Drive Device for an Electric Bicycle and Electric Bicycle

Abstract

In an embodiment a driving device for an electric bicycle includes a motor unit having an electric motor configured to drive the electric bicycle, a first gear stage and a second gear stage, wherein the first gear stage is coupled to the motor unit on the one hand and to the second gear stage on the other hand, wherein the second gear stage is configured to output a torque configured to drive the electric bicycle, and wherein the second gear stage is a strain wave gear and is arrangeable coaxially with respect to an axis of rotation of a pedal crank of the electric bicycle.

Claims

1-10. (canceled)

11. A driving device for an electric bicycle, the driving device comprising: a motor unit comprising an electric motor configured to drive the electric bicycle; a first gear stage; and a second gear stage, wherein the first gear stage is coupled to the motor unit on the one hand and to the second gear stage on the other hand, wherein the second gear stage is configured to output a torque configured to drive the electric bicycle, and wherein the second gear stage is a strain wave gear and is arrangeable coaxially with respect to an axis of rotation of a pedal crank of the electric bicycle.

12. The drive device according to claim 11, wherein the first gear stage is a belt gear, which comprises a first gear wheel, a second gear wheel and a belt element, which couples the two gear wheels to one another, and wherein the first gear wheel is coupled to the motor unit and the second gear wheel is coupled to the second gear stage.

13. The drive device according to claim 12, wherein the second gear wheel of the belt gear is coupled to an outer ring of the strain wave gear and a radial coupling element is coupled to the pedal crank.

14. The drive device according to claim 13, wherein the radial coupling element has, with respect to the axis of rotation of the pedal crank, on an outer side, a plurality of radial projections arranged in coordination with a plurality of recesses formed on an end face of a transmission element facing the radial coupling element so that the radial coupling element couplable to and decouplable from the transmission element along the axis of rotation of the pedal crank.

15. The drive device according to claim 14, wherein the radial projections of the radial coupling element, with respect to a state coupled to the transmission element, project along the axis of rotation of the pedal crank in a predetermined manner beyond the end face of the transmission element.

16. The drive device according to claim 11, wherein the second gear stage comprises: a wave generator, a cylindrical outer ring with internal toothing, an elastic transmission element having external toothing preformed to match the internal toothing of the outer ring, and a radial coupling element, wherein the wave generator is configured for predetermined deformation of the transmission element, wherein the outer ring is an input and the radial coupling element is an output of the second gear stage, and wherein the transmission element is arranged between the outer ring and the radial coupling element and provides a predetermined transmission ratio of the second gear stage.

17. The drive device according to claim 16, wherein a second gear wheel of a belt gear is coupled to the outer ring of the strain wave gear and the radial coupling element is coupled to the pedal crank.

18. The drive device according to claim 17, wherein the radial coupling element has, with respect to the axis of rotation of the pedal crank, on an outer side, a plurality of radial projections arranged in coordination with a plurality of recesses formed on an end face of the transmission element facing the radial coupling element so that the radial coupling element couplable to and decouplable from the transmission element along the axis of rotation of the pedal crank.

19. The drive device according to claim 18, wherein the radial projections of the radial coupling element, with respect to a state coupled to the transmission element, project along the axis of rotation of the pedal crank in a predetermined manner beyond the end face of the transmission element.

20. The drive device according to claim 11, wherein the second gear stage coaxially surrounds the pedal crank with respect to the axis of rotation of the pedal crank.

21. The drive device according to claim 11, wherein the motor unit and the two gear stages are arranged such that an axis of rotation of the motor unit is parallel to and spaced apart from the axis of rotation of the pedal crank.

22. The electric bicycle comprising: a bicycle frame having a lower frame portion extending to a bottom bracket having the pedal crank; and the drive device according to claim 11 coupled to the bicycle frame such that the second gear stage is arranged coaxially with the pedal crank.

23. The electric bicycle according to claim 22, wherein the drive device is arranged as an assembly in the already coupled state to the frame portion.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Embodiments, advantages and functions are explained in the following description by means of embodiments with the aid of the attached drawings.

[0032] FIG. 1 shows a schematic view of an electric bicycle with a mounted drive device;

[0033] FIGS. 2-6 show schematic perspective views of an embodiment of the drive device for the electric bicycle; and

[0034] FIG. 7 shows a schematic view of a sectional view of a second gear stage of the drive device for the electric bicycle.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0035] Identical, similar or similarly acting elements are provided with the same reference signs in the figures. For reasons of clarity, not all of the elements shown in all of the figures are marked with the corresponding reference signs, possibly.

[0036] FIG. 1 schematically shows an electric bicycle 1 with a bicycle frame 2 which has, among other things, a lower frame portion 3 which forms a down tube. The frame portion 3 extends towards a bottom bracket, which comprises a pedal crank 4 coupled or couplable to an electric drive device 5 for the electric bicycle 1.

[0037] FIGS. 2-6 schematically show an embodiment of the drive device 5 or components of the drive device 5 in various perspective views. FIG. 7 shows components of the drive device 5 in a schematic sectional view.

