Power distribution hybrid powertrain for electric bicycle

Abstract

An electric assist drive system for a bicycle, comprising a pedal crankshaft (7) operated by a rider, an epicyclic 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, an assist motor (M2) and a control motor (M1). The epicyclic gear comprises a ring gear (13), a sun gear (10) fixed for rotation with the output shaft (25), a planet gear (9) between the sun gear (10) and the ring gear (13), and a planet carrier (6) fixed for rotation with the pedal crankshaft (7) and supporting the planet gear (9). The booster motor (M2) has a rotor (4) drivingly connected to the sun gear (10) to drive the output shaft (25). A control motor (M1) is drivingly connected to the ring gear (13) to control the transmission ratio between the output shaft (25) and the pedal crankshaft (7).

Description

Technical Field

[0001] The present invention relates to the field of electrically powered bicycles (e-bikes) having an electric motor to assist the rider's pedaling power. More particularly, the present invention relates to a hybrid powertrain for an e-bike. Background Art

[0002] Most known designs of electric bicycle transmission systems are simply adapted from conventional bicycle transmission systems, particularly the gear mechanism, which is usually a derailleur or hub gear system. These systems suffer from poor durability or inefficiency when subjected to the additional torque generated by the electric assist motor. In addition, there are benefits to controlling the transmission ratio between the pedals and the rear wheel. Integrating the control of the assist motor with the transmission ratio minimizes the demands on the rider, thereby reducing their fatigue, while also reducing power consumption.

[0003] The power-split hybrid concept is well known in automotive engineering and has also been proposed for electric bicycles in academic research. The proposal describes a practical mechanical realization of this concept, which could potentially be equipped between the pedals of a bicycle.

[0004] To this day, the drivetrain of an electric bicycle generally uses standard bicycle components. The power motor is either mounted in the center of the frame or in a wheel hub, and the drive mechanism connecting the pedals to the rear wheel and the gear mechanism usually consists of a drive chain or belt, and a gear system or derailleur system mounted on the wheel hub to change the ratio. Usually, the gear selection is manual and at the discretion of the rider.

[0005] Some systems already on the market attempt to improve upon the traditional drivetrain concept - for example the NuVinci continuously variable planetary transmission, which is a hub mounted system that provides continuously variable gear ratios and can be electronically switched, also for electric assist motors to interface with controllers. See WO 2005 / 019686 A2.

[0006] The concept of hybridization of an automotive powertrain (by providing one or more electric machines coupled to an electrical energy storage device) has been studied in great detail in the automotive industry, where efficiency advantages are achieved by sizing the internal combustion engine to produce only the average power required to drive the vehicle, while relying on stored energy to supplement when peak power is required (e.g., when accelerating or climbing a hill). Notably, in the automotive industry, hybrid drive systems have been very successfully using epicyclic gear systems to couple an internal combustion engine to two electric machines, thereby providing a flexible and efficient hybrid powertrain concept. Exemplary patent publications that disclose "power-split" arrangements are JP H0946821A, EP 0791495 A2, and US2004 / 00550597A1.

[0007] The goal of providing electric assistance to a bicycle is to allow the rider to provide only the average power needed to move the vehicle, while the electric motor provides assistance during acceleration or climbing, which is very similar to the needs of internal combustion engine hybrid vehicles. Chen, Li, and Pen academically identified the potential of applying the concept of a "power-split" vehicle driveline to bicycles in 2014 and presented it at the ASME Dynamic Systems and Control Conference (DSCC 2014). They presented simulations and research on the benefits of using such a system on a bicycle, especially in terms of reducing rider fatigue.

[0008] WO 2020 / 260772 A1 discloses a power unit for a bicycle. The power unit comprises a pedal shaft, an output shaft, a main epicyclic gear set, a power-assist motor, and a control motor, wherein the output shaft is arranged to transmit torque to a wheel, the main epicyclic gear set is arranged to control the transmission ratio between the pedal shaft and the output shaft, the power-assist motor is connected to a power-assist gear of the main epicyclic gear set, and the control motor is connected to a control gear of the main epicyclic 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, which is associated with the control assembly of the power unit and is arranged to transmit rotation only in a first rotational direction.

