Powertrain having an automatic transmission for an electrically assisted bicycle

Abstract

The invention relates to a powertrain for an electrically assisted bicycle comprising a bottom bracket shaft (A1) having an axis (X1), a first electric motor (M1), an epicyclic reduction gear (R), a second electric motor (M2), and a chainring(12), the epicyclic reduction gear (R) and the chainring (12) having a longitudinal axis (X2) parallel to and separate from the axis (X1). The reduction gear (R, R') comprises a sun gear driven by the bottom bracket shaft (A1) and the first motor (M1), a planet frame driving the chainring (12) and a ring gear (22) that is moveably mounted so as to rotate about the axis (X2) of the reduction gear (R), the second electric motor (M2) being mechanically connected to the ring gear (22) in order to rotate it. The powertrain is automatically controlled by a control unit (UC) which is configured to control the first electric motor (M1) and the second electric motor (M2), the control unit (UC) controlling the speed of rotation of the ring gear (22) in order to modify the transmission ratio of the powertrain.

Description

[0001] DESCRIPTION

[0002] TITLE: POWERTRAIN WITH CONTROLLED TRANSMISSION FOR ELECTRICALLY ASSISTED BICYCLE

[0003] TECHNICAL FIELD AND PRIOR ART

[0004] The present invention relates to a powertrain for an electrically assisted bicycle and to an electrically assisted bicycle comprising such an actuator.

[0005] The electrically assisted bicycle is experiencing very strong development both because it offers an easier mode of transport with the assistance it provides by avoiding using the car, it also offers assistance, particularly on steep terrain, and allows the sport of cycling to the greatest number of people.

[0006] There are two types of electric bikes. The first type has a motor that drives the hub of the rear or front wheel directly. The second type has a motor integrated directly into the bottom bracket. This arrangement allows for a more compact device and places the center of gravity of the drive unit under the user.

[0007] Document US10773771 describes a hybrid drive device for an electric bicycle comprising a pedal crank actuated by physical force, an electric motor at the pedal crank, an epicyclic reduction gear whose crown is provided on its outer periphery with teeth which mesh with a chain which, itself, drives the rear wheel whose hub is provided with a sprocket.

[0008] The pedal assembly is rotationally fixed to the planet carrier of the reducer, the motor drives the planetary gear.

[0009] The bicycle has a reduction ratio changing device which may be a gear changing mechanism, for example, with gears on the rear wheel hub, manually or automatically operated. A number of reduction ratios can be obtained, for example 6. The transmission ratio change is achieved by operating the gear changing mechanism. However, with each gear change, there is a break in torque.

[0010] When the gear change is user-controlled, this torque break is considered acceptable. When this gear change is controlled automatically following the measurement of several parameters, this unexpected torque break is very negatively perceived by the user, who may even think of a malfunction in the powertrain.

[0011] In order to make gear changes more comfortable, document US10773771 proposes reducing the torque on the crown, but no details are given on the means to be implemented to achieve this result.

[0012] There are powertrains such as the one described in US2017 / 0183056, which includes a pedal axle, a planetary gearbox, a traction motor connected to the planet carrier that forms the input of the gearbox, and a second variable-speed motor connected to the sun gear that forms the transmission element of the gearbox. The output of the gearbox, formed by the crown wheel, is connected to the chainring. This powertrain is relatively complex to produce.

[0013] STATEMENT OF THE INVENTION

[0014] It is therefore an aim of the present application to offer a powertrain for an electrically assisted bicycle in which the inconveniences linked to torque breaks during gear changes are reduced, or even eliminated, and presents a simplified design.

[0015] The aim stated above is achieved by a powertrain for an electrically assisted bicycle incorporating a continuously variable transmission. For this purpose, the group comprises a first electric motor configured to provide assistance, an epicyclic reduction gear interposed between the output of the first motor and the crankset, a second electric motor configured to act on the epicyclic reduction gear so as to modify its reduction ratio. In addition, the crankset shaft and the shaft carrying the chainring are separate, which simplifies the production of the powertrain, in particular by reducing the number of hollow shafts required.

[0016] In addition, this design allows for a reduction in the width of the powertrain. Finally, it is easier to cover the tray with a casing to protect the user and improve the aesthetics of the actuator or powertrain.

