TW202423776A - Electric auxiliary drive system and electrically powered bicycle - Google Patents

Abstract

An electric auxiliary drive system for a bicycle comprises a pedal crankshaft (1), an epicyclic gearing mechanism (20), an assist motor (M2) for driving an output shaft (21), and a control motor (M1) for controlling, through the epicyclic gearing mechanism, the transmission ratio between the pedal crankshaft (1) and the output shaft (21). The epicyclic gearing mechanism (20) further comprises a first (5a) and a second (5b) sun gear, both secured for rotation with the output shaft (21). A planet carrier (2) is secured for rotation with the pedal crankshaft (1) and supports a first set of planet gears (3a) between the first sun gear (5a) and a first ring gear (4), and a second set of planet gears (3b) between the second sun gear (5b) and a second ring gear (16). A locking device (17) is operable to block the rotation of the second ring gear (16), allowing the rider to push the bicycle beyond a pre-set speed limit, relying only on his/her mechanical physical power, without being assisted electrically, while still pedalling at a comfortable speed of rotation of the pedals.

Description

Power-split hybrid transmission system for electric bicycles allowing the auxiliary power to be turned off

The present invention relates to the field of electrically powered bicycles (or "e-bikes") having an electric motor that assists the rider's pedaling power. More specifically, the present invention relates to an electric bicycle power-split hybrid drive system for an electric bicycle to allow the assist power to be turned off.

Recently, power-split hybrid transmission systems for electric bicycles have been proposed. Some of these systems include a pedal crankshaft for operation by the rider, 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 an output shaft, which is used to transfer rotation to the rear wheel of the bicycle. The epicyclic gear mechanism is called an epicyclic "power-split" gear mechanism because it is arranged to transfer 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 transfers power from the assist motor to the output shaft. In addition, the epicyclic gear mechanism adjusts the rotational speed of the pedal crankshaft by operating the control motor.

The epicyclic hybrid transmission system disclosed herein belongs to the so-called "I2" epicyclic transmission system layout for electric bicycles. In this layout, the pedals are connected to a planetary carrier, and a chain ring for driving the rear wheel is connected to a sun gear, which is assisted by a traction motor or an assist motor. A proportional control motor is connected to a gear ring 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 helps increase the overall gear ratio to maintain the rotational speed of the pedals (i.e., the rotational speed of the pedal shaft) at a speed comfortable for the rider.

One of the latest power-split hybrid transmission systems (Italian patent application number 102022000009794, filed on May 12, 2022 by the same applicant, not yet published on the filing date of the present application), for an electric bicycle, provides an electric auxiliary drive system, including a pedal crankshaft, an epicyclic gear mechanism, an auxiliary motor, and a control motor, the auxiliary 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 a gear ring of the epicyclic gear system from rotating 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 auxiliary motor to the output shaft when the auxiliary motor is turned on, and to decouple the auxiliary motor from the output shaft when the auxiliary motor is turned off but the output shaft continues to rotate in the forward rotational direction.

In the above drive system, a pedal shaft drives a planetary carrier with planets that engage with an outer gear ring, which is driven by a proportional control motor. A sun gear is connected to the sprocket and a pull gear, which is fixed to rotate with the sprocket and the planetary carrier. The sprocket is driven by the pull motor M2. A one-way clutch is connected to 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 a low speed, the planet pushes the gear ring, which is locked in place by the one-way clutch, thus providing the lowest transmission ratio. As the bike speed increases, the proportional control motor starts to rotate, the gear ring rotates in the opposite direction, slowing down the pedal speed relative to the sun gear through the planetary gears, allowing the bike to maintain a comfortable transmission ratio.

European regulations (European standard EN 15194:2017 for electric assist bicycles) require that the electric assistance be switched off above a certain speed (25 km/h) in order to limit the potential speed of the bicycle and reduce the safety risks associated with riding such vehicles.

