GB2357329A

GB2357329A - Motor assembly

Info

Publication number: GB2357329A
Application number: GB9929568A
Authority: GB
Inventors: Li Shu-Shien
Original assignee: SHU SHIEN LI
Current assignee: SHU SHIEN LI
Priority date: 1999-11-18
Filing date: 1999-12-14
Publication date: 2001-06-20
Anticipated expiration: 2019-12-14
Also published as: JP2001140996A; GB2357329B; GB9929568D0

Abstract

A motor assembly adapted to be mounted to a bicycle for driving a wheel of the bicycle comprising: an electric motor 2 and a speed reduction device 4. The speed reduction device 4 is a high reduction cycloidal reduction device and its method of operation can be seen in figures 8a-e. Balancing means such as a counterweight 425 or an additional cycloidal disc (42' figs 9 and 10) 180{ out of phase with respect to the other disc 42 may also be provided.

Description

2357329 MOTOR ASSEMBLY The present invention generally relates to a rim

(or hub) motor assembly for an electricity powered bicycle, and in particular to a rim motor assembly having a cycloid based speed reduction mechanism for providing a high reduction ratio with a simple structure and extending service life thereof An electricity-powered bicycle comprises an electrical motor to drive a wheel of the bicycle via a speed reduction mechanism. A conventional speed reduction mechanism comprises a gear train, such as a planetary gear system. A conventional rim motor assembly is shown in Figure I comprising a planetary gear system 60, serving as the speed reduction mechanism, arranged inside a casing 10 for coupling the casing 10 to a motor including a motor housing 20, a stator ring 30 and a rotor disk 40.

The rotor disk 40 comprises an output shaft 401 driving planet gears 601 (also see Figure 2) to orbit in a ring gear 602 for rotating an output disk 603 coupled to the casing 10. Using a planetary gear system to reduce the output speed of a motor has several disadvantages:

(1) Lubricant is needed between the meshed gears in order to protect the teeth thereof. Insufficient lubrication may cause abrasion as indicated by character A in Figure 3 or even serious wearing as indicated by character B in Figure 3. Both damages shorten the service life of the gears.

(2) Impact often occurs during the operation of the gears leading to crack of edges of the teeth as indicated by character C of Figure 3 or even break of teeth as indicated by character D.

I (3) The speed reduction ratio that can be accomplished by a gear pair is limited to be 1:10. Thus intermediate stages of gear train is required for a greater reduction ratio. The intermediate stages of gear train require a substantial amount of space and may be very heavy. Figure 4 shows an example of a conventional rim motor comprising a multistaged gear-based speed reduction device. The conventional speed reduction device comprises a driving gear 604' coupled to an output shaft 401' of a rotor disk 40 and meshing a gear 605'. A pinion 606' is rotatably attached to the gear 605' for engaging with a driven gear 607'. Such a structure is complicated making the rim motor heavy and bulky and thus not fit for a bicycle.

Thus, it is desired to provide a rim motor assembly that overcome the above problems.

A general aim of the present invention is to provide a rim motor assembly comprising a cycloid-based speed reduction device having a simple and compact structure, smooth operation and high speed reduction ratio.

A preferred aim of the invention is to provide a rim motor assembly comprising a cycloid-based speed reduction device having two cycloidal disks for force balance and thus smooth operation thereof.

Another preferred aim of the invention is to provide a motor assembly which is capable to be mounted at a suitable location on a bicycle frame and coupled to a wheel of the bicycle by a belt transmission.

in accordance with the present invention, there is provided a rim motor assembly comprising a casing 2 coaxially mounted in a bicycle wheel by being rotatably supported on an axle fixed to the bicycle frame defining a common axis. An electric motor is arranged m the casing and fixed to the axle. A speed reduction device is coupled between the motor and the casing comprising a fixed ring having an inner circumference to which a first number of rollers are rotatably supported in an equally-spaced manner. A cycloidal disk is eccentrically coupled to an output spindle of the motor for rotating about a central axis thereof and orbiting about the common axis. The cycloidal disk has an outer circumference in which a second number of recesses are defined for receivingly engagmg the rollers. The second number is smaller than the first number whereby when the cycloidal disk is driven by the motor to revolve about a central axis thereof at a high speed, the cycloidal disk is caused to orbit about the common axis at a low speed. The speed ratio is determined by the first and second numbers. An output disk has a central shaft coupled to the casing and at least one eccentric pin rotatably received in a hole defined in the cycloidal disk whereby the output disk is driven by the orbiting motion of the cycloidal disk to drive the casing and thus the wheel fixed to the casing at the low speed.

