GB2482704A

GB2482704A - Sealing arrangement for an electric motor or generator

Info

Publication number: GB2482704A
Application number: GB1013492.2A
Authority: GB
Inventors: Esad Jaganjac
Original assignee: Protean Electric Ltd
Current assignee: Protean Electric Ltd
Priority date: 2010-08-11
Filing date: 2010-08-11
Publication date: 2012-02-15
Anticipated expiration: 2030-08-11
Also published as: WO2012020349A3; GB2482704B; WO2012020349A2; GB201013492D0

Abstract

A rotor 220 of a motor or generator is mounted to a stator 100 by a coupling device including a coupling element 300 coupled to a radial wall (fig 2, 220) of the rotor; and another coupling element coupled to the stator with two bearings (fig 2, 320,330) mounted between the coupling elements to allow the rotor to rotate relative to the stator. A seal arrangement includes a third bearing 160 mounted between a surface of another radial wall 230 of the rotor and the stator. All three bearings can be radial bearings and third bearing 160 can include a seal on either side of its ball cage to prevent water and dirt ingress and be mounted to a radial wall 230 with seals such as O-rings 260. There can be a clearance gap between the third bearing and either rotor radial wall 230 or stator 100 that is selected to be larger than the cumulative tolerance of the two bearings to compensate for radial and angular misalignment of bearings 320,330 which can be matched angular contact bearings of a motor vehicle. A wheel can be fixed to the hub 300 allowing retrofitting of the motor to a vehicle.

Description

SEALING ARRANGMENT FOR AN ELECTRIC MOTOR OR GENERATOR

The present invention relates to a sealing arrangement for an electric motor or generator.

Electric motors work on the principle that a current carrying wire will experience a force in the presence of a magnetic field. For example, a rotor, carrying a set of permanent magnets, is arranged to rotate about a stator on which a set of coils arranged to carry an electric current are mounted, resulting in the rotor rotating about the stator and generating movement.

To allow the rotor to rotate about the stator it is necessary for there to be a gap between the rotor and stator. However, if an electric motor is likely to be used in a harsh environment, for example in-wheel electric motors that are used to drive wheels of a vehicle, there is a risk of dirt or other unwanted material entering into the electric motor, which can cause damage.

Accordingly, it is desirable for some form of seal to be placed between the rotor and stator, where typically a seal is place between a stator wall and a circumferential wall of a rotor. However, for an electric motor in which the rotor is arranged to rotate about the stator, the seal typically needs to be of a similar diameter to that of the rotor, which may be quite large.

With the seal being located at the periphery of the electric motor it can be subject to relatively high velocities, thereby increasing the wear of the seal.

It is desirable to improve this situation.

In accordance with an aspect of the present invention there is provided an electric motor or generator according to the accompanying claims.

The present invention provides the advantage of stabilising rotor dynamics by using a bearing to support the rotor housing on an opposite radial wall to the rotor radial wall used to mount the rotor to the stator. In other words, the invention provides support on two faces of a rotor. By increasing stabilisation, this minimises the risk of touch down occurring between magnetic components of the stator and the rotor during rotation of the rotor, for example between permanent magnets mounted on the rotor and stator teeth.

Additionally, improved stabilisation can help to minimise noise and vibration.

Further, the present invention allows a seal to be used between a stator and rotor which has a smaller radius than the outer radius of the rotor, thereby reducing the seal wear rate.

The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 illustrates an axial cross section of a motor assembly according to an embodiment of the present invention; Figure 2 illustrates an isometric view of the motor assembly illustrated in Figure 1.

The embodiment of the invention described is an electric motor for use in a wheel of a vehicle. The motor is of the type having a set of coils being part of the stator for attachment to a vehicle, radially surrounded by a rotor carrying a set of magnets for attachment to a wheel. For the avoidance of doubt, the various aspects of the invention are equally applicable to an electric generator having the same arrangement. In addition, some of the aspects of the invention are applicable to an arrangement having the rotor centrally mounted within radially surrounding coils.

The physical arrangement of the embodying assembly is best understood with respect to Figures 1 and 2. The assembly can be described as a motor and bearing, it can also be described as a hub motor or hub drive as it is built to accommodate a wheel.

Referring to Figures 1 and 2, the motor assembly 40 comprises a stator, a rotor and a bearing block.

