Rear wheel drive system of an electric-assist bicycle

Abstract

The present invention relates to a drive system for a rear wheel (7) of an electrically assisted bicycle, comprising: a rear arm (3) adapted to support said rear wheel (7), and an electric motor adapted to be coupled to the crankset (8) to drive said crankset in rotation, said motor comprising a stator (45), a rotor (46), and a transmission device arranged to transform a rotary motion of the rotor (46) into a rotary motion of the crankset, the crankset being adapted to cause rotation of the rear wheel (7) by means of a drive means (70), wherein the rear arm (3) comprises a first housing (40) in which the rotor (46) and the stator (45) are arranged, and a second housing (50) in which the transmission device is arranged, said second housing (50) containing a lubricant and being sealed from the lubricant to the first housing (40). Figure for the abstract: Fig. 2

Description

Title of the invention: Drive system for the rear wheel of an electrically assisted bicycle technical field

[0001] The invention relates to a drive system for a rear wheel of an electrically assisted bicycle. STATE OF THE ART

[0002] The market for electric-assist bicycles is developing widely by allowing their users to travel over longer distances and / or on routes with a significant incline.

[0003] On existing bicycles, a motor block is mounted in a housing which is assembled on the bicycle frame and the motor is connected to the rear wheel in order to drive it in rotation.

[0004] Generally speaking, the aim is to reduce the weight and size of electrically assisted bicycles. At the same time, the structural parts must be resistant to mechanical stresses and exhibit good rigidity.

[0005] Furthermore, another problem is the evacuation of the heat generated by the motor during the use of the bicycle. Summary of the invention

[0006] One object of the invention is to design an electrically assisted bicycle in which the integration of the motor is carried out in a simpler way, making it possible to reduce the weight of the bicycle and the number of parts constituting the bicycle.

[0007] To this end, the invention proposes a drive system for a rear wheel of an electrically assisted bicycle comprising: • a rear arm configured to be mounted on a front triangle of the frame, said rear arm being adapted to support said rear wheel, and • an electric motor adapted to be coupled to the crankset to drive said crankset in rotation, said motor comprising a stator, a rotor movable in rotation relative to the stator, and a transmission device arranged to transform a rotary motion of the rotor into a rotary motion of the crankset, the crankset being adapted to cause a rotation of the rear wheel by means of a drive means,

[0008] in which the rear arm comprises a first housing in which the rotor and stator are arranged and a second housing in which the transmission device is arranged, said second housing containing a lubricant and being sealed to the lubricant with respect to the first housing.

[0009] Thanks to this design, it is possible to eliminate the need for a motor housing, thus reducing the weight and size of the bicycle at the motor level. This also allows for a more compact frame design and greater design freedom compared to existing solutions, while maintaining stability.

[0010] Such an arrangement of the motor also allows the heat generated by the motor to be dissipated more efficiently.

[0011] Preferably, the motor further comprises an output shaft driven in rotation by the transmission device and fixed in rotation with the pedal assembly, said output shaft being at least partially arranged in the second housing.

[0012] Advantageously, the transmission device further includes a gearbox arranged in the second housing, said gearbox allowing the ratio between the rotational speed of the rotor and the rotational speed of the pedal assembly to be selectively changed.

[0013] The rear arm can be made by molding.

[0014] Advantageously, the first housing and the second housing are made in one piece in the rear arm.

[0015] Preferably, the drive system further comprises a reinforcement structure integrated into a wall of the rear arm. The reinforcement structure may comprise a plurality of reinforcing ribs.

[0016] Advantageously, the second housing includes a pair of openings adapted for the passage of the drive means connecting the crankset to the rear wheel.

[0017] Advantageously, the first housing includes one or more heat dissipation ports.

[0018] Preferably, the first housing includes an opening and a removable maintenance cover arranged to close said opening.

[0019] The invention also relates to an electric bicycle comprising

[0020] • a frame comprising a front triangle articulated on a fork carrying a wheel Before,

[0021] • a drive system as described above, the rear arm being mounted on the front triangle

[0022] • a rear wheel carried by the rear arm, and

[0023] • a drive means linking the crankset with the rear wheel so that a Rotation of the pedals causes rotation of the rear wheel.

[0024] Preferably, the drive means is a belt, a chain or a cardan.

[0025] Advantageously, the motor is arranged in the axis of a pedal assembly.

[0026] Advantageously, the front triangle includes a hollow oblique tube receiving a battery electrically connected to the motor.

