Torque transmission device, electric assistance device and associated cycle

Abstract

Torque transmission device, electric assistance device and associated cycle. The present invention relates to a torque transmission device (200) comprising: - an input washer (203a), - an output washer (203c), - an intermediate washer (203b) disposed between the input washer (203a) and the output washer (203c), - a first pair of links (205a, 205b) coupled on one side to the input washer (203a) and on the other side, opposite the first side, to the intermediate washer (203b), the links (205a, 205b) of the first pair being arranged diametrically opposite each other with respect to the intermediate central axis (X2), - a second pair of links (207a, 207b) coupled on one side to the intermediate washer (203b) and on the other side, opposite the first side, to the output washer. (203c), the links (207a,207b) of the second pair being arranged diametrically opposite with respect to the intermediate central axis (X2) of the intermediate washer (203b), the two pairs of links (205a, 205b and 207a, 207b) being aligned along two respective directions (d1, d2) perpendicular to each other.

Description

Title of the invention: Torque transmission device, electric assistance device and associated cycle

[0001] The present invention relates to a torque transmission device, in particular for a geared motor, an electric assistance device and a cycle comprising said torque transmission device.

[0002] Electric assist bicycles are booming because they attract diverse audiences, from city dwellers wanting to replace their car with a more practical and ecological vehicle to athletes wanting assistance to reduce the effort required when pedaling, especially on steep inclines.

[0003] Different technologies have been developed to meet the needs of these different users.

[0004] In the case of electric-assist bicycles designed for sport, it is important for users that the bicycle's weight be kept under control and that transmission losses be limited, as athletes want to use their bicycles as often as possible without relying on electric assistance, thus preserving the feel of a traditional bicycle. It is also important to obtain a bicycle with an appearance as close as possible to that of a traditional bicycle.

[0005] One of the technologies that allows for good adaptation to the cyclist's pedaling is to position the electric motor around the bottom bracket axle in the bottom bracket housing supporting the bottom bracket axle. Thus, the motorization will be able to benefit from the transmission ratio, which is the ratio between the rotation speed of the rear wheel and its pedaling cadence. This transmission ratio is chosen by the cyclist in order to optimize their pedaling cadence in all circumstances. This will also have the effect of adapting the motor speed so that it always works under good efficiency conditions and can thus deliver a very high torque of assistance to the rear wheel (at a lower speed) when climbing very steep hills.

[0006] Users of these electric-assist bicycles also want a very quiet motor so that they can fully enjoy cycling in complete peace and quiet.

[0007] The distance between the right and left pedals is a very important factor for cyclists, especially competitive cyclists. This distance between the two pedal contact surfaces is commonly called the "Q-factor" and is 146 mm for a road bike and up to 158 mm for a mountain bike (MTB), while electric assist motor units significantly increase this "Q-factor," from 163 mm to 220 mm. This is because the motor unit must incorporate numerous components. such as a torque sensor, a motor, a gearbox, and at least one freewheel. Assembling all these components takes up considerable space and leads to a widening of the Q-factor. This widening is immediately noticeable to an experienced cyclist. Indeed, during the pedaling motion, the cyclist's legs do not form a dynamically balanced mechanical system; the limbs undergo alternating accelerations, generating significant dynamic forces that increase with the square of the pedaling cadence. The imbalance of this system also increases with the distance between the pedals; thus, its increase inevitably reduces the cyclist's pedaling cadence and therefore their mechanical power output.Furthermore, the pedal spacing poses safety problems when the cyclist wants to continue pedaling while cornering. The bicycle's lean angle in a curve brings the pedal on the inside of the turn closer to the ground, which could then rub against the ground and cause the cyclist to fall. The increased "Q-factor" thus makes pedaling in curves much more dangerous. It is therefore important to design a motor with a very narrow axial angle, respecting the "Q-factor" of high-performance, unassisted bicycles.

[0008] In order to use a small, particularly small-diameter, and lightweight electric motor, it is preferable to limit its torque. Low electric motor torque results in a high output shaft rotation speed to obtain the desired power. It is therefore necessary to couple a gearbox to the electric motor to obtain a rotation speed adapted to the user's pedaling cadence. Furthermore, a freewheel is necessary to disengage the motor when the cyclist no longer uses motor assistance, for example, when their speed exceeds the maximum legal assistance speed or when they no longer wish to be assisted. This freewheel is also necessary to prevent damage to the electric motor, particularly when the user backpedals.These different elements can be mounted coaxially to the pedal axle and form a transmission chain configured to transmit the torque supplied by the electric motor to the bottom bracket axle.

[0009] The manufacturing of the gearbox and the components of the power transmission chain requires manufacturing tolerances, particularly coaxiality tolerances, which can combine their effects periodically. Manufacturing all these parts demands the utmost care to achieve a highly precise assembly, but reducing the tolerance ranges rapidly increases the manufacturing cost.

[0010] Furthermore, when the user applies a significant force to the pedals, this tends to deform the bottom bracket axle.

[0011] These manufacturing tolerances and this deformation tend to distort the coaxiality between the bottom bracket axle and the elements of the transmission chain, this This creates stress and increases friction, particularly in the bearings located between the drivetrain components and the bottom bracket axle. This friction results in a loss of efficiency that can be unpleasant for the user, especially when riding without electric assistance, as the cyclist must exert extra effort to overcome it. This friction also generates wear and tear, as well as periodic vibrations and noises that are unpleasant for cyclists seeking a peaceful ride.

[0012] To overcome this problem of lack of coaxiality between two mechanical assemblies, it is known to use an Oldham joint. Oldham joint type couplings are homokinetic couplings; they consist of a first slide between an input washer and an intermediate washer, and a second slide perpendicular to the first, linking the intermediate washer to the output washer.These two slides are preferably each made by a radial strip sliding in a radial groove. The problem encountered with this type of coupling is that these slides generate a lot of alternating friction, resulting in large parasitic radial forces. Indeed, with each revolution, each slide makes a back-and-forth movement, causing two reversals in the direction of the radial friction component. Since the two slides are out of phase by a quarter turn, the friction changes orientation four times per revolution, generating significant radial excitation of the input and output shafts, which in turn produces considerable noise. This friction problem could be solved by inserting rolling elements in the slides, but this solution is very expensive and axially bulky, and therefore not applicable in a compact geared motor.

[0013] It is therefore necessary to provide an economical solution, enabling the obtaining of electric assistance with limited weight and size so that it can be placed at the level of the bottom bracket and which limits friction and noise related to the deformation of the bottom bracket axle under the effect of the user's pedaling.

[0014] Also, these same problems can be encountered for other devices using electric assistance devices such as, for example, electric assistance devices for exoskeletons, portable power equipment or for robotic arms where operating noise and compactness are important criteria.

