NL2019304B9

NL2019304B9 - Magnet construction on a rotor of an electric motor and method of manufacturing such a magnet construction

Info

Publication number: NL2019304B9
Application number: NL2019304A
Authority: NL
Inventors: Petrus Maria Jonker Adrianus; Tang Yang
Original assignee: E Traction Europe Bv
Priority date: 2017-07-20
Filing date: 2017-07-20
Publication date: 2019-06-14
Also published as: NL2019304B1

Abstract

A method of manufacturing a rotor of an electric motor, the rotor including a cylindrical housing and having an arrangement of permanent magnets on an cylindrical surface, the cylindrical surface at a first end provided with a raised edge protruding radially inward. The method includes providing in the cylindrical surface a plurality of slots evenly spaced over the circumference and directed along the aXial direction of the housing; shaping each slot with a pair of adjacent parallel ridges, an abutment edge at the first end and an opening of the slot at a second end opposite the first end; placing in each slot a number of permanent magnets in a head-to-tail stacking by sliding each magnet in the slot from the opening towards the abutment edge until the magnet has reached a predetermined position and the slot has been filled; fixing the magnets at their predetermined positions by a glue.

Description

Magnet construction on a rotor of an electric motor and method of manufacturing such a magnet construction

Field of the invention

The present invention relates to a method of manufacturing a rotor part of an electric motor. Also, the invention relates to an electric motor comprising such a rotor part. Furthermore, the invention relates to a drive assembly for a wheel of a vehicle comprising such an electric motor.

Background

Such an electric motor is known from WO 2013/025096 that describes an electric vehicle with an in-wheel electric motor in which the rotor is coupled to a rim of the wheel carrying one or more tyres. The stator is mounted on the frame of the vehicle via a wheel suspension system. The known in-wheel motor is part of a direct drive wheel in which the electromagnets of the rotor directly drive the rim and the tyre without any intermediate gears. In this manner, weight and space are saved and the number of components in the drive assembly is minimized.

The torque that is generated by the in-wheel motor depends on the flux-carrying surface between the rotor and the stator and is a quadratic function of the rotor radius. The rotor magnets are placed as far outwardly as possible around the stator, to obtain a largest possible rotor radius and the motor design is optimised to minimize the gap between the rotor and the stator for delivering a maximum power and torque to the tyre. The gap width between rotor and stator is on the other hand designed to be large enough to absorb mechanical impacts on the wheel during driving conditions.

The windings of the stator are powered by control electronics that are situated within the stator, which control electronics convert electrical energy from a power supply system of the vehicle, e.g. a battery pack and/or an electric generator, to an AC current that is suitable for use by the electric motor. Such control electronics typically comprise power control electronics, e.g. IGBT current modules and a current regulator, such as described in EP 1 252 034. By using the control electronics to control the current and/or voltage supplied to the windings of the stator, the magnetic field vector of the flux generated by the stator is controlled and the electric motor is operated at the desired torque and/or speed of rotation. By integrating the control electronics within the stator, the length of bus bars which run from the control electronics to the electromagnets can remain short, which is highly desirable in view of minimizing losses of the high electrical currents and voltages generally required for operating such an electric motor, which may for instance amount to 300A at 700V or more.

In order to cool the electrical motor and/or the control electronics, the known drive assembly is provided with a cooling system having one or more cooling channels that are situated close to an outer surface of the stator and/or the control electronics, through which liquid coolant can flow into and out of the drive assembly.

The in-wheel drive assembly can be embodied as a substantially self-contained module, without any moving parts of the vehicle attached to and/or extending into the rotor. The interior space defined by the rotor is preferably substantially closed off to prevent ingress of foreign particles, such as dust and/or wear particles released by a brake system of the vehicle and/or by the road, into said interior.

The in-wheel drive assembly may be mounted on the vehicle in a variety of positions by connecting the vehicle side of the drive assembly to the vehicle frame. A rim for mounting a tire may be attached to the rotor, preferably to a substantially cylindrical outer surface of the rotor.

