HUBLESS WHEEL MOTOR

Abstract

The present invention relates to a drive system for an electric vehicle comprising: a wheel rim, a bearing arrangement, a plurality of rotor elements circumferentially arranged along a circumference coaxial with a circumference of the wheel rim and fixated to the wheel rim adjacent to the bearing arrangement; and a plurality of stator elements circumferentially arranged along a circumference coaxial with the circumference of the rotor elements and spaced apart from the rotor elements, the stator elements are non-rotationally arranged to the non-rotating portion of the bearing arrangement, whereby an air gap in is formed between a stator element and a rotor element, wherein a first distance from the axis of rotation to the bearing arrangement is larger than a second distance from the air gap to the bearing arrangement.

Claims

1. A drive system for an electric vehicle comprising: a wheel rim having an inner circumference on an inner surface and an axis of rotation and configured to provide driving motion for said vehicle; a bearing arrangement comprising a non-rotating inner portion, said bearing arrangement being configured to enable rotation of said wheel rim with respect to said non-rotating inner portion for providing the driving motion, said bearing arrangement being circumferentially arranged in contact with the inner surface of said wheel rim; a plurality of rotor elements circumferentially arranged along a circumference coaxial with the circumference of said wheel rim and fixated to said wheel rim adjacent to said bearing arrangement; and a plurality of stator elements circumferentially arranged along a circumference coaxial with the circumference of the rotor elements and spaced apart from said rotor elements, said stator elements are non-rotationally arranged to said non-rotating inner portion of said bearing arrangement, wherein an air gap is formed between a stator element and a rotor element, wherein a first distance from said axis of rotation to said bearing arrangement is larger than a second distance from said air gap to said bearing arrangement.

2. The drive system according to claim 1, wherein said stator element comprises a stator core, wherein said air gap is formed between said stator core and said rotor element.

3. The drive system according to claim 1, wherein said air gap is formed in a radial direction of said wheel rim.

4. The drive system according to claim 1, wherein said first distance is five times larger than said second distance.

5. The drive system according to claim 1, wherein said first distance is ten times larger than said second distance.

6. The drive system according to claim 1, wherein said contact between said bearing arrangement and said inner surface of said wheel rim is formed by rolling elements of said bearing arrangement.

7. The drive system according to claim 6, wherein said second distance is the distance from said rolling elements to said air gap.

8. The drive system according to claim 1, wherein an outer diameter of said bearing arrangement is substantially equal to an inner diameter of said wheel rim.

9. The drive system according to claim 1, wherein a cover member is arranged to cover said rotor elements and said stator elements in a hollow space formed inside and coaxial with said wheel rim, wherein said cover member seals the wheel rim in the direction of the cover member.

10. The drive system according to claim 9, wherein said hollow space houses an energy storage configured to provide power for operating said drive system.

11. The drive system according to claim 9, wherein said hollow space houses a control unit configured to control the drive system.

12. The drive system according to claim 1, wherein said plurality of stator elements are arranged on a non-rotating mounting arrangement.

13. The drive system according to claim 12, wherein the stator core of each of said stator elements is arranged on said non-rotating mounting arrangement.

14. The drive system according to claim 1, wherein a tire is arranged circumferentially on the outside of said wheel rim.

15. A powered wheelchair comprising the drive system according to claim 1.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0038] These and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing exemplary embodiments of the invention, wherein:

[0039] FIG. 1 schematically shows a wheelchair comprising a drive system according to an exemplary embodiment of the invention.

[0040] FIG. 2 shows a perspective cross-section of a drive system according to an exemplary embodiment of the invention;

[0041] FIG. 3 shows a cross-section of a part of the embodiment shown in FIG. 2;

[0042] FIG. 4 schematically shows a drive system according to an exemplary embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0043] In the following description, the present invention is mainly described with reference to a drive system for powered wheelchairs. However, it should be noted that the invention is equally applicable to other types of vehicles and is not limited to powered wheelchairs. Like reference numbers refer to like elements throughout.