[0015] To this end, the invention relates to a torque transmission device, in particular for a geared motor, comprising: - an inlet washer extending in a plane perpendicular to a central inlet axis, - an output washer extending in a plane perpendicular to a central output axis, - an intermediate washer disposed between the inlet washer and the outlet washer and extending in a plane perpendicular to an intermediate central axis, - a first pair of links coupled on one side to the inlet washer and on the other side, opposite to the first side, to the intermediate washer, the links of the first pair being arranged diametrically opposite with respect to an intermediate central axis, - a second pair of links coupled on one side to the intermediate washer and on the other side, opposite to the first side, to the output washer, the links of the second pair being arranged diametrically opposite with respect to the intermediate central axis, the two pairs of links being aligned along two respective perpendicular directions so as to allow torque transmission even in the absence of coaxiality between the central input axis and the central output axis.

[0016] The use of two pairs of links aligned along two respective perpendicular directions connecting washers mounted to rotate around a central axis makes it possible to obtain a transmission of torque between two axes which can be non-coaxial, in the manner of an Oldham joint, while having a reduced size and in particular a reduced axial width.

[0017] It should be noted that the links of the first or second pair may not be strictly diametrically opposed but may deviate by 10° from a diametrically opposite direction.

[0018] It should also be noted that the two pairs of links can be aligned along two directions not strictly perpendicular but forming an angle between 80° and 100°.

[0019] According to another aspect of the present invention, the input washer comprises two transmission shafts extending parallel to the central input shaft and received in two respective first holes, associated with a first end of the respective links of the first pair, the intermediate washer comprising two first transmission shafts extending parallel to its central shaft, arranged on a first face of the intermediate washer and received in two respective second holes, associated with a second end of the respective links of the first pair, and two second transmission shafts extending parallel to its central shaft, arranged on a second face of the intermediate washer and received in two respective first holes associated with the first side of the respective links of the second pair,The output washer comprises two transmission shafts extending parallel to the central output shaft and received in two respective second holes associated with the second side of the respective links of the second pair.

[0020] According to another aspect of the present invention, the links of the first pair are mounted rotatably on one side with the transmission axes of the input washer and on the other side with the first transmission axes of the intermediate washer and the links of the second pair are mounted rotatably on one side with the second transmission axes of the intermediate washer and on the other side with the transmission axes of the output washer.

[0021] According to another aspect of the present invention, the first and second transmission axes of the intermediate washer are arranged such that the links of the first and second pairs work in tension in a first direction of torque transmission and in compression in a second direction of torque transmission, opposite to the first direction of torque transmission. In the first direction of torque transmission, the input washer is driving and the output washer is driven, and in the second direction of torque transmission, the input washer is driven and the output washer is driving.

[0022] According to another aspect of the present invention, the first and second transmission axes of the intermediate washer are arranged so that for the first and second pairs of links, a first link of the pair works in tension and a second link of the pair works in compression when a torque is transmitted.

[0023] According to another aspect of the present invention, the links are standard chain links.

[0024] According to another aspect of the present invention, the intermediate washer comprises a collar extending axially on either side of the center of the washer to form a T-shaped section in order to prevent ovalization of said intermediate washer when the torque transmission device is under load.

[0025] According to another aspect of the present invention, the links are arranged in the thickness formed by the collar of the intermediate washer.

[0026] According to another aspect of the present invention, the transmission shafts protrude from the links and counterbores are provided in the input washer, the intermediate washer and the output washer opposite the transmission shafts associated with an adjacent washer to allow the transmission shafts to protrude.

[0027] The present invention also relates to an electric assistance device, particularly for bicycles, comprising: - an electric motor comprising an output shaft and configured to be mounted around a central axis, - a reducer configured to be mounted around the central axis, - a freewheel configured to be mounted around the central axis, - a torque transmission device as described above configured to be mounted around the central axis, the reducer, the freewheel and the torque transmission device forming a torque transmission chain between the output shaft of the electric motor and an output shaft of the electric assistance device.

[0028] Such a cycle assistance device increases the number of degrees of freedom and thus limits friction when the user, by pedaling, introduces deformations and stresses at the level of the crankset and has a reduced size which facilitates its integration into the bottom bracket.

[0029] According to another aspect of the present invention, the reducer comprises an input configured to be rotationally coupled to the output shaft of the electric motor and an output configured to be rotationally coupled to the input washer of the torque transmission device.

[0030] According to another aspect of the present invention, the freewheel comprises an input configured to be rotationally coupled to the output washer of the torque transmission device and an output configured to be rotationally coupled to the output shaft of the electric assistance device.

[0031] According to another aspect of the present invention, the central bottom bracket axle of the cycle is held in position by a single pair of bearings arranged between a frame of the cycle and the central bottom bracket axle.

[0032] The use of a single pair of bearings to support the bottom bracket axle reduces the stresses between the geared motor and the bottom bracket and thus reduces friction and noise caused by these stresses.

[0033] According to another aspect of the present invention, the electric motor, the reducer, the torque transmission device and the freewheel are configured to be arranged adjacently along the central axis of the bottom bracket.

[0034] The present invention also relates to a cycle comprising a frame, a central bottom bracket axle rotatably mounted on the frame and an electric assistance device as described above.

[0035] According to another aspect of the present invention, the electric motor and the reducer are mounted on the frame independently of the central bottom bracket axle.

[0036] Other features and advantages of the invention will become more apparent upon reading the following description, given by way of illustrative and non-limiting example, and the accompanying drawings, among which:

[0037] [Fig-1] represents a first schematic exploded and perspective view of a torque transmission device according to an embodiment of the present invention;

[0038] [Fig.2] represents a second schematic exploded and perspective view of the torque transmission device of the [Fig.l];

[0039] [Fig. 3a] shows a front view of an intermediate washer and the two pairs of links in the case of a misalignment of the XI axis of the input washer with the X3 axis of the output washer;

[0040] [Fig. 3b] represents a perspective view of an intermediate washer and the two pairs of links according to [Fig.3a];

[0041] [Fig. 3c] shows an exploded view of an intermediate washer and the two pairs of links in accordance with [Fig.3a];

[0042] [Fig.4] represents a diagram of a bicycle frame equipped with an assistance device electric for cycling;

[0043] [Fig.5] represents a perspective view of a crankset and an assistance device electric for cycling;

[0044] [Fig. 6] represents a perspective and axial sectional view of a device electric assistance for cycling according to the present invention;

[0045] [Fig.7] represents a radial cross-sectional view of an electric assistance device for cycle according to a first section;

[0046] [Fig.8] represents a radial cross-sectional view of an electric assistance device for cycle according to a second section;

[0047] [Fig.9] represents a schematic representation of an assistance device electric cycle according to the present invention;

[0048] [Fig. 10] represents an axial cross-sectional view of an electric assistance device for cycle according to the present invention;

[0049] [Fig. 11] shows a front view of an intermediate washer and the two pairs of links according to an alternative method of implementation.

