Power-split hybrid drive system for electric bicycles

Abstract

The bicycle electric assist drive system includes a pedal crankshaft (7) operated by a rider, a planetary gear mechanism (30) arranged to determine a gear ratio between the pedal crankshaft and an output shaft (25) for transmitting rotation to a rear wheel of the bicycle, an assist motor (M2), and a control motor (M1). The planetary gear mechanism includes a ring gear (13), a sun gear (10) fixed to rotate with the output shaft (25), planetary gears (9) provided between the sun gear (10) and the ring gear (13), and a planet carrier (6) fixed to rotate with the pedal crankshaft (7) and supporting the planetary gears (9). The assist motor (M2) has a rotor (4) drivingly connected to the sun gear (10) for driving the output shaft (25). The control motor (M1) is drivingly connected to the ring gear (13) for controlling the gear ratio between the output shaft (25) and the pedal crankshaft (7).

Description

[Technical field]

[0001] The present invention relates to the field of electric bicycles (or "e-bikes") that have an electric motor that assists the rider's pedaling force. More specifically, the present invention relates to a hybrid drivetrain for e-bikes. [Background technology]

[0002] Most of the known designs of e-bike drivelines are simple adaptations of conventional bicycle drivelines, specifically gearing, usually derailleur or hub gear systems. These systems suffer from the drawback of being less durable or efficient when exposed to the additional torque generated by the electric assist motor. Additionally, there are benefits to be gained from controlling the gear ratio between the pedals and the rear wheel. Integrating the assist motor and gear ratio control can also minimize rider demands, reduce fatigue, and reduce electricity consumption.

[0003] The power-split hybrid concept is well known in automotive engineering and has also been proposed for e-bikes in academic research, where a practical mechanical implementation of the concept is described that could potentially be packaged between the pedals of a bicycle.

[0004] To date, e-bike drivelines have used standard bicycle components. Whether the assist motor is mounted centrally in the frame or inside the wheel hub, the drive and gearing that connects the pedals to the rear wheel usually consists of a drive chain or belt and a hub-mounted gear or derailleur system to vary the gear ratio. Gear selection is usually manual and left to the rider's discretion.

[0005] There are several systems on the market that attempt to improve upon traditional driveline concepts, for example the NuVinci Continuously Variable Planetary Transmission is a hub mounted system that provides electronically shiftable, continuously variable gear ratios and can be interfaced with a controller for an electric assist motor, see WO 2005 / 019686.

[0006] The concept of hybridizing automotive powertrains (by providing an electric machine or machines coupled to an electric energy storage device) has been extensively explored in the automotive industry to realize efficiency benefits by sizing the internal combustion engine to generate only the average power required to drive the vehicle, while relying on stored energy to supplement when peak power is required (such as during acceleration or hill climbing). In particular, in the automotive industry, hybrid drive systems have successfully employed planetary gear systems to couple the internal combustion engine with two electric machines to provide a flexible and efficient hybrid driveline concept. Representative patent publications disclosing "power split" layouts include JP 09-46821 A, EP 0791495 A, and US 2004 / 00550597 A.

[0007] The objective of providing electric assistance to bicycles is very similar to the requirements for internal combustion engine hybrid vehicles, to provide only the average power required by the rider to propel the vehicle, while the electric machine assists when accelerating or climbing. The feasibility of applying the "power split" vehicle driveline concept to bicycles was academically confirmed in 2014 by Chen, Li, and Peng, and presented at the ASME Dynamic Systems and Control Conference (DSCC2014). They presented simulations and studies on the benefits of employing such a system on bicycles, especially on reducing rider fatigue.

[0008] WO 2020 / 260772 discloses a power unit for a pedal vehicle. The power unit comprises a pedal shaft, an output shaft for transmitting torque to wheels of the vehicle, a main planetary gear set arranged to control a transmission ratio between the pedal shaft and the output shaft, an assist motor connected to an assist gear of the main planetary gear set, and a control motor connected to a control gear of the main planetary gear set. The control motor and the control gear form a control assembly of the power unit. The power unit comprises a one-way clutch associated with the control assembly of the power unit and arranged to transmit rotation only in a first rotational direction.

