (6) introduced on both sides of each permanent magnet (8) of the leg of the V-shaped configuration,and the flux guides (6) on both sides of each permanent magnet (8) of the leg of the V-shaped configuration are arranged in a herringbone pattern and equidistant from one another with respect to the longitudinal extent of the permanent magnet (8) and orthogonal to the magnetic flux, and wherein the second group is formed by hole-shaped flux guides (7) separated radially outwardly adjacent to the recesses (5) by a web, and each leg of the V-shaped arrangement is assigned a hole-shaped recess as a separate flux guide (7), and that each recess (5) has an extension extending radially inwards to the axis of rotation (D) to form a cooling channel (9). [2] Rotor (3) of a permanent magnet electrical machine (1) according to claim 1, characterized by that the rotor body is formed from a plurality of layered rotor laminations. [3] Rotor (3) of a permanent magnet electrical machine (1) according to one of the preceding claims, characterized by that the rotor (3) comprises a total of six rotor poles (P1). [4] Rotor (3) of a permanent magnet electrical machine (1) according to one of the preceding claims, characterized by that the V-shaped configuration of the permanent magnets (8) is symmetrical to the pole axis (d), wherein the radially inner ends of the permanent magnets (8) form the tip of the V and are separated from one another by a web (3d). [5] Rotor (3) of a permanent magnet electrical machine (1) according to one of the preceding claims, characterized by that the arrangement of the flux guides (6, 7) of the first and second group is symmetrical to the pole axis (d). [6] Rotor (3) of a permanent magnet electrical machine (1) according to one of the preceding claims, characterized bythat the flow guides (7) of the second group are designed to be round, oval or polygonal in cross section. [7] Rotor (3) of a permanent magnet electrical machine (1) according to one of the preceding claims, characterized by that in the rotor pole (P1) a central flux guide is additionally formed along the pole axis d. [8] Rotor (3) of a permanent magnet electrical machine (1) according to one of the preceding claims, characterized by that the outer surface (3b) of the rotor (3) has notches and / or recesses.

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