GB2608625A - Electrically-assisted pedal cycles - Google Patents

Abstract

An electrically-assisted pedal cycle drive system comprises an input 80 that receives drive from a pedal of the cycle and an output that provides drive to a driven wheel of the cycle. An electrical machine 5,6 provides motor drive. The drive train comprises an epicyclic gear set having a sun gear 21, a planet carrier 23, a plurality of planet gears 22 and an annulus gear 24 that rotates with the output. The epicyclic gear set transmits drive from pedal to its annulus via its planet carrier 23. The sun gear 21 is driven by the electrical machine 5,6. The drive train also comprises a one-way clutch V between the planet carrier 23 and a fixed part of the drive system 1, to allow rotation of the planet carrier 23 in only one direction.

Description

ELECTRICALLY-ASSISTED PEDAL CYCLES

[0001] The present invention relates to electrically-assisted pedal cycles.

[0002] There are various forms of pedal cycle. One conventional form of pedal cycle is that which is only ever driven by a cyclist applying force to the pedals, such cycles sometimes being referred to as "push bikes". Another more recent form of pedal cycle is the electrically-assisted pedal cycle, commonly now known as an "e-Bike", in which electrical power is used to assist or replace the efforts of the rider. Both conventional pedal cycles and e-Bikes may have two, three or four wheels, and, in some, cases even more. In the present document, the term "pedal cycle" is used to include both conventional pedal cycles and e-Bikes.

[0003] As mentioned, in an e-Bike, electrical power is used to assist, or in some cases replace, the efforts of the rider. Accordingly, e-Bikes include means for storing electrical energy, such as batteries, and an electric motor arranged to propel, either in combination with pedal input, or to replace pedal input. The batteries can be recharged by plugging them into a supply of electrical energy, such as an outlet from a mains supply; in some cases, also by recovering energy from motion of the cycle by way of regenerative braking, and in others by generation of electricity in a series hybrid configuration. The principle of regenerative braking will be familiar to those skilled in this field of technology.

[0004] e-Bikes may be placed generally into one of two groups. The first group is that in which the cycle can provide electrical assistance on demand, at any time, regardless of whether or not the cyclist is pedalling. Cycles in this group can be thought of as being generally equivalent to electric mopeds. The pedal input may be rarely used or only as a "limp home" capability when the battery is -2 -discharged. Cycles in the second group only provide electrical assistance when the cyclist is pedalling. These are referred to as "pedelecs".

[0005] Currently, in many countries, including the UK, pedelecs are effectively legally classified as conventional bicycles and so may be ridden without a driving license or insurance, providing electrical assistance ceases at a speed of 25kph (although a separate category of "speed pedelecs" with a speed limitation of 45kph has license and insurance requirements). There are therefore few barriers to owning and operating a pedelec.

[0006] In recent years, technical advances have been made to the electro-mechanical drive arrangements and to the associated energy storage and recovery devices used in e-Bikes. These advances have resulted in e-Bikes that can be operated with greater efficiency, and hence greater ease, by the cyclist.

[0007] For all the reasons given above, e-Bikes are becoming increasing popular, all over the world.

[0008] By way of background, the reader is referred to our PCT publications W02010/092345, W02017/021715 and W02018/020259, where much information about e-Bikes is provided. There is particular reference to the use of continuously variable transmissions (CVTs) in pedelecs.

[0009] The use of CVT's in pedelecs is recent and is characterized by significant ease-of-use advantages. Nonetheless, given the earlier adoption of direct drive systems in pedelecs, the riding feeling of a CVT requires to be adapted to make it behave and feel similar to a direct drive, which has become the norm. This involves modifying the mechanical configuration of the CVT to provide additional boost capability at launch and in high torque requirement -3 -situations. The question then arises as to how that extra electrical assistance is switched in and out in a controlled and smooth manner.

[0010] Preferred embodiments of the present invention aim to provide pedelecs and drive systems for them, in which an electrical power boost may be provided in a predictable and repeatable manner, in order to afford a ride that feels as natural as possible to a rider. Embodiments of the invention may be particularly effective in the use of a 3-branch power combining epicyclic transmission (two inputs and one output) in a CVT transmission.

