WO2018020259A1

WO2018020259A1 - Boosting enabler for an electric pedal cycle

Info

Publication number: WO2018020259A1
Application number: PCT/GB2017/052200
Authority: WO
Inventors: Linan GONG
Original assignee: Nexxt E-Drive Limited
Priority date: 2016-07-29
Filing date: 2017-07-27
Publication date: 2018-02-01
Also published as: GB201613155D0

Abstract

There is provided a pedal cycle and a method of operating the same. The pedal cycle has an electro-mechanical drive arrangement including a continuously variable ratio transmission system having an input which is mounted to rotate about an axis and an output, the input being arranged to rotate with a common carrier coupled to a pedal system, and an electrical machine operable to provide power to the output via the continuously variable ratio transmission system. Operation of the pedal cycle comprises monitoring the rotation of the pedals within the pedal system; and when the monitored pedals are found to be stationary, selectively fixing the common carrier to fix the transmission ratio between the electrical machine and the output and applying a current to the electrical machine.

Description

BOOSTING ENABLER FOR AN ELECTRIC PEDAL CYCLE

Field

This disclosure relates to a method of operating a pedal cycle having an electromechanical drive arrangement.

Background

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 thereof, such cycles sometimes being referred to as "push bikes". Another, more recent, form of pedal cycle is the electrically-assisted pedal cycle (EAPC) in which electrical power is used to assist or replace the efforts of the rider. Both conventional pedal cycles and EAPCs 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 EAPCs. As mentioned, in an EAPC, electrical power is used to assist, or in some cases replace, the efforts of the rider. Accordingly, EAPCs 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 usually 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. As a result, the overall effort usually required by a cyclist to pedal an EAPC is lower than for a conventional cycle.

EAPCs can usually be placed 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 are sometimes referred to as "e-bikes", and can be thought of as being generally equivalent to electric mopeds, although one that is generally easier to pedal. Cycles in the second group only provide electrical assistance when the cyclist is pedalling. These are sometimes referred to as "pedelecs".

Currently, in most European countries, including the UK, pedelecs at least are effectively legally classified as conventional bicycles and so may be ridden without a driving licence or insurance, providing electric assistance ceases at a speed of 25kph. There are therefore few barriers to owning and operating a pedelec EAPC.

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 EAPCs. These advances have resulted in EAPCs that can be operated with greater efficiency, and hence greater ease, by the cyclist.

For all the reasons given above EAPCs are becoming increasing popular, particularly in some European countries. In some pedelecs the motor is either off or fully switched on (or perhaps subject to manual user control to define the level of assistance desired). That is to say, there is no relationship between the rider's pedalling and the level of assistance provided once the motor has started. However, this can provide a somewhat unnatural feeling to the riding experience and in other examples an attempt is made to introduce such a link. For example, control may be provided to cause the motor to provide greater assistance when the rider is pedalling at greater speed. However, this link can itself be counterintuitive since the speed or cadence of the rider's turning the pedals is not directly linked to the power output in geared bicycles. In a lower gear, a given cadence represents a lower power output than it would in a higher gear. Thus, control of the power output of the motor based on the cadence of the pedals does not provide an intuitive link between the effort exerted by the rider and the assistance provided by the motor. For example, greater assistance can be achieved by a rider by switching to a lower gear in order to increase cadence without exerting any greater effort. Variable transmission schemes can be employed to ensure a more intuitive feel to the rider's efforts. Whether by conventional gearing or continuous variable transmission (CVT) schemes, the level of assistance provided by the pedelec may vary without being directly proportional to the cadence of the pedals.

The experience of riding a pedelec may therefore be broadly similar to that of riding an unpowered bicycle, while an "e-bike" offers a more artificial sensation. However, these distinct approaches may have advantages in differing situations, and either approach may be sub-optimal at times. There is therefore a desire to combine the benefits of both approaches as far as possible.

Summary

According to a first aspect of the disclosure, there is provided a method of operating a pedal cycle, the pedal cycle having an electro-mechanical drive arrangement including a continuously variable ratio transmission system having an input which is mounted to rotate about an axis and an output, the input being arranged to rotate with a common carrier coupled to a pedal system, and an electrical machine operable to provide power to the output via the continuously variable ratio transmission system, wherein the method comprising:

monitoring the rotation of the pedals within the pedal system; and

when the monitored pedals are found to be stationary, selectively fixing the common carrier to fix the transmission ratio between the electrical machine and the output.

