Differential transmission method and transmission system for electrically assisted bicycle

Abstract

The present invention relates to an auxiliary differential transmission method for an electric bicycle and a transmission system associated with the method, comprising two motors articulated around a differential system comprising a ring gear having an inner surface and an element cooperating with the inner surface, the periphery of the element always contains the geometric center of the ring gear.

Description

Technical Field

[0001] The invention relates to a novel auxiliary transmission system for a bicycle. Background Art

[0002] The development of electric mobility has promoted the multiplication of electric assistance systems for bicycles. Most systems operate on the principle of simple torque assistance provided by a motor at the crankset level. The motor provides the power. The speed is transmitted to the rear wheel via a chain or belt. The gear ratio is managed by the rider via a system of sprockets (derailleur gears) on the rear wheel or a gearbox integrated into the rear hub of the wheel.

[0003] A differential system has been described in which an epicycloidal gear train ensures torque assistance and gear ratio management in the same box. Several improvements have equally been described, firstly enabling the bicycle to be used even when the battery is flat, and secondly adapting the speed and / or torque assistance to the force applied by the rider, primarily in order to facilitate the management of the reliefs and prevent the transmission from slipping.

[0004] Such a system is described, for example, in the following documents:

[0005] WO2016 / 034574, WO2019158503A1, WO2019043123 and WO 2021032548. In these systems, an epicycloidal gear train comprising a ring gear, a sun gear and a planet carrier (possibly a double planet carrier) is used in combination with a reduction stage to obtain the necessary reduction ratio. However, these systems lack compactness and the multiple parts lead to lower output, larger clearances, higher noise levels and higher costs. Therefore, the main challenge of electric assistance is to obtain a system that is at the same time very compact, lightweight and durable over time.

[0006] Different approaches have been taken to address these challenges. For example, DE202017007569U1 describes a system comprising two motors, each associated with a harmonic drive having a different axis, one harmonic drive defining the auxiliary speed and the other harmonic drive associated with an outlet for adjusting the rhythm. The two harmonic drives have non-overlapping parallel axes and are coupled via an intermediate gear transmission or direct engagement on the outside of the harmonic drive. The consequence is a significant obstacle that complicates the startup and operation of the system. In particular, the volume of the tulip-type flexible wheels of the harmonic system (associated with the fatigue and losses they produce) has prevented those skilled in the art from using them in electric auxiliary transmission systems. Therefore, the applicant finds it necessary to address the shortcomings and weaknesses of the existing systems. Summary of the invention

[0007] The object of the present invention is a method for auxiliary differential transmission of an electric bicycle, the method comprising the following steps:

[0008] - applying an angular velocity ω1 to a first inlet of the differential system by the action of a first motor;

[0009] - applying an angular velocity ω2 to a second inlet of the differential system through an inlet body transmitting at least the action of the rider on the crankset;

[0010] - combining the angular velocities ω1 and ω2 in a differential system and transmitting them to the outlet body at an angular velocity ω3, the differential system comprising a toothed ring having an inner surface and an element cooperating with the inner surface, the periphery of the element always containing the geometric center of the toothed ring;

[0011] The second motor regulates the assistance to the rider, the second motor being connected to the second inlet through the inlet body in combination with the rider's action, or to the outlet,

[0012] The axis of the outlet body, the main axis of the differential system, the axis of the first motor and the axis of the second motor are coincident and / or concentric with the axis of the inlet body.

[0013] The angular velocities ω1 and ω2 are combined in the differential system to the outlet body, which means that the angular velocities ω1 and ω2 are combined in the differential system to give an angular velocity ω3 at the differential outlet, and then the angular velocity ω3 is transmitted to the outlet body.

[0014] The invention also relates to a transmission system which makes it possible to carry out the method according to the invention.

[0015] The transmission system for an electric bicycle comprises:

[0016] a differential system comprising a toothed ring having an inner surface and an element cooperating with the inner surface, the periphery of the element defining a surface containing the geometric center of the toothed ring,

[0017] a first motor arranged to impart an angular velocity to a first inlet of the differential system,

[0018] an inlet body arranged to impart an angular velocity to the second inlet of the differential system,

[0019] - export body, and

[0020] a second motor, which regulates the assistance to the rider, the second motor being connected to a second inlet associated with the inlet body, or to the outlet,

[0021] Therein, the axis of the outlet body, the main axis of the differential system, the axis of the first motor and the axis of the second motor coincide with and / or are concentric with the axis of the inlet body.

[0022] The inlet body is an element known to the person skilled in the art. The inlet body constitutes the interface between the inside and the outside of the clamp or the box containing the transmission. The inlet body can be the interface with the upstream transmission. Alternatively, the inlet body can be directly connected or coincident with the crankset.

[0023] The outlet body is an element known to the person skilled in the art. The outlet body constitutes the interface between the inside and the outside of the clamp or the box containing the transmission system. The outlet body can be the interface with the downstream transmission. Alternatively, the outlet body can be directly connected or coincident with one of the rims.

[0024] Preferably, the inlet body is directly or indirectly (via the derailleur) associated with at least the action of the rider on the crankset (ie with the axis of the crankset).

[0025] In certain cases, the inlet body may coincide with the crankset. The transmission is then located at the crankset level, ie concentric with the crankset axis, and the transmission is arranged at the outlet body level.

[0026] In other cases, the transmission system may include an upstream transmission of the chain or belt type, for example an upstream transmission connecting the crankset to the inlet body of the transmission system (connected to the differential system). In this case, the transmission system is not concentric with the crankset. It may be concentric with the axis of the drive wheel, and in this case no downstream transmission is provided on the outlet body. Likewise it may be positioned neither concentrically with the crankset axis nor with the wheel axis; in this case, an upstream transmission and a downstream transmission may be provided.

[0027] In the remainder of the application, the expression "connected to" vaguely refers to a direct or indirect connection (via a transmission).

[0028] For maximum compactness, the axis of the outlet body, the main axis of the differential system, the axis of the first motor and the axis of the second motor are coincident and / or concentric with the axis of the inlet body.

[0029] By aligning / merging these axes, an extremely compact system is obtained. Heat dissipation is best managed when the two motors are arranged on opposite sides of the differential system.