[0027] In certain embodiments, the frame is further provided with a front suspension and a rear suspension, the rear arm being mounted in a single-pivot type pivot on an anterior part of the front triangle and the rear suspension being arranged between the rear arm and a rear part of the front triangle.

[0028] The bicycle may include at least one rear wheel support mounted on the rear arm, said support being adjustable between a mounting position of the drive means and a tensioning position of said drive means, located at the rear of the front arm relative to the mounting position.

[0029] Preferably, the rear arm includes a guide means, such as an oblong hole, and each rear wheel support is mounted on the rear arm by means of a screw engaging in said guide means.

[0030] The bicycle may be without a mechanical tensioning system for the drive means. BRIEF DESCRIPTION OF THE FIGURES

[0031] Other features and advantages will become apparent from the detailed description that follows, with reference to the accompanying drawings, on which:

[0032] - Fig. 1 is a right-side view of a bicycle comprising a system training according to the invention.

[0033] - [Fig.2] is an exploded view of the drive system;

[0034] - [Fig.3] is another exploded view of the drive system of [Fig.1];

[0035] - [Fig.4] is a top view of a drive system according to the invention;

[0036] - [Fig.5] is a perspective view of the drive system of [Fig.3];

[0037] - [Fig.6] is another perspective view of the drive system of [Fig.3]. DETAILED DESCRIPTION OF IMPLEMENTATION METHODS

[0038] In this text, the terms "front" and "rear", "anterior" and "posterior" refer to the direction of travel of the bicycle. The terms "right", "left", "horizontal", "upper", and "lower" refer to the position of the bicycle when traveling on a horizontal surface.

[0039] Figure 1 is an overview of an electrically assisted bicycle comprising a drive system according to the invention. The bicycle comprises a frame including a front triangle 2 and a rear arm 3.

[0040] The rear arm 3 is mounted on the front triangle 2 of the frame, typically at the bottom bracket 8. A rear end of the rear arm 3 carries the rear wheel 7.

[0041] The bicycle 100 includes an electric motor arranged in the rear arm near the crankset 8. Preferably, the motor is arranged in the axle 88 of the crankset 8. The electric motor is coupled to the crankset 8, which is in turn coupled to the rear wheel 7 and intended to drive the rear wheel 7 in rotation.

[0042] The motor comprises a stator 45 and a rotor 46 rotating relative to the stator.

[0043] By way of illustration and without limitation, the stator 45 comprises a plurality of coil elements arranged in a ring around the axis of rotation of the rotor 46. An alternating magnetic field is generated by the coils of the stator 45. The rotor 46 includes one or more permanent magnets that interact with the alternating magnetic field of the stator 45 so that the rotor 46 is driven into rotation. In operation, the rotor 46 typically has a rotational speed between 8000 and 18000 rpm.

[0044] The motor also includes a transmission device for transforming the rotary motion of the rotor 46 into a rotary motion of the pedal assembly 8. In Figures 2 and 3, the transmission device is a gearbox 55 comprising a reduction system 51, a plurality of gears of different sizes meshing with each other, and an output shaft 81 fixed in rotation with the pedal assembly 8.

[0045] The gearbox 55 may further have bearings to facilitate the rotation of the respective gears. Some bearings may be fitted onto the output shaft 81.

[0046] The gearbox 55 allows the user to modify the torque between the rotor 46 and the pedal 8 of the bicycle and thus to select the ratio between the rotational speed of the rotor 46 and the rotational speed of the pedal 8. The rotor 46 causes the movement of the pedal 8 via a reduction system 51 and the gearbox 55.

[0047] In other embodiments (not illustrated), the transmission device may be without a gearbox. In this case, the transmission device only allows the rotary motion of the rotor 46 to be transformed into a rotary motion of the pedal assembly 8, without the possibility of modifying the torque between the rotor 46 and the pedal assembly 8.

[0048] When the drive system does not include a gearbox, the transmission device is simpler than in Figures 2 and 3. The transmission device comprises a reduction system 51 with an output shaft 81 fixed for rotation with the crankset 8. Such a transmission device may also include sprockets, which are typically fewer in number than the sprockets of the gearbox. In this case, the ratio between the rotational speed of the rotor 46 and the rotational speed of the crankset is predefined and cannot be changed by the user.

[0049] The transmission device converts the motion of the rotor 46 into a rotary motion of the output shaft and, consequently, into a rotary motion of the crankset 8. The rotary motion of the output shaft 81 and the crankset 8 has a lower speed and a higher torque than the rotary motion of the rotor 46. Typically, the rotational speed of the crankset 8 is between 40 and 150 rpm when using the electric bicycle and can, if necessary, be modified via the gearbox 55.

