EP4665639A1

EP4665639A1 - Bi-cycloidal gear power-split mechanism and e-bike hybrid powertrain having such mechanism

Info

Publication number: EP4665639A1
Application number: EP23708562.6A
Authority: EP
Inventors: Pablo Carrasco Vergara; Diego Peinado Martin
Original assignee: Quaternion Ingenieria De Sistemas Electromecanicos Sl
Current assignee: Quaternion Ingenieria De Sistemas Electromecanicos Sl
Priority date: 2023-02-17
Filing date: 2023-02-17
Publication date: 2025-12-24
Also published as: CN120513197A; WO2024170938A1

Abstract

The present invention discloses a simple and efficient bi-cycloidal power-split gear mechanism optimized for a hybrid powertrain with a low-speed power input, a high-speed power input/output, and a low-speed power output, preferably applied to e-bikes. It also discloses a bi- cycloidal power-split hybrid powertrain with proportional electric assistance to human pedaling power without using any torque sensor, which applies to both mid-motor and hub-motor e-bikes. And a third object of the present invention reveals a high-performance electrically assisted powertrain with an electric continuously variable transmission (e-CVT) for e-bikes, combining power-split and parallel hybrid drives, optimized by using the bi-cycloidal gear technology.

Description

BI-CYCLOIDAL GEAR POWER-SPLIT MECHANISM AND E-BIKE HYBRID POWERTRAIN HAVING SUCH MECHANISM TECHNICAL FIELD The present invention relates primarily to hybrid powertrains with a low-speed power input, a high-speed power input/output, and a low-speed power output, especially for human-powered electric devices, hybrid pedaling vehicles, and, more specifically, e-bikes. STATE OF THE ART Hybrid powertrains use two energy sources (e.g., electric, pneumatic, animal, chemical, aerodynamical, etc.) and one mechanical power output. Mainly, an electrical–human power hybrid transmission is considered, as it combines the high speed of an electric motor with the low rate of a cyclist's pedaling cadence for delivering an also low-speed mechanical output as it happens in bicycles. E-bikes are used worldwide, usually under PEDELEC standard rules, where the electric motor aids the human power, which means that it only provides power if the human source already provides it. This additional power can be supplied in diverse ways, but proportional to the delivered pedaling power is preferred in high-end e-bikes. This approach usually demands that the torque provided by pedaling must be determined, being devices that allow this measurement object of numerous patents (US8939247B2, US9855991B2, US2019293503A1, US2022355897A1). The result of these sensor-proportional electric assistance hybrid powertrains is not always as expected. Many inventions have been made in this field, but their latency time response, poor sensibility, and high cost are areas for improvement. In general, when using just one electric machine, i.e., motor/generator, there are three primary hybridization schemes: • "Parallel Hybrid" arranges two power sources, e.g., pedaling and electrical power, to act simultaneously, driving one single output member. In this case, both torques are added, and the angular velocity is the same at one point of the kinematical transmission chain. Also, in more general terms, it can be stated that system constraints completely define the relative angular velocities of the different parts. The control variable is the torque: the electrical motor provides additional torque to the system. This scheme is the one commonly used in PEDELEC e-bikes. • "Series Hybrid" arranges one mechanical and one electric power source, where the mechanical, e.g., pedaling power, is only used to produce electricity using a corresponding generator. Therefore, the output power is only driven by a corresponding electric motor, using energy delivered by a battery or said generator. This scheme is used in Schaeffler's chainless electric drive system "Free Drive" for bicycles DE102011082082A1. It may be beneficial for 3- wheel cargo bikes, but it is too heavy and inefficient for a regular bicycle. • "Power-Split Hybrid" arranges one mechanical and one electric power source, where the torques provided are always proportional, one to the other. This proportional rate is defined by the gear ratio of their connecting mechanism, named power-split, although it works as well as power-joint, as it has a differential effect. The control variable is the angular velocity: the electrical motor provides additional speed to the system but not extra torque. Its use in e-bikes has been proposed in BOSCH's patent US9758212B2. This scheme is commonly used in the automotive industry (e.g., Toyota Hybrid System) using an epicyclic planetary gear as the power-split mechanism. The present invention is mainly centered on the Power-Split Hybrid scheme applied to e- bikes since there is no need to determine the torque provided by the pedaling power: as the two power input torques are always proportional, in order to get a desired balanced power output, the electronic control only must know the instantaneous value of the speed pedaling input to establish the proper rotational speed of the motor, giving more or less rate speed just based on the electric assistance level chosen by the user. In this scheme, torque is never increased by the electric assistance. The mentioned BOSCH's patent, US9758212B2, also uses an epicyclic planetary gear as the power-split mechanism. For this kind of solution, the problem is that a cyclist's pedaling torque, especially when making a sudden effort, is massive compared with any light motor suitable for a bicycle, even after being multiplied by the gear ratio of any corresponding epicyclic planetary gear. In this case, the motor's maximum torque, multiplied by a low gear ratio, is insufficient to prevent the electric motor from going in reverse or, in any case, stopping –when using a corresponding one-way clutch– giving the sensation of slipping during the pedaling downstroke. Fixing this problem would require a much bigger motor and a more complex planetary gear – especially in highly demanding applications– than any bike could have, considering their weight, cost, efficiency, and volume. The present invention copes with this problem so a final product can be released to the market. When combining mechanical power from a combustion engine and an electric motor, as both systems rotate at similar speeds (e.g., 2.000 - 5.000 rpm), a small gear ratio can ideally be used. Nevertheless, the pedaling usual rotation rate is much smaller, about 90 rpm at the bicycle's bottom bracket, which is why the need for such a more significant gear reduction when looking for a logical, compact, and economical e-bike motor. That is why Schaeffler's Free Drive generator is driven, from pedaling, through an inverted cycloidal reduction mechanism –a cycloidal multiplier–accommodating the low pedaling cadence to the very high speed needed for an electric generator to be efficient. There are more hybridization schemes when using