[0050] In these figures, identical elements bear the same reference numerals.

[0051] The following embodiments are examples. Although the description refers to one or more embodiments, this does not necessarily mean that each reference relates to the same embodiment, or that the features apply only to a single embodiment. Simple features from different embodiments can also be combined or interchanged to provide other embodiments.

[0052] In this description, certain elements or parameters can be indexed, such as first element or second element, first parameter and second parameter, first criterion and second criterion, etc. In this case, it is simply a matter of indexing to differentiate and name similar but not identical elements, parameters, or criteria. This indexing does not imply any priority of one element, parameter, or criterion over another, and such designations can easily be interchanged without departing from the scope of this description. description. This indexing also does not imply an order in time, for example, to assess one criterion or another.

[0053] Figures 1 and 2 show perspective views of a torque transmission device 200 according to an embodiment of the present invention. The torque transmission device 200 comprises an input washer 203a intended to be rotationally coupled to a first rotating mechanical assembly. The input washer 203a is configured to extend in a plane perpendicular to an axis referred to as the central input axis XL. The input washer 203a comprises two transmission axes 231 and 232 extending parallel to the central input axis XI, from a first side of the input washer 203a and in an axial direction. The transmission axes 231 and 232 are arranged equidistant from the central input axis XL. The transmission axes 231 and 232 are, for example, formed by cylindrical blocks.The cylindrical studs can be fixed to the inlet washer 203a, for example by press fitting, welding or crimping, or they can be formed from the same material as the inlet washer 203a. In the embodiment of Figures 1 and 2, the transmission shafts 231 and 232 are arranged diametrically opposite each other with respect to the central inlet shaft XI, but other positions are also possible.

[0054] The torque transmission device 200 also includes an output washer 203c intended to be rotationally coupled to a second rotating mechanical assembly. The output washer 203c is configured to extend in a plane perpendicular to an axis referred to as the central output axis X3. The output washer 203c comprises two transmission axes 233 and 234 extending parallel to the central output axis X3 on one side of the output washer 203c and in an axial direction. The transmission axes 233 and 234 are arranged equidistant from the central output axis X3. The transmission axes 233 and 234 are, for example, formed by cylindrical studs. The cylindrical studs may be fixed to the output washer 203c, for example, by press fitting, welding, or crimping, or may be formed as part of the output washer 203c.

[0055] In the embodiment of [Fig.1], the transmission axes 233 and 234 are arranged diametrically opposite with respect to the central output axis X3, but other positions are also possible.

[0056] The torque transmission device 200 also includes an intermediate washer 203b arranged axially between the input washer 203a and the output washer 203c. The intermediate washer 203b is more clearly visible in Figures 3a, 3b, and 3c. The intermediate washer 203b is configured to extend in a plane perpendicular to an axis called the intermediate central axis X2. The three washers 203a, 203b, and 203c are arranged substantially coaxially so that the three axes XI, X2, and X3 can be considered coincident. The intermediate washer 203b comprises two axes Transmission shafts 235 and 236 extend from one side of the intermediate washer 203b in an axial direction parallel to the intermediate central axis X2. This first side of the intermediate washer 203b is intended to be aligned with the side of the input washer 203a comprising the transmission shafts 231 and 232. In the embodiment of [Fig. 1], the transmission shafts 235 and 236 are arranged diametrically opposite each other with respect to the intermediate central axis X2, but other positions are also possible. The transmission shafts 235 and 236 are arranged equidistant from the intermediate axis X2.

[0057] The intermediate washer 203b includes two additional transmission shafts 237 and 238 extending from a second side of the intermediate washer 203b in an axial direction parallel to the intermediate central shaft X2. This second side of the intermediate washer 203b is intended to be aligned with the side of the output washer 203c comprising the transmission shafts 233 and 234. In the embodiment of [Fig. 1], the transmission shafts 237 and 238 are arranged diametrically opposite each other with respect to the intermediate central shaft X2, but other positions are also possible. The transmission shafts 237 and 238 are arranged equidistant from the intermediate central shaft X2. In addition, the transmission axes 237 and 238 (driven) are offset by less than a quarter turn (behind the normal direction of drive) relative to the transmission axes 235 and 236 (driving).

[0058] The transmission shafts 235, 236, 237 and 238 of the intermediate washer 203b are, for example, formed by cylindrical studs. The cylindrical studs can be fixed to the intermediate washer 3b, for example by welding or crimping, or can be formed as part of the material of the intermediate washer 203b. In this case, the intermediate washer 203b can have a local reinforcement zone on the face opposite the transmission shaft 235, 236, 237 and 238, in the form of a rectangular block, visible in Figures 1, 2, 3a, 3b, 3c, in order to reinforce the fixed position of the transmission shaft 235, 236, 237 and 238 in the web of the intermediate washer 203b.

[0059] The intermediate washer 203b may also include a collar 209, particularly in the central part of the annular shape of the intermediate washer, the collar 209 being able to extend axially on either side of the center of the intermediate washer 203b to form a T-section. The T-section makes it possible to radially stiffen the intermediate washer 203b and thus prevent its ovalization when the torque transmission device 200 is under load.

[0060] The torque transmission device 200 also includes a first pair of links 205a, 205b arranged between the input washer 203a and the intermediate washer 203b. The links 205a and 205b of the first pair are coupled on one side to the input washer 203a and on the other side, opposite the first side, to the intermediate washer 203b via the transmission shafts 231, 232, 235 and 236. The links 205a and 205b of the first pair comprise a first hole located at one end of the link 205a, 205b and configured to receive respectively a transmission shaft 231, 232 associated with the entry washer 203a, and a second hole located at the other end of the link 205a, 205b and configured to receive respectively a transmission shaft 235, 236 associated with the intermediate washer 203b. Preferably, the links 205a, 205b of the first pair are arranged diametrically opposite with respect to the intermediate central shaft X2 (or with respect to the central entry shaft XI), but a deviation of a few degrees, for example 10° with respect to the diametrically opposite direction, may be acceptable.

[0061] The torque transmission device 200 also includes a second pair of links 207a, 207b coupled on one side to the intermediate washer 203b and on the other side, opposite to the first side, to the output washer 203c via the transmission shafts 233, 234, 237 and 238, the links 207a, 207b of the second pair being arranged diametrically opposite with respect to the intermediate central shaft X2.

[0062] The links 207a and 207b of the second pair include a first hole located at a first end of the link 207a, 207b and configured to receive respectively a transmission shaft 237, 238 associated with the intermediate washer 203b and a second hole located at a second end of the link 207a, 207b and configured to receive respectively a transmission shaft 233, 234 associated with the output washer 203c.

[0063] Preferably, the links 207a, 207b of the second pair are arranged diametrically opposite with respect to the intermediate central axis X2 (or with respect to the exit central axis X3) but a deviation of a few degrees, for example 10° with respect to the diametrically opposite direction may be acceptable.

