CONTINUOUSLY VARIABLE TRANSMISSION POWERTRAIN WITH EPICYCLOIDAL REDUCER

Abstract

The invention relates to a powertrain (4) for an electrically assisted bicycle. The powertrain (4) comprises a first electric motor (M1), a second electric motor (M2), and a gearbox (5). The gearbox (5) includes an epicyclic transmission device (8) that is mechanically connected directly to the second electric motor (M2). The first electric motor (M1) is configured to drive an output transmission element (88) of the gearbox. The second electric motor (M2) is configured to drive the epicyclic transmission device (8). (See Figure 2 for abbreviations.)

Description

Title of the invention: CONTINUOUSLY VARIABLE TRANSMISSION POWERTRAIN AND EPICYCLOIDAL REDUCER TECHNICAL FIELD OF THE INVENTION

[0001] The invention relates to the general technical field of electrically assisted cycles. More specifically, the invention relates to a powertrain for an electrically assisted bicycle. STATE OF THE ART

[0002] An electrically assisted bicycle includes a drive unit that provides assistance to a user, enabling the user to travel on steep terrain and / or over long distances, which would, for example, be inaccessible with a conventional bicycle without assistance. Electric assistance also makes cycling easier for a large number of people, particularly as an alternative to using a car.

[0003] Patent application FR2202477 discloses a powertrain comprising a first electric motor, a second electric motor and an epicyclic reducer whose transmission elements are driven by the first electric motor and by the second electric motor.

[0004] The space available for the drive unit on or within the bicycle is limited. In particular, the space available for the gearbox is limited due to the size of the electric motor. The gearbox's reduction ratio is generally high to allow the use of a powerful electric motor and to enable the drive unit to provide effective electric assistance. The reduction ratio in a compact space is likely to be improved.

[0005] There is also a powertrain for an electrically assisted bicycle that comprises a single electric motor and a cycloidal reduction gear. However, such a powertrain is susceptible to torque interruptions during automatic gear changes. These unexpected torque interruptions are very poorly received by a user, who may believe there is a malfunction in the powertrain. The reduction ratio in a compact design can still be improved.

[0006] There is therefore a need to improve the electric assistance of a cycle, while limiting the mass and size of the powertrain for electrically assisted cycles, and while facilitating automatic gear changes without interruption of torque and improving the comfort of using the cycle. Description of the invention

[0007] The present invention aims to remedy all or part of the disadvantages of the prior art mentioned above.

[0008] To this end, the invention relates to a powertrain for an electrically assisted cycle. The powertrain comprises a first electric motor, a second electric motor separate from the first electric motor, an output shaft, and a reducer which includes an epicyclic transmission device.

[0009] According to one aspect of the invention, the reducer comprises an epicyclic transmission device connected to the second electric motor. The first electric motor is configured to drive an output transmission element of the reducer via a gear train. The second electric motor is configured to directly drive the epicyclic transmission device, the planet carrier of the latter being coupled to the rotor of the second electric motor.

[0010] Thus, the invention relates in particular to a powertrain for an electrically assisted cycle comprising: a first electric motor, a second electric motor distinct from the first electric motor, an output shaft and a reducer which includes an epicyclic transmission device, characterized in that a planet carrier of the epicyclic transmission device is directly connected to the rotor of the second electric motor, the first electric motor being configured to drive an output transmission element of the epicyclic transmission device via a gear train, the second electric motor being configured to directly drive the epicyclic transmission device.

[0011] A bottom bracket shaft, or first shaft, and the output shaft are concentric.

[0012] Thanks to a powertrain according to the invention, the electric assistance of the cycle is improved, while limiting the mass and size of the powertrain. In particular, automatic gear changing tends to be facilitated, the comfort of using the cycle to be improved, the maximum power delivered to be increased, the efficiency of the powertrain's gearbox to be increased, all while limiting the mass and size of the powertrain, and while having a relatively simple powertrain to manufacture.