From EP1605574 an electric motor comprising a stator and a rotor is known in which the stator surrounds the rotor. EP1605574 discloses a method for assembly of a rotor for a synchronous motor comprising the steps of gluing magnets on cylindrical sector metal plates that constitute rotor poles; magnetizing the rotor poles; positioning the magnetized rotor poles around a rotor core, and fixing the magnetized rotor poles to the outer surface of the rotor core. The fixation of the rotor poles is typically by the attractive magnetic forces between the rotor poles and the rotor core. In addition, a glue can be supplied between the rotor poles and the rotor core. Alternatively, the rotor poles are fixed to the rotor core by using retaining rings that hold the rotor poles in position on the rotor core. A disadvantage of the prior art method is that placing the rotor poles on the rotor surface is influenced by the attractive forces between the rotor pole and the rotor core which can adversely affect the positioning of the rotor poles on the rotor core.

Moreover, the method is less useful in cases where the rotor poles are to be installed on an internal cylindrical surface of a hollow rotor that surrounds a central stator, since magnetized rotor poles can attract each other within the hollow rotor.

Also, in electric motors with comparatively high power of for example 100 kW or more, during use vibrations in combination with internal heating can cause positions of rotor poles to change and accordingly, reduce the efficiency of the electric motor.

It is an object of the present invention to overcome or mitigate one or more of the disadvantages from the prior art.

Summary of the invention

The object is achieved by a method of manufacturing a rotor part of an electric motor, the rotor part comprising a cylindrical housing and provided with an arrangement of a plurality of permanent magnets on an inner cylindrical surface of the housing, the cylindrical surface at a first end of the housing provided with a raised edge protruding radially inward, the method comprising: creating in the cylindrical surface a plurality of slots evenly spaced over a/the circumference of the cylindrical surface and directed along an/the axial direction of the cylindrical housing; shaping each slot to have a pair of adjacent ridges parallel to the axial direction, an abutment edge at the raised edge at the first end and an opening of the slot at a second end opposite the first end; placing in each slot a number of permanent magnets from the plurality of permanent magnets in a head-to-tail stacking arrangement by sliding each magnet from the opening of the slot towards the abutment edge until the magnet has reached a predetermined position in the slot and the slot has been filled completely with the number of permanent magnets; fixing the magnets by glue at their respective predetermined positions in the slot.

The method provides that the permanent magnets are held at fixed locations within the slots and within the rotor, determined by the positions of the slots in the inner cylindrical surface of the rotor part. Moreover, the method provides that the magnets are fixed in axial direction within the rotor part. At one end of each slot an edge is provided that blocks the sliding of the magnets in the axial direction and provides accurate positioning within the slots. At the opposite end of the rotor a bearing plate is provided that comprises a bearing construction which connects the rotor part to the rotational axis of the electric motor. The permanent magnets that fill the slots are glued in the slots between the edge and the bearing plate. This set-up prevents motion of the magnets in the slots in the axial direction. As a result of this arrangement of the magnets in the slots the magnets are prevented to move out of the slots in either radial or axial direction or move in transverse direction within the slots.

According to an embodiment, the invention provides a method as described above, wherein the permanent magnet in the slot is arranged between the pair of adjacent ridges while the body of the permanent magnet touches the adjacent ridges. Accordingly, the method provides that the magnets are in a tight fit with the slots, which reduces the risk of displacement of one or magnets.

According to an embodiment, the invention provides a method as described above, wherein the glue is provided within the slot prior to the placement of the permanent magnet. After placing the magnet(s) the glue is cured to provide that the magnets is fixed within the slot.

According to an embodiment, the invention provides a method as described above, wherein the step of placing the permanent magnet in the slot comprises sliding the magnet over the glue in the slot and/or on the surface of the magnet. The glue provides lubrication during the placing of the magnets which enhances the positioning of the magnets at their proper locations within each slot.

According to an embodiment, the invention provides a method as described above, wherein the step of fixing the magnets at their respective predetermined positions in the slot comprises: providing the permanent magnets to have a dovetail shaped cross-section, and the creation of the plurality of slots comprises that the slots are shaped with a dovetail complementary cross-section for providing a sliding dovetail joint with the permanent magnet placed in the slot.

The application of a dove tail cross-section of the magnets and a matching complementary cross-section of the slot provides a mechanical locking of the magnets within the slots which prevents radial displacement, and thus simplifies the constmction of the rotor part.

