A cycloidal transmission and torque measurement device

Abstract

A cycloidal transmission in which a cam rotatably mounted in an inner gear mounted is driven so that as the cam rotates the centre of the inner gear moves in a circular path within a ring gear and the inner gear. A cycloidal driver is coupled to the inner gear by an eccentric coupling which may include eccentric bearings or eccentric driver pins with offset shafts, one shaft rotatably mounted to the cycloidal driver and the other shaft rotatably mounted to the inner gear. A torque sensing system may be used for measuring the torque applied to ends of a hollow axle having torque sensors located between end regions and a central region of a sensing body fixed to the axle.

Description

[0001] A CYCLOIDAL TRANSMISSION AND TORQUE MEASUREMENT DEVICE

[0002] FIELD

[0003] This invention relates to a cycloidal transmission and a torque measurement device.

[0004] BACKGROUND

[0005] Cycloidal transmissions can provide a high reduction ratio in a compact form factor. This is attractive in a range of applications, including electric bicycles (e- bikes) and other motor driven or assisted transport solutions. The high reduction ratio allows advantageous matching of electric motor performance characteristics to human assisted low rpm e-bike requirements.

[0006] A number of designs have been proposed utilising cycloidal transmissions for human assisted e-bike applications. Conventional cycloidal drive systems have, however, suffered from problems of high friction, wear, noise and vibration. As a result there has been no wide spread use of cycloidal drives in e-bikes.

[0007] For proper control of an electric motor in an e-bike the torque provided by a human via the cranks should be monitored. Available torque sensors are commonly located in the cranks or chain ring and are not integrated into the transmission. This can result in greater cost, complexity and inconvenience as well as requiring battery replacement for each torque sensor.

[0008] SUMMARY

[0009] According to one example there is provided a transmission comprising: a. an axle; b. a cam rotatably mounted about the axle; c. an inner gear mounted to the cam configured so that as the cam rotates the central axis of the inner gear moves in a circular path; d. a ring gear surrounding and engaging the inner gear arranged so that teeth of the inner gear engage teeth of the ring gear as the cam drives the inner gear around the ring gear; and e. a cycloidal driver coupled to the inner gear by an eccentric coupling.

[0010] According to another example there is provided a transmission comprising: a. an axle; b. a cam rotatably mounted about the axle; c. an inner gear mounted to the cam configured so that as the cam rotates the centre of the inner gear moves in a circular path; d. a ring gear surrounding and engaging the inner gear arranged so that teeth of the inner gear engage teeth of the ring gear as the cam drives the inner gear around the ring gear; and e. a cycloidal driver coupled to the inner gear by a plurality of eccentric driver pins wherein each driver pin has offset shafts with one shaft rotatably mounted to the cycloidal driver and the other shaft rotatably mounted to the inner gear.

[0011] According to another example there is provided a torque sensing system for measuring the torque applied to ends of a hollow axle comprising; a. a sensing body dimensioned to locate within a hollow axle having a central region linked to end regions on either side by linking regions, wherein the linking regions are dimensioned to allow a prescribed amount of rotational movement between the end regions and the central region for a prescribed range of torque measurement; and b. torque sensors located between each end region and the central region configured to measure the torque applied to each end of the axle relative to the central region. Embodiments may be implemented according to any one of the dependent claims.

[0012] It is acknowledged that the terms "comprise", "comprises" and "comprising" may, under varying jurisdictions, be attributed with either an exclusive or an inclusive meaning. For the purpose of this specification, and unless otherwise noted, these terms are intended to have an inclusive meaning - i.e., they will be taken to mean an inclusion of the listed components which the use directly references, and possibly also of other non-specified components or elements.

[0013] Reference to any document in this specification does not constitute an admission that it is prior art, validly combinable with other documents or that it forms part of the common general knowledge.

[0014] It is an object of the invention to provide an improved cycloidal transmission, an improved torque measurement device or to at least provide the public with a useful choice.