[0011] Preferred embodiments of the present invention aim to provide electrically-assisted pedal cycles and drive systems for them, in which the drive systems are relatively light and compact.

[0012] According to one aspect of the present invention, there is provided a drive system for an electrically-assisted pedal cycle, the system comprising: an input that, in use, receives drive from a pedal of the cycle and rotates about an axis; an output that, in use, rotates about said axis to provide drive to a driven wheel of the cycle; an electrical machine that, in use, provides motor drive to said output; and a drive train that, in use, receives drive from the electrical machine and the pedal and transmits drive to said output: wherein: the drive train comprises an epicyclic gear set having a sun gear, a planet carrier, a plurality of planet gears and an annulus gear, the planet gears being -4 -mounted on the planet carrier and meshing with both the sun gear and the annulus gear, and the annulus gear being connected to said output to rotate, in use, with said output: the epicyclic gear set, in use, transmits drive from a pedal to its annulus via its planet carrier: the sun gear is connected to be driven by the electrical machine: and the drive train further comprises a one-way clutch between the planet carrier and a fixed part of the drive system, to allow rotation of the planet carrier in only one direction.

[0013] Preferably, the drive train further comprises a one-way clutch between the planet carrier and annulus of the epicyclic gear set, to prevent the planet carrier from rotating faster than the annulus in the direction that causes the cycle to travel forward.

[0014] Each planet gear may be of compound configuration, having a smaller gear and a larger gear that are rotationally solid with one another, one of the smaller and larger gears meshing with the annulus and the other of the smaller and larger gears meshing with the sun.

[0015] Preferably, the epicyclic gear set is a dual gear set comprising a first set of first sun, planets, planet carrier and annulus; and a second set of second sun, planets, planet carrier and annulus; the second sun being rotationally solid with the first planet carrier; the second planet carrier receiving drive from a pedal, in use; the first sun receiving drive from the electric motor, in use; and both the first annulus and the second annulus rotating, in use, with said output. -5 -

[0016] The first annulus and second annulus may be formed as a common annulus.

[0017] In another aspect, the invention provides a drive system for an electrically-assisted pedal cycle, the system comprising: an input that, in use, receives drive from a pedal of the cycle and rotates about an axis; an output that, in use, rotates about said axis to provide drive to a driven wheel of the cycle; an electrical machine that, in use, provides motor drive to said output; and a drive train that, in use, receives drive from the electrical machine and the pedal and transmits drive to said output: wherein the drive train comprises a dual epicyclic gear set having a first set of first sun, planets, planet carrier and annulus; and a second set of second sun, planets, planet carrier and annulus; the second sun being rotationally solid with the first planet carrier; the second planet carrier receiving drive from a pedal, in use; the first sun receiving motor drive from the electric machine, in use; and both the first annulus and the second annulus rotating, in use, with said output.

[0018] Preferably, the drive train further comprises a one-way clutch between the second planet carrier and annulus of the epicyclic gear set, to prevent the second planet carrier from rotating faster than the annulus in the direction that causes the cycle to travel forward. -6 -

[0019] The drive train may further comprise a selectively actuable clutch between the second sun and a fixed part of the drive system.

[0020] The first annulus and second annulus may be formed as a common annulus.

[0021] Preferably, a drive system according to any of the preceding aspects of the invention further comprises a free-wheel mechanism that is operative between the pedals and driven wheel of the cycle.

[0022] Preferably, in a drive system according to any of the preceding aspects of the invention, the electrical machine is configured to operate selectively as a generator or a motor and the system further comprises a controller that alternately operates the electrical machine as a generator for a first period and then as a motor for a second period, the controller obtaining an indication of torque applied at the inner hub as a function of generator output, and then applying power to the motor as a function of the torque indicated.

[0023] A drive system according to any of the preceding aspects of the invention may be located at a mid-position of the cycle, wherein said axis is an axis of rotation of the pedals.

[0024] Alternatively, a drive system according to any of the preceding aspects of the invention may be located at a hub of a driven wheel of the cycle, wherein said axis is an axis of an axle about which the driven wheel rotates.