Preferred embodiments of the invention are described below with reference to the accompanying drawings, in which:

Figure 1 is a cross-sectional view of a conventional rim motor; Figure 2 is a planetary gear system adapted in the convention rim motor.

3 Figure 3 shows a gear of a speed reduction device adapted in the conventional rim motor illustrating damages occurring thereto during the operation of the speed reduction device; Figure 4 is a cross-sectional view of a conventional multi-staged gear- based speed reduction device; Figure 5 is an exploded view of a rim motor assembly constructed in accordance with a first embodiment of the present invention; Figure 6 is a cross-sectional View of the rim motor assembly of the present invention; Figure 7 is a plan view showing a portion of a speed reduction device in accordance with the present invention; Figures 8A-8E sequentially show the operation of the speed reduction device of the present invention; Figure 9 is an exploded view of a second embodiment of the present invention in which two 1800 out-of-phase cycloidal disks are incorporated in the cycloid-based speed reduction device for compensation of eccentricity thereof, Figure 10 is a cross-sectional view of the rim motor assembly in accordance with the second embodiment of the present invention; Figure I I is a cross-sectional View of a rim motor assembly constructed in accordance with a third embodiment of the present invention; Figure 12 is a plan view showing a portion of the cycloid-based speed reduction device in accordance with the third embodiment of the present invention; 4 Figure 13 is an exploded view of a motor assembly constructed in accordance with a fourth embodiment of the present invention; Figure 14 is a top view of a portion of a bicycle showing the motor assembly of the fourth embodiment mounted to the bicycle frame and coupled to a wheel by a belt transmission; and Figure 15 is a side elevational view of Figure 14.

With reference to the drawings and in particular to Figures 5-7, a motor assembly constructed in accordance with the present invention comprises a casing I rotatably and coaxially supported on a fixed axle 3 that is fixed to front forks of a bicycle frame (not shown) defining a rotational axis of the rim motor assembly, an electric motor 2 housed in the casing I and fixed to the axle 3 and a speed reduction device 4 coupled between the motor 2 and the casing I for driving the casing I when the motor 2 is actuated.

The casing I is coaxially mounted in a wheel of the bicycle. The casing I comprises a cylindrical member 12 and two covers 1.1, 11' attached to opposite open ends of the cylindrical member 12 for defining an interior space (not labeled) in which the motor 2 and the speed reduction device 4 are housed. The covers 11, 11' comprise hubs defining aligned central bores (not labeled) through which the axle 3 extends. The first cover I I comprises a clutch 13, such as a drum type clutch, coupled to the hub thereof. A bearing 14 is coaxially mounted in the central bore of the second cover I P for rotatably supporting the casing I on the axle 3. A plurality of eyelets I 11, 111' are defined along an outer rim portion of each casing member 11, 11' for connecting the rim motor assembly to the wheel by means of for example spokes (not shown) whereby the wheel is rotated by the rim. motor assembly when the electric motor 2 is actuated.

Alternatively, the casing I may be directly fixed to the wheel by means of fasteners.

The electric motor 2 may be a direct current electric motor or an alternate current electric motor having an output spindle 21 defining with a central bore 211 defined therein for receiving the axle 3 thereby fixing the motor 2 to the axle 3. Thus, the motor 2 remains stationary with the axle 3. The output spindle 21 of the motor 2 forms an eccentric shaft 22 which will be further described.

The axle 3 that extends between the front forks of the bicycle frame has threaded end sections 31, 3 F for engaging with nuts (not shown) to secure the axle 3 to the bicycle frame. The axle 3 extends through the bearing 14 of the cover I F and the clutch 13 of the cover I I of the casing I for rotatably supporting the casing 1. The axle 3 also extends through the central bore 211 of the motor 2 for supporting the motor 2 thereon. A slit 32 is defined in the axle 3 for receiving an electrical cable (not labeled) that supplies power to the motor 2.