[0030] Here, a differential system is a system having a ring gear with an inner surface. The element cooperating with this inner surface contains the geometric center of the ring gear, that is, the element has a periphery that evolves inside the ring gear, the periphery is in contact with the ring gear at at least one point, and the geometric center of the ring gear is always included in the surface defined by the periphery. This definition extends in the context of a cutout perpendicular to the main axis of the differential. Therefore, the differential system cannot be an epicycloidal gear train, the planetary gears of such a train do not actually meet this definition. However, there are several other types of differential systems that meet this condition, such as harmonic systems or cycloidal systems (simple or complex), which may include intermediate transmission wheels, such as those described in US4969376A, which are also reproduced in WO2023 / 042167A1.

[0031] The toothed ring has an inner surface which can, for example, carry an internal toothing, and the element cooperating with this inner surface is therefore an element arranged to engage in this toothing. In this case, the element presents a peripheral toothing which is apt to engage in these toothings of the toothed ring, and the geometric center of the toothed ring is always included in the surface defined within the toothed ring by the engagement circle of this element (the periphery or periphery of these toothings).

[0032] The term toothing is not limiting in a precise manner but generally refers to a relief that can engage in a complementary relief. A person skilled in the art knows how to choose the shape of the toothing depending on the application, the dimensions, the forces implied, etc.

[0033] The invention is not always limited to toothed engagement. The toothed ring can also cooperate with the inner element by adhesion. The invention therefore covers rolling systems based on adhesion which are also noteworthy.

[0034] For the remainder of this description, we will use the engagement alternative for clarity, but the engagement alternative is interchangeable with the rolling system.

[0035] Typically, the differential system uses an R reduction ratio established according to the following equation:

[0036]

[0037] where ωα, ωβ and ωγ are the angular velocities of the connecting parts of the differential.

[0038] The differential has two so-called "slow" connections and a so-called "fast" connection. Preferably, the first motor is associated with the fast connection in order to effectively influence the speed of the outlet body.

[0039] The reduction ratio RDU of the transmission system is defined as:

[0040]

[0041] Where ωO is the angular velocity of the outlet body and ωI is the angular velocity of the inlet body.

[0042] The RDU reduction ratio is modulated naturally, continuously or artificially, discretely by the first motor. The second motor is dedicated to regulating torque assistance.

[0043] In some cases, the drivetrain imparts motion to at least one of the two wheels of the bicycle even when the rider is not pedaling. If this mode is limited to low speeds, this is clearly a "walk assist" mode.

[0044] In some cases, the transmission system can be operated in a non-assisted mode. For example, this mode can be automatically adopted when the rider applies enough or too much force, especially relative to the legal constraints (above a threshold speed). This mode is also useful for bicycle operation when the battery is almost empty. In this mode, motor M1 and motor M2 can be controlled; only the constraint of zero net assistance is observed.

[0045] In some cases, ωO can be negative. This is the reverse mode.

[0046] In some cases, the velocity ωI of the inlet body or the ωO of the outlet body is zero. This is especially the case for the anti-theft mode.

[0047] In some cases, the first motor and / or the second motor acts as a generator. If the cumulative power of the two motors is negative, this is the case of a "regenerative braking" mode.

[0048] Furthermore, the transmission system may comprise a reducer system arranged to combine the action of the second motor with the action of the outlet or to combine the action of the second motor with the action of the inlet body. Preferably, the axis of the reducer associated with the second motor may coincide with the inlet axis and the outlet axis.

[0049] The transmission system of the present invention is compact enough to be installed at crankset level or wheel level.

[0050] Preferably, in order to optimize the heat dissipation of the motors while maintaining balance, the first motor and the second motor are placed on opposite sides of the element of the bicycle to which the transmission system is fixed. For example, the motors are placed on opposite sides of the wheel or on opposite sides of the crankset.

[0051] The differential system may be a cycloidal transmission system (or a gear train).

[0052] This type of system enables high reduction ratios to be achieved with particularly compact dimensions. In this case, the element engaged in the ring gear is a toothed wheel having a smaller diameter than the inner diameter of the ring gear and having a smaller number of teeth than the number of teeth of the ring gear. The eccentric motion is imparted by an eccentric exciter on which the toothed wheel is mounted. Due to its engagement in the ring gear and the eccentric exciter, the toothed wheel follows a cycloidal motion. The wheel is associated with one or more transmission eccentrics, which are associated with an eccentric carrier.

[0053] The ring gear, the eccentric exciter and the eccentric wheel carrier can each be operated as an inlet or outlet of the system. The eccentric exciter is a so-called "fast" connection, while the ring gear and the eccentric wheel carrier are so-called slow connections.

[0054] In a cycloid transmission, one or more cycloid wheels are engaged inside a cycloid ring gear, and the number of teeth Zc of the cycloid ring gear is slightly greater than the number of teeth Zr of these cycloid wheels. o :Zr<Zc.

[0055] For the sake of clarity and without loss of generality, let us assume for the purpose of explanation that the transmission has only one cycloidal wheel.

[0056] The eccentric exciter forms the first connecting part of the transmission. Its main axis is concentric with the ring gear. The slightly eccentric secondary axis is concentric with the cycloid wheel.

[0057] Let us consider, without loss of generality, that the toothed ring is also immobile here and is used only for explanation. The rotation of the eccentric exciter forces the wheel to roll inside the toothed ring while being engaged to it. For one rotation of the eccentric exciter, the insubstantial engagement point between the deformable wheel and the toothed ring has completed one rotation. At the end of the displacement, the wheel has turned by an angle corresponding to the difference in the number of teeth between the toothed ring and the wheel. It is therefore possible to choose a difference of only one tooth and thus obtain a very small angular displacement of the wheel.

[0058] We note that the displacement of the wheel is not a purely circular motion, but a cycloidal one.

[0059] The cycloid transmission system comprises at least one transmitting eccentric, preferably for greater robustness at least two transmitting eccentrics, arranged to transmit the cycloid movement of the wheel to the eccentric carrier, wherein the axis of rotation coincides with the axis of rotation of the ring gear.

[0060] In order to be able to transfer small displacements towards a pure circular movement as required, it is necessary to utilize a transmission eccentric which ensures the connection between the wheel and the eccentric carrier.

[0061] The eccentric carrier moves concentrically with respect to the main transmission axis in a pure circular motion. The transmission eccentric has a primary axis concentric with the axis fixed to the eccentric carrier and a secondary axis concentric with the axis fixed to the wheel, respectively. To ensure the operation of the system, the eccentricity of the eccentric exciter is identical to the eccentricity of the transmission eccentric. Although technically a single transmission eccentric is sufficient, two or even more significant numbers can be used to improve the robustness of the system.

