NL2024173B1

NL2024173B1 - Electric motor/generator with gap retaining element.

Info

Publication number: NL2024173B1
Application number: NL2024173A
Authority: NL
Inventors: Slingerland Hendrik; Jansen Wouter
Original assignee: Atlas Technologies Holding Bv
Priority date: 2019-11-06
Filing date: 2019-11-06
Publication date: 2021-07-20

Abstract

The invention relates to an electric motor/generator (M) comprising a stator (104 + 106) and a rotor (112 + 122), the stator showing an outer perimeter, the rotor at least coaxially enclosing the outer perimeter of the stator, the rotor rotatable around a rotation axis (102) , the rotor and the stator separated by a flux bearing gap (120) over which in working magnetic flux occurs, the flux bearing gap damaged when the flux bearing gap momentarily closes, the motor/generator showing a protective gap (202A, 202B), the protective gap during deformation of the rotor closing before the flux bearing gap closes, thereby avoiding closure of the flux bearing gap, characterized in that the stator comprises a gap retaining element (110) comprising a roller bearing (204) rotatable around an axle (206), the roller bearing comprising an outer bus (210), the protective gap located between the outer bus and the rotor, the protective gap open in normal use.

Description

Electric motor/generator with gap retaining element. Technical field of the invention.

[0001] The invention relates to an electric motor/generator comprising a stator and a rotor, the stator showing an outer perimeter, the rotor at least coaxially enclosing the outer perimeter of the stator, the rotor rotatable around a rotation axis, the rotor and the stator separated by a flux bearing gap over which in working magnetic flux occurs, the flux bearing gap damaged when the flux bearing gap momentarily closes, the motor/generator showing a protective gap, the protective gap during deformation of the rotor closing before the flux bearing gap closes, thereby avoiding closure of the flux bearing gap.

[0002] The invention further relates to vehicles and/or wind turbines equipped with such a motor/generator.

[0003]It is noted that in this context the phrase ‘motor’ includes a generator. Acknowledgement.

[0004] The project leading to this application has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No.

848820. Background of the invention.

[0005] Such a motor is known from international patent application publication WO2011045697 to Protean, showing a Radial Flux Permanent Magnet (RFPM) motor.

[0006] The motor shows a stator comprising electromagnets on its outer perimeter, and a rotor comprising permanent magnets, the rotor coaxially surrounding the stator. The rotor is mounted on the stator by axial motor bearings close to the center of the stator, enabling the rotor to rotate with respect to the stator. A (radial) flux bearing gap separates the electromagnets and the permanent magnets.

When a rotating electric field is generated by the electromagnets, the magnetic field induces a torque on the rotor.

[0007] The flux bearing gap for a RFPM motor is rather small: for a diameter of approximately 30 cm (the typical diameter for the rotor of an in-wheel motor) a typical gap of 1-2 mm is used.

[0008] The flux bearing gap separates electromagnets and permanent magnets. Permanent magnets are brittle, and the electromagnets are easily damaged as well (especially the insulation of the wiring and the magnetic properties of the material of the yokes). Even temporary closure of the flux bearing gap typically leads to damage of the permanent magnets, electromagnets, or both.

[0009] It is noted that the motor may show other gaps as well. For a motor with a radial flux bearing gap typically axial gaps are present (one at each side of the stator) and closure of such a gap is unwanted, as this may result in loss of power and efficiency and may generate particles (due to abrasion), said particles capable of damaging the flux bearing gap.

[0010] Obviously, the rotor and the bearing must be strong enough during normal radial load. However, when cornering a vehicle or hitting a curb, large bending and tilting forces are exerted on the rotor. To avoid deformation (bending, tilting) of the rotor to such an extent that the flux bearing gap closes and damage to the motor occurs, typically the rotor and the axial motor bearings {enabling the rotor to rotate around the stator) are made much stiffer than needed for the radial load only. This implies a large mass and an expensive rotor. The same is true when using the motor in a wind turbine, where large forces are exerted on the blades of the turbine and thus the motor.

[0011] WO2011045697 to Protean describes a solution to the problem of the closing of the radial flux bearing gap by adding a protective radial gap that closes before the radial flux bearing gap closes, the protective radial gap showing a sliding bearing by adding a low friction coefficient material on at least one of its surfaces.

[0012] However, even when using low friction surfaces non-negligible losses occur. Also, the coating is often a delicate coating, that easily damages, leading to even higher losses and wear of the coating. Also, particles can be generated due to abrasion, said particles possibly leading to damage of the permanent magnets and/or the electromagnets.