[0064] Furthermore, due to the position of the transmission axes 235, 236, 237, and 238 of the intermediate washer 203b, the two pairs of links 205a, 205b, 207a, 207b are aligned along two substantially perpendicular directions, denoted d1 for the first pair 205a and 205b and d2 for the second pair 207a, 207b in [Fig. 3a]. Such an arrangement of the links 205a, 205b, 207a, 207b allows for torque transmission even in the absence of coaxiality between the central input axis XI and the central output axis X3. Moreover, this transmission is practically completely homokinetic since the generated transmission error is not experimentally measurable. However, the calculation of the transmission error by numerical simulation or analytically gives a calculated transmission error < 6.10-6 for an eccentricity of the XI and X3 axes deliberately exaggerated by 1 mm, whereas the usual eccentricity will probably be less than one tenth of a mm.The homokinetic nature of this coupling in rotation is an essential factor for . the silent operation of the system in order to avoid periodic excitation pulsations in the torque transmission.

[0065] In the embodiment presented, due to the position of the transmission axes 231, 232, 233, 234, 235, 236, 237, 238 (the transmission axes on one side of a washer 203a, 203b, 203c are arranged diametrically opposite) the links 205a, 205b, 207a, 207b work in tension in a first direction of torque transmission and in compression in the opposite direction of torque transmission (which is not used in the case of an application related to a cycle crankset).

[0066] During torque transmission, the intermediate washer is subjected to the simultaneous tension of the four links 205a, 205b, 207a, 207b. The vector sum of these forces is substantially zero, resulting in the transmission of a pure torque. However, as can be seen in [Fig. 3a], the actions of link 205a and link 207b are substantially perpendicular, and the resultant of these two actions is a centripetal load directed along the median of the two links 205a and 207b. The same is true symmetrically with respect to the X2 axis for the other two links 205b and 207a. Thus, the intermediate washer 203b is subjected to two opposing centripetal forces, inducing a bending stress that tends to ovalize the intermediate washer 203b under the action of these two opposing centripetal forces.It is therefore desirable to reinforce and stiffen the core of this washer with a T-shaped section (visible in Figures 6 and 10) provided by the flange 209 in order to reduce its deformation and stresses while remaining very narrow, since the arms of the T corresponding to half the height of the flange 209 are approximately the same thickness as the links positioned on each side. The links 205a, 205b, 207a, 207b are thus configured to fit within the volume formed by the flange 209 on either side of the core of the intermediate washer 203b, so that the flange 209 provides increased rigidity to the intermediate washer 203b without increasing the axial thickness of the torque transmission device 200. This intermediate washer 203b structure is thus particularly strong, compact, and lightweight.

[0067] To ensure a secure connection between the links 205a, 205b, 207a, 207b and their respective axes 231, 232, 234, 235, 236, 237, 238, it is necessary that the axes pass completely through the associated link and that their end (which is preferably chamfered to facilitate assembly) protrudes several tenths of a millimeter from the outer plane of the link so that the link cannot be ejected from its transmission axis. Eight counterbores or recesses 211 are therefore provided in the various washers 203a, 203b, 203c. The diameter of the counterbores is larger than the diameter of the transmission axes 231, 232, 234, 235, 236, 237, 238. to allow the protruding end of the transmission shafts 231, 232, 234, 235, 236, 237, 238 to be accommodated with some play.

[0068] As can be seen in figures 1 and 2, the intermediate washer 203b and the output washer 203c are inserted into a housing made in the input washer 203a, the assembly being held axially by an elastic ring 213 allowing the coupling to be immobilized axially and in particular prevent the links 205a, 205b, 207a, 207b from being ejected axially from their transmission axis 231, 232, 234, 235, 236, 237, 238.

[0069] When the links 205a, 205b, 207a, 207b all work in tension, the intermediate washer 203b then has a unique very stable equilibrium position so that if one tries to move it away from its equilibrium position it will tend to return to its equilibrium position on its own, on the other hand when the links 205a, 205b, 207a, 207b work in compression, by reversing for example the direction of the transmitted torque, if one moves the intermediate washer 203b away from its equilibrium position it can diverge towards an eccentric position where the drive will then no longer be homokinetic, even if friction tends to stabilize the intermediate washer when the input axis XI and the output axis X3 are only slightly eccentric. It is therefore strongly recommended with this type of coupling to transmit a torque causing tension in the links 205a, 205b, 207a, 207b.

[0070] The links 205a, 205b, 207a, and 207b used are, for example, standard chain links, notably having a pitch of 9.525 mm (3 / 8 inch), but other types of links can also be used. The use of standard chain links reduces the production costs of the torque transmission device 200.

[0071] According to an alternative embodiment, at least some transmission axes on one side of a washer are offset from a diametrically opposite position so that one of the links of a pair works in tension and the other in compression in each direction of torque transmission so that the connection between the first input washer 203a and the intermediate washer 203b is driven by a deformable parallelogram composed of 2 links 205a and 205b thus releasing a first degree of freedom in a plane normal to the axis XI, the same may be true for the connection between the intermediate washer 203b and the output washer 203c formed by a second deformable parallelogram having a direction of movement substantially perpendicular to the first deformable parallelogram thus releasing the second degree of freedom in a plane normal to the axis XL. [Fig. 11] represents an example of such an embodiment. The [Fig.11] differs in particular from the [Fig.3a] by the reversed position of the transmission axes 232 and 236. Thus, in a first direction of torque transmission, the link 205a works in tension and the link 205b in . compression while in the direction of reverse torque transmission, link 205b works in tension and link 205a works in compression.

[0072] Similarly, a similar configuration can be implemented for the second pair of links 207a, 207b. This configuration makes it possible to obtain a perfectly homokinetic torque transmission device 200. This configuration will be preferred in applications where the torque must be transmitted in both directions.

[0073] In the embodiment shown in Figures 1 and 2, in a first direction of torque transmission, links 205a and 205b of the first pair and links 207a and 207b work in tension to transmit the torque between the input washer 203a and the output washer 203c, and in a second direction of torque transmission, links 205a and 205b of the first pair and links 207a and 207b work in compression to transmit the torque between the input washer 203a and the output washer 203c. As previously stated, in the case of unidirectional use (torque always transmitted in the same direction of torque transmission, as in the case of a cycle), the direction of torque transmission in which links 205a, 205b, 207a, and 207b work in tension will be preferred.

[0074] Furthermore, it should be noted that the links 205a, 205b of the first pair are mounted rotatably on one side with the transmission axes 231, 232 of the input washer 203a and on the other side with the first transmission axes 235, 236 of the intermediate washer 203b and the links 207a, 207b of the second pair are mounted rotatably on one side with the second transmission axes 237, 238 of the intermediate washer 203b and on the other side with the transmission axes 233, 234 of the output washer 203c so that the intermediate central axis X2 can be offset relative to the input central axis XI and the output central axis X3 can be offset relative to the intermediate central axis X2. Thus, the central output axis X3 can be offset in all directions relative to the central input axis XI.