[0050] The rotor 46 is coupled to the gearbox 55 or to the transmission device, for example via a primary shaft 43.

[0051] The crankset 8 is configured to drive a drive means 70 such as a chain, a belt, or a universal joint. The drive means 70 runs on an element 77 coaxial with the rear wheel 7 and thus drives the rear wheel in rotation. The element 77 coaxial with the rear wheel can be a sprocket, a gearbox, a sprocket adapted to be driven by a belt, or a universal joint attachment.

[0052] At the level of the pedal assembly 8, the drive means 70 can be engaged on a toothed wheel, a ring adapted for the circulation of a belt, or a universal joint attachment.

[0053] With reference to Figures 2 to 4, the rear arm 3 of the bicycle comprises a first housing 40 and a second housing 50 for housing the engine components. By way of illustration and without limitation, the first housing 40 has a smaller volume than the second housing 50. The first housing 40 may be located in the front part of the rear arm 3. In some embodiments, the first housing 40 is offset to one side of the rear arm, for example the right side as illustrated in [Fig. 4]. In other embodiments, the first housing may be offset to the left side of the rear arm or be located in a central position. The first housing preferably has an essentially cylindrical geometry, the axis of the cylinder being transverse to the direction of travel of the bicycle and parallel to the axis 88 of the crankset 8 and the axis 77 of the rear wheel 7.

[0054] The second housing 50 is advantageously positioned between the first housing 40 and the axis 88 of the pedal assembly 8. The first housing 40 and the second housing 50 are typically adjacent and separated by a wall 49.

[0055] The rotor 46 and the stator 45 are arranged in the first housing 40. The cylindrical shape of the housing 40 allows these elements to be housed with minimal space requirements. The axis of rotation of the rotor and the orientation of the primary shaft 43 correspond to the axis of the first housing and are parallel to the axis 88 of the crankset 8.

[0056] Optional electrical connectors and cables intended to provide power to the stator and an electronic circuit to control the motor may also be arranged in the first housing 40. The first housing contains no lubricant in order to avoid possible short circuits caused by the conduction of an electric current in the lubricant, and to ensure the proper electrical operation of the rotor 46 and the stator 45.

[0057] The gearbox 55, the reduction system 51 and at least a portion of the output shaft 81 are arranged in the second housing 50. A portion of the output shaft 81 is connected to the pedal assembly 8 and may protrude from the second housing 50.

[0058] The second housing also contains a lubricant intended to lubricate the gearbox, the reduction system, any bearings, the output shaft, and the drive means. Typically, the lubricant is an oil. The lubricant ensures proper operation and prevents the mechanical parts of the engine from seizing.

[0059] The second housing is lubricant-tight with respect to the first housing. For example, a lubricant-tight partition is arranged between the first and second housings. Seals may be arranged between the first and second housings to ensure a good lubricant seal. This lubricant seal protects the rotor 46, the stator 45, and all electrical components from lubricant contamination, thus preventing potential short circuits.

[0060] The primary shaft passes through an opening in the wall between the first housing 40 and the second housing 50 to connect the rotor 46 to the transmission device 55. The passage of the primary shaft is made in a lubricant-tight manner. For example, the primary shaft is mounted in a bearing arranged in the wall between the first and second housings, said bearing being lubricant-tight, for example comprising a lubricant-tight seal on at least one side of the wall.

[0061] The first housing 40 and the second housing 50 thus form a casing containing the entire motor. The motor parts can be mounted in the housings without the need for a dedicated casing. The electrical components of the motor, namely the stator 46, the rotor 45, the electrical cables and connectors necessary to supply the motor with electricity, and in some cases an electronic circuit, are arranged in the first housing 40. The mechanical components of the motor requiring lubrication are arranged in the second housing 50. The arrangement of the second housing 50 between the first housing 40 and the crankset 8 allows for easy transmission of the rotary motion from the rotor 46 to the crankset 8. The second housing 50 typically includes two openings forming an inlet and an outlet for the drive means 70. These openings allow the drive means 70 to pass between the crankset and the element at the axle 77 of the rear wheel 7.

[0062] With reference to [Fig.6], other openings 42 can be provided in the outer wall of the first housing 40 allowing the evacuation of heat generated by the motor.