[0009] DE 102017003945 A1 discloses an electric auxiliary drive system for a bicycle, comprising a power-assist motor, a control motor, a pedal crankshaft, and an epicyclic gear mechanism, wherein the pedal crankshaft is operated by a rider, and the epicyclic gear mechanism is arranged to determine the transmission ratio between the pedal crankshaft and an output shaft for transmitting rotation to a rear wheel of the bicycle. The power-assist motor and the control motor are designed as hollow shaft drives, and the internal teeth engage the planetary sets of the individual epicyclic gears. The first planetary gear set engaged by the power-assist motor has a planet carrier, and the second planetary gear set also has a planet carrier engaged with a sun gear, which is fixed to rotate with an output shaft and a ring gear. This ring gear is rigidly connected to the planet carrier of a third planetary gear set driven by the internal teeth of the control motor. The speed of the control motor determines the speed of the ring gear, thereby determining the transmission ratio between the pedal crankshaft and the output shaft. Summary of the invention

[0010] Against the foregoing background, the present invention provides an electric auxiliary 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, an epicyclic gear mechanism, a power-assist motor, and a control motor, wherein the pedal crankshaft is operated by a rider. The epicyclic gear mechanism is arranged to determine a transmission ratio between the pedal crankshaft and an output shaft, and the output shaft is used to transmit rotation to a rear wheel of the bicycle. In the epicyclic gear mechanism, a sun gear is fixed to rotate with the output shaft, and a planetary gear set is arranged between the sun gear and the ring gear. A planet carrier is fixed to rotate with the pedal crankshaft and supports the planetary gears. The power-assist motor has a rotor that is drivingly fixed to a gear or integrally formed with the sun gear to drive the output shaft. The control motor is drivingly connected to the ring gear to control the transmission ratio between the output shaft and the pedal crankshaft. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In order that the present invention can be better understood, some preferred embodiments will now be described by way of example with reference to the accompanying drawings, in which:

[0013] Figure 1 A schematic cross-sectional view of the main components of an electric bicycle driving system according to one embodiment of the present invention;

[0014] Figure 2 Shows Figure 1 A close-up view of the mechanical layout of the electric motor and one epicyclic gear mechanism;

[0015] Figure 3 The torque split relationship through the epicyclic gear mechanism is schematically shown;

[0016] Figure 4 is a schematic diagram showing the flow of power through the system during normal pedaling;

[0017] Figure 5A as well as Figure 5B They are simplified schematic diagrams of the speed relationship between the components of the turnover power distribution gear mechanism when the bicycle starts and when it is running;

[0018] Figure 6 is a schematic diagram showing the flow of power through the system during regenerative braking;

[0019] Figure 7 is a schematic cross-sectional view of the main components of an electric bicycle drive system according to an alternative embodiment of the present invention, wherein the electric motor is mounted on the side of the epicyclic gear mechanism;

[0020] Figure 8 It shows that according to Figure 7 An enlarged cross-sectional view of an alternative layout of a drive unit;

[0021] Fig. 9 is a cross-sectional view of an embodiment of an electric bicycle drive system, the system including a device that provides a fixed gear ratio to allow the bicycle to be ridden without electricity (flat battery);

[0022] Fig.9A as well as Fig. 9B yes Fig. 9 Detail of the enlarged view under two different operating conditions;

[0023] Fig.10 is a cross-sectional view of an embodiment of an electric bicycle drive system including a mechanical idler device; and

[0024] Fig.11 as well as Fig.12 is a schematic diagram of two different freewheeling devices that can be incorporated into an electric bicycle drive system. DETAILED DESCRIPTION

[0025] First reference Figure 1 , an electric bicycle drive system comprises a housing 1 which, in use, can be mounted in the centre of a bicycle frame (at the "bottom bracket"). The housing 1 contains two electric motors M1, M2, and an epicyclic gear mechanism 30 having an output shaft 25. A chain ring 11 is fixed for rotation with the output shaft 25, and the chain ring 11 drives the rear wheel 40 of the bicycle.

[0026] The housing 1 provides mounting points and reaction points, rolling bearings 19 rotatably support the pedal crankshaft 7, and may also contain an electronic controller 16 for the drive system.

[0027] The electric motor M1 is called the “control” motor because it drives a gear of an epicyclic gear mechanism which controls the transmission ratio between the output shaft and the pedal crankshaft.

[0028] The electric motor M2 , referred to herein as a “boost” motor, generates power that is transmitted to the output shaft 25 .