more electric machines, combining their functions of motor and generator. One essential solution combines a Power-Split Hybrid arrangement and a parallel hybrid arrangement, constituting an Electric Continuously Variable Transmission (e-CVT), eliminating the need for shifting gears. The successful Toyota e-CVT system is a perfect example of this arrangement, using as well an epicyclic planetary gear. This e-CVT solution applied to bicycles has been described in WO2010092331A1, US9254890B2, US10479447B2, US11091225B2, US11383791B2, US2021046998A1, US2022274670A1. These inventions for e-bikes also use only epicyclic planetary gears to implement their Power-Split Hybrid arrangements. This kind of mechanism introduces several problems, all addressed in the patents of E2 DRIVES (US9254890B2, US10479447B2, US11091225B2, US11383791B2, US2021046998A1, US2022274670A1). They are searching for a solution for the same problem, named the low gear ratio of the epicyclic gears. Then, to avoid a prevalent problem with the reverse rotation at the Power-Split hybridization subsystem, a compromise solution has been made by using bigger and heavier motor and epicyclic planetary gear in non- performance e-bikes, e.g., for commuting and city bikes. It is an object of the present invention, a distinct double cycloidal drive as the power-split mechanism with a desirably high gear ratio, high power transfer efficiency, and compact size. A double cycloidal speed reducer solution was described in 1940 by Bradford Foote Jr in US2250259. An alternative speed reducer embodiment is cited as a modification of the invention, as shown in FIG5 in the said document. That case is the closest State of the Art for the present invention. Maybe any corresponding embodiment to said modification never worked in the real world, as no information has been found. However, it should have been optimized to avoid teeth interferences and improve efficiency; for example, it claimed v-shaped teeth with straight load faces. TQ-Systems Gmbh uses a similar speed reducer solution in TQ HPR50 e-bike motors, as described in US10371240B2, but instead of a double cycloidal, it is based on the pin ring principle, as shown in GB303709. TQ uses a modified version called the "Harmonic Pin-Ring" drive, having a crown-shaped pin-ring with fixed pins instead of using rotating pins or bearings, and therefore, they work under slight sliding conditions. As this crown-shaped pin-ring's inner and outer protrusions correspond to virtual pins, it has the same number of teeth for engaging a sun gear as for a ring gear, therefore having the corresponding sun and ring, different teeth modulus. This point confirms that at least one of the gears is not rolling but sliding. In this TQ's motor, the Harmonic Pin-Ring is comprehended into a parallel hybrid arrangement where this speed reducer is concentric with a pedaling axle. There are other patents, e.g., DE102015100676B3 and WO2022106107A1, with similar parallel hybrid configurations. In these cases, they use a strain wave gear –or Harmonic Drive– as a speed reducer, allowing for a higher reduction ratio than the TQ's pin-ring gear (e.g., 50:1 vs. 17.5:1) but likely sacrificing more power transfer efficiency. In any case, strain wave gear, Harmonic Pin-Ring gear, or cycloidal gear reducers –as mentioned for Schaeffler's Free Drive– all work using sliding components, which means more friction loss. Therefore, they wouldn't be optimal for a power-split gear or a high-efficiency power transfer mechanism. SUMMARY OF THE INVENTION Looking for optimal mechanical efficiency and reliability, compact and lightweight construction, and easy to manufacture at a contained cost: • A first object of the present invention is to provide a simple and efficient power- split mechanism optimized for a hybrid powertrain with a low-speed power input, a high- speed power input/output, and a low-speed power output. Preferably applied to e-bikes, said high-speed input/output is coupled to an electric machine, motor/generator. • A second object of the present invention is a sensorless proportional electric assistance powertrain for e-bikes, or, in other words, a high-performance powertrain with proportional electric assistance to human pedaling power without using any torque sensor. Although with different architectures, the invention applies to both mid-drive and rear-wheel hub-drive motors. • A third object of the present invention is to provide a high-performance electrically assisted powertrain with an electric continuously variable transmission (e-CVT) for e-bikes. — THE POWER-SPLIT MECHANISM: For the first object, the invention proposes a cycloidal type power-split mechanism based on a double-cycloidal gear, hereafter called "bi-cycloidal gear". This solution has a much higher gear ratio and fewer parts than the planetary gears. At the same time, it increases the transmission efficiency due to the very tight concave-to-convex meshing, which minimizes the sliding at the gear meshing teeth and, therefore, the rolling friction loss of the gears. The working principle is as follows: The first cycloidal stage is based on an eccentrically moving first outer crown with ZO1 internal teeth, rolling around a smaller first inner crown with Zi1 external teeth. An eccentric axle in the form of a crankshaft, having a crankpin around which the first outer crown rotates freely, rotates concentrically with the first inner crown producing the cycloidal rolling movement. For each revolution of the eccentric axle, the first outer crown rotates partially, with only an angle corresponding to the teeth number difference between both crowns. Hence, its gear ratio is inversely proportional to its eccentricity, that is, to the difference of teeth between both crowns divided by the number of teeth of the first outer crown [gear ratio = ZO1/(ZO1-Zi1)]. The second cycloidal stage is based on an eccentrically moving second inner crown with Z i2 external teeth, rolling inside a larger second outer crown with ZO2 internal teeth. This rolling movement is forced by the same eccentric axle of the first stage, and the second inner crown rotates around said crankpin united and fixed to the first outer crown. As we have a double cycloidal gear, this partial rotation happens twice, resulting in a close to double rotation angle and, therefore, a gear ratio close to half of the classic cycloidal: depending on the second stage teeth counting. The second stage gear ratio is Z_i2/(Z_O1-Z_i1). The bi-cycloidal gear power-split mechanism object of the present invention comprises a first, a second, a third, and a fourth drive member, where: • The second drive member consists of a crankshaft that rotates around a central axis, either mechanically coupled or integrally performed in the same part with a crankpin that defines an eccentric parallel axis distanced δ from the central axis; • the fourth drive member has an axis of revolution and is either mechanically coupled or integrally performed in the same element with a concentric