[0013] Automatic gear changes are smooth thanks to the continuously variable transmission made possible by the two electric motors, and torque interruptions are avoided, for example, during automatic gear ratio changes. The powertrain is particularly compact due to the direct connection between the rotor of the second electric motor and the planet carrier of the epicyclic transmission device. This arrangement also simplifies the manufacturing of the powertrain and contributes to its compact size. The powertrain's manufacturing process, particularly the assembly of the gearbox's transmission components, is facilitated by the limited number of gears in the powertrain. The epicyclic transmission and the connection between the second electric motor and the gearbox further reduce the number of gears in the powertrain, thus minimizing its mass. The efficiency of the powertrain's gearbox tends to increase due to the reduced number of gears and the continuously variable transmission. The gearbox's compact size and high efficiency allow for the use of at least one particularly powerful electric motor.

[0014] According to one embodiment, the second electric motor is centered around the first shaft. The first electric motor is centered around a second shaft of the powertrain which is strictly parallel to the first shaft.

[0015] According to one embodiment, the gearbox includes at least one freewheel between the bottom bracket shaft and the output shaft of the gearbox. The freewheel is used, in particular, to operate the bicycle without electric assistance by directly connecting the bottom bracket shaft to the output shaft when the freewheel is engaged.

[0016] According to one embodiment, the gears of the gear train and the epicyclic transmission device are preferably arranged in parallel and juxtaposed or adjacent planes along an axis that is perpendicular to them.

[0017] Most advantageously, the first electric motor and the second electric motor are arranged on the same side of one of said planes.

[0018] According to another embodiment, the epicyclic transmission device comprises a first input transmission element and the output transmission element, the output transmission element being fixed relative to an output shaft of the powertrain.

[0019] The epicyclic transmission device may include a planet carrier(s) carrying at least one planet equipped with a first set of teeth and a second set of teeth distinct from the first set of teeth, this planet carrier forming an input transmission element. The planets may be uniformly distributed, or not.

[0020] According to one embodiment, the epicyclic transmission device comprises:

[0021] - a satellite carrier carrying at least one satellite equipped with a first set of teeth and a a second set of teeth distinct from the first set of teeth, this planet carrier forming a second input transmission element; and:

[0022] - a first planetary gear, engaged with the first gear and capable of forming a first element of input transmission, a 2nd planetary gear in contact with the 2nd gear set, the 2nd planetary gear forming the output element.

[0023] In this embodiment, the reducer may include a free wheel (or 2nd free wheel) between the crankshaft and the 1st planetary gear, so that when the crankshaft is driven in a backpedaling motion, this movement is not hindered either by the resistance of the motor or by that of the rotation of the epicyclic transmission device.

[0024] According to one embodiment, the epicyclic transmission device comprises:

[0025] - a satellite carrier carrying at least one satellite equipped with a first set of teeth and a a second set of teeth distinct from the first set of teeth, this planet carrier forming a second input transmission element; and:

[0026] - a first toothed crown, engaged with the first toothing, a second toothed crown in taken with the 2nd toothing, the 1st toothed ring forming the output element.

[0027] In this embodiment, the reducer may include a freewheel between the bottom bracket shaft and the second ring gear, so that when the bottom bracket shaft is driven by a backpedaling motion, this motion is not hindered by either the resistance of the motor or that of the rotation of the planetary gear train. The output shaft and the first ring gear may be fixed relative to each other.

[0028] According to yet another embodiment, the epicyclic transmission device comprises:

[0029] - a satellite carrier carrying at least one satellite equipped with a first set of teeth and a a second set of teeth distinct from the first set of teeth, this planet carrier forming a second input transmission element; and:

[0030] - a planetary gear, engaging with the first toothing, a toothed ring engaging with the 2nd gear, the toothed ring forming the output element; in this embodiment again, the reducer may include a free wheel (or 2nd free wheel) between the crankshaft and the planetary gear, so that when the crankshaft is driven in a backpedaling motion, this movement is not hindered either by the resistance of the motor or by that of the rotation of the epicyclic transmission device.