[0015] BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The accompanying drawings which are incorporated in and constitute part of the specification, illustrate embodiments of the invention and, together with the general description of the invention given above, and the detailed description of embodiments given below, serve to explain the principles of the invention, in which:

[0017] Figure 1 is a perspective view of a first example motor and transmission unit suitable for use with an e-bike;

[0018] Figure 2 is an exploded view of the components of the motor and transmission unit shown in Figure 1 from a first perspective;

[0019] Figure 3 is an exploded view of the components of the motor and transmission unit shown in Figure 1 from a second perspective; Figure 4 is a perspective view key transmission components of the motor and transmission unit shown in Figure 1 with the inner gear in a first position with respect to the ring gear;

[0020] Figure 5 is a perspective view key transmission components of the motor and transmission unit shown in Figure 1 with the inner gear in a second position with respect to the ring gear;

[0021] Figure 6 is a perspective view of the linkage between the inner gear and cycloidal driver via the eccentric driver pins of the motor and transmission unit shown in Figure 1;

[0022] Figure 7 is a perspective view of the inner gear and eccentric driver pins of the motor and transmission unit shown in Figure 1;

[0023] Figure 8 shows views of the eccentric driver pin from various perspectives;

[0024] Figures 9a-c show the cam in a side view, perspective view and end view;

[0025] Figure 10 shows the counterweight of the motor and transmission unit shown in Figure 1 balancing the inner gear;

[0026] Figure 11 is a cutaway perspective view of a torque sensing system provided within a hollow axle;

[0027] Figure 12 shows a second example transmission according to a second design;

[0028] Figure 13 shows a front view of the transmission shown in Figure 12;

[0029] Figure 14 shows a cross-sectional view along line A-A in Figure 13;

[0030] Figure 15 shows a side view of the transmission shown in Figure 12;

[0031] Figure 16 shows a cross-sectional view along line D-D in Figure 15; Figure 17 shows a cross-sectional view along line C-C in Figure 15;

[0032] Figure 18a shows a rear perspective view of the transmission shown in Figure 12;

[0033] Figure 18b shows front perspective view of the transmission shown in Figure 12;

[0034] Figure 19 shows an exploded front perspective view of the transmission shown in Figure 12;

[0035] Figure 20 shows an exploded rear perspective view of the transmission shown in Figure 12;

[0036] Figure 21 shows a third example transmission according to a second design employing eccentric bearings;

[0037] Figure 22 shows a front view of the transmission shown in Figure 21;

[0038] Figure 23 shows a cross-sectional view along line A-A in Figure 22;

[0039] Figure 24 shows a side view of the transmission shown in Figure 21;

[0040] Figure 25 shows a cross-sectional view along line D-D in Figure 24;

[0041] Figure 26 shows a cross-sectional view along line C-C in Figure 24;

[0042] Figure 27a shows a rear perspective view of the transmission shown in Figure 21;

[0043] Figure 27b shows front perspective view of the transmission shown in Figure 21;

[0044] Figure 28 shows an exploded front perspective view of the transmission shown in Figure 21; and

[0045] Figure 29 shows an exploded rear perspective view of the transmission shown in Figure 21. DETAILED DESCRIPTION

[0046] Figures 1 to 10 illustrate a cycloidal transmission according to an example embodiment. Complementary housing sections 1 and 2 enclose the transmission with chain ring 3 driven by axle 4.

[0047] Motor 5 is provided about axle 4 and its rotor drives cam 6 (shown in detail in Figures 9a to 9c). Cam 6 is rotatably mounted about axle 4 and has an eccentric cylindrical section 7 with its centre offset from the axle centre (indicated by the crosshairs). Inner gear 8 is rotatably mounted about eccentric cylindrical section 7 so that as the motor rotates cam 6 the centre of inner gear 8 moves in a circular path.