According to an aspect, the invention provides an electric motor comprising a stator part and a rotor part, the stator part and rotor part being coaxial with respect to a rotation axis, the rotor part comprising a cylindrical housing and provided with an arrangement of a plurality of permanent magnets on an inner cylindrical surface of the housing, the cylindrical surface at a first end of the housing provided with a raised edge, wherein the rotor comprises in the cylindrical surface a plurality of slots evenly spaced over a/the circumference of the cylindrical surface and directed along an/the axial direction of the cylindrical housing; with each slot having a pair of adjacent ridges parallel to the axial direction, an abutment edge at the raised edge at the first end and an opening at a second end opposite the first end; with a number of permanent magnets from the plurality of permanent magnets placed in a head-to-tail stacking arrangement with each magnet having a predetermined and fixed position in the slot by a glue layer between magnet and slot.

Additionally, the invention relates to a drive assembly for a wheel of a vehicle comprising an electric motor comprising a stator part and a rotor part, the stator part and rotor part being coaxial with respect to a rotation axis, wherein the rotor part is manufactured by a method as described above, and wherein the rotor part and the stator part are both adapted to be arranged at least partially within the wheel. The invention further relates to a drive assembly for a wheel of a vehicle comprising an electric motor as described above, wherein the rotor part and the stator part are both adapted to be arranged at least partially within the wheel.

Advantageous embodiments are further defined by the dependent claims.

Brief description of drawings

The invention will be explained in more detail below with reference to drawings in which illustrative embodiments thereof are shown. The drawings are intended exclusively for illustrative purposes and not as a restriction of the inventive concept.

In the drawings,

Figures 1 A, IB, 1C respectively show a cross-sectional view, a cut-away isometric view of a drive assembly and a cross-section of drive assembly for use with the present invention;

Figure 2 shows an exploded cross-sectional view of a rotor part of an electric motor in accordance with an embodiment of the invention,

Figure 3 shows an illustration related to a method in accordance with the invention, and

Figures 4A and 4B show cross-sections of a rotor part in accordance with an embodiment of the invention.

Detailed description of embodiments

Figure 1A shows a cross-sectional view of a drive assembly 1 for use with the present invention. The drive assembly comprises a stator 30 with a hollow stator body 31 which has an outer surface 32 around which a rotor 60 is arranged. The drive assembly further comprises an connector stub 33, arranged at a vehicle side 2 of the assembly 1 for attaching the drive assembly to the vehicle. The connector stub 33 is fixedly connected to the stator body 34 via a flange 35 which lies within the rotor 60 and has a larger diameter than a portion 36 of the stub 33 which lies outside the peripheral outer surface 63 of the rotor 60. For supporting rotational movement of the rotor 60 around the axis of rotation R, vehicle side bearings 52 are provided via which the rotor supported on the stub 33 on the vehicle side. On the road side 3, the rotor is rotatingly supported on the stator body 31 via road side bearings 54. A plurality of permanent magnets 61 is attached on an inner circumferential surface 62 of the rotor 60 and can rotate around electromagnets 41 of the stator 30. The electromagnets 41 are fixed on the stator body 31 and drive rotation of the rotor by interaction between the permanent magnets 61 and the magnetic flux generated by the electromagnets 41. The stator 30 and rotor 60 form an electric motor 4 adapted for directly driving rotation of a wheel around axis of rotation R. For controlling and powering the electromagnets 41, power control electronics 42 are arranged within the hollow stator body 31. The power control electronics 42 comprise components, such as IGBT’s, for converting electrical energy from a power supply system of the vehicle, e.g. a battery pack and/or an electric generator, to an AC form suitable for use by the electric motor. A resolver 81 provides an angular position signal indicative of an angular position of the rotor to the power control electronics so that the alternating current is supplied in phase with the magnetic field of the rotor.

