Electrically-assisted pedal cycles

Abstract

A drive train receives drive from an electrical machine and rider pedals. Under the control of a controller, it transmits drive to a cycle wheel (30). An encoder detects angular position of a rotary part (30,6) of the cycle and comprises a series of magnetic elements (33) mounted on the rotary part (30,6) and mutually spaced at a constant circumferential pitch P, with the poles of successive magnetic elements (33) arranged in opposite polarities. Two analog Hall sensors (34) are mounted in fixed positions on the cycle, to respond to magnetic elements (33) as they pass the sensors (34), which are mutually spaced by P / 4, a quarter of the pitch P of the magnetic elements (33). A processor receives the outputs of the sensors (34) and process the outputs to provide a signal representative of the angular position of the rotary part (30,6).

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 "eBike", in which electrical power is used to assist or replace the efforts of the rider. Both conventional pedal cycles and eBikes may have two, three or four wheels, and, in some, cases even more. Cycles that provide electrical assistance only when the cyclist is pedalling are commonly referred to as 'pedelecs'.

[0003] By way of background, the reader is referred to our PCT publications W02010 / 092345, W02017 / 021715, W02018 / 020259, WO 2020 / 245591, WO2022 / 023774, WO2023 / 281249, where much information about eBikes is provided. There is particular reference to the use of continuously variable transmissions (CVTs).

[0004] The use of CVTs in eBikes is relatively recent and is characterized by significant ease-of-use advantages. However, there is scope to improve the riding feeling of an eBike, both with and without CVT, particularly as the rider's pedalling input varies, and as the speed of the eBike varies.

[0005] Preferred embodiments of the present invention aim to provide eBikes in which the riding feeling is improved over a wide range of rider input and over a wide range of eBike speeds. Preferred embodiments of the present invention aim to provide improved encoders for data representing angular position and / or speed.

[0006] According to one aspect of the present invention, there is provided an electrically-assisted cycle having a drive train that receives drive from an electrical machine and drive from rider pedals and, under the control of a controller, transmits drive to an output that drives a wheel of the cycle, the cycle further comprising an encoder that detects angular position of a rotary part of the cycle, the encoder comprising: a series of magnetic elements mounted on the rotary part and mutually spaced at a constant circumferential pitch P, with the poles of successive magnetic elements arranged in opposite polarities; two analog Hall sensors mounted in fixed positions on the cycle, to respond to the series of magnetic elements as they pass the sensors, the sensors being mutually spaced by P / 4, that is, a quarter of the pitch P of the magnetic elements; and a processor configured to receive the outputs of the sensors and process the outputs to provide a signal representative of the angular position of the rotary part: the processor being configured to sample the outputs of the sensors at a frequency in the range 1000 to 10000 Hz.

[0007] Preferably, the output of one of the sensors is a sine wave, the output of the other sensor is a cosine wave and the processor divides one output by the other to provide a corresponding tan or cotan value.

[0008] Preferably, said rotary part is a driven wheel of the cycle.

[0009] Preferably, said frequency is in the range 1000 to 5000 Hz.

[0010] Said rotary part may be the rotor of the electrical machine.

[0011] Said frequency may be in the range 2000 to 10000 Hz.

[0012] There may be two said rotary parts with respective magnetic elements and analog Hall sensors.

[0013] The two said rotary parts may be a driven wheel of the cycle and the rotor of the electrical machine.

[0014] The sampling frequency for the rotor of the electrical machine may be n times that for the driven wheel of the cycle, n may be 2.

[0015] Preferably, the drive train provides a continuously variable transmission (CVT).

[0016] Preferably, the drive train provides a mechanical drive connection between the electrical machine, the pedals and a driven wheel of the cycle.

[0017] The invention extends to a method of operating an electrically- assisted cycle according to any of the preceding aspects of the invention, including the steps of sampling the outputs of the sensors at a frequency in the range 1000 to 10000 Hz; processing the outputs to provide a signal representative of the angular position of the or each rotary part; and controlling the drive train in response to the processed outputs.

[0018] 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:

[0019] Figure 1 is a side view of a pedelec;

[0020] Figure 2 is a diagrammatic view of a drive system for the pedelec;

[0021] Figure 3 is a diagrammatic representation of magnets and Hall sensors around a wheel or the rotor of an electric motor;

[0022] Figure 4 is a developed view of magnets and Hall sensors as represented in Figure 3;

[0023] Figures 5A, 5B and 5C show related graphs to indicate the use of magnets and Hall sensors as represented in Figures 3 and 4;

[0024] Figure 6 is a schematic diagram to show connections between Hall sensors, processing and control devices; and

[0025] Figure 7 is a graph to show comparisons between different configurations of speed sensors.

[0026] In the figures, like references denote like or corresponding parts.

[0027] 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.