[0063] A maintenance opening, 58, can be provided in the first housing 40 and / or the second housing 50. Advantageously, each opening, 58, is located on an easily accessible side face of the rear arm. A maintenance opening in the first housing (not shown) provides access to the stator 45, the rotor 46, cables, and any electrical connectors and / or electronic circuits associated with the stator. The maintenance opening 58 in the second housing provides access to the transmission device 55, the output shaft 81, and, if applicable, the gearbox. Such openings allow for easy maintenance operations. maintenance, lubrication, or engine repair. Advantageously, each maintenance opening is closed by a cover, 57, which is removable during bicycle use to prevent dirt and dust from entering the bicycle engine. A lubricant-tight seal is typically arranged between the edge of the maintenance opening of the first housing and the cover of the first housing 40 to prevent lubricant from entering the first housing 40. A lubricant-tight seal 59 may also be arranged between the edge of the maintenance opening 58 of the second housing and the cover 57 of the second housing 50 to prevent lubricant loss from the second housing.

[0064] The rear arm may include a reinforcing structure, for example, a plurality of ribs 60 on one or two lateral faces 36. Such ribs stabilize the rear arm 3 against impacts and thus allow for a thinner and lighter frame design. The geometry of the ribs can be adapted to the direction of impacts typically occurring at the rear arm during bicycle use. The geometry of the ribs also allows the aesthetic design of the bicycle to be adapted according to the manufacturer's wishes. Preferably, the reinforcing structure is integrated into the lateral face 36 of the rear arm 3. Each lateral face 36 can be covered with a cap 31a, 31b to prevent dirt from accumulating on the reinforcing structure 60.

[0065] With reference to [Fig. 3] and [Fig. 4], the rear arm can be made up of two half-arms 3a, 3b assembled on either side of the rear wheel. Such a design facilitates the formation of the respective housings 40, 50. For example, the first housing 40 can be entirely arranged in a first half-arm 3a or partially in the first half-arm 3a and partially in the second half-arm 3b. In this case, a lubricant-tight seal is arranged between the portion 40a of the first housing arranged in the first half-arm 3a and the portion 40b of the first housing arranged in the second half-arm 3b. Such a seal ensures lubricant tightness between the first housing and the second housing.

[0066] The second housing 50 can be arranged partially in the first half-arm 3a and partially in the second half-arm 3b, or entirely in a single half-arm 3a, 3b.

[0067] In this case, during bicycle assembly, the engine components are assembled in each housing before assembling the half-arms 3a, 3b. The two half-arms 3a, 3b are then assembled. With the housings 40, 50 formed in the two half-arms, assembling the half-arms 3a and 3b closes each housing. The half-arms 3a, 3b are assembled, for example, using screws 38.

[0068] Alternatively, the rear arm 3 can be formed in one piece. In this case, each housing includes an opening adapted for the insertion of the elements of the The engine is assembled, and a cover is fitted to close such an opening. The housings can also be formed as a single piece in the rear arm. This reduces the number of parts in the rear arm.

[0069] Advantageously, the rear arm is formed by molding, in particular by injection molding or casting. This manufacturing process makes it possible to form precisely dimensioned housings to receive the various engine components. Molding also makes it possible to form reinforcing structures such as ribs 60 in the wall of a housing, and / or openings adapted for the passage of the drive means and / or openings for heat dissipation. The formation of such structures is thus carried out in the same process, facilitating the manufacture of the bicycle's rear arm.

[0070] Advantageously, the front triangle 2 of the bicycle frame is hollow, which allows a battery for the electrical power supply of the motor to be housed there, for example in the oblique tube 20 or the tube 21 intended to support a saddle, and the brake cables and the cables connecting the battery to the electrical elements of the motor arranged in the first housing 40 to pass through it. In some embodiments, the front triangle 2 is also made by molding.

[0071] The bicycle may further include front and / or rear suspension. Advantageously, the front triangle 2 is pivotally mounted on the rear arm 3 about a horizontal axis 33. Said pivot axis is located in the lower part of the front triangle, typically at the junction between the seat tube 21 and the base 22 of the front triangle. This type of articulation is called a "mono-pivot".

[0072] As illustrated in [Fig. 2], the rear arm also supports, in its rear part, a rear wheel support 300. This support 300 is in the form of a tab adapted to receive the rear wheel hub, and includes one or more tapped holes to receive a respective fixing screw 302.

[0073] Advantageously, each fixing screw 302 passes through a respective oblong hole 301 in the rear arm. When the screw is not tightened, the bracket 300 can then be slid along the oblong hole between a forward position allowing the mounting of a drive means (chain or belt) between the crankset and the rear wheel, and a rear position allowing adjustment of the mechanical tension in the drive means. Once the required tension is reached, the screws 302 can be tightened to hold the bracket 300 in the bicycle's operating position. This eliminates the need for a tensioner or any other additional system for adjusting the mechanical tension in the drive means.

[0074] Naturally, any other guiding means than an oblong hole may be used, said guiding means enabling each screw 302 to be guided between the position of mounting and tension adjustment position, along a straight, curved or any other suitable trajectory.

[0075] This bicycle design therefore makes it possible in particular to use a belt which is a more reliable, quieter and maintenance-free means of drive, without requiring the addition of a tensioner in the form of a spring-mounted tensioner or eccentric or any other system of this type.

Claims

Demands

1. A drive system for a rear wheel (7) of an electrically assisted bicycle comprising: • a rear arm (3) configured to be mounted on a front triangle (2) of the frame, said rear arm (3) being adapted to support said rear wheel (7), and • an electric motor adapted to be coupled to the crankset (8) to drive said crankset in rotation, said motor comprising a stator (45), a rotor (46) rotatable relative to the stator (45), and a transmission device arranged to transform a rotary motion of the rotor (46) into a rotary motion of the crankset, the crankset being adapted to cause a rotation of the rear wheel (7) by means of a drive means (70), in which the rear arm (3) comprises a first housing (40) in which the rotor (46) and the stator (45) are arranged and a second housing (50) in which the transmission device is arranged,said second housing (50) containing a lubricant and being sealed to the lubricant with respect to the first housing (40).

2. A drive system according to claim 1, wherein the motor further comprises an output shaft driven in rotation by the transmission device and fixed in rotation with the pedal assembly (8), said output shaft being at least partially arranged in the second housing (50).

3. A drive system according to claim 1 or claim 2, wherein the transmission device further comprises a gearbox (55) arranged in the second housing (50), said gearbox allowing the ratio between the rotational speed of the rotor (46) and the rotational speed of the pedal assembly (8) to be selectively modified.

4. A drive system according to any one of the preceding claims, wherein the rear arm (3) is made by molding.

5. A drive system according to any one of the preceding claims, wherein the first housing (40) and the second housing (50) are made as a single unit in the rear arm (3).

6. A drive system according to any one of the preceding claims. previous, further comprising a reinforcement structure (60) integrated into a wall of the rear arm (3).

7. A drive system according to claim 6, wherein the reinforcement structure (60) comprises a plurality of reinforcing ribs.

8. A drive system according to any one of the preceding claims, wherein the second housing (50) includes a pair of ports adapted for the passage of the drive means (70) connecting the crankset (8) to the rear wheel (7).

9. A drive system according to any one of the preceding claims, wherein the first housing (40) includes one or more heat dissipation ports (42).

10. A drive system according to any one of the preceding claims, wherein the first housing (40) includes an opening and a removable maintenance cover arranged to close said opening.

11. Electric bicycle (100) comprising • a frame including a front triangle (2) articulated on a fork carrying a front wheel, • a drive system according to any one of claims 1 to 10, the rear arm (3) being mounted on the front triangle (2), • a rear wheel carried (7) by the rear arm (3), and • a drive means (70) linking the crankset (8) with the rear wheel (7) such that a rotation of the crankset (8) causes a rotation of the rear wheel (7).

12. Electric bicycle according to claim 11, wherein the drive means (70) is a belt, a chain or a cardan.

13. Electric bicycle according to claim 11 or claim 12, wherein the motor is arranged in the axis (88) of a crankset (8).

14. Electric bicycle according to any one of claims 11 to 13, wherein the front triangle (2) comprises a hollow oblique tube receiving a battery electrically connected to the motor.

15. Bicycle according to any one of claims 11 to 14, wherein the frame is further provided with a front suspension and a rear suspension, the rear swingarm being mounted in a single-pivot type on an anterior portion of the front triangle and the rear suspension being arranged between the rear swingarm and a rear portion of the front triangle.

16. Bicycle according to claim 15, comprising at least one rear wheel support mounted on the rear arm (3), said support being adjustable between a mounting position of the drive means (70) and a tensioning position of said drive means (70), located at the rear of the front arm relative to the mounting position.

17. Bicycle according to claim 16, wherein the rear arm (3) includes a guide means (301), such as an oblong hole, and each rear wheel support is mounted on the rear arm (3) by means of a screw (302) engaging in said guide means (301).

18. Bicycle according to any one of claims 15 to 17, devoid of a mechanical tensioning system for the drive means (70).

Images