ELECTRIC BICYCLE ASSISTANCE DEVICE

Description

[0001] The invention relates to bicycles equipped with an electric assist motor. More particularly, the invention relates to the means for transmitting torque between the assist motor and the transmission chain of the bicycle.

[0002] The particularity of an electrically assisted bicycle is that there must be two power transmission paths: a pedal-wheel path that transmits the torque generated by the cyclist, and a motor-wheel path. These two transmission paths must be able to overlap because, in principle and to comply with regulations, the motor must only provide torque to the wheel to the extent that the cyclist, himself, via the pedals, also provides torque to the wheel.

[0003] Different configurations of electrically assisted bicycles are now available, the present invention relates more particularly to bicycles for which the assistance motor is placed in the central part of the bicycle, in particular being integrated into the crankset.

[0004] When using an electrically assisted bicycle, different distinct functional phases must be considered: pedaling without assistance (phase 1), pedaling with assistance (phase 2), pedaling at a rotation speed higher than the maximum rotation speed generated by the motor (phase 3), sudden stopping of pedaling by the cyclist (phase 4) and back-pedalling (phase 5).

[0005] When pedaling without assistance, the behavior of the bicycle, for the cyclist, must resemble as much as possible that of a bicycle without a motor, that is to say that everything that is necessary for assistance such as the electric motor, the mechanical reducer or any other transmission component must neither add additional friction, nor generate additional noise, nor add additional inertia.

[0006] For this purpose, it is common to insert a freewheel device in series in the transmission path between the motor and the wheel. Traditional bicycles, that is, without electric assistance, are almost all already equipped with a freewheel mechanism between the crankset and the wheel. Therefore, it is necessary to provide two freewheel devices, each placed in one of the two separate transmission paths: motor-wheel and crankset-wheel.

[0007] It should also be noted that there are two main freewheel principles, ratchet freewheels which are light but tend to be noisy and friction freewheels transmitting torque by adhesion with the advantage of being silent, of having a very small engagement angle but having the disadvantages of being heavy and bulky, of requiring very high precision of execution making them quite expensive and having a residual friction torque which is often high in freewheel mode due to the engagement preload exerted on the friction cams or needles.

[0008] When pedaling with assistance (phase 2), the motor-wheel transmission path must be operational. The crankset-wheel transmission path must also be operational.

[0009] In the case of a mid-engine bike, it is common to design the bike so that the motor-to-wheel drivetrain and the crankset-to-wheel drivetrain share as many elements as possible in common. Typically, the motor and pedals drive a common chainring, which is connected to the wheel by a standard chain link. In this case, the motor must be able to connect mechanically to provide assist torque at the crankset or chainring.

[0010] When in this phase of pedaling with assistance, the cyclist wants to pedal faster than the maximum speed of the motor, the motor must disconnect so that the cyclist is not slowed down by the motor (phase 3). This is why a simple freewheel is placed at the output of the motor. In general, these freewheels are of two types, ratchet or roller.

[0011] Each of these freewheel types has disadvantages. A ratchet freewheel can become noisy, while a roller freewheel will be quiet but will be heavy and generate a higher friction torque during the freewheeling phase.

[0012] When the cyclist wants to stop pedaling suddenly (phase 4), for reasons of comfort and safety, it would be necessary that: The reaction time for cutting the engine be very short and that the inertia of the engine and its drive chain be reduced to avoid continuing to drive the cyclist's legs or continuing to move the bicycle forward when the cyclist wants to stop instantly. This is unfortunately not always what happens for bicycles of the prior art.

[0013] For example, in the prior art US 9,616,969 and US 8,757,311, we find, as on most electrically assisted bicycles, the drive plate which is driven in parallel via a first freewheel by the crankset allowing the transmission of the cyclist's pedaling torque and via a second freewheel by the assistance motor allowing the transmission of the assistance torque from the electric motor. With such an arrangement, in the event of a sudden stop of pedaling by the cyclist, the cyclist's legs will not be rotated because the first freewheel of the crankset will disengage and he will be able to stop pedaling immediately. On the other hand, the motor will continue to drive the bicycle while it decelerates, which can be dangerous if the cyclist has to stop urgently.

[0014] In other configurations, for example in EP 2 502 819 the chainring is not driven in parallel by two separate freewheels because the chainring is in direct connection with the cranks so that when the cyclist decides to stop pedaling abruptly, he must also stop the entire engine transmission chain. And since stopping this engine transmission path takes a certain amount of time, the pedals will continue to turn during this short period of time and drive the cyclist's legs. This is an unpleasant sensation that affects the comfort and quality of the cyclist's experience. In addition, when the cyclist suddenly stops pedaling, he can create a very high braking torque on the engine transmission chain which can lead to its degradation or breakage.

