WO2018004462A1

WO2018004462A1 - Electric drive unit for a bicycle

Info

Publication number: WO2018004462A1
Application number: PCT/SG2017/050322
Authority: WO
Inventors: Felix ROEMER; Marius Lionel MROSEK; Simon SCHMALFUSS
Original assignee: Tum Create Limited
Priority date: 2016-06-29
Filing date: 2017-06-29
Publication date: 2018-01-04

Abstract

An electric drive unit to power a bicycle, the electric drive unit comprising: an arm to be mounted on one side of the bicycle; a mounting unit provided at a first end of the arm to attach the electric drive unit to a mounting point on a frame of the bicycle; a friction roller provided at a second end of the arm to engage one wheel of the bicycle at a contact point, the friction roller rotating the one wheel to propel the bicycle when the friction roller is driven; a motor provided at the second end of the arm to drive the friction roller; a sensing unit to detect cadence of cycling of the bicycle and generate a sensing signal; and a control unit to control operation of the motor according to the sensing signal.

Description

ELECTRIC DRIVE UNIT FOR A BICYCLE

FIELD

This invention relates to an electric drive unit for a bicycle. BACKGROUND

Retrofitting bicycles with electric drive units currently needs time-consuming modifications and/or installations of parts. Retrofit kits mostly include separate components such as an electric motor, batteries, sensors, and further electronic components. If powered at the bottom bracket or the wheel hub of the bicycle, special tools and technical knowledge is necessary for a first-time installation of the system. Existing retrofit kits furthermore differ in the possibility of uninstalling the drive systems. An easy detachment is normally only intended for the battery in order to charge it. The rest of the electrification system remains on the bicycle, making it heavier and less agile in a nonelectric manner of use. It also increases the potential damage in case of theft. Furthermore, the mounting of existing devices is not easily reversible. In some cases, parts have to be replaced by others (e.g. wheel hub or bottom bracket motors) or components have to be permanently installed such as sensors, cables, plugs and brackets. Existing devices are thus restricted to a small scope of bicycles with specific characteristics (e.g. wheel hub geared or without pannier racks and mudguards). SUMMARY

Disclosed is an easily detachable electric drive unit for off-the-shelf bicycles. It is ready to go and includes all necessary components for operation on a standard bicycle. No additional parts have to be attached to the bicycle, e.g. a pedal assist sensor, while still fulfilling the applicable laws of electric assisted bicycles (small Pedelecs: 250W, up to 25km/h, pedal assist controlled).

No first time installation steps (like the positioning and calibration of sensors) are needed for the electric drive unit. It is a plug and play device achieving bicycle electrification within seconds. A recurrent mounting and unmounting procedure is part of its usual usage (e.g. for charging purposes) and does not need any gears or tools. As there is no change or modification of parts, no technical knowledge is needed allowing ordinary users to electrify bicycles.

The electric drive unit can be attached on the large majority of off the shelf bicycles, as it is highly unaffected by geometrical variances and attachments like pannier rack, mudguards, etc. The electric drive unit is a fully integrated unit which after unmounting does not leave any components behind on the bicycle. In a non-electric manner of bicycle usage it therefore neither affects the bicycle appearance nor its driving characteristics. The electric drive unit is thus an add-on kit for subsequent bicycle electrification. With the electric drive unit, it is now possible to electrify bicycles without fixing additional parts to the bicycle. Neither cabled sensors nor brackets or other mounting parts are needed. Furthermore, high bicycle coverage is achieved, i.e. it is useable on most standard bicycles. Variations in bicycle characteristics like attached mudguards and pannier racks, different gearing systems or the wheel and frame size will not interfere with the electric drive unit.

The electric drive unit comprises a motor that is mechanically coupled to a wheel of the bicycle through a friction engagement means, a sensing unit that is configured to detect the cadence of cycling and generate a corresponding sensing signal, and a control unit that is configured to control the operation of the motor according to a sensing signal.