[0062] Due to the use of the transmission eccentric, the eccentric carrier forming the second connecting element of the transmission is already concentrically turned to the main axis of the system at a weak angle corresponding to the difference in the number of teeth between the ring gear and the wheel, so that the transmission ratio is:

[0063]

[0064] ωp is the angular velocity of the eccentric wheel carrier [rad / s], and ωe is the angular velocity of the eccentric excitation element [rad / s].

[0065] The use of a transmission eccentric is one method of returning circular motion, but not the only method. This is not to be considered limiting.

[0066] In general, when the ring gear is not fixed but constitutes the third connection point of the system, the transmission is transformed into a differential system, where the kinematic equations can be summarized as:

[0067]

[0068] ωc is the angular velocity of the ring gear (rad / s).

[0069] In general, the eccentric exciter, the ring gear and the eccentric carrier are the three connections of the differential and can each operate as an inlet or outlet of the system. The eccentric exciter is the so-called "fast" connection, while the ring gear and the eccentric carrier are the so-called "slow" connections.

[0070] In one embodiment, the first motor is connected to the eccentric exciter and ω1=ωe, and the inlet body is connected to the ring gear and ω2=ωc, the outlet is via the eccentric wheel carrier and ω3=ωp. The second motor can be connected to the ring gear in combination with the inlet body, potentially via a reducer, or connected to the outlet body at the outlet, and the outlet body is connected to the eccentric wheel carrier.

[0071] In another embodiment, the inlet body is connected to the eccentric exciter and ω2=ωe, and the first motor is connected to the ring gear and ω1=ωc, the outlet is via the eccentric wheel carrier and ω3=ωp. The second motor can be connected to the eccentric exciter in combination with the inlet body, potentially via a reducer, or connected to the outlet body at the outlet, the outlet body being connected to the eccentric wheel carrier.

[0072] In another embodiment, the first motor is connected to the eccentric exciter and ω1=ωe, and the inlet body is connected to the eccentric carrier and ω2=ωp, the outlet is via the ring gear and ω3=ωc. The second motor can be connected to the eccentric carrier in combination with the inlet body, potentially via a reducer, or connected to the ring gear at the outlet.

[0073] In another embodiment, the inlet body is connected to the eccentric exciter and ω2=ωe, and the first motor is connected to the eccentric wheel carrier and ω1=ωp, the outlet is via the ring gear and ω3=ωc. The second motor can be connected to the eccentric exciter in combination with the inlet body, potentially via a reducer, or connected to the ring gear at the outlet.

[0074] In another embodiment, the first motor is connected to the eccentric wheel carrier and ω1=ωp, and the inlet body is connected to the ring gear and ω2=ωc, the outlet is via the eccentric excitation member and ω3=ωe. The second motor can be connected to the ring gear in combination with the inlet body, potentially via a reducer, or connected to the eccentric excitation member at the outlet.

[0075] In another embodiment, the first motor is connected to the ring gear and ω1=ωc, and the inlet body is connected to the eccentric wheel carrier and ω2=ωp, the outlet is via the eccentric excitation member and ω3=ωe. The second motor can be connected to the eccentric wheel carrier in combination with the inlet body, potentially via a reducer, or connected to the eccentric excitation member at the outlet.

[0076] The advantage of a cycloidal transmission is that it provides the possibility of a major reduction ratio for reducing size and complexity.

[0077] Preferably, the cycloidal transmission of the invention comprises at least two wheels. In practice, in the case of cycloidal transmissions with a transmission eccentric comprising a single cycloidal wheel, the main drawback is that the movement of the cycloidal wheel causes a rather important imbalance. The most common solution to the problem is to stack several identical transmission units, but with phasing. Then, the excitation and transmission eccentrics can be combined separately. It is likewise possible to use a single ring gear and a single eccentric carrier.

[0078] In a variant of the system described, the ring gear can be replaced by a set of Zc cylindrical shafts arranged in parallel and in a regular manner in the periphery of the shaft carrier.

[0079] In another variant, these transmission eccentrics are not implemented so that the shaft of the eccentric carrier rubs directly in the bore in the wheel.With the desired geometry, this configuration provides the same kinematics as a system with transmission eccentrics.

[0080] The latter two variations are known in the art.

[0081] Cycloid drive system variant: double cycloid engagement system.

[0082] In a second implementation of the cycloid transmission technology, two engagements or gear meshings can be utilized, possibly concentric. As in the above-described cycloid transmission system, the eccentric exciter constituting the first connection of the differential system supports a wheel that rotates freely along the eccentric axis on its eccentric axis. Each type of joint with at least one rotational degree of freedom can be used. However, joints with weak friction will be given priority. This wheel engages in the outer ring gear (internal gear) by virtue of its shape (preferably external gear) and through the kinematics imposed on it by the eccentric exciter. This constitutes the first engagement. In addition, the wheel is also equipped with an internal gear, which is axially juxtaposed near its connection with the eccentric exciter. In addition, the sprocket constituting the second connection of the cycloid system is rotatably articulated on the main axis of the cycloid module. The sprocket is equipped with an external gear compatible with the internal gear of the wheel so that it engages with the second engagement.

[0083] Thus, this "intermediate" wheel is a cylinder which presents on its outer surface means of adhesion (engagement) with the inner surface of the toothed ring in which it moves, and on its inner surface means of adhesion (engagement) with the sprocket around which it moves. Thus, the toothed wheel presents an inner surface, likewise toothed, arranged to engage with a sprocket rotatably articulated about an axis coinciding with the axis of the toothed ring.

[0084] The ring gear, which is rotatably movable along the main axis of the cycloid module, constitutes the third and final connection to the differential system.

[0085] The cycloidal motion of the intermediate wheel and its engagement with the sprocket imposes a simple rotation on the sprocket if certain geometrical conditions are observed.

[0086] To ensure operation of the system, the eccentricities of the two cycloid joints must be equal (unless compliance is introduced into the system).

[0087] The number of teeth of the ring gear (Zc), wheels (external Zre and internal Zri), and sprocket Zp satisfy the following ratios:

[0088] Zc>Zre

[0089] Zr>Zp

[0090] The R ratio of the system is therefore defined as:

[0091]

[0092] The special case is given by Zre=Zri=Zc-1=Zp+1, which simplifies the equation to:

[0093]

[0094] The combination of two cycloid joints advantageously makes it possible to eliminate the conversion of cycloid motion into circular motion by using a transmission eccentric. There are therefore fewer mechanical joints, thereby reducing cost, weight, volume, complexity and play. There are few moving parts, thereby reducing the inertia of the transmission. Furthermore, the mass moved eccentrically is reduced, thereby reducing parasitic vibrations. The solution is therefore more advantageous.