[0013] Another such a RFPM motor/generator is known from international patent application publication W02019151956 to Elaphe.

[9014] WO2019/151956 proposes another solution to avoid closing of the radial flux bearing gap. It is recognized that closure of the radial flux bearing gap occurs when the axial gaps change. By limiting the change of an axial protective gap, the change of the radial flux bearing gap is limited as well. The axial gap is turned in a gliding bearings by coating the rotor and/or stator part of the protective gap with a low friction material, such as a coating with PTFE. However, even when using low friction surfaces non-negligible losses occur. Also, the coating is often a delicate coating, that easily damages, leading to even higher losses and wear of the coating. Also, particles may be generated due to abrasion, said particles possibly leading to damage of the permanent magnets and/or the electromagnets. Summary of the invention.

[0015] The invention intends to provide an alternative solution of retention of the flux bearing gaps, resulting in lower abrasion and less chance of damage.

[0016] To that end the motor according to the invention is characterized in that the stator comprises a roller bearing rotatable around an axle, the roller bearing comprising an inner bus and an outer bus, the protective gap located between the outer bus and the rotor, the protective gap open in normal use.

[0017] The invention is based on the idea that using the outside of a gap retaining element in the form of a roller bearing (for example a ball bearing, needle roller bearings or cylinder bearings) as part of the protective gap, the protective gap (and thus the flux bearing gap) is protected without the disadvantages associated with a gliding bearing, such as abrasion. Also, friction of a roller bearing (for example a ball bearing) is typically much lower than the friction occurring in a gliding bearing, and thus dissipation (might the protective gap close) is much lower.

[0018] It is noted that, as the roller bearing are connected to the stator and does not rotate with the rotor, they need not be balanced.

[0019] It is further noted that also motors with axial flux bearing gaps are known, so-called Axial Flux Permanent Magnet motors, and motors without permanent magnets, such as inductance motors and reluctance motors, as well as other types of motors, synchronous, asynchronous, brushed or brushless, with a stator and a rotor coaxially enclosing said stator, to which the invention is equally applicable: by limiting change of the protective gap with a roller bearing, the flux bearing gap is protected.

[0020] It is worth mentioning that the invention is not limited to a motor with one gap retaining element, but that several gap retaining elements (roller bearings) may be used.

[0021] In an embodiment the axle is a radial axis.

[0022] By limiting the change of the axial gap, also the change of the radial gap is limited, as discussed in WO2019151956 to Elaphe. This embodiment is applicable to aradial flux bearing gap, but also axial flux bearing gaps, and thus to AFPM motors, RFPM motors, reluctance motors and induction motors.

[0023] In a further embodiment the stator comprises electromagnets and the roller bearing is positioned between the rotation axis and the electromagnets.

[0024] For a motor the axles and the protective bearings are preferably mounted within the radius where the electromagnets are mounted, so that the flux bearing gap is at the largest possible radius available in the motor package. The latter is preferred to get the highest torque for a given diameter of the motor.

[0025] In still another embodiment of the motor according to the invention the axis is a horizontal axis and the axle is a vertical axle pointing to the horizontal axis.

[0026] Typically, in vehicles with in-wheel motors and in wind turbines, the rotation axis is a horizontal axis and the rotor is in a vertical plane.

[0027]In a further embodiment of the motor according to the invention the roller bearing is at or close to the lowest position of the stator.

[0028] In vehicles the forces deforming the rotor often grabs at the lowest point of the rotor, for example as a result of cornering or hitting the curb. It is then most effective to place the axle and protective bearing at the lowest position around the vertical axis.

[0029] In still another embodiment of the motor according to the invention the axle 5 is a non-vertical axle pointing to the horizontal axis.

[0030] In wind generators the forces deforming the rotor can occur at different orientations, as they are typically generated by wind gusts. A good solution would be to equip the stator with several protective bearings, for example three or more.

[0031]In yet another embodiment of the motor according to the invention the axle is an axle parallel to the axis and the protective gap is a radial gap.

[0032] The axle is here piercing through the stator. It is beneficial to use two bearings, one at each side of the stator, to avoid torque on the axle as this could damage the bore in which the axle is mounted and/or the axle and/or the roller bearing.

[0033]In an aspect of the invention a vehicle is equipped with a motor, more specifically an in-wheel motor according to the invention.

