Power-split hybrid driveline for electric bicycles that allows the assist power to be turned off

Abstract

The bicycle electric assist drive system includes a pedal crankshaft (1), a planetary gear mechanism (20), an assist motor (M2) that drives an output shaft (21), and a control motor (M1) that controls the transmission ratio between the pedal crankshaft (1) and the output shaft (21) via the planetary gear mechanism. The planetary gear mechanism (20) further includes a first sun gear (5a) and a second sun gear (5b) that are fixed to rotate together with the output shaft (21). A planet carrier (2) is fixed to rotate together with the pedal crankshaft (1) and supports a first planetary gear set (3a) between the first sun gear (5a) and a first ring gear (4). The planet carrier (2) also supports a second planetary gear set (3b) between the second sun gear (5b) and a second ring gear (16). The locking device (17) is operable to prevent rotation of the second ring gear (16), thereby allowing the rider to push the bicycle beyond a preset speed limit while pedaling at a comfortable rotational speed using only their own mechanical power without receiving power assistance. [Reference diagram] Figure 1

Description

[Technical Field]

[0001] The present invention relates to the field of electric bicycles ("e-bikes"), where an electric motor assists the rider's pedaling power. More specifically, the present invention relates to a power-split hybrid driveline for an electric bicycle that allows for the assist power to be turned off. [Background technology]

[0002] Recently, power-split hybrid drivelines have been proposed for electric bicycles. These systems include a rider-operated pedal crankshaft, a planetary gear mechanism, an assist motor, and a control motor. The planetary gear mechanism is configured to determine the transmission ratio between the pedal crankshaft and an output shaft that transmits rotation to the bicycle's rear wheel. Because the planetary gear mechanism is configured to transmit power from the pedals to the bicycle's rear wheel via two paths, a mechanical path and an electrical path, it is called a planetary "power-split" gear mechanism. Specifically, the planetary gear mechanism transmits power from the assist motor to the output shaft. Furthermore, the planetary gear mechanism adjusts the rotational speed of the pedal crankshaft in response to the operation of the control motor.

[0003] The planetary gear hybrid driveline of this disclosure relates to a so-called "I2" planetary gear driveline layout for electric bicycles. In such a layout, the pedals are connected to a planet carrier, and the chainring driving the rear wheel is connected to a sun gear assisted by a traction or assist motor. A gear ratio control motor is connected to the ring gear of the planetary gear mechanism and controls the transmission ratio between the pedal crankshaft and the output shaft. As the bicycle speed increases, the gear ratio control motor assists and increases the overall gear ratio value, maintaining the pedal rotational speed (i.e., the rotational speed of the pedal shaft) at a comfortable speed for the rider.

[0004] One of the latest power-split hybrid drivelines for electric bicycles (Italian Patent Application No. 102022000009794, filed May 12, 2022, by the same applicant and not yet published as of the filing date of this application) provides an electric assist drive system including a pedal crankshaft, a planetary gear mechanism, an assist motor driving an output shaft, and a control motor controlling the transmission ratio between the pedal crankshaft and the output shaft via the planetary gear mechanism. A first one-way clutch operatively connected to the control motor is configured to prevent forward rotation of a ring gear of the planetary gear mechanism while allowing reverse rotation. A second one-way clutch is configured to drivingly connect the assist motor to the output shaft when the assist motor is on and to disconnect the assist motor from the output shaft when the assist motor is off and the output shaft continues to rotate in the forward direction.

[0005] In the drive system described above, the pedal shaft drives a planetary carrier equipped with planetary gears, which mesh with an outer ring gear driven by a gear ratio control motor. The sun gear is connected to a chain gear and a traction gear, which is fixed to rotate with the chain gear and planetary carrier. The chain gear is driven by a traction motor M2. A one-way clutch is connected to the gear ratio control motor, allowing the ring gear to rotate in only one direction. The gear ratio between the pedal crankshaft and the output shaft is determined by the gears in the planetary gear system. When the rider begins pedaling at a low speed, the planetary gears are pressed against the ring gear. Because the ring gear is fixed by the one-way clutch, the lowest gear ratio is achieved. As the bicycle speed increases, the gear ratio control motor begins to rotate, causing the ring gear to rotate in the reverse direction. This reduces the pedal rotation speed relative to the sun gear via the planetary gears, allowing the bicycle to maintain a comfortable gear ratio.

