Power-split hybrid driveline for electric bicycles

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 a gear ratio between the pedal crankshaft (1) and the output shaft (21) via the planetary gear mechanism (20). A first one-way clutch (10) operatively connected to the control motor (M1) is configured to prevent rotation of a first rotatable member (4) of the planetary gear system in a forward direction while allowing free rotation in a reverse direction. A second one-way clutch (12) is configured to drivingly connect the assist motor (M2) to the output shaft (21) when the assist motor is switched on, and to decouple the assist motor (M2) from the output shaft (21) when the assist motor is switched off and the output shaft (21) continues to rotate in the forward direction.

Description

[Technical field]

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

[0002] Recently, power-split hybrid drivelines have been proposed for electric bicycles. Some of these systems include a pedal crankshaft for operation by the rider, a planetary gear mechanism, an assist motor, and a control motor. The planetary gear mechanism is arranged to determine a transmission ratio between the pedal crankshaft and an output shaft that transmits rotation to the rear wheel of the bicycle. The planetary gear mechanism is referred to as a planetary "power-split" gear mechanism because it is arranged to transmit power from the pedals to the rear wheel of the bicycle in two paths, a mechanical path and an electrical path. Specifically, the planetary gear mechanism transmits power from the assist motor to the output shaft. In addition, the planetary gear mechanism regulates the rotational speed of the pedal crankshaft through the operation of the control motor.

[0003] WO 2020 / 260772 discloses a power unit for a pedal vehicle. The power unit comprises a pedal shaft, an output shaft arranged to transmit torque to wheels of the vehicle, a main planetary gear set arranged to control a transmission ratio between the pedal shaft and the output shaft, an assist motor connected to an assist gear of the main planetary gear set, and a control motor connected to a control gear of the main planetary gear set. The control motor and the control gear form a control assembly of the power unit. The power unit comprises a one-way clutch associated with the control assembly of the power unit and arranged to transmit rotation only in a first rotational direction.

[0004] The first problem encountered with some planetary "power split" drivelines is that the torque from the pedals is always counteracted by the gear ratio controlled motor. When a low gear ratio bicycle is ridden at low speeds, the gear ratio controlled motor rotates at a lower speed, making the motor very inefficient. Most of the electrical energy delivered to the motor is lost as heat. This shortens the motor's life and leads to inefficient use of the electrical energy stored in the battery.

[0005] Another problem with some planetary "power split" drivelines is that at high speeds and high gear ratios, the ratio control motor spins quickly and counteracts the torque from the pedal while still maintaining the desired pedal speed. As a result, the ratio control motor can provide a high level of mechanical power to the system, so no additional assist from the traction motor is needed, and the traction motor must rotate in unison with the rear wheels, although it may be switched off. Therefore, in these situations, the traction motor generates electrical energy that can damage the electronic systems. Summary of the Invention

[0006] Against this background, the present invention provides an electric assisted drive system for a bicycle having the features defined in claim 1. Preferred embodiments are defined in the dependent claims.

[0007] According to one aspect, the present invention provides an electric assisted drive system for a bicycle, the system including a pedal crankshaft for operation by a rider, a planetary gear mechanism, an assist motor, a control motor, and first and second one-way clutches. The planetary gear mechanism is arranged to determine a transmission ratio between the pedal crankshaft and an output shaft that transmits rotation to a rear wheel of the bicycle. The assist motor is drivingly connected to the output shaft. The control motor is drivingly connected to the planetary gear mechanism for controlling the transmission ratio between the pedal crankshaft and the output shaft. The first one-way clutch is operatively connected between the transmission ratio control motor and a rigid element fixedly mountable to the bicycle frame and configured to block and release rotation of a first rotatable member of the planetary gear system in a first forward direction and to allow free rotation of the first rotatable member of the planetary gear system in a second reverse direction. The second one-way clutch is configured to drivingly connect the assist motor to the output shaft to assist in driving the bicycle forward when the assist motor is switched on and the output shaft is driven in the forward direction, and to disconnect the assist motor from the output shaft when the assist motor is switched off and the output shaft continues to rotate in the forward direction.