A limitation encountered with some current I2 epicyclic transmission systems is that the rider is not allowed to comfortably pedal the bicycle above a preset upper speed limit of 25 km/h, at which the assistance of the electric motor is automatically cut off. In current I2 arrangements, the torque from the pedals always reacts against the proportional control motor. As the bicycle's traveling speed increases, the speed of the proportional control motor increases to maintain a comfortable pedaling speed for the rider. As a result, the proportional control motor provides considerable mechanical power to the system, which helps to assist the bicycle in moving forward. If the proportional control motor is turned off, the motor torque that counteracts the rider's pedaling is eliminated in order to meet regulatory requirements to remove the electric assist. As a result, the bicycle pedals rotate freely, making it impossible for the rider to continue pedaling.

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

Against the foregoing 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.

According to one aspect, the present invention provides an electric auxiliary drive system for a bicycle, comprising: a pedal crankshaft for a rider to operate; an output shaft for transmitting rotation to a rear wheel of the bicycle; an epicyclic 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 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 operably connected between the control motor and a rigid member fixedly mounted to the bicycle frame, wherein the first one-way clutch is configured to block a first gear ring of the epicyclic gear system from rotating in a first, forward rotational direction, and to release and allow the first gear ring of the epicyclic gear system to freely rotate in a second, reverse rotational direction. A second one-way clutch is operably connected between the assist motor and the output shaft, wherein the second one-way clutch is configured to drivingly connect the assist motor to the output shaft when the assist motor is turned on to drive the output shaft to drive the output shaft in a forward direction to assist in driving the bicycle forward, 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 direction. The epicyclic gear mechanism further includes: a second gear ring and an associated locking device, the locking device can be fixedly mounted to the bicycle frame and can be operated to engage and block the rotation of the second gear ring; a first sun gear and a second sun gear, both fixed to rotate with the output shaft; a first set of planetary gears, between the first sun gear and the first gear ring; and a second set of planetary gears, between the second sun gear and the second gear ring, and a planet carrier, fixed to rotate with the pedal crankshaft and support the first set of planetary gears and the second set of planetary gears. The first sun gear and the second sun gear, and the first set of planetary gears and the second set of planetary gears are configured to provide a desired transmission ratio between the pedal crankshaft and the output shaft to transmit the rotation to a rear wheel of the bicycle when the rotation of the second gear ring is locked by the locking device.

According to another aspect, the present invention provides an electric bicycle comprising a drive system as defined in the accompanying claims.

First, referring to FIG. 1 , an electric bicycle drive system includes two electric motors M1, M2, and a one-turn gear mechanism 20 having an output shaft 21. A chain ring 6 is fixed to rotate with the output shaft 21, and the chain ring 6 drives the rear wheel (not shown) of the electric bicycle.

Reference numeral 1 is a pedal shaft or crankshaft for operation by a rider R. The pedal shaft 1 passes through the assembly and connects two known pedal cranks and foot support assemblies (not shown in the figure), which are 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.

The M1 electric motor is called a "control" motor or "proportional control" motor because it drives one gear of the epicyclic gear mechanism, controlling the transmission ratio between the output shaft and the pedal crankshaft.

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

In this article, the epicyclic gear mechanism is also referred to as 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, 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 epicyclic gear mechanism adjusts the rotation speed of the pedal crankshaft 1 by controlling the operation of the motor M1.

The e-bike drive system is housed in a housing (not shown) which is preferably mounted in the center of the bicycle frame (at the "bottom bracket") when in use. Typically, the housing provides mountings and reaction points with rolling bearings rotatably supporting the pedal crankshaft 1. The housing may also contain an electronic controller C for the drive system (as shown in Figure 3).

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

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.

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

The first sun gear 5a has outer teeth that mesh with the first set of planetary gears 3a. The second sun gear 5b has outer teeth that mesh with the second set of planetary gears 3b.

As described below, according to a preferred embodiment, as shown in the example of FIG. 1 , the first set of planetary gears 3 a may be smaller, i.e., have a smaller diameter, than the complementary second set of planetary gears 3 b.

According to the exemplary embodiment shown in FIG. 1 , the diameter of the first sun gear 5a is larger than the diameter of the second sun gear 5b.