[0095] In general, the exciter eccentric, the ring gear and the sprocket are the three connections of the differential and can each operate as an inlet or outlet of the system. The eccentric exciter is the so-called "fast" connection, while the ring gear and sprocket are the so-called "slow" connections.

[0096] The differential system may be a harmonic drive system.

[0097] In a harmonic transmission, the element that engages with the tooth profile of the ring gear is a deformable toothed wheel. The number of teeth Zc of the ring gear is slightly greater than the number of teeth Zr of the deformable wheel. o :Zr<Zc.

[0098] The wave generator is directed to rotate around the main axis of the gear train. It has a certain number of lobes Zl, in the most common case two, but a configuration based on 1 lobe is foreseeable. However, the number of lobes must be significantly lower than the number of teeth of the ring gear and the number of teeth of the deformable wheel: Zl<<Zr<Zc.

[0099] Let us consider, without loss of generality, that the ring gear is immobile and is used only for explanation. The rotation of the wave generator forces the deformable wheel to roll inside the ring gear, while being engaged to each end of the wave lobe. For one rotation of the wave generator, the insubstantial engagement point between the deformable wheel and the ring gear has completed one rotation. At the end of this displacement, the deformable wheel has rotated concentrically with the main axis of the system by a small angle corresponding to the difference in the number of teeth between the ring gear and the deformable wheel, so that the transmission ratio is:

[0100]

[0101] ωr is the angular velocity of the flexible wheel [rad / s], and ωg is the angular velocity of the wave generator [rad / s].

[0102] In the case where the ring gear is not fixed but constitutes the third connection point of the system, the transmission is transformed into a differential system, in which the kinematic equations can be summarized as:

[0103]

[0104] ωc is the angular velocity of the ring gear [rad / s].

[0105] In general, the wave generator, ring gear and wheel are the three connections of the differential and can each operate as an inlet or outlet of the system. The wave generator is the so-called "fast" connection, while the ring gear and deformable wheel are the so-called "slow" connections.

[0106] In one embodiment, the first motor is connected to the wave generator and ω1=ωg, and the inlet body is connected to the ring gear and ω2=ωc, the outlet is via a flexible wheel and ω3=ωr. The second motor can be connected to the ring gear combined with the inlet body, or to the flexible wheel at the outlet, potentially via a reducer.

[0107] In this embodiment, if the second motor is connected to the ring gear in combination with the inlet body, this combination preferably does not take place via a harmonic transmission.

[0108] When the second motor is associated with or connected to the inlet body, a particular embodiment can potentially be excluded from the invention. In this case, the combination is achieved, for example, by means of a cycloidal or epicycloidal reducer.

[0109] In another embodiment, the inlet body is connected to the wave generator and ω2=ωg, and the first motor is connected to the ring gear and ω1=ωc, the outlet is via a flexible wheel and ω3=ωr. The second motor can be connected to the wave generator in combination with the inlet body, potentially via a speed reducer, or connected to a flexible wheel at the outlet.

[0110] In another embodiment, the first motor is connected to the wave generator and ω1=ωg, and the inlet body is connected to the flexible wheel and ω2=ωr, the outlet is via the ring gear ω3=ωc. The second motor can be connected to the flexible wheel in combination with the inlet body, potentially via a reducer, or connected to the ring gear at the outlet.

[0111] In this embodiment, preferably, if the second motor is connected to the outlet ring gear, this connection is not achieved via a harmonic transmission. When the second motor is associated with or connected to the outlet, the specific embodiment can potentially be excluded from the invention. In this case, the combination is achieved, for example, by means of a cycloidal or epicycloidal reducer.

[0112] In another embodiment, the inlet body is connected to the wave generator and ω2=ωg, and the first motor is connected to the flexible wheel and ω1=ωr, the outlet is via the ring gear and ω3=ωc. The second motor can be connected to the wave generator in combination with the inlet body, potentially via a speed reducer, or connected to the ring gear at the outlet.

[0113] In another embodiment, the first motor is connected to the flexible wheel and ω1=ωr, and the inlet body is connected to the ring gear and ω2=ωc, the outlet is via a wave generator and ω3=ωg. The second motor can be connected to the ring gear in combination with the inlet body, potentially via a speed reducer, or connected to a wave generator at the outlet.

[0114] In another embodiment, the first motor is connected to the ring gear and ω1=ωc, and the inlet body is connected to the flexible wheel and ω2=ωr, the outlet is via a wave generator and ω3=ωg. The second motor can be connected to the flexible wheel in combination with the inlet body, potentially via a speed reducer, or connected to a wave generator at the outlet.

[0115] An advantage of a harmonic transmission is that it provides the possibility of a major reduction ratio for reducing size and complexity compared to known epicycloidal gear trains.

[0116] In a harmonic transmission, the deformable wheel undergoes many significant deformation cycles. This can lead to the need for a long tulip and therefore to more general bulkiness or fatigue resistance issues. The contact between the wave generators of the deformable wheel can introduce a lot of friction. One solution to this problem is to use balls or rollers between the two bodies, as shown for example at https: / / commons.wikimedia.org / wiki / File:Harmonic-drive-explanation-contrast.gif.

[0117] Like the wheels of a cycloidal gear train, the deformable wheels of a harmonic transmission cover, within their tooth profile, a surface containing the geometrical centre of the ring gear.

[0118] The movement of the deformable wheel of the harmonic transmission is a rotational movement about the main axis of the gear train, superimposed by the deformation of the tulip and toothed parts at the level of the confinement zones imposed by the lobes of the wave generator.

[0119] Other equivalent transmission systems, especially variations of cycloid and harmonic systems, may equally be used within the scope of the present invention.

[0120] For example, it can be a transmission system similar to that described in WO 2023 / 042167A1, in which an intermediate transmission wheel (preferably flexible as in a harmonic transmission) is accommodated between a ring gear of a cycloid system driven by a cycloid motion and a toothed wheel. The transmission wheel has a toothing on its outer surface to engage with the ring gear and a toothing on its inner surface to engage with the toothed wheel. The number of gear teeth can be adjusted to increase the reduction ratio.

[0121] In a preferred embodiment, the differential system is a cycloidal gear train (or transmission).

[0122] A second inlet of the differential system receives torque from the rider through the inlet body via the crankset, the crankset including a crankset axis.

[0123] The first motor and the second motor are powered by batteries by means of suitable control electronics.