[0008] Preferably, the planetary gear mechanism comprises a sun gear fixed for rotation with the output shaft, a ring gear, a set of planetary gears provided between the sun gear and the ring gear, and a planet carrier fixed for rotation with the pedal crankshaft and supporting the planetary gears. According to one embodiment, the ring gear meshes with a first pinion gear mounted on a first shaft driven by a control motor, and a first one-way clutch is operably connected between the first shaft of the control motor and a rigid element fixedly mountable to the bicycle frame.

[0009] In order that the invention may be better understood, certain preferred embodiments will now be described, by way of example only, with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic cross-sectional view showing the main components of an e-bike drive system according to one embodiment of the present invention. [Diagram 2] FIG. 2 shows a schematic diagram of the torque division relationship by the planetary gear mechanism. [Diagram 3] Figure 3 shows a schematic of the power flow through the system during the three stages of bicycle acceleration. [Figure 4] Figure 4 shows a schematic of the power flow through the system during the three stages of bicycle acceleration. [Diagram 5] Figure 5 shows a schematic of the power flow through the system during the three stages of bicycle acceleration. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] 1, the e-bike drive system comprises two electric motors M1, M2 and a planetary gear set 20 having an output shaft 21. Fixed for rotation with the output shaft 21 is a chain ring 6 which drives the rear wheel of the bicycle (not shown).

[0012] A pedal shaft or crankshaft for operation by a rider R is shown at 1. The pedal shaft 1 passes through the assembly and connects two conventional pedal crank and foot support assemblies (not shown in the drawings) mounted externally to the drive unit. The pedal shaft 1 receives the torque and speed supplied by the rider and transmits it to the planet carrier 2.

[0013] Electric motor M1 is referred to as the "control" motor, or "ratio-controlled" motor, because it drives the gears of a planetary gear set that controls the gear ratio between the output shaft and the pedal crankshaft. Electric motor M2, referred to herein as the "assist" motor (or "traction" motor), generates power that is transmitted to output shaft 21.

[0014] In this context, the planetary gear mechanism is also referred to as a planetary "power split" gear mechanism, since the planetary gear mechanism is arranged to transmit power from the pedals to the rear wheel of the bicycle in two paths, a mechanical path MR and an electrical path ER, as will be explained later in this specification. Specifically, the planetary gear mechanism transmits power from the assist motor M2 to the output shaft. Furthermore, the planetary gear mechanism regulates the rotational speed of the pedal crankshaft 7 as a result of the operation of the control motor M1.

[0015] The e-bike drive system is contained within a housing (not shown in the drawings) and is preferably centrally mounted in the frame of the bicycle (at the "bottom bracket") for use. Typically the housing provides the attachment and reaction points for the rolling bearings that rotatably support the pedal crankshaft 1. The housing may also house an electronic controller (not shown in the drawings) for the drive system.

[0016] The planetary gear mechanism 20 comprises a planet carrier 2 which supports a number of planet gears 3 and applies the rider's torque and speed to the planetary gear system. The planet carrier 2 is fixed for rotation with the pedal shaft 1. The pedal shaft 1 receives the torque and speed supplied by the rider and transmits it to the planet carrier 2.

[0017] The power split planetary gear mechanism includes a sun gear 5 that is rotationally driven by the assist motor M2 and is fixed for rotation with a chain ring 6 located on the right side of the system. The sun gear 5 is fixed for rotation with the chain ring 6 and has external teeth that mesh with the planet gears 3.

[0018] The ring gear 4 has internal teeth that mesh with the planetary gears 3, and a large number of external teeth that mesh with a pinion gear 9 that is directly driven by the speed ratio control motor M1.