According to a second aspect of the disclosure, there is provided a pedal cycle having an electro-mechanical drive arrangement including a continuously variable ratio transmission system having an input which is mounted to rotate about an axis and an output, the input being arranged to rotate with a common carrier coupled to a pedal system, and an electrical machine operable to provide power to the output via the continuously variable ratio transmission system, and a controller arranged to:

monitor the rotation of the pedals within the pedal system; and when the monitored pedals are found to be stationary, selectively fix the common carrier to fix the transmission ratio between the electrical machine and the output. These aspects of the disclosure can enable a pedal cycle to switch from continuous variable transmission to fixed transmission when the pedals are no longer turned. In effect, this can allow pedelec control when the pedals are used and e-bike control when they are not, giving the user a range of control options during use. In preferred embodiments, there is provided the step of selectively fixing the common carrier and applying the current is carried out in dependence on an output of a user input device. This additional control avoids the e-bike mode be initiated without deliberate action by the user. Optionally, the user input device may further be operated to modify the current provided to the electrical machine. As such, the user may control the power provided by the electrical machine during the e-bike operation.

In some preferred embodiments, the continuously variable ratio transmission system comprises an epicyclic gear set including a sun gear in mesh with a plurality of planet gears mounted to rotate about respective planet shafts carried by the common carrier, the planet gears being in mesh with an annulus gear, which is connected to rotate with a hub member connected to the output, the sun gear being connected to rotate with a rotor of the electrical machine.

Optionally, the system may comprise a further electrical machine coupled to the annulus gear. Electrical connections of stators of the two electrical machines may be connected by a controller arranged to control the transmission of power from one electrical machine to the other.

In some preferred embodiments, the common carrier is selectively fixed using an overrunning clutch to prevent rotation of the carrier in a direction of rotation. Alternatively or additionally, the common carrier is selectively fixed using an operable element. The operable element may be mechanically or electrically actuated by the user.

The method may further comprise applying a time division multiplexed control algorithm to the input electrical machine, wherein the time division multiplexed control algorithm alternates between a first control mode in which current generated by the electrical input machine is monitored to infer torque applied to the crank arms of the cycle and a second control mode in which the current in the input electrical machine is controlled using the inferred torque. Accordingly, the torque applied to the crank arms by a rider of the pedal cycle can be inferred from the current generated by the electrical machine during riding. As a result, there is no requirement for an independent torque sensor to be provided. Moreover, during the second control mode the current in the input electrical machine is controlled. This effectively controls the torque on the input electrical machine during the second control mode (since this is proportional to current). As the input electrical machine is coupled to the crank arms by the epicyclic gear set, controlling the torque in the input electrical machine also controls the torque in the crank arms (the two are proportional), which is the torque that the cyclist applies. Thus, controlling the current in the input electrical machine determines the torque which the cyclist has to apply to maintain constant rotation during the second control mode.

Controlling the current in this way can enable the arrangement to automatically "change gear" during general operation. For example, should the cyclist press on the pedals with more force such that he or she applies torque that results in a current in the input electrical machine that exceeds that applied during the second control mode, the electrical machine "gives way" and so accelerates. This changes the transmission ratio of the input epicyclic gear set to, in effect, change into a lower gear. Thus, when the torque that the cyclist applies increases, the arrangement automatically changes down into a lower gear. Thus, the arrangement may automatically change down in conditions when this is needed, such as when climbing a hill or accelerating rapidly.

Similarly, should the cyclist press the pedals with less force and hence apply less torque than the torque that corresponds to the current of the input electrical machine during the second control mode, the electrical machine decelerates and resists motion of the crank arms by the cyclist. This deceleration of the input electrical machine again changes the transmission ratio of the epicyclic gear set to, in effect, change into a higher gear. Thus, when the torque that the cyclist applies falls, the arrangement automatically changes up into a higher gear. Thus, the arrangement automatically changes up in conditions when this is needed, such as when going downhill or when easing off and approaching a steady speed from a period of acceleration.

