Power split hybrid driveline for electric bicycle to allow shutdown of assist power

Abstract

An electric assist drive system for a bicycle, comprising a pedal crankshaft (1), an epicyclic gear mechanism (20), an assist motor (M2) for driving an output shaft (21), and a control motor (M1) for controlling the transmission ratio between the pedal crankshaft (1) and the output shaft (21) through the epicyclic gear mechanism (20). The epicyclic gear mechanism (20) further comprises a first sun gear (5a) and a second sun gear (5b) which are fixed for rotation with the output shaft (21). A planet carrier (2) is fixed for rotation with the pedal crankshaft (1) and supports a first set of planet gears (3a) between a first sun gear (5a) and a first ring gear (4) and a second set of planet gears (3b) between a second sun gear (5b) and a second ring gear (16). A locking device (17) is operable to block rotation of the second ring gear (16), allowing the rider to push the bicycle above a preset speed limit only with his / her mechanical physical power, without power assistance, while still stepping at a comfortable pedal rotational speed.

Description

Technical Field

[0001] The present invention relates to the field of electrically powered bicycles (or "e-bikes"), which have an electric motor to assist the rider's pedal power. More specifically, the present invention relates to an e-bike power split hybrid drive system for an electrically powered bicycle to allow the assist power to be turned off. Background Art

[0002] Recently, power split hybrid drive systems for e-bikes have been proposed. Some of these systems include a pedal crankshaft for the rider to operate, an epicyclic gear mechanism, an assist motor, and a control motor. The epicyclic gear mechanism is arranged to determine the transmission ratio between the pedal crankshaft and the output shaft, which is used to transmit rotation to the bicycle rear wheel. The epicyclic gear mechanism is called an epicyclic "power distribution" gear mechanism because it is arranged to transmit power from the pedals to the rear wheel of the bicycle through two routes: a mechanical route and an electronic route. Specifically, the epicyclic gear mechanism transmits power from the assist motor to the output shaft. In addition, the epicyclic gear mechanism adjusts the rotational speed of the pedal crankshaft by controlling the operation of the control motor.

[0003] The epicyclic hybrid drive system of the present disclosure belongs to the so-called "I2" epicyclic drive system layout for an e-bike. In this layout, the pedals are connected to a planet carrier, a link for driving the rear wheel is connected to a sun gear, and the sun gear is assisted by a traction motor or an assist motor. A proportional control motor is connected to a ring gear of the epicyclic gear system to control the transmission ratio between the pedal crankshaft and the output shaft. As the speed of the bicycle increases, the proportional control motor assists in increasing the overall gear ratio to maintain the rotational speed of the pedals (i.e., the rotational speed of the pedal shaft) at a comfortable speed for the rider.

[0004] One of the latest power split hybrid drive systems (Italian Patent Application No. 102022000009794, filed by the same applicant on May 12, 2022, not yet published at the filing date of the present application) for an e-bike provides an electric assist drive system including a pedal crankshaft, an epicyclic gear mechanism, an assist motor, and a control motor. The assist motor drives an output shaft, and the control motor controls the transmission ratio between the pedal crankshaft and the output shaft through the epicyclic gear mechanism. A first one-way clutch is operably connected to the control motor and is configured to block the rotation of a ring gear of the epicyclic gear system in a forward rotation direction while allowing it to rotate freely in a reverse rotation direction. A second one-way clutch is configured to drivingly connect the assist motor to the output shaft when the assist motor is turned on, and to disengage the assist motor from the output shaft when the assist motor is turned off but the output shaft continues to rotate in the forward rotation direction.

[0005] In the above drive system, a pedal shaft drives a planet carrier which has planets meshing with an external gear ring that is driven by a proportional control motor. A sun gear is connected to a sprocket and a traction gear which is fixed to rotate with the sprocket and the planet carrier. The sprocket is driven by a traction motor M2. A one-way clutch is associated with the proportional control motor so that the gear ring can only rotate in one direction. The transmission ratio between the pedal crankshaft and the output shaft is determined by the gears of the epicyclic system. When the rider starts pedaling at low speed, the planets push the gear ring which is locked in place by the one-way clutch, thus providing the lowest transmission ratio. As the speed of the bicycle increases, the proportional control motor starts to rotate and the gear ring rotates in the reverse direction, slowing down the speed of the pedals relative to the sun gear through the planetary gears, keeping a comfortable transmission ratio for the bicycle.