[0009] DE 10 2017 003 945 A1 discloses an electric assisted drive system for a bicycle, comprising an assist motor, a control motor, a pedal crankshaft for operation by the rider, and a planetary gear mechanism arranged to determine a transmission ratio between the pedal crankshaft and an output shaft for transmitting rotation to the rear wheel of the bicycle. The assist motor and the control motor are designed as hollow shaft drives, each having internal teeth engaging with a corresponding planetary gear. A first set of planetary gears engaged with the assist motor has a common planetary gear with a second set of planetary gears meshing with the output shaft and a rotatably fixed sun gear. Star The third set of planetary gears includes a planet carrier and a ring gear which is rigidly connected to the planet carrier of the third set of planetary gears driven by the internal teeth of the control motor. The speed of the control motor determines the speed of the ring gear and thus the transmission ratio between the pedal crankshaft and the output shaft. Summary of the Invention

[0010] Against this background, the present invention provides an electric assisted drive system for a bicycle having the features defined in claim 1. Preferred embodiments are defined in the dependent claims.

[0011] According to one aspect, a drive system includes a pedal crankshaft for operation by a rider, a planetary gear mechanism, an assist motor, and a control motor. The planetary gear mechanism is arranged to determine a transmission ratio between the pedal crankshaft and an output shaft for transmitting rotation to a rear wheel of the bicycle. In the planetary gear mechanism, a sun gear is fixed for rotation with the output shaft, and a set of planetary gears are arranged between the sun gear and a ring gear. A planet carrier is fixed for rotation with the pedal crankshaft and supports the planetary gears. The assist motor has a rotor drivingly connected to a gear fixed to or integral with the sun gear for driving the output shaft. The control motor is drivingly connected to the ring gear for controlling the transmission ratio between the output shaft and the pedal crankshaft.

[0012] In order that the invention may be better understood, certain preferred embodiments will now be described, by way of example only, with reference to the accompanying drawings in which: [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic cross-sectional view of the main components of an e-bike drive system according to one embodiment of the present invention. [Diagram 2] FIG. 2 is an enlarged view of the mechanical layout of the electric motor and planetary gear mechanism of FIG. [Diagram 3] FIG. 3 graphically illustrates the torque division relationship by the planetary gear mechanism. [Figure 4] FIG. 4 shows the power flowing through the system during normal pedaling. [Figure 5A] FIG. 5A is a simplified diagram showing the speed relationships among the elements of the power split gear mechanism when the bicycle starts moving. [Figure 5B] FIG. 5B is a simplified diagram showing the speed relationships among the elements of the power split gear mechanism during cruising. [Figure 6] FIG. 6 is a diagram showing the power flowing through the system during regenerative braking. [Figure 7]FIG. 7 is a schematic cross-sectional view of the main components of an e-bike drive system according to an alternative embodiment of the present invention, in which the electric motor is mounted to the side of the planetary gear mechanism. [Figure 8] FIG. 8 is an enlarged cross-sectional view of a drive unit according to an alternative layout to that of FIG. [Figure 9] FIG. 9 is a cross-sectional view of one embodiment of an e-bike drive system that includes a device that provides a fixed gear ratio so that the bike can run with a dead battery. [Figure 9A] FIG. 9A is an enlarged view of the detail of FIG. 9 in one operating condition. [Figure 9B] FIG. 9B is an enlarged view of a detail of FIG. 9 in a different operating condition than FIG. 9B. [Figure 10] FIG. 10 is a cross-sectional view of one embodiment of an e-bike drive system including a mechanical freewheel device. [Figure 11] FIG. 11 is a schematic diagram of a freewheel device that can be incorporated into an e-bike drive system. [Figure 12] FIG. 11 is a schematic diagram of a different freewheel device that can be incorporated into an e-bike drive system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Referring initially to Figure 1, the e-bike drive system comprises a housing 1 which, in use, may be centrally mounted within the frame of the bicycle (the "bottom bracket"). The housing 1 contains two electric motors M1, M2 and a planetary gear mechanism 30 having an output shaft 25. A chain ring 11 which drives the rear wheel 40 of the bicycle is fixed for rotation with the output shaft 25.

[0015] The housing 1 provides mounting and reaction points for rolling bearings 19 which rotatably support the pedal crankshaft 7, and may house an electronic controller 16 for the drive system.

[0016] The electric motor M1 is referred to as the "control" motor because it drives the gears of a planetary gear mechanism which controls the transmission ratio between the output shaft and the pedal crankshaft.