A first gear ring 4 has inner teeth meshing with the first set of planetary gears 3a and outer teeth, the outer teeth meshing with a small gear 9 directly driven by the proportional control motor M1.

The first set of planetary gears 3a rotates freely relative to the planet carrier 2 and therefore applies equal tangential forces to the first gear ring 4 and the first sun gear 5a, regardless of the relative speeds of these components. Therefore, a fixed part of the torque from the rider is distributed to the gear ring 4, while a remaining part of the torque from the rider is distributed to the sun gear 5a.

The second gear ring 16 has inner teeth that mesh with the second set of planetary gears 3b.

According to the exemplary embodiment of FIG. 1 , the second set of planetary gears 3 b may be supported around the same axis and at the same radius as the planetary gears 3 a.

Alternatively, according to an alternative embodiment (not shown), the second set of planetary gears 3b can be mounted to the planet carrier 2 by a single set of mounting pins mounted at a different radius. Thus, there does not need to be a fixed relationship between the geometries of the epicyclic gear subsystem comprising parts 3a, 4, and 5a and the epicyclic gear subsystem comprising parts 3b, 5b, and 16.

A locking device 17 is mounted to the bicycle frame 22 or is securely fixed to a rigid element of the bicycle frame 22. The locking device 17 is operable to engage the second gear ring 16 and prevent the second gear ring 16 from rotating. For example, the locking device 17 can be implemented as an electromagnetically operated clutch, such as an electromagnetic pin, which can extend to or engage a corresponding locking seat, such as an opening or a recess formed in the second gear ring 16.

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

The sprocket or sprocket 6 drives a chain or a toothed belt 7, and the chain or toothed belt 7 drives the rear wheel of the bicycle.

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

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

The purpose of the first one-way clutch 10 is to block the first gear ring 4 from rotating 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 allows the first gear ring 4 to rotate freely in the reverse direction.

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

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

The second pinion gear 11 is connected to a shaft S2 of the assist motor M2 via a second one-way clutch 12. The second pinion gear 11 is engaged with the traction gear 8, so that the assist motor M2 can assist in driving the bicycle forward.

The second one-way clutch 12 connecting the assist motor M2 and its pinion 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.

The one-way clutch 10, 12, 19 may be in the form of, for example, a pawl and ratchet, or a sprag clutch having a roller that climbs up a ramp in a cage, or in the form of a belt or strip wrapped around an axle.

Due to the above arrangement, the control motor M1 controls the ratio between the rotation speed of the pedal and the speed of the bicycle by controlling the rotation speed of the first gear ring 4. The assist motor M2 applies torque to the sprocket 6 by driving the traction gear 8 and assists the bicycle to move forward.

The above electric bicycle drive system operates as follows. When the bicycle starts from rest, the rider applies torque to the system via the pedals. This torque is transmitted into the system via the pedal shaft 1, the planetary carrier 2, and to the planetary gear 3a. The planetary gear then distributes the applied torque between the first gear ring 4 and the sun gear 5a.

The torque distribution diagram between the gear ring and the sun gear is shown in Figure 2, where: Tc = torque applied to planet carrier 2; Zr = radius of planet carrier 2; Zs = radius of planet gear 3a; Fr = tangential force applied to first gear ring 4; Fs = tangential force applied to sun gear 5a; Where Fr = Fs = 1/2 * Tc / Zr Tr = torque applied to the gear ring: Tr = Fr * (Zr + Zs); and Ts = torque applied to the sun gear: Ts = Fs * (Zr-Zs)

Initially, starting from a stationary state (Fig. 3), the control motor M1 is turned off. Torque Tr is applied to the first gear ring 4 in a positive direction, however, the first one-way clutch 10 is arranged to block the positive rotation of the first gear ring 4. Therefore, the torque Tr is reacted by the first one-way clutch 10, and the first gear ring 4 remains stationary. Therefore, all the power provided by the rider R is transferred to the sun gear 5a, and transferred to the bicycle wheel via the chain 6 and the chain or belt 7. The gear ratio between the bicycle pedal and the wheel is expressed as: Overall gear ratio =