[0017] Thanks to the invention, it is possible to continuously vary the reduction ratio automatically, torque disruptions are then reduced, or even eliminated, and user comfort is significantly improved.

[0018] In a preferred embodiment, the crankset pinion and the first motor drive the sun gear, the planet carrier is mechanically connected to the chainring, and the second motor interacts with the crown, which is mounted to rotate, so as to modify its speed and thus modify the reduction ratio of the epicyclic gear train.

[0019] The gear change is automatic, maintaining optimal operating conditions for the first motor. This optimizes power consumption and increases the motor's lifespan.

[0020] The invention also makes it possible to easily implement various functions, for example freewheeling without having to add additional mechanical elements, and without this preventing other functions such as reverse assistance.

[0021] Very advantageously, the second motor is an electric motor that does not generate resistive torque when driven mechanically, for example a magnetless motor, in order to improve user comfort when there is no assistance.

[0022] In one embodiment, an electromechanical brake is provided on the crown wheel to immobilize the crown wheel, for example, during very high torque phases, for example when starting on a slope. The brake then replaces the second motor and the power consumption can be reduced.

[0023] An object of the present application is then a powertrain for an electrically assisted bicycle comprising a crankshaft extending along a first longitudinal axis, a first electric motor, an epicyclic reduction gear, a second electric motor, a chainring, the epicyclic reduction gear and the chainring having a second longitudinal axis parallel to and distinct from the first longitudinal axis, in which the epicyclic reduction gear comprises an input element driven by the crankshaft, the first motor, and an output element driving the chainring and a toothed crown, in which the toothed crown is mounted to rotate about the second longitudinal axis of the epicyclic reduction gear and in which the second electric motor is mechanically connected to said crown to set it in rotation,the powertrain being intended to be controlled by a control unit which is configured to control the first electric motor and the second electric motor, the control unit controlling the rotational speed of the ring gear in order to modify the ratio of the epicyclic reduction gear and the transmission ratio of the powertrain.,

[0024] In a preferred example, the epicyclic reducer comprises a sun gear, the ring gear, satellites meshing the sun gear and the ring gear, a planet carrier carrying the satellites

[0025] The sun gear forms the input element of the gearbox and the planet carrier forms the output element of the gearbox, or the planet carrier forms the input of the gearbox and the sun gear forms the output of the gearbox. In other words, one of the sun gear and the planet carrier preferably forms the input of the gearbox, while the other of the sun gear and the planet carrier forms the output of the gearbox.

[0026] The plate is advantageously integral in rotation with the planet carrier. Alternatively, the plate is integral with the sun gear.

[0027] The crown may have teeth on its inner periphery meshing with the satellites and teeth on its outer periphery meshed by a pinion driven by the second motor.

[0028] Advantageously, the powertrain comprises immobilization means for immobilizing the toothed crown on command, said immobilization means advantageously comprising an electromechanical brake.

[0029] Very advantageously, the second motor is a magnetless motor. In an exemplary embodiment, the crankshaft carries a pinion which is connected to the input element of the epicyclic reducer by a gear train, and in which the first motor has on its output shaft a pinion meshing with a pinion secured to a shaft on which the input element of the epicyclic reducer is fixed.

[0030] Another subject of the present application is a powertrain system comprising a powertrain according to the invention and a powertrain control unit.

[0031] The control unit may be configured to rotate the ring gear in a first direction and in a second direction.

[0032] Very advantageously, the control unit is configured to provide a reverse assist function in which it controls the first motor to rotate at slow speed in a first direction of rotation and the second motor to rotate in a second direction of rotation opposite to the first direction of rotation, so that the planet carrier rotates in the second direction of rotation.

[0033] Another subject of the present application is an electrically assisted bicycle comprising a frame, two wheels, including a drive wheel carrying a sprocket, a powertrain system according to the invention, pedals mounted on the crankshaft, an electric battery powering the first electric motor and the second electric motor, a transmission element connecting the chainring and the sprocket of the drive wheel, at least one absolute position sensor of the first motor and at least one relative position sensor of the second motor, the control unit controlling the first motor and the second motor on the basis of the signals emitted by the sensors and the data deduced from these signals.

[0034] BRIEF DESCRIPTION OF THE FIGURES

[0035] The following description will be better understood with the help of the attached drawings, in which:

[0036] [Fig 1] is a schematic representation of an example of an electrically assisted bicycle comprising a powertrain according to the invention, [Fig 2] is a functional diagram of the powertrain according to a first embodiment,

[0037] [Fig 3] is a functional diagram of the powertrain according to a second embodiment.

