ELECTRIC MOTOR

Abstract

The invention relates to an embedded permanent magnet motor comprising a stator, a rotor body having an outer surface facing the stator, a set of pockets in the rotor body near the outer surface of the rotor, wherein the pocket has a top surface, a bottom surface spaced apart from the top surface and located closer to the axis of rotation of the rotor than the top surface is to the axis of rotation, and a pair of opposing side walls connecting the top surface to the bottom surface, and in each of the pockets a magnet arranged therein which is undersized relative to the pocket, wherein the motor further comprises a pocket lining which fits inside the pocket into a space between the magnet and the pocket, and wherein the pocket lining partially fills the space between the magnet and the pocket and mechanically positions the magnet in the pocket.

Description

[0001] This invention relates to improvements in electric motors incorporating permanent magnets and, more particularly, to improvements in embedded permanent magnet motors.

[0002] It is known to provide electric motors containing permanent magnets that generate a magnetic field that, during operation, interacts with a corresponding magnetic field generated by electric current flowing through motor windings. Various designs are known, each with specific advantages and disadvantages.

[0003] One type of motor is the embedded permanent magnet motor, sometimes referred to as a buried magnet motor. These motors comprise a rotor containing a set of magnets arranged in pockets machined into the rotor's outer surface. These magnets are typically arranged in a pattern of alternating north and south poles facing the outer surface. The stator is provided with a set of teeth around which windings of conducting wire are wound. By applying appropriate current patterns to the windings, the rotor can produce a controlled amount of torque and rotate at a controlled speed.

[0004] To prevent noise during motor operation, the magnets are tightly press-fitted into the pockets, ensuring the magnets and pockets have a complementary shape. This also ensures that there are no air gaps between the magnets and the surrounding pocket, which would disrupt the flow of the magnetic field between the rotor magnets and the magnetic field generated by the stator.

[0005] One difficulty associated with an embedding permanent magnet motor compared to a motor where the magnets are surface mounted is that it becomes difficult to repair or recycle the motor.

[0006] Since the rare earth metals used in permanent magnets are a limited resource, it is advantageous to recycle this material. However, separating the magnets from the rotor is extremely difficult. They are either tightly press-fitted or, in some cases, held in place by adhesive, or both.

[0007] GB2487656A, filed by the University of Birmingham, describes a process for recycling magnets using hydrogen. The magnets are exposed to hydrogen gas while in situ within an array, causing hydrogen decrepitation to occur. The decrepitation process causes the selected rare earth magnets to break down into particles that can be attracted to a magnet, allowing them to be removed from the remaining array. This process can be used to remove faulty or damaged rare earth magnets from assembly assemblies for various devices, such as motor or generator assemblies. The recovered rare earth particles can be reused to form new rare earth magnets.

[0008] The applicant has recognized that this process presents challenges when the magnets are embedded in a motor rotor, as is the case with an embedding permanent magnet motor. Because they are densely packed in pockets or held in place by adhesive, only a very small area is exposed to a hydrogen flow, and where the magnets are depressed, they expand and become even more tightly packed into the pockets.

[0009] According to a first aspect, the invention provides an embedded permanent magnet motor comprising: a stator, a rotor body having an outer surface facing the stator, a set of pockets in the rotor body near the outer surface of the rotor, wherein the pocket has a top surface, a bottom surface spaced opposite to the top surface and closer to the axis of rotation of the rotor than the top surface is to the axis of rotation, and a pair of opposite side walls, which connect the upper surface with the floor surface, and in each of the pockets a magnet arranged therein which is undersized relative to the pocket, the engine further comprising: a pocket lining that fits inside the pocket into a space between the magnet and the pocket, with the pocket lining partially filling the space between the magnet and the pocket and mechanically positioning the magnet in the pocket.

[0010] Most preferably, the pocket lining defines cavities into which the magnet can expand when subjected to a decrepitation process.

[0011] The pocket lining may include a plurality of spacer elements with rounded edges that engage the magnet.

[0012] Providing spacers with rounded edges provides a "guide" that aids the installation of the magnets into the pocket linings and prevents localized scraping of the magnet surface. These spacers can also be arranged in a manner that can provide higher localized contact pressure (improving retention) and potentially allow for better gas flow around the magnet for recycling. This can also aid in the removal of the magnets from the rotor at the end of its service life.

[0013] The pocket liner may include at least one outwardly facing positioning feature that locks the liner in place by engaging a corresponding recess provided in a side wall of the pocket. This positioning feature may be resilient, allowing it to deform when the magnet and liner are removed from or inserted into the pocket.

