BICYCLE DRIVING SYSTEM AND KIT

Abstract

The invention discloses a bicycle drive system (10) and a kit. The drive system comprises a drive unit (15) comprising a housing, a motor unit (20) having a stator (21), a rotor (22) and an output shaft and accommodated in the housing, and a first stage deceleration unit (30) having an input part connected to the output shaft of the motor unit and an output part; a mounting unit (50) configured to secure and hold the drive unit on a bicycle body (70); and a second stage deceleration unit (40) arranged external to the drive unit and detachably mounted on the first stage deceleration unit for connection to a pedal assembly (80) to transfer a drive force from the output part of the first stage deceleration unit to chainrings (82) of the pedal assembly. The drive unit, the mounting unit and the second stage deceleration unit are each provided as a modular part for assembling to the bicycle. The invention provides a customizability of the drive system.

Claims

1. A bicycle drive system configured to provide power for a pedal assembly of a bicycle, comprising: a drive unit comprising a housing, a motor unit having a stator, a rotor and an output shaft and accommodated in the housing, and a first stage deceleration unit having an input part connected to the output shaft of the motor unit to transmit a drive force from the motor unit to the first stage deceleration unit in the housing, and an output part; a mounting unit configured to secure and hold the drive unit on the pedal assembly; and a second stage deceleration unit arranged external to the drive unit and detachably mounted on the first stage deceleration unit for connection to the pedal assembly so that the drive force from the output part of the first stage deceleration unit is transferred to chainrings of the pedal assembly, wherein the drive unit, the mounting unit and the second stage deceleration unit are each provided as a modular part and are detachably mounted relative to each other.

2. The bicycle drive system of claim 1, wherein the first stage deceleration unit is a planetary gear deceleration mechanism, and the output shaft of the motor unit and the input part of the first stage deceleration unit are coaxially arranged.

3. The bicycle drive system of claim 1, wherein the first stage deceleration unit comprises: a sun gear attached to the output shaft of the motor unit and configured as the input part; a plurality of planetary gears surrounding the sun gear and engageable with the sun gear; a ring gear engageable with the plurality of planetary gears; a planetary gear carrier configured to hold the plurality of planetary gears; and a unidirectional transmission device provided between the planetary gear carrier and the output part.

4. The bicycle drive system of claim 1, wherein the housing of the drive unit comprises a housing portion adapted for housing the motor unit and a housing portion adapted for housing the first stage deceleration unit, which are detachably connected to each other.

5. The bicycle drive system of claim 1, wherein the second stage deceleration unit is configured as a deceleration mechanism selected from at least one of a chain deceleration mechanism, a belt deceleration mechanism and a gear deceleration mechanism, and the deceleration mechanism comprising a first transmission wheel mounted to the output part of the first stage deceleration unit and a second transmission wheel mounted to a spindle of the pedal assembly via a unidirectional transmission device.

6. The bicycle drive system of claim 1, further comprising a control unit electrically connected with the motor unit and having a separate housing, and the control unit being provided as a modular part which is detachably mounted on the mounting unit.

7. The bicycle drive system of claim 1, wherein the mounting unit comprises a pair of support plates arranged in a spaced apart manner, the support plate having a first mounting part and a second mounting part separated from each other by a predetermined distance, the first mounting part being fixed on a spindle of the pedal assembly, the second mounting part being attached to two opposite ends of the drive unit so that the drive unit is arranged away from the spindle after the bicycle drive system is mounted in place on the bicycle.

8. The bicycle drive system of claim 1, wherein the system further comprises a cadence sensor comprising a magnetic ring mounted to the pedal assembly and configured to rotate together with rotation of a crank of the pedal assembly, and a sensor element adjoining the magnetic ring and being held on the mounting unit to sense the rotation of the magnetic ring, and the cadence sensor being connected to a control unit of the bicycle drive system.

9. The bicycle drive system of claim 1, wherein the system further comprises a torque sensor which comprises a strain sleeve provided on the pedal assembly to measure a force exerted on the pedal assembly, and the torque sensor is connected to a control unit of the bicycle drive system.

10. The bicycle drive system of claim 9, wherein the strain sleeve is mounted on a spindle core of the spindle of the pedal assembly, and is connected to a unidirectional transmission device provided on a transmission wheel of the second stage deceleration unit.