[0038] DETAILED DESCRIPTION OF EMBODIMENTS

[0039] In the following description, the invention will be described more particularly in an application to a two-wheeled bicycle, but it will be understood that the present invention applies to any wheeled vehicle equipped with a pedal assembly and electric assistance, for example a three-wheeled bicycle, also called a cargo bicycle or carrier bicycle.

[0040] The X direction is the direction parallel to the crank axis and normal to the plane of the sheet in the representation of Figure 1 and the Y direction is orthogonal to the Y direction and extends from the front to the rear of the bicycle.

[0041] In Figure 1, we can see an electrically assisted bicycle V comprising a frame 2, a front wheel 4, a rear wheel 6, a crankset 8 provided with two pedals 10, a powertrain G1 arranged at the crankset 8. In addition, the bicycle comprises a chainring 12 for transmitting the driving force to the rear wheel motor sprocket 13 via a chain 15 or a belt.

[0042] Alternatively, the driving force is applied to the front wheel.

[0043] The pedal assembly comprises a shaft Al with an axis XI on the ends of which pedals 10 are fixed.

[0044] The plate 12 has an axis X2 parallel to the axis XI and distinct from XI.

[0045] The bicycle V also includes an electric battery B intended to power the powertrain in particular. In the example shown, the battery B is mounted on the frame, more specifically on the down tube 14. Alternatively, it can be mounted at the luggage rack.

[0046] The transmission of the motive force will be described below. The powertrain Gl, hereinafter referred to as the "group", comprises a reducer R, a first electric motor Ml intended to assist the user of the bicycle in generating the motive force, the first motor Ml can be referred to as the "traction motor" and a second motor M2 intended to modify the reduction ratio of the reducer R. The motor M2 can be referred to as the "variator motor".

[0047] The reducer R is interposed between the shaft Al of the crankset and the chainring 12.

[0048] The reducer R is a reducer or epicyclic gear train comprising a sun gear 16, satellites 18 meshing with the sun gear 16, a planet carrier 20 carrying the satellites 18 and a crown 22 meshed with the satellites.

[0049] In this example, the reducer R and the plate 12 are coaxial.

[0050] The shaft Al of the pedal set has a first pinion PI with axis XI and rotationally fixed to the shaft Al. Thus the rotation of the shaft caused by the action on the pedals sets the first pinion PI in rotation.

[0051] The first pinion PI is connected to the sun gear 16 of the reducer R.

[0052] The connection between the first pinion PI and the sun gear 16 comprises a second pinion P2 coaxial with the sun gear 16 and integral with the rotating one, a first idler pinion P3 which meshes with the pinion PI and a second idler pinion P4 which is coaxial and integral with the first idler pinion P3. The second idler pinion P4 meshes with the second pinion P2. Thus the sun gear 16 and the first pinion PI have the same direction of rotation.

[0053] The second pinion P2 and the sun gear 16 are carried by a shaft A2. A third pinion P5 is coaxial with the second pinion P2 and the sun gear 16 and is rotationally integral with them. In the example shown, the third pinion P5 is arranged between the second pinion P2 and the sun gear 16. Alternatively, the second pinion P2 is arranged between the sun gear 16 and the third pinion P5.

[0054] The traction motor M1 has an output shaft with a pinion P6 which meshes with the third pinion P5. The third pinion P5 is designated motor pinion P5.

[0055] The second motor M2 comprises an output shaft carrying a pinion P7 meshing with teeth formed on the outer periphery of the crown. Alternatively, the pinion P7 meshes with the inner teeth of the crown, making it possible to avoid producing outer teeth on the crown. The motor M2 is intended to rotate the crown 22 on command. In this example, the crown 22 has teeth on its inner periphery which mesh with the satellites and teeth on its outer periphery which mesh with the pinion of the second motor M2.

[0056] The P12 plate, coaxial and integral in rotation with the planet carrier 20, forms the output of the group. The plate 12 transmits the movement to the motor pinion of the rear wheel by a chain. Alternatively, a toothed belt is used.

[0057] The crown 22 is advantageously mounted to be able to rotate on the shaft A2 by means of a bearing. For example, the crown is fixedly mounted on a hollow shaft A3 which receives the shaft A2 carrying the sun gear 16.