[0124] The first motor M1 may be speed controlled so as to control the transmission ratio of the motor reducer to a desired ratio.

[0125] The second motor M2 may be torque controlled to relieve rider effort depending on the selected assist level.

[0126] In a first variant of the invention, the second motor M2 regulates the rider's assistance to the entry of the differential system. The reducer is used to make the operating speed / torque of the rider and the electric motor compatible with the following equation:

[0127]

[0128] ωM2 is the angular velocity of the motor M2 [rad / s], ωI is the angular velocity of the inlet body [rad / s], and RRM2 is the ratio of the reducer associated with the motor M2.

[0129] The second motor regulating the rider's assistance is thus connected to the second inlet in combination with the rider's action. The combination is preferably achieved by means of a reducer, the rotation of the second motor of which is associated with the inlet, the inlet body being associated with the outlet, which has an angular velocity ω2. For example, it refers to an epicycloid, cycloid or harmonic reducer or any other suitable reducer.

[0130] Preferably, the second motor is not associated with the wave generators of the harmonic transmission, in order to couple with the rider's movements.

[0131] Preferably, the reducer at the outlet of the motor M2 is a cycloid gear train, in which an eccentric wheel carrier (or a sprocket following the type of cycloid gear train used) or a ring gear is fixed, so that the differential system is degraded to a simple reducer. However, any other reducer system can also be used.

[0132] In a preferred embodiment according to the first variant, the differential system is a cycloidal transmission and the first motor applies the angular velocity ω1 to the eccentric exciter, which is the first inlet, the second motor and the inlet body apply the angular velocity ω2 to the ring gear, which is then the second inlet. The outlet is therefore the eccentric wheel carrier that transmits the angular velocity ω3 to the outlet body.

[0133] In another preferred embodiment according to the first variant, the differential system is a cycloid transmission and the first motor applies the angular velocity ω1 to the eccentric exciter, which is the first inlet, and the second motor and the inlet body apply the angular velocity ω2 to the eccentric wheel carrier, which is the second inlet. The outlet is therefore a ring gear that transmits the angular velocity ω3 to the outlet body.

[0134] In a second variant of the invention, the second motor regulating the assistance to the rider is connected to the outlet of the differential transmission. A reduction gear system can be used to combine the action of the second motor and the action of the outlet.

[0135] The possible variants described for the method according to the invention also apply to the design of the drive system.

[0136] Regardless of these variants and embodiments, a non-return mechanism may also be provided, although optionally, such as, for example, one or more freewheels.

[0137] For example, a freewheel is associated with the inlet body, allowing the crankset to drive the system but preventing the system from driving the crankset. This function is essentially determined by the safety of the rider. Nevertheless, this freewheel is still optional.

[0138] A freewheel may for example connect the inlet body and the outlet equally (or alternatively). Thus, the speed of the outlet body cannot be lower than the speed of the inlet body: ωO ≥ ωI. The aim is to ensure the operability of the bicycle even in case of system failure (battery dead or, to a lesser extent, some other failure).

[0139] Other freewheel arrangements are also foreseeable. A person skilled in the art will know how to judiciously implement the necessary freewheel. BRIEF DESCRIPTION OF THE DRAWINGS

[0140] The invention will now be explained in more detail with the aid of the accompanying drawings, in which:

[0141] Figure 1 It is the overall scheme of the transmission between the transmission system of the present invention and the elements outside the group;

[0142] Figure 2 is a block diagram illustrating the method of the present invention, according to which a second motor is installed in the inlet of the differential;

[0143] Figure 3 yes Figure 2 A simplified version of the block diagram of ;

[0144] Figure 4 is a block diagram illustrating the method of the present invention, according to which a second motor is installed in the outlet of the differential;

[0145] Figure 5 yes Figure 4 A simplified version of the block diagram of ;

[0146] Figure 6 Shows the basis Figure 3 The transmission system architecture of the present invention operates on the principle of the present invention and actually uses a cycloid differential;

[0147] Figure 7 Shows the basis Figure 3 Another transmission system architecture of the present invention that operates on the principle of the present invention and actually uses a cycloid differential;

[0148] Figure 8 Shows the basis Figure 3 Another transmission system architecture of the present invention that operates on the principle of the present invention and actually uses a cycloid differential;

[0149] Fig. 9 Shows the basis Figure 3 Another transmission system architecture of the present invention that operates on the principle of the present invention and actually uses a cycloid differential;

[0150] Fig.10 Shows the basis Figure 3 The transmission system architecture of the present invention operates on the principle of the present invention and actually uses a cycloid differential;

[0151] Fig.11 Shows the basis Figure 3 Another transmission system architecture of the present invention that operates on the principle of the present invention and actually uses a double-engaging cycloidal differential;

[0152] Fig.12 Shows the basis Figure 3 Another transmission system architecture of the present invention that operates on the principle of the present invention and actually uses a double-engaging cycloidal differential;

[0153] Fig.13 Shows the basis Figure 3 Another transmission system architecture of the present invention that operates on the principle of the present invention and actually uses a double-engaging cycloid differential;

[0154] Fig.14 is a side view of a double-engaging cycloid differential system.

[0155] Fig.15 is along Fig.14 A cross-sectional view of a plane B of the device, and

[0156] Fig.16 is along Fig.14 Cross-sectional view of plane C of the device. DETAILED DESCRIPTION

[0157] These same elements are identified by the same reference numerals in different figures without being limited to the use of single components, that is, for example, the ring gear mentioned in one figure may have a different shape, size, material than the ring gear shown in another figure.

[0158] The variants of the different embodiments described below are not mutually exclusive, as long as they are technically compatible.

[0159] Figure 1 The transmission ratios between the DU transmission system according to the invention and the elements outside the group are generally shown. The elements shown in dashed lines are optional depending on the location of the transmission system on the bicycle.

[0160] The DU transmission comprises an inlet body I associated with a crankset P on which a rider C can act, and an outlet body O associated with a wheel W. The term "associated" means that a direct or indirect ratio can be provided, as the case may be, via a T transmission.

[0161] When the transmission system DU is located at the crankset P (ie concentric with the axis of the crankset), the outlet body O is advantageously coupled to a Tout transmission coupled to at least one wheel of the bicycle. These transmissions are, for example, chains or belts.

[0162] When the transmission DU is located at the wheel W (ie concentric with the wheel), the axis of the crankset is advantageously coupled to a Tin transmission upstream of the transmission DU. These transmissions are, for example, chains or belts.