According to a first aspect, there is provided an electric drive unit to power a bicycle, the electric drive unit comprising: an arm to be mounted on one side of the bicycle; a mounting unit provided at a first end of the arm to attach the electric drive unit to a mounting point on a frame of the bicycle; a friction roller provided at a second end of the arm to engage one wheel of the bicycle at a contact point, the friction roller rotating the one wheel to propel the bicycle when the friction roller is driven; a motor provided at the second end of the arm to drive the friction roller; a sensing unit to detect cadence of cycling of the bicycle and generate a sensing signal; and a control unit to control operation of the motor according to the sensing signal.

The sensing unit may comprise a sensor provided at the first end of the arm to measure different positions of a leg of the cyclist on the bicycle during cycling. The sensing unit may further comprise a velocity sensor to detect speed of the motor.

The mounting point may be on a seat stay of the bicycle and the one wheel may be a rear wheel of the bicycle, and a connecting straight line between the mounting point and the contact point may be laterally angled from a top view centre line of the bicycle.

The friction roller may have an underlying conical shape.

The friction roller may have a concave surface provided on the underlying conical shape. The mounting point may be on a seat stay of the bicycle and a perpendicular to an axis of rotation of the motor may be laterally angled from a top view centre line of the bicycle. The arm may be foldable at a folding point of the arm between the mounting point and the contact point.

The mounting unit may comprise a tensioning mechanism to tightly mount the arm to the mounting point.

The tensioning mechanism may comprise a threaded shaft in threaded engagement with a threaded block provided within a main mounting axle of the mounting unit and a cable in connection with the main mounting axle; wherein when the cable is passed around the mounting point and attached to the main mounting axle, rotation of the threaded shaft laterally moves the threaded block towards the mounting point and away from the main mounting axle to increase distance between the mounting point and the main mounting axle, thereby creating tension in the cable.

A fitting configured to contact the mounting point may be provided on the threaded block, the fitting having a concave surface to increase contact area with the mounting point.

The motor may be operated to drive the friction roller only when cycling is detected and a speed of the bicycle is below a predetermined speed. The control unit may cut off power to the motor when a predetermined speed of the bicycle is reached or a cyclist of the bicycle stops pedalling.

BRIEF DESCRIPTION OF FIGURES

In order that the invention may be fully understood and readily put into practical effect there shall now be described by way of non-limitative example only exemplary embodiments of the present invention, the description being with reference to the accompanying illustrative drawings.

Fig. 1(a) is a rendering of an exemplary embodiment of an electric drive unit.

Fig. 1(b) is a schematic illustration of a top view of the electric drive unit attached to a bicycle.

Fig. 2 is a cross-sectional top view of a friction roller directly connected to a rotor of a motor (showing three bearings) of the electric drive unit.

Fig. 3 is a block diagram of a sensing and powering system of the electric drive unit.

Fig. 4 is a cross-sectional illustration of a mounting unit of the electric drive unit.

Fig. 5 is a perspective illustration of the mounting unit of Fig. 4.

Fig. 6 (a) is a back view of a bicycle having the electric drive unit attached thereto.

Fig. 6 (b) is a left view of a bicycle having the electric drive unit attached thereto.

Fig. 7 is a schematic illustration of a roller of the electric drive unit. Fig. 8(a) is a right view of a first cycling position where a crank shaft of the bicycle is 90° to the vertical.

Fig. 8(b) is a right view of a second cycling position where a crank shaft of the bicycle is vertical. Fig. 9 is a graph of signal patterns of motion detection by the electric drive unit of a lower leg of a rider cycling a bicycle to which the electric drive unit is attached.

DETAILED DESCRIPTION

Exemplary embodiments of an electric drive unit for a bicycle will be described below with reference to Figs. 1 to 9. The same reference numerals are used in the different figures to denote the same or similar parts.