[0019] The planet gears 3 are free to rotate relative to the planet carrier 2 and therefore exert equal tangential forces on the teeth of the ring gear 4 and sun gear 5 regardless of the relative speeds of these components. Thus, a constant percentage of the torque from the rider is distributed to the ring gear and the remaining percentage of the torque from the rider is distributed to the sun gear.

[0020] The output shaft 21 may be a hollow tubular shaft through which the pedal shaft 1 passes.

[0021] A chain or belt sprocket 6 drives either a chain or a toothed belt 7 which drives the rear wheel of the bicycle.

[0022] A traction gear 8 is fixed for rotation with the sun gear 5 and the sprocket or chainring 6. The traction gear 8 has external teeth which mesh with a second pinion gear 11 which is directly driven by the assist motor M2.

[0023] The first one-way clutch 10 releasably connects the shaft S1 of the ratio control motor M1 to a rigid element 22 fixed to or integrated in the bicycle frame. Preferably, the fixed rigid element 22 may be the housing of the drive unit.

[0024] The first one-way clutch 10 is arranged to prevent rotation of the ring gear 4 in a forward direction (i.e. the forward direction is the direction that the pedals, chain and wheels rotate when the bicycle is moving forward) but to allow free rotation of the ring gear 4 in the reverse direction. According to one embodiment, the first one-way clutch 10 may comprise a one-way roller bearing that is press fit into a bore in the housing 22.

[0025] As shown in the exemplary embodiment shown in FIG. 1, the first shaft S1 of the control motor M1 is parallel to the axis of rotation of the ring gear 4.

[0026] According to an alternative embodiment (not shown), the first shaft S1 of the control motor M1 may be oriented perpendicular to the axis of rotation of the ring gear 4, so that the ring gear 4 forms internal teeth that mesh with the planetary gears 3 and side teeth that mesh with the first pinion gear 9 according to a bevel gear arrangement.

[0027] 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 so that the assist motor M2 can assist in driving the bicycle forward.

[0028] A second one-way clutch 12 connecting the assist motor M2 and its pinion gear 11 is positioned to engage when the assist motor M2 attempts to drive the traction gear 8 in the forward direction, thereby assisting in driving the bicycle forward. The second one-way clutch 12 allows the traction gear 8 to rotate freely when the assist motor M2 is turned off and the traction gear 8 continues to rotate in the forward direction.

[0029] The first and second one-way clutches 10, 12 may be in the form of, for example, a pawl and ratchet, or a sprag clutch having rollers that ride up a ramp in a cage, or a belt or strap wrapped around a shaft.

[0030] With the above arrangement, the control motor M1 controls the ratio between the rotation speed of the pedals and the rotation speed of the bicycle by controlling the rotation speed of the ring gear 4. The assist motor M2 drives the traction gear 8 to apply torque to the chain gear 6, assisting the forward movement of the bicycle.

[0031] The e-bike drive system described above works as follows: When the bike starts moving from a stationary state, the rider applies a torque to the system via the pedals. This torque is transferred to the system via the pedal shaft 1, the planet carrier 2 and the planetary gears 3. The planetary gears then distribute this applied torque between the ring gear 4 and the sun gear 5.

[0032] The torque distribution between the ring gear and the sun gear is shown diagrammatically in FIG. Tc = Torque applied to planet carrier 2 Zr = radius of planet carrier 2 Zs = radius of planet gear Fr = tangential force on ring gear 4 Fs = tangential force acting on sun gear 5 Fr=Fs=1 / 2*Tc / Zr Tr = Torque applied to ring gear: Tr = Fr * (Zr + Zs) Ts = Torque acting on the sun gear: Ts = Fs * (Zr-Zs)

[0033] Starting from a stationary state (FIG. 3), the control motor M1 is switched off. A torque Tr is applied to the ring gear 4 in the forward direction, but the first one-way clutch 10 is arranged to prevent the ring gear 4 from rotating forward. The torque Tr is therefore counteracted by the first one-way clutch 10 and the ring gear 4 remains stationary. Thus, all the power provided by the rider R is diverted to the sun gear 5 and, via the sprocket or chain gear 6 and the chain or belt 7, to the bicycle wheel. The gear ratio between the bicycle pedals and the wheel is expressed as: Overall gear ratio = (rotational speed of bicycle wheel) / (rotational speed of pedal)

[0034] Due to the action of the first one-way clutch 10, which allows the ring gear 4 to rotate in the reverse direction but not in the forward direction, the overall gear ratio is lowest when the ring gear 4 is stationary. The planetary gear system ratio and the chain or belt ratio may be arranged so that the ratio with the ring gear stationary is equal to a ratio suitable for starting the bicycle from a stationary state and for climbing steep hills. Incidentally, this lowest ratio may be numerically equal to approximately 1 for a touring or commuting bicycle.

[0035] When starting from a stationary state, power may be applied to the traction motor M2 from the battery 17 via the control device 16 to assist the rider in moving the bicycle forward. The traction motor M2 applies torque to the traction gear 8 via the second one-way clutch 12 and the pinion gear 11 to move it in the forward direction, assisting in forward acceleration of the bicycle. The second one-way clutch 12 is arranged to be locked when the traction motor M2 is applying torque to the traction gear 8 in the forward direction.

[0036] As the bicycle begins to pick up speed, an increase in the overall gear ratio is required 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 ring gear 4 in the reverse direction. This action unlocks the first one-way clutch 10 which is arranged to allow free reverse rotation of the ring gear 4. The speed of the control motor M1 is controlled to maintain the desired ring gear rotational speed (Wr) given by: Wr = (Wc(Zr+Zs)-Ws×Zs) / Zr Where: Wc = desired rotation speed of pedal shaft 1 Ws = rotational speed of sun gear 5 Wr = the resulting required number of revolutions of ring gear 4 Zr and Zs are the system radii that define the lever ratio in the planetary gear system as shown graphically in Figure 2.

[0037] As the control motor M1 begins to increase its RPMs to maintain a comfortable pedaling speed, mechanical power begins to be supplied to the system. Power M1 =Wr*Tr where Tr is the torque applied to ring gear 4 to react to the rider's pedaling torque (as shown in FIG. 2).

[0038] 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 to assist the rider in propelling the bicycle forward.

[0039] As the speed of the bicycle increases further, the torque Tr applied by the rider tends to remain substantially constant, but the speed of the control motor M1 continues to increase in order to maintain a comfortable pedaling speed, thus increasing the power of the control motor M1. At some point, which can be set by programming the controller 16, the power of the control motor M1 increases. M1 is sufficient to provide the bicycle with the desired electrical assist force and no further assistance from the traction motor M2 is required. To conserve electrical energy, the traction motor M2 may be switched off (FIG. 5). The bicycle continues to move forward, assisted by power from the rider and the gear ratio control motor M1, so that the traction gear 8 continues to rotate in the forward direction. However, the traction motor M2 no longer exerts a forward torque on the traction gear, so that the second one-way clutch 12 is unlocked and the pinion gear 11 is free to rotate relative to the shaft of the traction motor M2. Thus, the traction motor M2 is stationary and no deceleration torque is transmitted to the traction gear 8 and thus to the bicycle wheel.

[0040] It can be observed that in the absence of the first one-way clutch 10, when starting from rest at low speed ratios (FIG. 3), the torque Tr needs to be countered only by the controlled motor M1. The controlled motor M1 consumes electrical energy, since a current needs to flow through the motor windings to generate the required single counter torque. However, since the controlled motor M1 is stationary, it does not generate mechanical energy. Therefore, all the electrical energy is converted to heat in the motor windings, which is inefficient and also negatively impacts the durability of the motor.

[0041] It can also be observed that, in the absence of the second one-way clutch 12, when accelerating at high speeds (Figure 5), the control motor M2 would continue to rotate and apply a deceleration torque to the traction gear 8 and, consequently, to the bicycle wheel. Also, voltages would be generated in the motor windings that could damage the motor's electronic control system.

[0042] The following advantages and benefits of the drive system are appreciated:

[0043] Heating of the gear ratio control motor M1 is reduced, thereby improving the efficiency and durability of the drive system.

[0044] The locking capability of the first one-way clutch 10 allows the bicycle to be run (in the lowest gear ratio) even when there is no power to either motor, such as when the battery is dead. This is an inherent property of the system operation and does not require the selection of special locking devices or operating modes of the system.

[0045] The traction motor M2 can be mechanically disconnected from the system when not required, improving system efficiency at higher road speeds.

[0046] Because the traction motor M2 does not generate braking torque, it does not generate voltages in its windings that could damage electronic systems.

[0047] Neither motor needs to regenerate electrical energy, which leads to simplified motor control and electronic systems, and a simplified battery management system that does not need to boost the motor voltage to charge the battery.

Claims

1. An electric assisted drive system for a bicycle, comprising: A pedal crankshaft (1) for operation by a rider; a planetary gear mechanism (20) arranged to determine a transmission ratio between the pedal crankshaft and an output shaft (21) for transmitting rotation to a rear wheel of the bicycle; an assist motor (M2) that drives the output shaft (21); a control motor (M1) drivingly connected to the planetary gear mechanism and controlling a gear ratio between the pedal crankshaft (1) and the output shaft (21) via the planetary gear mechanism (20); a first one-way clutch (10) operably connected between a transmission ratio control motor (M1) and a rigid element (22) fixedly mountable to a bicycle frame, said first one-way clutch (10) configured to block and release a first rotatable member (4) of a planetary gear system from rotating in a first forward direction while allowing free rotation of said first rotatable member (4) of said planetary gear system in a second reverse direction; a second one-way clutch (12) operably connected between the assist motor (M2) and the output shaft (21), the second one-way clutch (12) being configured to drivably connect the assist motor (M2) to the output shaft (21) to assist in the forward driving of the bicycle when the assist motor is switched on to drive the output shaft (21) in a forward direction, and to decouple the assist motor (M2) from the output shaft (21) when the assist motor is switched off and the output shaft (21) continues to rotate in the forward direction; and A drive system comprising:

2. The planetary gear mechanism (20) a sun gear (5) fixed for rotation with said output shaft (21); A ring gear (4), a set of planetary gears (3) disposed between the sun gear (5) and the ring gear (4); A planet carrier (2) fixed to rotate with the pedal crankshaft (1) and supporting the planet gear (3); Equipped with The ring gear (4) meshes with a first pinion gear (9) attached to a first shaft (S1) driven by the control motor (M1); 2. The drive system of claim 1, wherein the first one-way clutch (10) is operably connected between the first shaft (S1) of the control motor (M1) and the rigid element (22) that is fixedly mountable to the bicycle frame.

3. 3. A drive system according to claim 2, wherein the ring gear (4) forms internal teeth meshing with the planetary gears (3) and external teeth meshing with the first pinion gear (9).

4. 3. A drive system according to claim 2, wherein the ring gear (4) forms internal teeth meshing with the planetary gears (3) and side teeth meshing with the first pinion gear (9) according to a bevel gear arrangement.

5. a second pinion gear (11) releasably and drivably connected to a shaft (S2) of the assist motor (M2) via the second one-way clutch (12); a traction gear (8) fixed to rotate with the output shaft (21) and meshing with the second pinion gear (11); A drive system according to claim 1 , comprising:

6. 6. A drive system according to any one of claims 1 to 5, wherein the output shaft (21) comprises an axially extending central tubular portion coaxially surrounding the length of the pedal crankshaft (1).

7. An electric bicycle comprising a drive system according to any one of claims 1 to 6.

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