Drive device for an electric bicycle and electric bicycle

Abstract

A drive arrangement (5) for an electric bicycle (1) has a motor unit (6) with an electric motor for driving the electric bicycle (1). The drive arrangement (5) further has a first transmission stage (10) and a second transmission stage (20), which are configured for driving the electric bicycle (1). The first transmission stage (10) is coupled on the one hand to the motor unit (6) and on the other hand to the second transmission stage (20). The second transmission stage (20) is configured on the other hand for transmitting torque for driving the electric bicycle (1). The second transmission stage (20) is configured as a shaft transmission and can be arranged coaxially with respect to an axis of rotation (8) of a pedal crank (4) of the electric bicycle.

Description

Technical Field

[0001] The present invention relates to a drive mechanism for an electric bicycle and an electric bicycle having said drive mechanism. Background Technology

[0002] Bicycles have become a cost-effective, easy-to-operate, and emission-free mode of transportation. They have also expanded into exercise or fitness equipment, and various types have been developed specifically for different sports applications.

[0003] Enthusiasm for e-bikes (especially so-called "pedelecs") has been growing in recent years, despite their considerable weight and high price. Potential customers include not only older, less physically fit, or less athletic cyclists, but also younger, more active riders who may use them for work or to extend their range and / or increase their speed without overloading their bodies. Mountain bikers, in particular, are increasingly drawn to electric-assisted mountain bikes. A key aspect of e-bikes is the provision of a reliable auxiliary drive system that enables high power delivery. Summary of the Invention

[0004] The objective of this invention is to provide a reliable drive system for an electric bicycle, which achieves a particularly clear and space-saving structure.

[0005] According to one aspect, a drive unit for an electric bicycle is disclosed. The drive unit has a motor unit having an electric motor for driving the electric bicycle. The drive unit also has a first transmission stage and a second transmission stage, configured to drive the electric bicycle. The first transmission stage is coupled to the motor unit on one side and to the second transmission stage on the other. Therefore, the second transmission stage is coupled to the first transmission stage on one side or on the drive side and configured to output or provide torque for driving the electric bicycle on the other side or on the output side. The second transmission stage is here configured as a shaft drive and is arranged coaxially with respect to the rotation axis of the pedal crank of the electric bicycle, or arranged to be coaxially arranged with the pedal crank.

[0006] The aforementioned drive unit enables a reliable drive scheme for electric bicycles, achieving a distinctive and space-saving structure. The drive unit is particularly suitable for mounting on the bottom tube or seatpost of an electric bicycle, achieving an advantageous balance between low noise generation, high efficiency, and small structural dimensions.

[0007] The second-stage shaft drive achieves a backlash-free transmission for transmitting large torques and is also known as a strain wave gear drive or a so-called "Harmonic Drive." This achieves a high transmission ratio, for example, 100:1, and its outstanding feature is high rigidity. The harmonic drive also includes an elliptical disk element, which acts as a so-called "Wave Generator," constituting the drive element of the shaft drive. Furthermore, for example, there is a deformable cylindrical steel sleeve, called a "Flexspline," which constitutes the output element of the harmonic drive and is predetermined to deform by rotating the wave generator. Additionally, an external element, also called a "Circular Spline," is provided, and this external element interacts with the Flexspline by means of teeth, such that, for example, a weekly rotation of the wave generator causes relative movement of the two teeth of the Flexspline about the rigid spline.

[0008] Instead of a shaft drive, the second transmission stage of the drive unit may include a cycloidal drive, which also provides a backlash-free transmission for large torques. The cycloidal drive transmits torque by rolling motion via a cam disc.

[0009] When auxiliary drive is required, the second transmission stage is coupled to or can be coupled to the pedal crank of the electric bicycle, particularly by means of an output shaft. The output shaft is either fixedly coupled to a gear or sprocket of the electric bicycle or has one of these components constructed therein. The pedal crank is fixedly coupled to the pedal of the electric bicycle. The drive unit thus achieves space-saving and efficient drive, wherein pedal drive and auxiliary electric drive are combined and coupled by means of the output shaft or can be coupled when needed.

[0010] According to one embodiment of the drive device, the first transmission stage is configured as a belt drive, which includes a first drive pulley, a second drive pulley, and a belt element. The belt element couples the two drive pulleys to each other, wherein the first drive pulley is coupled to the motor unit, and the second drive pulley is coupled to the second transmission stage.