To prevent overheating of the power control electronics when the electric motor is in operation, cooling ducts (not shown) are provided close to the power control electronics 42 within the interior of the stator body 32 and spaced apart from the body 32. Coolant is supplied to the cooling ducts via a coolant supply channel 45 which runs through the connector stub 33 from the exterior of the rotor to its interior. After having cooled the power control electronics 42, the coolant flows via passage 46 in the connector stub 33, to a cooling jacket 37 which is provided on the outer surface 32 of the stator body 30. The cooling jacket 37 is provided with channels 38 which form a circuit that mns along the hollow cylindrical body 31 and provides a passage through which liquid coolant flows to cool the electromagnets 41 which are arranged at an outer side 40 of the cooling j acket 37. Relatively cold coolant can thus be supplied through the coolant supply channel 45 with the coolant warming up during its passage through the cooling ducts and absorbing heat energy from the power control electronics 42, and subsequently passing through channels 38 to absorb heat-energy from the electromagnets 41 before being removed from the drive assembly 1 and led back to the vehicle through a coolant discharge channel (not shown) which extends through the connector stub 33. The warmed-up coolant is preferably cooled in a heat exchanger on the vehicle, after which it is recirculated through the coolant supply channel 45.

Power supply lines 43a, 43b for supplying power to the power control electronics 42 run from the exterior of the rotor 60, through passage 44 in the connector stub 33, to the power control electronics.

The rotor 60 comprises a substantially cylindrical rotor body 71 which has transverse ends 72,73 respectively at its vehicle side 2 and at its road side 3. Both transverse ends 72,73 are substantially closed off in order to prevent foreign particles, such as dust and wear particles from the road or released by a braking system of the vehicle, from entering the interior of the hollow rotor 60. The vehicle side of the rotor is substantially closed off by a side plate 74 which extends transversely to the axis of rotation R and by a cover plate 75. The side plate 74 and cover plate 75 are each provided with an opening through which the portion 34 of the connector stub 33 extends. The side plate 74 supports the vehicle side bearings 52 while the cover plate 75 is attached to the side plate 74 to cover the bearings 51 at their transverse vehicle side 2 and comprises an opening 77 through which portion 34 extends. The cover plate 75 together with a shaft seal 78 which is arranged between the inner circumferential edge 79 of the opening 77 and the outer circumference of the shaft 34, prevents foreign particles from damaging the vehicle side bearings 52. Additionally, the cover plate 75 and shaft seal 78 substantially prevent such particles from entering the interior 5 of the rotor from the vehicle side 2, where the particles could interfere with the electromagnets 41.

The road side bearings 54, which are arranged at an inner side of the stator body 31, are covered on the road side 3 by a second cover plate 80. A resolver 81 rotationally connects the stator 30 to the second side plate 80 and is adapted for detecting an angular position of the rotor 60 relative to the stator 30.

Fig. IB shows a partially cut-away isometric view of the drive assembly of Fig. 1 A, in which the second cover plate 80 and the road side bearings 54 however are not shown to allow a better view of the hollow stator body 31 and the resolver 81.

Figure 1C shows a cross-section of a wheel drive assembly for use with the present invention. The wheel drive assembly comprises an in-wheel electric motor 4, a rim 82, and one or more tyres 84.

The in-wheel electric motor 4 comprises the stator part 60 and the rotor part 30. The stator part 60 is coupled to the axle stub which is part of the chassis of a vehicle.

The rim 82 is arranged at the outer circumference of the rotor part 60. The rim 82 can be attached to the rotor part by a bolted connection as known in the prior art.

On the rim 82, one or more tyres 84 are mounted. The rotor part 60 and the stator part 30 are both arranged at least partially within the wheel.

Figure 2 shows an exploded cross-sectional view of the rotor part 60 of the electric motor 4 in accordance with an embodiment of the invention.

The rotor part 60 comprises the cylindrical rotor body 71, the first side plate 74 and a circular end plate 75

In the electric motor 4, the roadside of the cylindrical rotor body 71 has a circular opening that is closed off by the circular end plate 75. The circular end plate 75 is provided on a surface facing the stator with a rotary bearing that is to support the roadside end of the stator 30.

On the cylindrical rotor body 71 the plurality of permanent magnets is arranged on the inner circumferential surface 62. The permanent magnets 61 are arranged in a number of slots 90 that extend on the inner circumferential surface 62 along the axial direction of the rotation axis R.

Within each slot 90, a number of permanent magnets 61 are arranged in a head-to-tail arrangement, such that within the slot 90 consecutive magnets 61 are directed by a same magnetic orientation by for example a repeated “north - south” arrangement of the magnets, and in a parallel adjacent slot with a repeated “south - north” arrangement of the magnets in that slot.