11. A auxiliary drive kit for a pedal assembly of a bicycle, wherein the kit is provided as a modular part and configured to comprise: an drive unit comprising a housing, a motor unit having a stator, a rotor and an output shaft and accommodated in the housing, and a first stage deceleration unit having an input part connected coaxially to the output shaft of the motor unit to transmit a drive force from the motor unit to the first stage deceleration unit in the housing, and an output part, and the first stage deceleration unit has an input part and an output part, the input part of the first stage deceleration unit being coaxially connected to an output shaft of the motor unit to transmit drive force from the motor unit to the first stage deceleration unit in the body; a mounting unit configured to secure and hold the motor unit and the first stage deceleration unit on a bicycle body, the mounting unit comprising a pair of or multiple pairs of support plates having different spacings and/or a selection of extension lengths; and a second stage deceleration unit arranged external to the drive unit and detachably mounted on the first stage deceleration unit for connection to the pedal assembly, and configured to transfer a drive force from the output part of the first stage deceleration unit to chainrings of the pedal assembly, and the second stage deceleration unit comprising a transmission wheel set having a selection of deceleration ratios.

12. The drive kit of claim 11, wherein the mounting unit further comprises a shim provided between the support plate and the drive unit for adjusting the spacing, or comprises an adapter for different models of spindle.

13. The bicycle drive system of claim 2, wherein the first stage deceleration unit comprises: a sun gear attached to the output shaft of the motor unit and configured as the input part; a plurality of planetary gears surrounding the sun gear and engageable with the sun gear; a ring gear engageable with the plurality of planetary gears; a planetary gear carrier configured to hold the plurality of planetary gears; and a unidirectional transmission device provided between the planetary gear carrier and the output part.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Hereinafter, preferred embodiments according to the invention will be described in detail with reference to the accompanying drawings, wherein:

[0024] FIG. 1 shows an exploded perspective view of a drive unit according to a preferred embodiment of the invention;

[0025] FIG. 2 shows a sectional view of the drive unit of according to the preferred embodiment of the invention, wherein the drive unit comprises a motor unit and a first stage deceleration unit;

[0026] FIG. 3 shows a sectional view of the first stage deceleration unit according to the preferred embodiment of the invention;

[0027] FIG. 4 shows a sectional view of a second stage deceleration unit according to a preferred embodiment of the invention;

[0028] FIG. 5A to FIG. 5C respectively show schematic views of a second stage deceleration unit according to another preferred embodiment of the invention;

[0029] FIG. 6 shows a schematic view of a bicycle drive system mounted to a triangular frame of the bicycle according to a preferred embodiment of the invention;

[0030] FIG. 7A shows a perspective view of the bicycle drive system with a cadence sensor according to a preferred embodiment of the invention;

[0031] FIG. 7B shows an enlarged view of details of the cadence sensor shown in FIG. 7A according to the preferred embodiment of the invention;

[0032] FIG. 8A shows a sectional view of the bicycle drive system with a torque sensor according to a preferred embodiment of the invention;

[0033] FIG. 8B shows a perspective view of a crank spindle of the bicycle drive system according to the preferred embodiment of the invention;

[0034] FIG. 9A to FIG. 9C respectively show schematic views of bicycle drive systems with different support plates according to preferred embodiments of the invention; and

[0035] FIG. 10A to FIG. 10C respectively show sectional views of the spindle and a carrier cover that are adaptable for different support plates and mounted to the bicycle crank.