[0011] The aforementioned method can provide a beneficial electric drive system for electric bicycles, the system having a low-speed transmission stage in the form of a belt drive and a high-speed transmission stage in the form of a shaft drive. Instead of a belt drive, the first transmission stage can also be constructed as a cylindrical gear drive.

[0012] According to another embodiment of the drive unit, the second transmission stage includes: a wave generator; a cylindrical outer ring having internal teeth; and a resilient transmission element having external teeth configured to predeterminely match the internal teeth of the outer ring. The second transmission stage also includes a radial coupling element. The wave generator, during operation, is used to predeterminely deform the transmission element, the outer ring is configured as the drive element of the second transmission stage, and the radial coupling element is configured as the output element of the second transmission stage. The transmission element is arranged between the outer ring and the radial coupling element and provides a predetermined transmission ratio for the second transmission stage.

[0013] The following embodiment specifically describes the structure of the second transmission stage of the shaft drive, wherein, for example, the external teeth of the elastic transmission element have two fewer teeth than the internal teeth of the outer ring. The shaft drive also includes a radial coupling element that reliably transmits torque from the output of the second transmission stage to the output shaft of the drive system or pedal crank.

[0014] If the first transmission stage, as described above, is constructed, for example, as a belt drive, then the second drive wheel of the belt drive is coupled to the outer ring of the shaft drive, and the radial connecting element is coupled to the pedal crank. This allows for a particularly compact and reliable structure of a drive unit with both low-speed and high-speed transmission stages.

[0015] According to another embodiment of the drive unit, the radial coupling element has a plurality of radial protrusions on its outer side about the rotational axis of the pedal crank. These protrusions are configured to mate with a plurality of recesses located on the end side of the transmission element facing the radial coupling element. The engagement of the protrusions and recesses allows the radial coupling element to be coupled to and decoupled from the transmission element along the rotational axis of the pedal crank.

[0016] According to a preferred embodiment, the radial coupling element is thus movable along the rotation axis of the pedal crank. The radial coupling element thus enables reliable transmission of torque from the output of the second transmission stage to the output of the drive system or drive unit in a coupled state, or enables independent rotation of the pedal crank in a decoupled state, unrestricted by the decoupled first and second transmission stages. Decoupling the pedal crank from the drive unit can be advantageous, for example, to decouple the force flow when the electric bicycle moves backward and thereby prevent the transmission from being linked to the motor, or to reset trouble-free or low-resistance operation when the drive unit requires maintenance. In this case, it is not necessary to rotate the transmission stages together and apply a corresponding additional force, and the electric bicycle equipped with the drive unit can thus be used as a conventional bicycle. The drive unit thus preferably has the aforementioned axial mobility of the radial coupling element. However, alternatively, an axially fixed radial coupling element can also be provided.

[0017] According to another embodiment of the drive unit, the radial protrusion of the radial connecting element is configured such that it protrudes from the end side of the transmission element about a predetermined state of coupling with the transmission element along the rotation axis of the pedal crank. In other words, the protrusion is constructed to be greater in depth or longer than the recess. This arrangement allows for more reliable coupling between the two components and reliable torque transmission from the transmission element to the radial connecting element. The coverage of the protrusion is particularly related to the applied force and can be, for example, a few millimeters. Alternatively, the protrusion of the radial connecting element and the end side of the transmission element can be configured such that a one-to-one coverage or contact surface overlap is achieved, thereby enabling mechanically reliable coupling.

[0018] According to another embodiment of the drive unit, the second transmission stage is specifically arranged and constructed such that, in its usable assembled state, it is coaxially positioned around the pedal crank about its axis of rotation. This achieves a particularly space-saving and straightforward structure for the drive unit of an electric bicycle and further helps to keep the overall weight low.

[0019] According to another embodiment of the drive unit, the motor unit and transmission stage are arranged such that the rotation axis of the motor unit is oriented parallel to and spaced apart from the rotation axis of the pedal crank. This embodiment also achieves a particularly space-saving and clear structure for the drive unit.

[0020] According to another aspect, an electric bicycle is disclosed, having a bicycle frame with a lower frame section extending to a pedal bearing having a pedal crank. The electric bicycle has a drive unit according to any of the foregoing embodiments, the drive unit being arranged in or on the frame section such that a second transmission stage is arranged coaxially with the pedal crank, so that torque for driving the electric bicycle can be transmitted by means of the second transmission stage. The electric bicycle substantially achieves the aforementioned characteristics, advantages, and functions.