[0006] European regulations (European standard EN 15194: 2017 for e-bikes) require that the electric assistance be switched off when exceeding a certain vehicle speed (25 km / h) to limit the potential speed of the bicycle and reduce the safety risks associated with riding such a vehicle.

[0007] Some of the limitations encountered in current I2 epicyclic drive systems are that the rider is not allowed to comfortably pedal the bicycle beyond a preset limit speed, i.e., 25 km / h, at which the assistance of the electric motor is automatically cut off. In the current I2 layout, the torque from the pedals always acts in the opposite direction on the proportional control motor. When the speed of the bicycle increases, the speed of the proportional control motor increases to maintain a comfortable pedaling speed for the rider. Thus, the proportional control motor provides a significant amount of mechanical power to the system which helps to assist the bicycle in moving forward. If the proportional control motor is switched off, to comply with the regulatory requirements the electric assistance needs to be removed and the motor torque counteracting the rider's pedaling is eliminated. As a result, the bicycle pedals rotate freely and the rider is unable to continue pedaling. Summary of the Invention

[0008] An object of the present invention is to allow the rider to push the bicycle beyond a preset speed limit (e.g., 25 km / h) relying only on his / her mechanical physical power without electric assistance while still pedaling at a comfortable pedal rotation speed.

[0009] In view of the foregoing background, the present invention provides an electric assist 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:

[0011] a pedal crankshaft for operation by a rider;

[0012] an output shaft for transmitting rotation to a rear wheel of the bicycle;

[0013] An epicyclic gear mechanism arranged to determine a transmission ratio between a pedal crankshaft and an output shaft;

[0014] An assisting motor for driving the output shaft;

[0015] A control motor drivingly connected to the epicyclic gear mechanism for controlling the transmission ratio between the pedal crankshaft and the output shaft through the epicyclic gear mechanism. At least one first one-way clutch is operatively connected between the control motor and a rigid element fixedly mounted to the bicycle frame, wherein the first one-way clutch is configured to block the rotation of a first annulus of the epicyclic gear system in a first forward rotation direction, and to release and allow the first annulus of the epicyclic gear system to rotate freely in a second reverse rotation direction. A second one-way clutch is operatively connected between the assisting motor and the output shaft, wherein the second one-way clutch is configured to drivingly connect the assisting motor to the output shaft when the assisting motor is turned on to drive the output shaft in a forward direction to assist in driving the bicycle forward, and to disconnect the assisting motor from the output shaft when the assisting motor is turned off but the output shaft continues to rotate in the forward direction. The epicyclic gear mechanism further includes:

[0016] A second annulus and an associated locking device, the locking device being fixedly mounted to the bicycle frame and operable to engage and block the rotation of the second annulus;

[0017] A first sun gear and a second sun gear, both fixed to rotate with the output shaft;

[0018] A first set of planet gears between the first sun gear and the first annulus; and a second set of planet gears between the second sun gear and the second annulus, and

[0019] A planet carrier fixed to rotate with the pedal crankshaft and supporting the first set of planet gears and the second set of planet gears. The first sun gear and the second sun gear, and the first set of planet gears and the second set of planet gears are configured to provide a desired transmission ratio between the pedal crankshaft and the output shaft to transfer rotation to a rear wheel of the bicycle when the rotation of the second annulus is locked by the locking device.

[0020] According to another aspect, the present invention provides an electric bicycle including a drive system as defined in the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] For a better understanding of the present invention, several preferred embodiments of the present invention will now be given by way of example with reference to the accompanying drawings, in which:

[0022] Figure 1Schematic cross-sectional view of the main components of an electric bicycle drive system according to an embodiment of the present invention;

[0023] Figure 2 Schematically shows the torque distribution relationship through the epicyclic gear mechanism;

[0024] Figures 3 to 6 Schematically depicts the power flow within the system during different stages of bicycle acceleration;

[0025] Figure 7 Schematic cross-sectional view of the main components of an electric bicycle drive system according to an alternative embodiment of the present invention. Detailed Description of the Invention

[0026] First, referring to Figure 1 , an electric bicycle drive system includes two electric motors M1, M2, and an epicyclic gear mechanism 20 having an output shaft 21. A link 6 is fixed to rotate with the output shaft 21, and the link 6 drives the rear wheel (not shown) of the electric bicycle.