externally toothed crown and a concentric internally toothed crown, embodying a dual-crown gear which is rotatably mounted onto said crankpin with corresponding bearing means next to the internally toothed crown, having said axis of revolution coincident with said eccentric parallel axis, defining a bi-cycloidal axial orientation, hereinafter referred to as a first end, the one corresponding to said internally toothed crown side, and the second end, at the bearing means side; • the first drive member has an axis of revolution being concentric with the central axis, is rotatably assembled with the second drive member, and is either mechanically coupled or integrally performed in the same part with an externally toothed sun gear which is meshing with the internally toothed crown of the fourth drive member; • the third drive member also has an axis of revolution being concentric with the central axis, is rotatably assembled with the first and the second drive members, and is either mechanically coupled or integrally performed in the same part with an internally toothed ring gear which is meshing with the externally toothed crown of the fourth drive member; and where each of the first, the second, and the third drive member respectively dispose of the corresponding mechanical coupling means as each may act as an input or an output element. The fourth drive member is just performing the dynamic connection between them. Each of these three power input/output elements can act as an input or as an output member, but there will always be at least one input and one output. The second drive element performs the high- speed power input/output. Let's then consider the different parameters: ω₁ (sun gear angular velocity) ω₂ (crankshaft angular velocity) ω3 (ring gear angular velocity) T1 (Torque input at the sun gear) T2 (Torque input at the crankshaft) T3 (Torque output at the ring gear) δ (crankpin eccentricity) m (gear modulus) Z1 (number of teeth of the sun gear) Z₃ (number of teeth of the ring gear) Z_4i (number of teeth of the internally toothed crown at the dual-crown gear) Z_4e (number of teeth of the externally toothed crown at the dual-crown gear) Δ_Z (difference in number between meshing gears) As the eccentricity defined by the crankpin is the same for both gear stages: Only if the second gear stage would have a different ΔZ in their meshing ( ^^₃ − ^^_{4 ^^} ≠ ^^_{4 ^^} − ^^₁) it would be possible to have a different modulus. Still, as the final gear ratio would be the same because the same primitive perimeter defines it, it makes no mechanical sense to use weaker teeth in one of the gear stages. Therefore, the modulus of the teeth of all gears will preferably be the same. Then, for a preferred realization, we have the following: • When developing the kinematical and dynamical equations, we found the following relations: Where K is a constant: with k ∈ (0, 1) ^^ 1 • ₂ ^^₁ = ^^ − 1 ^^₁ ^^₃ 1 • ^^₃ = ^^₁ + ^^₂ = ^^ ⇒ ^^₁ = ^^ And therefore: • Gear Ratio "crankshaft–to–Sun": • gear ratio "Ring–to–Sun": • gear ratio "crankshaft–to–Ring": Note that when ω₂ < 0, the electric machine we call a motor would operate as a generator. To maximize the gear ratio, in the preferred embodiments of the bi-cycloidal gear, the difference in number between meshing gears is one: ΔZ=1 In a preferred embodiment, to optimize gear meshing while minimizing friction at the teeth of the bi-cycloidal gear: • The teeth profile of the gears are involutes of the corresponding circles, which pressure angle (α)° of between and including 30° and 40°: α ∈ [30, 40] • The outer diameter of each of the two externally toothed gears is: ^^ _^^ = ^^ · ^^ + 2 · ^^ · ^^ and the inner diameter of each of the two internally toothed gears is: ^^ _^^ = ^^ · ^^ − 2 · ^^ · ^^ where: ^^ ∈ [0.20, 0.35] A preferred embodiment, in order to accommodate rpm at an electric motor to assist a cyclist pedaling power, gear ratio crankshaft-to-Ring –the ratio between the second drive member and third drive member rotational speeds– has a value of between and including 20:1 and 35:1, therefore: ∈ ^[20, 35^]⇒ K ∈ [0.95, 0.97] Furthermore, in a more preferred embodiment, in order to perform a tubular shape for simplifying the manufacturing process of the fourth drive member: Z_4e − Z_4i ∈ [6, 8] And in a more preferred embodiment: Z_4e − Z_4i = 6 ; and: 44 ≤ Z₃ ≤ 73 Therefore, the ring gear number of teeth is between and including 44 and 73. Furthermore, in a more preferred embodiment intended for being used in e-bikes, considering a cyclist's pedaling torque and an appropriate volume in between corresponding pedals, the modulus ^^ is between and including 1.0 mm and 1.6 mm For other applications, in general, those devices that use planetary gears combined with speed reducers –or multipliers– it may be convenient to substitute them by using a bi-cycloidal gear power-split mechanism. In addition, a low-torque electric input/output at the second member may manage a high-power variable speed mechanical input for delivering a constant speed output, or vice-versa. For example, in a wind turbine, a variable rotational speed of wind power input at the rotor could be accommodated by controlling the rotational speed at the second member to provide a constant rotational speed to a generator. In a particular case where one of the first or the third drive members is fixed, the power- split mechanism would work as an optimized speed reducer – or multiplier in the case of the second drive member as the output –. — SENSORLESS PROPORTIONAL ELECTRIC ASSISTANCE POWERTRAIN FOR E-BIKES: We will refer to a power-split hybrid arrangement using a bi-cycloidal gear as a "bi-cycloidal power-split hybrid drive". As a second object of the present invention, a preferred embodiment for a bi-cycloidal power-split hybrid drive combines a low-speed power input through the first drive member of a bi-cycloidal gear and high-speed electric power assistance through its second drive member and, as a result, a mechanical power output through its third drive member. An alternative solution may change said first and third drive members for the third and first. When using a bi-cycloidal power-split hybrid drive in a bike, the electric assistance torque is always proportional to the instantaneous pedaling torque without needing any torque sensor. This point brings some significant benefits compared to the existing e-bikes in the market: • It is cheaper because it saves the cost of an expensive component. • It results in a more compact design as it avoids such required space, which results in an improved bicycle frame design. • As just the pedals push the bike, it provides a more natural feeling of pedaling. Furthermore, it offers more accelerating control in comparison with a parallel hybrid arrangement because, in this last case, it exists some delay between the pedaling torque inputs and the electric torque output. This delay happens due to the filtering and computation of the pedaling measurements. This last point becomes essential in