Drive unit for an electric bicycle, comprising axially pre-tensioned sun gear shaft and planetary gear stage

Abstract

The invention relates to a drive unit (A) for an electric bicycle (1), comprising a transmission device that is arranged in a transmission housing (G) and comprises at least one planetary gear stage (PG) which has a sun gear (42), a planet carrier (51), and a ring gear (53), which has a transmission ratio that can be set using first and second electric motors (E1, E2), and via which a driveshaft (AT) and an output shaft (AW) are coupled together. The sun gear shaft (4) is axially pre-tensioned in the direction of a second bearing point (GS2) of the sun gear shaft (4) via a first element (WF1) which is supported against a part (G1) of the drive housing (G) at a first bearing point (GS1) of the sun gear shaft (4), whereas the planetary gear stage (PG) is axially pre-tensioned in the direction of the first bearing point (GS1) relative to the sun gear shaft (4) via a second element (WF2).

Description

[0001] Drive unit for an electric bicycle with axially preloaded sun gear shaft and planetary gear stage

[0002] Description

[0003] The proposed solution concerns a drive unit for an electric bicycle.

[0004] Drive units for electric bicycles, for example so-called e-bikes or pedelecs, are known. These are attached to a frame of the electric bicycle via a drive housing and, in addition to a rotatably mounted drive shaft for applying muscle-powered drive power to drive the electric bicycle, have an output shaft mounted coaxially to the drive shaft for transmitting the drive power to a wheel of the electric bicycle. To apply additional assist power, first and second electric motors and a transmission device with a planetary gear stage can be accommodated in the drive housing. The transmission ratio of the planetary gear stage can be adjustable using the first and second electric motors, so that the transmission device coupling the drive shaft and the output shaft allows a transmission ratio for a rider of the electric bicycle to be continuously adjusted.In a drive unit known from WO 2019 / 175022 A1, for example, three shaft trains are provided in order to accommodate the components of the transmission device, a first rotor shaft of the first electric motor and a second rotor shaft of the second electric motor as well as the drive shaft and the output shaft compactly in a drive housing.

[0005] However, there is still a need for drive units that enable improved assembly with a compact arrangement of the components within the drive housing and also allow space-saving axial preloading of components of the transmission device, so that disturbing noises due to unwanted play can be eliminated or at least reduced.

[0006] The proposed solution provides a remedy. It proposes a drive unit for an electric bicycle that has at least the following:

[0007] - a drive housing,

[0008] - a drive shaft rotatably mounted in the drive housing for applying a drive force for driving the electric bicycle by muscle power,

[0009] - an output shaft for transmitting the drive force to a wheel of the electric bicycle, which is arranged coaxially to the drive shaft on a first shaft train and is rotatably mounted in the drive housing,

[0010] - a first electric motor and a second electric motor and

[0011] - a transmission device arranged in the drive housing with at least one planetary gear stage having a sun gear, a planet carrier and a ring gear, the transmission ratio of which can be adjusted by means of the first and second electric motors and via which the input shaft and the output shaft are coupled to one another.

[0012] A torque generated by the first electric motor is partially transmittable to the output shaft. The transmission device further comprises a sun gear shaft which is non-rotatably connected to the sun gear and forms a physical bearing axis for a second shaft train on which the planetary gear stage is arranged. The sun gear shaft is rotatably mounted on the one hand via a first bearing at a first bearing point of the drive housing and on the other hand via a second bearing at a second bearing point of the drive housing. The transmission device further comprises a (first) coupling shaft which is connected to the drive shaft via a (first) transmission stage and which is non-rotatably connected to the planet carrier. The sun gear shaft is axially preloaded in the direction of the second bearing point and thus in a first axial direction relative to the bearing axis by a first (preloading) element which is supported at the first bearing point on a part of the drive housing.Via a second (preloading) element, the planetary gear stage is in turn axially preloaded relative to the sun gear shaft in the direction of the first bearing point and thus in an opposite second axial direction.