[0031] In this variant the output shaft and the toothed ring can be fixed relative to each other.

[0032] In a device according to the invention, the second toothing is preferably smaller than the first, in particular for p <1.

[0033] According to one embodiment, the first electric motor is mechanically connected to the output transmission element via a gear train with external teeth, for example straight or helical.

[0034] Preferably, said external gear train comprises only 4 gear wheels or pinions and / or a single intermediate shaft between an output shaft of the first electric motor and an output shaft of the powertrain, which allows for a particularly compact design.

[0035] Preferably, in a powertrain according to the invention, the first electric motor and the second electric motor are arranged on a 1st side, or turned towards a 1st side, of the powertrain, the gear train which enables the first electric motor to drive the output transmission element as well as the epicyclic transmission device being located on a 2nd side, or turned towards a 2nd side, of the powertrain.

[0036] Advantageously, the epicyclic transmission device of a powertrain according to the invention has a parameter p different from 1 but between 0.8 and 1.15; p is the planetary ratio, that is to say the ratio of the rotational speed of the driven member to the rotational speed of the driven member, the controlled member being at rest.

[0037] The invention also relates to an electrically assisted cycle comprising a powertrain as defined above. Preferably, the cycle is a bicycle or a cargo bike.

[0038] According to one embodiment, the electrically assisted cycle comprises a front wheel, a rear wheel, and a transmission system that includes a chain (or pulley-belt transmission), sprockets, and at least one chainring. The drive unit is configured to drive the chainring, which is fixed relative to an output shaft of the drive unit. BRIEF DESCRIPTION OF THE FIGURES

[0039] Other advantages, purposes and particular features of the present invention will become apparent from the following non-limiting description of at least one particular embodiment of the devices and methods of the present invention, with reference to the accompanying drawings, in which: • [Fig.1] is a schematic representation of an electrically assisted cycle, comprising a powertrain according to a first embodiment of the invention; • [Fig.2] is a kinematic representation of a powertrain for an electrically assisted cycle, according to a first embodiment; • [Fig.3] is another representation of a powertrain for an electrically assisted cycle, according to the first embodiment; • [Fig.4] is a partial kinematic representation of a powertrain for an electrically assisted cycle, according to a second embodiment; • [Fig. 5] is a partial kinematic representation of a group powertrain for an electrically assisted cycle, according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0040] The present description is given as a non-limiting example of an embodiment.

[0041] Figure 1 is a schematic representation of an electrically assisted cycle 1 according to a first embodiment shown. In the first embodiment shown, the electrically assisted cycle is a bicycle. The electrically assisted cycle 1 comprises a frame 2, a front wheel 10F, a rear wheel 10R, pedals 11, and a transmission and drive system 3.

[0042] The transmission and drive system 3 comprises a battery B, a drive unit 4, and a transmission system 30. In the embodiment shown, the battery B is mounted in a detachable manner to the bicycle frame 12, for example, on a downtube 22 of the frame. The transmission and drive system 3 is configured to drive the wheels 10F, 10R from the movement of the pedals 11, optionally with electric assistance.

[0043] The transmission system 30 comprises a chain 31, sprockets 34 and at least one chainring 32. The cycle 1 preferably comprises at least two chainrings 32, preferably three chainrings 32. The chain 31 mechanically connects at least one chainring 32 to one of the sprockets 34. The transmission system 30 drives, for example, the rear wheel 10R from the crankset.

[0044] With joint reference to Figures 2 to 5, the drive unit 4 comprises a first electric motor M1, a second electric motor M2, a reduction gear 5 which includes an epicyclic transmission device 8, a drive device, a control system, a monitoring system, a crankshaft 41, a traction motor shaft 42 M1, and a drive unit output shaft 49. The drive unit 4 is configured to electrically assist the pedaling of a cycle user. In the embodiment shown, the drive unit 4 is designed to drive each chainring 32.