LIST OF REFERENCE NUMBERS

[0036] 10 Drive system [0037] 15 Drive unit [0038] 20 Motor unit [0039] 21 Stator [0040] 22 Rotor [0041] 23 Rotation shaft [0042] 24 Motor unit housing portion [0043] 25 End cover [0044] 27 PCB [0045] 28 Coil [0046] 30 First stage deceleration unit [0047] 31 Sun gear [0048] 32 Planetary gear [0049] 33 Ring gear [0050] 34 Planetary gear carrier [0051] 35 Unidirectional transmission device [0052] 36 Output shaft [0053] 37 Housing [0054] 38 Large bearing [0055] 40, 40′ Second stage deceleration unit [0056] 41 Pinion gear [0057] 42 Bull gear [0058] 41′ Small sprocket [0059] 42′ Large sprocket [0060] 43′ Chain [0061] 46 Roller [0062] 47 Spring [0063] 48 Unidirectional transmission device [0064] 50 Mounting unit [0065] 511, 512, 513, 514, 515, 516 Support plates [0066] 60 Control unit [0067] 65 Cadence sensor [0068] 651 Magnetic ring [0069] 652 Sensor element [0070] 68 Torque sensor [0071] 681 Strain sleeve [0072] 70 Bicycle body [0073] 80 Pedal assembly [0074] 81 Crank [0075] 82 Chainring [0076] 83 Spindle [0077] 831 Spindle core [0078] 832 Spindle bowl [0079] 833 Tension nut

DETAILED DESCRIPTION OF THE INVENTION

[0080] The invention will be further described below in conjunction with the specific embodiments and the drawings. More details are set forth in the following description for better understanding of the invention, although it is apparent that the invention may be embodied in various manners other than those described herein. Those skilled in the art may make extension and deduction depending on the practical application situations without departing from the spirit of the invention. Thus, the scope of the invention is not intended to be limited by the contents of the specific embodiments.

[0081] A common power component in a bicycle is a pedal assembly 80. The pedal assembly 80 usually comprises a pedal, crank 81, chainrings 82 and a spindle 83 (which is also called a BB spindle) mounted on a mounting part of a bottom bracket of the bicycle. The pedaling of a rider drives the crank 81 and the chainrings 82 to rotate. The rotation of the chainrings 82 is transferred through a chain to the rear wheel of the bicycle.

[0082] FIG. 6 schematically shows a mid-drive system 10, which is mounted on the bicycle frame, according to a preferred embodiment of the invention. The mid-drive system 10 is arranged adjacent to the bicycle pedal assembly 80 to provide the auxiliary drive for the pedal assembly 80, particularly for the chainrings 82, to save physical strength of the rider.

[0083] In particular, the bicycle drive system 10 mainly comprises a drive unit 15, a second stage deceleration unit 40, a mounting unit 50 and a control unit 60, all of which are each provided as a modular part, enabling a user to appropriately select among these functional units according to the structure of the bicycle and actual needs, and integrally mount them on the bicycle. In the system 10 of the invention, the modularization of the units particularly means that each unit of the drive system 10 is configured as a structural module that can be separated, individually replaced and mounted relative to each other, and each unit can be modified and designed individually for customized needs.

[0084] FIG. 1 and FIG. 2 respectively show a perspective view and a sectional view of the drive unit 15 of the auxiliary drive for bicycles according to a preferred embodiment of the invention. The drive unit 15 further comprises a motor unit 20 and a first stage deceleration unit 30. Preferably, the motor unit 20 and the first stage deceleration unit 30 are coaxially integrated and accommodated in a housing of the drive unit 15 so as to form a modularized drive unit 15.

[0085] In a preferred embodiment of the drive unit 15, the motor unit is an inner rotor brushless motor. The motor unit 20 comprises a substantially cylindrical housing portion 24, a stator 21 fixed at the housing portion 24, a rotation shaft 23 extending along a rotation axis and a rotor 22 mounted to the rotation shaft 23 and arranged opposite the stator 21. The stator 21 comprises a plurality of stator teeth, each of which is wound with a coil 28. To prevent dislodgement of a magnet of the rotor 22 in the course of high-speed rotation, the magnet should be securely fixed to the rotor 22 so that the motor unit 20 according to the invention is able to achieve high-power output. For instance, in one embodiment, the magnet may be glued on the rotor with an adhesive. In another embodiment, the magnet may be attached to the rotor 22 by formfitting of a dovetail groove.

[0086] In a preferred embodiment, the housing portion 24 comprises a cylindrical wall and an end cover 25 on one side of the cylindrical wall, both of which are detachably connected via a fastener. In addition, as shown in FIG. 2, the outer surface of the cylindrical wall of the motor unit 20 has a plurality of radiating fins integrally formed thereon. Normally, the cylindrical wall of the housing portion 24 is made from a metallic material to facilitate heat dissipation of the motor unit 20. Preferably, the housing portion 24 is made from an aluminum alloy material. In a preferred embodiment, the end cover 25 is made from a transparent material. Examples of the transparent material include steel glass or a hard transparent resin material. The stator 21 and the rotor 22 inside the motor unit 20 are provided in the vicinity of the end cover 25 to make the stator 21 and the rotor 22 visible from outside for checking the operating condition of the motor.