[0029] In this document, the epicyclic gear mechanism is also referred to as a "power split" gear mechanism because it is arranged to transfer power from the pedals to the rear wheel of the bicycle via two routes, as described below: a mechanical route and an electronic route. Specifically, the epicyclic gear mechanism transfers power from the power assist motor M2 to the output shaft. In addition, the epicyclic gear mechanism regulates the rotational speed of the pedal crankshaft 7 due to the operation of the control motor M1.

[0030] 2 denotes a rotor of the control motor M1, which has a fixed winding 3. Preferably, the control motor M1 is an AC brushless synchronous motor arrangement, also known as a permanent magnet synchronous motor (PMSM). The control motor may have a maximum steady-state power of about 150 W and a peak power of about 300 W. As an indication, the maximum speed of the motor may be about 1600 rpm.

[0031] The power-assisting motor M2 includes a rotor 4 and a fixed winding 5 , and may also be a permanent magnet synchronous motor.

[0032] Preferably, the boost motor M2 has a maximum steady-state power of about 250 W, and a peak power of about 500 W. The maximum speed of this motor may be about 3000 rpm.

[0033] The epicyclic gear mechanism 30 includes a planet carrier 6 for planetary gears 9. The planet carrier 6 is fixed to rotate together with the pedal shaft 7.

[0034] A torque sensor 23 may be incorporated into the pedal shaft 7 or the planetary gear carrier 6 to detect the pedaling torque applied to the system by the rider.

[0035] The pedal shaft 7 passes through the entire assembly from side to side and connects together the left pedal crank assembly 8a and the right pedal crank assembly 8b, each of which includes a crank arm and a pedal, which is mounted on the arm in a conventional manner by a rotating joint.

[0036] The planetary gears 9 of the power distribution gear mechanism 30 are mounted on the gear carrier 6 using bearings that allow the planetary gears 9 to rotate freely relative to the gear carrier 6 .

[0037] The power distribution epicyclic gear mechanism 30 includes a sun gear 10 which is driven in rotation by the assist motor M2 and fixed in rotation by a chain ring 11 located on the right side of the system.

[0038] The sun gear 10 is fixed to or formed integrally with the chain ring 11 by an output shaft 25 which may be in the form of an axially extending central tubular portion coaxially surrounding a length of the pedal crankshaft 7 .

[0039] Furthermore, the sun gear 10 is fixed to a gear 15 or formed integrally with the gear 15 so as to be drivingly connected to the rotor 4 of the booster motor M2 directly or through a set of reduction gears 14 .

[0040] according to Figure 1 as well as Figure 2 In the embodiment shown, the gear 15 receiving the driving torque originating from the booster motor M2 is in the form of an internally toothed ring gear 15 .

[0041] The sun gear 10, the output shaft 25, and the gear 15 receiving the driving torque of the assist motor M2 may be fixed together to rotate as a unit. Embodiments may provide that the sun gear, the output shaft 25, and the gear 15 may form a single piece or consist of separate parts firmly fixed together.

[0042] According to a preferred embodiment (for example Figure 1 as well as Figure 2 As shown), the sun gear 10 is driven by the output shaft of the rotor 4 of the boost motor M2 through a set of reduction gears 14 acting between the output shaft 25 and the sun gear 10.

[0043] exist Figure 1 In the exemplary embodiment shown, the sun gear 10 may form or be fixed to a radial extension 24 which provides a gear 15 in the form of an internally toothed peripheral ring gear 15 which meshes with the reduction gear 14. Conveniently, the reduction gear 14 may be mounted so as to rotate freely about a respective stationary axial support pin formed integrally with the housing.

[0044] The chain ring 11 has a peripheral shape that allows it to drive a sprocket 18 mounted to a bicycle rear wheel hub 41 by a flexible transmission means 17, such as a roller chain, or by a toothed polymer belt ring, and sprocket 18. The rear wheel is indicated by 40. The sprocket 18 can be a fixed sprocket without any freewheel or gear device.

[0045] Preferably, the chainring / rear sprocket transmission ratio is less than 1 in value.

[0046] The rotor 2 of the control motor M1 transmits drive to a ring gear 13, which meshes with the planetary gears 9 (the planetary gears 9 are mounted on the planetary carrier 6, which is fixed to rotate with the pedal crankshaft 7). In addition, the rotor 4 of the assist motor M2 transmits drive to the sun gear 10 through the planetary gears 9.