[0045] The bottom bracket shaft 41 forms a first shaft of the drive unit. The bottom bracket shaft 41 is centered around a first longitudinal axis XI of the gearbox, which is also called the longitudinal axis XI of the bottom bracket shaft. The traction motor shaft 42 is strictly parallel to the bottom bracket shaft 41, extending around a second longitudinal axis X2 of the gearbox, located at a non-zero distance from XL. The output shaft 49 is concentric with the bottom bracket shaft 41. In the embodiment shown, the output shaft 49 is a hollow shaft located radially outside the bottom bracket shaft 41 and fixed relative to each chainring 32.

[0046] In the present document, a direction parallel to the first longitudinal axis XI is a transverse direction of the cycle and a longitudinal direction of the reducer 5. The direction Y which is represented in [Fig.1] is orthogonal to the direction of the first longitudinal axis XI and it corresponds to the longitudinal direction of the cycle.

[0047] The first electric motor M1 is centered around the second longitudinal axis X2 of the reducer, being located around the shaft 42 of the traction motor. The first electric motor M1 is called the traction motor. It is configured to drive the output shaft 49 via the drive device by assisting the user's pedaling.

[0048] In the embodiment shown, the drive device is a train 44 of external cylindrical gears comprising or consisting of cylindrical gears with spur or helical teeth. The gear train 44 comprises, in this order from the first electric motor M1 to the output shaft 49, a first pinion P1, a second pinion P1.2 mechanically engaging the first pinion P1, a third pinion P1.3 which is fixed relative to the second pinion P1.2, and a fourth pinion P1.4 which mechanically engages the third pinion. The fourth pinion P1.4 is fixed relative to the output shaft 49 and is called the drive pinion. The gear train 44 comprises 4 pinions and a single intermediate shaft 44i (on which, in this example, pinions P1.2 and P1.3 are fixed or around which they rotate) between the output shaft 42 of the electric motor and the output shaft 49.This limits the complexity and bulk of the entire device. The intermediate axis 44i is positioned parallel to each of the shafts 42, 49. The 2 pinions P1.2 and P1.3 can form a hollow shaft which rotates around a fixed shaft (for example on bearings) or the 2 pinions form a shaft at the end of which there are cylindrical bearing surfaces (which can be seen in [Fig.3]).

[0049] The second electric motor M2 is centered around the first longitudinal axis XI of the reducer. The second electric motor M2 is configured to directly drive the epicyclic transmission device 8, without any other intermediate transmission device. The second electric motor M2 is configured to vary the ratio of the reducer 5 (for example, so that the user can pedal at a constant pedaling cadence). The second motor M2 is called the variable-speed motor.

[0050] The control system may include at least one sensor. For example, it is configured to detect directly or indirectly the rotational speed of the first electric motor M1, the second electric motor M2, and the force exerted by the user on the pedals 11. In the embodiment shown, the control system includes a torque sensor 45 that detects the torque exerted by the user on the pedals 11. For example, this sensor 45 measures deformations of a part (not shown in [Fig.2]) located between the shaft 41 and the casing (not shown in [Fig.2]) which contains the powertrain (4).

[0051] The control system includes at least one control unit 43. The control unit 43 is configured to control the first electric motor M1, particularly its torque, and the second electric motor M2, particularly its speed, to assist pedaling based on data detected by the control system. The control unit 43 takes, for example, the form of an electronic control board for the powertrain 4.

[0052] The reducer 5 includes the epicyclic transmission device 8. The longitudinal axis of the reducer 5 is the first longitudinal axis XL. The reducer 5 is configured to control the pedaling cadence according to one or more cadence laws. The epicyclic transmission device 8 comprises, in this example, a first planetary gear 90, a planet carrier 82 (forming an input transmission element), and a second planetary gear 88. The planet carrier 82 carries a planetary gear with a first set of teeth 84 and a second set of teeth 86 distinct from the first set of teeth.