The electric drive unit 10 as shown in Fig. 1(a) and 1(b) is a fully integrated product and comprises an arm 20 serving as a casing or housing containing all components necessary for operation of the unit 10, such as an electric motor 90 (Fig. 2), a power source such as batteries (not shown), a control unit with micro- and power electronics (not shown) and a sensor system or unit 80 (Fig. 3), as well as friction engagement means comprising a mounting unit or clamp 70 (Figs. 4 and 5) at a front or first end 3 of the arm 20 and a friction roller 60 at a rear or second end 22 of the arm 20 to power the bicycle 100 at a contact point C on one of its wheels, such as its rear wheel 101 on the rear tire 111, as shown in Figs. 6(a) and 6(b).

The unit 10 has a fixed lever or arm 20 length (i.e., distance from an axle of the mounting unit 70 to an axle of the friction roller 60. The arm 20 length is preferably configured for bicycles with wheel diameters of 26 and 29 inches as these are the most common tire sizes for adult bicycles. Additionally, the unit 10 is preferably foldable in order to provide for a compact packaging of the electric drive unit 10. As the lever or arm 20 length is fixed, folding the unit 10 (as shown at point F in Fig. 1(b)) allows more compactness for off-bike handling operation, transportation and recharging. Alternatively, the arm 20 may be extendible (telescopic) to decrease handling measures and allowing easy transportation of the unit 10. The arm 20 is a structural part and bears all forces occurring during operation.

In the exemplary embodiment as can be seen in Fig. 1(b), Figs. 6(a) and 6(b), the unit 10 is mounted at the front or first end 3 of the arm 20 on a rotation axis or mounting axle 21 at a mounting point M on a frame 102 of the bicycle 100. In a preferred embodiment, the mounting point M is located at the seat stay 103 while the contact point C is on the rear wheel 101, allowing the roller 60 to move up and down along the rear tire 111. This mounting axle 21 is aligned parallel to the rear wheel axle 106. The friction roller 60 and the motor 90 driving the friction roller 60 are provided at a rear or second end 22 of the arm 20 such that the friction roller 60 sits approximately at a height of the centre of the rear wheel 101. This area is accessible on most bicycles. Mudguards, if provided, will end above the friction roller 60. Furthermore, the roller 60 has space to move down the tire 111 when powering, and additional ground clearance is secured. Variations of the mounting position M are possible, compensating for different tire and frame dimensions. For example, it is also possible to mount the first end 3 of the arm 20 of the electric drive unit 10 on the fork 107 of the bicycle 100 and have the roller 60 at the second end 22 of the arm 20 drive the front wheel 108 of the bicycle 100. The electric drive unit 10 does not interfere with any mounted pannier racks and other stays that may cover the rear tire 111.

The mounting unit 70 is preferably configured to attach the electric drive unit 10 to either the left or the right lateral side of the frame 102 of the bicycle 100, i.e. mounted on only one side of the bicycle 100, such that the friction roller 60 is tilted laterally with respect to a top view centre line of the wheel 101, as shown in Fig. 1(b). The centre line CL_B is parallel to the xz-plane of the bicycle 100. The mounting unit 70 is preferably mounted at one lateral point M, either on the left or on the right side of the bicycle 100 (e.g. at the seat stay 103). The mounting unit 70 may be built symmetrically.. Fig. 1(b) shows the engagement contact point C of the friction roller 60 with the bicycle tire 111 being on an opposing site of the bicycle center line CL_B, i.e. there is a tilted engagement of the friction roller 60 with the bicycle tire 111 to compensate for forces resulting from a lateral mounting. This is achieved by providing conical friction roller geometry as shown in Fig. 7 and/or a tilted motor axis 99 that is co-axial with the roller axle 61, as will be described in greater detail below.