the case of mid-drive e-bikes with chain, rear derailleur, and cassette. When the user shifts gears, high torque is still applied from the motor to the bicycle drive-train resulting in an increased risk of failure and poor life span for the chain and shifting system. Furthermore, not applying any torque to the rear wheel can sometimes be really convenient, especially in slippery conditions. If the motor is still pushing due to said delay, we have a risk of a fall. The present invention preferably comprises a speed sensor that can directly or indirectly measure the pedaling rotational angle or the pedaling speed. As the electric motor provides additional speed to the system but not extra torque, using a speed sensor allows the electronic control to establish a desired proportional power output. In addition, related to the pedelecs –where electric assistance must finish at 25 km/h– any power-split hybridization is very convenient, as they only add extra speed. When that legal limit has been reached, depending on the pedaling power input, the electric power is gradually reduced to keep adding just the necessary extra speed to maintain said 25 Km/h. The bi-cycloidal power-split hybrid drive can be successfully applied either for mid-drive or rear-wheel hub-drive motors. A bi-cycloidal power-split hybrid mid-drive motor for e-bikes comprises: • An electric motor, having a stator and a rotor; • a motor housing to be held in a bicycle, having a bottom bracket axis, and concentrically supporting the motor stator placed near its non-drive side –bicycle's left side –; • a bi-cycloidal gear power-split mechanism, arranged concentrically with the bottom bracket axis, placing its first end pointing to the drive side, where: o The first drive member is furthermore a bottom bracket axle rotatably mounted onto the motor housing, either mechanically coupled or integrally performed in the same element with the sun gear, having both end portions out of the housing for coupling respective pedaling crankarms; o the second drive member consists of a hollow crankshaft mounted onto the bottom bracket axle, arranged to rotate freely, at least in the forward sense, and mechanically fixed to the rotor; and o the third drive member, concentric with the bottom bracket axis and rotatably mounted into the motor housing, constitutes an output member disposing of mechanical coupling means in order to drive the power output from the mid-drive motor (e.g., attaching a chainring); The electric motor rotor can be arranged to rotate freely in both directions or only in the forward sense by means of a one-way clutch. In the former case, the electronic control may be arranged in a specific program, so the motor is set up as a generator. In this case, the cyclist's power input splits, so one part is delivered to the generator and used to generate electric current. For instance, the generated energy can be used to charge the battery. In the latter, when one direction clutch is used, reverse rotation of the rotor is prevented, and the "slippery feeling" produced by a sudden and high cyclist's effort is highly reduced. In this case, the possibility of regeneration is excluded. The one-way clutch could be preferably attached to the first drive member or the motor housing in alternative embodiments. A bi-cycloidal power-split hybrid hub-drive motor at a rear wheel comprises: • An electric motor, having a stator and a rotor; • a stationary axle, corresponding to a wheel's axis, that supports concentric and fixes a motor stator located near its non-drive side; • a bi-cycloidal gear power-split mechanism concentric and rotatably mounted onto the stationary axle and arranged to place its first end at the drive side, where: o the first drive member consists of a hollow input axle rotatably mounted around the stationary axle, either mechanically coupled or integrally performed in the same element with the sun gear, having coupling means at the drive side for a free-hub mechanism to be driven by a cyclist pedaling power (e.g., using a sprocket); o the second drive member consists of a hollow crankshaft placed at the non-drive side and mounted around the stationary axle arranged to rotate freely, at least in the forward sense, and mechanically fixed to the rotor; o the third drive member is concentric with the wheel's axis, rotatably mounted onto the stationary axle, and is either mechanically coupled or integrally performed in the same element with the hub shell of the wheel. As well as for the mid-drive motor, the rotor can be arranged to rotate freely in both directions or only in the forward sense by means of a one-way clutch. Nowadays, rear-wheel hub-drive motors are generally perceived as a low-performance and cheap solution. But still, this perception can change because, when using power-split hybridization, most significant problems related to the well-known hub-drive motor disappear or are minimized. Related problems to parallel hybrid hub-drive motors are: • Low torque: even when they use epicyclic planetary gears, hub-drive motors don't have a proper gear ratio, and because the wheel's torque does not take advantage of the bicycle-shifting gears, a bigger electric motor is needed, but there must be a compromise solution with the motor weight. • High weight: A relatively large electric motor is needed, even though the power must be "low", due to this compromise solution. • As the motor is at the wheel, this high weight doesn't have any advantage of using a full-suspension bike, as it happens with the mid-drive motors –unsprung vs. sprung mass–. • They offer lower efficiency than mid-drives because their rotational regime must cover the bike's whole speed range. • It is more difficult or expensive to make them work with proportional electric assistance to the pedaling power as they would generally request to be linked to an external powermeter. Nevertheless, all these negative points are solved, pretty much reduced, or don't apply anymore by introducing the bi-cycloidal power-split hybrid technology: • The torque has been amplified enough, thanks to the higher gear ratio. • Therefore the electric motor can be of equivalent size to that of a mid-drive e-bike. • The unsprung mass is consequently reduced. • Because, in this case, the motor puts additional speed to the pedaling input, its operating rpm range is reduced, allowing it to not work at non-efficient revolutions; furthermore, it takes advantage of superior mechanical efficiency at the speed reducer. • It doesn't need a powermeter as the torque is always proportional to the pedaling power. — POWERTRAIN WITH E-CVT FOR E-BIKES When combining a power-split hybrid arrangement with a parallel hybrid arrangement, the corresponding first motor delivers additional speed to a power input, and the corresponding second motor provides extra torque. Managing the electric energy to the first motor, we find hi- speed and low-torque, but when to the second motor, low-speed and hi-torque. Combining a bi-cycloidal power-split mid-drive motor