The lowest overall gear ratio exists when the first gear ring 4 is stationary, since the first one-way clutch 10 allows the first gear ring 4 to rotate in the reverse direction but not in the forward direction. The ratios of the epicyclic gear system and the ratios of the chain or belt can be arranged so that the ratio when the first gear ring is stationary is equal to a suitable ratio for starting the bicycle from a stationary state or climbing a steep hill. As an indication, for a touring or commuting bicycle, the lowest ratio may have a value of about 1:1, which means that one rotation of the pedals causes about one rotation of the rear wheel. This transmission ratio is achieved by setting the number of teeth and the diameter of the gears in the epicyclic system.

During starting from rest (FIG. 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 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 in accelerating forward. The second one-way clutch 12 is arranged so that when the traction motor M2 applies torque to the traction gear 8 in the forward direction, the second one-way clutch 12 is locked.

When the speed of the bicycle starts to increase, the overall gear ratio needs to increase in order to maintain the rotational speed of the pedals (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 gear ring 4 in the reverse direction. This action unlocks the first one-way clutch 10, which is arranged to allow the gear ring 4 to rotate freely 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 the following equation: Wr=(Wc(Zr+Zs)–WsxZs)/Zr Where: Wc=desired speed of pedal shaft 1; Ws=speed of sun gear 5; Wr=required speed of ring gear 4; Zr and Zs are the system radii, defining the lever ratio within the epicyclic gear system, as shown in Figure 2.

According to 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, assisting the rider to move the bicycle forward.

As the speed of the control motor M1 begins to increase, in order to maintain a comfortable pedaling speed, it begins to provide mechanical power to the system: Power _M1 = Wr*Tr

Where Tr is the torque applied to the gear ring 4 to respond to the rider's pedaling torque (as shown in FIG. 2 ).

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

As the bicycle speed increases further, 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, thereby increasing the power of the control motor M1. At a certain point, the controller C program can be designed to set that the power M1 of the control motor M1 becomes sufficient to deliver the desired electric assist power to the bicycle, and no further assistance from the traction motor M2 is required. The traction motor M2 (FIG. 5) can then be turned off to save power. The bicycle continues to move forward with the power of the rider and the assistance of the proportional control motor M1, so that the traction gear 8 continues to rotate in the forward direction. However, the traction motor M2 no longer applies forward torque to the traction gear 8, so the second one-way clutch 12 is unlocked, allowing the pinion 11 to rotate freely relative to the axis of the traction motor M2. Therefore, the traction motor M2 is allowed to stop and does not transmit the deceleration torque to the traction gear 8 or, therefore, to the wheels of the bicycle.

The lock device 17 continues to be de-energized, so that the second gear ring 16 rotates freely, and no torque is transmitted to the supplementary sun gear 5b through the planet. However, since the speed of the reverse rotation of the first gear ring 4 is still increasing, the speed difference between the supplementary sun gear 5b and the planet carrier 2 is further increased. Therefore, the second gear ring 16 continues to rotate forward, but the speed is further reduced.

The supplementary epicyclic subsystem consisting of the second sun gear 5b and the associated second set of planets 3b may advantageously be arranged to achieve a desired speed ratio between the associated components of the system.

Specifically, according to a preferred embodiment, as shown 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 set of planetary gears 3b is larger than the diameter of the first set of planetary gears 3a.

In this case, when the second gear ring 16 is stationary, it is desirable that the ratio of the supplementary epicyclic subsystem should allow a comfortable pedaling speed when the bicycle is traveling at the maximum legal assistance speed. For example, when the bicycle is traveling at the European maximum legal assistance speed of 25 km/h, an overall gear ratio of 3.5 ensures a pedaling speed of about 60 rpm.

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

However, due to the gear ratio selected by the supplementary epicyclic subsystem, the second gear ring 16 becomes stationary when the bicycle's running speed reaches 25 km/h. In order to make the movement smooth, the pedaling speed can be slightly adjusted to assist the rotation stop of the second gear ring 16, for example by controlling the speed of the control motor M1, so as to establish a suitable relationship between the running speed of the bicycle and the speed of the pedals to ensure that the second gear ring is completely stationary.