The mounting system or unit 70 is capable of compensating for different seat-stay 103 angles and allowing a one-point mount while ensuring a straight alignment of the friction roller 60 to the tire 111. The mounting unit 70 preferably comprises a tensioning mechanism 5 to tightly fit the unit 10 to the bicycle frame 102. For example, a threaded shaft 5 or clamp may serve as the tensioning mechanism 5 to generate tension. An exemplary embodiment of the mounting unit 70 as shown in Figs. 4 and 5, comprises a mounting clamp 71, a bearing 2 and a rotary damper 4. The mounting clamp 71 is able to rotate as a whole, and is located in the front or first end 3 of the housing or arm 20 (not shown in Fig. 5). The mounting clamp 71 comprises a main mounting axle 1 that serves as a housing for a threaded shaft 5 having a first end 5-1 in threaded engagement with a threaded block 7 also housed in the main mounting axle 1. The bearing 2 preferably comprises a bush bearing 2 and is provided between the main mounting axle 1 and the front or first end 3 of the arm 20 in order to allow rotation of the main mounting axle 1 relative to the arm 20. The threaded shaft 5 is co-axial with the mounting axle 21 of the electric drive unit 10. A knob 6 is attached to a second end 5-2 of the threaded shaft 5 while a fitting 8 is attached to the threaded block 7 for engagement with a seat stay 103. The fitting 8 is and has a concave surface 89 for increased contact with the curved surface of the seat stay 103, and is preferably also angled to compensate for an outside angle of the seat stay 103. The fitting 8 is preferably made of a high friction material such as plastic or rubber (as opposed to metal) for better grip against the seat stay 103.

Rotation of the knob 6 accordingly turns the threaded shaft 5 within the main mounting axle 1. Turning of the threaded shaft 5 against the threaded block 7 results in linear translation or a lateral movement of the threaded block 7 along the mounting axle 21, and consequently lateral movement of the fitting 8. The damper 4 prevents the unit 10 from skipping at the rear wheel 101, i.e., prevents the unit 10 from jumping when the bicycle goes over a hump or down a curb. For compact packaging, an inner ring 41 of the rotary damper 4 is directly fitted on a square shaft profile of the main mounting axle 1 while an outer ring 42 of the damper 4 is screwed into the housing or arm 20 of the electric drive unit 10. This allows the main mounting axle 1 to rotate in a damped way about the housing 20 as a result of the inner ring 41 rotating within the outer ring 42 of the damper 4.

A rubber coated cable 9 is attached at its two ends to the threaded block 7 to form a loop of cable 9 that extends beyond the fitting 8, as can be seen in Fig. 5. To mount the electric drive unit 10 to the bicycle frame 102, the looped cable 9 is passed around the seat stay 103 and hooked into a groove 19 provided at a front or first end 3 end of the main mounting axle 1, thereby forming a loop of two cables 9-1, 9-2 around the seat stay 103. The mounting unit 70 is then fastened by turning the knob 6 so that rotation of the knob 6 is transferred to a lateral movement of the threaded block 7 by the threaded shaft 5, thereby laterally moving the fitting 8 towards the seat stay tube 103 and away from the front or first end 3 end of the main mounting axle 1. As the fitting 8 is pushed against the seat stay 103 and away from the main mounting axle 1 while the cable 9 is hooked into the groove 19 on the main mounting axle 1, distance between the seat stay 103 and the groove 19 on the main mounting axle 1 is increased, thereby creating tension in the cable 9 to tightly mounting the arm 20 to the seat stay 103. The threaded block 7 functions to align the electric drive unit 10 towards the seat stay 103 in such a way that the roller 60 sits correctly on the tire 111.

An additional advantage of the functioning principle of the mounting unit 70 is that it compensates for different seat stay 103 distances. For example, road or racing bicycles with thinner tires tend to have shorter seat stay 103 distance and also thinner tubes. In this case, the threaded block 7 is screwed out and the distance from the seat stay tube 103 to the unit 10 increases. On the other hand, for mountain bicycles with thicker seat stay tubes 103 and higher distance between the seat tubes 103 due to larger tires, the threaded block 7 has to be screwed in, so that the unit 10 moves closer towards the tube 103. Preferably, the threaded shaft 5 and threaded block 7 use a fine pitch M8xl thread to gain higher tightening forces than a standard pitch. The pitch could also be modified for greater tightening force. As screwing devices are usually fastened by turning clockwise, the threaded shaft 5 preferably has a left-hand thread to provide intuitive handling of the knob 6 for users. It should be noted that in an alternative embodiment (not shown), the mounting unit 70 may comprise two separate parts - a first part comprising a pre-installed mounting axis and connection point on the bicycle 100 and a second part comprising a coupling/connector point on the arm 20 of the unit 10 for coupling/connecting with the first part. Preferably, the motor 90 provides assisted propulsion to the wheel 101 via the friction roller 60 only when a cyclist is pedalling and the speed of the bicycle 100 is less than a predetermined speed limit (e.g. 25km/h). In a preferred embodiment, the motor 90 is a brushless DC motor. When powering, the friction roller 60 will move down the tire 111 and the pressure between the roller 60 and the tire 111 is automatically augmented. Higher normal pressure leads to a higher transmissible frictional force for a certain friction coefficient. When the unit 10 is not powering, the opposite effect occurs, leading to a reduction of friction.

As the turning or mounting point M is not located in the mid plane of the bicycle 100, a lateral movement of the friction roller 60 has to be prevented by generating a contact surface 62 which is perpendicular to a connecting straight line L_MC between the mounting point M and the contact point C of the roller 60 with the tire 111, as shown in Fig. 1(b). This is achieved by a tilted motor axis 99 and/or a conical design of the friction roller 60. In an exemplary embodiment as shown in Fig. 1(b) and Fig. 7, a perpendicular 98 to the roller axle 61 or the motor axis 99 (the roller axle 61 and motor axis 99 being coaxial) is tilted or angled by 9 degrees laterally from the centre line CL_B of the bicycle 100 due to the dimensions and shape of the electric drive unit 10 and the bicycle 100, and also the actual mounting point M of the unit 10 on the seat stay 103. However, the connecting line L_Mc as described above is tilted or angled by only 7 degrees laterally from the centre line CL_B of the bicycle 100. The friction roller 60 is thus configured to have an underlying conical shape 62 having a 2-degree tilt relative to the roller axle 61, and an outer shape that is a concave 63 having a radius of negative curvature R of 80 cm (as shown in Fig. 7) in its longitudinal plane, so that at the contact point C between the tire 111 and the point of smallest diameter of the friction roller 60, a normal to the point C towards the mounting point M at the seat stay 103 is collinear with the connecting line L_MC, i.e., tilted at 7 degrees from the centre line CL_B of the bicycle 100. The geometry of the underlying conical roller 60 thus reduces the 9-degree tilt of the unit 10 and motor 90 to the needed 7 degrees of the connecting line L_MC to prevent lateral movement of the friction roller 60, thereby providing an indifferent system as the contact surface or point C lies in line with the direction L_MC to the lateral mounting position M (and therefore mounting force direction). Adding a negative radius R to the surface of the friction roller 60 (so that the ends of the friction roller 60 have a greater diameter than the diameter of the friction roller 60 at the contact point C) leads to a stable, self-centering system, but also implies relative speeds which generate frictional losses heating up the roller 60. As the mounting system is stiff, the radius R can be kept small, as shown in Fig. 1(b).

The smallest diameter of the roller 60 at the point contact point C determines the revolutions per minute (RPM) of the motor 90 at various bicycle speeds. Using a small diameter such as 30 cm and having big wheels 101 (such as 26 inches and bigger), the motor speed can reach 1000 rpm at 5 km/h of the bicycle velocity. At 25 km/h, the motor speed is above 4000 RPM, making additional gearing superfluous or unnecessary as those are already optimal turning speeds for brushless DC motors. For easy access to the powering location, the friction roller 60 is mounted only on one side and is directly connected to the rotor 97 of the electric motor 90 as shown in Fig. 2. This provides a small package of the unit 10 and makes easy mounting possible. The motor 90 uses a special bearing constellation 95 comprising a single big bearing lateral to the friction roller 60, taking most of the load and preventing the motor 60 from taking too much load. As the roller 60 is self-aligning under normal operation conditions, there is no additional precaution necessary to prevent it from falling. The stator 96 of the motor 90 is fixed to the housing or arm 20 of the electric drive unit 10.

By law, small pedelecs (pedal electric cycles) must only power when the cyclist is actively pedalling. A block diagram of the sensing 80 and powering system (comprising the motor 90 and roller 60) of the electric drive unit 10 is shown in Fig. 3, in which motion detection and motor speed are used for determination of a control input of the powering system. In an exemplary embodiment, the pedalling detection (measuring the desire for movement of the bicycle 100 by the cyclist) uses optical motion detection. Alternatively, a proximity sensor such as an ultrasonic distance sensor or inductive/capacitive proximity sensor may be used. The sensing system 80 additionally senses the bicycle speed provided by a sensor mounted at the rotating motor 90. The rotational speed of the motor 90 is directly linked to the bicycle speed, i.e. of the friction roller 80. The sensing system 80 then provides a control input for the power controller included in the powering system which in turn powers the electric motor 90 and supports the cyclist in accelerating the bicycle 100. The control signal of the motor 90 is derived from multiple sensors comprised in the sensing system 80 of the electrical driving unit 10. The sensors include an optical or proximity sensor, a velocity sensor, a current sensor and also an accelerometer and gyroscope. In order to detect pedalling by the cyclist, the sensor data trajectories are analysed for frequency (e.g. via a Fourier transformation of the signal), variance, standard deviation, mean, minima and maxima, i.e., for their characteristic signal properties. The analysing is done in real time. The control input is then derived by combining the analysed values of the different sensors in order to ensure safe cycling and to prevent malfunction. The control unit can control the rotation direction of the motor 90 according to the mounting position of the electrical driving unit 10. Sensing of the moving leg of the cyclist is done by the integrated optical sensor for contactless motion detection, measuring the cyclist's body movement. In a preferred embodiment, the optical sensor comprises an infrared sensor. To measure the cyclist's movement, the sensor is located at the front or first end 3 of the electric drive unit 10 and therefore at the side of the seat stay 103 in order to be able to detect the cadence of cycling by measuring the position of the cyclist's (lower) legs. As the sensor is located directly behind the cyclists' leg, motion detection is possible and can replace a fixed sensor installed at the bottom bracket. Fig. 8(a) shows a first position in which the crank-arm of the bicycle 100 is 90° to the vertical during pedalling and a corresponding first leg position of the cyclist, measured by the optical sensor as distance d_90° between the first leg position and the sensor at the front or first end 3 of the electric drive unit 10. Fig. 8(b) shows a second position in which the crank-arm of the bicycle 100 is 180° or vertical during pedalling and a corresponding second leg position of the cyclist, measured by the optical sensor as distance di_80° between the second leg position and the sensor at the front or first end 3 of the electric drive unit 10. It can be seen that d_90° is greater than di_80°. Thus, by measuring and recording the distance between the leg position and the sensor with time, cadence of cycling can be determined.

The measured variation in distance can then be used to determine the cadence (frequency of pedalling). The microcontroller analyses the optical data obtained, calculating different parameters such as the short term mean, standard deviation and frequency of the signal, as shown in Fig. 9. In combination with the measured cycling speed at the motor (the velocity sensor detects the speed of the motor 90 and thereby of the bicycle 100), the sensing unit 80 allows a safe and convenient way of contactless pedalling detection. The microprocessor then generates the control signal for the power electronics and motor controller. The microprocessor also cuts off the motor power when the predetermined speed (e.g. 25 km/h) is reached. The predetermined or maximum speed can be set electronically and therefore adapted to different applicable laws for electric assisted bicycles (e.g. the US with a maximum of 20 miles per hour).

The combination of mounting position of the electric drive unit 10 on the frame 102 and powering position on the tire 1 1 1 of the wheel 101 is designed like a swing in order to use the weight of the electric drive unit 10 as well as a "wedging" effect caused by the driving torque in order to increase contact pressure in the area of friction engagement and therefore higher transmittable forces.