[0048] Inner gear 8 is positioned within a stationary ring gear 9 so that the teeth of inner gear 8 mesh with the teeth of ring gear 9 as inner gear 8 rotates within ring gear 9 as it is driven by cam 6. Inner gear 8 and ring gear 9 preferably have complementary helical gears so as to intermesh more easily so as to run more smoothly and quietly and reduce noise and vibration. This also allows very close tooth ratios having a difference in teeth number between gears of only 3, 2 or even 1 tooth. The helical teeth preferably have a stub gear tooth profile or some other similar profile. The helix angle of the helical teeth is preferably sufficient that the termination of one tooth is laterally aligned with or overlapping with the start of an adjacent tooth (i.e. a plane through the axis of the axle intersects the termination of one tooth and the start of an adjacent tooth). Typically, the helix angle is greater than 10 degrees.

[0049] As shown in Figures 4 and 5 an eccentric coupling is provided by a plurality of eccentric driver pins 10 (only one indicated) that are rotatably mounted to inner gear 8. Three or more eccentric driver pins 10 may be employed depending upon the design. As shown in figure 8 each eccentric driver pin 10 has offset shafts 11a and lib (i.e. the axes of shafts 11a and lib are parallel but offset). Shaft 11a is rotatably mounted to inner gear 8, by way of a plain bearing or rolling element bearing. Shaft lib is rotatably mounted to cycloidal driver 12, by way of a plain bearing or rolling element bearing. A rolling element bearing is advantageous where high torque is to be transferred. As the shafts 11a and lib engage substantially the entire internal surface of each bearing there is improved force transmission and reduced wear and noise compared to the standard pin in hole cycloidal transmission.

[0050] Cycloidal driver 12 is rotatably mounted about axle 4 and is coupled via sprag clutch 13 to drive cap 14, which in turn is coupled to axle 4. This provides a unidirectional clutch or "freewheel" which provides power to assist forward rotation but disengages when the drive speed of the cycloidal driver 12 does not equal or exceed that of the axle.

[0051] A number of bearings, spacers, seals and other components are shown in the exploded view but will not be described in detail as the skilled addressee will understand the components and their placement.

[0052] Figures 4 and 5 Illustrate the movement of the inner gear 8 within the ring gear 9 as cam 6 is rotated about axle 4. In figure 4 the cam is in a first position in which the teeth of the innergear 8 mesh with the lower teeth of the ring gear 9. In figure 5 the cam has rotated 180 degrees to that the teeth of the inner gear 8 mesh with the upper teeth of the ring gear 9. The transmission ratio is the number of teeth of the inner gear / (number of teeth of ring gear - number of teeth of inner gear) i.e. Ti / (Tr-Ti). In this example the inner gear has 21 teeth and the ring gear has 22 teeth and so there is a gear difference of one and it will take 22 rotations of the cam for the eccentric driver pins 10 to perform one rotation; thus a 22:1 reduction ratio. The number of teeth of the inner gear and gear ring may be selected to achieve a desired reduction. Inner gear 8 moves in an eccentric cycloidal motion that is converted into pure rotation at the transmission output. For this purpose eccentric driver pins 10 couple the inner gear to the cycloidal driver 12. As will be seen in figures 4 and 5 these eccentric driver pins 10 are able to transfer rotation to the cycloidal drive 12 whilst removing the eccentric components due to their eccentric offset shafts 11a and lib. Each eccentric driver pin is counterweighted so that its mass is balanced about the axis of shaft lib. As can be seen in figure 4 shafts lib are rotated upwards when the inner gear 8 is low to compensate for the inner gear's offset from axle 4. Likewise in figure 5 shafts lib are rotated downwards when the inner gear 8 is high to compensate for the inner gear's offset from axle 4.

[0053] The shafts lib of eccentric driver pins 10 thus describe a circular path as they rotate when rotatably engaged with cycloidal driver 12. Cycloidal driver 12 can thus provide a purely rotational output which is provided through a unidirectional clutch in the form of sprag clutch 13 to drive cap 14 to axle 4.

[0054] The eccentric motion of the inner gear 8 may be offset by counterweight 26. Counterweight 26 may be fixed to cam 6 and opposed to the maximum offset of cam 6 so as to counterbalance the inner gear 8.

[0055] A single inner gear 8 provides simplicity but a plurality of inner gears may be used to provide balance without a counterweight and for load spreading.