[0027] Reference numeral 1 is a pedal shaft or crankshaft for the rider R to operate. The pedal shaft 1 passes through the assembly and connects two conventional pedal cranks and the assembly of the footrest (not shown in the figure). The assembly of the pedal cranks and the footrest is mounted outside the drive unit. The pedal shaft 1 receives the torque and speed provided by the rider and transmits the torque and speed to the planet carrier 2.

[0028] The electric motor M1 is referred to as the "control" motor or "proportional control" motor because it drives a gear of the epicyclic gear mechanism, which controls the transmission ratio between the output shaft and the pedal crankshaft.

[0029] The electric motor M2 is referred to herein as the "assist" motor (or "traction" motor), which generates power that is transmitted to the output shaft 21 for moving the electric bicycle forward.

[0030] Herein, the epicyclic gear mechanism is also referred to as an epicyclic "power distribution" gear mechanism because it is arranged to transmit power from the pedal to the rear wheel of the bicycle through two routes, as explained below: a mechanical route MR and an electronic route ER. Specifically, the assist motor M2 transmits power to the output shaft. In addition, the operation of the epicyclic gear mechanism is controlled by the control motor M1 to adjust the rotational speed of the pedal crankshaft 1.

[0031] The electric bicycle drive system is housed in a housing (not shown in the figure), preferably mounted in the center of the bicycle frame (at the 'bottom bracket') during use. Generally, the housing provides mounting parts and reaction points, with rolling bearings rotatably supporting the pedal crankshaft 1. The housing may also include an electronic controller C for the drive system (such asFigure 3 as shown

[0032] The epicyclic gear mechanism 20 includes a planet carrier 2 which supports two sets of planet gears, namely a first set of planet gears 3a and a supplementary second set of planet gears 3b, and applies the rider's torque and speed to the epicyclic gear system.

[0033] The planet carrier 2 is fixed to rotate together with the pedal shaft 1. The pedal shaft 1 receives the torque and speed provided by the rider and transmits the torque and speed to the planet carrier 2.

[0034] The power split epicyclic gear mechanism includes a first sun gear 5a and a second sun gear 5b, both of which are integrally formed with the chain ring 6 and the output shaft 21. Both the first sun gear 5a and the second sun gear 5b can be driven to rotate by the assist motor M2 through the traction gear 8, and the traction gear 8 is fixed to rotate together with the sun gear 5a, the sun gear 5b, and the chain ring 6.

[0035] The first sun gear 5a has external teeth that mesh with the first set of planet gears 3a. The second sun gear 5b has external teeth that mesh with the second set of planet gears 3b.

[0036] As described below, according to a preferred embodiment, as shown in the example, the first set of planet gears 3a can be smaller than the supplementary second set of planet gears 3b, that is, have a smaller diameter. Figure 1 As shown in the exemplary embodiment, the diameter of the first sun gear 5a is larger than the diameter of the second sun gear 5b.

[0037] According to Figure 1 As shown in the exemplary embodiment, the diameter of the first sun gear 5a is larger than the diameter of the second sun gear 5b.

[0038] A first ring gear 4 has internal teeth and external teeth that mesh with the first set of planet gears 3a, and the external teeth mesh with a pinion 9 directly driven by the proportional control motor M1.

[0039] The first set of planet gears 3a rotates freely relative to the planet carrier 2, so equal tangential forces are applied to the first ring gear 4 and the first sun gear 5a, regardless of the relative speeds of these components. Therefore, a fixed portion of the torque from the rider is distributed to the ring gear 4, and the remaining portion of the torque from the rider is distributed to the sun gear 5a.

[0040] The second ring gear 16 has internal teeth that mesh with the second set of planet gears 3b.

[0041] According to Figure 1 the exemplary embodiment, the second set of planet gears 3b can be supported around the same axis as the planet gears 3a and at the same radius.

[0042] Alternatively, according to an alternative embodiment (not shown), the second set of planetary gears 3b may be mounted to the planet carrier 2 by a separate set of mounting pins mounted at different radii. Accordingly, there is no need for a fixed relationship between the geometries of the epicyclic gear subsystem including components 3a, 4, and 5a and the epicyclic gear subsystem including components 3b, 5b, and 16.