[0006] European regulations (European Standard EN 15194: 2017 for Electrically Assisted Bicycles) require that the electric assistance be stopped above a certain speed (25 km / h) in order to limit the potential speed of the bicycle and reduce the safety risks associated with operating this type of vehicle.

[0007] Some current I2 epicycloidal drivelines have a limitation: once the bicycle exceeds a predetermined speed, i.e., 25 km / h, the electric motor automatically shuts off, preventing the rider from pedaling comfortably. In current I2 layouts, torque from the pedals always acts on the gear ratio control motor. As the bicycle's speed increases, the gear ratio control motor increases speed to maintain a pedaling speed that is comfortable for the rider. Thus, the gear ratio control motor provides significant mechanical power to the system, assisting the bicycle's forward movement. When the gear ratio control motor is turned off to satisfy the legal requirement to disengage the electric assist, the motor torque, which counteracts the rider's pedaling effort, is removed. As a result, the bicycle's pedals spin, preventing the rider from continuing to pedal. Summary of the Invention

[0008] The object of the present invention is to enable a rider to pedal a bicycle at a comfortable speed using only their own power, without receiving electric assistance, and at a speed exceeding a preset speed limit (e.g., 25 km / h).

[0009] Based on the above 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.

[0010] According to one aspect, the present invention provides an electric assist drive system for a bicycle, comprising: a pedal crankshaft operated by a rider; an output shaft for transmitting rotation to a rear wheel of the bicycle; a planetary gear mechanism arranged to determine a transmission ratio between the pedal crankshaft and the output shaft; an assist motor for driving the output shaft; a control motor drivingly connected to the planetary gear mechanism and controlling the transmission ratio between the pedal crankshaft and the output shaft via the planetary gear mechanism; and at least one first one-way clutch operatively connected between the control motor and a rigid element fixedly mountable to a bicycle frame. The first one-way clutch is configured to lock a first ring gear of the planetary gear mechanism against a first forward rotation and to release a second reverse rotation, allowing free rotation of the first ring gear of the planetary gear mechanism. The second one-way clutch is operatively connected between the assist motor and the output shaft (21) and is configured to drivingly connect the assist motor to the output shaft to assist forward movement of the bicycle when the assist motor is turned on and driving the output shaft in a forward direction, and to disconnect the assist motor from the output shaft so that the output shaft continues to rotate in a forward direction when the assist motor is turned off. The planetary gear mechanism further includes a second ring gear and an associated locking device (17) fixedly mounted to the bicycle frame and operable to allow and lock rotation of the second ring gear, first and second sun gears fixed for rotation with the output shaft, a first planetary gear set disposed between the first sun gear and the first ring gear, a second planetary gear set disposed between the second sun gear and the second ring gear, and a planet carrier fixed for rotation with the pedal crankshaft and supporting the first and second planetary gear sets. The first and second sun gears and the first and second planetary gear groups are configured to provide a desired transmission ratio between the pedal crankshaft and the output shaft and transmit rotation to the rear wheel of the bicycle when rotation of the second ring gear is locked by the locking device.

[0011] According to another aspect, the present invention provides an electric bicycle comprising a drive system as defined in the accompanying claims. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic cross-sectional view of the main components of an electric bicycle drive system according to one embodiment of the present invention. [Figure 2] FIG. 2 shows a schematic of the torque distribution relationship through the planetary gear mechanism. [Figure 3] Figure 3 shows a schematic of the power flow in the system during different stages of bicycle acceleration. [Figure 4] Figure 4 shows a schematic of the power flow in the system during different stages of bicycle acceleration. [Figure 5] Figure 5 shows a schematic of the power flow in the system during different stages of bicycle acceleration. [Figure 6] Figure 6 shows a schematic of the power flow in the system during different stages of bicycle acceleration. [Figure 7] FIG. 7 is a schematic cross-sectional view of the main components of an electric bicycle drive system according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] For a better understanding of the present invention, some preferred embodiments of the invention will be illustrated with reference to the accompanying drawings. Referring first to Figure 1, the drive system of an electric bicycle comprises two electric motors M1, M2 and a planetary gear mechanism 20 having an output shaft 21. Fixed for rotation with the output shaft 21 is a chain ring 6 which drives the rear wheel (not shown) of the bicycle.