[0087] Moreover, a PCB 27 useful for controlling the operation of the motor unit 20 is arranged inside the motor unit 20 at one end opposite the transparent end cover 25. In order to connect the motor unit 20 to the separate control unit 60 of the drive system 10, a control line (not shown) is led out of the housing portion 24 from the top of the PCB 27.

[0088] Advantageously, a heat conducting sealant may be used to seal the interior of the motor unit 20. In particular, a static portion in the motor unit 20, where the stator 21, the coil 28 and the PCB 27 are arranged, is hermetically filled with the heat conducting sealant. In this way, heat of the motor unit 20 generated in the course of operation can be dissipated through the radiating fins to the ambient environment, which not only can increase the reliability of the operation of the motor unit 20, but also ensure that the interior of the motor unit 20 is protected from external water and moisture.

[0089] As shown in FIG. 1 and FIG. 2, the first stage deceleration unit 30 in the motor unit 15 adopts a planetary gear deceleration mechanism coaxially arranged with the motor unit 20, i.e. the output end of the rotation shaft 23 of the motor unit 20 and a rotation axis of the input part of the first stage deceleration unit 30 are arranged on a common axis. Preferably, a positioning member such as a positioning step is provided between the motor unit 20 and the first stage deceleration unit 30. The interaction with the positioning member ensures that the output end of the motor unit 20 and the input part of the first stage deceleration unit 30 keep staying coaxially.

[0090] In a preferred embodiment, the first stage deceleration unit 30 mainly comprises a sun gear 31, planetary gears 32, a ring gear 33, a planetary gear carrier 34, an output shaft 36 configured as an output part and a housing portion 37. As shown in FIG. 3, the sun gear 31 is connected to the output end of the rotation shaft 23 of the motor unit 20, for example via a splined-shaft connection. Three planetary gears 32 are held by the planetary gear carrier 34, are arranged in a spaced-apart manner around the sun gear 31 and engage with the sun gear 31. One ring gear 33 is provided around the outer circumference of the planetary gears 32. This ring gear 33 is secured to the housing portion 37 of the first deceleration unit 30 so that the ring gear 33 on the outer circumference is engageable with each of the planetary gears 32.

[0091] In a preferred embodiment, a large bearing 38 is provided on the outer circumference of the planetary gear carrier 34 and connected to the housing portion 37 of the deceleration unit 30 to enable the planetary gear carrier 34 to rotate inside the housing portion 37.

[0092] Inside the interior of the planetary gear carrier 34, there is a unidirectional transmission device 35 comprising an inner ring connected to an output shaft 36, and an outer ring. The unidirectional transmission device 35 and the output shaft 36 are connected to each other for example in a manner of press-fitting or splined-shaft connection so as to realize restrictions on circumferential movement. It is particularly beneficial to the bicycle mid-drive system 10 to integrate one unidirectional transmission device 35 into the first stage deceleration unit 30. On one hand, the unidirectional transmission device 35 can prevent the output shaft 36 of the first stage deceleration unit 30 to drive the motor unit in reverse, because a reverse rotation force exerted on the output shaft 36 of the first stage deceleration unit 30 would cause the transmission device 35 to idle, thereby the rotation force cannot be transferred to the motor unit 20. On the other hand, the unidirectional transmission device 35 can protect the rider in the event that undesirable rotation of the motor unit 20 occurs, that is to say, when the motor unit 20 rotates in the direction opposite to the drive direction, the unidirectional transmission device 35 will also idle, causing a failure in transferring the reverse drive force to the output shaft 36 of the first stage deceleration unit. Preferably, a positioning step is formed between the front end cover of the first stage deceleration unit 30 and the housing portion 37 of the first stage deceleration unit 30, thereby by means of the positioning effect of the positioning step, it is ensured that the output shaft 36, the motor unit 20 and the deceleration unit 30 are arranged coaxially.