[0056] In use the transmission may be fitted to a bicycle with cranks and pedals fitted to each end of the axle. Force applied to the axle 4 by the cranks will be directly supplied to chain ring 3. When a motor control system determines that motor power is to be provided, motor 5 rotates cam 6, which causes inner gear 8 to rotate within ring gear 9 and rotate cycloidal driver 12 via eccentric driver pins 10. Cycloidal driver 12 provides additional torque to axle 4 through sprag clutch 13. The transmission provides a high reduction ratio allowing a compact design that is well matched to the performance characteristics of an electric motor. The transmission has high torque capacity with low backlash. The high surface contact between relatively rotating surfaces of the driver pins and inner gear and cycloidal drive results in reduced friction, wear, noise and vibration. The provision of bearings at these points further reduces friction, wear and noise. It also allows greater loads to be transmitted and more efficiently.

[0057] The use of helical gears means a pair of teeth first make contact at a single point at one side of the gear wheel with a moving curve of contact progressing gradually across the tooth face to a maximum and then recedes until the teeth break contact at a single point on the opposite side. This results in low vibration and noise due to helical gears run more smoothly and quietly.

[0058] The transmission is also balanced with a counterweight balancing the inner gear and each eccentric driver pin also being balanced. This further reduces vibration and improves efficiency.

[0059] The overall arrangement of the transmission and electrical components allows separation of electronics in a waterproof region and a compact mechanical drive region allowing a wet lubrication zone separated from electronics.

[0060] Figure 11 shows an in-axle torque measuring system according to one example. The torque sensing system is able to measure the torque applied to each end of hollow axle 4. A sensing body, in this case comprising upper and lower sections 15 and 16, is provided within hollow axle 4 and secured thereto by screws 17 engaged in threads in section 16. Other fixing features or techniques may be employed to secure the sensing body to the axle and the sensing body need not be formed by longitudinally separated sections and could be of unitary or other construction. The sensing body has a central region 18 linked to end regions 19 and 20 on either side by linking regions 21 and 22. The linking regions 21 and 22 are dimensioned to allow a prescribed amount of rotational movement between the end regions 19 and 20 and the central region 18 for a prescribed range of torque measurement (i.e. the linking regions have reduced cross-sectional area with amount of material removed and geometry of the linking regions designed to allow a prescribed flexure for a prescribed applied torque).

[0061] Torque sensors 23 and 24 are sandwiched between sections 15 and 16 and between each end region 19 and 20 and the central region 18 to measure the torque applied to each end of the axle relative to the central region 18. The power from the motor may be applied to the central region 18 so that the torque sensors measure the torque applied at each end of the axle relative to the central region where the motor force is applied. The torque sensors 23 and 24 may be strain gauges or other suitable torque measurement devices.

[0062] A wireless communication circuit 25 may wirelessly communicate sensed torque information to a motor controller to control the motor 5 in response to torque information. The torque information may be supplied to other devices such as performance monitoring devices including smart phones running suitable apps. Bluetooth protocol or another suitable communications protocol may be employed.

[0063] Power for the torque sensing system may be provided by a battery, dynamo (coil within axle 4 exposed to changing magnetic field due to magnet rotating about the axle), wireless power transfer or other means. In the case of wireless power transfer a coil around the outside of axle 4 may generate an oscillating magnetic field received by a coil supplying power to the torque sensing system.

[0064] The torque sensing system being integrated in the axle provides ease of installation and continuous power supply to the torque sensing system. Independent left and right torque sensing allows optimum control of the electric motor.

[0065] Figures 12 to 20 show another example transmission 27 in which a smaller inner gear 28 and ring gear 29 are employed. Cam 30 is mounted on bearings 31, 38 and 39 and rotates about axle 32 when driven by a motor (not shown in this example for simplification). Inner gear 28 is rotationally mounted to cam 30 by bearings 40 and 41. As in the first example rotation of cam 30 causes the central axis of inner gear 28 to rotate in a circular path so that the teeth of inner gear 28 mesh with the teeth of ring gear 29 as inner gear 28 rotates around and within stationary ring gear 29. This causes the inner gear 28 to rotate at a reduced ratio. In this example the inner gear 28 has 39 teeth and the ring gear 29 has 42 teeth and so the ratio is 39 / (42 - 39) = 13:1. Thus, for every 13 rotations of cam 30 the inner gear 28 rotates one rotation.