[0014] Reference numeral 1 denotes the pedal shaft or crank shaft operated by the rider R. The pedal shaft 1 passes through the assembly and connects to two conventional pedal crank and foot support assemblies (not shown) mounted on the outside of the drive unit. The pedal shaft 1 receives the torque and speed supplied by the rider and transmits it to the planet carrier 2.

[0015] The electric motor M1 is called the "control" motor or "ratio-controlled" motor because it drives the gears of a planetary gear mechanism that controls the transmission ratio between the output shaft and the pedal crankshaft.

[0016] Electric motor M2, referred to herein as the "assist" motor (or "traction" motor), generates power that is transmitted to output shaft 21 to propel the electric bicycle forward.

[0017] In this context, the planetary gear mechanism is also referred to as a "planetary power split" gear mechanism because it is configured to transmit power from the pedals to the rear wheel of the bicycle via two paths: a mechanical path MR and an electrical path ER, as described below. Specifically, the assist motor M2 transmits power to the output shaft. Furthermore, the planetary gear mechanism adjusts the rotational speed of the pedal crankshaft 1 based on the operation of the control motor M1.

[0018] The electric bicycle drive system is preferably contained in a housing (not shown) which, in use, is mounted in the centre of the bicycle frame (the "bottom bracket"). Typically, the housing includes a mounting and reaction point with rolling bearings that rotatably support the pedal crankshaft 1. The housing may also include an electronic control unit C (see Figure 3) for the drive system.

[0019] The planetary gear mechanism 20 comprises a planet carrier 2 which supports two sets of planet gears, a first planetary gear set 3a and a secondary planetary gear set 3b, and transmits the torque and speed of the rider to the planetary gear mechanism.

[0020] The planetary carrier 2 is rotatably fixed to the pedal shaft 1. The pedal shaft 1 receives torque and rotational speed supplied by the rider and transmits them to the planetary carrier 2.

[0021] The power split planetary gear mechanism includes a first sun gear 5a and a second sun gear 5b that are integrated with the chain ring 6 and the output shaft 21. The first sun gear 5a and the second sun gear 5b are rotationally driven by an assist motor M2 via a traction gear 8 that is rotatably fixed to the sun gears 5a, 5b and the chain ring 6.

[0022] The first sun gear 5a has external teeth that mesh with the first planetary gear set 3a, and the second sun gear 5b has external teeth that mesh with the second planetary gears 3b.

[0023] As will be explained below, in a preferred embodiment such as the example shown in FIG. 1, the first planetary gear set 3a is smaller, i.e. has a smaller diameter, than the second auxiliary planetary gear set 3b.

[0024] In the exemplary embodiment shown in FIG. 1, the first sun gear 5a has a larger diameter than the second sun gear 5b.

[0025] The first ring gear 4 has internal teeth that mesh with the first planetary gear set 3a, and external teeth that mesh with a pinion gear 9 that is directly driven by the speed ratio control motor M1.

[0026] Because the first planetary gear set 3a rotates freely relative to the planet carrier 2, it exerts equal tangential forces on the first ring gear 4 and the first sun gear 5a, regardless of the relative speeds of these parts. Thus, a certain percentage of the torque from the rider is distributed to the ring gear 4, and the remaining percentage of the torque from the rider is distributed to the sun gear 5a.

[0027] The second ring gear 16 has internal teeth that mesh with the second planetary gear set 3b.

[0028] According to the exemplary embodiment of FIG. 1, the second planetary gear set 3b may be supported about the same axis and at the same radius as the first planetary gear set 3a.

[0029] According to an alternative embodiment (not shown), the second planetary gear set 3b may be attached to the planet carrier 2 by means of another set of mounting pins mounted at a different radius. Thus, the geometries of the planetary gear subsystem comprising parts 3a, 4 and 5a and the planetary gear subsystem comprising parts 3b, 5b and 16 do not necessarily have to be in a fixed relationship.