[0075] Thus, the torque transmission device 200 described above allows two rotating mechanical assemblies to be coupled in rotation even if they have a coaxiality deviation, meaning that the axis of rotation of the first rotating mechanical assembly may not coincide with the axis of rotation of the second rotating mechanical assembly. Nevertheless, the axes of rotation must be substantially coincident, that is, contained within a common cylinder whose diameter is less than a few millimeters, for example, less than 2 mm, for example, equal to 0.7 mm. The torque transmission device 200 thus acts as an Oldham joint and ensures torque transmission between two rotating mechanical assemblies without generating losses or noise, even in the event of coaxiality deviation. Furthermore, the use of a torque transmission device 200 comprising a first pair of links Connecting an input washer 203a and an intermediate washer 203b, and a second pair of links connecting an output washer 203c and the intermediate washer 203b, makes it possible to obtain a torque transmission device 200 with a reduced axial dimension, for example between 3.5 mm and 6 mm, since the thickness of the washers and links, which can be made of high-strength steel, can be reduced and the washers can be arranged close to each other.

[0076] One of the advantages of using pivoting links is that they greatly reduce friction because the sliding speed in the link holes is much lower than with a slide, as in the case of an Oldham joint. Friction is thus reduced by the ratio L / d, where L represents the center distance of the link and d the diameter of the transmission shafts. In our example, L = 9.525 mm and d = 3.2 mm, representing a reduction ratio of one-third. The coefficient of friction and shaft wear can be considerably reduced by nitriding the shafts and / or links to optimize the long-lasting and low-friction operation of this coupling.Such a 200 Nm torque transmission device is particularly well-suited for use in an electric bicycle geared motor positioned at the bottom bracket. This design prevents friction or unwanted noise from the cyclist's actions, which tend to deform the bottom bracket shell and thus create a non-coaxial connection between the geared motor output and the bottom bracket axle. An example of such a geared motor incorporating a 200 Nm torque device will be described in more detail later.

[0077] Figure 4 shows a frame 100 of a cycle comprising an assistance device Electric 101.

[0078] The electric assistance device 101 includes a geared motor 1 mounted in a crankset 102 of the cycle, on the central axle 103 of the crankset, in a housing of the frame 100 (figures 4 and 5).

[0079] In a manner known per se, the central axis 103 of the crankset, rotating, is connected to the pedals (not shown) via two cranks 104. The crankset 102 also includes at least one toothed chainring 105, here two, fixed(s) to the base of one of the cranks 104 and configured(s) to drive the chain driving the rear wheel of the cycle.

[0080] Better seen in the axial cross-sectional view of [Fig.6], the geared motor 1 comprises a reducer 2, an electric motor 3 and a torque transmission device 200, configured to be able to be mounted coaxially on the central shaft 103.

[0081] The electric motor 3 comprises a rotor 4 fixed in rotation to a shaft 5, and a stator 6 fixed in a housing 7 of the geared motor 1, the housing 7 itself being received and fixed in the frame 100.

[0082] The electric motor 3 is, for example, a brushless motor, the rotor 4 comprising permanent magnets rotating inside the stator 6 including windings, for example three-phase. The permanent magnets of the rotor 4 are fixed to the shaft 5. Angular position sensors of the rotor 4 and of the central axis 103 of the pedal assembly 102, further enable the control of the electric motor 3.

[0083] The shaft 5 is tubular, i.e. hollow, to allow the passage of the central axis 103 connected here to the cranks 104. It forms the input of the reducer 2.

[0084] The reducer 2 comprises a toothed ring 10 fixed to the housing 7 and thus to the stator 6, a planet carrier 11 pivotally mounted via at least one flange bearing 22, 23 around the shaft 5, and at least two eccentric planet gears 12, 13 situated on two parallel planes. The toothed ring 10 meshes the two planet gears 12, 13 on the inner side of the toothed ring 10 in two different planes. The planet carrier 11 forms the output of the reducer 2.

[0085] The planetary gears 12, 13 are mounted on the one hand, on respective eccentric cams 14 via a respective bearing 15 and are on the other hand, traversed by at least three axes 16 of the planet carrier 11. The reducer 2 has for example six axes 16. The eccentric cams 14 are fixed to the shaft 5.

[0086] The reducer 2 is of the cycloidal type; it allows the speed of the shaft 5 to be reduced by a relatively high ratio in relatively compact dimensions. The shaft 5 drives the eccentric bearings 15, which in turn drive the planetary gears 12, 13 in an eccentric cycloidal motion.

[0087] The planetary gears 12, 13 mesh with the ring gear 10, being out of phase in rotation. The planetary gears 12, 13 have teeth of truncated cycloidal shape (or involute teeth), here numbering 45, and the ring gear 10 has teeth, here numbering 46, having cylindrical (or involute) segments cooperating with the shape of the gears 12, 13. These truncated cycloidal teeth are visible in [Fig. 7]. The reducer 2, for example, has two planetary gears 12, 13 out of phase in rotation by 180° ([Fig. 6]) or three planetary gears out of phase with each other by 120° (not shown). The use of several satellite gears 12, 13 with phase shifts in rotation makes it possible to compensate for the radial forces exerted in particular on the satellite gears 12, 13 due to the high output torque.

[0088] According to one embodiment, the satellite carrier 11 comprises a first flange 17 and a second flange 18 connected to each other by a series of spacers 19 (at least three), for example six spacers 19 (visible on the cross-sectional view of [Fig.7]). These spacers 19 are fixed in each of the flanges 17, 18 by screws 20 passing through the spacers 19 (one screw 20 per spacer 19) connecting the two flanges 17, 18. The planetary gears 12, 13 are axially interposed between the flanges 17, 18, the planet carrier 11 thus forming a cage coaxial with the shaft 5 and the toothed ring 10 for the planetary gears 12, 13 eccentric by the eccentric cams 14.

[0089] The spacers 19 pass through the planetary gears 12, 13 via openings 21, here six (as many openings 21 as there are spacers 19), for example cylindrical. There is sufficient clearance between the spacers 19 and the openings 21 so that they do not come into contact with each other. The openings 21 are regularly formed on a circle in the faces of the planetary gears 12, 13.

[0090] The reducer 2 also includes at least one flange bearing 22, 23 for centering the planet carrier 11 around the shaft 5. For example, the reducer 2 includes a first flange bearing 22 interposed between the first flange 17 of the planet carrier 11 and the shaft 5, to center the first flange 17, and a second flange bearing 23 interposed between the second flange 18 of the planet carrier 11 and the shaft 5 to center the second flange 18 ([Fig.6]).