The stator includes a heat sink l00 multiple coils 110 formed on stator tooth laminations 120 and electronics (not shown) to drive the coils.

The rotor comprises a front portion 220 and a rear portion 230. The front portion 220 includes a front radial wall and a cylindrical portion 221. The rear portion 230 comprises a rear radial wall that forms an annular disc. The rear portion 230 is coupled to the front portion 220. When coupled together, the rotor front portion 220 and rear portion 230 substantially surround the stator. The rear portion 230 can be coupled to the front portion 220 by any suitable means, for example the rear portion 230 can be bolted to the front portion 220.

The rotor includes a plurality of magnets 242 arranged around the inside of the cylindrical portion 221. The plurality of magnets 242 are preferably mounted on a rotor back iron 243. The magnets 242 are thus in close proximity to the coils 110 mounted on the stator tooth laminations 120 so that magnetic fields generated by the coils 110 generate a force on the magnets 242 arranged around the inside of the cylindrical portion 221 of the rotor thereby causing a torque to be applied to the rotor.

The rotor is attached to the stator using the bearing block.

The bearing block can be a standard bearing block as would be used in a vehicle to which the motor assembly 40 is to be fitted. The bearing block comprises two parts, a first coupling element 300 that is arranged to be coupled to the rotor and a second coupling element 310 that is arranged to be coupled to the stator. For the purposes of the present embodiment the second coupling element 310 is fixed to a central portion of the heat sink 100, for example by bolting the second coupling element 310 to the heat sink. The first coupling element 300 is fixed to a central portion on the front radial wall of the rotor front portion 220.

Mounted between the bearing block's first coupling element 300 and second coupling element 310 are two angular contact ball bearings 320, 330. As shown in Figure 1 and 2, the two angular contact ball bearings 320, 330 are arranged as matching front to front angular contact ball bearings.

Angular contact ball bearings can sustain significant axial loads in one direction together with radial loads. As a result of their design, when a radial load is applied an axial force component is produced. Accordingly, in circumstances when radial loads and axial loads in both directions are likely to be sustained, for example when used on a vehicle as a hub motor, it is desirable to use two angular contact ball bearings, for example matched angular contact ball bearings.

The first coupling element 300 and the second coupling element 310 act as the inner and outer rings, respectively, of the two angular contact ball bearings 320, 330. The balls (not shown) of the angular contact ball bearings are mounted within cages (not shown) placed between the ball bearings inner and outer rings.

Although the bearing block is described using matched angular contact ball bearings, other types of ball bearings can be used.

The rotor can thus be rotationally fixed to a vehicle with which it is to be used via the bearing block at the central portion on the front radial wall of the front portion 220 of the rotor. This has a significant advantage in that a wheel rim and tyre can then be fixed to the rotor at the central portion using the normal wheel bolts to fix the wheel rim to the central portion of the rotor and consequently firmly onto the rotatable side of the bearing block. The wheel bolts may be fitted through the central portion of the rotor through into the bearing block itself. An advantage of this arrangement is that the motor assembly 40 may be retrofitted to an existing vehicle by removing the wheel, bearing block and any other components such as the braking arrangement.

The existing bearing block can then be fitted inside the assembly and the whole arrangement fitted to the vehicle on the stator side and the normal rim and wheel fitted to the rotor so that the rim and wheel surrounds the whole motor assembly. Accordingly, retrofitting to existing vehicles becomes very simple.

A further advantage is that there are no forces for supporting the vehicle on the outside of the rotor, particularly on the circumferential wall 221 carrying the magnets on the inside circumference. This is because the forces for carrying the vehicle are transmitted directly from the suspension fixed to one side of the bearing block (via the central portion of the stator) to the central portion of the wheel surrounding the rotor fixed to the other side of the bearing block (via the central portion of the rotor wall) The rotor also includes a focusing ring and magnets 227 for position sensing.

As illustrated in Figures 1 and 2, when mounted to the rotor front portion 220, the rear portion 230 of the rotor extends in a radial direction towards the axis to form an annular disc.

The stator's heat sink 100 includes an annular ring 130 that extends in an axial direction from a radial portion of the heat sink 100. The heat sink's annular ring 130 extends to substantially the same axial position as the rear portion 230 of the rotor so that an inner radial surface 250 of the rear portion 230 of the rotor substantially overlaps the heat sink's annular ring 130. The radius of the heat sink's annular ring 130 is chosen so that a radial gap exists between the inner surface 250 of the rear portion 230 of the rotor and an outer surface 140 of the heat sink's annular ring 130.