[0058] The first Ml motor is for example a brushless motor with a power of for example between 100 W and 1000 W.

[0059] In the example shown, the epicyclic reducer is of type I, however a powertrain using an epicyclic reducer of type II, III or IV does not depart from the scope of the present invention.

[0060] Advantageously, mechanical or electromechanical immobilization means are provided to immobilize the crown 22 in rotation relative to the bicycle frame. For example, these means comprise an electromechanical brake F which is applied and immobilizes the crown in the absence of electrical power and is released, and leaves the crown 22 free to rotate, when the brake is supplied with electricity. Advantageously, the brake is installed in the motor M2, it then benefits from the reduction ratio, which reduces the braking torque to be provided. The brake comprises, for example, jaws which are clamped on the crown by means of a spring-type return system. The jaws are separated under the action of an electromagnet.

[0061] Alternatively, it is the second motor M2 which ensures this immobilization function, by braking the rotor of the motor M2, an electrical consumption is then to be expected to ensure this immobilization.

[0062] The powertrain G1 also includes a control unit UC intended to control the first motor M1 and the second motor M2 according to information provided by different sensors. For this purpose, the shaft of the motor M1 is equipped with an absolute position sensor which makes it possible to synchronize the commands of the power switches in order to magnetize the phases of the motor in an adequate sequence. M2 has its own relative position sensor or a speed-controlled sensor, in order to carry out speed control. The power consumption of M2 makes it possible to estimate the torque applied to the pedals by the cyclist. This information on the torque applied by the cyclist contributes to the management of the electric assistance. In addition, the estimation based on the consumption of the motor M2 makes it possible to avoid using a specific complex and expensive torque sensor.

[0063] By rotating the crown 22, its speed relative to the satellites is modified. By controlling the rotation speed of the crown 22, the output speed of the reducer which is mechanically connected to the pedal assembly is controlled.

[0064] Since the speed of the crown 22 can vary continuously between a low value and a high value, the output speed of the reducer varies continuously.

[0065] The crown speed control is controlled by the control unit UC based on information provided by the various sensors mentioned above. By rotating the crown in the direction of rotation of the first motor Ml, the reduction ratio is reduced; the higher the crown speed, the closer the reduction ratio is to 1. When the crown is stationary, the reduction ratio is that of the fixed crown epicyclic gear train.

[0066] The operation of group G1 will now be described.

[0067] The user presses the pedals, which sets the pinion PI in rotation; this rotation is detected. The control unit UC then sends a command signal to activate the traction motor M1, which sets the pinion P5 in rotation, which drives the sun gear. In the absence of rotation of the crown, the reduction ratio is that of the reduction gear R. The satellites and the planet carrier are rotated, driving with them the chainring 12, which drives the rear wheel via the chain or belt. The bicycle is set in motion. The assistance provided by the motor depends on the external measurements transmitted to the unit UC by the sensors mentioned above and by the power consumption of the second motor M2. In addition, the control unit sends a signal to the motor M2 to set the crown in rotation to modify the reduction ratio and thus assist pedaling despite the change in slope.Since the gear change is directly linked to the rotation speed of the crown, the gear change is continuous and therefore transparent to the user.

[0068] Since the crankset is separate from the chainring 12, the user can maintain the same pedaling cadence while varying the speed of the bike depending on the slope. The control unit controls the M2 motor and therefore the rotation speed of the crown as best as possible to vary the transmission ratio and adapt it to the terrain.

[0069] Since the pedal axle is not integral with the chainring 12, the pedaling frequency can be kept constant and the speed of the bicycle can vary, for example depending on the slope on which the bicycle is traveling.

[0070] In this embodiment in which the motor M1 drives the satellite carrier, the motor M2 can be of lower power because the torque to be applied by it is reduced.

[0071] In forward motion, the crown and the motor Ml rotate in a first direction of rotation. For very low speeds, the crown is rotated in a second direction of rotation opposite to the first direction of rotation.

[0072] In reverse, in assisted mode as will be described below, the crown turns in the second direction of rotation.