[0047] According to a preferred embodiment, Figure 1 As shown, the ring gear 13 is configured with a dual set of teeth, which is arranged to mesh with the planetary gears 9 and a set of planetary reduction gears 12, which mesh with the output shaft 2a of the rotor 2 of the control motor M1 and are driven by the output shaft 2a of the rotor 2 of the control motor M1.

[0048] Preferably, the reduction gear 14 of the booster motor M2 is mounted so as to rotate freely about a respective stationary axial support pin integral with the housing.

[0049] according to Figure 1 In an exemplary and particularly compact design of the embodiment shown, the double set of teeth is formed as internal teeth on the ring gear 13 .

[0050] like Figure 1 As shown in the example of , an embodiment may provide that the teeth of the double set of teeth on the ring gear 13 are arranged on axially staggered or axially offset portions of the ring gear 13. An alternative embodiment (not shown) may provide that one of the double set of teeth is arranged on the radially inner surface of the ring gear and the other is arranged on the radially outer surface of the ring gear. Although in Figure 1 In the example shown, the teeth of the ring gear 13 meshing with the reduction gear 12 are arranged on a larger diameter than the teeth meshing with the planetary gears 9, alternative embodiments (not shown) may provide both teeth with the same diameter, or provide the teeth meshing with the planetary gears 9 with a wider diameter.

[0051] A plurality of rolling bearing assemblies, such as indicated generally at 19, are included within the mechanism to support and permit rotation between the motor rotor, the epicyclic gear element, and the pedal crankshaft.

[0052] 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 booster motor M2 relative to the housing 1.

[0053] An electronic controller 16 receives information about the angular position of the control and assist motors from angular position sensors 21, 22, and about the torque applied by the rider to the pedals from torque sensor 23. Using this information, the controller 16 calculates the actual speed of the bicycle and pedals and the effort expended by the rider, and uses a predetermined control strategy to calculate the required degree of torque assistance and the desired speed ratio between the pedals and the bicycle wheels. The controller thus commutates the current in the windings 3, 5 of the motors M1, M2 in accordance with the measured angular position of their respective rotors (2, 4) to achieve a speed set point for the control motor M1 and a torque set point for the assist motor M2. The internal power circuitry within the controller 16 is arranged so that the motors 1 and 2 can be used as both motors and generators, and so that power can flow in either direction between the motors and a battery 20. The battery 20 provides the necessary electrical energy to assist the rider in powering the bicycle.

[0054] During operation, when torque from the pedals is applied to the planet carrier 6, the torque is distributed to both the sun gear 10 and the ring gear 13 via the planet gears 9. The relationship between these torques is as follows: Figure 3 As shown. 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" mentioned above). The torque applied to the ring gear 13 is transmitted to the rotor 2 of the control motor M1, thereby generating electrical energy, which is supplied to the power circuit within the electronic controller 16. The electrical energy is then supplied to the power assist motor M2, the rotor 4 of which is connected to the sun gear 10 via its reduction gear 14, thus helping to power the bicycle. If additional assistance is required, additional power is provided to the power assist motor M2 from the battery 20, and the degree of assistance is increased. Figure 4 The power flow through the system during normal pedaling is shown.

[0055] Figure 3 The torque distribution relationship through the epicyclic gear mechanism is schematically shown. Figure 3 middle:

[0056] Tc = torque applied to the planet carrier 6

[0057] Zr = radius of the planet carrier 6;

[0058] Zs = radius of planetary gear 9;

[0059] Fr = tangential force applied to the ring gear 13

[0060] Fs = tangential force applied to the sun gear 10,

[0061] in:

[0062]

[0063] Tr = torque applied to the ring gear

[0064] Tr=Fr(Zr+Zs)

[0065] Ts = torque applied to the sun gear 10

[0066] Ts=Fs(Zr–Zs)

[0067] refer to Figure 4 Let's discuss the power that flows through the system during normal pedaling. When the bicycle is pedaled normally, the control strategy for the electric motor is as follows. The electronic controller 16 varies the current through the windings of the motor M1 to maintain the required speed - regardless of the torque applied to the control motor M1. The required speed set point for this motor is selected so that the rider achieves the desired pedaling speed, thereby maximizing rider comfort and minimizing fatigue. In order to calculate the required pedaling speed (i.e. the desired rotational speed of the planet carrier 6), the speed of the sun gear 10 needs to be measured first. This can be directly inferred using the angular position sensor 22 of the power assist motor M2. The desired speed of the ring gear 13, and therefore the speed of the control motor M1, can then be calculated in real time.