[0093] In the first stage deceleration unit 30 according to a preferred embodiment, the large bearing, the planetary gear carrier 34, the unidirectional transmission device 35 and the output shaft 36 are connected to form a partition, so that the space in which the sun gear 31, the planetary gear 32 and the ring gear 33 are located is separated hermetically from the space in which the portion of the output shaft 36 extending outward is located. In this way, dust and water will not enter the spaces in which various gear components of the deceleration unit 30 are located; thereby the lubricant lubricating various gear components can be prevented from being contaminated.

[0094] In a preferred embodiment, the first stage deceleration unit 30 has a preset deceleration ratio in the range of 3:1 to 10:1. Various gear components in the deceleration unit 30 all adopt straight teeth. However, it should be understood that teeth in other shapes can also be used instead.

[0095] As shown in FIG. 2, in the preferred embodiment according to the invention, the motor unit 20 and the first stage deceleration unit 30 are integrated as a unitary drive unit 15, thereby providing a compact structure. The cylindrical wall of the motor unit 20 has an outer diameter that is substantially the same as that of the first stage deceleration unit 30 substantially the same. The motor unit 20 and the first stage deceleration unit 30 are preferably separated from each other by a partition wall. The rotation shaft 23 of the first stage deceleration unit 30 extends through a hole formed on the partition wall into the housing portion of the first stage deceleration unit 30. As shown in FIG. 1, on both the cylindrical wall and the end caps on the both sides of the drive unit 15 are provided fasteners through which bolts pass to fasten various components inside the housing portion. The unitary drive unit 15 can be mounted as a module on the bicycle.

[0096] Furthermore, a second stage deceleration unit 40, 40′ is provided between the drive unit 15 and the bicycle pedal assembly 80 in a manner to transmit the drive force between two parallel rotation axes in the direction perpendicular to a plane comprising the rotation axis of a spindle 83 of the pedal assembly 80. In particular, the second stage deceleration unit 40, 40′ according to the invention may be implanted in various forms.

[0097] FIG. 4 shows a second stage deceleration unit 40 configured as a gear type deceleration mechanism. As shown in FIG. 4, this second stage deceleration unit comprises a pinion gear 41 mounted on the output shaft 36 of the first stage deceleration unit 30 and a bull gear 42 fixed on the chainrings 82 of the bicycle. The pinion gear 41 can be fixed to the output shaft of the first stage deceleration unit 30 by means of a spline connector, and the bull gear 42 is sleeved on the spindle 83 by means of the unidirectional transmission device 48, and also detachably fixed to the chainrings 82 of the bicycle. The engagement of the pinion gear 41 and the bull gear 42 allows for transfer of the drive force from the output shaft 36 of the first stage deceleration unit 30 to the chainrings 82 of the bicycle to directly provide the auxiliary drive for the bicycle or form an amplified force together with the pedaling force of the rider to provide the drive for the bicycle. The gear ratio of the bull gear 42 to the pinion gear 41 of the second stage deceleration unit can be set in the range of 3:1 to 10:1, thereby providing respective deceleration ratios.

[0098] FIG. 5A shows a second stage deceleration unit 40′ configured as a chain type deceleration mechanism. This chain second stage deceleration unit 40′ comprises a small sprocket 41′ mounted on the output shaft 36 of the first stage deceleration unit 30, a large sprocket 42′ mounted at the pedal assembly and a chain 43′ connecting the two sprockets 41′, 42′. Moreover, the large sprocket 42′ has an inner circumference connected to the spindle 83 via the unidirectional transmission device so that the drive force of the drive unit 15 would not cause the crank 81 to rotate, thereby the rider is protected from potential danger.

[0099] The second stage deceleration unit 40′ having a chain deceleration mechanism can further comprise a tensioner for providing the chain 43′ with a proper tension while the chain 43′ is trained. As shown in FIG. 5A, the tensioner mainly comprises a roller 46 and a spring 47 attached to the roller 46 which is rendered to abut against the chain 43′ to tension the chain 43′ under the elastic force of the spring 47. The deceleration unit 40′ of chain type provides the flexibility of mounting the drive unit 15 in terms of its mounting position.