[0015] Finally, there is a final functional phase of using an electrically assisted bicycle that poses a problem in certain configurations (phase 5). The first of these configurations is when the cyclist wants to pedal backward to reposition his pedals, for example when approaching a bend so that they do not rub against the road or when the cyclist wants to start and position his call foot in a substantially horizontal position.

[0016] There is a second configuration during which reverse gear occurs, which is when maneuvering your bike to park it. Indeed, if the bike moves in reverse, the rear wheel transmission freewheel will lock and drive the pedals in reverse. During this phase, which can be called back-pedaling, electric bikes with a simple freewheel, for example a ratchet, in the motor-wheel transmission path, will see this freewheel also lock in reverse and consequently drive the motor in reverse. The rotation of the motor in reverse generates a high friction torque and a very high equivalent inertia.In this case, the cyclist is able to provide a high backpedal torque, which will cause a high negative angular acceleration and therefore a very high negative torque due to the significant equivalent inertia of the motor, which risks destroying the gears of the geared motor. On the other hand, on this type of motorization, the reduction ratio between the rotation speed of the motor and the rotation speed of the bottom bracket shaft is of the order of 100, which inevitably reduces the efficiency of this type of reducer, the reducer can even become irreversible and lock up as soon as the slightest lubrication or wear defect appears and this is why patent WO 2016 / 128789 incorporates a torque limiter which allows the motor to be disconnected in the event of excessive torque to avoid breaking the teeth.

[0017] Furthermore, DE 10 2014 221514 A1 describes an electrical assistance device for a bicycle comprising a shaft rotatably connected to a pair of cranks and comprising an electric motor.

[0018] This backpedaling phase is also often implemented in the store when purchasing the bike. Indeed, it is common for an experienced cyclist to turn the cranks backwards to estimate the friction losses of the drive chain (including the friction of the bottom bracket seals and bearings, the chain and its pulleys as well as the rear freewheel bearings), which allows the quality of the transmission friction to be estimated.When this experiment is carried out on a single freewheel e-bike, the freewheel locks in reverse and drives the motor in reverse, as the reduction ratio between the motor and the crankset is high, the motor is therefore driven in reverse at a high rotation speed, thus increasing the sensation of inertia and generating a high friction torque due to the mechanical and electromagnetic friction of the motor which is multiplied by the high reduction ratio as well as by the inverse of the efficiency of the reducer, thus making this reverse experiment very negative.

[0019] The freewheels used in prior art electrically assisted bicycles are simple freewheels that lock when a positive motor torque is applied to the input element (assist motor) and which is then transmitted to the output element (the bottom bracket shaft). On the other hand, the freewheel does not allow a negative torque to be transmitted in the opposite direction to the same input element and will then start to rotate freely in this freewheel direction. Thus, everything happens as desired when the direction of rotation is the normal direction of use, on the other hand, when the direction of rotation is reversed on the output element, the bottom bracket shaft, everything is reversed, that is to say, the freewheel will lock and transmit torque in reverse, thus driving the entire transmission chain in reverse, which has the disadvantages listed above.

[0020] The objective of the invention is to provide an electrically assisted bicycle that does not have the disadvantages of prior art bicycles. In particular, the objective of the invention is to provide an electrically assisted bicycle device that operates optimally in the various functional phases described above. The objective of the invention is also to provide an assistance device that operates silently and with extremely low friction. The objective of the invention is also to provide an assistance device that is as small and light as possible.

[0021] The objective of the invention is achieved by providing an electric assistance device which comprises a disengageable connection device which allows the automatic disengagement of the motor in the backpedaling phase without receiving any resistance and without risking breaking the reducer during this phase without needing to add a torque limiter as in the prior art cited above.

[0022] The object of the invention is achieved by providing an electrical assistance device for a bicycle according to claim 1.

[0023] The objective of the invention is achieved in particular by providing an electric assistance device for a bicycle comprising a shaft which can be driven in rotation in a positive direction simultaneously by a pair of cranks and by an electric motor, said device comprising a clutch mechanism which is placed between the motor and the shaft, comprising a closed position in which the motor and the shaft are integral in rotation in a bidirectional manner, and an open position in which a rotation of the shaft in a negative direction does not cause the rotation of the motor, said open position being effective when the motor has a zero rotation speed.