[0043] A locking device 17 is mounted to the bicycle frame 22 or to a rigid element firmly fixed to the bicycle frame 22. The locking device 17 is operable to engage the second toothed ring 16 and block rotation of the second toothed ring 16. For example, the locking device 17 may be embodied as an electromagnetically operated clutch, such as an electromagnetic pin, that may extend into or engage a corresponding locking seat, such as an opening or a recess formed in the second toothed ring 16.

[0044] The output shaft 21 may be a hollow tubular shaft through which the pedal shaft 1 passes.

[0045] A sprocket or sprocket wheel 6 drives a chain or a toothed belt 7, which drives the rear wheel of the bicycle.

[0046] The traction gear 8 has external teeth that mesh with a second pinion 11 directly driven by the assisting motor M2.

[0047] A first one-way clutch 10 may be arranged to releasably connect a shaft S1 of the proportional control motor M1 to a rigid element 22 that is firmly fixed to the bicycle frame or integrally formed with the bicycle frame. Preferably, the fixed rigid assembly 22 may be a housing of the drive unit.

[0048] The purpose of the first one-way clutch 10 is to block rotation of the first toothed ring 4 in the forward direction (i.e., the forward direction is the direction of rotation of the pedals, chain, and wheels when the bicycle moves forward), but to allow the first toothed ring 4 to rotate freely in the reverse direction.

[0049] A supplementary one-way clutch 19 may be arranged between the pinion 9 and the shaft S1 of the control motor M1.

[0050] The purpose of the supplementary one-way clutch 19 is to lock the rotation of the first toothed ring 4 when the control motor M1 attempts to drive the first toothed ring 4 in the reverse direction, in order to counteract the torque applied by the rider to the first toothed ring 4. As explained below, when the control motor M1 is turned off but the first toothed ring continues to rotate in the reverse direction, the supplementary one-way clutch 19 allows the first toothed ring 4 to rotate freely.

[0051] The second pinion 11 is connected to a shaft S2 of the assisting motor M2 via a second one-way clutch 12. The second pinion 11 meshes with the traction gear 8 such that the assisting motor M2 can assist in driving the bicycle forward.

[0052] A second one-way clutch 12 that assists in connecting the assist motor M2 to its pinion gear 11 is arranged to engage when the assist motor M2 attempts to drive the traction gear 8 in the forward direction to assist in driving the bicycle forward. When the assist motor M2 is turned off but the traction gear 8 continues to rotate in the forward direction, the second one-way clutch 12 allows the traction gear 8 to rotate freely.

[0053] The one-way clutches 10, 12, 19 can be in the form of, for example, a ratchet and pawl, or a wedge clutch having rollers that climb a ramp within a cage, or in the form of a belt or strip wound around a shaft.

[0054] Due to the above arrangement, the control motor M1 controls the ratio between the rotational speed of the pedal and the speed of the bicycle by controlling the rotational speed of the first ring gear 4. The assist motor M2 drives the traction gear 8, applies torque to the sprocket 6, and assists the bicycle in moving forward.

[0055] The above electric bicycle drive system operates as follows. When the bicycle starts from a standstill, the rider applies torque to the system via the pedals. This torque is transmitted into the system via the pedal shaft 1 and the planet carrier 2, and is transmitted to the planet gears 3a. Subsequently, the planet gears distribute the applied torque between the first ring gear 4 and the sun gear 5a.

[0056] A schematic diagram of the torque distribution between the ring gear and the sun gear is as Figure 2 shown, where:

[0057] Tc = torque applied to the planet carrier 2;

[0058] Zr = radius of the planet carrier 2;

[0059] Zs = radius of the planet gear 3a;

[0060] Fr = tangential force applied to the first ring gear 4;

[0061] Fs = tangential force applied to the sun gear 5a;

[0062] where Fr = Fs = 1 / 2 * Tc / Zr

[0063] Tr = torque applied to the ring gear: Tr = Fr * (Zr + Zs); and

[0064] Ts = torque applied to the sun gear: Ts = Fs * (Zr - Zs)