[0163] If the transmission system is neither concentric with the W wheel nor at the W wheel, nor concentric with the axis of the crankset, it is possible to have the transmission with both an upstream Tin and a downstream Tout.

[0164] In a first variant of the invention, Figure 2 As shown, the second motor M2 assists the rider when entering the differential system.

[0165] about Figure 2 , a method for auxiliary differential transmission of an electric bicycle comprises the following steps:

[0166] - The angular velocity ω1 is applied to the first inlet of the differential system D by the action of the first motor M1 ; the RM1 reducer is optionally inserted between the first motor M1 and the first inlet.

[0167] - The angular velocity ω2 generated by the action of the rider C on the crankset CK is combined with the action of the second motor M2 with the help of the RM2 reducer to apply this angular velocity ω2 to the second inlet of the differential system D; the axis of the crankset CK potentially imparts the angular velocity ωCK to the inlet body I of the transmission system DU via the Tin transmission (optionally according to the position of the DU group on the bicycle).

[0168] The angular velocities ω1 and ω2 are combined in the differential system D and transmitted to the outlet body O at an angular velocity ω3. Optionally, a RO reducer is installed between the outlet of the differential D and the outlet body. An optional free flywheel F1 is optionally installed between the inlet body I and the second inlet of the differential system D via the RI1 reducer system. The angular velocity at the outlet of the free flywheel F1 is denoted as ωF1. The function of the free flywheel is to allow the inlet body to drive the system but prevent the system from driving the inlet body. This function is essentially determined by the safety considerations of the rider. Nevertheless, the free flywheel remains optional.

[0169] Here another optional freewheel F2 is shown between the inlet body I and the outlet O, with a potential reducer RI2 in between. The angular velocity at the outlet of the freewheel F2 is denoted ωF2, and the function of this freewheel is to make it impossible for the speed of the outlet sprocket to fall below the speed of the inlet body: ωO ≥ ωI. The purpose is to ensure the operability of the bicycle even in the event of a system failure (battery dead or, to a lesser extent, some other failure).

[0170] Motor M1 and motor M2 are powered by battery B (which may be a single battery or different batteries).

[0171] The motor M1 and the motor M2 are controlled by a control unit E.

[0172] The RM2 reducer is used to make the operating speed / torque of the rider and the electric motor compatible with the following equation:

[0173]

[0174] ωM2 is the angular velocity [rad / s] of the motor M2 , ωF1 is the angular velocity of the inlet body (after potential passage via the freewheel F1 ), and RRM2 is the ratio of the reducer associated with the motor M2 .

[0175] The angular velocity ωO of the outlet of the outlet body O is transmitted to the wheel W. Depending on the position of the transmission system on the bicycle, a transmission Tout can be arranged downstream of the outlet O (ωTO), potentially completed by a freewheel F3, for transmitting the angular velocity ωW to the wheel W.

[0176] When elements F1, RM1, RI1, RI2, RO, Tin, Tout, F3 are redundant, they are connected instead. In particular, when F2 is absent, all branches including RI2 are omitted.

[0177] All elements included in the DU transmission system are shown in dashed boxes. Other elements are located outside the transmission system.

[0178] Figure 3 Shown Figure 2 A simplified implementation of the embodiment described in , in which the optional reducers RM1, RI1, RI2 and RO are omitted.

[0179] In a second variant of the present invention, Figure 4 As shown, the second motor M2 regulates the assistance at the outlet of the differential system.

[0180] In this embodiment, Figure 2 The embodiment of the invention is different in that the angular velocity ω2 generated by the action of the rider C on the crankset CK is not combined with the angular velocity of the second motor M2. The angular velocity ωM2 is combined with the angular velocity ω3 at the outlet of the differential D via the reducer R'M2. Other elements and Figure 2 The same as the embodiment.

[0181] An optional freewheel F1 is here mounted between the inlet body and the second inlet of the differential system D (optionally with reduction gear RI1). Its function is to allow the crankset to drive the system but prevent the system from driving the crankset. This function is essentially determined by the safety considerations of the rider. Nevertheless, this freewheel remains optional.

[0182] Here there is a further optional freewheel F2 (via an optional reducer RI2) between the inlet body and the outlet O. Its function is to make it impossible for the speed of the outlet sprocket to fall below the speed of the inlet body (associated with the crankset): ωO ≥ ωI. The aim is to ensure the operability of the bicycle even in the event of a system failure (dead battery or, to a lesser extent, some other failure).

[0183] Here too, motor M1 and motor M2 are powered by battery B (which may be a single battery or different batteries).

[0184] The motor M1 and the motor M2 are controlled by a control unit E.

[0185] The speed / output torque of the differential and the electric motor M2 are made compatible by means of the reduction gear R'M2 according to the following equation:

[0186]

[0187] ωM2 is the angular velocity of the motor M2 in [rad / s], and RR′M2 is the ratio of the reducer R′M2 associated with the motor M2 .

[0188] In order for the motor M2 to regulate the entry or exit assistance of the differential D, the system applies the reduction ratio Rm established according to the following equation:

[0189]

[0190] Figure 5 Shown Figure 4 A simplified implementation of the embodiment described in , in which the optional reducers RM1, RI1, RI2 and RO are omitted.

[0191] Having established these two general modes of operation, a structural embodiment in the form of an architecture will now be described. The following Figures (6 to 9) are based on Figure 1 Principle (M2 in the entrance).

[0192] about Figure 6 , the transmission system for an electric bicycle is integrated into a box 1 which is fixed to the frame of the bicycle, here at the crankset P level.

[0193] The (mechanical) inlet is realized by the crankset 2 axis, which receives energy from the rider via the pedals. The (mechanical) outlet of the system is the outlet body 3, which supports, for example, a toothed sprocket in the case of a transmission by a chain or a toothed pulley in the case of a transmission by a belt, both solutions being fully compatible with the transmission system. Other transmission systems are equally possible and compatible (universal, drive shaft, other). The transmission here is directed toward one wheel of the bicycle, preferably toward the rear wheel.

[0194] The drivetrain is powered by a battery pack located elsewhere on the bicycle. In general, the drivetrain (and in particular the motor) exchanges information (transmit-receive) with other electrical and / or electronic components of the bicycle: displays, command modules, battery management systems, sensors, etc. The CAN exchange protocol is a possible solution.

[0195] Inside the case 1 , the mechanical assembly is organized concentrically around the axis 2 of the crankset.