Once the bicycle's running speed exceeds the maximum legal assistance speed (usually 25 km/h) and the second gear ring 16 stops rotating completely, the controller C activates the locking device 17 to lock the angular position of the second gear ring 16 and prevent it from rotating. For example, the electromagnetic device may include a solenoid powered by the controller C.

The engagement of the locking device 17 and the resulting locking of the second gear ring 16 creates a supplemental torque path through the system from the pedal axle 1 to the chain tooth 6, providing a fixed overall gear ratio between the pedal axle and the rear wheel of the bicycle. For example, a suitable gear ratio between the pedal axle and the rear wheel of the bicycle may be between 1:3 and 1:4. A particularly comfortable transmission ratio between the pedal axle and the rear wheel of a bicycle is approximately 1:3.5.

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

Once the bicycle reaches the maximum legal assistance speed (Fig. 6), control motor M1 is completely switched off. All electronic assistance in the e-bike drivetrain is thus cancelled and the bicycle complies with the regulations.

The epicyclic gear system (specifically, the first sun gear 5a, the first set of planets 3a, and the first gear ring 4) continues to rotate, however the one-way clutch 19 connecting the pinion 9 to the shaft S1 of the control motor M1 is disengaged because the control motor M1 no longer applies torque in one direction through the clutch to assist the first gear ring 4 in rotating in the reverse direction. Therefore, the control motor M1 is allowed to become stationary while the first gear ring 4 and the pinion 9 are allowed 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 only by the power of the rider's pedaling action. The torque at the pedal axle 1 is transmitted to the supplementary or second set of planetary gears 3b through the planet carrier 2, which applies equal tangential forces to the teeth of the supplementary second gear ring 16 and the supplementary or second sun gear 5b. Due to the engagement of the locking device 17, the second gear ring 16 cannot rotate, so all the pedaling power of the rider is transmitted to the second sun gear 5b at a fixed speed ratio, and thus transmitted to the rear wheel of the bicycle via the chain ring 6 and the chain 7.

Referring to Fig. 7, a particularly compact alternative embodiment of the drive system is schematically depicted. The drive system of Fig. 7 provides a two-stage epicyclic gear mechanism, which, in addition to the components disclosed in the embodiment of Fig. 1, further includes an intermediate supplementary epicyclic subsystem acting between the second set of planetary gears 3b and the second sun gear 5b.

The supplementary epicyclic subsystem of Figure 7 includes a supplementary or intermediate planet carrier 18 and a third set of supplementary planetary gears 3c.

The intermediate planet carrier 18 has a set of teeth facing radially outward, schematically shown as 18c on a smaller diameter, and carries a third set of supplementary planetary gears 3c, which are supported on pins 18d for free rotation, and the diameter of the pins 18d is greater than the diameter of the teeth 18c.

The supplementary planetary gear 3c radially engages with the second sun gear 5b inwardly and radially engages with the inner teeth 16c of the second gear ring 16 inwardly.

The second gear ring 16 provides a pair of axially adjacent inner teeth, an inner tooth 16b for engaging the second set of planetary gears 3b, and an inner tooth 16c for engaging the supplementary planetary gear 3c.

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

Alternatively, according to an alternative embodiment (not shown), the additional planetary gear 3c can be mounted to the intermediate planet carrier 18 on mounting pins which are arranged at a different radius relative to the planetary gears 3a and/or 3b. Therefore, there does not need to be a fixed relationship between the geometry of the epicyclic gear subsystem comprising the components 3a, 4 and 5a and the components of the epicyclic gear subsystem comprising the components 3c, 5b and 16.