[0065] Initially, starting from a standstill ( Figure 3), the control motor M1 is turned off. A torque Tr is applied to the first ring gear 4 in a forward direction. However, the first one-way clutch 10 is arranged to block the forward rotation of the first ring gear 4. Therefore, the torque Tr is reacted by the first one-way clutch 10, and the first ring gear 4 remains stationary. Thus, all the power provided by the rider R is transferred to the sun gear 5a and then transferred to the bicycle wheel via the sprocket 6 and the chain or belt 7. The gear ratio between the bicycle pedal and the wheel is expressed as:

[0066]

[0067] Due to the action of the first one-way clutch 10, which allows the first ring gear 4 to rotate in the reverse direction but not in the forward direction, the lowest overall gear ratio exists when the first ring gear 4 is stationary. The ratios of the epicyclic gear system and the chain or belt can be arranged such that the ratio when the first ring gear is stationary is equal to a suitable ratio for starting the bicycle from a stationary state or climbing a steep slope. As an indication, for a touring bicycle or a commuter bicycle, the lowest ratio can have a value of approximately 1:1, which means that one turn of the pedal causes the rear wheel to turn approximately one turn. This transmission ratio is achieved by setting the number of teeth and the diameters of the gears in the epicyclic system.

[0068] During starting from rest ( Figure 3 ), the traction motor M2 can be powered by the battery B via the controller C to assist the rider in moving the bicycle forward. The traction motor M2 applies a torque via the second one-way clutch 12 and the pinion 11 to move the traction gear 8 in a forward direction, thereby assisting the bicycle to accelerate forward. The second one-way clutch 12 is arranged to be locked when the traction motor M2 applies a torque to the traction gear 8 in the forward direction.

[0069] When the speed of the bicycle starts to increase, an increase in the overall gear ratio value is required to maintain the rotational speed of the pedal (i.e., the rotational speed of the pedal shaft 1) at a comfortable speed 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 arranged to allow the ring gear 4 to rotate freely in the reverse direction. The speed of the control motor M1 is controlled to maintain the required ring gear speed (Wr), and the required ring gear speed is obtained from the following equation:

[0070] Wr = (Wc(Zr + Zs) – WsxZs) / Zr

[0071] Where:

[0072] Wc = the desired rotational speed of the pedal shaft 1;

[0073] Ws = the rotational speed of the sun gear 5;

[0074] Wr = Rotational speed required for the ring gear 4;

[0075] Zr and Zs are the system radii, which define the leverage ratio within the epicyclic gear system, as Figure 2 shown.

[0076] According to the law of conservation of energy, the mechanical power provided by the control motor M1 is controlled to supplement the mechanical power provided by the traction motor M2, assisting the rider to move the bicycle forward.

[0077] As the speed of the control motor M1 begins to increase, to maintain a comfortable pedaling speed, it starts to supply mechanical power to the system:

[0078] Power M1 = Wr * Tr

[0079] where Tr is the torque applied to the ring gear 4 in response to the rider's pedaling torque (as Figure 2 illustrated).

[0080] The locking device 17 remains de-energized, allowing the second ring gear 16 to rotate freely, and no torque is transmitted through the planet to the supplementary sun gear 5b. However, due to the reverse rotation of the first ring gear 4, the speed difference between the supplementary sun gear 5b and the planet carrier 2 increases. Therefore, the second ring gear 16 continues to rotate forward, but at a reduced speed.

[0081] As the speed of the bicycle further increases, the torque Tr applied by the rider tends to remain substantially constant, while the speed of the control motor M1 continues to increase to maintain a comfortable pedaling speed. Thus, the power of the control motor M1 increases. To a certain extent, it can be set by programming the controller C such that the power M1 of the control motor M1 becomes sufficient to transmit the desired electric assist power to the bicycle, and no further assistance from the traction motor M2 is required. Subsequently, the traction motor M2 can be turned off ( Figure 5 ) to save power. The bicycle continues to move forward with the rider's power and the assistance of the proportional control motor M1, causing the traction gear 8 to continue rotating in the forward direction. However, the traction motor M2 no longer applies a forward torque to the traction gear 8. Thus, the second one-way clutch 12 unlocks, allowing the pinion 11 to rotate freely relative to the shaft of the traction motor M2. Therefore, the traction motor M2 is allowed to stop and not transmit a deceleration torque to the traction gear 8 or thus to the bicycle wheels.