[0024] It will be noted that in the context of the invention, a difference in principle is made between a freewheel and a clutch mechanism. Indeed, a clutch mechanism is a mechanical coupling device which, when in the "closed" position, makes a first element rotate in both directions with a second element. A freewheel, for its part, allows both the driving of element 2 (driven element) by element 1 (driving element) in a first direction of relative rotation, called the positive direction; and allows a relative rotation without drive, in the positive direction of element 2 with respect to element 1. In the latter case, element 2 rotates faster, in the positive direction, than element 1. On the other hand, its specific construction also allows the driving in the negative direction of relative rotation of element 1, by element 2, which then becomes the driving element.

[0025] The object of the invention is also achieved by providing an electrical assistance device having one or more of the following characteristics, in any technically acceptable combination: the cranks are fixed to both ends of the shaft, a reducer is placed between the motor and the shaft so as to reduce the rotational speed of the motor, the reducer comprises a gear train, the reducer is of the epicyclic type, the connection mechanism comprises a freewheel is placed between the motor and the shaft, said freewheel allowing the motor to drive the shaft in the positive direction and the shaft to drive the motor in the negative direction, the freewheel is placed between the reducer and the shaft and in that the freewheel comprises locking parts moving (in particular pivoting pawls) between an "engaged" position and a "disengaged" position, and the distal ends of which are capable of engaging with teeth secured to the shaft when the pawls are in the lowered position.

[0026] The objective of the invention is further achieved by an electrical assistance method for a bicycle equipped with a device as described in the preceding paragraphs and further comprising a microcontroller which controls the rotation of the motor in a first direction, called the positive direction, when assistance is desired, said positive direction being such that it generates the forward movement of the bicycle; characterized in that, when the rotation speed of the cranks is zero or when they rotate in the direction opposite to the forward movement of the bicycle, the microcontroller controls the rotation of the motor in the direction opposite to the first direction, for a short period of time. This short period of time is less than a few seconds, preferably less than one second. This is in fact to generate the rotation of a few degrees to ensure the relative rotation of the synchronizing ring with respect to the drive ring.

[0027] In one embodiment of the invention, the connection mechanism comprises a disengageable freewheel. One way of achieving this result is to equip the connection mechanism with means for holding the pawls of the freewheel in the disengaged position. These means for holding the pawls in the disengaged position may comprise a pawl synchronization ring and a friction ring, integral with one another, said friction ring coming into contact with a fixed part of the assistance device so as to generate a friction torque during its rotation. The friction ring is an elastically deformable ring bearing prestressed on the fixed part of the device on at least two zones regularly distributed on the circumference of the fixed part. The fixed part may for example be a cylindrical barrel.When the friction ring rotates in the positive direction, it generates a torque which tends to engage the pawls and conversely, when it rotates in the negative direction, the friction ring generates an opposite torque which tends to disengage the pawls.

[0028] In this first embodiment configuration of the invention, when the connection mechanism is in the disconnected state (state 3), the freewheel is no longer operational. This will correspond to functional phases 1, 3 and 4, as described above.

[0029] The disengageable freewheel system according to the invention is a more advanced freewheel which is connected to three bodies (instead of only two in a simple freewheel), there is an input and an output but also a third reference body linked to the fixed frame of the bicycle, which will make it possible to manage the locking / unlocking function of the freewheel at a speed condition relative to the frame of the bicycle.

[0030] So, when the crankset turns in the normal direction of rotation, the freewheel will operate like a simple freewheel. On the other hand, as soon as the assistance motor turns in reverse, the freewheel will tend to disconnect, preventing the motor from being driven into rotation in reverse by the crankset shaft.

[0031] This freewheel system can be placed at different positions in the transmission chain, it can be located very far upstream at the output of the motor shaft, in which case the freewheel will have to transmit a very low torque but at a high rotation speed, or located downstream of the reducer at the location of the mechanical connection with the pedal shaft, in which case the rotation speed will be reduced but with a significantly higher level of torque to be transmitted. This latter embodiment corresponds to the first embodiment of the invention which will be described in detail below.

[0032] In another configuration of the invention, the connection mechanism comprises a freewheel and a clutch. The clutch and the freewheel are then not necessarily adjacent in the motor-wheel transmission path. This configuration corresponds to the second embodiment of the invention.