[0025] Preferably, said driven wheel is a rear wheel of the cycle.

[0026] The invention extends to an electrically-assisted pedal cycle having a drive system according to any of the preceding aspects of the invention. -7 -

[0027] Such an electrically-assisted pedal cycle may be a pedelec in which electrical assistance is provided only when the cyclist is pedalling.

[0028] Alternatively, electrical assistance may be available both when the cyclist is pedalling and also when the cyclist is not pedalling.

[0029] Such an electrically-assisted pedal cycle may have a throttle control by which a cyclist can apply or superimpose a desired amount of electrical assistance.

[0030] A method of operating an electrically-assisted pedal cycle as above, comprising the steps of providing motor drive to the driven wheel of the cycle by said electrical machine and providing pedal drive to the driven wheel of the cycle, via said drive train.

[0031] In the context of this specification, the term 'pedelec' means an electrically-assisted pedal cycle in which electrical assistance is provided only when the cyclist is pedalling.

[0032] For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings, in which: [0033] Figure 1 is a side view of a pedelec; [0034] Figure 2 is a mostly sectional view of a drive system for the pedelec; [0035] Figures 3A and 3B illustrate the motion of gears of an epicyclic gear set of the drive system; -8 - [0036] Figure 4 is a diagrammatic representation of an alternative drive system for the pedelec, employing a compound epicyclic gear set; [0037] Figure 5 is a diagrammatic representation of another alternative drive system for the pedelec, employing a dual epicyclic gear set; [0038] Figure 6 is a mostly sectional view of another alternative drive system for the pedelec, in a mid-drive configuration; and [0039] Figure 7 is a diagrammatic representation similar to Figure 5, but showing an alternative clutch configuration.

[0040] In the figures, like references denote like or corresponding parts.

[0041] It is to be understood that the various features that are described in the following and/or illustrated in the drawings are preferred but not essential. Combinations of features described and/or illustrated are not considered to be the only possible combinations. Unless stated to the contrary, individual features may be omitted, varied or combined in different combinations, where practical.

[0042] Figure 1 shows a pedelec in the form of a bicycle 10. The bicycle 10 is similar to a conventional bicycle in having a steerable wheel 20 at the front and a driveable wheel 30 at the back. The bicycle 10 also has a conventional arrangement of pedals 40 on crank arms 50 that drive a front toothed cog 60 connected by a chain 70 to a rear sprocket 80, the rear sprocket being mounted co-axially with the rear wheel 30. However, the bicycle 10 differs from a conventional bicycle in that the rear sprocket 80 is not fixedly mounted to a hub 100 of the rear wheel 30 to drive that wheel directly. Instead, the rear sprocket 80 provides a rider's power input to a drive system that is disposed within the -9 -hub 100. A control housing 90 and a battery housing 92 are fitted to the frame of the bicycle 10.

[0043] A drive system is mounted within the hub 100 and is described as follows, with reference to Figure 2. For ease of explanation, the hub 100 is referred to in the following as an outer hub 100 and provides an output of the system. The outer hub 100 is typically connected to the outside of the rear wheel 30 by spokes, or by any other connection, to provide drive to the rear wheel 30.

[0044] As mentioned above, the sprocket 80 is not connected directly to the outer hub 100, as would be the case with a regular bicycle. Instead, it is connected to an inner hub 2 (not shown in section) that is mounted on bearings for rotation about a fixed axle 1, which is secured to the bicycle frame. The sprocket 80 incorporates a freewheel mechanism, as found on many regular bicycles. The outer hub 100 is of generally cylindrical shape and is mounted at a first end on the inner hub 2, via a first one-way clutch K. An opposite end of the outer hub 100 is mounted on the axle 1 by way of bearings 101. The outer hub 100 and the inner hub 2 are rotatable about a common axis, which is the axis of the axle 1. The one-way clutch K could be made up of a bearing and a separate clutch.

[0045] An electrical machine comprises a stator 5 that is fixedly mounted on the axle 1 and a rotor 6 that is mounted on a split shaft 7A, 7B (not shown in section) that is mounted on suitable bearings for rotation about the axle 1. A single epicyclic gear set EP connects the shaft 7B to the outer hub 100. The axle 1 is hollow and receives cables to connect a controller 91 (and a battery 93) to components of the drive system. In a variant, the shaft 7A could be omitted.