[0068] The speed relationship between the components within the power split epicyclic gear mechanism is given by the following equation:

[0069] Ws*Zs+Wr*Zr=Wc*(Zr+Zs)

[0070] in:

[0071] Ws = rotation speed of sun gear

[0072] Wc = planet carrier speed

[0073] Wr = the speed of the ring gear, and

[0074] Zr and Zs are the radii of the mechanism, which define the lever ratio in the epicyclic gear mechanism, such as Figure 3 As schematically described in .

[0075] Therefore, in order to achieve the desired pedaling speed Wc, the speed of motor 1 should be

[0076] Wm1=M1n*Wr=M1n*[Wc*(Zr+Zs)–Ws*Zs] / Zr

[0077] in:

[0078] Wm1=control the speed of motor M1

[0079] M1n = speed reduction ratio of control motor M1.

[0080] The speed relationship between the planet carrier 6, the sun gear 10, and the ring gear 13 is Figure 5A as well as Figure 5B The reducer 14 for controlling the motor is not shown in these figures.

[0081] Figure 5A This depicts the situation when the bicycle is moving slowly. In order to maintain a comfortable pedaling speed for the rider, it is desirable that the pedals rotate faster than the sprocket 18. The control motor M1 should rotate the ring gear 13 at a higher speed than the pedals to maintain the desired pedaling speed.

[0082] Figure 5B Describe the situation when the bicycle is moving, that is, moving quickly. In order to maintain the comfort of the rider, the pedals should rotate slower than the front sprocket 18. Therefore, the control motor M1 needs to rotate the ring gear 13 slower than the pedals to maintain the required pedaling speed.

[0083] Various strategies or operating modes can be used to determine the torque set point of the power-assist motor M2. For example, a "power-assist mode" can be selected, whereby the control system measures the torque or power provided by the rider to the system. The torque can be calculated in real time by measuring the torque applied by the rider using the torque sensor 23, and measuring the speed of the two motor rotors 2, 4 using the angular position sensors 21, 22. The proportional power-assist power can then be determined, which is based on the desired degree of power-assist specified by the rider. Alternatively, a "charge maintenance" mode can be selected, in which a negative torque set point is applied to the control algorithm of the power-assist motor M2 under certain riding conditions, such as when riding at a steady speed on a level or slightly downhill road slope. By applying a negative torque set point, the power-assist motor M2 acts as a generator under these road conditions, and the power generated can be stored by the battery 20 and then reused during acceleration or climbing. The usable range of the electric power-assist system can be extended without overly tiring the rider.

[0084] Using the proposed maximum speed and power characteristics of electric motor M1 and electric motor M2, typical values ​​for motor reduction ratios, planetary gear ratios, and chainring / rear sprocket ratios are as follows, assuming the electric bicycle is equipped with conventional touring wheels and tires, and the power assistance is limited to 25 km / h (the maximum legal speed for electric bicycle assistance in some jurisdictions):

[0085] - The reduction ratio of the control motor M1 (i.e. the speed of the control motor M1) / (speed of the power distribution planetary ring gear) should be in the order of 15;

[0086] - The reduction ratio of the booster motor M2 (i.e. the speed of the booster motor M2) / (the speed of the power distribution planetary sun gear) should be in the order of 10;

[0087] - The planetary gear ratio (i.e. Zr / Zs) should be of the order of 3.5;

[0088] - The ratio of the chain or belt system, ie (number of teeth on the chain ring) / (number of teeth on the sprocket) should be of the order of 0.8.

[0089] Figure 6 The power flow through the system is shown while braking with a stationary pedal. When decelerating a bicycle, a different set of control strategies can be employed. It is expected that when the bicycle is decelerating, the rider will want to stop pedaling the bicycle or "freewheel". This function can be achieved without the use of a specific freewheeling device by controlling the speed of the control motor M1 relative to the speed of the sun gear 10 in the planetary mechanism. By substituting a desired planet carrier speed Wc=0 into the previous equation, the speed set point of the control motor M1 is as follows:

[0090] Wm1=M1n*Wr=-M1n*Ws*Zs / Zr

[0091] That is, if the control motor M1 is rotating in the reverse direction at the appropriate speed, the pedal speed can be controlled to 0. It is expected that the rider will not apply any significant torque to the pedals in this situation, and therefore will not provide any significant torque to the control motor M1. Only minimal energy needs to be provided to the control motor M1 to rotate it at the required speed.