with a parallel hybrid drive motor results in a high-performance electrically assisted powertrain for e-bikes with electric continuously variable transmission (e-CVT). Said parallel hybrid drive e-bike motor could be a hub-drive motor at a rear wheel. Still, a more preferred e-CVT solution combines two electric machines –motor/generator– inside a mid- drive motor housing, the first arranged under a bi-cycloidal power-split hybrid scheme and the second under a parallel hybrid scheme. In any case, it is preferred to use a bi-cycloidal gear as the speed reducer for any parallel hybrid arrangement. A preferred embodiment comprises: • A first electric motor, having a first stator and a first rotor, and a second electric motor, having a second stator and a second rotor; • a motor housing to be held in a bicycle, having a bottom bracket axis, and supporting a concentric first electric motor stator placed near its non-drive side; • a first bi-cycloidal gear power-split mechanism, arranged concentrically with the bottom bracket axis, placing its first end pointing to the drive side, where: o its first drive member is furthermore a bottom bracket axle rotatably mounted onto the motor housing, either mechanically coupled or integrally performed in the same element with the sun gear, having both ends out for coupling respective pedaling crankarms; o its second drive member consists of a hollow crankshaft mounted onto the bottom bracket axle arranged to rotate freely, at least in the forward sense, and mechanically fixed to the first rotor; and o its third drive member, concentric with the bottom bracket axis and rotatably mounted into the motor housing, also comprises an external teeth profile which is a meshing input for receiving the torque assistance from the second electric motor, constituting the total output member, e.g., attaching a chainring via its corresponding mechanical coupling means; • where the second electric motor is equipped with a speed reducer that meshes with the total output member. In this preferred e-CVT embodiment, said speed reducer is performed by a second bi- cycloidal gear: The power from the second motor is driven by the second drive member of the second bi-cycloidal gear, and either the second bi-cycloidal gear's first or third drive member is blocked or fixed to the housing, resulting in the other as the output of the second motor. The various preferred embodiments and further advantages will be best understood by reference to the following detailed description in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS FIG.1 shows, in a front view, the essential parts of a bi-cycloidal gear according to the invention: a central axis (AX0); an eccentric parallel axis (AX2) distanced ( ^) from the central axis is representing a second drive member; a sun gear (10) provided with Z₁ external teeth (10e) is representing a first drive member (1); a ring gear (30) provided with Z₃ internal teeth (30i) is representing a third drive member (3); and a fourth drive member (4) is performed by a dual- crown gear provided with Z_4e external teeth (40e) and Z_4i internal teeth (40i) FIG.2 is an exploded perspective view of a bi-cycloidal gear power-split mechanism. FIG.3 is a sectional lateral view of the bi-cycloidal gear of FIG.2 FIG.4 is a schematic cross-sectional illustration of a preferred embodiment of a bi-cycloidal power-split hybrid mid-drive motor for e-bikes. FIG.5 is a perspective view of a detailed embodiment of an e-bike mid-drive motor mechanism, showing a housing (0), right and left crankarms (1110, 1120), and a chainring (301). FIG.6 is the perspective view of the mechanism of FIG.5 without housing (0), crankarms (101, 102), or chainring (301). It includes the bi-cycloidal gear mechanism of FIG.2 FIG.7 is a sectional view of the embodiment shown in FIG.6, including the bi-cycloidal gear power-split mechanism of FIG.2 FIG.8 is a schematic cross-sectional illustration of a preferred embodiment of a bi-cycloidal power-split hybrid hub-drive motor for e-bikes. FIG.9 is a schematic cross-sectional illustration of an embodiment of an electrically assisted bi-cycloidal powertrain with e-CVT for e-bikes. FIG.10 is a schematic cross-sectional illustration of a preferred embodiment of a bi-cycloidal powertrain with e-CVT for e-bikes using two bi-cycloidal gears. FIG.11 is a schematic cross-sectional illustration of a parallel hybrid embodiment, arranged as a hub motor, using a bi-cycloidal gear speed reducer. DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT A preferred embodiment of the first object of the present invention corresponds to a bi- cycloidal gear power-split mechanism comprising a first, a second, a third, and a fourth drive member, where: • The second drive member (2) consists of a crankshaft (20) that rotates around a central axis (AX0), including a crankpin (22) that defines an eccentric parallel axis (AX2) distanced δ; • the fourth drive member (4) has an axis of revolution and comprises a concentric externally toothed crown (4e) having Z_4e=57 teeth (40e) and a concentric internally toothed crown (4i) having Z_4i=51 teeth (40i), embodying a dual-crown gear which is rotatably mounted onto said crankpin (22) with said axis of revolution coincident with said eccentric parallel axis (AX2); • the first drive member (1) has an axis of revolution being concentric with the central axis (AX0), is rotatably assembled with the second drive member (2), and is either mechanically coupled or integrally performed in the same part with an externally toothed sun gear (10) having Z1=50 teeth (10e), which is meshing with the internally toothed crown (4i) of the fourth drive member (4); • the third drive member (3) also has an axis of revolution being concentric with the central axis (AX0), is rotatably assembled with the first and the second drive members (1 and 2), and is either mechanically coupled or integrally performed in the same part with an internally toothed ring gear (30) provided with Z3=58 internal teeth (30i), which is meshing with the externally toothed crown (4e) of the fourth drive member (4); and where each of the first (1), the second (2), and the third drive member (3) respectively dispose of the corresponding mechanical coupling means (111-112, 200, and 300) as each may act as an input or as an output element. In this case: • Gear ratio "crankshaft–to–sun": -26.39 : 1 • Gear ratio "sun–to–ring": 1.04 : 1 • Gear ratio "ring–to–sun": 0.96 : 1 • Gear ratio "crankshaft–to–ring": 27.39 : 1 For this embodiment: • The modulus " ^^" is the same for the four cited gears: the sun, the ring, and the dual- crown gear. • The outer diameter of every externally toothed gear is: ^^ _^^ = ^^ · ^^ + 2 · ^^ · 0.275 ; And the inner diameter of every internally toothed gear is: ^^ _^^ = ^^ · ^^ − 2 · ^^ · 0.275 • And the teeth profile of the gears are involutes of the corresponding circles, which pressure angle _α = 35 ° • Being the modulus ^^ = 1.3mm and therefore the eccentricity ^^ = 0.65 ^^ ^^ A preferred embodiment