[0014] The rotor body may include at least one groove extending downwardly from an edge of the rotor pocket into the pocket and acting as a guide for the at least one positioning feature toward and into the recess during assembly.

[0015] The depth of the groove may be less than the depth of the recess for engaging the locking feature, wherein the locking feature or a part of the pocket liner carrying the locking member is elastically deformable to snap into the recess when in the correct position.

[0016] The pocket lining may include at least one inwardly directed spacer element that keeps one side of the magnet spaced from a side wall of the pocket lining. Preferably, at least two spacers are provided—one for each side of the magnet. These may each have a rounded tip where they engage the magnets.

[0017] The pocket lining may comprise a resilient spacer element disposed between the bottom surface of the pocket and the magnet, exerting a biasing force on the magnet to press the magnet into contact with the top surface of the pocket, i.e., to bias it with a radial component away from the axis of rotation of the rotor.

[0018] The pocket may comprise at least one channel formed in the base into which a positioning portion of the pocket lining is received.

[0019] The pocket liner, the pocket, and the magnet may be shaped such that a central portion of a surface of the magnet is in direct contact with the bottom of the pocket, while the magnet is simultaneously in contact with the top surface of the pocket. The base of the pocket liner may therefore include at least one cutout through which the bottom of the pocket or the bottom of the magnet, or both, protrude to allow direct contact between them.

[0020] Alternatively, the base of the magnet and the bottom surface of the pocket can be in indirect contact via the pocket lining.

[0021] Two or more of the pocket liner, the magnet, and the pocket walls may define at least one channel extending from a surface of the magnet and terminating at an outer surface of the rotor body. This channel or channels allows the hydrogen used in magnet recycling to come into contact with the magnets.

[0022] The channels can be located between the pocket and the outer surface of the pocket lining facing away from the magnet or between the inner surface of the pocket lining and the magnet.

[0023] The channel or channels may be located at the edges of the magnet or in the immediate vicinity of the edges, with no channel being located in a central region of the magnet walls or the magnet base.

[0024] "Central region" is defined as a zone extending over a maximum of 25 percent of the surface and centered on a centerline of the surface. "Near the edges" means that the distance between the edge of the magnet and each edge of the channel is less than 25 percent of the width of the magnet's surface.

[0025] The pocket liner may comprise a U-shaped body having two opposite sides connected by a base portion, the side walls and the base portion carrying the spacer elements.

[0026] The body may comprise a plate of material, preferably steel, folded to form the required U-shape. This may include a series of cutouts extending through the U-shaped body and a series of projections projecting from the main plane of the body to form positioning features or spacers.

[0027] The U-shaped body may include features at both ends that can be folded into position after the U-shaped body is inserted into the pocket to secure the U-shaped body in place or to prevent the magnet from being accidentally removed from the assembly.

[0028] The spacers on the side walls may protrude outward from the side walls, away from the magnet, to contact the pocket, or may protrude inward from the side walls to contact the magnet.

[0029] The walls of the U-shaped body may have openings extending through the support to expose a surface of the magnets.

[0030] One or more of the spacers arranged on the sides of the magnet can be elastic. This allows the pocket lining to securely hold the magnet in place without adhesive. If preferred, one or more separate channels can be defined that can accommodate adhesive without the adhesive spreading into other channels or recesses intended for magnet expansion.

[0031] The rotor body may comprise a solid rotor or a laminated rotor formed from a stack of rotor laminations.

[0032] The pocket lining may comprise an elastic material, such as spring steel. It may comprise the same material used to construct the rotor body or may comprise a different material. The pocket lining may comprise a magnetic material.

[0033] The magnets can comprise a range of different compositions. One possible suitable magnet material is NdFeB, which is suitable for use in a hydrogen-based decrepitation process to remove the magnets. Other materials include, but are not limited to, strontium cobalt, SrCo, and strontium ferrite, SrFe.

[0034] The magnets may generally have a rectangular cross-section and the pockets may also generally have a rectangular cross-section but be oversized relative to the magnet.

[0035] According to a second aspect, the invention provides a method of assembling an engine according to the first aspect, comprising: providing the rotor body; inserting a pocket liner into a pocket in the body; and pressing a magnet into the pocket by guiding it through the pocket lining.

[0036] The method may include inserting all pocket liners before inserting magnets, or may include inserting the pocket liner and magnets at the same time.