[0013] By providing additional first and second elements and applying a predetermined preload force to the sun gear shaft on the one hand, and to the planetary gear stage with respect to the sun gear shaft on the other, a defined preload can be applied to the components of the transmission device arranged on the second shaft train with comparatively few elements. The respective components are axially preloaded with a minimum load, thus reducing play in the second shaft train. This significantly reduces acoustic problems during operation of the drive unit.

[0014] The (first) coupling shaft, which is connected to the planetary carrier for rotation, can be rotatably mounted on the sun gear shaft via a third bearing. In one design variant, the second element for preloading the planetary gear stage can be supported on this third bearing. For example, in this context, it can be provided that the second element for preloading the planetary gear stage is supported on the one hand by an outer ring of the third bearing connected to the (first) coupling shaft and on the other hand by a section of the (first) coupling shaft.

[0015] In one design variant, the second element is supported on a web section of the coupling shaft axially opposite the outer ring of the third bearing, protruding radially inward, and extending annularly around the bearing axis. The preload of the planetary gear stage relative to the sun gear shaft can then be adjusted using the second element via the connection of the third bearing to the sun gear shaft.

[0016] In one embodiment, in order to make the rotationally fixed connection between the (first) coupling shaft and the planet carrier more compact, it is provided that a region of the coupling shaft forming the web section is frictionally and / or positively connected to the planet carrier on a radially outward-facing section. In one embodiment, this includes the coupling shaft carrying an output gear of the first gear stage and at least one tooth tip of the drive gear being pressed into a bearing opening in the planet carrier for the rotationally fixed connection to the planet carrier. Here, therefore, at least one tooth tip of a tooth of the drive gear is used for a press connection to the planet carrier in order to save axial installation space. By pressing in, a positive connection can be provided between a tooth tip and the planet carrier at the bearing opening, in that an elastic deformation occurs at the tooth tip and / or at the bearing opening.

[0017] The first (preload) element provided for preloading the sun gear shaft, via which a preload force is set in the direction of the second housing-side bearing point, can be supported, for example, on the one hand on an outer ring of the first bearing and on the other hand on the part of the drive housing defining the first bearing point. In principle, a preload force applied by the first element and acting in a first axial direction can be greater, or set to be greater, than a preload force applied by the second (preload) element and acting in an opposite second axial direction. The preload force on the sun gear shaft at the first bearing point thus compensates for the opposing preload force with which the planetary gear stage is preloaded.This makes it easier to ensure that all bearings on the second shaft train are preloaded with a minimum load and that as few preloading (preloading) elements as possible are required.

[0018] In principle, the first element and / or the second element can be elastic. In particular, both the first element and the second element can comprise a wave spring washer. A wave spring washer allows a sufficiently high preload force to be set relatively inexpensively while simultaneously being easy to install.

[0019] In one embodiment, the second electric motor of the drive unit drives a (second) rotor shaft mounted coaxially with the input shaft and the output shaft and thus located on the first shaft train. The transmission device then has a gear for a further (third) gear stage that is connected in a rotationally fixed manner to the sun gear shaft and meshes with a gear of the (second) rotor shaft. The gear of the further (third) gear stage that is connected in a rotationally fixed manner to the sun gear shaft can then be arranged between the first element and the second element, viewed along the bearing axis. For example, the gear that is connected in a rotationally fixed manner to the sun gear shaft can be provided on a shaft section of the sun gear shaft that extends between the first and third bearings. This allows the components provided on the second shaft train to be arranged in a comparatively space-saving manner.

[0020] The coupling shaft, which is connected in a rotationally fixed manner to the planet carrier, can be a first coupling shaft for a first gear stage of the transmission device. The ring gear of the planetary gear stage can then in turn be connected in a rotationally fixed manner to a second coupling shaft, which carries an output gear for a second gear stage, via which the ring gear is connected to the output shaft. In one design variant, this second coupling shaft is also rotatably mounted on the sun gear shaft via a fourth bearing. Several components of the transmission device are thus rotatably mounted coaxially to one another about the bearing axis physically defined by the sun gear shaft and are arranged relatively compactly relative to one another. In addition, the rotatable bearing on the sun gear shaft makes it relatively easy to apply axial preload to the respective components.In one design variant, the output gear can also be supported on a part of the housing via a fifth bearing. In one design variant, a sixth bearing is provided to support the planet carrier on the ring gear, which is non-rotatably connected to the output gear.