-10 - [0046] The epicyclic gear set EP comprises a sun gear 21 that is mounted on the shaft 7B at one side of the motor 5,6, three planet gears 22 that are mounted on a planet carrier 23, and an annulus gear 24 that is secured to the outer hub 100. The planet carrier 23 is connected to the inner hub 2, to rotate with it. The epicyclic gear set EP thus provides drive between the rotor 6 of the electrical machine and the outer hub 100. It also provides drive between the sprocket 80 and the outer hub 100. The planet carrier 23 is also connected to the axle 1 via a second one-way clutch V. There may be a different number of planet gears 22 2, 3 or more.

[0047] The epicyclic gear set EP translates physical effort from the pedals 40 into motion of the rear wheel 30, via the sprocket 80 and planet carrier 23. The one-way clutch K prevents the planet carrier 23 from rotating faster, in the direction of motion corresponding to the bike moving forward, than the annulus 24 and outer hub 100.

[0048] With reference to Figure 3A, when the outer hub 100 and therefore the annulus 24 are stationary, if an anticlockwise rotation of the planet carrier 23, which would cause the sun 21 to rotate anticlockwise, is resisted by the electric motor through the sun 21, it will create a torque on the annulus 24 tending to rotate the annulus 24 and outer hub 100 anticlockwise, in the direction of ride. With reference to Figure 3B, when the outer hub 100 and therefore the annulus 24 are stationary, if the sun 21 is driven clockwise by the rotor shaft 7B, and the planet carrier 23 is prevented from rotating clockwise by the rider through the chain and pedals, it creates a torque on the annulus tending to rotate the annulus 24 and outer hub 100 anticlockwise, in the direction of ride.

[0049] Motor drive from the rotor 6 is used to boost speed by driving the sun gear 21 clockwise (as seen from the left-hand side of Figure 2 in the direction of arrow A). In this case, without the rider rotating the planet carrier anticlockwise, the planet carrier 23 would also tend to rotate clockwise, but it is fixed to the axle 1 via the clutch V, which allows the planet carrier 23 to rotate only in an anticlockwise direction. Thus, the planet gears 22 rotate anticlockwise, causing anticlockwise rotation of the annulus gear 24 and thus the outer hub 100, in the direction of ride.

[0050] In summary, power input by a rider from the pedals 40 is transmitted to the planet carrier 23 via the sprocket 80 and thus to the outer hub 100 to drive the rear wheel 20. Electrical assistance from the rotor 6 is supplied via the sun 21. EP thereby affords a continuously variable transmission (CVT). Examples of such CVTs are given in our WO publications mentioned above.

[0051] Upon setting off, an electrical boost is provided via the epicyclic gear set. As the planet carrier 23 is locked by one-way clutch V, a direct drive is provided from the rotor 6 to the sun 21 and thereby through the gear train to the outer hub 100. Electrical boost is also available at other times when required such as, for example, climbing a hill. When pedalling stops and/or a brake of the bicycle 10 is applied, this is detected and controller 91 ceases the supply of power to the motor 5,6.

[0052] By adopting the option of a torque sensor, to which the controller 91 responds, it is possible for the motor 5,6 to react closely to natural variation in rider pedalling torque, within a revolution of the cranks, and minimise consequent variation in rider cadence.

-12 - [0053] In a direct drive option, an additional advantage of the use of a torque sensor could be the capability of controlling the motor torque output by sensing the torque on the pedal, rather than through the use of a custom device for torque modulation.

[0054] The clutch V grounding the carrier 23, by connection to the fixed axle 1, allows the motor 5,6 to drive the bike directly. It also serves as a crankbackward-movement preventer, which can eliminate the risk that the crank 50 is turned backwards by the motor 5,6. The illustrated configuration allows the bicycle 10 to be pushed in a walk-by-side mode, without blocking the hub 100. Whilst pushing, some motor assistance may be provided. For example, according to regulations in the EU, whilst pushing a pedelec, the person pushing the vehicle may use a walk-by-assist button to activate the motor to provide him/her with additional torque up to a bike speed of 6 km/h.