[0053] The gearbox 5 may include at least one freewheel 51, which may be located between the bottom bracket shaft 41 and the output shaft 49 of the gearbox. When the freewheel 51 is engaged, the three members of the planetary gear train (bottom bracket shaft, output shaft, and planet carrier) rotate at the same speed as a single unit. Thus, the bottom bracket shaft drives the output shaft; as a consequence, the motor M2 is driven via the epicyclic transmission device 8, in particular via the gears 84, 86. The freewheel 51 notably allows the output shaft 49 to be driven directly by the bottom bracket shaft 41 when the second electric motor M2 is no longer able to control the speed of the planet carrier s 84 to maintain it at a sufficient speed.In practice, such a situation occurs, for example, when the torque on the bottom bracket shaft 41 around the first longitudinal axis XI is greater than the torque that the motor M2 can supply. The freewheel 51 is used, in particular, to operate cycle 1 without electric assistance.

[0054] In other words, this freewheel 51 engages when the rotational speed of the output shaft becomes less than or equal to the pedal shaft, thus ensuring a transmission of the movement from the pedals to the wheel of the bicycle even when the motor M2 is not able to ensure this transmission.

[0055] A second free wheel 53 can be provided between the crankshaft 41 and the first planetary gear 90, so that when the crankshaft is driven in a backpedaling motion, this movement is not hindered either by the resistance of the motor M2 or by that of the rotation of the epicyclic transmission device.

[0056] As mentioned above, the epicyclic transmission device 8 in this example comprises the first planet gear 90, the planet carrier 82, which carries a planet gear with a first set of teeth 84 (which meshes with the first planet gear 90) and a second set of teeth 86, and a second planet gear 88 (which meshes with the second set of teeth 86). In the example of [Fig. 2], the epicyclic transmission device is of type IV (satellite gear with double teeth 84, 86 and two inner planet gears 90, 88). However, alternatively, it can be of type II ([Fig. 4]), or of type III ([Fig. 5]). In the embodiment shown in [Fig. 2], the planet carrier s 82 (connected to the rotor of motor M2) is the second input transmission element of the epicyclic transmission device. The first planet gear 90 is fixed relative to the bottom bracket shaft 41, which forms the first input transmission element of the epicyclic reducer. The planet gear 88 is the output transmission element.It is fixed relative to the output shaft 49.

[0057] The epicyclic transmission device 8 is configured to drive the output shaft 49 from the crankshaft shaft 41 and the drive by the second electric motor M2.

[0058] Preferably, the ratio p (which is the ratio or planetary ratio, i.e. the ratio of the rotational speed of the driven member to the rotational speed of the driven member, the controlled member being at rest) of the planetary gear is close to 1, while being different from 1; for example: p 1 and 0.8 < p < 1.15. This makes it possible to choose a motor M2 of dimensions compatible with the allocated space.

[0059] As can be seen from the diagram in [Fig.2], the resulting structure is quite simple. Furthermore, the two motors are located on the same side of the device (on the left side of [Fig.2]), leaving access on the right side to the various elements of the gear trains.

[0060] During operation of the drive unit 4, the pedals 11 drive the bottom bracket shaft 41, which forms the first input transmission element of the epicyclic transmission device 8. The control unit 43 controls the first electric motor M1, which drives the output shaft 49 via the gear train 44, based on data from the sensor 45. The control unit 43 controls the second electric motor M2 to change the rotational speed of the planet carrier 82, based on data from the sensor 45. The control of the second electric motor M2 aims, for example, to maintain a similar pedaling cadence regardless of the speed of cycle 1 and the incline, taking into account the user's physical condition. When no electric assistance is required, the freewheel 51 allows the output shaft 49 to be driven directly by the bottom bracket shaft 41.

[0061] Thanks to the powertrain 4 according to the invention, the electric assistance of cycle 1 is improved, while limiting the mass and size of the powertrain 4.