[0092] Additionally, if the bicycle braking system (e.g. a switch mounted on the rear brake lever) can provide an electrical signal to the controller 16, a negative torque set point can be applied to the controller of the power assist motor M2, causing it to act as a generator while applying braking torque through the drive train and thereby allowing some electrical energy to be recovered and stored in the battery 20.

[0093] According to a particularly compact embodiment, Figure 1 As shown, the electric motors M1 and M2 are axially aligned and concentrically arranged around the pedal crankshaft 7 .

[0094] Also for Figure 1 The system outlined in proposes an alternative embodiment. Figure 7 as well as Figure 8 An alternative mechanical layout of the electric motor and power distribution epicyclic mechanism is shown in FIG, in which the electric motors M1 and M2 are mounted on the sides of the epicyclic gear mechanism (rather than being concentrically coupled), and the motor reduction gearing is implemented using spur gears rather than an epicyclic arrangement. This arrangement may not be as good as Figure 1 The concentric arrangement proposed in is compact, however the benefit is a reduced number of parts and potentially simpler motor technology, which may result in lower system cost.

[0095] exist Figure 8 In the embodiment of FIG. 1 , the gear 15 driven by the rotor 4 of the booster motor M2 is an externally toothed peripheral gear which is fixed for rotation or formed integrally with the sun gear 10 and the output shaft 25 .

[0096] Fig. 9 , Fig.9A , Fig. 9B ,as well as Fig.10 A further embodiment is schematically shown, which discloses that Figure 1 as well as Figure 2 The embodiments described in Figure 7 as well as Figure 8 Any additional features implemented in the alternative embodiments described in.

[0097] In order to allow the bicycle to be ridden when the battery is dead, it may be necessary to provide an emergency mechanism that allows the power distribution epicyclic gear mechanism to be bypassed.

[0098] Fig. 9 An exemplary arrangement of an optional coupling device 42 is shown, which is coupled to rotate with the output shaft 25 and can be selectively coupled to rotate with the planet carrier 6, thereby fixing the rotation of the output shaft 25 and the pedal shaft 7. Fig. 9 In the exemplary embodiment shown, the coupling device 42 includes an external axial keyway tube 42 that slides concentrically within a mating keyway in the tubular extension (or output shaft) 25 of the epicyclic sun gear 10. The tube 42 includes an external collar 43 that is accessible from the outside of the assembly on one side of the chain ring 11. The tube 42 also includes axial teeth 44 that engage mating axial features, such as axial seats or grooves 45 formed in the planetary gear carrier 6, when the keyway tube 42 is slid into the assembly. These axial engaging features perform the function of a "bite clutch". When disengaged ( Fig.9A ), the power distribution device can act freely; when engaged ( Fig. 9B ), motion is transmitted directly from the pedal shaft 7 to the tubular output shaft (or sun gear extension) 25 and chain ring 11 via the planet carrier 6 and tube 42. Thus, although no variable speed ratio or freewheeling function is available, the same functionality as a conventional fixed gear bicycle is achieved when riding the bicycle.

[0099] Optionally, a mechanical "idle motion" device 46 may be introduced into the structure, at the connection between the pedal shaft 7 and the planetary gear carrier 6, such as Fig.10 This device can be a "pawl and ratchet" type mechanism ( Fig.11) where a spring loaded pawl 47 engages with an inclined form 48 arranged around the inner (or outer) diameter. Alternatively, a "sprag clutch" type device may be used ( Fig.12 ), which employs rolling elements 49 arranged around an inclined cylindrical device 48 and biased by a spring 50. The rolling elements 49 frictionally lock the devices when the components rotate relative to each other in one direction and provide free relative movement in the opposite direction. Adding a mechanical lost motion device can improve rider safety, otherwise the rider may be surprised by unexpected rotation of the pedals if the lost motion motor control strategy fails.