[0037] The method may include inserting a plate of low-friction material into the pocket lining prior to inserting the magnet, pressing the magnet into the pocket while sliding on the plate of material, and removing the plate of material once the magnet is at least partially inserted into the pocket. Alternatively, the method may comprise the following steps: providing the rotor body; inserting a magnet into each pocket lining outside a pocket in the body; and pressing the pocket lining and magnet into the pocket.

[0038] The two alternative methods may each additionally include inserting a plate of low-friction material into the pocket lining prior to inserting the magnet, pressing the magnet into the pocket while sliding on the material plate, and removing the material plate once the magnet is at least partially inserted into the pocket. This prevents scratches from forming during insertion of the magnets. The risk of scratches is significantly reduced if the pocket lining includes spacers with rounded ends that engage the magnets.

[0039] According to a further aspect, the invention provides a rotor assembly for an embedded permanent magnet motor of the first aspect of the invention.

[0040] Two embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings as illustrated therein. In the drawings: the Fig. 1 shows an embedded permanent magnet motor according to the present invention; the Fig. 2 a first arrangement of a pocket lining arranged in the rotor body in cross section; the Fig. 3 a second arrangement of a pocket lining arranged in the rotor body in cross section; the Fig. 4 the pocket lining of the first embodiment in perspective and separate from the rest of the engine; the Fig. 5 shows the magnet, the pocket lining and the pocket of the first embodiment in an exploded view; the Fig. 6 the pocket lining of the second embodiment in perspective and separate from the rest of the engine; the Fig. 7 shows the magnet, the pocket lining and the pocket of the second embodiment in an exploded view; the Fig. 8 an alternative arrangement in which the pocket lining is spaced from the sides of the magnets by spacer elements, and the Fig. 9 shows a further arrangement of a pocket lining and a pocket; the Fig. 10 a modification of the pocket lining of the Fig. 2, which comprises inwardly facing spacer elements; and the Fig. 11 and Fig. Figure 12 shows the pocket liner of the first embodiment in perspective and separate from the rest of the motor with additional features for enclosing the ends of the magnet to prevent accidental release when subjected to axial loading.

[0041] As in the Fig. 1, an embodiment 100 of a motor according to the present invention comprises a stator 101 and a rotor 102. The stator and the rotor are each generally cylindrical and have an axis of rotational symmetry located in the Fig. 1 extends into the side. The rotor is located inside the stator, and their axes are aligned.

[0042] The stator includes a yoke from which extends a set of inwardly facing teeth 103. Windings of conducting wire (not shown) are wound around each tooth and interconnected to form a set of phases, typically three phases. The tips of the teeth are positioned near and facing the outer peripheral surface of the rotor.

[0043] The rotor comprises a rotor body with an outer surface facing the tips of the stator teeth. The body comprises a stack of laminations made of magnetically conductive material. The laminations are laminated together to form a solid body.

[0044] A set of one-sided closed pockets 104 is incorporated into the rotor body. As shown in the Fig. 1, there are 8 pockets, but there may be more or fewer pockets. Each pocket 104 is formed by cutouts in each lamination which are aligned to form recesses extending from a free end of the rotor into the rotor body. The pockets 104 are closely spaced beneath a continuous and generally smooth cylindrical peripheral surface of the rotor. In this example, the rotor is cylindrical, but it is within the scope of this invention to provide a rotor which has no peripheral surface. The invention could be applied to a spoke-shaped rotor in which the magnets within each spoke extend radially from the center, or in which the rotors form a series of V-shaped sections, each containing two magnets.They are closed in that they have a top surface and a bottom surface connected by sides, and are open to the outside of the rotor only at the axial ends of the rotor body. These ends can be capped if desired to cover and protect the magnets.

[0045] Each pocket 104 accommodates a magnet 105. In this example, the magnets are rare-earth permanent magnets containing NdFeB. The magnets have a cross-section generally corresponding to the pocket's cross-section, but are undersized.

[0046] To hold the magnets in place, each pocket also receives a pocket lining 106. The design of this pocket lining and the shape of the pocket differ between the first and second embodiments and are shown in the Fig. 2 to 5 of the drawings. The function of the pocket lining is the same in each case—to position the magnets and simultaneously define channels that allow the magnet to expand when it is decrepitated during recycling.

[0047] The overall shape of the pocket liner is the same in each embodiment. The liner 106 comprises a U-shaped body formed by pressing a flat metal sheet, although other shapes are also possible. The body surrounds the sides and bottom of the magnet when it is fitted into the pocket. In these examples, the body does not cover the ends of the magnets. Fig. 11 and Fig. 12 show alternative embodiments for a liner 206, 306 in which foldable tabs 207, 307 are provided which hold the magnets in the slot and prevent them from being removed axially until the tabs are folded away.