[0021] For the axial preload of the components provided on the second shaft train, one design variant additionally provides a third (preload) element, for example an elastic element and in particular comprising a (third) wave spring washer. This third element axially preloads the fourth bearing, via which the second coupling shaft is rotatably mounted on the sun gear shaft, in the direction of the first bearing point of the sun gear shaft (and thus in the second axial direction). This third element can be supported on the one hand on an inner ring of the first bearing and on the other hand on an inner ring of the fourth bearing. The fourth bearing is thus preloaded by the third element in the second axial direction (for example elastically) and thus subjected to a defined preload force.

[0022] In principle, the fourth bearing can be at least partially relieved by a preload force applied by the second element, which acts in the direction of the first bearing point. For example, the preload force applied by the second element can counteract a toothing force of the planets of the planetary gear set in the axial direction, whereby this toothing force – then acting in the first axial direction – must be absorbed by the fourth bearing. Accordingly, the preload force of the second element, applied in the opposite second axial direction, has a relieving effect on the fourth bearing.

[0023] In one embodiment, starting from the first bearing point in the first axial direction along the bearing axis, the following components of the transmission device are arranged consecutively and thus one behind the other: a. the gear wheel connected in a rotationally fixed manner to the sun gear shaft, b. the (first) coupling shaft connected in a rotationally fixed manner to the planet carrier, c. the planetary gear stage and d. the output gear wheel connected to the second coupling shaft.

[0024] In principle, it can be provided that the first electric motor drives a first rotor shaft, and that this first rotor shaft of the first electric motor is located on a third shaft train. This first rotor shaft is then connected via a fourth gear stage to the ring gear of the planetary gear stage located on the second shaft train. The proposed solution can ensure a more compact arrangement and axial preload of the gear components on the second shaft train with comparatively few elements, especially in such a drive unit design variant, in which three shafts are mounted coaxially to one another on the second shaft train and four gear stages are provided.

[0025] In principle, at least one or all of the drive unit's gear stages can be designed as spur gear stages. For the first and third bearings, for example, the use of double-row angular contact ball bearings is recommended. However, this is by no means mandatory.

[0026] The proposed solution also concerns an electric bicycle with a variant of a proposed drive unit.

[0027] The attached figures illustrate possible embodiments of the proposed solution.

[0028] Here we show:

[0029] Figure 1 shows a sectioned view of a variant of a proposed drive unit with a view of a second shaft train on which, in particular, a planetary gear stage is provided;

[0030] Figure 2 shows a further sectional view of the drive unit of Figure 1, in particular with supplemented force curves;

[0031] Figure 3 shows in perspective single representation the planetary gear stage without

[0032] ring gear;

[0033] Figure 3A is a sectional view of the planetary gear stage of Figure 3;

[0034] Figure 4 shows schematically an electric bicycle in which the drive unit of the

[0035] Figures 1 and 2 with the planetary gear stage of Figures 3 and 3A is used. Figure 4 shows an electric bicycle 1 with an electric motor drive unit A. The electric bicycle 1 has a frame 10, which here, for example, comprises a top tube, a down tube and a seat tube and to which the drive unit A is attached in the region of an intersection point of the seat tube and the down tube. Part of the drive unit A are control electronics SE and a sensor device 15, for example designed with a torque sensor and a position sensor, for sensorically detecting a torque introduced into a drive shaft AT (in the form of a bottom bracket shaft) of the drive unit A by muscle power. The sensor device 15 can alternatively or additionally comprise a speed sensor, via which the speed of the drive shaft AT can be detected.