[0028] 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 or toothed belt 70 to a rear sprocket 80, the rear sprocket being mounted co-axially with the rear wheel 30. However, the bicycle 10 differsfrom 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 hub 100. A control housing 90 and a battery housing 92 are fitted to the frame of the bicycle 10.

[0029] A drive system is mounted within the hub 100 and is described as follows, with reference to Figure 2. The drive system provides a drive train that receives drive from an electrical machine and the pedals 40 and transmits drive to an output. For ease of explanation, the hub 100 is referred to in the following as an outer hub 100 and provides the output of the drive system. The outer hub 100 is typically connected to the outer part of the rear wheel 30 by spokes, or by any other connection, to provide drive to the rear wheel 30.

[0030] It will be noted that, for ease of explanation, the diagrammatic view of Figure 2 shows just an upper part of the drive system with multiple planets, arranged around the axis of a central axle 1 fixed to the bike frame.

[0031] 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 that is mounted on bearings (not shown) for rotation about fixed axle 1, which is secured to the bicycle frame. The sprocket 80 preferably 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 one-way clutch KI. An opposite end of the outer hub 100 is mounted on the axle 1 by way of one or more bearings. 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 KI could be made up of a bearing and a separate clutch.

[0032] An electrical machine comprises a stator 5 that is fixedly mounted on the axle 1 and a rotor 6 that is mounted on a shaft 7 that is mounted on suitable bearings (not shown) for rotation about the axle 1. A first stage EPl of a dual epicyclic gear set EPl, EP2 connects the shaft 7 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.

[0033] The dual epicyclic gear set EPl, EP2 affords a high gear ratio and a small packaging space for a given torque capacity. The first epicyclic stage EPl comprises first sun 21a, planets 22a, planet carrier 23a and annulus or ring 24a. The first annulus or ring 24a is rotationally solid with the outer hub 100. The first sun 21a is optionally connected to the shaft 7 via a one-way clutch K3. There may be two, three or more planets 22a.

[0034] The second epicyclic stage EP2 comprises second sun 21b, planets 22b, planet carrier 23b and annulus or ring 24b. The second annulus or ring 24b is connected to the first planet carrier 23a, and both are also connected to the axle 1 via a one-way clutch K2 that can be selectively activated and deactivated (i.e. allowed or disallowed to prevent rotation in one direction). The second sun 21b is connected for rotation with the outer hub 100. There may be two, three or more planets 22b.

[0035] The one-way clutch K2 may be selectively activated and deactivated in response to a sensed speed of angular rotation of the outer hub 100, which is proportional to the linear speed of travel of the bicycle 10. To this end, a wheel speed sensor 31 is provided. This may act directly on the clutch K2, which responds passively to be activated or deactivated. For example, a governor type mechanism could be employed. A magnetic fluid could alternatively be employed to use the motion of the hub 100 to enable the clutch K2.Alternatively, a solenoid or other actuator 32 may respond to sensed speed to activate and deactivate the clutch K2.

[0036] A rotor speed sensor 41 may also be provided as an addition or alternative to wheel speed sensor 31. It is connected at 42 to, for example, processor 35, controller 91 and / or another component such as solenoid or other actuator.

[0037] In use, pedal drive is transmitted to rear sprocket 80 that is connected to planet carrier 23b to drive it in rotation. Planet gears 22b transmit drive to sun gear 21b that rotates with outer hub 100. In summary, power input by a rider from the pedals 40 is transmitted to the planet carrier 23b via the sprocket 80 and thus to the outer hub 100 to drive the rear wheel 30. Electrical assistance from the rotor 6 is supplied via the sun 21a. The speed of the electric motor can be varied in relation to the hub speed to continuously alter the rider cadence, whereby EPl and EP2 afford a continuously variable transmission (CVT).Examples of such CVTs are given in our WO publications mentioned above.

[0038] In order to provide smooth electrical drive assistance to the pedelec, it is important that the wheel speed sensor 31 and the rotor speed sensor (41) provide an accurate indication of speed and angular position over a wide range of rider input and over a wide range of eBike speeds. Providing such indications with minimal lag is also of importance. A further very practical factor is that the cost of providing such indications should be reasonable in the context of an eBike intended for everyday use - not necessarily an expensive, high end item.

[0039] Preferred embodiments of the invention provide data encoders that provide higher quality speed and angular position data, at a reasonable cost. Such encoders are described as follows.

[0040] Figure 3 shows diagrammatically a series of magnets 33 mounted on wheel 30 for rotation with the wheel 30 about axis 1. Analog Hall sensors 34 are mounted to be stationary with respect to the bicycle frame and to respond to passage of the moving magnets 33. These are components of wheel speed sensor 31.