[0100] In the preferred embodiment, the second stage deceleration unit of chain type comprises a plurality of large sprockets of different dimensions as optional accessories. Two sprockets 42′-1 and 42′-2 of different dimensions are shown in FIG. 5B and FIG. 5C, which can provide different output torques and deceleration ratios. For instance, a mountain bike may adopt the larger sprocket 42′-1 for a higher torque output and for prevention of damage to the sprocket. Apart from the above, the second stage deceleration unit 40 of chain type is able to provide the flexibility of mounting the drive unit 15 in terms of its mounting position.

[0101] In one preferred embodiment according to the invention, the first stage deceleration unit 30 and the second stage deceleration unit 40, 40′ are used in combination to achieve a total deceleration ratio in the range of 9:1 to 100:1.

[0102] Furthermore, in an alternative embodiment, the second stage deceleration unit can also adopt a belt type deceleration mechanism, which is arranged in a similar manner to the chain type deceleration mechanism and is not described here again.

[0103] The drive system 10 according to the preferred embodiment of the invention further comprises a mounting unit 50 provided as a modular part for mounting the drive unit 15 and the second stage deceleration unit 40, 40′ on the bicycle body 70, and this mounting unit module is adaptable for spindle 83 of different specifications. Preferably, the mounting unit 50 comprises a pair of support plates 51, between which an additional support rod connecting inner surfaces of the two support plates 51. Each of the support plates 51 has a mounting part at one end. The two mounting parts are respectively connected to the two opposite ends of the drive unit 15, i.e. respectively attached to the transparent end cover 25 of the motor unit 20 and the end cover of the first stage deceleration unit 30 opposite to the transparent end cover 25. After the mounting unit 50 is held to the end of the mounting unit 15 in place, the output shaft 36 of the first stage deceleration unit 30 can protrude beyond the outer surface of the support plate 51 such that the pinion gear 41 or the small sprocket 41′ is located external to the outer surface of the support plate 51 after the second stage deceleration unit 40, 40′ is mounted in position.

[0104] The support plate 51 is normally made from a rigid material, such as metallic materials. The material and the thickness of the support plate are selected in such a way that the rigidity of the support plate is sufficient to hold the weight of the drive unit 15. When the drive system 10 according to the invention is mounted on the bicycle, as shown in FIG. 6, the support plate 51 extends upward from the position of the spindle of the pedal assembly 80 to hold the drive unit 15 above the pedal assembly 80. In particular, the drive unit 15 can be held within a space defined by the triangular frame of the bicycle body 70 to lift the entire drive unit 15 away from the ground. This solves the problem of the mid-drive motor prone to scratching the ground that may occur in prior art.

[0105] To adapt for different types of bicycle and different second stage deceleration units 40, 40′, the mounting unit 50 of the drive system 10 of the invention comprises support plates in different forms, as those shown in FIG. 9A, FIG. 9B and FIG. 9C. FIG. 9A shows the first type mounting unit 50′ having two planar support plates 511 and 512 arranged in parallel. These two support plates 511 and 512 have a substantially same extension length. The spacing between the support plates 511 and 512 at the drive unit 15 is equal to the spacing between the support plates 511 and 512 at the spindle 83, which is suitable for the spindle having a longer axial length. FIG. 9B shows the second type mounting unit 50″ comprising a support plate 513 carried on one side of the first stage deceleration unit 30 and having an offset part, and a support plate 514 extending in a planar manner from a position offset inward relative to the outer surface of the transparent end cover 25 of the drive unit 15.

[0106] FIG. 9C shows a third type mounting unit 50′″ comprising a support plate 515 carried on one side of the first stage deceleration unit 30 and extending in a planar manner, and a support plate 516 extending in a planar manner from a position offset inward relative to the outer surface of the transparent end cover 25 of the drive unit 15, so that the two support plates 515, 516 defines a smaller spacing at the spindle 83, which is suitable for the spindle having a shorter axial length.

[0107] Selection of the above-mentioned support plates is flexible depending on mounting conditions, so that the auxiliary drive system according to the invention can be mounted on various types of bicycle. In order to adapt for certain models of spindle, the respective spacings between the support plates 511 and 512, between the support plates 513 and 514 and between the support plates 515 and 516 can be adjusted, and preferably a shim is provided between the support plate 511, 513, 515 and the end cover of the drive unit 15 to adjust the spacing therebetween. One or more shims with different shim thicknesses may be used. Alternatively, using an adaptor is also possible for mounting different models of spindle.

[0108] In a preferred embodiment, mounting the support plates 511 and 512 such as those shown in FIG. 9A on the pedal assembly shown in FIG. 8A and mounting the drive unit 15 on the support plates comprise step 1 of securing the drive unit 15 on the respective ends of the support plates 511 and 512; step 2 of aligning the respective opposite ends of the support plates 511 and 512 with the spindle 83 of the pedal assembly 80, and inserting and threadably fastening the spindle bowl 832, which is normally formed by two parts, to both sides of the spindle; and step 3 of inserting the spindle core 831 into the spindle bowl 832 and locking the spindle core 831 the spindle bowl 832 by a tension nut 833 to mount the support plates 511 and 512 on the spindle 83. The rider is then able to orient the support plates 511 and 512 in the frame of the bicycle body, if desirable, with the aid of a strap or a suspension (not shown).

[0109] FIG. 10A to FIG. 10C respectively show the spindles 83 of the pedal assembly 80 of three different structures, which spindles are respectively corresponding to the mounting units of FIG. 9A to FIG. 9C and have different axial lengths. The spindle 83 has a spindle core 831 and a pair of spindle bowls 832. It is very convenient to attach or detach the spindle 831 to or from the bicycle drive system 10 according to the invention by unscrewing the fastener of fastening the spindle 83, followed by pulling the spindle 83 out from the bicycle body 70, inserting a desirable spindle core 831 and a pair of spindle bowls 832 associated with the desirable spindle core, and engaging the spindle bowls 832 into the corresponding support plates of the mounting unit 50 shown in one of FIG. 9A to FIG. 9C to secure the drive unit 15 in place.

[0110] As described in the above embodiments, the mid-drive system 10 according to the invention can be mounted to spindles having different lengths and different diameters. For example, the mounting unit 50 according to the invention is adaptable for the spindle having a length in the range of 68 mm to 120 mm and a diameter in the range of 36 mm to 45 mm.

[0111] Furthermore, it is illustrated in FIG. 7A that the mounting unit 50 is further provided with a mounting part for the control unit 60, which, for instance, is formed on one of the support plates 51 adjacent to the drive unit 15, through, for instance, fixation of the control unit on the support plate 51 with a bolt. According to a preferred embodiment of the invention, the control unit 60 is provided as a modular part comprising a separate housing and a circuit board accommodated in the housing with leading protruding from the circuit board beyond the housing of the control unit 60 for connection with the PCB 27 of the motor unit 20 to enable the control unit 60 to take control of the motor unit 20.

[0112] In an alternative embodiment, according to the structure per se of a bicycle and individual needs of users, the control unit can also be mounted at a position other than on the support plates by means of extended leading wires. For example, the control unit may be mounted directly on the frame of the bicycle.

[0113] Preferably, the housing of the control unit 60 is filled with an electrical insulating sealant to seal the interior of the housing for the sake of preventing a short-circuit connection of electrical components placed in the interior of the control unit 60 and the housing of the control unit or the mounting unit 50. In addition, the housing of the control unit 60 is preferably made from a metallic material, and the insulating sealant is thermally conductive to assist dissipation of heat generated from the interior of the control unit 60.

[0114] Additionally or alternatively, the control unit 60 can also be provided with a radiator (not shown) arranged on the housing of the control unit 60 to dissipate the heat to the ambient environment.

[0115] According to a preferred embodiment of the invention, the control unit 60 is connected to a sensor device located at the pedal assembly 80 for collection of signals indicating running states of the bicycle to control the motor unit 20.

[0116] In a preferred embodiment, the sensor device comprises a cadence sensor 65 for collecting a rotation speed of the bicycle crank 81. As shown in FIG. 7A and FIG. 7B, the cadence sensor 65 comprises a magnetic ring 651 and a sensor element 652, which are closely arranged. Specifically, the magnetic ring 651 is mounted at the pedal assembly 80 and rotates together with rotation of the crank 81, and the sensor element 652 adjoins the magnetic ring 651 and is held on the mounting unit 50 to sense the rotation of the magnetic ring 651. The periphery of the magnetic ring 651 has a plurality of magnetic poles. The magnetic ring 651 is configured to rotate as the bicycle crank 81 rotates, such that the sensor element 652 counts and records the number of the magnetic poles 651 that are caused to rotate by the rotation of the magnetic ring 651 to pass the sensor element 652. The sensor element 652 sends the number of the passing magnetic poles 651 recorded to the control unit 60 where rotation time and rotation speed of the crank 81 are calculated. When the speed reaches a predetermined value, the drive system 10 can intervene the drive operation to provide power assist for the pedal assembly 80. In addition, the cadence sensor 65 is also configured to detect a rotation direction of the crank 81. The control unit 60 is configured in such a way that the drive system 10 is not be activated when the sensor device detects the reverse rotation of the crank 81, which provides safety protection for the auxiliary drive system 10.