[0034] External forces occurring for in-wheel motors occur, for example, when cornering or hitting a curb.

[0035] In another aspect of the invention the motor is part of a wind turbine.

[0036] In a wind turbine external forces external forces occur as a result of wind gusts on the rotor blades and due to the vertical pole on which the turbine rests.

Brief description of the drawings.

[0037] The invention is now elucidated using figures, in which identical reference signs indicate corresponding features. To that end: figure 1 schematically shows a motor according to the invention, figure 2 schematically shows a first embodiment of the gap retaining element to be used in the motor of figure 1, figure 3 schematically shows a second embodiment of the gap retaining element to be used in the motor of figure 1,

figure 4 schematically shows another motor according to the invention, figure 5 schematically shows an embodiment of the gap retaining element to be used in the motor of figure 4, figure 5 schematically shows another embodiment of the gap retaining element to be used in the motor of figure 4, Detailed description of the invention.

[0038] It is noted that, although the invention is explained on the hand of a Radial Flux Permanent Magnet (RFPM) motor, the invention is not limited to only this type of motor. The invention is intended to cover any motor where a narrow flux bearing gap between rotor and stator exists and large off-axis axial forces occur, such as Axial Flux Permanent Magnet motors, reluctance motors and inductance motors.

[0039] Figure 1 schematically shows an electric motor according to the invention.

[9040] Figure 1 shows an electric motor 100 comprising a rotation axis 102. A rotor 112 + 122 is rotationally mounted on a stator 104 + 106 using axial motor bearings 114 and 116, enabling it to rotate around axis 102. The rotor is equipped with a multitude of permanent magnets 118, which face a number of electromagnets 108 in the stator. It is noted that the number of permanent magnets typically differs from the number of electromagnets, but this need not be the case. Between the permanent magnets and the electromagnets, a flux bearing gap 120 exists. The flux bearing gap is typically between 1 — 2 mm. Figure 1 further shows a gap retaining element 110, which is shown in more detail in figure

2.

[9041]In working the electromagnets 112 induce a rotating magnetic field that interacts with the permanent magnets 110 over the flux bearing gap 120, resulting in a torque on the rotor. When the motor is a hub motor for a vehicle (an in-wheel motor), it is surrounded by a rim 130 and a tire 132, when the vehicle corners, or hits a curb, this results in a force F gripping at the patch between road 134 and tire. This force F tends to tilt or bend the rotor. This in turn influences the size of the flux bearing gap 120 and other gaps.

[0042] A gap retaining element 110 comprising a roller bearing is attached to the stator 106, protecting a protective gap. The protective gap is in a vertical plane.

As mentioned in WO2019151956 to Elaphe control of the (axial) protective gap also protects the radial gap. Such a gap retaining element is thus effective when the flux bearing gap is a radial, an axial or any mixture thereof (an angled gap).

[0043]lt is noted that the gap retaining element does not rotate, as it is connected to the stator. Therefore, the gap retaining element has no effect on the balancing of the motor.

[0044] It is further noted that, as the force F grips at the patch between road 134 and tire 132, a preferred position of the gap retaining element is at the lowest position. A limitation is that there are also reasons to place the electromagnets 108 and the permanent magnets 118 as far removed from the axis 102 as possible (needed for a large torque), and therefore the lowest position just within the radius on which the electromagnets are placed is preferred.

[0045] It is worth mentioning that the gap retaining element not only limits the direct effect (tilt and bending) of, for example, cornering, but also the effect of vibration of rotor and/or stator. To limit vibrations, the gap retaining element may be equally effective at other (tangential) positions.

[0046] Figure 2 schematically shows a first embodiment of the gap retaining element.

[0047] Figure 2 shows a gap retaining element in the form of a ball bearing 202. The ball bearing comprises an inner bus 204 and an outer bus 206. An axle 208 is inserted in a bore in the stator 106. Two spacers 210A, 210B are placed around the axle as well to keep the outer bus free from the stator. If the inner bus is slightly longer than the outer bus, these spacers might be superfluous.

[0048] The ball bearing is preferably placed in a more or less rectangular slot in the stator. The axle may be inserted in a bore that is drilled in the stator before the electromagnets are mounted thereon.

[0049] Between the outer bus and the rotor parts 112, 122 protective gaps 212A and 212B exist. When the rotor bends or tilts, one of these protective gaps will close and the rotor will roll over the outer bus. The force that is then exerted on the ball bearing may bend or tilt the stator together with the rotor (a stator that is not stiff in the axial direction is then beneficial), or it may stiffen the rotor sufficiently to limit further deformation.

