NL2022078B1

NL2022078B1 - Improved permanent magnet motor/generator.

Info

Publication number: NL2022078B1
Application number: NL2022078A
Authority: NL
Inventors: Willem Vorster Christiaan; Peters Gilbert; Josephus Antonius Janssen Wiebe; Smulders Patrick
Original assignee: Atlas Technologies Holding Bv
Priority date: 2018-11-27
Filing date: 2018-11-27
Publication date: 2020-06-09
Also published as: WO2020108921A1

Abstract

The invention relates to a permanent magnet motor/generator (Æ) showing a rotation axis (102), the motor/generator (Æ) showing a first side (A) and a second side (B), the first side and the second side axially displaced with respect to each other, the motor/generator comprising a stator (104+114), the stator comprising a multitude of electromagnets (116), and a first rotor (106+108) rotatable with respect to the stator using one or more bearings (110, 112), and the motor/generator comprising a multitude of permanent magnets (118, 120), the first rotor during load conditions deforming and/or tilting, characterized in that the motor/generator comprises a second rotor (230+232) comprising the permanent magnets, the second rotor tangentially coupled to the first rotor, the second rotor axially and/or radially at least partly decoupled from the first rotor, as a result of which under load conditions the deformation and/or tilt of the second rotor is less than the deformation and/or tilt of the first rotor. [0001] When used, for example, as an in-wheel motor for a car, the air gap between stator and rotor shows improved stability under load, the load for example resulting from cornering of the car.

Description

Improved permanent magnet motor/generator.

Technical field of the invention.

[0001] The invention relates to a permanent magnet motor/generator showing a rotation axis, the motor/generator showing a first side and a second side, the first side and the second side axially displaced with respect to each other, the motor/generator comprising a stator, the stator comprising a multitude of electromagnets, and a first rotor rotatable with respect to the stator using one or more bearings, and the motor/generator comprising a multitude of permanent magnets, the first rotor during load conditions deforming.

Background of the invention.

[0002] Permanent magnet motor/generators (further referred to as “motors”) using permanent magnets on the rotor and electromagnets on the stator are well known. Such motors are commercially available for powers of less than 1 kW to more than 5 MW. [0003] In this context the phrase “motor” is used to encompass both motors delivering mechanical power using electric energy, generators that generate electric energy using mechanical power (for example windmills or wind turbines), as well as motor/generators that intermittently perform both functions, like in-wheel motors for vehicles that are used to generate mechanical power to propel the vehicle as well as generate electric power during (regenerative) braking.

[0004] Permanent Magnetic motors, especially Axial Flux Permanent Magnet motors, have a higher density of energy compared to general motors and structurally a slimmer structure with shorter axial length. Also, when an Axial Flux Permanent agent motor is used as an in-wheel motor for a vehicle it drastically decreases the overall weight of the motor as it attaches directly onto the wheels without gearbox. Another advantage of such motors, compared to other motors, is their high efficiency, typically 95% or more, combined with their high power-to-mass ratio.

[0005] In a motor employing permanent magnets a rotating magnetic field, generated by electromagnets, results in a torque between stator and rotor. This torque results in a rotation of the rotor. Characteristic for these motors is the air gap between the rotor (typically comprising the permanent magnets) and the stator (typically comprising the electromagnets and a back yoke). For high efficiency this air gap should be small, typically between 0.5 mm and 2 mm. The air gap between stator and rotor should remain as stable as possible. Too big and the motor loses performance and efficiency, too small and the rotor and stator may touch, destroying the motor.

[0006] When such a motor is used as, for example, an in-wheel motor for a vehicle, during cornering large forces are exerted to the motor that tend to (temporarily) deform the rotor. Also tilt of the rotor and play in the bearing result in (temporarily) changes of the gap. To counter this, prior art solutions include strong bearings and a stiff (thick) rotor, resulting in added weight and higher cost.

[0007] In this context the phrase “displacement” will be used in the following text to describe any displacement of (part of) the rotor with respect to the stator and includes for example deformation, and a tilt of the rotor with respect to the stator (for example due to tolerance of the bearings), more specifically for a change in rotor resulting in a change of the air gap.

[0008] More permanent changes of the air gap are caused by permanent displacement of the rotor. This is typically determined by measuring (monitoring) the air gap (either with a sensor or derived from the back EMF of the motor) and generating an error signal when the air gap changes too much from a nominal value. This is described in e.g. European patent application publication EP2953242 A1.

[0009] US patent application publication US20130119802 describes a system in which the motor has a sensor and means to change the air gap. In a closed loop the air gap is then kept constant.

[0010] It is noted that a changing airgap is especially a problem of so-called Axial Flux Permanent Magnet motors, as a displacement results in first order a change of the air gap (change proportional to displacement). However, also other motors, such as the Radial Flux Permanent Magnet motors, have an air gap that can change when the rotor deforms too much. In a Radial Flux Permanent Magnet motor the air gap is radial and changes in second order with the displacement (change proportional to displacement squared).