[0021] For mounting on a frame section, the frame section may have a notch, allowing the drive device to be reliably received. According to one embodiment, the drive device is arranged, for example as a component, in a coupled state, particularly assembled onto the frame section.

[0022] In addition to the electric motor, the electric drive unit for the electric bicycle further includes: a low-speed first transmission stage, preferably configured as a belt drive or a gear drive; and a high-speed second transmission stage, preferably configured as a shaft drive or a cycloidal drive. Preferably, the drive unit also includes a movable radial coupling element that transmits torque from the output of the second transmission stage to the output of the drive system, thereby facilitating beneficial and reliable power transfer from the motor unit to the pedal cranks of the electric bicycle.

[0023] The drive unit realizes a highly efficient mechanical system for assisting in cycling, while also keeping noise generation low and the structure compact. This is achieved in particular through a two-stage transmission configuration, where, for example, a belt drive can operate very efficiently and with low noise at low power and high speeds, while a shaft drive can transmit high torque based on a very compact structural space.

[0024] In order to design the required structural space of the shaft drive to be particularly short in the axial orientation along the rotation axis of the pedal crank, the radial connecting element is preferably located between the output of the shaft drive and the output of the whole system.

[0025] The described embodiment of the drive device also achieves the following advantageous operating characteristics:

[0026] ● Low noise generation and high efficiency are achieved through the belt drive in the first transmission stage.

[0027] ● Achieving high power density and small space requirements in the second transmission stage through a shaft drive device under high torque.

[0028] ●The small space requirement of the second transmission stage is due to the fact that the typically long end of the output component of the shaft drive can be replaced by a short radial connecting element.

[0029] ●Low cost, because the second drive stage can be made of plastic parts produced by WKZ by means of plastic injection molding or by means of metal die casting, such as aluminum or magnesium, in which the competitive power density and high positional accuracy of the drive unit can be sacrificed, while at the same time the small weight of the drive unit can be achieved. Attached Figure Description

[0030] In the following description, embodiments, advantages, and functions are illustrated with reference to the accompanying drawings. The drawings show:

[0031] Figure 1 A schematic diagram of an electric bicycle with an assembled drive unit is shown.

[0032] Figure 2-6 A schematic perspective view showing an embodiment of a drive unit for an electric bicycle, and

[0033] Figure 7 A schematic diagram showing a cross-sectional view of the second transmission stage of a drive unit for an electric bicycle.

[0034] Identical, similar, or functional elements are given the same reference numerals in the accompanying drawings. For the sake of simplicity, not all elements shown may be labeled with their respective reference numerals in all drawings if necessary. Detailed Implementation

[0035] Figure 1 An electric bicycle 1 with a bicycle frame 2 is schematically shown. The bicycle frame also has a lower frame section 3 that forms a bottom tube. The frame section 3 extends in the direction of the pedal bearing and includes a pedal crank 4 that is coupled or can be coupled to an electric drive unit 5 for the electric bicycle 1.

[0036] Figure 2-6 Embodiments of the drive device 5 or its components are shown schematically in different perspective views. Figure 7 The components of the drive unit 5 are shown in a schematic cross-sectional view.

[0037] The drive unit 5 includes a motor unit 6 having an electric motor for driving the electric bicycle 1, a first transmission stage, and a second transmission stage, both configured to drive the electric bicycle 1. The first transmission stage is configured as a belt drive 10 and is coupled to both the motor unit 6 and the second transmission stage. The second transmission stage is configured as a shaft drive 20 and is coupled to both the first transmission stage and the belt drive 10, and is configured to output or transmit torque for driving the electric bicycle 1. The side of the second transmission stage coupled to the first transmission stage is thus the drive side of the shaft drive 20. The side of the second transmission stage configured to output torque and drive the electric bicycle 1 is thus the output side of the shaft drive 20.

[0038] The drive unit 5 is not directly coupled to the pedal crank 4, but rather coupled via the output shaft 25, or, when necessary, to the pedal crank (see [link to relevant documentation]). Figure 5 and 6 The output shaft 25 is connected to the sprocket of the electric bicycle 1 via an adapter, also known as a "spider." The sprocket drives the rear wheel of the electric bicycle 1 via a chain. The shaft of the pedal crank 4 can be decoupled from the output shaft 25 via a freewheel to prevent linkage of the crank caused by the motor or drive unit 5.