The electric drive unit 10 described above is thus an add-on kit for subsequent bicycle electrification. Unlike prior art, with the present electric drive unit 10, it is possible to electrify bicycles without fixing additional parts to the bicycle. Neither cabled sensors nor brackets or other mounting parts are needed. Furthermore, high bicycle coverage is achieved, i.e., the present electric drive unit 10 is useable on most standard bicycles. Variations in bicycle characteristics like attached mudguards and pannier racks, different gearing systems or the wheel and frame size will not interfere with the drive unit 10, which is directly mounted onto the bicycle without requiring attachment of any other devices such as pannier racks on the bicycle beforehand. Whilst there has been described in the foregoing description exemplary embodiments of the present invention, it will be understood by those skilled in the technology concerned that many variations and combination in details of design, construction and/or operation may be made without departing from the present invention. For example, while it has been described above that a perpendicular to the roller axle or the motor axis is tilted or angled by 9 degrees laterally from the centre line CLB of the bicycle, it will be understood that various other angles of tilt can be expected depending on the size and shape of the specific bicycle and the electric drive unit can be configured for such variations accordingly. While it has been mentioned that the arm serves as a casing for housing the power source such as a battery, it should be noted that an extra battery may be located outside the main enclosure 20. In alternative embodiments, the motor may be integrated with the friction roller for an even more compact packaging of the electric drive unit.

Claims

1. An electric drive unit to power a bicycle, the electric drive unit comprising:

an arm to be mounted on one side of the bicycle;

a mounting unit provided at a first end of the arm to attach the electric drive unit to a mounting point on a frame of the bicycle;

a friction roller provided at a second end of the arm to engage one wheel of the bicycle at a contact point, the friction roller rotating the one wheel to propel the bicycle when the friction roller is driven;

a motor provided at the second end of the arm to drive the friction roller;

a sensing unit to detect cadence of cycling of the bicycle and generate a sensing signal; and a control unit to control operation of the motor according to the sensing signal.

2. The electric drive unit of claim 1, wherein the sensing unit comprises a sensor provided at the first end of the arm to measure different positions of a leg of the cyclist on the bicycle during cycling.

3. The electric drive unit of claim 2, wherein the sensing unit further comprises a velocity sensor to detect speed of the motor.

4. The electric drive unit of any one of the preceding claims, wherein the mounting point is on a seat stay of the bicycle and the one wheel is a rear wheel of the bicycle, and wherein a connecting straight line between the mounting point and the contact point is laterally angled from a top view centre line of the bicycle.

5. The electric drive unit of any one of the preceding claims, wherein the friction roller has an underlying conical shape.

6. The electric drive unit of claim 5, wherein the friction roller has a concave surface provided on the underlying conical shape.

7. The electric drive unit of any one of the preceding claims, wherein the mounting point is on a seat stay of the bicycle and a perpendicular to an axis of rotation of the motor is laterally angled from a top view centre line of the bicycle.

8. The electric drive unit of any one of the preceding claims, wherein the arm is foldable at a folding point of the arm between the mounting point and the contact point.

9. The electric drive unit of any one of the preceding claims, wherein the mounting unit comprises a tensioning mechanism to tightly mount the arm to the mounting point.

10. The electric drive unit of claim 9, wherein the tensioning mechanism comprises

a threaded shaft in threaded engagement with a threaded block provided within a main mounting axle of the mounting unit and

a cable in connection with the main mounting axle;

wherein when the cable is passed around the mounting point and attached to the main mounting axle, rotation of the threaded shaft laterally moves the threaded block towards the mounting point and away from the main mounting axle to increase distance between the mounting point and the main mounting axle, thereby creating tension in the cable.

11. The electric drive unit of claim 10, wherein a fitting configured to contact the mounting point is provided on the threaded block, the fitting having a concave surface to increase contact area with the mounting point.

12. The electric drive unit of any one of the preceding claims, wherein the motor is operated to drive the friction roller only when cycling is detected and a speed of the bicycle is below a predetermined speed.

13. The electric drive unit of any one of the preceding claims, wherein the control unit cuts off power to the motor when a predetermined speed of the bicycle is reached or a cyclist of the bicycle stops pedalling.