[0017] Electric motor M2, referred to herein as the “assist” motor, generates power that is transmitted to output shaft 25.

[0018] In this context, the planetary gear mechanism is also referred to as a planetary "power split" gear mechanism, since it is arranged to transmit power from the pedals to the rear wheel of the bicycle in two paths, a mechanical path and an electrical path, as will be explained later in this specification. Specifically, the planetary gear mechanism transmits power from the assist motor M2 to the output shaft. Furthermore, the planetary gear mechanism regulates the rotational speed of the pedal crankshaft 7 as a result of the operation of the control motor M1.

[0019] The rotor of the control motor M1 having a fixed winding 3 is shown at 2. Preferably, the control motor M1 is an AC, brushless, synchronous motor arrangement, also known as PMSM (Permanent Magnet Synchronous Motor). The control motor may have a maximum steady power of about 150 W and a peak power of about 300 W. Incidentally, the maximum rotational speed of this motor is about 1600 rpm.

[0020] The assist motor M2 including the rotor 4 and the stationary winding 5 may also be a PMSM motor.

[0021] Preferably, the assist motor M2 has a maximum steady power output of about 250 W and a peak power output of about 500 W. The maximum rotational speed of this motor may be about 3000 rpm.

[0022] The planetary gear mechanism 30 includes a planetary carrier 6 for the planetary gears 9. The carrier 6 is connected to the pedal crank It is fixed to rotate with the shaft 7.

[0023] The torque sensor 23 is a pedal crankIt may be incorporated into the shaft 7 or planetary gear carrier 6 to sense the pedaling torque applied to the system by the rider.

[0024] pedal crank A shaft 7 passes laterally through the entire assembly and connects left and right pedal crank assemblies 8a, 8b, each of which comprises a crank arm and a pedal attached by a revolute joint in a conventional manner.

[0025] The planetary gears 9 of the power split gear mechanism 30 are mounted to the carrier 6 using bearings which allow free rotation of the gears 9 relative to the carrier 6 .

[0026] The power split planetary gear mechanism 30 comprises a sun gear 10 which is rotationally driven by the assist motor M2 and which is fixed for rotation with a chain ring 11 located on the right side of the system.

[0027] The sun gear 10 is fixed to or integral with the chainring 11 via an output shaft 25, which may be in the form of an axially extending central tubular section coaxially surrounding the length of the pedal crankshaft 7.

[0028] Furthermore, the sun gear 10 is fixed to or integral with a gear 15 so as to be drivingly connected to the rotor 4 of the assist motor M2 directly or via a set of reduction gears 14.

[0029] According to the embodiment shown in FIGS. 1 and 2, the gear 15 which receives the driving torque generated by the assist motor M2 is in the form of an internally toothed ring gear 15.

[0030] The sun gear 10, the output shaft 25, and the gear 15 that receive the driving torque of the assist motor M2 may be fixed so as to rotate together. In an embodiment, the sun gear, the output shaft 25, and the gear 15 may be integrally formed, or may be composed of separate parts that are firmly fixed to each other.

[0031] According to a preferred embodiment (e.g. as shown in Figures 1 and 2), the sun gear 10 is driven by the output shaft of the rotor 4 of the assist motor M2 via a set of reduction gears 14 acting between the output shaft 25 and the sun gear 10.

[0032] In the exemplary embodiment shown in Figure 1, the sun gear 10 may be formed with or fixed to a radial extension 24 providing a gear 15 in the form of an internally toothed outer circumferential ring gear 15 that meshes with the reduction gear 14. Conveniently, the reduction gears 14 may be mounted to rotate freely about respective fixed axial support pins integral with the housing.

[0033] The chainring 11 has a peripheral shape that allows it to drive a sprocket 18 attached to the rear wheel hub 41 of the bicycle, either through a flexible transmission means 17, such as a roller chain or a toothed polymer belt ring, and the sprocket 18. The rear wheel is designated 40. The sprocket 18 may be a freewheel or a fixed sprocket without gearing.

[0034] Preferably, the chainring / rear sprocket transmission ratio is numerically less than one.

[0035] The rotor 2 of the control motor M1 transmits drive to a ring gear 13 that meshes with planetary gears 9 (mounted on a carrier 6 fixed for rotation with the pedal crankshaft). In addition, the rotor 4 of the assist motor M2 transmits drive to a sun gear 10 via the planetary gears 9.