[0117] Preferably, the sensor device of the control unit 60 may adopt a torque sensor 68 as shown in FIG. 8A and FIG. 8B. In a preferred embodiment, the torque sensor 68 mainly comprises a strain sleeve 681 sleeved on the spindle core 831 of the spindle 83. The strain sleeve 681 has a plurality of micro-sensors capable of detecting a small amount of torque occurring in the body of the strain sleeve 681. The power arising from the pedaling of the rider is transmitted through the crank 81 and the spindle core 831 of the spindle 83 to the strain sleeve 681. In addition, the strain sleeve 681 is in spline teeth connection, for example, to the unidirectional transmission device 48 of the second stage deceleration unit. When the bicycle is running, the strain sleeve 681 rotates to come into contact with the static unidirectional transmission device 48, thereby allowing the torque sensor 68 to measure the pedaling force applied by the rider to the pedal assembly 80, and generate and deliver a signal to the control unit 60, which receives and processes the signal to control the drive unit 15 to provide power assist in the case that criteria are met.

[0118] The bicycle drive system 10 according to the invention provides a modularized structure, which allows riders for customized selection of the mounting unit 50, the second stage deceleration unit 40, 40′, and the drive unit 15 comprising the motor unit 20 and the first stage deceleration unit 30 as desirable for mounting on the bicycle body 70 according to their own bicycle, providing power assist for the chainrings 82 of the pedal assembly 80.

[0119] In the preferred embodiment mentioned above, the motor unit 20 is an inner rotor brushless motor. In an alternative embodiment, an outer rotor brushless motor is possible for the invention, and an outer rotor brushless motor and a planetary gear deceleration mechanism are integrated to form a drive unit module.

[0120] The drive system of the invention has two stage deceleration units comprising the first stage deceleration unit 30 integral with the motor unit 20, and the second stage deceleration unit 40 external to the drive unit 15 and installable on the bicycle body 70. A wide selection of sprockets and gears allows the customers to customize an optimal output torque of the drive unit 15.

[0121] Advantageously, the bicycle drive system 10 according to the invention is provided in the form of a kit. Specifically, the mounting unit 50 of the system may comprise a pair of support plates or selectable multiple pairs of support plates, such as support plates of 511 and 512, support plates of 513 and 514, and support plates 515 and 516 shown in FIG. 9A to FIG. 9C respectively. In a preferred embodiment, the multiple pairs of support plates have different extension lengths different relative to each other.

[0122] Alternatively and preferably, the mounting unit 50 in the kit may have one or more shims to be provided between the drive unit 15 and the mounting part of the support plate to adjust the spacing between the pair of support plates to adapt for different models of spindle. Additionally, the mounting unit 50 may comprise an adaptor for different models of spindle.

[0123] In another aspect, the second stage deceleration unit of the bicycle drive kit may comprise a transmission wheel set having a selection of deceleration ratios, for example those transmission wheels shown in FIG. 5B and FIG. 5C, to allow maximum customizability of the drive system.

[0124] The drive system 10 according to the invention may aid in upgrading power assist for an existing bicycle to provide power assist for the rider. However, it should be understood that in other alternative embodiments, the drive system 10 may also be used alone to power the bicycle.

[0125] The invention has been disclosed above with preferred embodiments, but they are not intended to limit the invention. Any person skilled in the art can make possible changes and alterations without departing from the spirit and scope of the invention. Therefore, any alterations, equivalent changes and modifications made to the foregoing embodiments according to the technical substance of the invention without departing from the content of the technical solution of the invention should fall within the protection scope defined by the claims of the invention.