[0030] A locking device 17 is mounted on the bicycle frame 22 or a rigid element secured thereto. The locking device 17 is operable to engage and stop rotation of the second ring gear 16. For example, the locking device 17 may be configured as an electromagnetically actuated clutch, such as an electromagnetic pin that can extend into or engage a corresponding locking seat, such as an opening or recess formed in the second ring gear 16.

[0031] The output shaft 21 may be a hollow tubular shaft through which the pedal shaft 1 passes.

[0032] A chain or belt sprocket 6 drives a chain or toothed belt 7 which drives the rear wheel of the bicycle.

[0033] The traction gear 8 has external teeth that mesh with a second pinion gear 11 that is directly driven by the assist motor M2.

[0034] The first one-way clutch 10 may be arranged to releasably connect the shaft S1 of the ratio control motor M1 to a rigid element 22 fixed to or integrated in the bicycle frame. Preferably, the rigid fixed element 22 may be the housing of the drive unit.

[0035] The purpose of the first one-way clutch 10 is to prevent the first ring gear 4 from rotating in the forward direction (i.e., the direction in which the pedals, chain, and wheel rotate when the bicycle is moving forward) and to allow the first ring gear 4 to rotate in the reverse direction.

[0036] An auxiliary one-way clutch 19 can be arranged between the pinion gear 9 and the shaft S1 of the control motor M1.

[0037] The purpose of the auxiliary one-way clutch 19 is to lock the rotation of the first ring gear 4 and counteract the rider's torque acting on the first ring gear 4 when the control motor M1 is attempting to drive the first ring gear 4 in the reverse direction. As will be described below, the auxiliary one-way clutch 19 allows the first ring gear 4 to rotate freely when the first ring gear continues to rotate in the reverse direction even though the power to the control motor M1 is turned off.

[0038] The second pinion gear 11 is connected to the shaft S2 of the assist motor M2 via a second one-way clutch 12. The second pinion gear 11 meshes with the traction gear 8, and the assist motor M2 assists in moving the bicycle forward.

[0039] The second one-way clutch 12, which connects the assist motor M2 and its pinion gear 11, is positioned to engage when the assist motor M2 is attempting to drive the traction gear 8 forward, thereby assisting the bicycle in moving forward. The second one-way clutch 12 allows the traction gear 8 to rotate freely when the assist motor M2 is turned off but the traction gear 8 continues to rotate forward.

[0040] The one-way clutches 10, 12, 19 may take the form of, for example, a pawl and ratchet, a sprag clutch with rollers that climb an inclined surface in a cage, or a belt or strap wrapped around a shaft.

[0041] With the above configuration, the control motor M1 controls the ratio of the pedal speed to the bicycle speed p by controlling the speed of the first ring gear 4. The assist motor M2 drives the traction gear 8 to apply torque to the chain gear 6, assisting the bicycle in moving forward.

[0042] The electric bicycle drive system described above functions as follows: When the bicycle starts moving from a standstill, the rider applies torque to the system via the pedals. This torque is transmitted to the system via the pedal shaft 1, the planet carrier 2, and the planetary gear set 3a. The planetary gears then distribute this applied torque between the first ring gear 4 and the sun gear 5a.

[0043] The torque distribution between the ring gear and the sun gear is shown diagrammatically in Figure 2, where: Tc = Torque acting on planet carrier 2 Zr = radius of planet carrier 2 Zs = radius of planetary gear set 3a Fr = tangential force acting on the first ring gear 4 Fs = tangential force acting on sun gear 5a Then, Fr=Fs=1 / 2*Tc / Zr where: Tr = Torque acting on the ring gear: Tr = Fr * (Zr + Zs) Ts = Torque acting on the sun gear: Ts = Fs * (Zr - Zs) is.