[0055] An advantage of the design of Figure 2 is that the single epicyclic gear set EP can be relatively light and compact. However, it may be desirable to attain a relatively high gear ratio -for example of the order of 15:1, 18:1 or 25:1. In the configuration of Figure 2, this might dictate a relatively large overall diameter.

[0056] Figure 4 illustrates an alternative configuration that employs a compound epicyclic gear set, to obtain a relatively high gear ratio for a given torque capacity, without a relatively large overall diameter. In Figure 4, corresponding reference numerals denote parts corresponding to those of Figure 2, which have been explained above. Figure 4 is somewhat more diagrammatic than Figure 2, but will connect with a controller 91 and battery 93, along the lines of those shown in Figure 2.

-13 - [0057] In Figure 4, pedal drive is transmitted to rear sprocket 80 that is connected to planet carrier 23 to drive it in rotation. Planet gears (22) transmit drive to annulus gear 24 that rotates with outer hub 100. However, in Figure 4, each planet gear (22) is of compound configuration, comprising a smaller gear 22a that meshes with the annulus gear 24 and is rotationally solidly connected with a larger gear 22b that meshes with the sun 21 that is driven by the rotor 6 of the motor 5, 6. In this way, the gear ratio afforded by the planet gears (22) between the sun 21 and annulus 24 can be increased, without significantly increasing the overall diameter of the epicyclic gear set.

[0058] As before, one-way clutch K is connected between the planet carrier 23 and outer hub 100. One-way clutch V is connected between the planet carrier 23 and axle 1.

[0059] In the further alternative of Figure 5, a dual epicyclic gear set is employed, to achieve a high gear ratio and, in particular, a small packaging space for a given torque capacity. The dual epicyclic gear set comprises a first epicyclic set of first sun 21c, planets 22c, planet carrier 23c and annulus 24c; and a second epicyclic set of second sun 21, planets 22, planet carrier 23 and annulus 24.

[0060] As in Figure 4, pedal drive is transmitted to rear sprocket 80 that is connected to planet carrier 23 to drive it in rotation. Planet gears 22 transmit drive to annulus gear 24 that rotates with outer hub 100. However, in Figure 5, the sun gear 21 that meshes with the planet gears 22 is rotationally solidly connected to planet carrier 23c of the first epicyclic gear set. Planet carrier 23c meshes with annulus gear 24c that rotates with outer hub 100, and also with sun gear 21c that is driven by the rotor 6 of motor 5, 6.

-14 - [0061] As before, one-way clutch K is connected between the planet carrier 23 and outer hub 100. One-way clutch V is connected between the planet carrier 23 and axle 1.

[0062] The configurations or Figures 4 and 5 may avoid the need for large planets with a high number of fine teeth, whilst still achieving a high gear ratio. In the case of a large planet with a high number of fine teeth, the teeth may have to be relatively wide, to have the requisite strength to transmit the requisite torque. Employing additional gears, as in Figures 4 and 5, may enable less fine teeth requiring less width, and therefore less space and weight.

[0063] Enabling higher gear ratios enables the motor 5,6 to generate a given output power at higher speeds and lower torques, often leading to higher efficiency under varying conditions.

[0064] Figure 7 shows an arrangement similar to Figure 5. However, in Figure 7, the one-way clutch V of Figure 5 is replaced with a lockable clutch C connected between the sun 21 and axle 1. Selective actuation of the clutch could be manual or electronic, by a mechanical, electromagnetic or hydraulic arrangement.

[0065] The drive system shown in Figure 6 operates in a similar manner to the system of Figure 2. However, the Figure 6 variant is configured for use as a central or mid-drive location, around a spindle connecting two pedal cranks 50.

[0066] Drive from the pedals 40 is transmitted to planet carrier 23 which, in this case, is secured to shaft 150 that is driven in rotation with the pedal cranks 50. Shaft 150 therefore provides the input.