[0036] According to a preferred embodiment, as shown in FIG. 1, the ring gear 13 is configured to have two sets of teeth arranged to mesh with both the planetary gears 9 and a set of reduction gears 12 which are driven in mesh with the output shaft 2a of the rotor 2 of the control motor M1.

[0037] Preferably, the reduction gears 14 of the assist motor M2 are mounted for free rotation about respective fixed axle support pins integral with the housing.

[0038] According to an exemplary and particularly compact design of the embodiment shown in FIG. 1, the two sets of teeth are formed as internal teeth on the ring gear 13 .

[0039] An embodiment can provide that the toothing of the two sets of teeth on the ring gear 13 is provided on axially displaced or axially offset portions of the ring gear 13, as shown by way of example in Fig. 1. In another embodiment (not shown), it can be provided that the two sets of teeth are arranged such that one is provided on the radially inner circumferential surface of the gear ring and the other on the radially outer circumferential surface. While in the example depicted in Fig. 1 the toothing of the gear ring 13 which meshes with the reduction gear 12 is set to a larger diameter than the toothing which meshes with the planet gears 9, in another embodiment (not shown) both toothings can be provided with the same diameter or the toothing which meshes with the planet gears 9 can be provided with a larger diameter.

[0040] A number of rolling bearing elements such as 19 are included within the mechanism to support and allow rotation between the motor rotor, the planetary gear elements, and the pedal crankshaft.

[0041] A first rotation sensor, preferably an angular position sensor 21, measures the angular position of the rotor 2 of the control motor M1 relative to the housing 1. A second rotation sensor, preferably an angular position sensor 22, measures the angular position of the rotor 4 of the assist motor M2 relative to the housing 1.

[0042] The electronic controller 16 receives information about the angular positions of the control motor and the assist motor from the angular position sensors 21, 22, and the torque applied by the rider to the pedals from the torque sensor 23. Using this information, the controller 16 calculates the actual speed of the bicycle and pedals and the rider's effort, and, using a predefined control strategy, calculates the desired torque assist level and the desired speed ratio between the pedals and the bicycle wheels. The controller then commutates the currents in the windings 3, 5 of the electric motors M1, M2 according to the measured angular positions of the corresponding rotors (2, 4) to achieve the speed set point of the control motor M1 and the torque set point of the assist motor M2. The internal power circuitry within the control device 16 is arranged so that motors 1 and 2 can function both as motors and as generators, and so that power can flow in either direction between the motors and the battery 20. The battery 20 provides the electrical energy required by the rider to move the bicycle.

[0043] During riding, when torque from the pedals is applied to the planetary carrier 6, the torque is distributed to both the sun gear 10 and the ring gear 13 via the planetary gears 9. The relationship of these torques is shown in FIG. 3. The torque applied to the sun gear 10 is directly transmitted to the chain ring 11 and thus to the bicycle wheel 40 (this is the "mechanical path" described earlier in this specification). The torque applied to the ring gear 13 is transmitted to the rotor 2 of the control motor M1, which in turn generates power that is supplied to a power circuit in the electronic controller 16. This power is supplied to the assist motor M2, which has a rotor 4 connected to the sun gear 10 via a reduction gear 14, to assist in moving the bicycle. If more assistance is required, more power is supplied from the battery 20 to the assist motor M2 to increase the assist level. FIG. 4 shows the flow of power through the system during normal pedaling.

[0044] FIG. 3 shows a diagram of the torque division relationship by the planetary gear mechanism. In Figure 3, Tc = torque applied to carrier 6 Zr = radius of carrier 6 Zs = radius of planet gear 9 Fr = tangential force on ring gear 13 Fs = tangential force acting on sun gear 10 where: Fr=Fs=1 / 2×Tc / Zr Tr = Torque applied to the ring gear Tr = Fr (Zr + Zs) Ts = Torque applied to sun gear 10 Ts = Fs (Zr-Zs) It is.

[0045] With reference to FIG. 4, the power flowing through the system during normal pedaling will be described. When pedaling the bicycle normally, the control strategy of the electric motor is as follows: The electronic controller 16 varies the current through the windings of the motor M1 to maintain the requested speed, regardless of the torque applied to the control motor M1. In order to maximize the rider's comfort and minimize fatigue, the requested speed set point of this motor is selected to achieve the desired pedaling speed for the rider. To calculate the desired pedaling speed (i.e. the desired rotational speed of the planet carrier 6), it is first necessary to measure the speed of the sun gear 10. This may be directly inferred using the angular position sensor 22 for the assist motor M2. The desired speed of the ring gear 13, and therefore the speed of the control motor M1, may be calculated in real time.