Placed between the inner radial surface 250 of the rear portion 230 of the rotor and the outer surface 140 of the heat sink's annular ring 130 is a third bearing 160. For the purposes of the present embodiment the third bearing 160 is a deep groove ball bearing having an inner and outer ring 161, 162. Preferably, to minimize the ingress of dirt into the electric motor, the ball bearing is either a non-contact or contact sealed type ball bearing. However, other types of bearing could be used, for example an conventional radial bearing with an added seal on a side of the bear that faces outwardly from the rear portion 230.

The diameter of the inner surface of the third bearings inner ring 161 will typically be slightly smaller than the diameter of the outer surface 140 of the heat sink's annular ring 130 so that the third bearing 160 can be mounted onto the heat sink's annular ring 130.

The inner surface 140 of the third bearing 160 is mounted to the annular ring 130 using a press fit.

As the third bearing 160 is on the same axis as the two bearings 320, 330 incorporated within the bearing block, to compensate for any radial or angular misalignment of the third bearing 160 with respect to the two bearings 320, 330 incorporated within the bearing block, sufficient clearance is provided between the outer surface of the third ball bearings outer ring 162 and the inner radial surface 250 of the rear portion 230 of the rotor. The clearance between the outer surface of the third ball bearing outer ring 162 and the inner radial surface 250 of the rear portion 230 of the rotor is preferably selected to be larger than the cumulative tolerance value for the bearings 320, 330 in the bearing block caused by radial and angular misalignment of these bearings.

Preferably, to avoid the ingress of dirt between the gap formed between the outer surface of the third ball bearings outer ring 162 and the inner radial surface 250 of the rear portion 230 of the rotor, and to ensure that contact is maintained between the third bearing 160 and the rear portion 230 of the rotor, an elastic element 260 is placed in this gap, for example one or more 0 rings and/or plastic rings that are embedded within the outer ring 162 of the third bearing 160. For the purposes of the present embodiment, two 0 rings 260 are located in the clearance between the outer surface of the third ball bearing outer ring 162 and the inner radial surface 250 of the rear portion 230 of the rotor. Additionally, a tolerance ring could also located in the clearance between the outer surface of the third ball bearing outer ring 162 and the inner radial surface 250 of the rear portion 230 of the rotor.

Alternatively, the radius of the inner surface of the third bearings inner ring 161 and the outer surface 140 of the heat sink's annular ring 130 are selected to allow a gap to be formed between these surfaces, which can be used to compensate for radial and angular misalignment between the different bearings. Similarly, to avoid the ingress of dirt through this gap an elastic element is placed between the inner surface of the third bearings inner ring 161 and the outer surface 140 of the heat sink's annular ring 130. If the gap formed between the inner surface of the third bearings inner ring 161 and the outer surface 140 of the heat sink's annular ring 130 is sufficiently large to compensate for the radial and angular misalignment of the ball bearings 320, 330 in the bearing block the clearance provided between the upper surface of the third ball bearing outer ring 162 and the lower surface 250 of the rear portion 230 can optionally be removed with the third bearing being press fit to the rear portion 230 of the rotor.

Preferably, the rear portion 230 of the rotor is arranged to have a radially extending lip 260 that radially extends from the inner radial surface 250 of the rear portion 230 upon which the third bearing 160 is mounted. The radially extending lip 260 of the rear portion 230 is arranged to extend pass the side of the third bearing 160, thereby at least partially concealing the third bearing 160. The axial length of the heat sink's annular ring 130 is selected so that an axial gap exists between the inner surface of the radially extending lip and the outer surface of the third bearing 160. Preferably, a bearing preload washer (not shown) is inserted in the axial gap. The use of the preload washer helps to reduce noise from the bearing and reduce wear of the bearing.

To minimize wear on the third bearing 160, and any seals incorporated within the third bearing 160, preferably the dimensions of the rotor's rear portion and the heat sinks annular ring 130 are selected so that the radius of the third bearing 160 is kept to a minimum while being sufficiently large for any cable and/or conduits required by the motor assembly 40 to be feed through the center of the third bearing 160.