[0196] The transmission is concentrated between two motors M1 and M2, which respectively comprise rotors 11 and 21 and stators 12 and 22. This configuration enables the motors to be glued to the sides on opposite sides of the box and to be cooled to the maximum. As an element that releases most of its energy through losses, this positioning of the motors is optimal from a thermal point of view.

[0197] The rotor 21 of M2 is the inlet of the reducer A represented by thin dashed lines, here for example a cycloidal gear train with a ring gear A1 fixed to the box 1. The ring gear A1 presents a toothing on its inner face and inside it is a toothed wheel A2 which engages in a cycloidal motion (depending on the position of the point of contact with the ring gear, represented here by more or less closely spaced ripples at the top of the figure) to drive a transmission eccentric A3 associated with an eccentric carrier A4. The eccentric carrier is connected to the axis 2 of the crankset at the level of the freewheel F1 so as to combine the movement of the crankset and that of the second motor at the inlet of the differential D, as represented by thin dashed lines on the right side of the reducer A. The eccentric carrier is located at the outlet of the reducer.

[0198] The differential D is here also a cycloid system with a ring gear D1, which is the inlet connected to the outlet of the above-mentioned reducer A. The rotor 11 of the first motor is connected to the eccentric exciter D2, thus supporting the wheel D3. The outlet of the differential D is an eccentric wheel carrier D4, which is connected to the outlet body 3.

[0199] Here about Figure 1 The optional freewheel F2 described is arranged between the eccentric carrier D4 and the axis 2 of the crankset.

[0200] For this embodiment, for the following embodiment and all other possible embodiments, different types of bearings, rollers and friction bearings are used for the guide assembly. Several arrangements of these elements are possible, but their functions are similar, to the extent that the inventive features of the invention do not depend on this.

[0201] The M1 motor and the M2 motor can independently be radial or axial flux motors.

[0202] Figure 7 The embodiments shown in Figure 6 The difference between the embodiments in FIG. 1 and FIG. 2 is the implementation of the reducer A. Here, the reducer A' is always a cycloid system, but the outlet is the ring gear A1, and the eccentric wheel carrier is fixed to the box 1.

[0203] Figure 8 The embodiment shown in FIG. 1 is different from the embodiment shown in FIG. 2 in terms of the realization of the differential D. Figure 6 Here, the ring gear D'1 is the outlet of the differential D', while the eccentric wheel carrier D'3 and the rotor 11 of the first motor M1 are arranged at the inlet of the differential via an eccentric excitation element.

[0204] Fig. 9 Describes the Figure 7 The reducer A' shown in Figure 8 An embodiment of the differential D' combination shown in FIG.

[0205] Figures 6 to 9 A cycloid system is described. Nevertheless, the cycloid system can be replaced by any other type of reducer, such as, for example, an epicycloid reducer, a harmonic reducer or others.

[0206] Even so, the cycloid transmission for the differential can be replaced by all other differentials, so that the differential meets the following conditions: the periphery of the element moving inside the ring gear always contains the geometric center of the ring gear. This ensures the compactness of the system, unlike the use of epicycloid gear trains, for example.

[0207] Fig.10 Shown Figure 6 Implementation method, in which the reducer A and the differential D are both replaced by a double cycloid engagement system.

[0208] In particular, the reducer A" comprises a toothed ring A1 which exhibits a toothing on its inner face and inside which is a toothed intermediate wheel A"2 which engages on its outer face in the form of a cycloidal motion (represented by more or less closely spaced corrugations depending on the position of the point of contact with the ring gear), the toothed intermediate wheel A"2 also having teeth on its inner face A"3, engaging the outlet sprocket A"4.

[0209] The differential D" is here also a double-engaging system with a ring gear D1, which is the inlet connected to the outlet of the above-mentioned reducer A". The rotor 11 of the first motor is connected to the eccentric excitation member D"2, thereby driving the intermediate wheel D"3 to move in a cycloidal motion between the ring gear D1 and the sprocket D"4, which is the outlet of the differential D connected to the outlet body 3.

[0210] about Figure 2 The optional freewheel F2 described is here arranged between the wheel D″ 4 and the axis 2 of the crankset.

[0211] Fig.11 The embodiment shown in FIG. 1 is different from the embodiment shown in FIG. 1 in terms of the implementation of the reducer A″. Fig.10 The embodiment in is different. Here, the reducer A" is always a double-engaged cycloid system, but in this case the inlet is the ring gear A1, and the sprocket A"4 is fixed to the box.

[0212] Fig.12 The embodiment shown in FIG. 1 is different from the embodiment shown in FIG. 2 in terms of the realization of the differential D″. Fig.10 Here, the ring gear D"1 is the outlet of the differential D", while the sprocket D"4 and the rotor 11 of the first motor M1 are arranged as the inlet of the differential via the intermediate gear.

[0213] Fig.13 Describes the Fig.11 The reducer A'' and Fig.12 An embodiment of a differential D"' combination is shown.

[0214] All elements of the drive train can be positioned around a single axis.

[0215] exist Figures 6 to 13 In the embodiment, the axis centre is the axis of the crankset, which axis coincides with the axis of the outlet body, ie the axis of the sprocket associated with the transmission which allows driving one wheel of the bicycle.

[0216] According to a similar embodiment, the axis centre may be the outlet axis, advantageously for example the axis of the wheel, and the inlet is the axis of the sprocket to which the action of the crankset is to be transmitted.

[0217] The method of the present invention and the associated transmission system thus provide substantial flexibility in implementation.

[0218] Figures 14 to 16 A concentric cycloidal dual clutch transmission 140 is depicted herein. Fig.14 is a side view, and Fig.15 and Fig.16 They are cross-sectional views along the B plane and the C plane respectively.

[0219] As in the cycloid transmission system described above, the eccentric exciter 141, which constitutes the first connection of the differential system, supports a wheel 142 on its eccentric axis, and the wheel 142 rotates freely along the eccentric secondary axis of the eccentric exciter. Any type of connection with at least one rotational degree of freedom can be used. This wheel 142 is given an external toothing and engages in an outer ring gear 143 (with an internal toothing). This constitutes a first joint. In addition, the wheel is also equipped with an internal toothing, which is axially juxtaposed near its connection with the eccentric exciter 141. In addition, the sprocket 144, which constitutes the second inlet of the cycloid system, is rotatably hinged on the main axis AA of the cycloid module. The sprocket is equipped with an external toothing 145 compatible with the internal toothing of the wheel 142, so that it engages with the second joint.

[0220] The ring gear 143 is rotatably movable along the main axis AA of the cycloid module, constituting the third and final connection to the differential system.