[0038] The drive device 5 comprises a motor unit 6 with an electric motor for driving the electric bicycle 1 and a first gear stage and a second gear stage, which are designed for driving the electric bicycle 1. The first gear stage is configured as a belt gear 10 and is connected, on the one hand, to the motor unit 6 and, on the other hand, to the second gear stage configured as a strain wave gear 20 and that is connected, on the one hand, to the first gear stage or the belt gear 10 and is configured to output or transmit, on the other hand, a torque for driving the electric bicycle 1. The side of the second gear stage that is coupled to the first gear stage thus constitutes a drive side of the strain wave gear 20. The side of the second gear stage provided for delivering the torque and driving the electric bicycle 1 thus represents an output side of the strain wave gear 20.

[0039] In particular, the drive device 5 is not coupled directly to the pedal crank 4, but by means of an output shaft 25, or can be coupled to the pedal crank 4 if required (see FIGS. 5 and 6). The output shaft 25 is in turn connected to a chain ring of the electric bicycle 1 by means of an adapter, a so-called spider. The chain ring in turn drives a rear wheel of the electric bicycle 1 via a chain. A shaft of the pedal crank 4 can be decoupled from the output shaft 25 by a free wheel to prevent the cranks from being dragged along by the motor or the drive device 5.

[0040] The belt gear 10 comprises a first gear wheel 11 and a second gear wheel 12 as well as a belt element 13 coupling the two gear wheels 11, 12 to each other. The first gear wheel 11 is coupled to the motor unit 6 so that an axis of rotation 7 of the motor unit 6 coincides with an axis of rotation of the first gear wheel 11. The second gear wheel 12 is coupled to the strain wave gear 20 so that a rotation axis 8 of the pedal crank 4 coincides with a rotation axis of the strain wave gear 20 and the second gear wheel 12.

[0041] The strain wave gear 20 is configured to coaxially surround the pedal crank 4 with respect to the axis of rotation 8. The motor unit 6 and the belt gear 10, as well as the strain wave gear 20, are arranged such that the rotation axes 7 and 8 are substantially parallel to each other. Moreover, the motor unit 6, the belt gear 10 and the strain wave gear 20 are assembled together in a housing 30.

[0042] The strain wave gear 20 comprises a cylindrical outer ring 22 with internal toothing 221 (see FIGS. 5 and 6). The strain wave gear 20 further comprises an elastic transmission element 21 having an external toothing 213 predefined in coordination with the internal toothing 221 of the outer ring 22. In particular, the external toothing 213 of the transmission element 21 comprise fewer teeth than the internal toothing 221 of the outer ring 22. The strain wave gear 20 further comprises a radial coupling element 23, with the outer ring 22 acting as the input and the radial coupling element 23 acting as the output of the strain wave gear 20. The transmission element 21 is disposed between the outer ring 22 and the radial coupling element 23, and provides a predetermined transmission ratio due to the matched external toothing 213 and internal toothing 221. The strain wave gear 20 further comprises a wave generator 24, also referred to as a wave generator, which is configured to provide predetermined deformation of the transmission element 21. The strain wave gear 20 thus realizes a so-called harmonic drive.

[0043] According to FIG. 3, the second gear wheel 12 of the belt gear 10 is in contact with the outer ring 22 of the strain wave gear 20 and acts as a drive in this respect. The radial coupling element 23 is coupled to the pedal crank 4 directly or by means of one or more transmission elements (see FIG. 5).

[0044] With respect to the axis of rotation 8, the radial coupling element 23 has, on an outer side, a plurality of radial projections 232 formed in coordination with a plurality of recesses 212 formed on an end face 214 of the transmission element 21 facing the radial coupling element 23. Thus, the radial coupling element 23 is couplable to the transmission element 21 along the axis of rotation 8 by the radial projections 232 engaging the recesses 212.

[0045] In other words, the transmission element 21 has a plurality of projections 211 extending along the end face 214 in the direction of the radial coupling element 23 and limiting the recesses 212 in a predetermined manner. The projections 232, in turn, also limit recesses 231 on the circumferential outer surface of the radial coupling element 23. In a coupled state of the transmission element 21 with the radial coupling element 23, the projections 211 also engage the recesses 231.

[0046] Preferably, the radial projections 232 and the recesses 212 are formed equidistantly distributed on the respective component. Alternatively, the projections 211, 232 and the recesses 232, 212 may also be distributed differently and/or formed in different numbers.

[0047] The radial coupling element 23 enables a particularly short design of the strain wave gear 20 and also a decoupling of the drive device 5 from the pedal crank 4 or from the output shaft 25, in that the radial coupling element 23 is configured to be displaceable along the axis of rotation 8 and can be decoupled from the transmission element 21 (see FIG. 6). If required, the electric bicycle 1 can thus be used as a normal bicycle, so to speak, without having to rotate components of the drive device 5. This can be useful, for example, if the drive device 5 does not function without malfunction or requires maintenance.

[0048] The radial coupling element 23 is also coupled to the pedal crank 4 by means of the output shaft 25. Alternatively, the radial coupling element 23 may also be coupled directly or by means of one or more transmission elements to the pedal crank 4 or the output shaft 25.

[0049] By means of the drive device 5 described, a reliable drive concept for electric bicycles can be realized, which enables a particularly and space-saving structure. The drive device 5 is particularly suitable for mounting on a down tube or on a seat tube of the electric bicycle 1 and enables an advantageous drive system particularly with respect to a low noise level, a high efficiency and a small size.