[0062] Automatic gear changes are smooth thanks to the continuously variable transmission made possible by the two electric motors M1, M2. Torque interruptions are avoided, for example, during the automatic variation of the transmission ratios in cycle 1. The electric assistance in cycle 1 is thus improved.

[0063] The freewheel 51 improves pedaling comfort when no electric assistance is required. In particular, the freewheel 51 improves pedaling comfort by directly connecting the bottom bracket shaft 41 to the output shaft 49 in order to ensure the transmission of torque from the cyclist to the wheel of the cycle 1 when the second electric motor M2 is unable to control the speed of the satellite carrier 82 (for example when the torque of the pedal shaft is too high, or when there is a fault in electrical power (due in particular to a missing or discharged battery).

[0064] The powertrain 4 is compact due to the direct link between the motor M2, which rotates around the bottom bracket shaft 41, and the satellite carrier 82, without the need for additional gears.

[0065] The manufacture of the powertrain 4, in particular the assembly of the transmission elements of the reducer, is facilitated by the low number of gears in the powertrain 4. The manufacture of the powertrain 4 is facilitated by the mounting of the motors M1 and M2 on one side of the device, the gears being arranged on the other side.

[0066] The low number of gears in the powertrain 4 also tends to reduce the mass of the powertrain 4.

[0067] The efficiency of the gearbox 5 of the powertrain 4 is generally high, due to the small number of gears in the gearbox 5 and the continuously variable transmission. Since the planetary gear 90, which forms the first input element of the epicyclic transmission device 8, is fixed relative to the crankshaft 41, energy losses are reduced between the pedals 11 and the input of the epicyclic gearbox 8, and the efficiency of the gearbox 5 tends to increase. The efficiency of the gearbox 5 is particularly high with the epicyclic transmission device of the gearbox 5 as shown in [Fig. 2].

[0068] The compactness and high efficiency of the reducer 5 allow the use of at least one electric motor M1, M2 adapted to the powers to be transmitted.

[0069] Figure 3 shows an embodiment of the device in its housing 60, the kinematic chain of which has been explained above, in relation to Figure 2. As can be seen in this figure, the resulting assembly forms a particularly compact powertrain. The gear elements can be arranged in three adjacent planes, a first plane E1 comprising the 1st planetary gear 90 and the 1st satellite gear 84, a 2nd plane E2 comprising the 2nd planetary gear 88, the 2nd satellite gear 86 as well as the pinions PI.2 and Pl.1, and a 3rd plane E3 comprising the pinions PI.3 and P1.4. The 3 planes are parallel and juxtaposed or close together along an axis which is perpendicular to them.

[0070] Figures 4 and 5 show variants of a powertrain according to the invention. The elements shown above, in particular the P1.1-P1.4 gear train, the control unit 43, etc., apply to these two variants. Reference numerals identical to those in Figures 2 and 3 designate identical or similar elements. The efficiency of the gearbox 5 of the powertrain in [Fig. 4] is entirely comparable to that of Figures 2 and 3. One or more freewheels 51, 53 can be used with these variants of Figures 4 and 5, just as in Figures 2 and 3.

[0071] In the variant of [Fig. 4], the epicyclic transmission device comprises the first inner toothed ring 92, the planet carrier 82, and a second inner toothed ring 94. The planet carrier 82 carries a planet equipped with a first toothed ring 84a (which meshes with the first inner toothed ring 92) and a second toothed ring 86a, distinct from the first toothed ring, which meshes with the second inner toothed ring 94, which is in contact with the second toothed ring 86a. In this architecture, an input element is formed by the ring 94, the output element is the ring 92, and another input element is formed by the planet carrier 82.

[0072] In the variant of [Fig. 5] the epicyclic transmission device comprises a planet gear 90, the planet carrier 82, and an internal toothed ring 98. The planet carrier 82 carries a planet gear equipped with a first set of teeth 84b (which meshes with the planet gear 90) and a second set of teeth 86b, which mesh with the internal toothed ring 98. In this architecture, one input element is the planet gear 90, another input element is formed by the planet carrier 82, and the output element is the ring 98.