[0044] First, from a stationary state (Fig. 3), the control motor M1 is turned off. A torque Tr acts on the first ring gear 4 in the forward direction, but the first one-way clutch 10 is arranged to prevent the first ring gear 4 from rotating in the forward direction. Therefore, the torque Tr is reacted by the first one-way clutch 10, and the first ring gear 4 remains stationary. All of the power supplied by the rider R is transmitted to the sun gear 5a, and then to the bicycle wheel via the chain gear 6 and the chain or belt 7. The gear ratio between the bicycle pedals and wheel is expressed as follows: Overall gear ratio = (bicycle wheel rotation speed) / (pedal rotation speed)

[0045] The first one-way clutch 10 allows the first ring gear 4 to rotate in the reverse direction but not in the forward direction. Therefore, the overall gear ratio is lowest when the first ring gear 4 is stationary. The ratio between the planetary gear system and the chain or belt can be adjusted so that the ratio when the first ring gear is stationary is appropriate for starting the bicycle or climbing steep hills. For reference, for touring bikes and commuter bikes, this minimum ratio is approximately 1:1. This means that one rotation of the pedals results in approximately one rotation of the rear wheel. This transmission ratio is achieved by setting the number of teeth and diameter of the gears in the planetary gear system.

[0046] When starting off (Figure 3), traction motor M2 receives power from battery B via controller C to assist the rider in propelling the bicycle forward. Traction motor M2 applies torque through second one-way clutch 12 and pinion gear 11 to move traction gear 8 in the forward direction, thereby assisting the bicycle in accelerating forward. Second one-way clutch 12 is arranged to be locked when traction motor M2 is applying torque to traction gear 8 in the forward direction.

[0047] As the bicycle begins to accelerate, the overall gear ratio must be increased to maintain a pedal rotational speed (i.e., the rotational speed of the pedal shaft 1) that is comfortable for the rider. This is achieved by energizing the control motor M1 (Figure 4) to rotate the ring gear 4 in the reverse direction. This action unlocks the first one-way clutch 10, which is positioned to allow free rotation of the ring gear 4 in the reverse direction. The speed of the control motor M1 is controlled to maintain the desired ring gear speed (Wr), which is given by:

[0048] Wr=(Wcx(Zr+Zs)-WsxZs) / Zr where: Wc = desired rotational speed of pedal shaft 1 Ws = rotational speed of sun gear 5 Wr = required rotation speed of ring gear 4 Zr and Zs are the system radii that define the leverage ratio within the planetary gear mechanism, as shown in Figure 2.

[0049] In accordance with the law of conservation of energy, the mechanical power provided by the control motor M1 supplements the mechanical power provided by the traction motor M2 to assist the rider in propelling the bicycle forward.

[0050] As the control motor M1 begins to increase in speed, it begins to supply mechanical power to the system to maintain a comfortable pedaling speed.

[0051] Power M1 =Wr*Tr where Tr is the torque applied to the ring gear 4 to counteract the rider's pedaling torque (see FIG. 2).

[0052] Because the locking device 17 remains de-energized, the second ring gear 16 rotates freely and torque is not transmitted to the auxiliary sun gear 5b via the planetary gear. However, because the first ring gear 4 rotates in the reverse direction, the speed difference between the auxiliary sun gear 5b and the planetary carrier 2 increases. As a result, the second ring gear 16 continues to move forward, but at a reduced speed.

[0053] As the bicycle's speed increases further, the torque Tr applied by the rider tends to remain approximately constant, while the speed of the control motor M1 continues to increase to maintain a comfortable pedaling speed, thus increasing the power output of the control motor M1. At some point, which can be set by programming the controller C, the power output PowerM1 of the control motor M1 becomes sufficient to provide the desired electric assist force to the bicycle, and further assistance from the traction motor M2 is no longer required. To conserve electrical energy, the traction motor M2 can then be turned off (Figure 5). The bicycle continues to move forward thanks to the power output from the rider and the gear ratio control motor M1, resulting in the traction gear 8 continuing to rotate in the forward direction. However, because the traction motor M2 is no longer applying forward torque to the traction gear 8, the second one-way clutch 12 is unlocked, allowing the pinion gear 11 to rotate freely relative to the shaft of the traction motor M2. Therefore, the traction motor M2 is at a standstill and does not transmit any deceleration torque to the traction gear 8, and thus to the bicycle wheel.