[0044] FIG. 1 illustrates an exemplary embodiment of the invention. FIG. 1 shows a powered wheelchair 100 comprising a drive system 102 according to an exemplary embodiment of the invention. Each of the drive systems 102 is arranged as a wheel of the powered wheelchair 100. By using the drive system 102 as a wheel, the required electronic components and energy storage is kept inside the wheel 102 (as will be shown with reference to FIGS. 2-4), thus the overall powered wheelchair 100 is less bulky compared to prior art powered wheelchairs. Furthermore, the drive system 102 has a large diameter meaning that the diameter of the rotor and stator arrangements is relatively large, providing for a large torque of the electric drive system 102, and thus eliminating the need for a gearbox. Moreover, the drive system 102 for the powered wheelchair 100 is a direct drive. Thereby, a rotatable part 104, comprising a tire, of the wheel 102 is allowed to rotate freely such that a user of the powered wheelchair 100 may operate the driving of the wheelchair 100 manually by hand if needed. The elimination of the gearbox and arranging the energy storage and drive electronics in the wheel enables a new design of the chassis for the wheelchair 100 compared to traditional wheelchair chassis.

[0045] FIG. 2 shows a perspective cross-sectional view of an exemplary embodiment of the invention and FIG. 3 is a cross-section of a portion of the exemplary embodiment in FIG. 2. Now with reference to FIG. 2 and FIG. 3, there is shown a drive system 200 comprising a wheel rim 202, a bearing arrangement 204, rotor elements 206, and stator elements 208 (only one or the rotor elements and one of the stator elements are numbered in order to avoid cluttering in the drawing) each comprising a coil 246. The rotor elements 206 are preferably magnetic elements. In this way, no electrical connections are needed to the moving parts (e.g. rotor elements) of the drive system 200. The wheel rim 202 has an axis of rotation 210 about which the wheel rim 202 is configured to rotate when in use. A non-rotating inner portion 216 of the bearing arrangement 204 is arranged along the circumference 212 of the wheel rim 202 and in contact with the wheel rim 202 via rolling elements 214, in the form of spherical balls, of the bearing arrangement 204. Note that the bearing arrangement 204 is not limited to having ball elements but may comprise other such elements. With the bearing arrangement 204, the wheel rim 202 is rotatable with respect to the inner portion 216 of the bearing arrangement 204, thus the bearing arrangement 204 enables rotation of the wheel rim 202. The rotor elements 206 are circumferentially arranged along a circumference coaxial with the circumference 212 of the wheel rim 202. Furthermore, the rotor elements 206 are fixated to the wheel rim 202, adjacent to the bearing arrangement 204. The stator elements 208 are circumferentially arranged adjacent to the rotor elements 206 and coaxial with the circumference of the rotor elements 206, preferably along a circumferential with a smaller diameter than the circumference along which the rotor elements 206 are arranged. Thus, the stator elements 208 are arranged closer to the axis of rotation 210 compared to the rotor elements 206. Moreover, the stator elements 208 are arranged spaced apart from the rotor elements 206. Note that stator elements 208 and rotor elements 206 are arranged along the entire corresponding circumference, although in the drawing not all rotor and stator elements are shown. Thus, a plurality of stator elements 208 are coaxially arranged with respect to a plurality of rotor elements 206. As a result of the arrangement of the stator 208 and rotor elements 206, an air gap 222 is formed in the radial direction 224 from the stator core 209 (only shown in FIG. 3) of the stator elements 208 to the rotor elements 206. As depicted herein, most clearly seen in FIG. 3, the stator element 208 comprises a coil 246 mounted on a stator core 209. As shown in FIG. 3, the stator core 209 may extend outside the coil 246 in a direction towards the rotor element 206. However, other configurations are possible with e.g. the stator core 209 being arranged in-between two or more coils such that the stator core 209 is placed within (or in-between) the coils. Note that the air gap 222 here in FIG. 3 is depicted in the radial direction 224; however, the air gap 222 may in other configurations be formed in other directions without departing from the scope of the invention.