Thus, a similar overall ratio between pedal and wheel speeds can be achieved when the electronically operated locking device 17 is engaged and the second gear ring 16 is stationary, but with a more favorable number of teeth on the second sun gear 5b and the second gear ring 16. For example, to achieve a pedaling speed of 60 rpm required for 25 km/h using the arrangement shown in Figure 1, the second gear ring 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 axle 1 to pass through the center of the second sun gear 5b. However, the alternative embodiment shown in FIG. 7 can provide similar overall system proportions by using a second gear ring 16 having 76 teeth, a second set of planetary gears 3b having 20 teeth, and a set of supplementary planetary gears having 16 teeth. The number of teeth 18c on the middle planet carrier can be 36, and the second sun gear 5b can require 44 teeth. Therefore, the outer diameter of the second gear ring 16 can be reduced by more than 20%, and the diameter of the second, smaller second sun gear 5b can be increased by more than 150%.

It should be understood that the drive system disclosed herein provides a number of advantages and benefits: The epicyclic gear system allows the bicycle to be ridden at high speeds without any electrical assistance; When the electrical assist motor is turned on, the epicyclic gear system can achieve all the functions and advantages of a power-assisted bicycle; When both motors are turned off, system efficiency is optimized at higher driving speeds because both the proportional control motor M1 and the traction motor M2 can be mechanically disengaged from the system when not needed; Neither motor needs to regenerate any electrical energy. This results in a simplified motor control and electronic system, as well as a simplified battery management system that can charge the battery without increasing the motor voltage.

1: Pedal shaft/pedal crankshaft 2: Planet carrier 3a: First set of planetary gears 3b: Second set of planetary gears 3c: Third set of supplementary planetary gears 4: First gear ring 5a: First sun gear 5b: Second sun gear 6: Chain ring 7: Chain/sprocket belt 8: Traction gear 9: Pinion 10: First one-way clutch 11: Second pinion 12: Second one-way clutch 16: Second gear ring 16b, 16c: Internal teeth 17: Locking device 18: Intermediate planetary carrier 18c: Teeth 18d: Pin 19: Supplementary one-way clutch 20: Epicyclic gear mechanism 21: Output shaft 22: Bicycle frame/rigid element M1: Proportional control motor/Control motor M2: Auxiliary motor S ₁ , _S2 : shaft Tc: torque applied to planet carrier 2 Zr: radius of planet carrier 2 Zs: radius of planet gear 3a Fr: tangential force applied to first gear ring 4 Fs: tangential force applied to sun gear 5a Tr: torque applied to gear ring Ts: torque applied to sun gear B: battery C: controller R: rider MR: mechanical route ER: electronic route

In order to better understand the present invention, several preferred embodiments of the present invention will now be given by way of example with reference to the accompanying drawings, wherein: FIG. 1 is a schematic cross-sectional view of the main components of an electric bicycle drive system according to an embodiment of the present invention. FIG. 2 schematically shows the torque distribution relationship through the epicyclic gear mechanism. FIG. 3 to FIG. 6 schematically depict the power flow within the system during different stages of bicycle acceleration. FIG. 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.

without

1: Pedal shaft/pedal crank

2: Planetary carrier

3a: The first set of planetary gears

3b: Second set of planetary gears

4: First tooth ring

5a: First sun gear

5b: Second sun gear

6: Chain

7: Chain/tooth belt

8: Traction gear

9: Small gear

10: First one-way clutch

11: Second small gear

12: Second one-way clutch

16: Second ring

17: Locking device

19: Refill the one-way clutch

20: Epicyclic gear mechanism

21: Output shaft

22: Bicycle frame/rigid components

M1: Proportional control motor

M2: Assisting motor

S ₁ , S ₂ : Axis

Claims (9)