[0048] The body has a base facing the bottom of the magnet and two sidewalls, each facing a corresponding side surface of the magnet. Cutouts are provided within the sidewalls and base, defining recesses that allow hydrogen gas to flow through during recycling of the rotor and magnets. These recesses connect to channels that can support the inflow of hydrogen gas when the motor rotor is to be recycled. As described below, resilient spacers are provided to apply a biasing force to the magnet, and optional locking features may be provided that engage recesses in the rotor body to lock the pocket liner in place. First embodiment.

[0049] As in the Fig. 2, Fig. 4 and Fig. 5, the pocket liner 106 comprises a U-shaped body having a generally planar base 107 and two side walls 108 extending orthogonally from opposite edges of the base. The side walls each have two outwardly facing resilient spacers 109 pressed from the side walls and a through hole. The base has two cutouts 110 located at the center of each free edge to provide an H-shaped or I-shaped base section. Six holes are machined into the base, and two pairs of outwardly facing resilient spacers 109 are provided. These are best seen in the Fig. 4 and Fig. 5 can be seen.

[0050] The magnet 105 is a bar magnet with a regular rectangular cross-section that fits snugly into the U-shaped pocket lining 106.

[0051] The pocket 104 itself has projections 104a in a bottom surface, which are spaced apart from each other such that the central web of the H-shaped base is located exactly between them when the pocket lining and the magnet are correctly positioned in the pocket. These are shown in the Fig. 5 can be seen.

[0052] The elastic spacers space the walls of the pocket lining 106 from the side walls of the pocket to define channels 111. The gas in these channels can pass through the hole in each side wall to contact the sides of the magnets.

[0053] Where the two projections are present, the bottom of the magnet 105 rests against the bottom of the pocket, and the top surface of the magnet is pressed into contact with the top of the pocket by the elastic spacers on the base.

[0054] In use, the pocket liner 106 is first inserted into a pocket 104, then the magnet 105 is pushed into the pocket until the base snaps between the two raised projections at the bottom of the pocket. These hold the pocket liner in place. The magnet 105 can be held in place by the resilient biasing force generated by the spacers. If tabs are provided at the axial ends of the liner, these can be folded into place to provide additional support and further secure the magnet to the pocket liner.

[0055] In the Fig. 10, an alternative pocket lining 406 is shown, which can be used instead of the Fig. 2, or in addition to them, a set of resilient spacers 407. These maintain the sidewalls and base of the pocket liner at a distance from the magnet. This can be advantageous in providing a larger surface area of ​​the magnet that can be exposed to hydrogen during recycling. The provision of rounded tips on these spacers also helps reduce potential scratch damage to the magnet when it is pressed into the pocket liner during assembly. Second embodiment

[0056] As in the Fig. 3, the Fig. 6 and the Fig. 7, an alternative pocket liner 506 and magnet are similar to those of the first embodiment, except for the base of the pocket liner and the bottom surface of the pocket. The base of the pocket liner 506 has a central square opening 507 to provide an O-shaped base, and the bottom surface of the pocket is provided with a single square protrusion 508 complementary to the opening in the pocket liner. This holds the pocket liner in place within the pocket.

[0057] In the first and second embodiments, the elastic spacer elements extending outwardly from the sides of the pocket liner may be disposed in recesses in the side walls of the pocket to lock the pocket liner in place. This may replace or supplement the protrusion at the bottom of the pocket. Third embodiment

[0058] The Fig. 8 is a view to the Fig. A cross-sectional view similar to Figure 2 of an alternative arrangement of a pocket liner 606, in which the resilient spacers 607 extend inward toward the magnet rather than outward. In this arrangement, the side walls of the pocket liner contact the pocket wall rather than the magnet. Gas channels are provided between the pocket liner and the magnet. Outwardly directed locking features are formed at the base of the pocket liner and are located in grooves formed in the bottom of the pocket. Fourth embodiment

[0059] In the Fig. 9 shows a further modified arrangement of a pocket lining 706 in which the magnet and the side walls of the pocket lining are the same as in the embodiment of the Fig.8. This differs in that the base has a cutout similar to the cutouts of the first and second embodiments, to establish direct contact between the bottom of the magnet and the pocket. Areas of the pocket bottom toward the edges of the magnet are cut out to provide additional channels for gas flow.