In this way, the torque sensing capabilities of the second electrical machine may be used in conventional pedal cycles and in EAPCs to provide an arrangement for automatically changing gear while the rider is cycling the pedal cycle.

In preferred embodiments, the control of the current applied to the input electrical machine in response to the inferred torque during the second control mode is dependent upon whether the pedal cycle is in a launch routine or an in-motion routine. Both the input electrical machine and the output electrical machine may be coupled to a single electrical power source (such as a battery).

During the launch routine, the output electrical machine may take priority over the input electrical machine for receiving current from the electrical power source. As such, the output electrical machine may be used to assist the rider in bringing the pedal cycle up to the desired speed without sacrificing electrical power to control of the input electrical machine. This will also have the effect of shifting the pedals to a relatively low gear as the torque provided by the rider exceeds that generated by input electrical machine during the second control mode. The rider is therefore able to start the pedals moving at a preferred cadence without having to work against the input electrical machine.

In some embodiments, the method may further comprise the step of determining that the bicycle and/or the crank arms are substantially stationary and, in response thereto, substantially short-circuiting the input electrical machine. This can include short circuiting one, two or all three phases of the input electrical machine. Furthermore, in some embodiments, the method includes the step of maintaining the substantial short- circuiting of the input electrical machine until the actual current in the input electrical machine reaches a predetermined threshold current. This threshold may be set in software. During an in-motion routine, the input electrical machine may take priority over the output electrical machine for receiving current from the electrical power source. In this manner, a current may be applied to the input electrical machine during the second control mode which is calculated to match the inferred torque identified during the first control mode. Accordingly, the rider is provided with consistent feedback from the pedals during the in-motion routine. This is found to offer a satisfying and intuitive riding experience. It will be appreciated by the skilled person that current control of an electrical machine may be readily accomplished with existing electrical components. Thus, embodiments of the method can be used to provide automatic transmission-ratio control in a straightforward and inexpensive manner. It should also be noted that the use of an epicyclic gear set in this way provides continuously-variable transmission, rather than the stepped gearing usual with cycles that often changes gear unsatisfactorily under heavy loads.

During the second control mode, and particularly during the in-motion routine, the current in the input electrical machine may be controlled to lie in a range between a maximum current and a minimum current, the maximum and minimum currents being calculated using the inferred torque. The maximum current and the minimum current may be different values; they may be the same value. Where they are different values, this creates a band within which the torque applied by the cyclist may vary without the arrangement "changing gear", i.e. varying the transmission ratio. In this way, the arrangement mimics, at least to some degree, the behaviour of a conventional geared cycle and so may find favour with some cyclists more used to such conventional cycles. Where the maximum current and minimum current are the same, this results in the arrangement varying the transmission ratio whenever the torque applied by the cyclist differs from that corresponding to the current drawn from the input electrical machine during the second control mode. This arrangement can be used to cause the cyclist to cycle with a torque that is close to, or coincides with, optimum cycling efficiency.

In some preferred embodiments, the electrical drive arrangement further includes a oneway clutch, which includes a drive member, which is constituted by the common carrier, and a driven member, which is connected to rotate with the hub members, the one-way clutch being arranged to connect the hub member to rotate with the carrier as soon as the carrier rotates faster than the hub member. Accordingly, the hub may include a one-way clutch which is arranged to connect the hub member to rotate with the carrier if the carrier attempts to rotate faster than the hub member which in practice occurs as soon as any substantial torque is applied to the input. This means that if the hub is fitted to a bicycle, as soon as the rider applies any significant pressure to the pedals, thereby applying a torque to the input of the transmission system, the one-way clutch engages and thus connects the carrier to the hub member. This results in the input immediately being connected to rotate with the hub member and thus in the propulsive force exerted by the cyclist immediately being transmitted to the hub member and thus to the bicycle wheel. This reduces the possibility of the pedal crank initially rotating with much reduced resistance before engaging fully, which phenomenon is inconvenient and disconcerting for the rider, particularly at launch.

According to a further aspect of the disclosure, there is provided a pedal cycle arranged to carry out a method as defined hereinabove.