[0039] The belt drive 10 includes a first drive pulley 11, a second drive pulley 12, and a belt element 13, which couples the two drive pulleys 11 and 12 together. The first drive pulley 11 is coupled to the motor unit 6, such that the rotation axis 7 of the motor unit 6 coincides with the rotation axis of the first drive pulley 11. The second drive pulley 12 is coupled to the shaft drive 20, such that the rotation axis 8 of the pedal crank 4 coincides with the rotation axes of the shaft drive 20 and the second drive pulley 12.

[0040] The shaft drive 20 is configured such that it is coaxial with respect to the rotation axis 8 around the pedal crank 4. The motor unit 6, the belt drive 10, and the shaft drive 20 are arranged such that the rotation axes 7 and 8 are substantially parallel to each other. Furthermore, the motor unit 6, the belt drive 10, and the shaft drive 20 are all assembled together in the housing 30.

[0041] The shaft drive device 20 includes a cylindrical outer ring 22, which has internal teeth 221 (see...). Figure 5 and 6 The shaft drive 20 also includes a resilient transmission element 21 having external teeth 213 configured to mate with the internal teeth 221 of an outer ring 22. The external teeth 213 of the transmission element 21 specifically include fewer teeth than the internal teeth 221 of the outer ring 22. The shaft drive 20 also includes a radial coupling element 23. The outer ring 22 serves as the drive element of the shaft drive 20, and the radial coupling element 23 serves as the output element of the shaft drive 20. The transmission element 21 is arranged between the outer ring 22 and the radial coupling element 23 and provides a predetermined transmission ratio through the mating external teeth 213 and internal teeth 221. The shaft drive 20 also includes a wave generator 24, also referred to as a "Wave Generator," configured to deform the transmission element 21 in a predetermined manner. The shaft drive 20 thus achieves a so-called "Harmonic Drive."

[0042] according to Figure 3 The second drive wheel 12 of the belt drive 10 is coupled to the outer ring 22 of the shaft drive 20 and serves as the drive element therein. The radial coupling element 23 is coupled directly or by means of one or more transmission elements to the pedal crank 4 (see [link to related document]). Figure 5 ).

[0043] The radial connecting element 23 has a plurality of radial protrusions 232 on its outer side about the rotation axis 8. These protrusions are configured to mate with a plurality of recesses 212 located on the end side 214 of the transmission element 21 facing the radial connecting element 23. Thus, the radial connecting element 23 can be coupled to the transmission element 21 along the rotation axis 8 by means of the radial protrusions 232 engaging with the recesses 212.

[0044] In other words, the transmission element 21 has a plurality of protrusions 211 that extend on the end side 214 toward the radial connecting element 23 and predeterminely define the recesses 212. The protrusions 232 also define the boundaries of the recesses 231 on the outer periphery of the radial connecting element 23. In the coupled state of the transmission element 21 and the radial connecting element 23, the protrusions 211 also engage with the recesses 231.

[0045] Preferably, the radial protrusions 232 and recesses 212 are configured to be distributed at equal intervals on the respective components. Alternatively, the protrusions 211, 232 and the recesses 231, 212 may also be distributed differently and / or constructed in different numbers.

[0046] The radial coupling element 23 enables a particularly short configuration of the shaft drive 20 and further decouples the drive unit 5 from the pedal crank 4 or the output shaft 25 by means that the radial coupling element 23 is movably constructed along the axis of rotation 8 and can be decoupled from the transmission element 21 (see [link to original text]). Figure 6 The electric bicycle 1 can thus be used as a regular bicycle when needed, without the components of the drive unit 5 needing to rotate together. This can be beneficial, for example, when the drive unit 5 is impaired or requires maintenance.

[0047] The radial coupling element 23 is further coupled to the pedal crank 4 by means of the output shaft 25. Alternatively, the radial coupling element 23 may also be coupled to the pedal crank 4 or the output shaft 25 directly or by means of one or more transmission elements.

[0048] The drive unit 5 enables a reliable drive system for electric bicycles, achieving a distinctive and space-saving structure. The drive unit 5 is particularly suitable for mounting on the bottom tube or seatpost of the electric bicycle 1, resulting in a drive system that is advantageous in terms of low noise generation, high efficiency, and small structural dimensions.