[0066] In this example a carrier 33 is driven by inner gear 28 and is coupled by a plurality of eccentric driver pins 34 which locate in bearings 35 in carrier 33 and journals of cycloidal driver 36 (bearings may also be provided in cycloidal driver 36 to receive eccentric driver pins where required). This eccentric coupling allows the cycloidal motion of the carrier 33 to be converted to pure rotation of cycloidal driver 36. Rotation of cycloidal driver 36 effects rotation of axle 32 through sprag clutch 37. If rotation in both directions is required, for regenerative braking for example, sprag clutch 37 may be replaced with a direct connection. This design may be used in an e-bike as per the first example with pedals attached to axle 32 to allow rider input or may be used in any other type of motorised vehicle with or without human assistance.

[0067] Referring now to figures 21 to 29 a further example transmission is shown. This design is as per the second example of Figures 12 to 20 except that the cycloidal coupling uses eccentric bearings instead of eccentric driver pins. The same reference numerals are used in Figures 21 to 29 as were used in Figures 12 to 20 and the operation is the same except for the cycloidal coupling elements explained below.

[0068] In this example a plurality of eccentric bearings 43 (only one indicated) are provided in carrier 33. Each eccentric bearing includes an outer bearing 44 having an insert 45 having an eccentric aperture formed therein containing an inner bearing 46. Straight driver 47 pins (only one indicated) mounted to cycloidal driver 36 locate within the inner ring ball race of inner bearings 46. It will be appreciated that the eccentric bearings could be mounted to cycloidal driver 36 and the drive pins 46 to carrier 33 if desired. This design may use standard eccentric bearing designs, if appropriate.

[0069] It will be appreciated that in alternative implementations different elements may be driven and different elements may provide an output drive. Referring to the third embodiment in Figures 21 to 28 (although applicable to all examples) cycloidal driver 36 may be restrained from rotating (e.g. if fixed to a stationary axle or if secured to a housing for a rotating axle). In this case if ring gear 29 is driven it will cause inner gear 28 to move around the teeth of ring gear 29 without inner gear 28 rotating about its axis but causing cam 30 to rotate. Carrier 33 and ring gear 28 will not rotate about their axes but their central axes will move in circular paths due to the eccentric coupling between carrier 33 and cycloidal drive 36 and rotation of cam 30. In this case cam 30 could be the output. Alternatively, in this arrangement (i.e. with cycloidal driver 36 restrained from rotating) cam 30 could be driven and ring gear 29 could be the output.

[0070] While the present invention has been illustrated by the description of the embodiments thereof, and while the embodiments have been described in detail, it is not the intention of the Applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details, representative apparatus and method, and illustrative examples shown and described. Accordingly, departures may be made from such details without departure from the spirit or scope of the Applicant's general inventive concept.

Claims

CLAIMS:

1. A transmission comprising: i. an axle; ii. a cam rotatably mounted about the axle; ill. an inner gear mounted to the cam configured so that as the cam rotates the central axis of the inner gear moves in a circular path; iv. a ring gear surrounding and engaging the inner gear arranged so that teeth of the inner gear engage teeth of the ring gear as the cam drives the inner gear around the ring gear; and v. a cycloidal driver coupled to the inner gear by an eccentric coupling.

2. A transmission as claimed in claim 1 wherein the eccentric coupling comprises a plurality of eccentric drivers having eccentric couplings between the cycloidal driver and the inner gear.

3. A transmission as claimed in claim 1 wherein each eccentric driver includes an eccentric bearing.

4. A transmission as claimed in claim 1 wherein each cycloidal driver includes an eccentric driver pin having offset shafts with one shaft rotatably mounted to the cycloidal driver and the other shaft rotatably mounted to the inner gear.