[0054] Because the locking device 17 remains de-energized, the second ring gear 16 rotates freely and torque is not transmitted to the auxiliary sun gear 5b via the planetary gear. However, the reverse rotation speed of the first ring gear 4 further increases, further increasing the speed difference between the auxiliary sun gear 5b and the planetary gear carrier 2. Therefore, the second ring gear 16 continues to rotate in the forward direction, but its speed further decreases.

[0055] The auxiliary planetary gear subsystem, consisting of the second sun gear 5b and its corresponding second planetary gear 3b, can be advantageously configured to achieve a desired speed ratio between the associated components of the system.

[0056] Specifically, in a preferred embodiment, as shown schematically in FIG. 1, the diameter of the second sun gear 5b is smaller than the diameter of the first sun gear 5a, and the diameter of the second planetary gear 3b is larger than the diameter of the planet of the first planetary gear 3a.

[0057] In this case, when the second ring gear 16 is stationary, the gear ratio through the auxiliary planetary gear subsystem is preferably such that a comfortable pedaling speed is possible when the bicycle is traveling at the legal maximum assist speed. For example, an overall gear ratio of 3.5 would ensure a pedaling speed of approximately 60 rpm when the bicycle is traveling at the European legal maximum assist speed of 25 km / h.

[0058] Therefore, when the bicycle approaches the legal maximum assist speed, the locking device 17 remains de-energized, the second ring gear 16 rotates freely, and no torque is transmitted via the planet to the second or auxiliary sun gear 5b.

[0059] However, due to the gear ratio of the auxiliary planetary gear mechanism, the second ring gear 16 will stop when the bicycle's traveling speed reaches 25 km / h. To ensure that the second ring gear 16 stops rotating smoothly, for example, the pedaling speed is slightly adjusted by controlling the speed of the control motor M1, thereby creating an appropriate relationship between the bicycle's traveling speed and the pedal speed, thereby ensuring that the second ring gear stops completely.

[0060] When the traveling speed of the bicycle exceeds the legal maximum assist speed (usually 25 km / h) and the second ring gear 16 stops rotating completely, the controller C activates the locking device 17 to lock the angular position of the second ring gear 16 and prevent it from rotating. For example, the electromagnetic device includes a solenoid that is energized by the controller C.

[0061] By operating the locking device 17 and locking the second ring gear 16, an auxiliary torque path from the pedal shaft 1 to the chain gear 6 is formed throughout the system, and the overall gear ratio between the pedal shaft and the rear wheel of the bicycle is constant. For example, a suitable gear ratio between the pedal shaft and the rear wheel of the bicycle is in the range of 1:3 to 1:4. In particular, a comfortable gear ratio between the pedal shaft and the rear wheel of the bicycle is approximately 1:3.5.

[0062] The main planetary gear mechanism (first sun gear 5a, first planetary gears 5a, and first outer ring 4) continues to rotate, and power assist by motor M1 continues to be provided, supplying an assist torque that rotates the first ring gear 4 in the reverse direction. However, because the pedal-to-wheel speed ratio is fixed, the torque supplied by control motor M1 is gradually reduced to provide a smooth transition to turning the bicycle's power assist off.

[0063] When the bicycle's traveling speed reaches the legal maximum assist speed (Figure 6), the control motor M1 is completely turned off, thus removing all power assistance from the e-bike's driveline system and making the bicycle legally compliant.

[0064] The planetary gear mechanism (particularly the first sun gear 5a, first planetary gear set 3a, and first ring gear 4) continues to rotate, but the one-way clutch 19 connecting the pinion gear 9 to the shaft S1 of the control motor M1 is disengaged because the control motor M1 no longer applies torque in the direction that assists the reverse rotation of the first ring gear 4 through the clutch. The control motor M1 is therefore stopped, and the first ring gear 4 and pinion gear 9 continue to rotate freely. Therefore, the control motor M1 does not provide regenerative or braking torque to the system. The bicycle moves forward solely through the force generated by the rider's pedaling action. The torque of the pedal shaft 1 is transmitted to the auxiliary planetary gear set 3b via the planet carrier 2, and the auxiliary planetary gear set 3b applies equal tangential forces to the teeth of the auxiliary second ring gear 16 and the auxiliary planetary gear set 5b. Since the second ring gear 16 cannot rotate due to the engagement of the locking device 17, all of the rider's pedaling power is transmitted to the second sun gear 5b at a fixed speed ratio, and then transmitted to the rear wheel of the bicycle via the chain ring 6 and chain 7.