[0067] The motor 5, 6 has a stator 5 mounted to a housing 130 that is secured to a frame of the cycle at 140. The housing 130 has bearings 101 at one end, -15 -which engage with the shaft 150, and bearings 103 that engage at the other end with an output member 100 which, in turn, is mounted on bearings that engage the shaft 150 and provides the output. The output member 100 and the shaft 150 are rotatable about a common axis, which is the axis of rotation of the pedal cranks 50. The housing 130 has an intermediate wall 131 to form an enclosure around the motor 5, 6.

[0068] The rotor 6 is mounted on output shaft 7 which, in turn, is mounted on shaft 150 via bearings. Sun gear 21 is mounted on shaft 7. Planet carrier 23 is connected to the intermediate wall 131 of the housing 130, or directly to the housing 130, via one-way clutch V, which grounds the clutch V in one direction. Annulus gear 24 is connected to the output member 100. One-way clutch K is effective between the planet carrier 23 and output member 100, to prevent the pedals from rotating faster than the element transmitting drive to the rear wheel (in Figure 6, this is chain ring or wheel 60).

[0069] In use, input from the pedal cranks 50 is applied to planet carrier 23.

Motor drive is provided to sun gear 21. Drive from output member 100 is transmitted to a driven wheel via chain ring or wheel 60 that connects to a drive sprocket on the driven wheel, typically via a freewheel mechanism. Whilst a chain drive is most common, other configurations such as belt drive or drive shaft are possible.

[0070] Other than the changes in configuration, the drive system of Figure 6 operates in a similar manner to that of Figure 2. However, it is more suited to location as a central or mid-drive, adjacent to the pedal cranks 50 and their connecting spindle. In this configuration, the gear ratio of the epicyclic gear set may be different to that in the rear drive configuration.

-16 - [0071] Whilst the drive system of Figure 6 relates to the embodiment of Figure 2, with a single epicyclic gear set, it may alternatively be configured with a compound or dual epicyclic gear set, along the lines of the embodiments of Figures 4, 5 and 7.

[0072] As an option, the electrical machine 5,6 may be configured to operate selectively as a generator or a motor and the controller 91 alternately operates the electrical machine 5,6 as a generator for a first period and then as a motor for a second period, the controller 91 obtaining an indication of torque applied at the inner hub 2 as a function of generator output, and then applying power to the motor 5,6 as a function of the torque indicated. Such an arrangement is disclosed in our publication W02017/021715.

[0073] The above description is given with reference to a pedelec, in which electrical assistance is provided only when the cyclist is pedalling. At the present time, pedelecs are commercially attractive since, in many countries, as mentioned above, a licence is not needed to ride a pedelec. However, different countries have different licensing regimes and, in some countries, an electrically-assisted pedal cycle may be ridden without a licence, even when electrical assistance is provided when the cyclist is not pedalling. Thus, there is an option to modify operation of the above-described embodiments to include electrical assistance when the cyclist is not pedalling.

[0074] Such an option needs no modification of the mechanical arrangement of the above-described drive systems. It can be achieved by providing the user with a throttle control -for example, a twist-grip control incorporated in the handlebar of the cycle. Referring to Figure 2 by way of example, the output of the throttle control is connected to the controller 91. In normal pedelec mode, the controller 91 runs an algorithm that calculates in real time a PWM value as a -17 -command to control the motor 5,6. This PWM value determines how much current is applied to the motor and what torque the motor produces. In the case of electrical assistance when the cyclist is not pedalling, if the rider wishes to increase speed, the rider uses the throttle control to simply increase the motor torque by increasing the PWM value at the rider's will.

[0075] Examples of operation of the above described and illustrated embodiments are as follows.

[0076] In the embodiment of Figure 5, in pedelec operation, the rider starts pedalling and clutch K is engaged. In certain countries, the law requires that motor assistance is not allowed until a speed of 5 kph is reached. At 5 kph or more, the motor 5,6 starts applying power and it rotates in the direction that will result in slowing the pedalling action, therefore contributing to powering the bike, as the rider will try to oppose the resistance.

[0077] In throttle operation, the motor 5,6 can power the bike at any speed and the rider is not applying any torque to, or rotating the pedals. In this case, the motor will try to turn the planet carrier 23c in the opposite sense to the normal pedal action, but it will be prevented from doing so by the one-way clutch V, therefore propelling the bike forward.