[0033] In this other embodiment of the invention, the clutch mechanism may be of the centrifugal clutch type which moves from the closed (engaged) position to the open (disengaged) position when the rotational speed of the engine is lower than a given speed V1. One way of producing such a clutch mechanism is to make a centrifugal clutch which comprises a plurality of sectors, each equipped with friction pads capable of coming into contact with a friction cylinder. In the open position, the friction pads are not in contact with the friction cylinder, while in the closed position, the sectors, subjected to centrifugal force, exert a force on the friction cylinder such that the sectors and the friction cylinder are integral in rotation and the engine can transmit a non-zero torque to the drive shaft.

[0034] Such a clutch mechanism can be placed at different locations within the motor-wheel power transmission path. In one embodiment of the invention the clutch mechanism is placed between the motor and the reduction gear.

[0035] The speed V1 is chosen such that V1 / R is less than 25 rpm, R being the reduction ratio of the reducer.

[0036] The invention will be better understood in light of the following description. The drawing attached thereto comprises; There figure 1 is an overview of a bicycle incorporating an electric assistance system according to an example of the invention. The figure 2 is a view of an enlargement of part of the figure 1 , centered on the bottom bracket. The figure 3 is a perspective view of the device according to a first embodiment of the invention. The figure 4 is an exploded and partial perspective view of the device of the figure 3 . There figure 5 is a longitudinal sectional view of the device of the figure 3 . THE figures 6 et 7 are respectively cross-sectional views DD and BB of the device of the figure 3 when the clutch mechanism is in the closed position. The figures 8 et 9 are respectively cross-sectional views DD and BB of the device of the figure 3 when the clutch mechanism is in the open position. The figure 10 is a cross-sectional view along plane EE. The figure 11 is a longitudinal sectional view of a device according to a second embodiment of the invention. figure 12 is an exploded and partial perspective view of the device of the figure 11 . There figure 13 is a detail view of the figure 12 . There figure 14 is a cross-sectional view FF, when the clutch mechanism is in the closed position. The figure 15 is a cross-sectional view FF, when the clutch mechanism is in the open position. There figure 1 illustrates an electrically assisted bicycle 1 incorporating an assistance system according to the present invention. In known manner, this bicycle comprises a frame on which two wheels are fixed. The rear wheel 15 is the drive wheel and is driven by the crankset consisting of a pair of cranks 16 and two pedals 17. The right crank comprises a star 161 whose ends are used to fix a toothed chainring 18. The transmission chain 19.

[0037] There figure 2 shows the bottom bracket 2 which is an integral part of the frame and connects the various tubes thereof. The assistance motor 3 is housed inside an element forming the frame of the cycle. It can for example be housed inside the seat tube 12, or in the down tube 13, or in one of the bases 14 connecting the crankset to the hub of the rear wheel 5. Alternatively, the motor can be attached to the frame, for example by being fixed to one of these tubes 12, 13, 14 or by being fixed to the bottom bracket 2.

[0038] The motor 3 is an electric motor. It is preferably powered by a battery attached to the frame, or housed inside the frame, or worn by the user. The motor 3 rotates a motor member 31.

[0039] Preferably, the motor member 31 is driven in rotation about the same axis of rotation as the output of the motor. This axis of rotation is perpendicular to that about which the drive shaft 4 of the crankset rotates. The axis of rotation of the crankset 4 and the axis of rotation of the motor 3 correspond respectively to the axes X and Z of the orthogonal reference frame illustrated in figure 2 . Thus, the axis of rotation of the motor 3 is perpendicular to that of the shaft 4 of the pedal assembly.

[0040] A casing 21 is housed inside the housing 2, this casing is closed by a cover 22. The shaft 4 of the pedal assembly passes right through the casing 21. The figure 3 shows the casing 21 before it is inserted into the bottom bracket. At each of its ends, the shaft 4 comprises means 41 allowing the fixing of the cranks 17. In the case described here, these means consist of splines.

[0041] The casing 21 has a through opening allowing the passage of the shaft 4 of the pedal assembly. In order to allow precise guidance and good rigidity of the shaft 4 inside the housing 2, two rolling members 43, 44 are provided, typically ball bearings. These ball bearings are visible at figure 5 .

[0042] The housing 2 and the casing 21 also have an upper passage 23 allowing the motor member 31 to penetrate inside the housing 2.

[0043] A reducer 5 allows the forces to be transmitted from the motor member 31 to the shaft 4 of the pedal assembly. The reducer 5 is of the double satellite epicyclic type, in order to allow a high reduction ratio in a reduced volume.

[0044] The driving member 31 is a pinion which meshes with a movable crown 51 rotating around an axis identical to that X of the shaft 4.

[0045] Preferably, the driving member 31 is a bevel pinion and the movable crown 51 carries a bevel toothing complementary to that of the driving member 31.