[0041] A similar arrangement to that now described with respect to wheel 30 may alternatively or additionally be provided for the rotor 6 of the electric machine, as components of rotor speed sensor 41.As may be seen in both Figure 3 and the developed view of Figure 4, consecutive magnets 33 are of alternating polarity, with the South pole of one magnet 33 adjacent the North pole of the next magnet 33. The magnets P are spaced from one another by a regular pitch P. The analog Hall sensors 34 are spaced from one another by a quarter of the pitch of the magnets 33, that is P / 4. Thus, the two analog Hall sensors 34 are arranged in quadrature with a phase offset of 90°, with respect to 360° period of the passing magnets 33.

[0042] Although the magnets 33 are represented as discrete elements, they could alternatively be provided as a magnetized disk or ring. The ring would have alternating polarities as do the discrete magnets, performing an identical role in speed and angle sensing.

[0043] In use, when the wheel 30 is moving, each of the analog Hall sensors 34 responds to the magnetic field generated by each passing magnet 33, to generate a sinusoidal output. When a given magnet 33 passes the two analog Hall sensors 34 sequentially, the output of the second analog Hall sensor 34 lags the output of the first analog Hall by 90°. If the output of the first analog Hall sensor 34 is regarded as a sinewave, then the output of the second analog Hall sensor 34 is a cosine wave. This is illustrated in Figures 5A and 5B, where Figure5A illustrates a sinewave output y of a first analog Hall sensor 34 with respect to angular position x and Figure 5B illustrates a cosine wave output y of the second analog Hall sensor 34 with respect to angular position x.

[0044] A problem with using a single output from a single analog Hall sensor 34 - as in Figure 5A for example - is that there is not a monotonic relationship between output y and angle x. For example, points A in Figure 5A have the same value for y but represent different values of angle x. Any given value of y does not indicate a unique value of angle x.

[0045] A similar situation arises in Figure 5B, where points B have the same magnitude value of y, but indicate different values of angle x.

[0046] In order to resolve this ambiguity, the outputs of the two analog Hall sensors 34 are processed together in processor 35 to divide the sine output by the cosine output (or viceversa) and arrive at a tan (or cotan) output y as illustrated in Figure 5C. In this case, the relationship between y and x is monotonic insofar as any given magnitude of output y indicates a unique value of angle x.

[0047] Thus, the output of processor 35 may be fed to controller 91 in order to provide an accurate indication of the angular position of the wheel 30, which the controller 91 may process with respect to time in order to provide an indication of the angular speed of the wheel 30 and / or the linear speed of travel of the bicycle 1. The controller 91 may use this data, along with other data such as pedal input from a rider, in order to control the output of the electrical machine 5, 6 and any selectively operable clutch.

[0048] Due to the way that the outputs from the analog Hall sensors 34 are processed, any variations in amplitude of those outputs due to variations indistance between magnets 33 and analog Hall sensors 34 are cancelled out. The accuracy of the sensing and processing may be maintained, irrespective of distance between magnets 33 and analog Hall sensors 34.

[0049] As indicated above, rotor 6 speed and position may be sensed in a similar way by way of rotor speed sensor 41 that is similar to wheel speed sensor 31.

[0050] Although processor 35 and controller 91 are shown as separate items for ease of explanation, they could be combined into a single unit such as controller 91.

[0051] The sensors 34 could be embedded together in a common unit, and possibly integrated with processor 35 or other electronic devices, for ease of packaging, improved performance, or cost reduction.

[0052] In order to achieve acceptable accuracy of the data from the analog Hall sensors 34, the processor 35 transmits (or reports) the outputs of the analog Hall sensors 34 at a rate that is high with respect to the rpm of the wheel 30 and the motor rotor 6. This is particularly important when the wheel 30 and / or the motor are rotating slowly - for example, when the bicycle 1 is starting or stopping.

[0053] In prior configurations, digital Hall sensors have been used to detect passage of a magnetic element with each rotation of wheel such as 30. Such digital Hall sensors detect presence of a magnetic element in a simple binary fashion - either present (above a detection threshold) or not. This is a relatively simple and cheap option, but is prone to inaccuracy and therefore jerky operation of the bicycle - especially at low speeds, when the spacing between two consecutive pulses could be 1 or 2 seconds out of sync. Therefore, acontroller such as 91 could be reacting far too slowly to changing conditions. If the rider would suddenly stop, the motor 5,6 could overrun to drive the wheel 30 backwards, which is most disconcerting to the rider and potentially unsafe.

[0054] It is preferred to use analog Hall sensors in embodiments of the present invention, to provide an analog response to nearby magnetic elements and, in the presently described embodiments, to sample the outputs of the analog Hall sensors 34 at a frequency in the range 1000 to 5000 Hz - for example, 2000 Hz. This can be achieved with components and circuitry of relatively modest cost, in contrast to much higher frequency controllers that might be used with electric motors in other applications.