[0046] Preferably, the air gap 222 should be kept as small as possible as long as the rotor elements 206 and the stator elements 208 are not in physical contact. A typical air gap 222 is smaller than 1 mm, for example in the radial direction 224. The air gap 222 extends around the entire circumference of the arrangement of the rotor and stator elements 208. A first distance 226 is measured as the distance from the axis of rotation 210 of the wheel rim 202 to a point in the bearing arrangement 204 and a second distance 228 is measured as the distance from the air gap 222 to the bearing arrangement 204. The point in the air gap 222 from which second 228 distance is measured is preferably a center point of the air gap 222, and the point of the bearing arrangement 204 to which the first distance 226 and the second distance 228 are measured may be a center point of the bearing arrangement 204, here depicted as the center of a rolling element 214. However, the first 226 distance is larger than the second 228 distance. Preferably, the first 226 distance is twice the second distance 228, or five times larger, or ten times larger. In an exemplary embodiment, the air gap 222 between the rotor elements 206 and the stator elements 208 is approximately 0.5 mm, the width of the air gap is approximately 20 mm, the diameter of the circumferential air gap 222 is approximately 400 mm, the diameter of the wheel rim 202 is thereby close to 400 mm, and the second distance 228 is 25 mm. The second distance is normally between 5 millimeter and 50 millimeter, preferably smaller than 30 mm.

[0047] In FIG. 2 and FIG. 3, the rotor elements 206 are magnetic elements and the stator elements 208 each comprises a coil 246 arranged on a stator core 209. In operation, a modulation scheme of magnetic field generated by the coils 208 enables the rotor elements 206 to move by applying appropriate magnetic field pulses produced by the coil 246 to the rotor elements 206, thereby also moving the wheel rim 202. The modulation scheme may for example be a 3-phase scheme for a brushless electric motor. Preferably, the coils 246 are arranged such that a central axis of each coil is pointing towards the axis of rotation 210 of the wheel rim 202.

[0048] Again with reference to FIG. 2, the stator elements 208 are mounted on a non-rotating mounting 231 arrangement which is fixated with the inner portion 216 of the bearing arrangement 204. Moreover, a central plate 234 is fixated to the inner portion 216 of the bearing arrangement 204 by screws or bolts 230 (only one is numbered in order to avoid cluttering in the drawing). Furthermore, a hollow space 236 coaxial with the wheel rim 202 is formed between the central plate 234 and a cover member 240. In the hollow space 236, a plurality of support members 238 (only one is numbered in order to avoid cluttering in the drawing) is mounted on the central plate. The support members 238 and their function will be explained in more detail with reference to FIG. 4. For mounting of the drive system 200 as a wheel on a wheelchair chassis, a mounting element 232 is arranged on the side of the drive system 200. The drive system 200 may thus be mounted on a wheelchair using e.g. bolts.

[0049] FIG. 4 illustrates an embodiment of the present invention. In FIG. 4 a drive system 400 is shown similar to the drive system 200 as described with reference to FIG. 2. Furthermore, in the hollow space 236 formed in the center of the wheel rim 202, an energy storage 402 (only one is numbered in order to avoid cluttering in the drawing) and a control unit 404 are arranged. Preferably, the energy storage 402 and the control unit 404 are mounted on the support members 238. The hollow space 236 is provided between the central plate 234 and the cover member 240. The energy storage 402 is arranged to provide power to the stator elements 208, and the control unit 404 is configured to control the drive system 400, for example, the control unit 404 may provide a suitable pulse scheme for current provided to the stator elements 208 for enabling motion of the rotor elements 206 and thereby the wheel rim 202. In addition, a tire 406 is arranged around the circumference of the wheel rim 202, and circumferentially attached to the wheel rim on the outside of the circumference. By having a tire 406 mounted on the wheel rim, the drive system 400 may be used as a wheel for a vehicle driving both indoor and outdoor depending on the type of tire and the type of vehicle. Moreover, the support members 238 advantageously provide mechanical support for the drive system when operating as a wheel. For example, the support members provide efficient support for absorbing shear forces acting on the wheel rim 202.

[0050] Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. For example, the central plate, the cover member and the support members may be embodied in other variations than what is depicted in the exemplary embodiments. Furthermore, the mounting element may be configured differently as long as a proper mounting to a wheelchair is made possible.

[0051] In accordance with the invention a control unit is preferably a micro processor or any other type of computing device. Similarly, a computer readable medium, which may be part of or separate from the control unit and may be used for storing e.g. software for controlling various functions related to the drive system, may be any type of memory device, including one of a removable nonvolatile/volatile random access memory, a hard disk drive, a floppy disk, a CD-ROM, a DVD-ROM, a USB memory, an SD memory card, or a similar computer readable medium known in the art.

[0052] In the claims, the word comprising does not exclude other elements or steps, and the indefinite article a or an does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage.