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 a 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 electrically assisted bicycles is growing significantly, allowing their users to travel longer distances and / or on routes with a significant slope.

[0003] On existing bicycles, a motor unit is mounted in a housing which is assembled on the bicycle frame and the motor is connected to the rear wheel in order to allow it to be driven 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 stress and have good rigidity.

[0005] Furthermore, another problem is the evacuation of heat generated by the engine when using the bicycle. Summary of the invention

[0006] An aim of the invention is to design an electrically assisted bicycle in which the integration of the motor is carried out in a simpler manner, 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 system for driving 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 pedal assembly to drive said pedal assembly 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 movement of the rotor into a rotary movement of the pedal assembly, the pedal assembly being adapted to cause rotation of the rear wheel by means of a drive means,

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

[0009] Thanks to this design, it is possible to do without a motor housing and thus reduce the weight and bulk of the bicycle at the motor level. This also allows the frame to have a more compact construction shape and allows more design freedom compared to existing solutions, while maintaining its stability.

[0010] Such an arrangement of the engine also makes it possible to evacuate the heat generated by the engine more efficiently.

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

[0012] Advantageously, the transmission device further comprises a gearbox arranged in the second housing, said gearbox making it possible to selectively modify the ratio between the rotational speed of the rotor and the rotational speed of the pedal assembly.

[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 reinforcing structure integrated into a wall of the rear arm. The reinforcing structure may comprise a plurality of reinforcing ribs.

[0016] Advantageously, the second housing comprises a pair of holes adapted for the passage of the drive means connecting the pedal assembly to the rear wheel.

[0017] Advantageously, the first housing comprises one or more heat evacuation orifices.

[0018] Preferably, the first housing comprises 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 crankset 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 comprises a hollow oblique tube receiving a battery electrically connected to the motor.

[0027] In some 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 a front portion of the front triangle and the rear suspension being arranged between the rear arm and a rear portion of the front triangle.

[0028] The bicycle may comprise 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 tension position of said drive means, located at the rear of the front arm relative to the mounting position.

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

[0030] The bicycle may be devoid of a mechanical tensioning system for the drive means. BRIEF DESCRIPTION OF THE FIGURES

[0031] Other characteristics and advantages will emerge from the detailed description which follows, with reference to the attached drawings, in which:

[0032] - [Fig.l] is a right-hand 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.l];

[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 EMBODIMENTS

[0038] In this text, the terms "front" and "rear", "anterior" and "posterior" are understood in the direction of rolling of the bicycle. The terms "right", "left", "horizontal", "upper", "lower" are understood in the position of the bicycle when rolling on horizontal ground.

[0039] [Fig.l] is an overall view of an electrically assisted bicycle 100 comprising a drive system according to the invention. The bicycle comprises a frame comprising 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 level of the crankset 8. A rear end of the rear arm 3 carries the rear wheel 7.

[0041] The bicycle 100 comprises an electric motor arranged in the rear arm near the crankset 8. Preferably, the motor is arranged in the axis 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] In an illustrative and non-limiting manner, 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 comprises one or more permanent magnets which interact with the alternating magnetic field of the stator 45 so that the rotor 46 is driven in rotation. In operation, the rotor 46 typically has a rotational speed of between 8000 and 18000 rpm.

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

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

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

[0047] In other embodiments (not shown), the transmission device may be without a gearbox. In this case, the transmission device only allows the rotary movement of the rotor 46 to be transformed into a rotary movement of the crankset 8 without the possibility of modifying the torque between the rotor 46 and the crankset 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 rotationally fixed to the crankset 8. Such a transmission device may also include pinions, which are typically fewer in number than the pinions 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 modified by the user.

[0049] The transmission device converts the movement of the rotor 46 into a rotary movement of the output shaft and, consequently, into a rotary movement of the crankset 8. The rotary movement of the output shaft 81 and the crankset 8 has a lower speed and a higher torque than the rotary movement 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 by means of the 55 gearbox.

[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 actuate a drive means 70 such as a chain, a belt or a universal joint. The drive means 70 circulates 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 may be a pinion, a gearbox, a crown adapted to be driven by a belt or a fixing of a universal joint.

[0052] At the level of the pedal assembly 8, the drive means 70 can be engaged on a toothed wheel, a crown adapted for the circulation of a belt, or a cardan 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 intended to house the elements of the motor. In an illustrative and non-limiting manner, the first housing 40 has a volume smaller than the volume of the second housing 50. The first housing 40 may be arranged in the front part of the rear arm 3. In certain 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 arranged in a central position. The first housing preferably has an essentially cylindrical geometry, the axis of the cylinder being transverse to the direction of movement 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 crankset 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 makes it possible to house these elements with minimal bulk. 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 pedal assembly 8.

[0056] Possible electrical connectors and cables intended to provide an electrical power supply to the stator and an electronic circuit for controlling the motor can also be arranged in the first housing 40. The first housing does not contain any lubricant in order to avoid possible short circuits caused by the conduction of an electric current in the lubricant, and to ensure the correct 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 can protrude from the second housing 50.

[0058] The second housing further 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 to prevent blockage of the mechanical part of the engine.

[0059] The second housing is lubricant-tight relative to the first housing. For example, a lubricant-tight wall is arranged between the first housing and the second housing. Seals may be arranged between the first housing and the second housing to ensure good lubricant tightness. The lubricant tightness protects the rotor 46, the stator 45 and all electrical components from contamination by the lubricant, and thus prevents possible short circuits.

[0060] The primary shaft passes through an orifice 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 carried out in a lubricant-tight manner. For example, the primary shaft is mounted in a bearing arranged in the wall between the first housing and the second housing, 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 engine. The engine parts can be mounted in the housings without the need for a dedicated casing. The electrical elements of the motor, namely the stator 46, the rotor 45, the electrical cables and connectors necessary to supply the motor with electricity, and in certain cases an electronic circuit, are arranged in the first housing 40. The mechanical elements 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 easy transmission of the rotary movement of the rotor 46 to the crankset 8. The second housing 50 typically comprises two orifices forming an inlet and an outlet of the drive means 70. Said orifices allow the passage of the drive means 70 between the crankset and the element at the level of the axle 77 of the rear wheel 7.

[0062] With reference to [Fig.6], other orifices 42 may be provided in the outer wall of the first housing 40 allowing the heat generated by the engine to be evacuated.

[0063] A maintenance opening, 58 may be provided in the first housing 40 and / or the second housing 50. Advantageously, each opening, 58 is arranged on an easily accessible lateral face of the rear arm. A maintenance opening in the first housing (not shown) allows access to the stator 45, the rotor 46, cables and any electrical connectors and / or electronic circuits connected to the stator. The maintenance opening 58 in the second housing allows access to the transmission device 55, the output shaft 81 and, where appropriate, the gearbox. Such openings allow easy maintenance operations to be carried out. maintenance, lubrication or repair of the engine. Advantageously, each maintenance opening is closed by a respective cover 57 removable during use of the bicycle in order to prevent the penetration of dirt, dust into the engine of the bicycle. 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 in order to prevent any penetration of lubricant into the first housing 40. A lubricant-tight seal 59 may further be arranged between the edge of the maintenance opening 58 of the second housing and the cover 57 of the second housing 50 in order to prevent loss of lubricant from the second housing.

[0064] The rear arm may comprise 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 a thinner and lighter design of the wall. The geometry of the ribs may be adapted to the direction of impacts typically occurring at the rear arm during use of the bicycle. The geometry of the ribs also makes it possible to adapt the aesthetic design of the bicycle according to the wishes of the manufacturer. Preferably, the reinforcing structure is integrated into the lateral face 36 of the rear arm 3. Each lateral face 36 may be covered with a cover 31a, 31b in order to prevent the deposition of dirt on the reinforcing structure 60.

[0065] With reference to [Fig. 3] and [Fig. 4], the rear arm may consist 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 may 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 makes it possible to ensure the lubricant-tight seal between the first housing and the second housing.

[0066] The second housing 50 may 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, when assembling the bicycle, the motor elements are assembled in each housing before assembling the half-arms 3a, 3b. The two half-arms 3a, 3b are then assembled. The housings 40, 50 being formed in the two half-arms, the assembly of the half-arms 3a and 3b makes it possible to close each housing. The half-arms 3a, 3b are assembled for example by screws 38.

[0068] Alternatively, the rear arm 3 may be formed in one piece. In this case, each housing comprises an opening suitable for the insertion of the elements of the engine during assembly and a cover 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 of the rear arm.

[0069] Advantageously, the rear arm is formed by molding, in particular by injection or by casting. This manufacturing method makes it possible to form housings precisely sized to receive the various elements of the engine. Manufacturing by molding also makes it possible to form reinforcement structures such as ribs 60 in the wall of a housing, and / or orifices adapted for the passage of the drive means and / or orifices intended for the evacuation of heat. The formation of such structures is thus carried out in the same process, facilitating the manufacture of the rear arm of the bicycle.

[0070] Advantageously, the front triangle 2 of the bicycle frame is hollow, which makes it possible to house a battery there for the electrical power supply of the motor, for example in the oblique tube 20 or the tube 21 intended to carry a saddle, and to pass there the brake cables and the cables connecting the battery to the electrical elements of the motor arranged in the first housing 40. In certain embodiments, the front triangle 2 is also produced by molding.

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

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

[0073] Particularly advantageously, each fixing screw 302 passes through a respective oblong hole 301 of the rear arm. When the screw is not tightened, it is then possible to slide the support 300 along the oblong hole, between a front position allowing the mounting of a drive means (chain or belt) between the crankset and the rear wheel, and a rear position allowing the mechanical tension in the drive means to be adjusted. Once the required tension is reached, the screws 302 can be tightened in order to maintain the support 300 in the position of use of the bicycle. It is thus possible to dispense with a tensioner or any other additional system allowing the mechanical tension in the drive means to be adjusted.

[0074] Naturally, any other guiding means than an oblong hole can be used, said guiding means making it possible to guide each screw 302 between the position of mounting and tension adjustment position, according to a rectilinear, curvilinear or any other suitable shape.

[0075] This design of the bicycle therefore makes it possible in particular to use a belt which is a more reliable, silent 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

Claims

1. A system for driving 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) movable in rotation relative to the stator (45), and a transmission device arranged to transform a rotary movement of the rotor (46) into a rotary movement of the crankset, the crankset being adapted to cause 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 against the lubricant with respect to the first housing (40).,

2. Drive system according to claim 1, wherein the motor further comprises an output shaft driven in rotation by the transmission device and integral 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 selective modification of the ratio between the rotational speed of the rotor (46) and the rotational speed of the pedal assembly (8).

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

5. A drive system according to any preceding claim, wherein the first housing (40) and the second housing (50) are integrally formed in the rear arm (3).

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

7. The drive system of claim 6, wherein the reinforcing structure (60) comprises a plurality of reinforcing ribs.

8. A drive system according to any preceding claim, wherein the second housing (50) comprises a pair of holes 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 preceding claim, wherein the first housing (40) comprises one or more heat removal ports (42).

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

11. Electric bicycle (100) comprising • a frame comprising a front triangle (2) articulated on a fork carrying a front wheel, • a drive system according to 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) so that a rotation of the crankset (8) causes a rotation of the rear wheel (7).

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

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

14. An 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. A 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 arm being mounted in a single-pivot type pivot on a front portion of the front triangle and the rear suspension being arranged between the rear arm 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 tension position of said drive means (70), located at the rear of the front arm relative to the mounting position.

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

18. Bicycle according to one of claims 15 to 17, without a system for mechanically tensioning the drive means (70).

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