[0060] The provision of the pocket lining offers significant advantages in terms of the ease with which the motor can be recycled at the end of its service life. The rotor and stator can be easily separated by machining. The magnets can then be easily removed from the pockets using a process known as hydrogen decrepitation, as described in GB2387656A.

[0061] The channels provided between at least two of the pocket, pocket liner, and magnet allow the sides of the magnet and the bottom to be directly exposed to hydrogen, and also define cavities that provide space for the magnet to expand as it pulverizes. Once the magnet has pulverized, it can be easily extracted and separated from the other parts of the motor. By using a liner made of the same material type as the rotor, it does not need to be mechanically extracted; however, this is possible if desired, allowing the rotor body and even the pocket liners to be reused to form a new motor rotor with fresh magnets.In some arrangements, the shape of the liners allows the magnets to be easily mechanically pressed out of the intact rotor pockets, allowing the magnets to be reused in other applications after inspection and, if necessary, recoating for corrosion protection. This improves the sustainability of the products, as minimal energy is required to extract magnets and reuse them. Confirmation

[0062] The project leading to this application has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 821114. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] GB 2487656A

[0007] GB 2387656A

[0060]

Claims

[1] Embedded permanent magnet motor, comprising: a stator; a rotor body having an outer surface facing the stator; a set of pockets in the rotor body near the outer surface of the rotor, wherein the pocket has a top surface, a bottom surface spaced opposite to the top surface and closer to the axis of rotation of the rotor than the top surface is to the axis of rotation, and a pair of opposite side walls, which connect the top surface with the bottom surface; and in each of the pockets a magnet arranged therein which is undersized relative to the pocket; the engine further comprising: a pocket lining that fits inside the pocket into a space between the magnet and the pocket, with the pocket lining partially filling the space between the magnet and the pocket and mechanically positioning the magnet in the pocket. [2] An embedded permanent magnet motor according to claim 1, wherein the pocket liner defines cavities into which the magnet can expand when subjected to a decrepitation process. [3] An embeddable permanent magnet motor according to claim 1 or claim 2, wherein the pocket liner comprises a plurality of spacers having rounded edges that engage the magnet. [4] An embeddable permanent magnet motor according to any preceding claim, wherein the pocket liner includes at least one outwardly facing locating feature that locks the liner in place by engaging a corresponding recess provided in a side wall of the pocket. [5] The embedded permanent magnet motor of claim 4, wherein the rotor body includes at least one groove extending downwardly from an edge of the rotor pocket into the pocket and acting as a guide for the at least one positioning feature toward and into the recess during assembly. [6] An embeddable permanent magnet motor according to any preceding claim, wherein the pocket liner comprises at least one inwardly facing spacer element that keeps one side of the magnet spaced from a side wall of the pocket liner. [7] An embeddable permanent magnet motor according to any preceding claim, wherein the pocket liner comprises an elastic spacer disposed between the bottom surface of the pocket and the magnet and exerting a biasing force on the magnet to press the magnet into contact with the top surface of the pocket. [8] An embedded permanent magnet motor according to any preceding claim, wherein the pocket liner, the pocket and the magnet are shaped such that a central portion of a surface of the magnet is in direct contact with the bottom of the pocket while the magnet is simultaneously in contact with the top surface of the pocket. [9] An embedded permanent magnet motor according to any preceding claim, wherein two or more of the pocket liner, the magnet and the pocket walls define at least one channel extending from a surface of the magnet and terminating at an outer surface of the rotor body. [10] An embeddable permanent magnet motor according to any one of the preceding claims, wherein the pocket liner comprises a U-shaped body having two opposite sides connected by a base portion, the side walls and the base portion carrying the spacer elements. [11] A method of assembling an engine according to the first aspect, comprising: providing the rotor body; inserting a pocket liner into a pocket in the body; and pressing a magnet into the pocket by guiding it through the pocket lining. [12] A method according to claim 11, comprising inserting all pocket liners before inserting magnets, or comprising allowing the liner and magnets to be inserted simultaneously. [13] A method according to claim 11 or claim 12, comprising inserting a plate of low-friction material into the pocket lining prior to insertion of the magnet, pressing the magnet into the pocket while sliding on the plate of material, and removing the plate of material once the magnet is at least partially inserted into the pocket. [14] A method according to claim 11, comprising the following steps: Providing the rotor body; Inserting a magnet into each pocket lining outside a pocket in the body; and Pressing the pocket lining and magnet into the pocket. [15] Rotor assembly for an embedded permanent magnet motor according to one of claims 1 to 10.

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