[0036] An output element of the drive unit A, here in the form of a hollow output shaft AW mounted coaxially to the drive shaft AT, is connected to a rear wheel 12 of the electric bicycle 1 via a belt or chain 13 as a power transmission element in order to drive the electric bicycle 1. A wheel sensor 14 for determining a travel speed of the electric bicycle 1 is assigned to this rear wheel 12, for example. Of course, the wheel sensor 14 can instead be provided on a front wheel 11 of the electric bicycle 1.

[0037] The drive unit A is part of a drive system of the electric bicycle 1, which further comprises an operating part 2. The operating part 2 is fastened in Figure 4, for example, in the area of ​​a handlebar of the electric bicycle 1 and is connected to the control electronics SE of the drive unit A. A user input can be recorded via the operating part 2 and used to control the drive unit A. For example, the operating part 2 further comprises at least one display to inform a user of the electric bicycle 1 about

[0038] - the current operating status of the drive unit A, for example with regard to a set support level,

[0039] - a charge state of a battery unit 3 supplying the drive unit A with electrical energy, which contains at least one (rechargeable) battery, and / or

[0040] - a set gear which specifies the ratio with which a drive torque introduced by muscle power at the drive shaft AT is transmitted to the output element of the drive unit A.

[0041] Figure 1 shows details of the drive unit A with a view into the interior of a drive housing G of the drive unit A. The drive shaft AT extends through the drive housing G and is connected on each side to a pedal crank, via which a rider of the electric bicycle 1 can apply drive force using muscle power. An output shaft AW protrudes from the drive housing G only on one side and is then connected, for example, to an output element in the form of a chain wheel or a toothed belt pulley, in order to drive the rear wheel 12 of the electric bicycle 1.

[0042] The drive unit A further comprises a first electric motor E1, which drives a first rotor shaft. This first electric motor E1, together with a second electric motor E2, which drives a second rotor shaft RW, is housed in a first housing part G1 of the drive housing G. The first housing part G1 is connected to a second housing part G2, which, together with the first housing part G1, defines an interior of the drive housing G, in which, in addition to the electric motors E1 and E2, a transmission device is housed. The first and second electric motors E1 and E2 are connected in this case via a power control and form a continuously variable electric actuating gear in order to be able to continuously adjust a transmission ratio of a planetary gear stage PG of the transmission device.The planetary gear stage PG is part of a multi-stage superposition gear, via which the input shaft AT, the output shaft AW and the two rotor shafts of the first and second electric motors E1 and E2 are coupled to one another, whereby in the illustration in Figure 1 only the second rotor shaft RW of the second electric motor E2 is visible.

[0043] The input shaft AT, the output shaft AW, and the rotor shaft RW of the second electric motor E2 are arranged coaxially on a first shaft train, while the planetary gear stage PG—in this case with three shafts—is arranged on a second shaft train, for which a physical bearing axis S is defined by a sun gear shaft 4. The first rotor shaft of the first electric motor E1 is in turn arranged on a third shaft train within the drive housing G, which runs parallel to the first and second shaft trains.

[0044] For the kinematic coupling of the gear elements of the drive unit A arranged on the three shaft trains, four gear stages GP1, GP2, GP3 and GP4, each designed as spur gear stages, are provided.

[0045] The drive shaft AT on the first shaft train is connected via a first gear stage GP1 to a first coupling shaft K1 on the second shaft train. For this purpose, the first coupling shaft K1 carries a drive gear 41 that meshes with an intermediate gear ZR. This intermediate gear ZR is rotationally fixedly connected to the drive shaft AT, optionally coupled to a freewheel. The first coupling shaft K1 is in turn rotationally fixedly connected to a planet carrier 51 of the planetary gear stage PG and is rotatably mounted on the sun gear shaft 4 via a third bearing L3—here designed as a double-row angular contact ball bearing.