The slots 90 are arranged as recesses in the inner circumferential surface 62 that each are delimited by a pair of parallel ridges 91 inbetween the magnets 61 are positioned. In addition, at the road side end 3 of the cylindrical rotor body 71, the recesses (slots 90) are each provided with an abutment edge 92 that functions as an end stop for the magnets 61 in the slot 90.

In an embodiment, the abutment edge 92 corresponds with a raised edge of the inner circumferential surface 62 of the cylindrical rotor body 71 protaiding radially inwards.

At the vehicle side 2 of the cylindrical rotor body 71, the axial ends 93 of the slots 90 on the inner circumferential surface 62 are preferably open but when the first end plate 74 is in position, an annular surface 94 of the first end plate 74 that faces the axial ends 94, may close off the axial ends 94 of the slots 90.

The permanent magnets 61 are dimensioned in a manner that each slot 90 is completely filled by the number of permanent magnets.

Preferably, the parallel ridges 91 of the slots 90 are dimensioned to correspond substantially with the width of the permanent magnets 61 within the slot so as to have a tight fit between ridges 91 and magnets 61 in which the sides of the permanent magnets touch the walls of the parallel ridges 91. In this manner, the ridges prevent the magnets to move in a transverse direction relative to the axial direction A within each slot 90.

In addition, a fixation is provided between the slot 90 and the magnets 61 to prevent radial displacement of the magnets out from the slots. As will be explained in more detail with reference to Figure 3A and 3B, fixation is provided by means of a glue layer between the contacting surfaces of magnet and slot and optionally by a mechanical confinement of the magnet within the slot. A method is provided for manufacturing the rotor part of the electric motor, which is illustrated in Figure 3.

Figure 3 schematically shows a single slot on the inner circumferential surface 62 of the cylindrical rotor body 71.

The method comprises a number of steps:

In a first step, in the inner circumferential surface 62 of the cylindrical rotor body 71 a plurality of slots 90 directed in the axial direction A of the rotor body is provided or created. In correspondence to the (magnetic) design of rotor part 60 and stator part 30 the slots 90 are evenly spaced over the circumference of the inner circumferential surface 62 of the cylindrical rotor body 71. Next, or additionally, each slot 90 is shaped with a pair of adjacent ridges 91 parallel to the axial direction. Each slot 90 is provided with the abutment edge 92 at the road side end 3. At the vehicle side end 2 of the inner circumferential surface 62, the slots 90 have axial ends 93 that are open. In each slot 90 a number of permanent magnets 61 are placed in the head-to-tail stacking arrangement with an appropriate magnetic direction by sliding, as indicated by arrow S, each magnet 61 from the opening of the slot 90 in the direction of the abutment edge 92 until the magnet 90 has reached a predetermined position in the slot 90 and the slot has been filled completely with the number of permanent magnets 61. When the permanent magnets 61 have been placed, the magnets are fixed by glue at their respective predetermined positions in the slot 90.

Figure 4A shows a cross-section of a rotor part in accordance with an embodiment of the invention.

The permanent magnets 61 are being fixed to their predetermined positions by using a glue, therefore in an embodiment the method comprises that glue 95 is applied in the slots 90 and the magnet(s) 61 is then placed in the slot and is positioned by sliding over the glue in the slot. Alternatively, the glue may be applied to a surface of the magnet that is to be entered into the slot to be adjacent to the surface of the slot. In a further embodiment, a two-component glue can be used, one glue component is then applied on the surface of the slot and the other glue component is applied to the surface of the magnet to be entered into the slot.

After sliding the magnet(s) into the respective predetermined position, the glue is cured to provide binding between the surface of the magnet(s) 61 and the surface of the slot 90.

In the cross-section of a portion of the rotor part, permanent magnets 61 are shown positioned in a slot 90 on the inner circumferential surface 62 of the cylindrical rotor body 71.

The magnets 61 are attached to the surface of the slots 90 by a glue layer 95 between the surface of the magnet and the surface of the slot. The surface of the slots may comprise one or more of the bottom surface and the ridges thereof.

The drawing in Figure 4A is only shown schematically and not on scale.