[0221] The cycloidal motion of the intermediate wheel 142 and its engagement with the sprocket 144 imparts a simple rotation to the sprocket 144 .

[0222] To ensure operation of the system, the eccentricities of the two cycloid joints (ring gear-intermediate wheel and intermediate wheel-sprocket) should be equal (unless flexibility is introduced in the system).

Claims

1. A method for auxiliary differential transmission of an electric bicycle, comprising the following steps: - applying an angular velocity ω1 to a first inlet of the differential system by the action of a first motor; - applying an angular velocity ω2 to a second inlet of the differential system through an inlet body transmitting at least the action of the rider on the crankset; - combining the angular velocity ω1 and the angular velocity ω2 in the differential system and transmitting them to the outlet of the differential at the angular velocity ω3, the differential system comprising a ring gear having an inner surface and an element cooperating with the inner surface, the periphery of the element always containing the geometric center of the ring gear; - transmitting said angular velocity ω3 to the outlet body; A second motor regulates the assistance to the rider, the second motor being connected to the second inlet through the inlet body in conjunction with the rider's action, or to the outlet, The axis of the outlet body, the main axis of the differential system, the axis of the first motor and the axis of the second motor are coincident and / or concentric with the axis of the inlet body.

2. The method according to claim 1, wherein: The inlet body is indirectly associated with the axis of the crankset.

3. The method according to claim 1 or 2, wherein: The inner surface of the gear ring presents an internal toothing, and the element cooperating with the inner surface is arranged to engage with the toothing.

4. The method according to any one of claims 1 to 3, wherein: The differential system is a cycloid transmission system.

5. The method according to claim 4, wherein: The ring gear has a toothed inner surface, and the element cooperating with the inner surface is a toothed wheel movable according to a cycloidal motion, the tooth profile of the ring gear having a number of teeth Zc greater than the number of teeth Zr of the toothed wheel.

6. The method according to claim 4 or 5, wherein: The cycloid transmission system comprises at least one transmitting eccentric associated with an eccentric carrier, arranged to transmit the cycloid movement of the toothed wheel to the outlet, wherein the rotation axis coincides with the rotation axis of the toothed ring.

7. The method according to claim 5 or 6, wherein: The toothed wheel also presents a likewise toothed inner surface arranged to engage with a sprocket rotatably articulated about an axis coinciding with the axis of the toothed ring.

8. Method according to any one of claims 4 to 7, according to which the cycloid transmission comprises at least two toothed wheels.

9. The method according to any one of claims 1 to 8, according to which the differential system is a cycloid transmission, and the first motor applies an angular velocity ω1 to an eccentric excitation member serving as the first inlet, the second motor and the inlet body impart an angular velocity ω2 to the ring gear serving as the second inlet, and the outlet is an eccentric wheel carrier or sprocket that transmits an angular velocity ω3.

10. A method according to any one of claims 1 to 8, according to which the differential system is a cycloid transmission, and the first motor applies an angular velocity ω1 to an eccentric excitation member serving as the first inlet, the second motor and the inlet body impart an angular velocity ω2 to an eccentric reducer or the sprocket, the eccentric reducer or the sprocket then serving as the second inlet, and the outlet is a ring gear transmitting an angular velocity ω3.

11. The method according to any one of claims 1 to 3, according to which the differential system is a harmonic drive system, the ring gear of the harmonic drive system has a toothed inner surface, and the element cooperating with the inner surface is a toothed deformable wheel surrounding a wave generator, the number of teeth Zc of the ring gear being greater than the number of teeth Zr of the deformable wheel.

12. A method according to any one of claims 1 to 11, according to which a torque control is applied to the second motor.

13. A transmission system for an electric bicycle, comprising: - a differential system comprising a toothed ring having an inner surface and an element cooperating with said inner surface, the periphery of said element defining a surface containing the geometrical centre of said toothed ring, - a first motor arranged to impart an angular velocity to a first inlet of the differential system, - an inlet body arranged to impart an angular velocity to the second inlet of the differential system, - an outlet of the differential system, the outlet of the differential system being arranged to impart a velocity to the outlet body, and - a second motor regulating the assistance to the rider, the second motor being connected to a second inlet associated with the inlet body or to the outlet, Wherein, the axis of the outlet body, the main axis of the differential system, the axis of the first motor and the axis of the second motor coincide with and / or are concentric with the axis of the inlet body.

14. The transmission system according to claim 13, wherein: The inlet body is directly or indirectly associated with the axis of the crankset.

15. The transmission system according to claim 13 or 14, wherein: The outlet body is coupled to at least one wheel of the bicycle via a transmission mechanism.

16. A transmission system according to any one of claims 12 to 15, wherein: The inlet body is coupled to the axis of the crankset via a transmission mechanism.

17. A transmission system according to any one of claims 13 to 16, wherein: The inner surface of the gear ring presents an internal toothing, and the element cooperating with the inner surface is arranged to engage with the toothing.

18. A transmission system according to any one of claims 13 to 17, wherein: The differential system is a cycloid transmission system, wherein the inner surface of the ring gear presents an internal toothing, and the element engaged with the internal toothing of the ring gear is a toothed wheel, the toothing of the cycloid ring gear having a tooth number Zc greater than the tooth number Zr of the toothed wheel.

19. The transmission system according to claim 18, wherein: The toothed wheel also presents a likewise toothed inner surface arranged to engage with a sprocket rotatably articulated about an axis coinciding with the axis of the toothed ring.

20. A transmission system according to any one of claims 13 to 17, wherein: The differential system is a harmonic drive system, wherein the inner surface of the ring gear presents an internal tooth profile, and the element engaged with the internal tooth profile of the ring gear is a toothed deformable wheel surrounding a wave generator, the number of teeth Zc of the ring gear being greater than the number of teeth Zr of the deformable wheel.

21. A transmission system according to any one of claims 13 to 20, further comprising a non-return mechanism.

22. A transmission system according to any one of claims 13 to 21, comprising a system reducer arranged to allow combining the action of the second motor with the action of the outlet or combining the action of the second motor with the action of the inlet body.

23. A transmission system according to any one of claims 13 to 22, wherein: The axis of the outlet body coincides and / or is concentric with the axis of the reducer associated with the second motor M2 .

24. A transmission system according to any one of claims 13 to 23, wherein: Two motors are mounted on opposite sides of the differential system.

25. An electric bicycle comprising a transmission system according to any one of claims 13 to 24, wherein: The axis of the ring gear is coincident and / or concentric with the axis of the wheel of the bicycle.

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