[0091] The output torque of the reducer 2 is transmitted to the central axle 103 of the crankset via the torque transmission device 200, which allows the torque to be transmitted while tolerating a slight radial misalignment. A freewheel 25 can be interposed between the output shaft 26 connected to the toothed chainring 105 of the cycle and the output of the torque transmission device 200. The freewheel 25 allows, in particular, the geared motor 1 to be disengaged in case of excessive speed, backpedaling, or when the cyclist no longer wishes to receive assistance.

[0092] The toothed ring 10 is fixed to the housing 7 of the geared motor 1. The teeth of the ring 10 are, for example, directly made in the housing 7. The pinions 12, 13 are meshed with the "fixed" toothed ring 10.

[0093] The shafts 16, passing through the faces of the planetary gears 12, 13, transmit the thrust exerted by the planetary gears 12, 13 to the planet carrier 11, which is the output member of the gearbox 2. The shafts 16 (or output shafts) drive the output of the gearbox 2 in rotation, coaxially with the shaft 5, when the planetary gears 12, 13 rotate. The direction of rotation of the planetary gears 12, 13 and the output is opposite to that of the shaft 5, and when the shaft 5 rotates one revolution, the planetary gears 12, 13 shift angularly by one tooth in the opposite direction, driving the output at a rotational speed lower than the rotational speed of the shaft 5, here forty-five times lower.

[0094] The shafts 16 pass through all the planetary gears 12, 13. Each shaft 16 is in contact with a hole 31 of each planetary gear 12, 13, i.e., two holes 31 in the case of a reducer 2 with two planetary gears 12, 13. Since the shafts 16 are cylindrical, the holes 31 must have at least one cylindrical portion in the direction transmitting the torque. The holes 31 are, for example, cylindrical.

[0095] The geared motor 1 may further include a pair of shaft bearings 33 per shaft 16, one shaft bearing 33 being mounted at each end of the shafts 16 ([Fig. 6]). There are thus twelve small shaft bearings 33 received in the flanges 17, 18 of the planet carrier 11 of the illustrated geared motor 1. The advantage of these shaft bearings 33 is to To minimize losses in each of the bearings of the axes 16 during their rotation under load. The axes 16 roll without slipping in the holes 31 of each of the planetary gears 12, 13, thus minimizing losses that would be due to slippage under load.

[0096] The holes 31 of the satellite gears 12, 13 are regularly provided in the faces of the satellite gears 12, 13, on a circle, the holes 31 alternating with the openings 21 through which the spacers 19 pass ([Fig.7]).

[0097] According to one embodiment, the geared motor 1 further comprises a rotor bearing 34 configured to center a first end of the shaft 5, the driving end (motor side), on a fixed axis of the geared motor 1 and a bearing device 36 comprising deformable rolling elements 37, the bearing device 36 being interposed between the planet carrier 11 and a cylindrical housing of the casing 7, for centering the shaft 5 in the cylindrical housing, at a second end, the driven end (Figures 6 and 9).

[0098] The cylindrical housing is formed in the casing 7. The casing 7 is fixed relative to the frame, i.e., relative to the frame 100 of the cycle. The fixed axis is the axis of the cylindrical housing in the casing 7.

[0099] In the example of figures 4 to 10, the deformable rolling elements 37 are interposed between the second flange 18 of the planet carrier 11 and the cylindrical housing of the casing 7. A bearing surface receiving the deformable rolling elements 37 can be provided in the planet carrier 11, in the second flange 18, and in the cylindrical housing of the casing 7.

[0100] The shaft 5, which is rotationally fixed to the rotor 4 of the electric motor 3, rotates on the rotor bearing 34 located at one of its ends, the driving end, while the other driven end is left "free or floating" to self-center under the opposing radial thrust of the planetary gears 12, 13 (see schematic [Fig. 9]). Thus, this second end positions itself radially when a significant transmission torque is transmitted.

[0101] On the other hand, in the no-load operating phases, that is to say when no transmission torque is transmitted or for low torques, the second driven end of the reducer 2 is self-centered by the elastic deformable rolling elements 37.

[0102] The centering of the second end by the deformable rolling elements 37 in the case of low torques makes it possible to prevent the satellite gears 12, 13 from navigating or rather flapping in their functional play, which could then cause an unpleasant noise, indeed in their absence the reducer 2 could not preposition itself properly by itself, which could also damage the teeth.

[0103] The self-centering of the shaft 5 by the deformable rolling elements 37 means that it is no longer rigidly guided radially at its second end on the side of the planetary gears 12, 13 by a ball bearing, as in the prior art. In contrast, in the invention schematically illustrated in [Fig. 9], this second end is allowed to self-center until the radial forces generated by each of the planetary gears 12, 13 are in equilibrium. This equilibrium is made possible by the release of two degrees of freedom in a planar movement substantially normal to the axis of rotation of the rotor 4.

[0104] Furthermore, the self-centering of the planetary gears 12, 13 allows for better distribution of the torque transmitted by each of the gears 12, 13. This improved torque distribution makes it possible to manufacture a geared motor 1 with less precision, which simplifies its production and reduces its manufacturing cost. Also, the eccentric cams 14 of the planetary gears 12, 13 no longer need to be perfectly phase-shifted. This type of defect is no longer problematic at all because the shaft 5 self-centers in the middle of the eccentric cams 14 under the balance of the radial forces of the satellite gears 12, 13. In addition, the absence of rigid radial guidance on the side of the gears 12, 13 allows that possible asymmetries of the torque transmitted between the satellite gears 12, 13 can no longer generate radial overload of the bearing on the side of the gears 12, 13 which cause noise, loss of efficiency and increased wear.

[0105] It goes without saying that in order to allow a small planar displacement of the pinions 12, 13, it is necessary to provide sufficient operating clearance in the meshing of the pinions 12, 13 in the ring 10.

[0106] According to one embodiment, the deformable rolling elements 37 are mounted radially pre-stressed on the raceway so that the bearing has no initial radial play. This pre-stress must not, however, hinder self-centering by the planetary gears 12, 13 in the event of high torques. The deformable rolling elements 37 are therefore deformable within the elastic range, and it is necessary that they retain their elastic properties, particularly over time and throughout the entire operating temperature range (avoiding any stress relaxation and / or creep).

[0107] Preferably, the deformable rolling elements 37 have sufficient radial preload so that, in all extreme cases of maximum play between the planet carrier 12, 13, the deformable rolling elements 37, and the cylindrical housing, the nominal diameter of the deformable rolling elements 37 is such that there is no radial play. In this case, the deformable rolling elements 37 must have sufficient radial elasticity to accept the radial deformation imposed this time by the clamping assembly to which is superimposed the radial stroke necessary for self-centering.

[0108] It is however possible to tolerate a limited radial play, i.e. without initial preload of the deformable rolling elements 37, to limit the amplitude of the potential radial beat of the satellite gears 12, 13 in the toothed ring 10 but this play must then be less than the functional radial play of the satellite gears 12, 13 in the toothed ring 10.