[0073] The variants of figures 4 and 5 can be the subject of more detailed representations, of the type of that in [Fig.3].

[0074] These variants of figures 4 and 5 offer similar advantages to the embodiment explained above in relation to figures 2 and 3.

[0075] Preferably, and in particular for the realization of figures 2 and 3, the second tooth 86 of the satellite is smaller than the first tooth 84 to have p < 1. For p > 1, we seek to have the second tooth 86 be larger than the first 84, but this makes the assembly less easy.

[0076] Various modifications can be made by a person skilled in the art to the invention which has just been described without going out of the scope of the disclosure of the invention.

[0077] Alternatively, the electrically assisted cycle 1 is a cargo bike. Alternatively still, the electrically assisted cycle 1 is, for example, a unicycle or a tricycle.

[0078] Alternatively, battery B is housed inside frame 12. Alternatively, battery B is fixed to the rear of the bicycle, for example on a luggage rack.

[0079] Alternatively, the drive unit 4 is connected directly to the hub of a wheel 10F, 10R of the electrically assisted cycle, instead of being integrated at least partially into the cycle's crankset.

[0080] Alternatively, the bottom bracket shaft 41 is hollow.

[0081] Alternatively, the drive device may include transmission elements other than spur or helical gears, for example a flat gear. The number of gears in the drive device may vary.

[0082] In addition or alternatively, the control system includes at least one relative and / or absolute sensor to detect the rotational speed of the first electric motor M1 and / or the second electric motor M2. This sensor is, for example, a Hall effect sensor.

[0083] As already explained, the reducer 5 can include at least one freewheel 53 between the second electric motor M2 and the crankshaft 41, which in particular makes it easier to reposition the pedals 11 at the start of cycle 1.

[0084] Alternatively, the epicyclic transmission device 8 includes at least one cylindrical gear.

[0085] The shape and arrangement of the teeth and / or lobes of the transmission elements of the reducer 5 is likely to vary.

Claims

Demands

1. Powertrain (4) for an electrically assisted cycle (1) comprising: a first electric motor (M1), a second electric motor (M2) separate from the first electric motor (M1), an output shaft (49) and a reducer (5) which includes an epicyclic transmission device (8), characterized in that a planet carrier (82) of the epicyclic transmission device (8) is directly connected to the rotor of the second electric motor (M2), the first electric motor (M1) being configured to drive an output transmission element (88, 92, 98) of the reducer via a gear train (44), the second electric motor (M2) being configured to directly drive the epicyclic transmission device (8), a bottom bracket shaft (41), or first shaft, and the output shaft (49) being concentric.

2. Powertrain (4) according to the preceding claim, wherein the second electric motor (M2) is centered around the first shaft (41), the first electric motor (M1) being centered around a second shaft (42) of the powertrain which is strictly parallel to the first shaft (41).

3. Powertrain (4) according to the preceding claim, wherein the reducer (5) includes at least one freewheel (51) between the bottom bracket shaft (41) and the output shaft (49) of the reducer, in particular for using the cycle (1) without electric assistance by directly connecting the bottom bracket shaft (41) to the output shaft (49), when the freewheel (51) is engaged.

4. Powertrain (4) according to any one of claims 1 to 3, wherein the gears of the gear train (44) and of the epicyclic transmission device (8) are arranged in parallel and juxtaposed or adjacent planes (E1, E2, E3) along an axis which is perpendicular to them.

5. Powertrain (4) according to the preceding claim, wherein the first electric motor (M1) and the second electric motor (M2) are arranged on the same side of one of said planes.

6. Powertrain (4) according to any one of claims 1 to 5, wherein the epicyclic transmission device (8) comprises an input transmission element (82), the transmission element of output (88, 92, 98) being fixed relative to the output shaft (49) of the powertrain.