[0046] The crown 51 is mounted in free rotation around the shaft 4 of the crankset. For this purpose, rolling members, such as ball bearings 511, 512, may be provided, arranged between the shaft 4 and the crown 51.

[0047] The movable crown 51 is integral in rotation with a planet carrier 52. Preferably, the movable crown 51 and the planet carrier 52 form a single part. Alternatively, it may be provided that the crown and the planet carrier are separate parts secured to each other.

[0048] The planet carrier 52 has housings configured to accommodate satellites 53. These satellites 53 are preferably at least three in number and are configured to move in the same plane perpendicular to the axis X of the shaft 4.

[0049] In this non-limiting example, each satellite is integral with a shaft mounted in rotation in a housing carried by the planet carrier 52. For this purpose, bearings are provided, typically ball bearings mounted between the shaft of the satellite and the housing in order to minimize the friction losses of this reducer.

[0050] Each satellite 53 comprises two pinions 531, 532. The two pinions 531, 532 of each satellite 53 are placed parallel to each other and are integral with each other in their movement.

[0051] A first pinion 531 meshes with a fixed crown 54 secured to the casing 21 and therefore secured to the frame of the cycle. This fixed crown 54 carries internal teeth. A second pinion 532 meshes with teeth carried by a second crown 55. The second crown 55 is secured to a drive part 56 which constitutes the output of the reducer 5. The rotation speed of the electric motor which can be a few thousand revolutions per minute is reduced until the output of the reducer to less than 100 rpm. For example, in the configuration drawn, the reduction ratio of the bevel gear is 5 followed by the epicyclic reducer which has a ratio of 21, i.e. a total ratio of 105 between the speed of the motor and the output speed of the reducer.

[0052] The drive part 56 is connected to the shaft 4 via the connection mechanism according to the invention. This comprises a disengageable freewheel 6, which comprises two pawls 61 and a synchronizing ring 62. The pawls 61 are pivotally mounted inside a housing 561 provided in the drive part 56. They are held there by means of a cage 57 fixed to the drive part 56 by four screws. The pawls 61 pivot between an “engaged” position shown in figure 7 , in which their distal end is engaged with one of the teeth 42 provided on the drive shaft 4, and a “disengaged” position shown in figure 9 .

[0053] A synchronizing ring 62 synchronizes the tilting movement of the two pawls 61. It is pivotally mounted around the X axis by means of a flange 562 which guides it. The synchronizing ring 62 has a small amplitude of rotation relative to the drive ring 56. In fact, the synchronizing ring is fixed to the pawls at a distance of a few millimeters from their pivot point.

[0054] The two pawls 61 are opposed at 180° allowing the transmitted forces to be balanced by transmitting, in theory, a pure torque without radial component, and by substantially dividing by two, the force transmitted by each of the pawls. The pawls preferably have one end with a beak engaging with teeth 42 arranged on the shaft 4. Thus, as soon as the end of the pawl comes into contact with the shaft 4, the pawl will then continue its travel to automatically engage at the bottom of the tooth despite the friction opposing its engagement, allowing them to remain perfectly stable once engaged, the synchronization ring 62 mounted as a pivot on the output of the reducer makes it possible to synchronize the rotation of the latter so that they engage well simultaneously. figures 7 And 9 show in section BB, the two pawls 61, as well as the synchronizing ring 62, in the engaged position, respectively, in the disengaged position.

[0055] The connection mechanism 8 also comprises means which make it possible to control the pawls 61, and in particular to keep them in the disengaged position. These means comprise a friction ring 72 and two pins 73. The figures 4 , 5 And 10show the geometry and operation of the friction ring 72. The friction ring is an elastically deformable ring which comes into prestressed support on a fixed part of the device on at least two zones. In the embodiment shown, the fixed part is a cylindrical barrel 221, projecting from the inner face of the cover 22. This ring comprises two diametrically opposed beads 721 arranged on the inner face of the ring. These beads are intended to slide on the outer surface of the barrel 221 coming from the cover 22. The friction ring 72 is integral in rotation with the synchronization ring 62 by means of two pins 73 inserted into two diametrically opposed radially oblong holes. To ensure a certain tightening of the friction ring on the barrel 221, the internal diameter between the two beads is, in the free state, slightly less than the external diameter of the barrel 221 by approximately 0.5 mm.The installation of the friction ring will generate a certain ovalization of the latter, the geometry of this friction ring must be dimensioned to generate two diametrically opposed radial forces during its ovalization of 0.5 mm without generating high stresses on the latter so that it can withstand this level of stress without creep during the entire service life of the product. A PBT or POM type material can be chosen to produce the ring because this friction part must have very good wear resistance, and very good elasticity as well as good behavior at the operating temperature to guarantee very good stability of its tightening preload over the entire service life of the product.