[0109] In the example of figures 4 to 10, the rotor bearing 34 is interposed between the shaft 5 and the stator 6 of the electric motor 3 for the centering of the shaft 5 at the first driving end of the geared motor 1, the shaft 5 being mounted independently of the central axis 103, in particular with sufficient radial clearance to avoid any contact (schematic [Fig.6] and [Fig.9].

[0110] With this assembly, the geared motor 1 is totally isolated from the central axis 103. The shaft 5 mounted independently of the central axis 103 is self-centered by the deformable rolling elements 37.

[0111] As can be seen more clearly in the schematic [Fig. 9], the shaft 5 is guided only at the first driving end by the rotor bearing 34 centered in the stator 6 of the electric motor 3. The planetary gears 12 and 13 are pivot-mounted on their respective eccentric cams 14 and mesh with the toothed ring 10 attached to the housing 7 (in this diagram, the deformable rolling elements are not shown for ease of understanding). Thus, the planetary gears 12 and 13 self-center under the effect of the equilibrium of the radial forces generated by the thrust of their respective teeth during torque transmission. The satellite carrier 11, which is also centered on the shaft 5, transmits the output torque to the central axis 103 of the crankset 104 via the torque transmission device 200 (schematized in a simplified way on [Fig.9] to illustrate that a radial displacement is possible between the satellite carrier 11 and the central axis 103 of the crankset).This self-centering of the shaft 5 and the satellite carrier II containing the satellite gears 12, 13 is made possible by the torque coupling device 200, which allows its input shaft XI, forming the output of the geared motor 1, to self-center freely without being disturbed by the radial displacement of its output shaft X3 embodied by the central shaft 103, which moves radially under the effect of pedaling forces.

[0112] The use of a known Oldham sliding-joint type coupling, as indicated in the introduction, generates alternating radial forces that vary in direction, sense, and intensity four times per revolution. The use of this type of coupling at the output of the reducer 2 generates radial forces that tend to oppose the free self-centering of the pinions 12, 13 in their meshing with the ring gear 10. The use of pivoting links 205a, 205b, 207a, 207b generates, contrary to to the slides, radial forces are considerably reduced, making operation much freer and therefore quieter.

[0113] According to one embodiment, the deformable rolling elements 37 are formed by a series of tubular rollers arranged in a circle with their respective axes parallel to each other and to an axis of the shaft 5 ([Fig. 8]). The tubular rollers (or rollers or tubes) are cylindrical, i.e., hollow, parts, which increases their radial flexibility under compression and reduces stress when they undergo ovalization of a few hundredths of a millimeter.

[0114] Tubular rollers are for example dimensioned to allow a radial displacement of between 0.02mm and 0.15mm without risk of fatigue damage over the entire life of the geared motor 1.

[0115] When the gearbox 2 transmits torque under load, the tubular rollers must be sufficiently radially flexible so as not to impede the self-centering of the planetary gears 12, 13 of the gearbox 2, allowing them to find their radial equilibrium without excessive stress. The radial rigidity of the tubular rollers must be sufficient to allow the deformable rolling elements 37 to deform, permitting some movement of the gearbox 2, while remaining rigid enough to center the gearbox 2.

[0116] During operation, the tubular rollers rotate on their own axis like a ball or roller bearing. This rotation causes the tubular walls of the rollers to undergo rotational bending because the tubular walls deform alternately in tension and then in compression; therefore, the tubular roller must be dimensioned to withstand, preferably, unlimited fatigue.

[0117] The bearing arrangement 36 comprises, for example, between ten and fifty deformable rolling elements 37. Increasing the number of deformable rolling elements 37 makes it possible to increase the initial radial stiffness of the reducer 2 without loss of torque.

[0118] According to one embodiment, the deformable rolling elements 37 are made of polymer material, such as thermoplastic material, such as PEEK or PAI material.

[0119] Many polymer materials, and more specifically thermoplastic materials such as PEEK or PAI, retain their properties at high temperatures and are not susceptible to sagging. They can withstand mechanical and thermal stresses without losing their elasticity. However, the heat generated by the losses of the electric motor 3 and the gearbox 2 may require the geared motor 1 to operate at high temperatures (up to 90°C). Resistance to sagging and / or stress relaxation ensures that, when the deformable rolling elements 37 remain static for a long period, they do not come to They become oval and generate a torque that opposes their restart. PEEK or PAI materials therefore allow for a very stable prestress over time.

[0120] PEEK or PAI materials also have particularly low mechanical hysteresis properties which mean that the energy loss, linked to their cyclic deformation and the rolling of the deformable rolling elements 37, is negligible, thus ensuring a connection without significant friction.

[0121] Many thermoplastic materials, including PEEK, PAI, or POM, also have very good tribological properties, allowing the deformable rolling elements 37 to roll directly on a raceway, for example, made of aluminum alloy, without a surface coating. It is then possible to machine the raceway by a simple turning operation, directly in a flange 18 of the planet carrier 11 or in the cylindrical housing of the casing 7, making this rotational guidance function very simple and economical to implement.

[0122] The bearing assembly 36 comprises, for example, a series of deformable rolling elements 37, for example tubular rollers, arranged side by side, all identical ([Fig. 8]). The deformable rolling elements 37 are arranged with clearance on the raceway allowing them to become oval.

[0123] By way of example, the deformable rolling elements 37 are PEEK tubular rollers with a diameter of 7.4 mm, a length of 3.8 mm, and a tubular wall thickness of 0.65 mm, which gives them a diametral stiffness of 60 N / mm. For example, there are 26 tubular rollers made of PEEK material having a stiffness K = 60 N / mm, resulting in a radial stiffness of the bearing of 780 N / mm.

[0124] The cylindrical housing of the casing 7 has a diameter of 72.62 mm + / - 0.015 and the diameter of the shaft of the planet carrier 11 of the reducer 2 is 58 mm + / - 0.01 mm. The nominal clamping force of the tubular rollers (preload) is therefore (72.62-58) / 2-7.4 = 7.31 - 7.4 = 0.09 mm + / - 0.04 mm, which generates a radial force of 60 x 0.09 = 5.4 N, which is a stress level that PEEK can withstand for a virtually indefinite period without risk of relaxation at the operating temperature (maximum permanent stress on the order of 20 MPa).

[0125] Deformable rolling elements 37 made in the form of tubular rollers of polymer material are extremely lightweight compared to steel balls or solid rollers, since their density is approximately six times lower than that of steel and they are hollow instead of solid. Thus, a tubular roller made of polymer material weighs, for example, on the order of 0.1g (0.07g for a PEEK tubular roller), i.e., less than 3g for a set of twenty-six PEEK tubular rollers, and this without adding weight to the raceways since these can be directly machined into the parts. This construction where the deformable rolling elements 37 are hollow polymer rollers, therefore it is possible to make a particularly light geared motor 1.