[0073] Thanks to the invention, a continuously variable transmission or continuously variable gearbox or CVT (Continuously Variable Transmission in English terminology) is produced. The bicycle no longer has a derailleur with sprockets or other gear changing system with a discrete ratio. There is then no longer any loss of torque when varying the transmission ratios. User comfort is significantly improved. The disadvantages linked to the derailleur are therefore eliminated, in particular the risks of derailment, its relative fragility and its maintenance. In addition, its mass is eliminated. Furthermore, the integrated continuously variable transmission, the reduction ratio of which is known by the speed of M2, allows the measurement of the bicycle's speed without the need to add a specific sensor on the wheels or another part of the bicycle.

[0074] The number of speeds available is infinite since it is a continuous variation resulting from a continuous variation of the rotation speed of the crown.

[0075] In addition, this automatic transmission change allows the first Ml engine to operate at its maximum efficiency, which optimizes power consumption and increases the life of the first Ml engine.

[0076] The second motor M2 has for example a power between 1W and 100W. Preferably, the second motor M2 is a motor which does not generate resistive torque or drag torque, when it is not powered, in particular in order to perform a freewheel function and allow use of the bicycle without assistance with reduced effort, as will be described below.

[0077] For example, the second motor is a magnetless motor, such as a switched reluctance motor or SRM.

[0078] As a non-limiting example, we will give value ranges for the different elements making up group G1:

[0079] - the reason for the reducer between the crankshaft and the planetary is included in 1 and 10.

[0080] - the ratio of the reducer between the traction motor Ml and planetary is between 1 and 10.

[0081] - the crown speed is between - 1000 rpm and + 1000 rpm.

[0082] - the ratio of the reducer R is between -2 and 2.

[0083] - chainring 12 has between 10 and 40 teeth.

[0084] - the rear wheel sprocket has between 10 and 60 teeth. - the wheel diameter is between 254 mm (10 inches) and 737 mm (29 inches).

[0085] In a particular example, we choose a group in which the ratio of the reducer between the crankshaft and the planetary is equal to 7, the ratio of the reducer between the traction motor Ml and the planetary is equal to 5.

[0086] The rotation speed imposed on the crown is equal to 700 rpm; using an epicyclic reducer whose sun gear, satellites and crown have respectively 15, 39, 94 teeth, the ratio of the epicyclic reducer is equal to 0.7404. Furthermore, the 12 plate has 20 teeth, the rear wheel pinion has 51 teeth and the wheels have a diameter of 700 mm.

[0087] When the user pedals at a cadence of 100 strokes per minute, the speed of the bicycle is Tl km / h.

[0088] The powertrain according to the invention has a large number of advantages.

[0089] Thanks to the separation between the pedaling axis, i.e. the axis of application of the input torque by the user, and the propulsion axis, i.e. the output axis of the torque generated by the group and applied to the drive wheel, the transverse size can be reduced, and allow the integration of the group in an environment 90 mm wide between the pedals, as desired by manufacturers of electrically assisted bicycles.

[0090] The drivetrain has a larger footprint in the Y direction, which runs from the front to the rear of the bike, however this footprint is less of a problem than the footprint in the X direction.

[0091] Furthermore, the production of the powertrain is simplified, since a single hollow shaft can be implemented, for example the one on which the crown 22 is fixed and which receives the shaft A2.

[0092] Furthermore, the integration of the tray into a CA housing cover (figure 1) is easier due to the reduced transverse size.

[0093] The groupset is also easily adaptable to any type of electronically assisted bicycle by changing the control unit settings, for example it is easily adaptable to different wheel diameters. This modification is easily done by factory programming. It can even be considered to modify the parameters during the life of the bicycle, if the user wishes to change the wheel diameter or another characteristic taken into account for the determination of the transmission. This new setting is carried out by a software update.

[0094] Electrically assisted bicycles are required to incorporate a freewheel function that decouples the traction motor and the drive wheel if no assistance is required, for example when the bicycle speed is higher than the maximum assistance speed. In prior art electrically assisted bicycles, such a function is generally achieved by additional mechanical means. For example, in the bicycle described in document US10772771, locking means between the rotor of the traction motor and the planetary gear are implemented.

[0095] The powertrain according to the invention directly integrates this function. This freewheel function is obtained by allowing the crown 22 to rotate freely, which disconnects the traction motor from the drive wheel, the reduction gear no longer providing a reduction function. This freewheel function can be advantageously obtained by implementing a reduction motor M2 which generates little or no resistive torque when it is driven by an external force, i.e. when the crankset drives the planet carrier and the satellites alone, via the sun gear. This freewheel function ensures great pedaling comfort for the user, particularly when the battery is discharged.