[0082] The locking device 17 remains de-energized, allowing the second ring gear 16 to rotate freely, and no torque is transmitted through the planet to the supplementary sun gear 5b. However, since the speed of the reverse rotation of the first ring gear 4 is still increasing, the speed difference between the supplementary sun gear 5b and the planet carrier 2 further increases. Therefore, the second ring gear 16 continues to rotate in the forward direction, but at a further reduced speed.

[0083] A supplementary epicyclic subsystem consisting of the second sun gear 5b and the associated second set of planet gears 3b can be advantageously provided to achieve the desired speed ratios between the associated components of the system.

[0084] Specifically, according to a preferred embodiment, as Figure 1 shown, 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 set of planet gears 3b is larger than the diameter of the first set of planet gears 3a.

[0085] In this case, when the second ring gear 16 is stationary, it is desirable that when the bicycle is traveling at the maximum legal assistance speed, the ratio through the supplementary epicyclic subsystem should allow a comfortable pedaling speed. For example, when the bicycle is traveling at the maximum legal assistance speed of 25 km / h in Europe, an overall gear ratio of 3.5 can ensure a pedaling speed of approximately 60 revolutions per minute.

[0086] Therefore, when the bicycle approaches the maximum legal assistance speed, the locking device 17 remains de-energized, allowing the second ring gear 16 to rotate freely, and no torque is transmitted through the planet gears to the second or supplementary sun gear 5b.

[0087] However, due to the gear ratio selected for the supplementary epicyclic subsystem, when the traveling speed of the bicycle reaches 25 km / h, the second ring gear 16 becomes stationary. To make the movement smooth, the pedaling speed can be slightly adjusted, for example by controlling the speed of the control motor M1, to assist the rotation stop of the second ring gear 16, in order to establish an appropriate relationship between the traveling speed of the bicycle and the speed of the pedal, to ensure that the second ring gear is completely stationary.

[0088] Once the traveling speed of the bicycle exceeds the maximum legal assistance speed (usually 25 km / h) and the second ring gear 16 has completely stopped rotating, the controller C activates the locking device 17 to lock the angular position of the second ring gear 16 and prevent its rotation. For example, the electromagnetic device can include a solenoid powered by the controller C.

[0089] The engagement of the locking device 17 and the resulting locking of the second ring gear 16 creates a supplementary torque path through the system from the pedal shaft 1 to the chain sprocket 6, which provides a fixed overall gear ratio between the pedal shaft and the rear wheel of the bicycle. For example, a suitable gear ratio between the pedal shaft and the rear wheel of the bicycle can be between 1:3 and 1:4. A particularly comfortable transmission ratio between the pedal shaft and the rear wheel of the bicycle is approximately 1:3.5.

[0090] The main epicyclic system (the first sun gear 5a, the first set of planetary gears 5a, and the first outer ring 4) continues to rotate and is still assisted by the motor M1, providing torque to assist the first ring gear 4 in reverse rotation. However, since the speed ratio between the pedal and the wheel is now fixed, the torque provided by the motor M1 can now be gradually reduced to provide a smooth transition to turning off the power assistance of the bicycle.

[0091] Once the bicycle's traveling speed reaches the maximum legal assistance speed ( Figure 6 ), the control of the motor M1 can be completely turned off. Thus, all electronic assistance in the electric bicycle drive system has been canceled, and the bicycle complies with the regulations.

[0092] The epicyclic gear system (specifically, the first sun gear 5a, the first set of planets 3a, and the first outer ring 4) continues to rotate, however, the one-way clutch 19 that connects the pinion 9 to the shaft S1 of the control motor M1 disengages because the control motor M1 no longer applies torque in one direction through the clutch to assist the first ring gear 4 in rotating in the reverse direction. Thus, the control motor M1 is allowed to become stationary while allowing the first ring gear 4 and the pinion 9 to continue to rotate freely. Therefore, the control motor M1 does not apply any regenerative or braking torque to the system. The bicycle is driven forward solely by the power of the rider's pedaling action. The torque at the pedal shaft 1 is transmitted through the planet carrier 2 to the supplementary or second set of planetary gears 3b, which apply equal tangential forces to the teeth of the supplementary second ring gear 16 and the supplementary or second sun gear 5b. Due to the engagement of the locking device 17, the second ring gear 16 cannot rotate, so all of the rider's pedaling power is transmitted to the second sun gear 5b at a fixed speed ratio and is thus transmitted to the bicycle's rear wheel via the chain links 6 and 7.