[0126] According to another example, the deformable rolling elements 37 are metallic tubular rollers. The tubular walls are then thinner because the moduli of elasticity are significantly higher than with polymer materials. These deformable rolling elements 37 are, for example, made of copper alloy (brass or bronze), aluminum alloy, titanium alloy, or steel. However, coatings or surface treatments of the raceways and / or the deformable rolling elements and lubrication are preferably provided to prevent any problems of contact corrosion wear ("fretting corrosion") related to the metal-to-metal interfaces.

[0127] Although the invention has been described with reference to an electric assistance device for a cycle, the invention also applies to any device comprising an electric assistance device including a geared motor, such as an exoskeleton, a portable power device or a robotic arm.

[0128] In addition, the torque transmission device 200 can be used in other types of geared motors or other mechanical assemblies requiring torque transmission between two elements that may have a coaxiality defect.

Claims

Demands

1. Torque transmission device (200) comprising: - an input washer (203a) extending in a plane perpendicular to a central input axis (X1), - an output washer (203c) extending in a plane perpendicular to a central output axis (X3), - an intermediate washer (203b) disposed between the input washer (203a) and the output washer (203c) and extending in a plane perpendicular to an intermediate central axis (X2), - a first pair of links (205a, 205b) coupled on one side to the input washer (203a) and on the other side, opposite the first side, to the intermediate washer (203b), the links (205a, 205b) of the first pair being arranged diametrically opposite with respect to the intermediate central axis (X2), - a second pair of links (207a, 207b) coupled on one side to the intermediate washer (203b) and on the other side, opposite to the first side, to the exit washer (203c),the links (207a, 207b) of the second pair being arranged diametrically opposite with respect to the intermediate central axis (X2) of the intermediate washer (203b), the two pairs of links (205a, 205b and 207a, 207b) being aligned along two respective perpendicular directions (dl, d2) so as to allow torque transmission even in the absence of coaxiality between the central input axis (XI) and the central output axis (X3) in which the intermediate washer (203b) includes a collar (209) extending axially on either side of the center of the intermediate washer (203b) to form a T-shaped section in order to prevent ovalization of said intermediate washer (203b) when the torque transmission device (200) is under load.

2. A torque transmission device (200) according to the preceding claim, wherein the input washer (203a) comprises two transmission shafts (231, 232) extending parallel to the central input shaft (XI) and received in two respective first holes associated with a first end of the respective links (205a, 205b) of the first pair, the intermediate washer (203b) comprising two first transmission shafts (235, 236). extending parallel to its central axis (X2), arranged on a first face of the intermediate washer (203b) and received in two respective second holes associated with a second end of the respective links (205a, 205b) of the first pair, and two second transmission axes (237, 238) extending parallel to its central axis (X2), arranged on a second face of the intermediate washer (203b) and received in two respective first holes associated with the first side of the respective links (207a, 207b) of the second pair, the output washer (203c) comprising two transmission axes (233, 234) extending parallel to the central output axis (X3) and received in two respective second holes associated with the second side of the respective links (207a, 207b) of the second pair.

3. Torque transmission device (200) according to the preceding claim in which the links (205a, 205b) of the first pair are rotatably mounted on one side with the transmission axes (231, 232) of the input washer (203a) and on the other side with the first transmission axes (235, 236) of the intermediate washer (203b) and the links (207a, 207b) of the second pair are rotatably mounted on one side with the second transmission axes (237, 238) of the intermediate washer (203b) and on the other side with the transmission axes (233, 234) of the output washer (203c).

4. Torque transmission device (200) according to any one of the preceding claims wherein the first (235, 236) and second (237, 238) transmission axes of the intermediate washer (203b) are arranged so that the links (205a, 205b, 207a, 207b) of the first and second pairs work in tension in a first direction of torque transmission and in compression in a second direction of torque transmission, opposite to the first direction of torque transmission.

5. Torque transmission device (200) according to any one of claims 1 to 3 wherein the first (235, 236) and second (237, 238) transmission axes of the intermediate washer (203b) are arranged so that for the first (205a, 205b) and second (207a, 207b) link pairs, a first link (205a, 207a) of the pair works in tension and a second link (205b, 207b) of the pair works in compression when a torque is transmitted.

6. Torque transmission device (200) according to any one of the preceding claims wherein the links (205a, 205b, 207a, 207b) are standard chain links.

7. Torque transmission device (200) according to any one of the preceding claims in which the links (205a, 205b, 207a, 207b) are arranged in the thickness formed by the collar (209) of the intermediate washer (203b).

8. Torque transmission device (200) according to any one of the preceding claims wherein the transmission shafts (231, 232, 233, 234, 235, 236, 237, 238) are projecting from the links (205a, 205b, 207a, 207b) and counterbores are provided in the input washer (203a), the intermediate washer (203b) and the output washer (203c) opposite the transmission shafts associated with an adjacent washer to permit the projection of the transmission shafts (231, 232, 233, 234, 235, 236, 237, 238).

9. Electric assistance device (101), in particular for a cycle, comprising: - an electric motor (3) including an output shaft (5) and configured to be mounted around a central shaft (103), - a reduction gear (2) configured to be mounted around the central shaft (103), - a freewheel (25) configured to be mounted around the central shaft (103), - a torque transmission device (200) according to any one of the preceding claims configured to be mounted around the central shaft (103), the reduction gear (2), the freewheel (25) and the torque transmission device (200) forming a torque transmission chain between the output shaft (5) of the electric motor (3) and an output shaft (26) of the electric assistance device (101).

10. Electric assistance device (101) according to the preceding claim in which the reducer (2) comprises an input (5) configured to be rotationally coupled to the output shaft (5) of the electric motor (3) and an output (11) configured to be rotationally coupled to the input washer (203a) of the torque transmission device (200).

11. An electric assistance device (101) according to any one of claims 9 or 10, wherein the freewheel (25) comprises a

12.

13.

14.

15. input configured to be rotationally coupled to the output washer (203c) of the torque transmission device (200) and an output configured to be rotationally coupled to the output shaft (26) of the electric assistance device (101). Electric assistance device (101) according to any one of claims 9 to 11 wherein the electric motor (3), the reducer (2), the torque transmission device (200) and the freewheel (25) are configured to be arranged adjacently along the central axis of the bottom bracket (103). Cycle comprising a frame (100), a central bottom bracket axle (103) rotatably mounted on the frame (100) and an electric assistance device (101) according to any one of claims 9 to 12. Cycle according to the preceding claim in which the electric motor (3) and the reducer (2) are mounted on the frame (100) independently of the central bottom bracket axle (103). Cycle according to claim 13 or 14 in which the central axle (103) of the cycle's bottom bracket is held in position by a single pair of bearings arranged between a frame (100) of the cycle and the central axle (103) of the bottom bracket.

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