[0050] It is noted that in this example a ball bearing is discussed, but the person skilled in the art will recognize that also needle roller bearings, cylinder bearings and the like can be used.

[0051] Figure 3 schematically shows a second embodiment of the gap retaining element.

[0052] Figure 3 can be thought to be derived from figure 2. Figure 3 shows a gap retaining element in the form of a roller bearing 202 and an axle 302 that is not inserted in the stator but instead mounted on the stator. Caps 304A, 304B keep the axle 302 and the roller bearing 202 in place. The caps can be mounted to the stator using screws, or by (spot)welding. A closure of the gap 302 results in a force against the stator, and the caps 304A, 304B need not be overly strong or overly strongly mounted on the stator.

[0053] This gap retaining element only protects one protective gap 304, but the person skilled in the art will recognize that a second gap retaining element placed at the opposite side of the stator and, for example, tangentially displaced, can be used to protect another protective gap.

[0054] Figure 4 schematically shows another motor according to the invention.

[0055] Figure 4 can be thought to be derived from figure 1, but instead of gap retaining element 110 a gap retaining element 402 is used, protecting a radial flux bearing gap against movement of the rotor in the z-direction.

[0056] Figure 5 schematically shows the gap retaining element used in figure 4.

[0057]Figure 5 shows two roller bearings 502A and 502B, mounted on a common axle 504. The common axle protrudes through stator element 106. Protective gaps 506A and 506B between the roller bearings and the rotor part 112, 122 close when the rotor moves in the z-direction and thereby protects a radial flux bearing gap.

[00358] lt is noted that the form of the axle, having a thickened part in the middle, makes spacers as shown in figure 2 superfluous.

[0059] Figure 6 schematically shows another embodiment of the gap retaining element used in figure 4.

[0060] Figure 6 can be thought to be derived from figure 5, but the rotor elements 112 and 122 have a slightly different form and the roller bearing is thereby positioned in an annular chamber.

As a results thereof not two (506A and 506B), but four protective gaps (506A, 506B 602A and 602B) are present.

One pair is used when the rotor is moved in the z-direction, one pair when the rotor is moved in the negative z-direction.

The latter is not normally the case, but when placing one gap retaining element in the uppermost position, a movement of the rotor in the z-direction means that in the upper gap retaining element gaps 602A and 602B close.

Thereby the forces on each gap retaining element are less.

Claims

Conclusions.

An electric motor/generator (100) comprising a stator (104 + 106) and a rotor (112 + 122), the stator having an outer circumference, the rotor at least coaxially enclosing the outer circumference of the stator, the rotor being rotatable around an axis of rotation (102), the rotor and stator separated by a flux-carrying gap (120) over which magnetic flux occurs in operation, the flux-carrying gap is damaged when the flux-carrying gap temporarily closes, with the motor/generator forming a protective gap ( 202A, 202B, 506A, 506B, 602A, 602B), closing the protective gap during deformation of the rotor before closing the flux-bearing gap, preventing closure of the flux-bearing gap, characterized in that the stator has a roller bearing (204 502A, 502B) rotatably about an axis of rotation (206, 504), the roller bearing comprising an inner sleeve (208) and an outer sleeve (210), the protective gap formed by the outer sleeve and the rotor, the protective opening o pen under normal use.

The motor/generator of claim 1, wherein the shaft (206) is a radial shaft.

The motor/generator of claim 2, wherein the stator (104 + 106) comprises solenoids (108) and the roller bearing (204) is disposed between the rotational shaft (102) and the solenoids (108).

The motor/generator of any preceding claim, wherein the axis of rotation (102) is a horizontal axis of rotation and the axis (208) is a vertical axis pointing toward the horizontal axis of rotation.

The motor/generator of claim 4, wherein the roller bearing (204) is located at or near the lowest position of the stator (106).

The motor/generator of any one of claims 1 to 3, wherein the axis (206) is a non-vertical axis pointing toward the axis of rotation (102).

The motor/generator of any preceding claim, wherein the axis (504) is an axis parallel to the rotational axis (102) and the protective gap (506A, 506B, 602A, 602B) is a radial gap.

A vehicle equipped with a motor/generator (100) according to any one of the preceding claims, more specifically an in-wheel motor/generator (100) according to any one of the preceding claims.

A wind turbine equipped with a motor/generator (100) according to any one of claims 1-7.