[0046] The output shaft AW on the first shaft train is in turn connected to a second coupling shaft K2 via a second gear stage GP2. This second coupling shaft K2 carries an output gear 6, which meshes with a gear on the output shaft AW for the second gear stage GP2. The first gear stage GP1 increases the speed of the input shaft AT to a higher absolute speed of the first coupling shaft K1, which is connected to the second coupling shaft K2 via the planetary gear stage PG. The speed of the second coupling shaft K2 is transmitted to a lower speed of the output shaft AW with the gear ratio of the second gear stage GP2.

[0047] The (second) rotor shaft RW of the second electric motor E2 on the first shaft train is connected to the sun gear shaft 4 (as the third coupling shaft) on the second shaft train via a third gear stage GP3. For this purpose, a gear on the rotor shaft side meshes with a gear 43 that is non-rotatably connected to the sun gear shaft 4. The sun gear shaft 4 carries a sun gear 42 of the planetary gear stage PG, which meshes with the planet gears 52 of the planetary gear stage PG.

[0048] A ring gear 53 of the planetary gear stage PG is in turn connected in a rotationally fixed manner to the output gear 6 and is connected to the first rotor shaft of the first electric motor E1 via an external toothing via a fourth gear stage GP4.

[0049] In the embodiment of a proposed drive unit A shown in Figure 1, the sun gear shaft 4 is rotatably mounted at both of its longitudinal ends on the housing G. A first (lower in Figure 1) shaft end of the sun gear shaft 4 is rotatably mounted at a first housing-side bearing point GS1 via a first bearing L1 on the first housing part G1. The second (upper in Figure 1) longitudinal end of the sun gear shaft 4 is in turn rotatably mounted at a second housing-side bearing point GS2 via a second bearing L2. The second bearing point GS2 is defined by the second housing part G2. Viewed along the bearing axis S, starting from the first bearing point GS1 in a first axial direction, there follows a shaft section of the sun gear shaft 4, to which the gear 43 of the third gear stage GP3 is fixed.This is followed in the first axial direction along the bearing axis S by the third bearing L3 for the rotatable support of the first coupling shaft K1, before the sun gear 42 and thus the planetary gear stage PG follow in the first axial direction. This is followed in the first axial direction by the output gear 6 of the fourth gear stage GP4 in front of the second bearing point GS2 on the housing side.

[0050] Viewed in the axial direction, a printed circuit board P for the electronic control of the electric motors E1 and E2 is provided in the interior of the drive housing G between the gear 43 of the third gear stage GP3 and the first bearing L1 for the sun gear shaft 4. In this case, this circuit board is located in the area of ​​a parting plane between the two housing parts G1 and G2 for easier assembly.

[0051] In the illustrated drive unit A, the individual components of the transmission device are arranged very compactly on the bearing axis S of the second shaft train, defined by the sun gear shaft 4. At the same time, a comparatively small number of preload elements in the form of three wave spring washers WF1, WF2, and WF3, each applying a preload force, ensure that all bearings for the rotatable mounting of the components on the second shaft train are preloaded with a minimum load. This significantly reduces the occurrence of disturbing noises during operation of the drive unit A.

[0052] For example, a first wave spring washer WF1 is provided at the first bearing point GS1, which is supported on the one hand on the first housing part G1 and on the other hand on an outer ring of the first bearing L1 which rotatably supports the sun gear shaft 4 and is also designed as a double-row angular contact ball bearing.

[0053] A second wave spring washer WF2 serves to axially preload the planetary gear stage PG. While the first wave spring washer WF1 axially preloads the sun gear shaft 4 in the direction of its second bearing point and thus in the first axial direction (upwards in Figure 1) along the bearing axis S, the second wave spring washer WF2 axially preloads the planetary gear stage PG relative to the sun gear shaft 4 in the direction of the first bearing point GS1 and thus in the opposite, second axial direction. For this purpose, the second wave spring washer WF2 is supported in this case on an outer ring of the third bearing L3, via which the first coupling shaft K1 is rotatably mounted on the sun gear shaft 4. In addition, the second wave spring washer WF2 is supported on a web 411 of the first coupling shaft K1, which runs annularly around the bearing axis S and projects radially inwards.Since the first coupling shaft K1 is non-rotatably connected to the planet carrier 51 of the planetary gear stage PG, this achieves an axial preload of the planetary gear stage PG. The preload force applied by the first wave spring washer WF1 and acting in the first axial direction is set greater than the preload force applied by the second wave spring washer WF2 and acting in the opposite second axial direction. The preload of the planetary gear stage PG by the second wave spring washer WF2 is thus compensated by the larger, opposing preload force on the sun gear shaft 4 (and thus also a sun gear assembly comprising the sun gear shaft 4 and the components of the transmission device connected thereto in a non-rotatably manner).