Preferably, the radius of the outer surface of the third ball bearings outer ring 162 is less than half the radius of the rotor.

The use of the third bearing 160 provides additional support to a radial wall of the rotor that is opposite to the radial wall used for mounting the rotor to the stator via the bearing block, thereby improving that stability of rotor dynamics, reduces the risk of the cylindrical portion of the rotor touching down on the stator, and reduces motor noise.

Claims

CLAIMS1. An electric motor or generator comprising a coupling device, a rotor and a stator, wherein the coupling device includes a first coupling element coupled to a first radial wall of the rotor and a second coupling element coupled to the stator with a first and second bearing mounted between the first coupling element and the second coupling element to allow the rotor and the stator to rotate relative to each other; and a seal arrangement, wherein the seal arrangement includes a third bearing mounted between a surface of a second radial wall of the rotor and the stator.
2. An electric motor or generator according to claim 1, wherein the first, second and third bearings are radial bearings.
3. An electric motor or generator according to claim 1 or 2, wherein the third bearing includes one or more seals.
4. An electric motor or generator according to any one of the preceding claims, wherein the third bearing includes a plurality of balls located in a ball cage within a bearing housing, wherein a seal is located on one or both sides of the ball cage.
5. An electric motor or generator according to any one of the preceding claims, wherein the second radial wall of the rotor is substantially parallel to the first radial wall of the rotor.
6. An electric motor or generator according to any one of the preceding claim, wherein the third bearing is mounted between a lower surface of the second radial wall of the rotor and the stator.
7. An electric motor or generator according to any one of the preceding claims, wherein one or more seals are mounted between the third bearing and the surface of the second radial wall and/or the stator.
8. An electric motor or generator according to any one of the preceding claims, wherein the third bearing is mounted between the surface of the second radial wall of the rotor and stator at a position that is less than half the radius of the rotor.
9. An electric motor or generator according to any one of the preceding claims, wherein there is a clearance between the third bearing and the surface of the second radial wall of the rotor and/or the stator that is greater than a predetermined value.
10. An electric motor or generator according to claim 9, wherein the predetermined value corresponds to the radial angular run-out of the first and second bearing.
11. A vehicle comprising one or more electric motors according to any one of the preceding claims.AMENDMENTS TO THE CLAIMS HAVE BEEN FILED AS FOLLOWSCLAIMS1. An electric motor or generator comprising a coupling device, a rotor and a stator, wherein the coupling device includes a first coupling element coupled to a first radial wall of the rotor and a second coupling element coupled to the stator with a first and second bearing mounted between the first coupling element and the second coupling element to allow the rotor and the stator to rotate relative to each other; and a third bearing mounted between a surface of a second radial wall of the rotor and the stator, wherein there is a clearance between the third bearing and the surface of the second radial wall of the rotor and/or the stator that is greater than a predetermined value.2. An electric motor or generator according to claim 1, wherein the first, second and third bearings are radial bearings.3. An electric motor or generator according to claim 1 or 2, wherein the third bearing includes one or more seals.4. An electric motor or generator according to any one of the preceding claims, wherein the third bearing includes a plurality of balls located in a ball cage within a bearing housing, wherein a seal is located on one or both sides of the ball cage.5. An electric motor or generator according to any one of the preceding claims, wherein the second radial wall of the rotor is substantially parallel to the first radial wall of the rotor.6. An electric motor or generator according to any one of the preceding claim, wherein the third bearing is mounted between a surface of the second radial wall of the rotor and the stator.7. An electric motor or generator according to any one of the preceding claims, wherein one or more seals are mounted between the third bearing and the surface of the second radial wall and/or the stator.8. An electric motor or generator according to any one of the preceding claims, wherein the third bearing is mounted between the surface of the second radial wall of the rotor and stator having a radius that is less than half the radius of the rotor.9. An electric motor or generator according to claim 1, wherein the clearance between the outer ring of the third bearing and the rear portion is selected to be larger than the cumulative tolerance resulting from the radial and angular misalignment of the first, second and third bearing.10. An electric motor or generator according to any one of the preceding claims, further comprising an elastic element placed in the clearance between the third bearing and the surface of the second radial wall of the rotor and/or the stator.11. A vehicle comprising one or more electric motors according to any one of the preceding claims.