of the second object of the present invention, a sensorless proportional electric assistance powertrain, is a bi-cycloidal power-split hybrid drive for a mid- drive motor for e-bikes, as shown in FIG.2 to FIG.7. It comprises: • An electric motor (M1), having a stator (S1) and a rotor (R1); • A motor housing (0) to be held in a bicycle, having a bottom bracket axis (AX0), and concentrically supporting the motor stator (S1) placed near its non-drive side – bicycle's left side–; • a bi-cycloidal gear power-split mechanism (BiCy1), arranged concentrically with the bottom bracket axis (AX0), placing its first end pointing to the drive side, where: o The first drive member (1) is furthermore a bottom bracket axle (11) rotatably mounted onto the motor housing (0), either mechanically coupled or integrally performed in the same element with the sun gear (10), having both end portions (111, 112) out of the housing for coupling respective pedaling crankarms (1110, 1120); o the second drive member (2) consists of a hollow crankshaft (20) mounted onto the bottom bracket axle (11) arranged to rotate freely, at least in the forward sense, and mechanically fixed to the rotor (R1); and o the third drive member (3), concentric with the bottom bracket axis (AX0) and rotatably mounted into the motor housing (0), constitutes an output member disposing of mechanical coupling means (300) in order to drive the power output from the mid-drive motor attaching a corresponding chainring (301); • and a speed sensor (SS1) that can measure the pedaling rotational angle of the bottom bracket axle (11). A second option of a preferred embodiment of the second object of the present invention is a bi-cycloidal power-split hybrid drive for a hub-drive motor for an e-bike rear wheel, as schematically shown in FIG.8. It comprises: • An electric motor (M1), having a stator (S1) and a rotor (R1); • a stationary axle (AXL0), corresponding to the axis of a wheel (3000), that concentrically supports and fixes the motor stator (S1) located near its non-drive side; • a bi-cycloidal gear power-split mechanism (BiCy1) concentric and rotatably mounted onto the stationary axle (AXL0) and arranged to place its first end at the drive side, where: o the first drive member (1) is a hollow input axle rotatably mounted around the stationary axle (AXL0), either mechanically coupled or integrally performed in the same element with the sun gear, having coupling means at the drive side for a free-hub mechanism to be driven by a cyclist pedaling power using a sprocket (1000); o the second drive member (2) consists of a hollow crankshaft placed at the non-drive side and mounted around the stationary axle (AXL0) arranged to rotate freely, at least in the forward sense, and mechanically fixed to the rotor (R1); o the third drive member (3) is concentric with the wheel's axis and rotatably mounted onto the stationary axle (AXL0) and is either mechanically coupled or integrally performed in the same element with the hub shell of the wheel (3000); A preferred embodiment of the third object of the present invention is a powertrain with e- CVT for e-bikes, as schematically shown in FIG.10. It comprises: • A first electric motor (M1), having a first stator (S1) and a first rotor (R1), and a second electric motor (M2), having a second stator (S2) and a second rotor (R2); • a motor housing (0) to be held in a bicycle, having a bottom bracket axis (AX0), and concentrically supporting the first stator (S1) placed near its non-drive side; • a bi-cycloidal gear power-split mechanism, referred to as first bi-cycloidal gear (BiCy1), arranged concentrically with the bottom bracket axis (AX0), placing its first end pointing to the drive side, where: o its first drive member (1) is furthermore a bottom bracket axle rotatably mounted onto the motor housing, either mechanically coupled or integrally performed in the same element with the sun gear, having both ends out for coupling respective pedaling crankarms (1110, 1120); o its second drive member (2) consists of a hollow crankshaft mounted onto the bottom bracket axle arranged to rotate freely, at least in the forward sense, and mechanically fixed to the first rotor (R1); and o its third drive member (3), concentric with the bottom bracket axis (AX0) and rotatably mounted into the motor housing (0), also comprises an external teeth profile (332) which is a meshing input for receiving the torque assistance from the second electric motor, constituting the total output member, coupled to a chainring (301); • and a bi-cycloidal gear speed reducer mechanism, referred to as second bi- cycloidal gear (BiCy2), where: o its first drive member (2001) is fixed to the housing (0); o its second drive member (2002) is mechanically coupled to the second rotor (R2); and o its third drive member (2003), being the output of the second motor (M2), is connected to the said total output member by corresponding meshing gears (2300 and 332). OTHER EMBODIMENTS Concerning the above-described embodiments of the present invention, other modifications may be employed without departing from the scope of the present invention as defined by the appended claims. For example, the various components' size, shape, location, or orientation may vary. Components shown as directly connected or in contact with each other may have intermediate structures arranged between them. The functions of one element may be performed by two and vice versa. Therefore, the scope of the invention should not be limited by the specific embodiments described but by the appended claims. In an alternative embodiment of a bi-cycloidal gear mechanism, one of the first or the third drive members (2001, 2003) is either mechanically fixed or integrally performed in the same part with a housing. The resultant mechanism is a preferred bi-cycloidal gear speed reducer (BiCy2) – or multiplier in the case of the second drive member (2002) as the output–, which is optimized by having the four gears ––with Z₁, Z₃, Z_4e, and Z_4i teeth– corresponding to the first, third, and fourth drive members (2001, 2003, and 2004): • the same modulus "m" for, with ^^ ∈ [1.0, 1.6] mm, or in a more preferred option, ^^ = 1.3 ^^ ^^; and ^^· ^^ ^^ ^^ • ΔZ = Z₃ − Z_4e = Z_4i − Z₁= 1 ; and therefore, with the eccentricity ^^ = = 2 ; and • the teeth profile of the gears are involutes of the corresponding circles, which pressure angle α is between and including 30° and 40°, or in a more preferred option ^=35°; and • the outer diameter of each of the two externally toothed gears is: ^^ _^^ = ^^ · ^^ + 2 · ^^ · ^^ and the inner diameter of each of the two internally toothed gears is: ^^ _^^ = ^^ · ^^ − 2 · ^^ · ^^ where: ε ∈ [0.20, 0.35], or in a more preferred option ε = 0.275 This bi-cycloidal gear speed reducer (BiCy2) allows for improved embodiments of parallel hybrid motors for e-bikes, always having an electric motor input at its second drive member (2002). As shown in FIG.11, the first drive member (2001) is fixed in the case of a hub drive motor.