[0055] As indicated above, an arrangement as just described can equally well be employed to monitor the speed and / or angular position of the rotor 6, providing data that is fed to the controller 91 in order to control operation of the bicycle 1 smoothly at all speeds.

[0056] For improved control of the bike, it is preferred to transmit the processed outputs of the analog Hall sensors 34 at a frequency that is n times the transmission frequency for the wheel 30 or rotor 6. For example, n may be 2 to give a sampling frequency for the rotor 6 in the range 2000 to 10000 Hz - for example, 4000 Hz.

[0057] Figure 7 illustrates significant improvements that may be achieved by employing encoders that are embodiments of the invention. In this example, for comparison purposes, the outputs of analog Hall sensors 34 for both wheel 30 and rotor 6 are filtered and transmitted at 1000 Hz, as indicated by steady line F. Line C indicates twice pedalling frequency - the rider will pedal at a fairly uniform cadence, whilst the drive train provides CVT electrical assistance. Curve Dindicates sampling frequency of wheel speed against bike speed, as detected by a digital Hall sensor and filtered, as previously. Curve E indicates sampling frequency of motor speed against bike speed, as detected by a digital Hall sensor and filtered, as previously.

[0058] It may readily be seen that there is a huge difference in sampling accuracy at low speeds, as between, on the one hand, encoders of the type illustrated and discussed above and, on the other hand, previously used digital Hall sensors. Even at maximum bike speed, the present encoders are at least 10 times more accurate at a sampling frequency of 1000 Hz.

[0059] It will be appreciated that the illustrated embodiments of the invention provide novel and advantageous encoders for speed and position data in eBikes, enabling much improved and smoother control and therefore much improved and smoother rider experience, especially with CVTs.

[0060] Embodiments of the present invention may be realised as pedelecs, and / or as eBikes with electrical power assistance on demand. Whilst embodiments of the invention may be of particular advantage when used with CVT drive systems, they may also be used with other drive systems.

[0061] Whilst the illustrated embodiment of the invention has a rear drive configuration, other embodiments may be realised in other configurations, such as mid-drive or multiple drive configurations.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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

CLAIMS1. An electrically-assisted cycle having a drive train that receives drive from an electrical machine and drive from rider pedals and, under the control of a controller, transmits drive to an output that drives a wheel of the cycle, the cycle further comprising an encoder that detects angular position of a rotary part of the cycle, the encoder comprising: a series of magnetic elements mounted on the rotary part and mutually spaced at a constant circumferential pitch P, with the poles of successive magnetic elements arranged in opposite polarities; two analog Hall sensors mounted in fixed positions on the cycle, to respond to the series of magnetic elements as they pass the sensors, the sensors being mutually spaced by P / 4, that is, a quarter of the pitch P of the magnetic elements; and a processor configured to receive the outputs of the sensors and process the outputs to provide a signal representative of the angular position of the rotary part: the processor being configured to sample the outputs of the sensors at a frequency in the range 1000 to 10000 Hz.

2. An electrically-assisted cycle according to claim 1, wherein the output of one of the sensors is a sine wave, the output of the other sensor is a cosine wave and the processor divides one output by the other to provide a corresponding tan or cotan value.

3. An electrically-assisted cycle according to claim 1 or 2, wherein said rotary part is a driven wheel of the cycle.

4. An electrically-assisted cycle according to claim 3, wherein said frequency is in the range 1000 to 5000 Hz.

5. An electrically-assisted cycle according to claim 1 or 2, wherein said rotary part is the rotor of the electrical machine.

6. An electrically-assisted cycle according to claim 5, wherein said frequency is in the range 2000 to 10000 Hz.

7. An electrically-assisted cycle according to any of the preceding claims, wherein there are two said rotary parts with respective magnetic elements and analog Hall sensors.

8. An electrically-assisted cycle according to claim 7 , wherein the two said rotary parts are a driven wheel of the cycle and the rotor of the electrical machine.

9. An electrically-assisted cycle according to claim 8, wherein the sampling frequency for the rotor of the electrical machine is n times that for the driven wheel of the cycle.

10. An electrically-assisted cycle according to claim 9, where n = 2.

11. An electrically-assisted cycle according to any of the preceding claims, wherein the drive train provides a continuously variable transmission (CVT).

12. An electrically-assisted cycle according to any of the preceding claims, wherein the drive train provides a mechanical drive connection between the electrical machine, the pedals and a driven wheel of the cycle.

13. An electrically-assisted cycle substantially as hereinbefore described with reference to the accompanying drawings.

14. A method of operating an electrically-assisted cycle according to any of the preceding claims, including the steps of sampling the outputs of the sensors at a frequency in the range 1000 to 10000 Hz; processing the outputs to provide a signal representative of the angular position of the or each rotary part; and controlling the drive train in response to the processed outputs.

15. A method of operating an electrically-assisted cycle, substantially as hereinbefore described with reference to the accompanying drawings.

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