Figure 4B shows a cross-section of a rotor part 60 in accordance with an embodiment of the invention.

In an embodiment, the permanent magnets 61 are being fixed to their predetermined positions by glue within the slots and additionally by a mechanical constriction of the slot cross-section, in a manner that the constriction prevents a motion of the magnet out of the slot in a radial direction, i.e., towards the central axis R of the cylindrical rotor body.

The constriction can be embodied by providing the permanent magnets to have for example a tapered or dovetail shaped cross-section, and to shape the slots with a complementary cross-section. In this manner, a sliding tapered or dovetail joint with the permanent magnet placed in the slot is provided. A permanent magnet 61 is brought into its predetermined position in a slot 90, by inserting the magnet into the slot at the opening of the slot at the axial end 93 and sliding the magnet along the path of the sliding dovetail joint until the magnet has reached the predetermined position in the slot. Gluing and subsequent curing is used as described above with reference to Figures 3 and 4A.

The magnets are configured to be thicker than a depth of the slots and thus protaide from the slots in radial direction. In an embodiment, the depth of the slots is between about 50% and about 100% of the thickness of the magnets. In preferred embodiment, the depth of the slots is about 50% of the thickness of the magnets.

In Figure 4B the cross-section of a portion of the rotor part is shown with a permanent magnet 61 positioned in a slot 90 on the inner circumferential surface 62 of the cylindrical rotor body 71. The cross-section of the slot 90 has a constricted shape, in this case is a dove-tail shaped cross-section.

The permanent magnet 61 has a matching complementary shape that matches the shape of the slot 90, in this case a complementary dove-tail. It will be appreciated that the invention is not limited to a dove-tail cross-section. The skilled in the art will recognize that other constricted shapes of the cross-sections of the slot and the magnet can be used as well to the same effect.

The permanent magnets 61 can be placed into the slots 90 of the cylindrical rotor body 71 in various orders, for example by fdling a slot 90 completely from the axial end opening 93 upto the abutment edge 92 and repeating this step for each of the remaining unfilled slots. In an alternative and preferred embodiment, the invention provides a method in which the placement of the permanent magnets in the slots 90 is done by placing in each slot a permanent magnet 61 along a circumferential layer of the cylindrical surface. This combination of steps is then repeated for a next circumferential layer until each slot has been filled completely from the axial end opening 93 to the abutment edge 92 with the number of permanent magnets that fit the slot 90.

The magnets are configured to be thicker than a depth of the slots and thus protrude from the slots in radial direction. In an embodiment, the depth of the slots is between about 50% and about 100% of the thickness of the magnets. In preferred embodiment, the depth of the slots is about 50% of the thickness of the magnets.

The invention has been described with reference to the preferred embodiment. Obvious modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims.

Claims

A method for manufacturing a rotor part (60) of an electric motor (4), wherein the rotor part comprises a cylindrical housing (71) and is provided with an arrangement of a plurality of permanent magnets (61) on an internal cylindrical surface (62) of the cylindrical housing, wherein the inner cylindrical surface is provided at a first end (3) of the housing with a raised edge protruding radially inward, the method comprising: providing in the inner cylindrical surface (62) a plurality or slots (90) spaced uniformly on a circumference of the inner cylindrical surface (62) and directed along an axial direction (A) of the cylindrical housing (71); forming each slot (90) with a pair of adjacent edges (91) parallel to the axial direction, a support edge (92) at the raised edge at the first end (3) and an opening (93) of the slot ( 90) at a second end (2) opposite the first end; placing in each slot a plurality of permanent magnets (61) from the plurality of permanent magnets in a head-tail stacking sequence by sliding (S) each magnet from the opening (93) from the slot (90) to the abutment edge (92) until the magnet has reached a predetermined position in the slot and the slot is completely filled with the number of permanent magnets; fixing the magnets (61) at their respective predetermined positions in the slot (90) by an adhesive between the magnet and the slot.

The method according to any of the preceding claims, wherein the permanent magnet is disposed in the slot between the pair of adjacent edges while the body of the permanent magnet touches the adjacent edges.

The method of claim 1 or 2, wherein the step of fixing the magnets at their respective predetermined positions in the slot comprises: providing the glue (95) within the slot (90) prior to placement of the permanent magnet.