[0100] It can be appreciated that the following advantages and benefits of the present drive system are:

[0101] - The electric bicycle power assist motor and the device for changing the speed ratio between the pedals and the wheel can be integrated into a single unit mounted in the center of the bicycle;

[0102] -The rear wheel of the bicycle can be completely simplified;

[0103] - All devices required for shifting gears (e.g., derailleurs or hub-mounted gearboxes), shifting mechanisms, and freewheeling devices are removed; the removal of wheel weight and the centralization of weight in the center of the bicycle optimize stability;

[0104] - the drive system gives the opportunity to provide a very wide range of speed ratios between the pedals and the wheels within the normal operating speed range of the bicycle;

[0105] - No mechanical switching gear mechanism required to select speed ratios;

[0106] - The drive system has only one continuously meshed transmission system, including a transmission gear mechanism and a chain or belt drive; therefore, the drive system can be optimized for efficiency and durability;

[0107] - Speed ​​ratio selection and torque assistance are electronically controlled simultaneously according to a comprehensive overall strategy: this has the potential to minimise electric energy use and rider fatigue, and optimise range and rider comfort.

Claims

1. An electric auxiliary drive system for an electric bicycle, comprising: a pedal crank (7) operated by the rider; An epicyclic gear mechanism (30) arranged to determine a transmission ratio between the pedal crankshaft and an output shaft (25) for transmitting rotation to the rear wheel of the bicycle, the epicyclic gear comprising: a sun gear (10) fixed to rotate together with the output shaft (25); Ring gear (13); a planetary gear set (9) between the sun gear (10) and the ring gear (13); and a planet carrier (6) fixed to rotate together with the pedal crankshaft (7) and supporting the planetary gear (9); a booster motor (M2) having a rotor (4) drivingly connected to a gear (15) fixed to or integrally formed with the sun gear (10) to drive the output shaft (25); A control motor (M1) is drivingly connected to the ring gear (13) to control the transmission ratio between the output shaft (25) and the pedal crankshaft (7).

2. The drive system according to claim 1, wherein The gear (15) driven by the rotor (4) of the booster motor (M2) is an internally toothed peripheral ring gear (15) fixed for rotation or integrally formed with the sun gear (10) and the output shaft (25), and The epicyclic gear mechanism (30) comprises a reduction gear set (14) acting between the rotor (4) of the booster motor (M2) and the internally toothed peripheral ring gear (15).

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. A drive system according to any one of claims 1 to 3, wherein the ring gear (13) is provided with a double set of teeth, wherein The first set of teeth is arranged to mesh with the planetary gears (9), and The second set of teeth is arranged to mesh with another set of planetary reduction gears (12) acting between the ring gear (13) and the rotor (2) of the control motor (M1).

5. The drive system according to claim 4, wherein the first set of teeth and the second set of teeth on the ring gear (13) are arranged on axially staggered or axially offset portions of the ring gear (13).

6. A drive system according to any one of the preceding claims, comprising a chain ring (11) integrally formed with the output shaft (25) and having a peripheral shape allowing it to drive a sprocket (18) fitted to the rear wheel hub (41) of the bicycle, whereby the chain ring (11) and the sprocket (18) of the rear wheel define a transmission ratio numerically less than 1.

7. Drive system according to any of the preceding claims, wherein the electric motors (M1, M2) are axially aligned and concentrically arranged around the pedal crankshaft (7).

8. A drive system according to any one of claims 1 to 6, wherein the electric motors (M1, M2) are arranged radially offset or outside the pedal crankshaft (7), and each of the motors (M1, M2) has its own rotor (2, 4), and the rotor (2, 4) is drive-connected to a corresponding single-stage spur gear arrangement for speed reduction.

9. A drive system according to any one of the preceding claims, further comprising: A first rotation sensor (21) for sensing the rotation of a rotor (2) of the control motor (M1); a second rotation sensor (22) for sensing the rotation of the rotor (4) of the booster motor (M2); a torque sensor (23) operably connected to the pedal crankshaft (7) or the planetary gear carrier (6) to detect the pedaling torque applied to the system by the rider; an electronic controller (16) electrically connected to the sensors (21, 22, 23); A rechargeable battery unit (20) is electrically connected to the electronic controller (16).

10. The drive system according to claim 9, wherein the electronic controller (16) is configured to rotate the power assist motor (M2) in the forward direction and simultaneously rotate the control motor (M1) in the reverse direction to rotate the ring gear (13) and the sun gear (10) in the reverse direction to achieve an idling state.

11. The drive system according to any of the preceding claims, further comprising a coupling device (42) for selectively locking the sun gear (10) in rotation with the planet carrier (6).

12. The drive system according to any of the preceding claims, further comprising an idler device (46) operatively connected to the pedal crankshaft (7) and the planetary gear carrier (6).

Images