[0093] Figure 7 An alternative embodiment of the drive system is schematically depicted as being particularly compact. Figure 7 The drive system provides a two-stage epicyclic gear mechanism, which, in addition to Figure 1 the components disclosed in the embodiment of

[0094] Figure 7 also includes an intermediate supplementary epicyclic subsystem that acts between the second set of planetary gears 3b and the second sun gear 5b.

[0095] The intermediate planet carrier 18 has a set of radially outward teeth, schematically shown at 18c at a smaller diameter, and carries the third set of supplementary planetary gears 3c, which are freely rotatably supported on pins 18d, the diameter of the pins 18d being larger than the diameter of the teeth 18c.

[0096] The supplementary planet gear 3c meshes radially inwardly with the second sun gear 5b and radially outwardly with the internal teeth 16c of the second ring gear 16.

[0097] The second ring gear 16 provides a pair of axially adjacent internal teeth, one internal tooth 16b for meshing with the second set of planet gears 3b and one internal tooth 16c for meshing with the supplementary planet gear 3c.

[0098] According to Figure 7 an exemplary embodiment of, the supplementary planet gear 3c can be supported about the same axis and at the same radius as the planet gears 3a and / or the planet gears 3b.

[0099] Optionally, according to an alternative embodiment (not shown), the supplementary planet gear 3c can be mounted to the intermediate planet carrier 18 on mounting pins that are arranged at different radii relative to the planet gears 3a and / or the planet gears 3b. Thus, there need not be a fixed relationship between the geometries of the epicyclic gear subsystem including components 3a, 4, and 5a and the components of the epicyclic gear subsystem including components 3c, 5b, and 16.

[0100] Thus, when the electronically operated locking device 17 engages and the second ring gear 16 is stationary, but the second sun gear 5b and the second ring gear 16 have more favorable tooth numbers, a similar overall ratio between the pedal and wheel speeds can be achieved. For example, to achieve a pedaling speed of 60 revolutions per minute required for 25 kilometers per hour using the Figure 1 arrangement shown, the second ring gear 16 typically has 98 teeth, the second set of planet gears 3b can have 42 teeth, and the second sun gear 5b can have 14 teeth. The diameter of the second sun gear 5b may be too small for the pedal shaft 1 to pass through the center of the second sun gear 5b. However, Figure 7 the alternative embodiment shown can provide a similar overall system ratio by using a second ring gear 16 having 76 teeth, a second set of planet gears 3b having 20 teeth, and a set of supplementary planet gears having 16 teeth. The number of teeth 18c on the intermediate planet carrier can be 36, and the second sun gear 5b may require 44 teeth. Thus, the outer diameter of the second ring gear 16 can be reduced by more than 20%, and the diameter of the smaller second sun gear 5b can be increased by more than 150%.

[0101] It should be understood that the drive system of the present disclosure provides several advantages and benefits:

[0102] The epicyclic gear system enables a bicycle to be ridden at high speeds without any electric assistance;

[0103] When the electric assist motor is turned on, the epicyclic gear system can achieve all the functions and advantages of an electric assist bicycle;

[0104] When all motors are turned off, system efficiency is optimized at higher driving speeds because the proportional control motor M1 and the traction motor M2 can both be mechanically disengaged from the system when not needed;

[0105] Neither motor needs to regenerate any electrical energy. This results in a simplified motor control and electronics system, as well as a simplified battery management system, and the battery can be charged without increasing the motor voltage.