[0054] A third wave spring washer WF3 is provided between the second bearing L2 for supporting the sun gear shaft 4 at the second housing-side bearing point GS2 and a fourth bearing L4, via which the second coupling shaft K2 carrying the output gear 6 is rotatably mounted on a shaft section of the sun gear shaft 4. This third wave spring washer WF3 is supported on the inner ring of the second bearing L2 and on the inner ring of the fourth bearing L4. In this way, the fourth bearing L4 is axially preloaded in the second axial direction (downward in Figure 1) via the third wave spring washer WF3. The second wave spring washer WF2 has a load-relieving effect on the fourth bearing L4, via whose outer ring - according to the force curve "3" shown in Figure 2 - a toothing force of the four planetary gears 52 must be diverted in the first axial direction during operation of the drive unit A.

[0055] The sectional view in Figure 2 further illustrates a force curve marked with “D” for the preload force introduced via the first wave spring washer WF1 and acting in the first axial direction along the bearing axis S. A force curve illustrated with “C” in Figure 2 for the (lower) preload force applied by the second wave spring washer WF2 in the opposite, second axial direction to the planetary gear stage PG in turn counteracts the preload force of the first wave spring washer WF1 in the sun gear shaft 4 and the toothing force of the four planet gears 52 during operation of the drive unit A. The preload force of the third wave spring washer WF3, for which a force curve is illustrated with a “B” in Figure 2, in turn acts in the second axial direction on the inner ring of the fourth bearing L4.

[0056] The planet carrier 51 is mounted on the ring gear 53 via a sixth bearing L6, here designed as a deep groove bearing. This sixth bearing L6 is responsible, in particular, for absorbing the toothing force of the drive gear 41, which acts in the first drive direction during operation of the drive unit A via the first gear stage GP1. The sixth bearing L6 is secured by an inner ring to a shoulder 511 of the planet carrier 51 that protrudes in the first axial direction.

[0057] The ring gear 53 is in turn supported on the drive housing G via the output gear 6 connected thereto by a fifth bearing L5. This fifth bearing L5 is arranged at a bearing point of the second housing part G2, which is concentric to the second bearing point GS2 for the sun gear shaft 4 and is provided radially further outward on the second housing part G2 with respect to the bearing axis S.

[0058] In order to further reduce the axial installation space, in the illustrated embodiment for the rotationally fixed connection between the first coupling shaft K1 and the planet carrier 51, a part of a tooth head 410 of the drive gear 41 is pressed into a bearing opening 510 of a cylindrical extension of the planet carrier 51.

[0059] As can be seen particularly in the enlarged views of Figures 3 and 3A, the bearing opening 510 is provided centrally on the planet carrier 51, which has a plurality of bearing pins 54 for the rotatable mounting of the plurality (in this case four) planet gears 52. Tooth tips 410 of the drive gear 41 are pressed into the central bearing opening 510, so that elastic deformation on the tip surfaces of the tooth tips 410 and / or on the inner wall of the bearing opening 510 creates a positive and frictional connection between a) the drive gear 41 and thus the first coupling shaft K1 and b) the planet carrier 51. Thus, a part of the drive gear 43, via which the connection to the drive shaft AT is established at the first gear stage GP1, is used for the rotationally fixed connection to the planet carrier 51.