An electric auxiliary drive system for a bicycle comprises: a pedal crankshaft (1) for operation by a rider; an output shaft (21) for transmitting rotation to a rear wheel of the bicycle; an epicyclic gear mechanism (20) arranged to determine a transmission ratio between the pedal crankshaft and the output shaft (21); an auxiliary motor (M2) for driving the output shaft (21); a control motor (M1) drivingly connected to the epicyclic gear mechanism for controlling the transmission ratio between the pedal crankshaft (1) and the output shaft (21) through the epicyclic 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 prevent a first gear ring (4) of the epicyclic gear system from rotating in a first forward rotational direction, and release and allow the first gear ring (4) of the epicyclic gear system to rotate freely in a second reverse rotational direction; A second one-way clutch (12) is operably connected between the auxiliary motor (M2) and the output shaft (21), wherein when the auxiliary motor is turned on, the second one-way clutch (12) is configured to drive the auxiliary motor (M2) to the output shaft (21) to drive the output shaft (21) in a forward direction, thereby assisting in driving the bicycle forward, and when the auxiliary motor is turned off but the output shaft (21) continues to rotate in the forward direction, the auxiliary motor (M2) is disengaged from the output shaft (21); Wherein, the epicyclic gear mechanism (20) further includes: a second gear ring (16) and an associated locking device (17), the locking device (17) being fixedly mounted to a bicycle frame (22) and operable to engage and prevent rotation of the second gear ring (16); a first sun gear (5a) and a second sun gear (5b), both fixed to rotate with the output shaft (21); A first set of planetary gears (3a) and a second set of planetary gears (3b), wherein the first set of planetary gears (3a) is between the first sun gear (5a) and the first gear ring (4), and the second set of planetary gears (3b) is between the second sun gear (5b) and the second gear ring (16); and a planet carrier (2) fixed to rotate with the pedal crankshaft (1) and supporting the first set of planetary gears (3a) and the second set of planetary gears (3b); wherein the first sun gear (5a) and the second sun gear (5b) , and the first set of planetary gears (3a) and the second set of planetary gears (3b) are configured to provide a desired transmission ratio between the pedal crankshaft (1) and the output shaft (21) for transmitting the rotation of the second gear ring (16) to a rear wheel of the bicycle when the rotation of the second gear ring (16) is locked by the locking device (17). An electric auxiliary drive system as described in claim 1, wherein the plurality of planetary gears of the first set of planetary gears (3a) have a diameter that is smaller than the diameter of the plurality of planetary gears of the second set of planetary gears (3b), and wherein the first sun gear (5a) has a diameter that is larger than the diameter of the second sun gear (5b). An electric assisted drive system as described in claim 1 or 2, wherein the transmission ratio is set in the range between 1:3 and 1:4, whereby when the locking device (17) locks the rotation of the second gear ring (16), a single complete revolution of the pedal crankshaft (1) corresponds to a revolution of the rear wheel of the bicycle between 3 and 4. An electric assisted drive system as described in claim 3, wherein the transmission ratio is approximately 1:3.5, whereby when the locking device (17) locks the rotation of the second gear ring (16), a single full revolution of the pedal crankshaft (1) corresponds to 3.5 revolutions of the rear wheel of the bicycle. An electric auxiliary drive system as described in any of the preceding claims, wherein the gears of the epicyclic system are configured to stop the second gear ring (16) from rotating at a predetermined driving speed of the bicycle, and to activate the locking device (17) to lock the second gear ring (16) in place when the driving speed of the bicycle exceeds the predetermined driving speed. An electric assisted propulsion system as described in claim 3, wherein the bicycle has a travel speed of 25 km/h. The bicycle electric auxiliary drive system as described in any of the above claims further includes an intermediate supplementary epicyclic subsystem (18, 3c) acting between the second set of planetary gears (3b) and the second sun gear (5b), the supplementary epicyclic subsystem comprising: an intermediate planetary carrier (18), and a third set of supplementary planetary gears (3c), freely supported on a pin (18d) arranged on the intermediate planetary carrier (18) along a given diameter for rotation, wherein the intermediate planetary carrier (18) has a set of teeth (18c) arranged along a diameter that is smaller than the given diameter of the pin (18d), And the supplementary planetary gear (3c) is radially inwardly engaged with the second sun gear (5b), and radially outwardly engaged with an inner tooth (16c) of the second gear ring (16). An electric auxiliary drive system as described in claim 7, wherein the second gear ring (16) is provided with a pair of axially adjacent inner teeth (16b, 16c), one of the inner teeth (16b) is used to mesh with the second set of planetary gears (3b), and one of the inner teeth (16c) is used to mesh with the supplementary planetary gear (3c). An electric bicycle comprises an electric auxiliary drive system for a bicycle according to any of the preceding claims.