[0049] List of reference numerals

[0050] 1 bicycle

[0051] 2 bicycle frames

[0052] 3-frame section (bottom pipe)

[0053] 4 pedals and cranks

[0054] 5 drive units

[0055] 6 motor units

[0056] 7. Rotation axis of motor unit / first transmission stage

[0057] 8. Rotation axis of the pedal crank / second transmission stage

[0058] 10 Belt Drive / First Transmission Stage

[0059] 11 First transmission wheel

[0060] 12 Second transmission wheel

[0061] 13 with components

[0062] 20-axis transmission device / second transmission stage

[0063] 21. Flexible transmission elements

[0064] 211 Protrusions of transmission components

[0065] 212 Recessed portion of transmission element

[0066] 213 External gears of transmission components

[0067] 214 End side of transmission element

[0068] 22-column outer ring

[0069] 221 outer ring internal teeth

[0070] 23 Radial connection elements

[0071] 231 Recessed portion of radial connecting element

[0072] 232 Protrusion of radial connecting element

[0073] 24-wave generator

[0074] 25 pedal crank output shaft

[0075] 30. Housing.

Claims

1. A drive unit (5) for an electric bicycle (1), comprising: - Motor unit (6), the motor unit having an electric motor for driving the electric bicycle (1), and - A first transmission stage (10) and a second transmission stage (20), the first transmission stage and the second transmission stage being configured to drive the electric bicycle (1), wherein, The first transmission stage (10) is coupled to the motor unit (6) on one side and to the second transmission stage (20) on the other side, and the second transmission stage (20) is configured to output torque for driving the electric bicycle (1), wherein the second transmission stage (20) is constructed as a shaft drive and can be arranged coaxially about the rotation axis (8) of the pedal crank (4) of the electric bicycle (1), wherein the second transmission stage (20) includes: - Wave generator (24), - A cylindrical outer ring (22), the outer ring having internal teeth (221), - An elastic transmission element (21) having external teeth (213) configured to mate with the internal teeth (221) of the outer ring (22), and - A radial connecting element (23), wherein the wave generator (24) is configured to deform the transmission element (21) in a predetermined manner, the outer ring (22) is configured as a drive element of the second transmission stage, and the radial connecting element (23) is configured as an output element of the second transmission stage (20), wherein the transmission element (21) is arranged between the outer ring (22) and the radial connecting element (23) and provides a predetermined transmission ratio of the second transmission stage (20).

2. The driving device (5) according to claim 1, wherein, The first transmission stage (10) is configured as a belt drive device, which includes a first drive wheel (11) and a second drive wheel (12) and a belt element (13). The belt element couples the two drive wheels (11, 12) to each other. The first drive wheel (11) is coupled to the motor unit (6), and the second drive wheel (12) is coupled to the second transmission stage (20).

3. The driving device (5) according to claim 2, wherein, The second drive wheel (12) of the belt drive is coupled to the outer ring (22) of the shaft drive, and the radial connecting element (23) is coupled to the pedal crank (4).

4. The drive device (5) according to any one of claims 1 to 3, wherein, The radial connecting element (23) has a plurality of radial protrusions (232) on its outer side about the rotation axis (8) of the pedal crank (4), the protrusions being configured to match a plurality of recesses (212) being configured on the end side (214) of the transmission element (21) facing the radial connecting element (23), so that the radial connecting element (23) can be coupled to and decoupled from the transmission element (21) along the rotation axis (8) of the pedal crank (4).

5. The driving device (5) according to claim 4, wherein, The radial protrusion (232) of the radial connecting element (23) is pre-determined to protrude from the end side (214) of the transmission element (21) about the rotation axis (8) along the pedal crank (4) of the transmission element (21).

6. The drive device (5) according to any one of claims 1 to 3, wherein, The second transmission stage (20) is coaxial with respect to the rotation axis (8) of the pedal crank (4) around the pedal crank (4).

7. The drive device (5) according to any one of claims 1 to 3, wherein, The motor unit (6) and the transmission stage (10, 20) are arranged such that the rotation axis (7) of the motor unit (6) is oriented parallel to and spaced apart from the rotation axis (8) of the pedal crank (4).

8. An electric bicycle (1), comprising: - A bicycle frame (2), the bicycle frame having a lower frame section (3) extending to a pedal bearing having a pedal crank (4), and - The drive device (5) according to any one of the preceding claims is coupled to the bicycle frame (2) to drive the electric bicycle (1), such that the second transmission stage (20) is arranged coaxially with the pedal crank (4).

9. The electric bicycle (1) according to claim 8, wherein, The drive unit (5) is arranged as a component on the frame segment (3) in a coupled state.

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