[0056] The diametrical tightening of this friction ring 72 on the barrel 221 will induce a stable and controlled friction torque opposing the rotation of the latter relative to the barrel 221 itself linked to the housing of the frame 1.

[0057] For example, very good operation is obtained by sizing the friction ring to obtain two diametrically opposed radial forces at the friction beads of approximately 5N under a diametrical tightening of 0.5 mm with a stress level of less than 10 MPa on the latter, thus avoiding any risk of relaxation or creep over time, these radial forces generated on the 35 mm diameter barrel make it possible to generate a friction torque of approximately 25 mN.m in both directions of rotation, largely sufficient to engage and disengage the pawls, while generating a sufficiently low torque not to induce a significant loss of power when the latter slides, since this friction torque of 25 mN.m only generates a loss of 0.2 Watt at 80 revolutions per minute, which is negligible compared to the assistance power and which does not allow the area of ​​the beads in contact with the barrel 221 to heat up and wear out.The operation of the clutch mechanism will now be described in detail.

[0058] When the output of the reducer, i.e. the drive ring 56, is driven in the positive direction (normal pedaling direction marked with a + sign in the figures), the synchronizing ring 62 will be rotated in the same direction and it will drive with it the friction ring 72, the friction of the two beads 721 on the barrel of the cover 22 will generate a friction torque which will be transmitted to the synchronizing ring 62. As the latter has a certain amplitude of relative rotation with respect to the drive ring 56, the friction torque will have the effect of forcing it in the direction opposite to the movement and therefore to make it rotate backwards relative to the output of the reducer. This relative rotation tends to pivot the pawls in their direction of engagement causing the rotational connection of the motor with the drive shaft 4. The freewheel is then engaged. This state of engagement of the freewheel is shown in figures 6 et 7 This corresponds to state 1 of the connection mechanism, called the assistance state, or to the assisted pedaling mode (phase 2) when the cyclist pedals less quickly than the assistance provided by the motor.

[0059] In the case where the cyclist increases his pedaling frequency until he exceeds the reduction gear output speed (phase 3), the teeth 42 of the shaft 4 will lift the pawls 61 at each passage of teeth and no torque will be transmitted between the drive ring and the shaft 4. The freewheel is then sliding. This is the classic operation of a freewheel. This corresponds to state 2, called the freewheel state, of the connection mechanism.We can note that when the pawl is going to be lifted by a tooth 42 of the shaft 4, the synchronization ring 62 and the friction ring 72 will then take a little advance relative to the drive ring but the friction torque of the friction ring caused by the friction of the beads 721 on the cover 22 will remain substantially constant causing the immediate re-engagement of the pawls as soon as the tooth 42 has passed, thus in this freewheel phase, the friction ring acts in a similar way to the return springs of conventional pawl freewheels.

[0060] Now, if the cyclist decides to backpedal (phase 5), the shaft 4 which rotates in the negative direction will drive, via the pawls, the drive ring 56 and the friction ring 72. The friction of the beads 721 with the cover 221 generates a friction torque which opposes the rotation and rotates the synchronizing ring relative to the drive ring until the two pawls lift making motor coupling impossible. The connection mechanism is then in state 3, called the disconnection state, as shown in figures 8 et 9 .

[0061] In fact, this disengagement of the pawls is linked to the relative direction of rotation between the crown of the reducer and the cover of the bottom bracket (fixed), so it will be possible to control the engagement of the pawls by controlling the direction of rotation of the motor so that it is sufficient to order a small reverse rotation of the motor to pivot the drive ring 56 at least a few degrees backwards, that is to say in the negative direction, to disengage the freewheel.

[0062] In practice, if the cyclist is moving forward with motor assistance (phase 2), the pawls are then engaged. From this state, if the cyclist decides to suddenly reverse (phase 5), or to stop pedaling in order to be able to stop (phase 4), as the pawls have engaging beaks, it may be possible that the pawls cannot easily disengage despite the friction torque applied to the synchronizing ring, for this it is desirable that a control microcontroller (not shown) can detect this event either by a pedaling torque sensor (not shown) which suddenly becomes zero or negative, or by a zero crank rotation speed detected by an angular sensor (not shown),either by a strong angular deceleration or by a reversal of the direction of rotation of the motor or the pedals and then order a reverse rotation of the motor with a rear acceleration greater than that of the cyclist for a fraction of a turn which will disengage the pawls and allow them to lift, this reverse gear can be stopped almost immediately and the freewheel will then remain in this stable disengaged state without inducing the slightest friction or the slightest additional noise for the cyclist.,

[0063] Finally, when the cyclist decides to do without assistance or the battery is exhausted (phase 1), the microcontroller will order a reverse rotation of the motor in order to place the freewheel in the disengaged state. Thus, the presence of the assistance device does not induce any additional friction or noise.