[0011] The invention intends to provide a better solution to the problem of a changing air gap due to displacement (deformation and/or tilt) of the rotor.

Summary of the invention.

[0012] To solve the before mentioned problems the invention provides a motor that overcomes said problems.

[0013] To that end the motor according to the invention is characterized in that the motor comprises a second rotor comprising the permanent magnets, the second rotor tangentially coupled to the first rotor, the second rotor axially and/or radially at least partly decoupled from the first rotor, as a result of which under load conditions the displacement of the second rotor is less than the displacement of the first rotor.

[0014] Prior art motors use one rotor that must cope with both the tangential forces (the torque generated by the rotating electromagnetic field) and the axial forces exerted on the rotor, for example caused by cornering of a wheel, or the varying force of the blades of a wind turbine (windmill). The axial forces result in a displacement of the rotor, resulting in a change of the air gap between permanent magnets (in or on the rotor) and electromagnets (in or on the stator). This is countered using a stiff rotor, using thick flanges and strong bearings. The result is an increase in weight and price.

[0015] The invention proposes to use two rotors that are axially decoupled, The two rotors are coupled for tangential forces (the rotation of one is thus translated to the other), but the axial coupling is such that a displacement of one rotor results in a much lower displacement of the other.

[0016] In an embodiment of the motor according to the invention the first rotor comprises a first side first rotor part located at the first side of the stator, and a second side first rotor part located at the second side of the stator, the two first rotor parts fixedly connected to each other.

[0017] By using two first rotor parts axially displaced with respect to each other a stiffer construction can be made (for the same weight or material use) than when only one first rotor part is used.

[0018] Preferably the two first rotor parts are fixedly connected to each other such that the stator is completely enclosed by the first rotor. This enables a sealed interior of the motor, and thus a protection of magnets and electromagnets to environmental contamination, such as dirt and moisture. Also, connecting the two first rotor parts contributes to the stiffness of the first rotor.

[0019] In another embodiment of the motor according to the invention the second rotor comprises a first side second rotor part located at the first side of the stator, and a second side second rotor part located at the second side of the stator.

[0020] This arrangement is especially suited for an axial flux permanent magnet motor.

[0021] In yet another embodiment of the motor according to the invention the first rotor comprises a first side first rotor part located at the first side of the stator, and a second side first rotor part located at the second side of the stator, and an first side second rotor part is mounted on the first side first rotor part, and an second side second rotor part is mounted on the second side first rotor part.

[0022] This arrangement combines the advantages of the two aforementioned embodiments.

[0023] In still another embodiment of the motor according to the invention the first rotor hermetically seals the first side (A) of the motor, thereby protecting the first side of the motor from environmental contamination, such as dirt and water.

[0024] In yet another embodiment of the motor according to the invention the motor is a motor from the group of Axial Field Permanent Magnet motors and Radial Field Permanent Magnet motors.

[0025] In still another embodiment of the invention a vehicle, a vessel or a wind turbine is equipped with a motor according to the invention.

Brief description of the drawings.

[0026] The invention is now elucidated using figures, in which identical reference signs indicate corresponding features. To that end: Figure 1 schematically shows a prior art in-wheel motor, Figure 2 schematically shows an in-wheel motor according to the invention, Figure 3 schematically shows another in-wheel motor according to the invention.

Detailed description of the invention.

[0027] Figure 1 schematically shows a prior art in-wheel motor 100, [0028] The motor 100 is typically used in vehicles. Such a motor typically shows a first side A, often referred to as the outboard side, and a second side, often referred to as the inboard side. The motor shows a stator, here depicted by parts 104 and 114, and a first rotor, here consisting of the parts 106 and 108, that are rotationally symmetric around rotation axis 102. The first rotor 106+108 is mounted on stator 104+114 via bearings 110 and 112, and the first rotor can rotate round the rotation axis 102. On the first rotor a multitude of permanent magnets 118 and 120 are mounted, while on the stator a multitude of electromagnets 116 are mounted. Between the permanent magnets and the electromagnets, a gap 128 (at the first side) and a gap 130 (at the second side) is present. On the first rotor a rim 122 is mounted, on which in turn a tire 124 is mounted. The tire in turn is in contact with the road 126, or another surface on which the vehicle rests or drives. The area where the tire touches the ground is called the contact patch. [0029] The electromagnets 116 generate, in working, a rotating magnetic field. This results in a torque between the electromagnets and the permanent magnet, and thus between stator and first rotor.

[0030] When a vehicle corners, a force parallel to the rotation axis acts on the tire where the tire touches the ground. This force may result in a displacement of the first rotor, a movement of the first rotor along the axis (due to axial play of the bearings) and a tilt of the first rotor (due to radial play of the bearings).

[0031] A similar condition may occur when the tire hits a stone or a curb: a temporary and asymmetric loading of the first rotor occurs.

[0032] In for example a wind turbine this may occur when the turbine blades (in contact with the first rotor, the motor being used as a generator) pass the pole on which the turbine is mounted: a temporary and asymmetric loading of the first rotor occurs.