[0046] The speed relationships between the elements in the power split planetary gear mechanism are given by the following equations: Ws×Zs+Wr×Zr=Wc×(Zr+Zs) Where: Ws = rotational speed of the sun gear Wc = Planet carrier rotation speed Wr = rotational speed of the ring gear and Zr and Zs are the radii of the mechanisms that define the lever ratio in the planetary gear mechanism, as illustrated in FIG.

[0047] Therefore, to achieve a desired pedaling speed Wc, the rotation speed of the motor 1 is Wm1=M1n×Wr=M1n×[Wc×(Zr+Zs)-Ws×Zs] / Zr where: Wm1 = RPM of control motor M1 M1n = Reduction gear ratio of control motor M1 It is.

[0048] The speed relationships between the planet carrier 6, the sun gear 10, and the ring gear 13 are shown in highly simplified diagrammatic form in Figures 5A and 5B. The reduction gear 14 for the control motor is not shown in these figures.

[0049] Figure 5A shows the situation when the bicycle is moving slowly. To maintain a pedaling speed that is comfortable for the rider, it is desirable for the pedals to rotate faster than the sprocket 18. The control motor M1 needs to rotate the ring gear 13 faster than the pedals to maintain the required pedaling speed.

[0050] Figure 5B shows the situation when the bicycle is cruising, i.e. moving quickly: to maintain the rider's comfort, the pedals need to rotate slower than the front chain sprocket 18. Therefore, the control motor M1 needs to rotate the ring gear 13 slower than the pedals to maintain the required pedaling speed.

[0051] Various strategies and operating modes may be employed to determine the torque set point of the assist motor M2. For example, an "assist mode" may be selected in which the control system measures the torque or power supplied to the system by the rider. The torque may be calculated in real time by measuring the torque applied by the rider using the torque transducer 23 and measuring the speed of the two motor rotors 2, 4 using the angular position sensors 21, 22. A proportional assist force may then be determined based on the desired assist level specified by the rider. Alternatively, a "maintain charge" mode may be selected in which a negative torque set point is applied to the control algorithm of the assist motor M2 in certain riding conditions, for example when riding at a constant speed on a flat or slightly downhill road gradient. By applying a negative torque set point, the assist motor M2 acts as a generator under such road conditions, and the generated energy may be stored in the battery 20 and reused when accelerating or climbing. The usable range of the electric assist system may be extended without subjecting the rider to undue fatigue.

[0052] Using the maximum speed and power characteristics of electric motor M1 and electric motor M2 proposed above, representative values ​​for the motor reduction gear ratio, planetary gear ratio, and chainring / rear sprocket ratio are as follows: Assume that the e-bike is fitted with conventional touring wheels and tires, and that the assist is limited to 25 km / h (the legal maximum speed for e-bike assist in some jurisdictions). The reduction ratio of the control motor M1 (ie, (speed of control motor M1) / (power split planetary ring gear speed)) must be in the order of fifteen. The reduction ratio of the assist motor M2 (i.e. (speed of assist motor M2) / (power split planetary sun gear speed)) must be in the order of ten. The planetary gear ratio (i.e., Zr / Zs) should be on the order of 3.5. The system ratio of a chain or belt, i.e. (number of teeth on the chainring) / (number of teeth on the sprocket), should be in the order of 0.8.

[0053] Figure 6 shows the power flow through the system when braking with a stationary pedal. When decelerating the bicycle, a different set of control strategies may be employed. It is expected that when the bicycle is decelerating, the rider will want to stop pedaling or "freewheel". This function may be achieved by controlling the speed of the control motor M1 relative to the speed of the sun gear 10 in the planetary mechanism, without the use of a specific freewheel device. Substituting the desired planet carrier speed Wc as 0 into the above equation, the speed setpoint of the control motor M1 is: Wm1 = M1n × Wr = -M1n × Ws × Zs / Zr That is, by rotating the control motor M1 in the reverse direction at an appropriate speed, the pedal speed can be controlled to 0. In this state, it is not expected that the rider will apply a large torque to the pedal, and therefore a large torque is not supplied to the control motor M1. A minimum amount of energy is required to rotate the control motor M1 at the required speed.