The speed reduction device 4 is coupled between the eccentric section 22 of the output spindle 21 and the casing I for transmitting torque/rotation of the motor 2 to the casing 1. The speed reduction device 4 comprises a fixed ring 41 fixed to the motor 2 as shown in Figure 6 thereby stationary with respect to the casing 1, a cycloidal disk 42 rotatably received in the ring 41 and driven by the motor 2 and an output disk 43 drivingly coupled to the cycloidal disk 42. The ring 41 comprises an annular body 411 having an inner circumference defining an inner diameter. A plurality of first arc recesses (not labeled) are defined in and spaced along the inner circumference thereof for receiving and retaining rollers 412 whereby the rollers 412 partially project beyond the inner circumference. A annular 6 support member 413 having an inner diameter smaller than the inner diameter of the body 411 is attached to or integrally formed with the body 411 whereby an inner rim portion thereof extends inwardly beyond the inner circumference of the body 411 for supporting and axially retaining the rollers 412 in position.

The cycloidal disk 42 has an outside diameter smaller than the inside diameter of the body 411 for being movably received in the body 411 of the fixed ring 41 whereby the cycloidal disk 42 is allowed to orbit about the rotational axis of the motor assembly. A plurality of second arc recesses 421 are defined in and spaced along an outer circumference of the cycloidal disk 42 forming a plurality of teeth 422 therebetween. The second arc recesses 421 correspond in size to the rollers 421 for selectively and sequentially receiving the rollers 421 therein when' the cycloidal disk 42 moves inside the ring 41. The cycloidal disk 42 defines a central bore (not labeled) in which a bearing or bushing 422 is fit for rotatably supporting the cycloidal disk 42 on the eccentric section 22 of the output spindle 21 of the motor 2 whereby when the motor 2 is actuated, the cycloidal disk 42 is driven by the eccentric section 22 of the output spindle 21 to orbit about the rotational axis of the motor assembly.

The number of the first are recesses or the rollers 412 is different from the number of the second arc recesses 421 or the teeth 422. In the embodiment illustrated, the number of the rollers 412 is less than the number of the teeth 422 for speed reduction purpose. This will be fiirther explained.

At least one pin-receiving hole 423 is defined in the cycloidal disk 42 eccentric with respect to a central axis of the cycloidal disk 42. In the embodiment, a plurality of such pin receiving holes 423 is defined in the cycloidal disk 42. Preferably, the pin receiving holes 423 are equally 7 spaced along a circular trace eccentric with respect to the cycloidal disk 42 and substantially coaxial with respect to the rotational axis of the motor assembly. The eccentricity is determined corresponding to the eccentricity of the eccentric section 22 with respect to the rotational axis.

Preferably, a counterweight 425 is attached to the cycloidal disk 42 for compensating force imbalance caused by the eccentricity of the cycloidal disk 42.

The output disk 43 comprises a plurality of pins 431 extending from a first face thereof and a central output shaft 433 extending from a second face thereof. A central bore 434 is defined in the output disk 43 through which the axle 3 extends. A bearing 435 is arranged in the central bore 434 for rotatably supporting the output disk 43 on the axle 3. The output shaft 433 is coupled to the casing member I I by the clutch 13.

The pins 431 are arranged corresponding to the pin receiving holes 423 of the cycloidal disk 42 and have a diameter smaller than that of the pin receiving holes 423 whereby the pins 431 are movably received in the pin receiving holes 423 and a line contact is formed between each pin 431 and the corresponding pin receiving hole 423. Preferably, a bearing or bushing 432 is fit over each pin 431 for protection from mechanical abrasion and wearing.

As shown in Figure 7, the fixed ring 41 and the cycloidal disk 42 are dimensioned so that due to the eccentricity of the cycloidal disk 42, a portion of the outer circumference of the cycloidal disk 42 engages the inner circumference of the fixed ring 41 and the second arc recesses 421 of the cycloidal disk 42 sequentially engage with the corresponding rollers 412 when the cycloidal disk 42 moves. Due to the fact that the ring 41 is maintained stationary, when the motor spindle 21 rotates in a given direction, the cycloidal disk 42 is caused to orbit about the rotational axis 8 in the same direction, while revolving in a reversed direction. Thus, the cycloidal disk 41 is driven by the motor 2 via the eccentric section 22 of the motor output spindle 21 to orbit about the rotational axis with accompanying revolution about the central axis thereof which in turn drives the output disk 43 to rotate about the rotational axis by means of the pins 431 received in the pin receiving holes 423 of the cycloidal disk 42. The rotation of the output disk 43 is transmitted to the casing I via the clutch 13.