It can also be appreciated that aspects of the disclosure can be implemented using computer program code. Indeed, according to a further aspect of the present disclosure, there is therefore provided a computer program product comprising computer executable instructions for carrying out the method of the first aspect. The computer program product may be a physical / tangible storage medium. For example, the storage medium may be a Read Only Memory (ROM) or other memory chip. Alternatively, it may be a disk such as a Digital Versatile Disk (DVD-ROM) or Compact Disk (CD-ROM) or other data carrier. It could also be a signal such as an electronic signal over wires, an optical signal or a radio signal such as to a satellite or the like. The disclosure also extends to a processor running the software or code, e.g. a computer configured to carry out the method described above.

Brief Description of the Drawings

Specific embodiments will now be described by way of example only and with reference to the accompanying drawings, in which: Figure 1 shows a pedal cycle;

Figure 2A shows an axial sectional view of the upper half of a bicycle hub according to a first embodiment;

Figure 2B shows a view of a one-way clutch, seen from the right in Figure 2A, above an axial sectional view of the one-way clutch; and Figure 3 is schematic representation of control means for controlling operation of the drive arrangement; and

Figure 4 is a flow diagram of a method of operating the pedal cycle, the steps including steps of a "launch" routine and an "in-motion" routine.

Detailed Description

[STRUCTURAL ARRANGEMENT] Figure 1 shows an electrically-assisted pedal cycle 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 the 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 the hub 100 of the rear wheel 30 to drive that wheel directly. Instead, the rear sprocket 80 drives certain components of an electromechanical drive arrangement that are housed within the hub 100. A user input device 91 may be provided on the handlebars of the bicycle 10. The user input device may comprise a mode selector and/or a twist throttle. The mode selector may be used to choose effect a change of operation between a pedelec mode and a e- bike mode when the pedals are stationary. The throttle may be operated to control the current applied to an electrical machine providing power to the bicycle in the e-bike mode.

Figure 2a shows the hub 100 of a first embodiment and its contents in detail. The hub is mounted on a central shaft 2 which, in use, is fixedly secured to a bicycle frame by means of two nuts 4. The hub includes an annular input member 6, which is connected to a conventional bicycle sprocket wheel 80 via a conventional freewheel mechanism 9, which is not shown in detail. The input member 6 is mounted on a number of bearings 101 to rotate about the shaft 2. The input member 6 is also connected to a single three- branch epicyclic gear set, all three branches or shafts of which rotate. The transmission system includes a sun gear 12, which is mounted to rotate about the shaft 2 and carries teeth in mesh with teeth carried by a number, typically 3, of planet gears 14. The planet gears 14 are rotatably carried by way of bearings 16 by respective planet shafts 18, which are connected to a common carrier 201. The teeth on the planet gears 14 are also in mesh with the teeth on an annulus gear 22, which is fixedly connected to the right- hand portion 24 of a hub housing. The right-hand portion 24 of the hub housing is connected to a left-hand portion 26 by means of a central portion 28, which is connected to the right- and left-hand portions 24, 26 by means of bolts 301. Accommodated within the hub housing is a single motor/generator (electrical machine). The motor/generator, or input electrical machine 120, includes a rotor 32 which is connected to rotate with the sun gear 12, and a stator 34. The electrical connections of the stators 34 are connected to a controller 200, which is shown only schematically and is also connected to a rechargeable electric battery 208. The controller 200 is programmed to control the flow of electrical power between the electric battery 208 and the motor/generator in accordance with requirements. The amount of electrical power so transmitted may be selectively varied by means of the controller 200, thereby altering the transmission ratio of the transmission system. Power is transmitted through the transmission system both mechanically and electrically in proportions which vary with the varying transmission ratio

In other embodiments, two electric motor/generators (electrical machines) may be provided. In use, one of the motor/generators generally acts as a generator and transmits electrical power to the other motor/generator, which acts as a motor. These motor/generators can be arranged coaxially, with one motor/generator situated within the other. The further, outer motor/generator, or output electrical machine may include a rotor, which is fixedly connected to the central portion of the hub housing, and a stator. The electrical connections of the two stators in such embodiments are connected to the controller 200. The controller 200 may be programmed to control the flow of electrical power between the two motor/generators and between the electric battery 208 and each of the two motor/generators in accordance with requirements.