Claims

CLAIMS 1. A bi-cycloidal gear power-split mechanism comprising a first, a second, a third, and a fourth drive member, where: – The second drive member (2) consists of a crankshaft (20) that rotates around a central axis (AX0), either mechanically coupled or integrally performed in the same part with a crankpin (22) that defines an eccentric parallel axis (AX2) distanced δ from the central axis; – the fourth drive member (4) has an axis of revolution and is either mechanically coupled or integrally performed in the same element with a concentric externally toothed crown (4e) having Z4e teeth (40e) and a concentric internally toothed crown (4i) having Z4iteeth (40i), embodying a dual-crown gear which is rotatably mounted onto said crankpin (22) disposing of corresponding bearing means (242) next to the internally toothed crown (4i), being said axis of revolution coincident with said eccentric parallel axis (AX2), defining a bi-cycloidal axial orientation, hereinafter referred to as a first end, the one corresponding to said internally toothed crown side (4i), and the second end, at the bearing means (242) side; – the first drive member (1) has an axis of revolution being concentric with the central axis (AX0), is rotatably assembled with the second drive member (2), and is either mechanically coupled or integrally performed in the same part with an externally toothed sun gear (10) having Z₁ teeth (10e), which is meshing with the internally toothed crown (4i) of the fourth drive member (4); – the third drive member (3) also has an axis of revolution being concentric with the central axis (AX0), is rotatably assembled with the first and the second drive members (1 and 2), and is either mechanically coupled or integrally performed in the same part with an internally toothed ring gear (30) provided with Z3 internal teeth (30i), which is meshing with the externally toothed crown (4e) of the fourth drive member (4); wherein each of the first (1), the second (2), and the third drive member (3) respectively dispose of the corresponding mechanical coupling means (111-112, 200, and 300) as each may act as an input or as an output element.

2. The bi-cycloidal gear power-split mechanism of claim 1, wherein the second drive member is coupled to an electric machine, motor/generator.

3. The bi-cycloidal gear power-split mechanism of claim 2, wherein either the first or the third drive member (1 or 3) is driven by a human power pedaling input.

4. The bi-cycloidal gear power-split mechanism of claims 1, 2, or 3, wherein the sun gear (10), the internally toothed crown (4i), the externally toothed crown (4e), and the ring gear (30) have the same teeth modulus ^^.

5. The bi-cycloidal gear power-split mechanism of claim 4, wherein: ^^ Z₃ − Z_4e = Z_4i − Z₁ = 1 ; with ^^ = 2 6. The bi-cycloidal gear power-split mechanism of claim 5, wherein the teeth profile of said four gears (10, 30, 4i, and 4e) are involutes of the corresponding circles, which pressure angle α of between and including 30° and 40° 7. The bi-cycloidal gear power-split mechanism of claim 6, wherein: the outer diameter of each of the two externally toothed gears is: ^^ _^^ = ^^ · ^^ + 2 · ^^ · ^^ and the inner diameter of each of the two internally toothed gears is: ^^ _^^ = ^^ · ^^ − 2 · ^^ · ^^ where: ε is between and including 0.20 and 0.35 8. The bi-cycloidal gear power-split mechanism of claim 5, wherein the gear ratio crankshaft- to-Ring is between and including 20:1 and 35:1 9. The bi-cycloidal gear power-split mechanism of claim 8, wherein the ring gear's number of teeth Z3 is between and including 44 and 73 10. The bi-cycloidal gear power-split mechanism of claim 9, wherein the modulus ^^ is between and including 1.0 mm and 1.6 mm 11. A bi-cycloidal gear speed reducer or multiplier mechanism comprising a first, a second, a third, and a fourth drive member, where: – The second drive member (2002) consists of a crankshaft that rotates around a central axis, either mechanically coupled or integrally performed in the same part with a crankpin that defines an eccentric parallel axis distanced δ from the central axis; – the fourth drive member (2004) has an axis of revolution and is either mechanically coupled or integrally performed in the same element with a concentric externally toothed crown and a concentric internally toothed crown, embodying a dual-crown gear which is rotatably mounted onto said crankpin with corresponding bearing means next to the internally toothed crown, having said axis of revolution coincident with said eccentric parallel axis, defining a bi-cycloidal axial orientation, hereinafter referred to as a first end, the one corresponding to said internally toothed crown side, and the second end, at the bearing means side; – the first drive member (2001) has an axis of revolution being concentric with the central axis, is rotatably assembled with the second drive member (2002), and is either mechanically coupled or integrally performed in the same part with an externally toothed sun gear, which is meshing with the internally toothed crown of the fourth drive member (2004); – the third drive member (2003) also has an axis of revolution being concentric with the central axis, is rotatably assembled with the first and the second drive members (2001 and 2002), and is either mechanically coupled or integrally performed in the same part with an internally toothed ring gear, which is meshing with the externally toothed crown of the fourth drive member (2004); wherein: – one of the first or the third drive members (2001 or 2003) is either mechanically fixed or integrally performed in the same part with a housing, and the second drive member is coupled to an electric machine, motor/generator; and – the sun gear, the internally toothed crown, the externally toothed crown, and the ring gear have the same teeth modulus ^^; and – the eccentricity – the teeth profile of said gears are involutes of the corresponding circles, which pressure angle α of between and including 30° and 40°; and – the outer diameter of each of the two externally toothed gears is: ^^ _^^ = ^^ · ^^ + 2 · ^^ · ^^ and the inner diameter of each of the two internally toothed gears is: ^^ _^^ = ^^ · ^^ − 2 · ^^ · ^^ where ε has a value of between and including 0.20 and 0.35; and – the ring gear number of teeth is between and including 44 and 73 12. The bi-cycloidal gear speed reducer or multiplier mechanism of claim 11, wherein the modulus ^^ is between and including 1.0 mm and 1.6 mm 13. A bi-cycloidal power-split hybrid drive for a mid-drive motor for e-bikes comprising: – An electric motor (M1), having a stator (S1) and a rotor (R1); – A motor housing (0) to be held in a bicycle, having a bottom bracket axis (AX0), and concentrically supporting the motor stator (S1) placed near its non-drive side; – the bi-cycloidal gear power-split mechanism (BiCy1) of any of the claims 1 to 10, arranged concentrically with the bottom bracket axis (AX0), placing its first end pointing to the drive side, where: o The first drive member (1) is furthermore a bottom bracket axle (11) rotatably mounted onto the motor housing (0), either mechanically coupled or integrally performed in the same element with the sun gear (10), having both end portions (111, 112) out of the housing (0) for coupling respective pedaling crankarms (1110, 1120); o the second drive member (2) consists of a hollow crankshaft (20) mounted onto the bottom bracket axle (11) arranged to rotate freely, at least in the forward sense, and mechanically fixed to the rotor (R1); and o the third drive member (3), concentric with the bottom bracket axis (AX0) and rotatably mounted into the motor housing (0), constitutes an output member disposing of mechanical coupling means (300) in order to drive the power output from the mid-drive motor; – and a speed sensor (SS1) that can measure the pedaling rotational angle of the bottom bracket axle (11). 14. A bi-cycloidal power-split hybrid drive for a hub-drive motor for an e-bike rear wheel comprising: – An electric motor (M1), having a stator (S1) and a rotor (R1); – a stationary axle (AXL0), corresponding to the axis of a wheel (3000), that concentrically supports and fixes the motor stator (S1) located near its non-drive side; – the bi-cycloidal gear power-split mechanism (BiCy1) of any of the claims 1 to 10, concentric and rotatably mounted onto the stationary axle (AXL0) and arranged to place its first end at the drive side, where: o the first drive member (1) is a hollow input axle rotatably mounted around the stationary axle (AXL0), either mechanically coupled or integrally performed in the same element with the sun gear, having coupling means at the drive side for a free-hub mechanism to be driven by a cyclist pedaling power (1000); o the second drive member (2) consists of a hollow crankshaft placed at the non-drive side and mounted around the stationary axle (AXL0) arranged to rotate freely, at least in the forward sense, and mechanically fixed to the rotor (R1); o the third drive member (3) is concentric with the wheel's axis and rotatably mounted onto the stationary axle (AXL0) and is either mechanically coupled or integrally performed in the same element with the hub shell of the wheel (3000) 15. An electrically assisted bi-cycloidal powertrain with an electric continuously variable transmission, hereinafter referred to as "e-CVT" for e-bikes, combining the bi-cycloidal power-split hybrid drive for a mid-drive motor of claim 13 with a parallel hybrid drive motor. 16. The electrically assisted bi-cycloidal powertrain with an e-CVT of claim 15, comprising: – A first electric motor (M1), having a first stator (S1) and a first rotor (R1), and a second electric motor (M2), having a second stator (S2) and a second rotor (R2); – a motor housing (0) to be held in a bicycle, having a bottom bracket axis (AX0), and concentrically supporting the first stator (S1) placed near its non-drive side; – the bi-cycloidal gear power-split mechanism of any of the claims 1 to 10, referred to as the first bi-cycloidal gear (BiCy1), arranged concentrically with the bottom bracket axis (AX0), placing its first end pointing to the drive side, where: o its first drive member (1) is furthermore a bottom bracket axle rotatably mounted onto the motor housing (0), either mechanically coupled or integrally performed in the same element with the sun gear, having both end portions out for coupling respective pedaling crankarms (1110, 1120); o its second drive member (2) consists of a hollow crankshaft mounted onto the bottom bracket axle arranged to rotate freely, at least in the forward sense, and mechanically fixed to the first rotor (R1); and o its third drive member (3), concentric with the bottom bracket axis (AX0) and rotatably mounted into the motor housing (0), also comprises an external teeth profile (332) which is a meshing input for receiving the torque assistance from the second electric motor (M2), constituting the total output member; – and the bi-cycloidal gear speed reducer mechanism of claims 11 or 12, referred to as the second bi-cycloidal gear (BiCy2), where: o one of its first and third drive members (2001 or 2003) is fixed; o its second drive member (2002) is mechanically coupled to the second rotor (R2); and its third or first drive member (2003 or 2001), being the output of the second motor (M2), is connected to the said total output member by corresponding meshing gears (2300 and 332).