[0078] Turning now to the embodiment of Figure 7, in pedelec operation, the rider starts pedalling and if clutch C is not engaged, then the one-way clutch K will prevent the planet carrier 23 from rotating faster than the annulus 24, therefore allowing the rider to propel the bike forward. If clutch C is engaged (either electronically or manually), this will change the rider cadence for the same bike speed. Thus, the clutch C acts as a kind of gearbox.

-18 - [0079] At 5 kph or more, the motor 5,6 starts applying power and it rotates in a direction to slow the pedalling action. At the same time, the clutch C is disengaged (if it was previously engaged) and the motor 5,6 will start slowing the pedalling action, therefore contributing to powering the bike, as the rider will try to oppose the resistance.

[0080] In throttle operation, as in Figure 5, the motor 5,6 can power the bike at any speed and the rider is not applying any torque to the pedals. The clutch C needs to be engaged. Then, as before, the motor 5,6 will try to turn the planet carrier 23c in the opposite sense to the normal pedal action, but it will be prevented from doing so by the clutch C, therefore propelling the bike forward. In this mode, clutch K does not come into play.

[0081] Clutch C may allow the rider to switch between pedelec and throttle modes.

[0082] In a variant of Figure 7, the one-way clutch K is omitted. Pedelec operation is similar to that described above. However, the absence of clutch K makes it possible for the rider to reverse the rotation of the motor by applying a large pedal torque, therefore feeling the pedals slip, unless clutch C is reengaged promptly at the appropriate motor speed. Throttle operation in the variant of Figure 7 is the same as before.

[0083] In both Figures 5 and 7, all of the gears contribute to the overall gear ratio in pedelec mode. In Figure 5, all of the gears contribute to the overall gear ratio from motor to wheel. The embodiments of both Figures 5 and 7 are particularly well suited to transmitting torque that is high for the size of the gear sets, since torque is transmitted to the outer hub 100 via both of the annulus gears 24 and 24c.

-19 - [0084] The above-described and illustrated examples of the invention may provide drive systems for electrically-assisted pedal cycles that are effective whilst being relatively light and compact. They are conducive to providing improved matching, or balancing, between rider input and motor input.

[0085] The epicyclic gear sets may employ either straight or helical gearing with tooth profiles of either involute or cycloidal geometry-e.g. of the type disclosed in WO 2009/008767 and EP 2177788 -for best trade-off of packaging space and torque capability.

[0086] In this specification, the verb "comprise" has its normal dictionary meaning, to denote non-exclusive inclusion. That is, use of the word "comprise" (or any of its derivatives) to include one feature or more, does not exclude the possibility of also including further features. The word "preferable" (or any of its derivatives) indicates one feature or more that is preferred but not essential.

[0087] The reader's attention is directed to all and any priority documents identified in connection with this application and to all and any papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

[0088] All or any of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all or any of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

-2 0 - [0089] Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

[0090] The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims (22)