The common carrier 201 is integral with the input member 6, and constitutes the input member or drive member of a one-way clutch. It has a circular outer periphery, which is closely surrounded by the circular inner periphery of an annular driven member 44 of the one-way clutch, the outer periphery of which bears teeth 46, which are also in mesh with the internal teeth on the annulus gear 22, which is fixedly connected to the hub housing portion 24. Formed in the outer periphery of the inner or drive member 20 of the one-way clutch is a plurality, in this case three, of recesses 47 extending in the peripheral direction. Accommodated in each of these recesses is a jamming ball 48 and a biasing spring 50. The dimension or width of each recess 47 in the radial direction is greatest at the end remote from the spring 50 and at this end it has a value greater than the diameter of the associated jamming ball 48. However, its width decreases in the direction towards the biasing spring 50 to a value less than the diameter of the jamming ball 48. The biasing springs urge the balls 48 to the ends of the recesses 47 remote from the springs 50 at which the width of the recess is greater than the diameter of the balls and when the balls are in this position the drive and driven members 20 and 44 of the one-way clutch are freely rotatable with respect to one another and the clutch is thus disengaged.

However, if the inner or drive member of the clutch should move in the clockwise direction as seen in Figure 2b, that is to say if the user of the bicycle should exert a force on the pedals, which is transmitted by the bicycle chain to the sprocket 8 and then to the drive member 201 in the form of a torque tending to rotate the drive member 201, the balls 48 are caused to move in the anti -clockwise direction, seen in Figure 2b, and thus towards the region in which the width of the recesses is less than the diameter of the balls. As the balls approach this region, they become jammed between the bases of the recesses 47 and the inner periphery of the outer or driven clutch member 44 and thus act to rotationally connect the two clutch members 20 and 44. Continued rotation of the input member 6 and thus of the clutch member 20 is therefore transmitted directly to the driven clutch member 44 and thus also to the annulus gear 22 and to the hub housing 24, 26, 28, thereby resulting in rotation of the bicycle wheel. If the user should subsequently cease to exert a pressure on the pedals, the force exerted by the biasing springs 50 will be able to return the balls 48 into the regions of the recesses 47 where their width is greater than the diameter of the balls and the rotary connection of the two clutch members is therefore released. In a pedelec mode, the output speed of the transmission system and thus the speed of the hub member may be varied independently of the input speed, which means that the speed of the wheel connected to the hub member in accordance with the invention may be varied independently of the speed at which the pedals are rotated and/or the speed of that one of the motor/generators which is operating as a motor and is providing a motive torque to propel the bicycle or to assist the user in propelling the bicycle. This means that the transmission may be operated precisely at the speed which is the most appropriate for the conditions and matches the wishes of the user, as indicated by one or more user-operable controls. In pedelec mode, one or both of the electric motor/generators are used in motor mode to drive the bicycle for a major proportion of the time, but this supplements the input provided by the user. In an e-bike mode, the user provides no input power themselves; instead one or both electrical machines provide the power. In the preferred embodiments, two criteria are used to identify when a transfer from a pedelec mode to an e-bike mode is initiated: i) that the pedals are stationary; and 2) that a user input (typically the input 91) provides a defined output to indicate the user's desire for additional power to be provided. This defined output may be the result of turning a twist throttle to a desired position (such as a minimum position) or making another selection.

When the e-bike mode is selected, the rotation of the common carrier is inhibited. In some preferred embodiments, this is by means of an overrunning clutch (or freewheel) mechanism which prevents rotation of the common carrier in a reverse direction. As such, the overrunning clutch allows the rider to pedal forwards, thereby rotating the carrier in a first, forward, direction, but prevents rotation of the carrier, and thus chain and pedals in an opposite, reverse direction. When the rider holds the pedals stationary, and the input electric machine is provided with an input power, this will push the carrier into the stop engagement of the overrunning clutch, and therefore hold the common carrier in position.

In alternative embodiments, an alternative or additional operable element may be provided to selectively engage with the carrier to prevent its rotation. This may be electrically actuated (such as through user selection using an electronic display, for example) or may be physically actuated (such as through a Bowden cable, for example). In all combinations, a twist throttle may allow for user selection of the boost provided by the electric machine or machines during an e-bike mode.