7. Powertrain (4) according to any one of claims 1 to 6, wherein the epicyclic transmission device (8) comprises: - a planet carrier (82) carrying a planet having a first set of teeth (84) and a second set of teeth (86) distinct from the first set of teeth, this planet carrier (82) forming an input transmission element; and: - a first planet (90), in mesh with the first set of teeth (84), a second planet (88) in mesh with the second set of teeth, the second planet (88) forming an output element.

8. Powertrain (4) according to claim 7, wherein the reducer (5) includes a freewheel (53) between the crankshaft (41) and the 1st planetary gear (90), so that when the crankshaft is driven in a backpedaling motion, this motion is not hindered by the resistance of the motor (M2) or by that of the rotation of the planetary gear train.

9. Powertrain (4) according to any one of claims 1 to 6, wherein the epicyclic transmission device (8) comprises: - a planet carrier (82), carrying a 1st planet having a 1st toothing (84a) and a 2nd toothing (86a) distinct from the 1st toothing, this planet carrier (82) forming an input transmission element; and: - a 1st toothed ring (92), meshing with the 1st toothing (84a), a 2nd toothed ring (94) meshing with the 2nd toothing (86a), the 1st toothed ring (92) forming an output element.

10. Powertrain (4) according to claim 9, wherein the reducer (5) includes a freewheel (53) between the crankshaft (41) and the 2nd toothed ring (94), such that when the crankshaft is driven in a backpedaling motion, this motion is not hindered by the resistance of the motor (M2) or by that of the rotation of the planetary gear train.

11. Powertrain (4) according to claim 9 or 10, wherein the output shaft (49) and the first toothed ring (92) are fixed relative to each other.

12. Powertrain (4) according to any one of claims 1 to 6, wherein the epicyclic transmission device (8) comprises: - a planet carrier (82), carrying a planet having a first toothed tooth (84b) and a second toothed tooth (86b) distinct from the first tooth, this planet carrier (82) forming an input transmission element; and: - a planetary gear (90), meshing with the first toothed tooth (84b), a ring gear (98) meshing with the second toothed tooth (86b), the ring gear (98) forming an output element.

13. Powertrain (4) according to claim 12, wherein the output shaft (49) and the toothed ring (98) are fixed relative to each other.

14. Powertrain (4) according to claim 12 or 13, wherein the reducer (5) includes a freewheel (53) between the crankshaft (41) and the planetary gear (90), so that when the crankshaft is driven in a backpedaling motion, this motion is not hindered by the resistance of the motor (M2) or by that of the rotation of the planetary gear train.

15. Powertrain (4) according to any one of the preceding claims, wherein the first electric motor (M1) is mechanically connected to the output transmission element (88) via a straight or helical external gear train.

16. Powertrain (4) according to claim 15, wherein said external gear train comprises 4 pinions and / or a single intermediate shaft (44i) between an output shaft (42) of the first electric motor (M1) and an output shaft (49) of the powertrain (M2).

17. Powertrain (4) according to any one of the preceding claims, wherein the first electric motor (M1) and the second electric motor (M2) are disposed on a 1st side, or turned towards a 1st side, of the powertrain, the gear train which enables the first electric motor (M1) to drive the output transmission element (88) and the epicyclic transmission device (8) being situated on a 2nd side, or turned towards a 2nd side, of the powertrain.

18. Powertrain (4) according to any one of the preceding claims, wherein the epicyclic transmission device has a planetary ratio, p not equal to 1 but between 0.8 and 1.

15.

19. Electrically assisted cycle (1) comprising a powertrain (4) according to any one of the preceding claims, wherein the cycle (1) is a bicycle or a cargo bike.

20. Electrically assisted cycle (1) according to the preceding claim, comprising a front wheel (10F), a rear wheel (10R), a transmission system (30) comprising a chain (31), sprockets (34) and at least one chainring (32), the drive unit (4) being configured to drive the chainring (32) which is fixed relative to a drive unit output shaft (49).

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