[0054] Additionally, if an electrical signal can be provided to the controller 16 by the bicycle's braking system (e.g., a switch mounted on the rear brake lever), a negative torque set point for the assist motor M2 can be applied to the controller, in which case the assist motor M2 acts as a generator while applying braking torque via the drive line, thereby allowing some electrical energy to be recovered and stored in the battery 20.

[0055] According to a particularly compact embodiment, the electric motors M1, M2 are axially aligned and arranged concentrically around the pedal crankshaft 7, as shown in FIG.

[0056] An alternative embodiment of the system shown diagrammatically in Figure 1 is also proposed. One alternative mechanical layout of the electric motors and power splitting planetary mechanism is shown in Figures 7 and 8, where the electric motors M1, M2 are mounted to the side of the planetary gear mechanism (instead of concentric) and the motor reduction gear is realized using spur gears instead of a planetary arrangement. This arrangement may be less compact than the concentric arrangement proposed in Figure 1, but has the advantage of a lower part count and potentially simpler motor technology, leading to a lower system cost.

[0057] In the embodiment of FIG. 8, the gear 15 driven by the rotor 4 of the assist motor M2 is an outwardly inverted toothed peripheral gear fixed or integral for rotation with the sun gear 10 and the output shaft 25.

[0058] Further embodiments are shown generally in Figures 9, 9A, 9B and 10, which disclose additional features that may be implemented in the embodiments described in Figures 1 and 2, or in the alternative embodiments described in Figures 7 and 8.

[0059] It is desirable to have an emergency mechanism that can bypass the power split planetary gear mechanism so that the bicycle can be ridden even if the battery is dead.

[0060] FIG. 9 illustrates a pedal-driven gearbox that is rotatably coupled to the output shaft 25 and selectively rotatably coupled to the planetary carrier 6, thereby allowing the output shaft 25 and the pedal crank 9 shows an exemplary arrangement of an optional coupling device 42 for fixing the shaft 7 for rotation. In the exemplary embodiment shown in FIG. 9, the coupling device 42 comprises an externally axially splined tube 42 that slides concentrically within mating splines in the tubular extension (or output shaft) 25 of the planetary sun gear 10. The tube 42 incorporates an external collar 43 that is accessible outside the assembly and is mounted to the side of the chainring 11. The tube 42 also incorporates axial teeth 44 that rotate freely when the splined tube 42 is slid into the assembly. Star 9A) the power split device is free to function, and when engaged (FIG. 9B) the motion is controlled by the pedal. crank From shaft 7, through planet carrier 6 and tube 42, power is transmitted directly to tubular output shaft (or sun gear extension) 25 and chainring 11. The bicycle can therefore be ridden with the same functionality as a conventional fixed gear bicycle, although without variable speed ratio or freewheel functionality.

[0061] Optionally, as shown in FIG. 10, the pedal crank At the connection between the shaft 7 and the planetary gear carrier 6, a mechanical "freewheel" device 46 may be introduced into the structure. This may be a "pawl and ratchet" type mechanism (FIG. 11) in which a spring-loaded pawl 47 engages an inclined feature 48 arranged around the inner (or outer) diameter. Alternatively, a "sprag clutch" type device may be used (FIG. 12), employing rolling elements 49 arranged around an inclined cylindrical device 48 and biased by a spring 50. The rolling elements 49 frictionally lock the device when the components rotate relatively in one direction, while providing free relative motion in the opposite direction. The addition of a mechanical freewheel device may increase rider safety, who may otherwise be surprised by unexpected rotation of the pedals if a failure occurs within the freewheel motor control strategy.

[0062] This drive system has the following advantages and benefits: The e-bike assist motor and the means for varying the speed ratio between the pedals and the wheel can be integrated into a single unit that is mid-mounted to the bicycle. The rear wheel of the bicycle can be completely simplified. All shifting devices (such as derailleurs or hub mounted derailleurs), gear shifting mechanisms, and freewheel devices can be removed. By removing the mass from the wheels and concentrating the mass in the center of the bicycle, stability is optimized. The drive system offers the opportunity to provide a very wide range of variable speed ratios between the pedals and the wheel within the normal riding speed range of the bicycle. No mechanical shift mechanism is required to select the gear ratio. The drive system has only one constant mesh drive train, including both transmission gears and a chain or belt drive, and therefore can be optimized for efficiency and durability. Speed ​​ratio selection and torque assist may be electronically controlled simultaneously according to an integrated overall strategy, minimizing electrical energy use and rider fatigue, optimizing range and rider comfort.