Further details of controller 200 can be understood with reference to Figure 3. In particular, the control means is connected and arranged to control the input and output motor-generators 110, 120 in response to inputs received from input means. The controller 200 is in the form of an electronic control unit (ECU) 205, a battery management unit 207 and one or two motor-generator controllers: one of which will be termed the "input controller" 210 and is for controlling the input motor-generator 120, and the other one of which will be termed the "output controller" 220 and is for controlling the output motor-generator 110 if present. The ECU 205 includes a microprocessor that is programmable and operable to carry out the steps of a method that embodies this invention. That method will be described hereinbelow with reference to Figure 3. The ECU 205 is connected to the input controller 210, the output controller 220 and the battery management unit 207 for controlling operation of those three units.

The input means that provide inputs to the controller 40 includes user input means 250 (equivalent to element 91 of Figure 1) and a crank speed and position sensor 260, which may be a hall sensor. The user input means 250 includes, in this embodiment, a user- operable power input device and a user-operable brake input device (none of which is shown). The power input device is arranged to be operated by a user to indicate generally the power, that is the rate of working, with which he or she wishes to pedal. The brake input device is arranged to be operated by the user to indicate a rate at which the bicycle 10 should be slowed.

In this embodiment, it is envisaged that the power input device is a user-operable selector that indexes between each of a plurality of different positions. Examples of such selector switches are twistable grip-shifts and thumb shifters commonly used in gear-change mechanisms of conventional bicycles. It is envisaged that the brake input device may be similar to a conventional brake lever. However, in the present embodiment, it is envisaged that electrical versions of such selector switches and of the brake lever be used such that each is able to produce an electrical signal indicative of its user-selected position. The crank speed and position sensor 260 is a conventional device that is arranged to sense the speed and angular position of the crank arms 50 and to output an electrical signal indicative of this. Each of the input means is connected and arranged to provide its respective electrical signal to the ECU 205.

An output speed sensor 265, which may be a hall sensor, may be provided to measure the speed at which the bike is moving. The output speed sensor 265 may monitor the front or rear wheel, for example. The output speed sensor 265 provides this information to the controller 200. As illustrated in Figure 2a, the sensor 265 may be embedded in the hub itself. It acts as a high precision sensing system to measure the speed of the rear wheel in this embodiment.

A further output from the control means 200 is connected to an instrument panel 270. The battery management unit 207 is connected to electrical energy storage means in the form of a rechargeable battery 208.

With reference again to Figure 1, the ECU 205, the input controller 210, the output controller 220 and the battery management unit are housed within a control housing 90 fitted to the frame of the bicycle 10. The battery 208 is housed within a battery housing 92 that is also fitted to the frame.

[OPERATION] Operation of the bicycle 10 in a pedelec mode will now be described with reference to Figure 4. This description will take the form of a description of the steps of a method carried out by the ECU 205 in executing instructions contained in a computer program with which it is programmed. During this process, movement of the pedals is monitored, and if no such movement is present, an e-bike mode may be selected in which the transmission ratio is fixed.

With reference to Figure 4, the method begins from a stationary start at step 300 in which the crank speed and position sensor 260 is used to sense movement of the pedals 40. If no movement of the pedals is identified then the method continues to monitor for further events.

If movement of the pedals is identified, the method moves to step 310, wherein the torque applied to pedals 40 is sensed using the input electrical machine 120. The input electrical machine is operated throughout the method according to a time division multiplexed control algorithm to the input electrical machine. The time division multiplexed control algorithm alternates between a first control mode in which current generated by the input electrical machine 120 is monitored to infer torque applied to the crank arms of the cycle and a second control mode in which the current in the input electrical machine 120 is controlled in dependence on the inferred torque. At step 310, the torque is sensed during the first control mode.

At step 320, the controller 200 determines if the torque sensed at step 310 exceeds an initiation threshold. If the torque sensed at step 310 exceeds the initiation threshold, a launch routine 330 is initiated.

During launch routine 330, the input electrical machine 120 is initiated at step 331 in response to the detection of torque exceeding the initiation threshold, such that a fixed current is imparted to the input electrical machine 120 during launch routine 330. By using the torque sensed during the first control mode to control entry into the launch routine 330, accidental initiation can be prevented.