Claims

1. An electric assist drive system for a bicycle, comprising: a pedal crankshaft (1) for a rider to operate; an output shaft (21) for transmitting rotation to a rear wheel of the bicycle; a planetary gear mechanism (20), the planetary gear mechanism (20) being arranged to determine a transmission ratio, which is the transmission ratio between the pedal crankshaft and the output shaft (21); an assist motor (M2) for driving the output shaft (21); a control motor (M1), drivingly connected to the planetary gear mechanism, for controlling the transmission ratio between the pedal crankshaft (1) and the output shaft (21) through the planetary gear mechanism (20); at least one first one-way clutch (10), operably connected between the control motor (M1) and a rigid element (22), the rigid element (22) being fixedly mounted to the frame of the bicycle, wherein the first one-way clutch (10) is configured to block the rotation of a first ring gear (4) of the planetary gear system in a first forward rotation direction and release and allow the first ring gear (4) of the planetary gear system to rotate freely in a second reverse rotation direction; a second one-way clutch (12), operably connected between the assist motor (M2) and the output shaft (21), wherein when the assist motor is turned on to drive the output shaft (21) in a forward direction, the second one-way clutch (12) is configured to drivingly connect the assist motor (M2) to the output shaft (21) to assist in driving the bicycle forward, and when the assist motor is turned off but the output shaft (21) continues to rotate in the forward direction, to disengage the assist motor (M2) from the output shaft (21); wherein the planetary gear mechanism (20) further comprises: a second ring gear (16) and an associated locking device (17), the locking device (17) being capable of being fixedly mounted to a bicycle frame (22) and operable to engage and block the rotation of the second ring gear (16); a first sun gear (5a) and a second sun gear (5b), both fixed to rotate together with the output shaft (21); a first set of planetary gears (3a) and a second set of planetary gears (3b), the first set of planetary gears (3a) being between the first sun gear (5a) and the first ring gear (4), the second set of planetary gears (3b) being between the second sun gear (5b) and the second ring gear (16), and a planet carrier (2), which is fixed to rotate together with the pedal crankshaft (1) and supports the first set of planetary gears (3a) and the second set of planetary gears (3b); And wherein the first sun gear (5a), and the second sun gear (5b), and the first set of planet gears (3a) and the second set of planet gears (3b) are configured to provide a desired transmission ratio between the pedal crankshaft (1) and the output shaft (21) for transmitting rotation to a rear wheel of the bicycle when rotation of the second ring gear (16) is locked by the locking means (17).

2. The drive system according to claim 1, wherein the planet gears of the first set of planet gears (3a) have a diameter which is smaller than the diameter of the planet gears of the second set of planet gears (3b), and wherein the first sun gear (5a) has a diameter which is larger than the diameter of the second sun gear (5b).

3. The drive system according to claim 1 or 2, wherein the transmission ratio is set in the range between 1:3 and 1:4, whereby when the locking means (17) locks the rotation of the second ring gear (16), a single complete revolution of the pedal crankshaft (1) corresponds to between 3 and 4 revolutions of the rear wheel of the bicycle.

4. The drive system according to claim 3, wherein the transmission ratio is approximately 1:3.5, whereby when the locking means (17) locks the rotation of the second ring gear (16), a single complete revolution of the pedal crankshaft (1) corresponds to 3.5 revolutions of the rear wheel of the bicycle.

5. The drive system according to any one of the preceding claims, wherein the gears of the epicyclic system are configured to cause the second ring gear (16) to stop rotating at a predetermined driving speed of the bicycle and, at a driving speed of the bicycle exceeding the predetermined driving speed, to activate the locking means (17) to lock the second ring gear (16) in place.

6. The drive system according to claim 3, wherein the driving speed of the bicycle is 25 km / h.

7. The drive system according to any one of the preceding claims, further comprising an intermediate supplementary epicyclic subsystem (18, 3c), the intermediate supplementary epicyclic subsystem (18, 3c) acting between the second set of planet gears (3b) and the second sun gear (5b), the supplementary epicyclic subsystem comprising: an intermediate planet carrier (18), and a third set of supplementary planet gears (3c) which are freely supported to rotate on a pin (18d) arranged on the intermediate planet carrier (18) along a given diameter, wherein the intermediate planet carrier (18) has a set of teeth (18c) which are arranged along a diameter smaller than the given diameter of the pin (18d), and wherein the supplementary planet gears (3c) mesh radially inwards with the second sun gear (5b) and radially outwards with an internal tooth (16c) of the second ring gear (16).

8. The drive system according to claim 7, wherein the second toothed ring (16) is provided with a pair of axially adjacent internal teeth (16b, 16c), one of the internal teeth (16b) being adapted to mesh with the second set of planet gears (3b), and one of the internal teeth (16c) being adapted to mesh with the supplementary planet gears (3c).

9. An electric bicycle, comprising a drive system according to any one of the preceding claims.

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