[0064] In an alternative embodiment of the first embodiment of the invention, a spring placed between the drive ring 56 and the synchronizing ring 62, maintains the pawls in the disengaged position, for an absence of rotation or a negative rotation of the friction ring. The return torque of the spring must be less than the friction torque of the friction ring so that a rotation of the latter in the positive direction causes the pawls to engage. Thus, if the cyclist backpedals, he will disengage the pawls which will find, thanks to the spring, a stable disengaged position (state 3). In this alternative, controlling the motor in reverse is not necessary.

[0065] THE figures 11 à 15 describe a second embodiment of the invention in which the connection mechanism 8 comprises a freewheel 6 and a separate clutch mechanism 7. In addition, the freewheel and clutch are not directly adjacent in the motor-wheel power transmission path. Indeed, as will be seen later, a reduction gear 5 is inserted between the clutch and the freewheel. This embodiment also differs in that the assistance motor 3 is a motor concentric with the drive shaft 4. It is understood that the type and arrangement of the motor are not limiting within the scope of the invention and that the first embodiment described above could very well be equipped with a motor concentric with the drive shaft.

[0066] There figure 11 shows in longitudinal section, the complete block before it is inserted inside the bottom bracket of the bicycle as shown in the figure 2 All of the elements are housed inside a casing 21 closed by a cover 22. The motor 3 drives the motor member 31 in rotation. The latter comprises three pins 311 projecting from its front surface which allow the reduction gear 5 to be driven through a clutch mechanism 7, the operation of which will be explained below.

[0067] The reducer 5 in this embodiment is substantially identical to that described with the first embodiment. It will not be described again in detail. It is a reducer having a reduction ratio R which is equal to 41 in this second embodiment. The input of the reducer is via the planet carrier 52 and the output of the reducer 5 is constituted by a drive ring 56 which drives the shaft 4 through a single freewheel 6. This is a single ratchet freewheel substantially identical to that described for the first embodiment of the invention but whose ratchets are engaged in a traditional manner each by a small spring in their engagement position.

[0068] The clutch mechanism 7 comprises a clutch ring 77 and three sectors 74 housed inside said ring and distributed over the entire circumference. The clutch ring 77 is integral with the planet carrier 52. Each sector is pivotally mounted on a pin 311 and is constrained by a return spring 75 which connects it to another pin. A friction pad 76 covers, at least partially, the periphery of each of the sectors 74. The springs 75 are chosen in such a way that when the clutch 7 is not rotating, the return force of the springs 75 constrains the sectors 74 towards the shaft 4 as can be seen in figure 14 .

[0069] When the motor is not rotating, or rotating at a low speed, there is no contact, or not sufficient friction, between the friction pads 76 and the friction cylinder 771 of the clutch ring 77, the clutch is open. The motor 3 is then no longer rotationally integral with the reducer 5, and consequently the drive shaft, and this, in both directions of rotation.

[0070] When the engine starts at a sufficiently high speed, it drives the sectors, which, subjected to centrifugal force, pivot around the pins 311. The centrifugal force exerted on the sectors then exceeds the restoring force of the springs and the friction pads are applied against the friction cylinder 771 of the clutch ring. The engine speed is then V1, which is the speed at which slipping begins. The centrifugal forces exerted on the sectors increase with the square of the speed, the forces generated on the friction pad will very quickly allow the clutch to stop the slipping of the latter relative to the friction cylinder. The engine speed is then V2, that is to say the speed at which slipping ends at the maximum torque of the engine. We are then in the configuration described in figure 15This configuration corresponds to the closed position of the clutch mechanism in which the motor is completely secured to the reducer 5 and the drive shaft 4.

[0071] The operation of a cycle equipped with an assistance device according to the second embodiment of the invention is detailed below.

[0072] When the cyclist does not want assistance or the battery is exhausted (phase 1), the centrifugal clutch 7 is opened and the motor 3 is disconnected from the drive shaft 4. The motor-wheel transmission path is broken. This corresponds to state 3 of the connection mechanism 8. Consequently, the motor cannot be damaged in any way by rotating the pedals, regardless of the speed at which they are rotated.