During the launch routine, the current in the input machine is maintained at a minimal level. This effective short-circuit quickly builds up a reaction torque in the input motor- generator 120 against rotation thereof (this build up happens within about 5 to 10 degrees of crank angle). This reaction is transmitted through the epicyclic gear set 140 to the crank arms 50 and pedals 40 and so gives the cyclist something to push against in setting off on the cycle. Furthermore, the one-way clutch ensures the cyclist receives feedback to the effort provided at this stage.

At step 332 of the launch routine 330, the movement of the pedals is again sensed by the sensor 260. The cadence (i.e. the rate of revolution) of the crank arms 50 is determined from the signal sensed thereby, and if this remains below an in-motion threshold the launch routine continues. The in-motion threshold may be, for example, one revolution per second. Once the cadence meets or exceeds the threshold, the method moves to in motion routine 340. In a preferred embodiment, the in-motion threshold may be one revolution per second. During the in-motion routine 340 the torque is sensed using the input electrical machine 120 at step 341. As referenced above, this occurs during the first control mode of the time division multiplexed control algorithm. The sensed torque is then used to set the current in the input electrical machine 120 during the second control mode at step 342. In particular, the current within the input electrical machine 120 during the second control mode is set to provide a torque output of the input electrical machine 120 which corresponds to the torque sensed during the first control mode.

It should be understood that, by controlling the current in the input motor-generator 120 in this way, the torque on that machine, which is proportional to current, is also controlled. As the input motor-generator 120 is coupled to the crank arms 50 by the epicyclic gear set, controlling the torque in the input motor-generator 120 also controls the torque in the crank arms 50 (the two torques are proportional), which is the torque that the cyclist applies to the crank arms 50 through the pedals 40. Thus, controlling the current in the input motor-generator 120 determines the force which the cyclist must apply to the pedals 40 to maintain a steady state.

Controlling the current in this way results in the bicycle 10 automatically changing the transmission ratio between the crank arms 50 and the rear wheel. For example, should the cyclist press on the pedals 40 with more force such that he or she applies torque that exceeds the torque corresponding to the current drawn from the input motor-generator 120 for the determined crank position, the motor-generator "gives way" and so accelerates. This effect can be used in some embodiments to change the transmission ratio of the epicyclic gear set 140 to change to a lower ratio. Thus, when the torque that the cyclist applies exceeds a certain limit, the arrangement automatically changes to a lower ratio. Thus, the arrangement automatically changes down in conditions when this is needed, such as when climbing a hill or accelerating rapidly.

Similarly, should the cyclist press the pedals 40 with less force and hence apply less torque than the torque that corresponds to the determined current that is to be drawn from the input motor-generator 120, the motor-generator 120 decelerates and resists motion of the crank arms 50 by the cyclist. This deceleration of the input motor- generator 120 can again be used to change the transmission ratio of the epicyclic gear set to a higher ratio. Thus, when the torque that the cyclist applies falls below a certain limit, the arrangement automatically changes to a higher ratio. Thus, the arrangement automatically changes up in conditions when this is needed, such as when going downhill or when easing off and approaching a steady speed from a period of acceleration. This variable transmission ratio is applicable during the pedelec mode of operation. When no movement of the pedals is detected, the user may select an e-bike mode of operation. In this case, the position of the carrier is fixed, leading to a fixed transmission ratio from the input electrical machine to the hub. The output can be controlled using the user input means 91 which will control the current provided to the electrical machine.

As mentioned above, the carrier may be fixed during the e-bike mode by a combination of the action of an overrunning clutch and the electric machine, and/or by an operable element designed to selectively engage with the carrier.

Although fixing of the carrier will in theory prevent movement of the pedals, continued monitoring may be provided to assess, for example, whether the pedals are moved backwards. This would indicate a failure of the fixing of the carrier, and to avoid undesired consequences, as a safety mechanism in such circumstances the electrical machine may be turned off and the carrier released by the operable element.