[0033] The displacement of the first rotor will change the air gaps 128 and 130. This has a detrimental effect on the functioning of the motor and may well lead to damage of the motor. Therefore, the air gap is often chosen larger than necessary for an optimal working of the motor.

[0034] It is noted that to lower weight often non-essential material is deleted or cut-out. For example stator part 114 often shows holes, or is formed as a disk with spokes.

It is further noted that for the electromagnets electric connections must be made to driver electronics outside the motor. These electric connections are made by wiring going through the central part 104 of the stator and through or along the stator part 114. Also any cooling of the stator, if necessary, can follow a similar path.

[0035] It is noted that any axial play of the of the bearings results in a change of the two air gaps. Therefore, the use of a pre-loaded bearing is a necessity.

[0036] Figure 2 schematically shows an in-wheel motor (200) according to the invention. [0037] Figure 2 can be thought to be derived from figure 1. However, the permanent magnets 118, 120 are now attached to second side second rotor part 230 and a first side second rotor part 232. The first rotor parts and the second rotor parts are connected to each other close to the axis, and therefore, when a displacement of the first rotor occurs, the displacement of the second rotor will be smaller than the displacement of the first rotor.

[0038] It is noted that, when first and second rotor (parts) are rigidly connected to each other, any axial play of the two will be identical, and thus any axial play results in a change of the two air gaps. Therefore, the use of a pre-loaded bearing is still a necessity. [0039] When used, for example, as an in-wheel motor for a car, the air gap between stator and rotor shows improved stability under load, the load for example resulting from cornering of the car.

[0040] Figure 3 schematically shows another in-wheel motor (300) according to the invention.

[0041] Figure 3 can be thought to be derived from figure 2. The main difference between motor 300 and motor 200 is that motor 300 shows only one first rotor part 306.

[0042] The motor shows a first side A, often referred to as the outboard side, and a second side B, often referred to as the inboard side. The motor shows a stator 304 + 114 and a first rotor 306, that is rotationally symmetric around rotation axis 102. The first rotor is mounted on stator 304+114 via bearing 310, and the first rotor can rotate round the rotation axis 102. On the first rotor second rotor parts 332+334 are mounted. Second rotor parts 332 and 334 are connected by spacer/connector 336. On the second rotor 332+334 a multitude of permanent magnets 118+120 are mounted, while on the stator a multitude of electromagnets 116 are mounted. Bearing 310 is pre-loaded by bush 312 and bush 314. On the first rotor a rim 122 is mounted, on which in turn a tire 124 is mounted. The tire in turn is in contact with the road 126, or another surface on which the vehicle rests or drives. The area where the tire touches the ground is called the contact patch. A non-load bearing part 330 seals and protects the interior of the motor, thereby avoiding contamination of the interior with dust and moisture.

[0043] It is noted that spacer/connect 336 can equally be used in the motor of figure 2 to keep the distance of first rotor part 230 and second rotor part 232 constant, thereby keeping the sum of the air gaps equal.

Claims

A permanent magnet motor / generator (200) exhibiting a rotation axis (102), the motor / generator (200) exhibiting a first side (A) and a second side (B), the first side and the second side axially displaced relative to each other, the motor / generator containing a stator (104 + 114), the stator containing a plurality of electromagnets (116), and a first rotor (106 + 108) rotatable relative to the stator using one or more bearings (110, 112), and the motor / generator comprising a plurality of permanent magnets (118, 120), deforming and / or tilting the first rotor during load, characterized in that the motor / generator includes a second rotor (230/232), the second rotor containing the permanent magnets, the second rotor tangentially coupled to the first rotor, the second rotor axially and / or radially at least partially decoupled from the first rotor, with the result that under load the deformation and / or tilt of the second rotor is less than the deformation and / or t ilt from the first rotor.

The engine / generator of claim 1 wherein the first rotor includes a first side first rotor portion (106) located on first side (A), and a second side first rotor portion (108) located on the second side ( B), the two first rotor parts are fixedly connected to each other.

The engine / generator according to any one of the preceding claims, wherein the second rotor includes a first side second rotor portion (230) located on first side (A), and a second side second rotor portion (232) located on the second side (B).

The engine / generator of claim 1 wherein the first rotor includes a first side first rotor portion (106) located on first side (A), and a second side first rotor portion (108) located on the second side ( B), and a first side second rotor portion (230) is mounted on the first side first rotor portion (106), and a second side second rotor portion (232) is mounted on the second side first rotor portion (108).

The engine / generator according to any one of the preceding claims, wherein the first rotor hermetically seals the first side (A) of the engine / generator, thereby protecting the first side of the engine / generator from environmental contamination, such as dirt and water.

The motor / generator according to any one of the preceding claims, wherein the motor / generator is part of the group Axial Field Permanent Magnet motor / generators and Radial Field Permanent Magnet motor / generators.

A vehicle, a vessel or a windmill equipped with an engine / generator according to any one of the preceding claims.