The operation of the rim motor assembly is sequentially illustrated in Figures 8A-8E.

It is to be noted that the direction of the rotation of the output spindle 21 of the motor 2 is opposite to the revolving direction of the cycloidal disk 42. In other words, the rotation direction of the motor 2 is opposite to the rotation direction of the casing 1.

Without losing generality, taking a cycloidal disk 42 having seventeen (17) teeth 422 (equivalently 17 arc recesses 42 1) and a fixed ring 41 having eighteen (18) rollers 412 as an example, when motor 2 is actuated to rotate in a first direction, the cycloidal disk 42 is driven by the eccentric section 22 of the output spindle 21 of the motor 2 to orbit about the rotational axis in an opposite second direction. The movement of the cycloidal disk 42 causes the roller 412 that currently engages the corresponding second arc recess 421 to separate from the second arc recess 421 and then the next roller 412 starts to engage the corresponding second arc recess 421 as shown in Figures 8A-8D. Since the numbers of the rollers 412 and the teeth 422 is different by one (1), a full turn of the output spindle 21 of the motor 2 causes the cycloidal disk 42 to advance a circumferential distance corresponding that between two adjacent rollers 412, namely one eighteenth of the inner circumference of the fixed ring 4 1, and the cycloidal.

disk 42 makes a 1/18 turn of revolution about the central axis thereof. In 9 other words, the output disk 43 that is driven by the cycloidal disk 42 rotates at a speed only 1/18 of the motor spindle 21. Thus a reduction ratio 1/18 is achieved. In view of this, it can be observed that the speed reduction device 4 based on the cycloidal disk 42 may provide, with a simple structure, a higher reduction ratio than a speed reduction mechanism based on gears.

Figures 9 and 10 show a second embodiment of the present invention in which two cycloidal disks 42, 42' are arranged in the ring 41 and rotatably and eccentrically mounted to the output spindle 21 of the motor 2.

However, the cycloidal disks 42, 42' are 180' out of phase. The purpose of MCorporation of the second cycloidal disk 42' is to replace the counterweight 425 for providing a smoother and less noisy operation of the rim motor assembly.

Figures I I and 12 show a modification of the first embodiment of the present invention in which the second arc recesses 421 and the teeth 422 of the cycloidal disk 42 of the first embodiment are replaced by a wavy outer circumference having a first number of prOjections. In other words, a cycloidal disk 42A having a wavy outer circumference with a first number of projections 421A formed therealong is movably received in a ring 41A having a wavy inner circumference having a second number of projections 41 IA. The second number is different from the first number as discussed above. The engagement between the projections 411A, 421A of the wavy circumferences resembles to that between the rollers 412 and the teeth 422 of the first embodiment.

Although in the above description, the rim motor assembly is intended to be coaxially mounted in and to a wheel, it is possible to fix the rim motor assembly of the present invention to any suitable location in the bicycle frame. Figures 13-15 show a variation of the rim motor assembly described above wherein the motor assembly is fixed to a location of the bicycle frame other than the wheel and is coupled to the wheel by a belt 5 1.

In the embodiment shown in Figures 13-15, the casing I is removed and replaced by a shielding cap 6 and a drum type clutch 5 is coupled to and driven by the output disk 43. The belt 51 mechanically connects the clutch 5 to the wheel.

Although the present invention has been described with respect to the preferred embodiments, it is contemplated that a variety of modifications, variations and substitutions may be done without departing from the scope of the present invention that is intended to be defined by the appended claims.