The method of claim 3, comprising: curing the glue between walls of the slot and the permanent magnets after the placement of the permanent magnets in the slots.

The method of claim 3, wherein the placement of the permanent magnets in the slots is done by placing in each slot of a permanent magnet along a peripheral layer of the cylindrical surface, until each slot is completely filled with the plurality of permanent magnets.

The method of any one of claims 3 to 5, wherein the glue is a multi-component glue comprising at least a first component and a second component; the method comprising: applying the first component of the glue to the slot, and applying the second component to a surface of the permanent magnet before the permanent magnet is inserted into the slot at the opening (93) of the slot.

The method of claim 3 or claim 6, wherein placing the permanent magnet in the slot comprises sliding the magnet over the glue in the slot and / or on the surface of the magnet.

The method according to any of the preceding claims 1 to 7, wherein the step of fixing the magnets at their respective predetermined positions in the slot further comprises: providing the permanent magnets with a cross-section with a narrowed shape, and forming the plurality of slots comprises that the slots are formed with a complementary shape of the cross-section with narrowed shape to provide a sliding narrowed connection to the permanent magnet disposed in the slot.

The method according to any of the preceding claims, wherein the magnet has reached its predetermined position in the stacking sequence when the sliding of the magnet is blocked by either the support edge (92) or a previous magnet (61) already arranged at its respective predetermined position in the slot.

The method of any one of the preceding claims 1-9, further comprising locking the stacking order of the number of permanent magnets in each slot by placing a bearing plate (74) over the second end of the housing (71) which closes the opening (93) of each slot.

An electric motor (4) comprising a stator part (30) and a rotor part (60), wherein the stator part and rotor part coaxially with respect to a axis of rotation (R), the rotor part comprises a cylindrical housing (71) and is provided with an arrangement of a plurality of permanent magnets (61) on an inner cylindrical surface (62) of the housing, the cylindrical surface at a first end (3) of the housing being provided with a raised edge, the rotor part in the inner cylindrical surface (62) includes a plurality of slots (90) spaced uniformly about a circumference of the inner cylindrical surface and directed along an axial direction (A) of the cylindrical housing; each slot having a pair of adjacent edges (91) parallel to the axial direction, having a support edge (92) at the raised edge at the first end (3) and an opening (93) at a second end (2) ) opposite the first end (3); with a plurality of permanent magnets (61) placed from the plurality of permanent magnets in a head-to-tail stacking sequence, each magnet having a predetermined and fixed position in the slot (90) through an adhesive layer between magnet and slot.

The electric motor of claim 11, wherein the adhesive layer (95) is present between sides of the permanent magnets (61) in each slot (90) and walls of the respective slot to provide the fixed position.

The electric motor according to any of the preceding claims 11-12, wherein the permanent magnets (61) have a narrowed section, and the slots (90) are formed with a complementary, narrowed section for providing sliding narrowed connection to the permanent magnet disposed in the slot.

The electric motor of claim 13, wherein the constricted form is one selected from a group of constricted forms comprising a tapered form and a dovetail.

The electric motor according to any of the preceding claims 11-14, wherein the permanent magnets are arranged in each slot between the pair of adjacent edges (91) with the body of the permanent magnets touching on the adjacent sides of the respective sides slot.

The electric motor according to any of the preceding claims 11-15, wherein the rotor member (60) encloses the stator member (30); the stator member has an external cylindrical surface disposed within the inner cylindrical surface of the rotor member, the external cylindrical surface of the stator member having a plurality of electromagnetic pole shoes spaced uniformly along the circumference of the cylindrical external surface with an elongated shape of the pole shoes in the axial direction (A).

A vehicle wheel drive assembly (1) comprising an electric motor (4), the motor comprising a stator member (30) and a rotor member (60), the stator member and rotor member being coaxial with respect to a pivot axis (R) wherein the rotor member is manufactured by a method according to any of the preceding claims 1-10, wherein the rotor member and the stator member are both adapted to be fitted at least partially within the wheel.

A vehicle wheel drive assembly (1) comprising an electric motor (4) according to any of the preceding claims 11-16, wherein the rotor member (60) and the stator member (30) are both adapted to be arranged at least partially within the wheel.