[0065] An alternative, particularly compact embodiment of the drive system is shown diagrammatically in Figure 7. The drive system of Figure 7 comprises a two-stage planetary gear mechanism, which in addition to the components disclosed in the embodiment of Figure 1 includes an intermediate auxiliary planetary gear subsystem acting between the second planetary gear 3b and the second sun gear 5b.

[0066] The auxiliary planetary gear subsystem of Figure 7 includes an auxiliary or intermediate planet carrier 18 and a third auxiliary planetary gear 3c.

[0067] The intermediate planetary carrier 18 has a third auxiliary planetary gear 3c on its small diameter side which has a row of radially outward teeth, diagrammatically indicated by the reference numeral 18c, supported on a pin 18d which is arranged at a larger diameter than the teeth 18c.

[0068] The auxiliary planetary gear 3c meshes with the second sun gear 5b radially inward and with the internal teeth 16c of the second ring gear 16 radially outward.

[0069] The second ring gear 16 has a pair of internal teeth adjacent to each other in the axial direction, one of which, 16b, meshes with the second planetary gear 3b, and the other, 16c, meshes with the auxiliary planetary gear 3c.

[0070] According to the exemplary embodiment of FIG. 7, the auxiliary planetary gear 3c may be supported around the same axis and at the same radius as the planetary gears 3a and / or 3b.

[0071] According to an alternative embodiment (not shown), auxiliary planetary gear 3c may be attached to intermediate planet carrier 18 via mounting pins located at a different radius relative to planetary gears 3a and / or 3b. Thus, there need not be a fixed relationship between the shape of the planetary gear subsystem including components 3a, 4 and 5a and the components of the planetary gear subsystem including components 3c, 5b and 16.

[0072] Therefore, even when the electric locking device 17 is activated and the second ring gear 16 is stationary, the same overall pedal speed to wheel speed ratio can be achieved by setting the number of teeth on the second sun gear 5b and the second ring gear 16 to a more appropriate value. For example, to achieve the required pedaling speed of 60 rpm at 25 km / h using the layout shown in FIG. 1, the second ring gear 16 would typically have 98 teeth, the second set of planetary gears 3b would have 42 teeth, and the second sun gear 5b would have 14 teeth. The diameter of the second sun gear 5b may be too small for the pedal shaft 1 to pass through its center. However, in an alternative embodiment shown in FIG. 7, a similar overall system ratio can be achieved by using a second ring gear 16 with 76 teeth, a second set of planetary gears 3b with 20 teeth, and an auxiliary planetary gear group with 16 teeth. The number of teeth on the intermediate planetary carrier 18c can be 36, while the second sun gear 5b requires 44 teeth. Therefore, the outer diameter of the second ring gear 16 can be reduced by more than 20% and the diameter of the second smaller sun gear 5b can be increased by more than 150%.

[0073] It will be appreciated that the drive system of the present disclosure offers several advantages and benefits.

[0074] The planetary gear system allows the bike to travel at high speeds without electric assistance.

[0075] The planetary gear system allows you to enjoy all the features and benefits of an e-bike, even when the e-motor is on.

[0076] Both the transmission ratio control motor M1 and the traction motor M2 can be mechanically disconnected from the system when not needed, so that turning both motors off optimizes system efficiency at higher road speeds.

[0077] Neither motor needs to regenerate electrical energy, which simplifies the motor control and electronics, as well as the battery management system, which does not need to boost the motor voltage to recharge the battery.