Claims

CLAIMS:

1 1. A motor assembly adapted to be mounted to a bicycle for driving a 2 wheel of the bicycle comprising:

3 an electric motor fixed to the bicycle and having an output spindle 4 defining a first axis of the motor assembly; and a speed reduction device comprising:

6 a fixed ring fixed to the bicycle coaxial with the first axis, the 7 ring having an inner circumference on which first 8 engagement means is formed; 9 a first disk rotatably and eccentrically mounted to the output spindle of the motor and rotatably arranged inside the ring 11 whereby when the motor is actuated, the first disk orbits 12 about the first axis, the first disk having an outer 13 circumference in which second engagement means is 14 formed for inter-engaging with the first engagement means to provide a cycloidal motion therebetween when the first 16 disk orbits thereby causing he first disk to revolve about a 17 central axis thereof, at least a pin receiving hole being 18 defined in the first disk whereby when the first disk 19 revolves, the pin receiving hole rotates about the first axis; and 21 a second disk rotatably supported on the bicycle coaxial with the 22 first axis, the second disk having a central output shaft 23 adapted to be coupled to the bicycle wheel and an eccentric 24 pin rotatably received in and engaging with the hole of the first disk whereby the second disk is driven by the 26 revolution of the first disk to drive the wheel.

12 1 2. The motor assembly as claimed in Claim I wherein the first 2 engagement means comprises a first number of equally-spaced rollers 3 rotatably mounted on the inner circumference of the fixed ring and the 4 second engagement means comprises a second number of equally spaced arc recesses defined in the outer circumference of the first disk 6 for selectively and sequentially engaging the corresponding rollers 7 when the first disk orbits.

1 3. The motor assembly as claimed in Claim 1 wherein the first 2 engagement means comprises a first number of wavy projections 3 formed on the inner circumference of the fixed ring and the second 4 engagement means comprises a second number of wavy projections defined in the outer circumference of the first disk for selectively and 6 sequentially engaging the corresponding projections of the fixed ring 7 when the first disk orbits.

1 4. The motor assembly of any one of claims 1 to 3 further comprising a casing 2 rotatably mounted to the bicycle with the electric motor and the speed 3 reduction device housed therein, the output shaft of the second disk 4 being coupled to the casing for driving the casing to rotate about the first axis.

1 5. The motor assembly as claimed in Claim 4, wherein the casing is 2 coaxially arranged in and mounted to the bicycle wheel which is 3 rotatably mounted to the bicycle by an axle extending through the 4 casing, the motor spindle and the fixed ring being fixed to the axle.

1 6. The motor assembly of any one of claims 1 to 5 wherein the output spindle 2 of the electric motor forms an eccentric section to which the first disk 3 is rotatably mounted.

13 1 7. The motor assembly of any one of claims 1 to 6 wherein balancing means 2 is mounted to the first disk for compensating the eccentricity of the 3 first disk.

1 8. The motor assembly as claimed in Claim 7, wherein the balancing 2 means comprises a counterweight fixed to the first disk.

1 9. The motor assembly as claimed m Claim 7, wherein the balancing 2 means comprises a third disk identical in size and shape to the first 3 disk and coupled to the output spindle of the electric motor, the first 4 disk and third disk being 180' out of phase with respect to each other.

1 10. The motor assembly as claimed in Claim 4, wherein the output shaft 2 of the second disk is coupled to the casing by means of a clutch.

1 11. The motor assembly as claimed in Claim 1, wherein the first disk 2 defining a plurality of pin receiving holes equally spaced along a 3 circuit trace coaxially with the first axis and wherein the second disk 4 forms a plurality of pins receivingly engaging with the pin receiving holes of the first disk to be driven thereby.

1 12. The motor assembly as claimed in Claim 2, wherein the fixed ring 2 defines arc recesses in the inner circumference thereof for rotatably 3 receiving and retaining the rollers.

1 13. The motor assembly as claimed in Claim 12, wherein a 2 circumferential flange is formed along the inner circumference of the 3 fixed ring for supporting and axially retaining the rollers.

1 14. The motor assembly as claimed in Claim 1, wherein the output shaft 2 of the second disk is coupled to the wheel by means of belt 3 transmission.

14 15. The motor assembly as claimed in claim 14, wherein the belt and the motor assembly are separated by a shielding cap.

16. The motor assembly of any one of claims 1 to 15 wherein the electric motor is a direct current motor.

17. The motor of any one of claims 1 to 15 wherein the electric motor is an alternate current motor.

18. A motor assembly substantially as described herein with reference to Figs. 5-8, 9 and 10, 11 and 12, or 13-15 of the accompanying drawings.