[0096] Alternatively, if the second motor generates a resistive torque, the control unit actuates the second motor to rotate the crown in order to compensate for the resistive torque and generate smooth pedaling feedback to the user without assistance. This operating mode nevertheless consumes energy; it can be implemented with a low state of charge of the battery, if suitable management of the battery state of charge is implemented.

[0097] The powertrain according to the invention can be controlled by the control unit to integrate an anti-theft function. For example, when an attempted theft is detected, the first motor M1 is deactivated and the second motor M2 is rotated so that the transmission ensures that an action on the pedals by the thief generates a very slow speed of the bicycle and renders the bicycle unusable. For example, for a two-wheeled bicycle, the speed is slow enough to prevent balance, and therefore to prevent use of the bicycle.

[0098] If the battery is almost discharged, the battery management is advantageously such that enough power is available to activate the M2 motor.

[0099] The powertrain according to the invention also makes it possible to provide the reversing assistance function.

[0100] Either the traction motor is commanded to rotate in the second direction of rotation.

[0101] Either the first motor M1 is activated to rotate in the first direction of rotation but at slow speed, and the second motor M2 is activated to rotate in the second direction of rotation. The direction of rotation of the planet carrier can then be reversed and thus generate a reverse gear. This operating mode allows the freewheel to be maintained on the axis A2.

[0102] The reverse assist function is particularly interesting for cargo bikes. State-of-the-art e-bikes generally incorporate a mechanical freewheel that disconnects the traction motor from the drive wheel when reversing. Reverse assistance is then not available.

[0103] As explained above, the powertrain according to the invention may comprise means for immobilizing the crown in rotation. These means are particularly advantageous when operating at high torque and low speed. Thanks to the immobilization means, it is not the second motor which ensures this immobilization. These immobilization means, in the case of an electromechanical brake, can consume electrical energy but relatively little compared to what the second motor would consume to ensure the same immobilization. Preferably, the brake is applied in the absence of electrical power supply so it does not consume electrical energy to immobilize the crown, for example under the action of a spring-type return system.

[0104] This is all the more advantageous since the rotation lock of the crown 22 also allows the bicycle to be used without assistance in the event of the battery being completely discharged, the brake is then applied by default without energy with the spring return system.

[0105] In one operating variant, the control unit controls the variable speed motor so as to rotate the ring gear in the opposite direction in order to increase the ratio of the reduction gear, thereby relieving the traction motor.

[0106] The powertrain according to the invention can also be adapted to perform regenerative braking, since the freewheel function is obtained on command. The control unit is configured to control the crown wheel and the first motor so that it operates as a generator.

[0107] In addition, the powertrain according to the invention makes it possible to know the speed of the bicycle from the speed of the crown which is set by the control unit. This speed can be displayed on a screen to inform the user and / or allows the speed of the bicycle to be limited. Indeed, the maximum speed of an electrically assisted bicycle varies according to local speed legislation. For example, in the European Union, the maximum authorized speed is 25 km / h and in the USA it is 33 km / h. The invention makes it easy to adapt the group to local legislation.

[0108] Furthermore, the pedaling cadence is known by the motor speed Ml and the crown speed.

[0109] The pedal torque can also be deduced by measuring the supply current of the M2 variable speed motor, which eliminates the need for a high-cost torque sensor.

[0110] It can be arranged to define discrete pseudo gears and program the gearbox so that the user can manually shift gears.

[0111] When the battery is no longer sufficiently charged to power the M1 motor and provide pedal assistance, battery management is optimized to maintain a very low power supply to the M2 motor, ensuring an acceptable transmission ratio for the user and allowing them to reach their destination relatively easily.

[0112] In Figure 3, another embodiment G2 of a powertrain according to the invention can be seen. The same references as those used for group G1 to designate the elements having the same function.

[0113] Group G2 differs from group G1 in that the reducer R' has the planet carrier 20' as its input element and the sun gear 16' as its output element. The pinion P2 and the planet carrier 20' are carried by a shaft A2' with axis X2.

[0114] The crown is also fixed on a hollow shaft which is mounted around an A4 shaft carrying the 16' planetary and the 12 plate, with axis X2. Its manufacture is also simplified.