1. CLAIMS1. A drive system for an electrically-assisted pedal cycle, the system comprising: an input that, in use, receives drive from a pedal of the cycle and rotates about an axis; an output that, in use, rotates about said axis to provide drive to a driven wheel of the cycle; an electrical machine that, in use, provides motor drive to said output; and a drive train that, in use, receives drive from the electrical machine and the pedal and transmits drive to said output: wherein: the drive train comprises an epicyclic gear set having a sun gear, a planet carrier, a plurality of planet gears and an annulus gear, the planet gears being mounted on the planet carrier and meshing with both the sun gear and the annulus gear, and the annulus gear being connected to said output to rotate, in use, with said output: the epicyclic gear set, in use, transmits drive from a pedal to its annulus via its planet carrier: the sun gear is connected to be driven by the electrical machine: and the drive train further comprises a one-way clutch between the planet carrier and a fixed part of the drive system, to allow rotation of the planet carrier in only one direction.
2. 2. A drive system according to claim 1, wherein the drive train further comprises a one-way clutch between the planet carrier and annulus of the epicyclic gear set, to prevent the planet carrier from rotating faster than the annulus in the direction that causes the cycle to travel forward.
3. 3. A drive system according to claim 1 or 2, wherein each planet gear is of compound configuration, having a smaller gear and a larger gear that are rotationally solid with one another, one of the smaller and larger gears meshing with the annulus and the other of the smaller and larger gears meshing with the sun.
4. 4. A drive system according to claim 1 or 2, wherein the epicyclic gear set is a dual gear set comprising a first set of first sun, planets, planet carrier and annulus; and a second set of second sun, planets, planet carrier and annulus; the second sun being rotationally solid with the first planet carrier; the second planet carrier receiving drive from a pedal, in use; the first sun receiving drive from the electric motor, in use; and both the first annulus and the second annulus rotating, in use, with said output.
5. 5. A drive system according to claim 4, wherein the first annulus and second annulus are formed as a common annulus.
6. 6. A drive system for an electrically-assisted pedal cycle, the system comprising: an input that, in use, receives drive from a pedal of the cycle and rotates about an axis; an output that, in use, rotates about said axis to provide drive to a driven wheel of the cycle; an electrical machine that, in use, provides motor drive to said output; and a drive train that, in use, receives drive from the electrical machine and the pedal and transmits drive to said output: wherein the drive train comprises a dual epicyclic gear set having a first set of first sun, planets, planet carrier and annulus; and a second set of second sun, planets, planet carrier and annulus; the second sun being rotationally solid with the first planet carrier; the second planet carrier receiving drive from a pedal, in use; the first sun receiving motor drive from the electric machine, in use; and both the first annulus and the second annulus rotating, in use, with said output.
7. 7. A drive system according to claim 6, wherein the drive train further comprises a one-way clutch between the second planet carrier and annulus of the epicyclic gear set, to prevent the second planet carrier from rotating faster than the annulus in the direction that causes the cycle to travel forward.
8. 8. A drive system according to claim 6 or 7, wherein the drive train further comprises a selectively actuable clutch between the second sun and a fixed part of the drive system.
9. 9. A drive system according to claim 6, 7 or 8, wherein the first annulus and 20 second annulus are formed as a common annulus.
10. 10. A drive system according to any of the preceding claims, further comprising a free-wheel mechanism that is operative between the pedals and driven wheel of the cycle.
11. 11. A drive system according any of the preceding claims, wherein the electrical machine is configured to operate selectively as a generator or a motor and the system further comprises a controller that alternately operates the electrical machine as a generator for a first period and then as a motor for a second period, the controller obtaining an indication of torque applied at the inner hub as a function of generator output, and then applying power to the motor as a function of the torque indicated.
12. 12. A drive system according to any of the preceding claims, located at a mid-position of the cycle, wherein said axis is an axis of rotation of the pedals.
13. 13. A drive system according to any of claims 1 to 11, located at a hub of a driven wheel of the cycle, wherein said axis is an axis of an axle about which the driven wheel rotates.
14. 14. A drive system according to claim 13, wherein said driven wheel is a rear wheel of the cycle.
15. 15. An electrically-assisted pedal cycle having a drive system according to any of the preceding claims.
16. 16. An electrically-assisted pedal cycle according to claim 15, being a pedelec in which electrical assistance is provided only when the cyclist is pedalling.
17. 17. An electrically-assisted pedal cycle according to claim 15, in which electrical assistance is available both when the cyclist is pedalling and also when the cyclist is not pedalling.
18. 18. An electrically-assisted pedal cycle according to claim 17, having a throttle control by which a cyclist can apply or superimpose a desired amount of electrical assistance.
19. 19. A method of operating an electrically-assisted pedal cycle according to any of claims 15 to 18, comprising the steps of providing motor drive to the driven wheel of the cycle by said electrical machine and providing pedal drive to the driven wheel of the cycle, via said drive train.
20. 20. A drive system for an electrically-assisted pedal cycle, the system being substantially as hereinbefore described with reference to the accompanying 10 drawings.
21. 21. An electrically-assisted pedal cycle substantially as hereinbefore described with reference to the accompanying drawings.
22. 22. A method of operating an electrically-assisted pedal cycle, substantially as hereinbefore described with reference to the accompanying drawings.