[0060] For precise adjustment of the press fit, the tooth tips 410 each have a shoulder 4110 with a grinding area in an area located in the press-in direction. Here, the tip diameter is a few hundredths of a millimeter larger to allow for grinding of the diameter in the press fit area.

[0061] 1 electric bike

[0062] 10 (bicycle) frames

[0063] 11 Front wheel

[0064] 12 rear wheel

[0065] 13 Belt / Chain

[0066] 14 Wheel sensor

[0067] 15 Sensor device

[0068] 2 Control panel

[0069] 3 Battery unit (energy storage)

[0070] 4 sun gear shaft

[0071] 41 Drive gear

[0072] 410 tooth head

[0073] 4100 heel / grinding area

[0074] 411 Bridge (section)

[0075] 42 Sun gear

[0076] 43 gear

[0077] 51 planet carrier

[0078] 510 warehouse opening

[0079] 511 paragraph

[0080] 52 Planetary gear

[0081] 53 ring gear

[0082] 54 bearing journals

[0083] 6 Output gear

[0084] A drive unit

[0085] AT drive shaft

[0086] AW output shaft

[0087] E1, E2 electric motor

[0088] G Drive housing

[0089] G1, G2 housing part

[0090] GP1 - GP4 gear stage

[0091] GS1, GS2 storage location

[0092] K1 First coupling shaft

[0093] K2 Second coupling shaft

[0094] L1 - L6 bearings

[0095] P Circuit board PG Planetary gear stage

[0096] RW rotor shaft

[0097] S bearing axis

[0098] SE control electronics

[0099] WF1, WF2, WF3 wave spring washer

[0100] ZR intermediate gear

Claims

Claims 1. A drive unit for an electric bicycle (1), comprising a drive housing (G), a drive shaft (AT) rotatably mounted in the drive housing (G) for applying a drive force for driving the electric bicycle (F) by muscle power, an output shaft (AW) for transmitting the drive force to a wheel (12) of the electric bicycle (1), which output shaft is arranged coaxially to the drive shaft (AT) on a first shaft train and is rotatably mounted in the drive housing (G), a first electric motor (E1), a second electric motor (E2), and a transmission device arranged in the drive housing (G) with at least one planetary gear stage (PG) comprising a sun gear (42), a planet carrier (51), and a ring gear (53), the transmission ratio of which is adjustable by means of the first and second electric motors (E1, E2), and via which the drive shaft (AT) and the output shaft (AW) are coupled to one another.wherein a torque generated by the first electric motor (E1) is at least partially transmittable to the output shaft (AW), the transmission device comprises a sun gear shaft (4) which is connected in a rotationally fixed manner to the sun gear (42), which forms a physical bearing axis (S) for a second shaft train on which the planetary gear stage (PG) is arranged, and which is rotatably mounted on the one hand via a first bearing (L1) at a first bearing point (GS1) of the drive housing (G) and via a second bearing (L2) at a second bearing point (GS2) of the drive housing (G), and the transmission device comprises a coupling shaft (K1) which is connected to the drive shaft (AT) via a transmission stage (GP1) and which is rotationally fixedly connected to the planet carrier (51), characterized in that via a first element (WF1), which is supported at the first bearing point (GS1) on a part (G1) of the drive housing (G), the sun gear shaft (4) is driven in the direction of the second Storage location (GS2),relative to the bearing axis (S), is axially preloaded, and, via a second element (WF2) the planetary gear stage (PG) is axially preloaded relative to the sun gear shaft (4) in the direction of the first bearing point (GS1).

2. Drive unit according to claim 1, characterized in that the coupling shaft (K1) which is connected to the planet carrier (51) in a rotationally fixed manner is rotatably mounted on the sun gear shaft (4) via a third bearing (L3).

3. Drive unit according to claim 2, characterized in that the second element (WF2) for preloading the planetary gear stage (PG) is supported on the third bearing (L3).

4. Drive unit according to claim 3, characterized in that the second element (WF2) for preloading the planetary gear stage (PG) is supported on the one hand on an outer ring of the third bearing (L3) connected to the coupling shaft (K1) and on the other hand on a section (411) of the coupling shaft (K1).