[0115] The crankshaft therefore attacks the planet carrier and the 12th chainring is rotationally fixed to the planetary.

[0116] The G2 powertrain is satisfactory, however moving the crown requires applying a greater torque than in the Gl group. A more powerful M2 variator motor is then implemented, which increases the mass of the group and its size.

[0117] The powertrain according to the invention offers great pedaling comfort for the user while being relatively simple and robust to produce. In addition, the fact of implementing two separate axles for the crankset and for the chainring makes it possible to limit the width of the powertrain and to integrate it more easily between the pedals.

Claims

DEMANDS 1. Powertrain for an electrically assisted bicycle comprising: a bottom bracket shaft (Al) extending along a first longitudinal axis (XI), a first electric motor (M1), an epicyclic gearbox (R, R'), a second electric motor (M2), a chainring (12), the epicyclic gearbox (R, R') and the chainring (12) having a second longitudinal axis (X2) parallel to and distinct from the first longitudinal axis (XI), wherein the epicyclic gearbox (R, R') comprises: an input element driven by the bottom bracket shaft (Al) and the first motor (M1), an output element driving the chainring (12), and a ring gear (22), wherein the ring gear (22) is mounted to rotate freely about the second longitudinal axis (X2) of the epicyclic gearbox (R, R'), and wherein the second electric motor (M2) is mechanically connected to said ring gear (22) for the rotatethe powertrain being intended to be controlled by a control unit (CU) which is configured to control the first electric motor (M1) and the second electric motor (M2), the control unit (CU) controlling the rotational speed of the ring gear (22) in order to modify the ratio of the epicyclic reducer (R, R') and the transmission ratio of the powertrain.

2. Powertrain according to claim 1, in which the epicyclic reducer (R) comprises: a planet gear (16), the toothed ring (22), planet gears (18) meshing the planet gear (16) and the toothed ring (22), a planet carrier (20) carrying the planet gears (18), the planetary gear (16) forming the input element of the reducer and the planet carrier (20) forming the output element of the reducer, or the input element being formed by the planet carrier (20') and the output element being formed by the planetary gear (16').

3. Powertrain according to claim 2, in which the plate (12) is rotationally fixed to the satellite carrier (20), or in which the plate (12) is rotationally fixed to the planetary gear (16').

4. Powertrain according to claim 1, 2 or 3, wherein the ring (22) comprises: teeth on its inner periphery engaging the satellites (18) and teeth on its outer periphery engaged by a pinion driven by the second motor (M2).

5. Powertrain according to any one of claims 1 to 4, comprising immobilizing means for immobilizing the toothed ring (22) on command, said immobilizing means advantageously comprising an electromechanical brake (F).

6. Powertrain according to any one of the preceding claims, wherein the second motor (M2) is a magnet-free motor.

7. Powertrain according to any one of the preceding claims, wherein the crankshaft carries a pinion (PI) which is connected to the input element of the epicyclic reducer by a gear train, and wherein the first motor (M1) has on its output shaft a pinion (P6) meshing with a pinion (P5) fixed to a shaft (A2) on which is fixed the input element of the epicyclic reducer (R, R').

8. Powertrain system comprising a powertrain according to one of the preceding claims and a powertrain control unit (CU).

9. Powertrain system according to claim 8, wherein the control unit (CU) is configured to rotate the toothed ring (22) in a first direction and in a second direction.

10. Powertrain system according to claim 8 or claim 9, wherein the control unit is configured to provide a reverse assist function in which it commands the first motor (M1) to rotate at slow speed in a first direction of rotation and the second motor (M2) to rotate in a second direction of rotation opposite to the first direction of rotation, so that the satellite carrier rotates in the second direction of rotation.

11. Electric assisted bicycle comprising: a frame, two wheels, one of which is a drive wheel carrying a sprocket, a drive system according to claim 8, 9 or 10, pedals mounted on the bottom bracket shaft, an electric battery (B) supplying the first electric motor (M1) and the second electric motor (M2), a transmission element connecting the chainring and the sprocket of the drive wheel, at least one absolute position sensor of the first motor (M1) and at least one relative position sensor of the second motor (M2), the control unit controlling the first motor (M1) and the second motor (M2) on the basis of the signals emitted by the sensors and the data deduced from these signals.

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