Claims

1. An electric assist drive system for a bicycle, comprising: a pedal crankshaft (7) for operation by the rider; a planetary gear mechanism (30) arranged to determine a transmission ratio between the pedal crankshaft and an output shaft (25) for transmitting rotation to a rear wheel of the bicycle, the planetary gear mechanism (30) comprising: a sun gear (10) fixed for rotation with said output shaft (25); Ring gear (13), A set of planetary gears (9) disposed between the sun gear (10) and the ring gear (13), and the planetary gear mechanism (30) comprising a planet carrier (6) fixed to rotate with the pedal crankshaft (7) and supporting the planet gears (9); an electric assist motor (M2) having a rotor (4) drivingly connected to a gear (15) fixed to or integral with the sun gear (10) for driving the output shaft (25); an electric control motor (M1) drivingly connected to the ring gear (13) for controlling the transmission ratio between the output shaft (25) and the pedal crankshaft (7); A drive system comprising:

2. The gear (15) driven by the rotor (4) of the electric assist motor (M2) is an internally toothed outer peripheral ring gear (15) fixed to or integrally provided with the sun gear (10) and the output shaft (25) so as to rotate with them, 2. The drive system according to claim 1, wherein the planetary gear mechanism (30) comprises a set of reduction gears (14) acting between the rotor (4) of the electric assist motor (M2) and the internally toothed outer ring gear (15).

3. 3. A drive system according to claim 1 or 2, wherein the output shaft (25) comprises an axially extending central tubular portion coaxially surrounding the length of the pedal crankshaft (7).

4. The ring gear (13) presents two sets of teeth, The first set of teeth is arranged to mesh with said planetary gear (9), 2. A drive system according to claim 1, wherein the second set of teeth is arranged to mesh with an additional set of planetary reduction gears (12) acting between the ring gear (13) and the rotor (2) of the electric control motor (M1).

5. A drive system as described in claim 4, wherein the first set of teeth and the second set of teeth of the ring gear (13) are provided on an axially shifted or axially offset portion of the ring gear (13).

6. a chain ring (11) integral with the output shaft (25) and having an outer peripheral shape capable of driving a sprocket (18) attached to a rear wheel hub (41) of the bicycle; 2. The drive system of claim 1, wherein the chain ring (11) and the rear sprocket (18) define a transmission ratio numerically less than one.

7. 2. A drive system according to claim 1, wherein the electric control motor and the electric assist motor (M1, M2) are axially aligned and arranged concentrically around the pedal crankshaft (7).

8. the electric control motor and the electric assist motor (M1, M2) are both arranged radially offset from the pedal crankshaft (7) or arranged outside the pedal crankshaft (7); 2. A drive system according to claim 1, wherein the electric control motor and the electric assist motor (M1, M2) each have a respective rotor (2, 4) drivingly connected with a respective single-stage spur gear arrangement for speed reduction.

9. a first rotation sensor (21) for detecting the rotation of the rotor (2) of the electric control motor (M1); a second rotation sensor (22) that detects the rotation of the rotor (4) of the electric assist motor (M2); a torque sensor (23) operatively connected to the pedal crankshaft (7) or the planet carrier (6) for detecting pedaling torque applied to the system by a rider; an electronic controller (16) electrically connected to the sensors (21, 22, 23); a rechargeable battery unit (20) electrically connected to the electronic controller (16); The drive system of claim 1 further comprising:

10. 10. The drive system of claim 9, wherein the electronic controller (16) is configured to rotate the electric assist motor (M2) in a forward direction while rotating the electric control motor (M1) in a reverse direction to rotate the gear ring (13) and the sun gear (10) in opposite directions to achieve a freewheel condition.

11. 2. The drive system of claim 1, further comprising a coupling device (42) for selectively locking the sun gear (10) and the planet carrier (6) for rotation together.

12. 2. The drive system of claim 1, further comprising a freewheel device (46) operatively connected to the pedal crankshaft (7) and the planet carrier (6).

Images