5. A transmission as claimed in claim 4 wherein each eccentric driver pin is counterweighted so that its mass is balanced about the axis of the shaft rotatably mounted to the cycloidal driver.

6. A transmission as claimed in claim 4 or claim 5 wherein each shaft of each eccentric driver pin is connected to the cycloidal driver and the inner gear via a rolling element bearing.

7. A transmission as claimed in claim 6 wherein each shaft of each eccentric driver pin engages substantially the entire internal surface of each bearing.

8. A transmission as claimed in any one of the preceding claims wherein the inner and ring gears have complimentary helical teeth.

9. A transmission as claimed in claim 8 wherein the termination of one tooth is laterally aligned with or overlapping with the start of an adjacent tooth.

10. A transmission as claimed in claim 8 or claim 9 wherein the helical teeth have a stub gear profile.

11. A transmission as claimed in any one of the preceding claims including a counterweight configured to rotate with the cam providing a mass offsetting the off-centre mass of the inner gear.

12. A transmission as claimed in claim 11 wherein the counterweight is attached to the cam.

13. A transmission as claimed in any one of the preceding claims including a unidirectional clutch configured to provide power from the cycloidal driver to the axle.

14. A transmission as claimed in claim 13 wherein the unidirectional clutch is a sprag clutch.

15. A transmission as claimed in any one of the preceding claims wherein the tooth difference between the inner and ring gear is between 1 and 3.

16. A transmission as claimed in any one of the preceding claims wherein the tooth difference between the inner and ring gear is 1.

17. A transmission as claimed in any one of the preceding claims wherein a plurality of inner gears are provided.

18. A transmission as claimed in any one of the preceding claims including cranks and pedals for human power input.

19. A transmission as claimed in any one of the preceding claims including an electric motor driving the cam.

20. A transmission as claimed in any one of claims 1 to 19 wherein the ring gear is driven by an electric motor.

21. A transmission as claimed in claim 19 or claim 20 including a torque sensing system configured to measure torque applied to the axle and a motor controller for governing the power provided to the motor based at least in part on signals from the torque sensing system.

22. A transmission as claimed in any one of the preceding claims incorporated into an electric bicycle.

23. A torque sensing system for measuring the torque applied to ends of a hollow axle comprising; i. a sensing body dimensioned to locate within a hollow axle having a central region linked to end regions on either side by linking regions, wherein the linking regions are dimensioned to allow a prescribed amount of rotational movement between the end regions and the central region for a prescribed range of torque measurement; and ii. torque sensors located between each end region and the central region configured to measure the torque applied to each end of the axle relative to the central region.

24. A torque sensing system as claimed in claim 23 wherein the central and end regions include fixing features configured to secure the sections to a hollow axle.

25. A torque sensing system as claimed in claim 24 wherein the fixing features are threads provided in the central and end regions.

26. A torque sensing system as claimed in any one of claims 23 to 25 wherein the central and end regions are generally cylindrical and the linking regions have reduced cross-sectional area.

27. A torque sensing system as claimed in claim 26 wherein the body section is formed in two longitudinally separated sections.

28. A torque sensing system as claimed in claim 27 wherein the two longitudinally separated sections are each integrally formed.

29. A torque sensing system as claimed in claim 27 or claim 28 wherein each torque sensor is sandwiched between the two longitudinally separated sections between the central region and a respective end region.

30. A torque sensing system as claimed in claim 29 wherein each torque sensor is a strain gauge.

31. A torque sensing system as claimed in any one of claims 23 to 30 including a communication circuit for wirelessly communicating sensed torque information to another device.

32. A torque sensing system as claimed in claim 31 wherein the communication circuit communicates using a Bluetooth protocol.

33. A torque sensing system as claimed in any one of claim3 23 to 32 including a wireless power receiver.

34. A torque sensing assembly comprising a hollow axle and a torque sensing system as claimed in any one of claims 23 to 33 provided within the axle with the central and end regions secured to the axle.

35. A torque sensing assembly as claimed in claim 34 including a power transmitting coil provided about the axle and a power receiving coil provided within the axle configured to provide electrical power to the communication circuit.

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