Variations and modifications will be apparent to the skilled person. Such variations and modifications may involve equivalent and other features which are already known and which may be used instead of, or in addition to, features described herein. Features that are described in the context of separate embodiments may be provided in combination in a single embodiment. Conversely, features which are described in the context of a single embodiment may also be provided separately or in any suitable sub-combination.

It should be noted that the term "comprising" does not exclude other elements or steps, the term "a" or "an" does not exclude a plurality, a single feature may fulfil the functions of several features recited in the claims and reference signs in the claims shall not be construed as limiting the scope of the claims. It should also be noted that the Figures are not necessarily to scale; emphasis instead generally being placed upon illustrating the principles of the present invention.

Claims

1. A method of operating a pedal cycle, the pedal cycle having an electromechanical drive arrangement including a continuously variable ratio transmission system having an input which is mounted to rotate about an axis and an output, the input being arranged to rotate with a common carrier coupled to a pedal system, and an electrical machine operable to provide power to the output via the continuously variable ratio transmission system, wherein the method comprising:

monitoring the rotation of the pedals within the pedal system; and

when the monitored pedals are found to be stationary, selectively fixing the common carrier to fix the transmission ratio between the electrical machine and the output and applying a current to the electrical machine.

2. A method according to claim 1, wherein the step of selectively fixing the common carrier and applying the current is carried out in dependence on an output of a user input device.

3. A method according to claim 2, wherein the user input device may further be operated to modify the current provided to the electrical machine.

4. A method according to any one of the preceding claims, wherein the continuously variable ratio transmission system comprises an epicyclic gear set including a sun gear in mesh with a plurality of planet gears mounted to rotate about respective planet shafts carried by the common carrier, the planet gears being in mesh with an annulus gear, which is connected to rotate with a hub member connected to the output, the sun gear being connected to rotate with a rotor of the electrical machine.

5. A method according to claim 4, further comprising a further additional machine coupled to the annulus gear.

6. A method according to claim 5, wherein electrical connections of stators of the two electrical machines being connected by a controller arranged to control the transmission of power from one electrical machine to the other.

7. A method according to any one of the preceding claims, wherein the common carrier is selectively fixed using an overrunning clutch to prevent rotation of the carrier in a direction of rotation.

8. A method according to any one of claims 1 to 7, wherein the common carrier is selectively fixed using an operable element.

9. A method according to claim 8, wherein the operable element is mechanically actuated.

10. A method according to claim 8, wherein the operable element is electronically actuated.

11. A pedal cycle having an electro-mechanical drive arrangement including a continuously variable ratio transmission system having an input which is mounted to rotate about an axis and an output, the input being arranged to rotate with a common carrier coupled to a pedal system, and an electrical machine operable to provide power to the output via the continuously variable ratio transmission system, and a controller arranged to:

monitor the rotation of the pedals within the pedal system; and

when the monitored pedals are found to be stationary, selectively fix the common carrier to fix the transmission ratio between the electrical machine and the output and apply a current to the electrical machine.

12. A cycle according to claim 11, further comprising a user input device, wherein the controller is arranged to selectively fix the common carrier and apply the current in dependence on an output of a user input device.

13. A cycle according to claim 12, wherein the user input device may be operated to modify the current provided to the electrical machine.

14. A cycle according to any one of claims 11 to 13, wherein the continuously variable ratio transmission system comprises an epicyclic gear set including a sun gear in mesh with a plurality of planet gears mounted to rotate about respective planet shafts carried by the common carrier, the planet gears being in mesh with an annulus gear, which is connected to rotate with a hub member connected to the output, the sun gear being connected to rotate with a rotor of the electrical machine.

15. A cycle according to claim 14, further comprising a further additional machine coupled to the annulus gear.

16. A cycle according to claim 15, wherein electrical connections of stators of the two electrical machines are connected by the controller which is arranged to control the transmission of power from one electrical machine to the other.

17. A cycle according to any one of claims 11 to 16, further comprising an overrunning clutch coupled to the common carrier, the overrunning clutch being effective to selectively fix the common carrier.

18. A cycle according to any one of claims 11 to 17, wherein the common carrier is selectively fixed using an operable element.

19. A cycle according to claim 18 ,wherein the operable element is mechanically actuated.

20. A cycle according to claim 18, wherein the operable element is electronically actuated.