5. Drive unit according to claim 4, characterized in that the second element (WF2) is supported on a web section (411) of the coupling shaft (K1) which is axially opposite the outer ring and projects radially inward and extends in an annular manner.

6. Drive unit according to claim 5, characterized in that a region of the coupling shaft (K1) forming the web section (411) is connected to the planet carrier (51) in a frictional and / or positively locking manner at a radially outwardly facing section (410).

7. Drive unit according to claim 6, characterized in that the coupling shaft (K1) carries a drive gear (41) of the gear stage (GP1) and a tooth head (410) of the drive gear (41) is pressed into a bearing opening (510) of the planet carrier (51) for the rotationally fixed connection with the planet carrier (51).

8. Drive unit according to one of the preceding claims, characterized in that the first element (WF1) is supported on the one hand on an outer ring of the first bearing (L1) and on the other hand on the part (G1) of the drive housing (G).

9. Drive unit according to one of the preceding claims, characterized in that a prestressing force applied by the first element (WF1) and acting in a first axial direction is greater than a prestressing force applied by the second Preload force applied to the element (WF2) and acting in an opposite second axial direction.

10. Drive unit according to one of the preceding claims, characterized in that the first element (WF1) and / or the second element (WF2) is designed to be elastic, in particular comprising a wave spring washer.

11. Drive unit according to one of the preceding claims, characterized in that the second electric motor (E2) drives a rotor shaft (RW) which is mounted coaxially to the input shaft (AT) and the output shaft (AW) and lies on the first shaft train, and the gear device comprises a gear (43) which is connected in a rotationally fixed manner to the sun gear shaft (4) and meshes with a gear of the rotor shaft (RW) for a further gear stage (GP3).

12. Drive unit according to claim 11, characterized in that the gear (43) of the further gear stage (GP3) which is connected in a rotationally fixed manner to the sun gear shaft (4) is arranged between the first element (WF1) and the second element (WF2) when viewed along the bearing axis (S).

13. Drive unit according to one of the preceding claims, characterized in that the coupling shaft (K1) connected in a rotationally fixed manner to the planet carrier (51) is a first coupling shaft for a first gear stage (GP1) of the transmission device and the ring gear (53) is connected in a rotationally fixed manner to a second coupling shaft (K2) which carries an output gear (6) for a second gear stage (GP2), via which the ring gear (53) is connected to the output shaft (AW).

14. Drive unit according to claim 13, characterized in that the second coupling shaft (K2) is rotatably mounted on the sun gear shaft (4) via a fourth bearing (L4).

15. Drive unit according to claim 14, characterized in that the drive unit (A) comprises a third element (WF3) which is axially preloaded with the fourth bearing (L4) in the direction of the first bearing point (GS1), 16. Drive unit according to claim 15, characterized in that the third element (WF3) is supported on the one hand on an inner ring of the first bearing (L1) and on the other hand on an inner ring of the fourth bearing (L4).

17. Drive unit according to one of claims 14 to 16, characterized in that a pretensioning force applied by the second element (WF2) which is in towards the first bearing point (GS1), the fourth bearing (L4) is at least partially relieved.

18. Drive unit according to claim 11 or 12 and according to one of claims 13 to 17, characterized in that viewed in an axial direction along the bearing axis (S), starting from the first bearing point (GS1), a. the gear (43) which is rotatably connected to the sun gear shaft (4), b. the coupling shaft (K1) which is rotatably connected to the planet carrier (51), c. the planetary gear stage (PG) and d. the output gear (6) which is connected to the second coupling shaft (K2) follow one another.

19. Drive unit according to one of the preceding claims, characterized in that the first electric motor (E1) drives a first rotor shaft and the first rotor shaft of the first electric motor (E1) is located on a third shaft train and is connected to the ring gear (53) on the second shaft train via a fourth gear stage (GP4).

20. Electric bicycle with a drive unit (A) according to one of the preceding claims.

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