Claims

1. 1. An electric assist drive system for a bicycle, a pedal crankshaft (1) operated by the rider; an output shaft (21) that transmits rotation to the rear wheel of the bicycle; a planetary gear mechanism (20) arranged to determine a transmission ratio between the pedal crankshaft and the output shaft (21); an assist motor (M2) that drives the output shaft (21); a control motor (M1) drivingly connected to the planetary gear mechanism (20) and controlling the transmission ratio between the pedal crankshaft (1) and the output shaft (21) via the planetary gear mechanism (20); at least one first one-way clutch (10) operatively connected between said control motor (M1) and a rigid element (22) fixedly mountable to the bicycle frame; a second one-way clutch (12) operatively connected between the assist motor (M2) and the output shaft (21); Equipped with the first one-way clutch (10) is configured to block a first forward rotation of a first ring gear (4) of the planetary gear mechanism (20) and release a second reverse rotation thereof to allow free rotation of the first ring gear (4) of the planetary gear mechanism (20); The second one-way clutch (12) is configured to drive the assist motor (M2) to the output shaft (21) when the assist motor is turned on to drive the output shaft (21) in the forward direction, thereby assisting the forward movement of the bicycle, and to disconnect the assist motor (M2) from the output shaft (21) when the assist motor is turned off, thereby allowing the output shaft (21) to continue rotating in the forward direction; The planetary gear mechanism (20) further comprises: a second ring gear (16) and an associated locking device (17) fixedly attached to the bicycle frame (22) and operable to permit and lock rotation of said second ring gear (16); a first sun gear (5a) and a second sun gear (5b) fixed to rotate together with the output shaft (21); a first planetary gear set (3a) disposed between the first sun gear (5a) and the first ring gear (4), and a second planetary gear set (3b) disposed between the second sun gear (5b) and the second ring gear (16); a planet carrier (2) fixed to rotate together with the pedal crankshaft (1) and supporting the first planetary gear set (3a) and the second planetary gear set (3b); Equipped with the first and second sun gears (5a, 5b) and the first and second planetary gear sets (3a, 3b) are configured to provide a desired transmission ratio between the pedal crankshaft (1) and the output shaft (21) and transmit rotation to the rear wheel of the bicycle when the rotation of the second ring gear (16) is locked by the locking device (17).

2. the planet gears of the first planet gear set (3a) have a diameter smaller than the diameter of the planet gears of the second planet gear set (3b); 2. A drive system according to claim 1, wherein the first sun gear (5a) has a diameter greater than the diameter of the second sun gear (5b).

3. 3. A drive system according to claim 1 or 2, wherein the transmission ratio is set in the range of 1:3 to 1:4, and when the locking device (17) locks the rotation of the second ring gear (16), one rotation of the pedal crankshaft (1) corresponds to three to four rotations of the rear wheel of the bicycle.

4. 4. A drive system according to claim 3, wherein the transmission ratio is approximately 1:3.5, and when the locking device (17) locks the rotation of the second ring gear (16), one rotation of the pedal crankshaft (1) corresponds to 3.5 rotations of the rear wheel of the bicycle.

5. 5. A drive system according to any one of claims 1 to 4, wherein the gears of the planetary gear mechanism (20) are configured such that the second ring gear (16) stops rotating when the bicycle reaches a predetermined speed, and the second ring gear (16) is locked in a stationary position by the activated locking device (17) at bicycle speeds above the predetermined speed.

6. 4. The drive system of claim 3, wherein the bicycle travels at a speed of 25 kilometers per hour.

7. an intermediate auxiliary planetary gear subsystem (18, 3c) acting between the second planetary gear set (3b) and the second sun gear (5b); The intermediate auxiliary planetary gear subsystem (18, 3c) an intermediate planet carrier (18); a third auxiliary planetary gear set (3c) supported for free rotation on pins (18d) arranged along a predetermined diameter on the intermediate planetary carrier (18); Equipped with the intermediate planet carrier (18) has a set of teeth (18c) arranged along a diameter smaller than the predetermined diameter of the pin (18d); 7. A drive system according to claim 1, wherein the third auxiliary planetary gear set (3c) meshes radially inward with the second sun gear (5b) and radially outward with the internal teeth (16c) of the second ring gear (16).

8. 8. A drive system according to claim 7, wherein the second ring gear (16) has a pair of axially adjacent inverted teeth (16b, 16c), one of which meshes with the second planetary gear set (3b) and the other of which meshes with the third auxiliary planetary gear set (3c).

9. An electric bicycle comprising the drive system according to any one of claims 1 to 8.

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