[0073] When the cyclist wishes to benefit from assistance and the motor is running, rotating the motor at a speed higher than a given speed V2, for example 500 revolutions per minute, puts the clutch in the closed position. Motor 3 contributes to driving shaft 4 with the pedals (phase 2). This corresponds to state 1 of the connection mechanism. If the cyclist pedals at a faster cadence than motor 3 is able to provide to shaft 4, then freewheel 6 disconnects. In this configuration, the motor no longer contributes to driving the shaft (phase 3), the connection mechanism is in state 2.

[0074] When the cyclist stops pedaling (phase 4), a pedaling cadence sensor informs the microcontroller, which stops the motor. As soon as the motor's rotation falls below the value V1, clutch 7 switches to the open configuration.

[0075] If, during use with assistance, the cyclist reverses with the pedals (phase 5), the passage of the rotation speed of the pedals through a zero speed (and consequently lower than V1) has the effect, as for phase 4, of opening the clutch and disconnecting the motor. The connection mechanism goes to state 3. In these last two cases, state 3 of the connection mechanism is an unstable transient state because as soon as the motor is again driven at a speed V1, the connection mechanism returns to state 1.

[0076] In practice, the speed V1 is chosen in such a way that when the motor is running at speed V1, the shaft 4, whose speed is V1 / R, is between 1 and 25 rpm. These speeds do not correspond to usual pedaling cadences, which are between 30 and 110 rpm. In the example shown here, the ratio of the reducer R being equal to 41, the speed V1 is between 41 and 1025 rpm.

[0077] The designer must determine the mechanical characteristics of the sectors and springs so that when the motor is running at speed V2, 100% of the maximum torque of the motor is transmitted, i.e. there is no more slippage. Preferably, speed V2 corresponds to a speed of shaft 4, V2 / R, of approximately 40 rpm. In the example shown, V2 is approximately 1640 rpm. When the motor runs at a speed higher than V2, it is ensured that there will be no slippage, i.e. slippage and therefore heating and energy loss.

Claims

1. Electrical assistance device for a bicycle comprising a shaft (4) secured in rotation with a pair of cranks (16) and that can be driven in rotation in a positive direction by an electric motor (3), characterized in that a connection mechanism (8) is placed between the motor (3) and the shaft (4), which connection mechanism comprising either a declutchable freewheel, or a freewheel and a clutch, such that the connection mechanism is configured to have at least three distinct states: - State 1, called assistance state, in which the motor transmits a torque to the shaft (4) via a drive piece which revolves at the same speed as the shaft (4), - State 2, called freewheel state, in which the rotation of the shaft (4) in the positive direction is greater than that of the drive piece (56), - State 3, called disconnection state, in which a rotation in the positive direction or in the negative direction of the shaft (4) cannot drive the rotation of the motor (3).

2. Device according to the preceding claim, characterized in that the cranks (16) are fixed to the two ends of the shaft (4).

3. Device according to one of the preceding claims, characterized in that a reducing gear (5) is placed between the motor (3) and the shaft (4) so as to reduce the speed of rotation of the motor.

4. Device according to the preceding claim, characterized in that the reducing gear (5) comprises a gear train.

5. Device according to the preceding claim, characterized in that the reducing gear (5) is a reducing gear of epicyclic type.

6. Device according to one of the preceding claims, characterized in that the connection mechanism comprises blocking pieces that are displaced between an "engaged" position and a "disengaged" position and means that make it possible to keep the blocking pieces (61) in disengaged position.

7. Device according to the preceding claim, characterized in that the blocking pieces are pivoting ratchets (61) whose distal ends are capable of meshing with teeth secured to the shaft (4) when the ratchets are in engaged position.

8. Device according to the preceding claim, characterized in that the means making it possible to keep the ratchets in disengaged position comprise a synchronization ring of the ratchets (61) and a friction ring (73), secured to one another, said friction ring (73) coming into contact with a fixed part of the assistance device so as to generate a friction torque during its rotation.

9. Device according to the preceding claim, characterized in that, in a rotation of the friction ring in the positive direction, the latter generates a torque which tends to engage the ratchets and, conversely, in a rotation in the negative direction, the friction ring generates an opposite torque which tends to disengage the ratchets.

10. Device according to one of the two preceding claims, characterized in that the friction ring (73) is a ring that is elastically deformable by prestressed bearing on the fixed part of the device on at least two zones.

11. Device according to one of Claims 1 to 5, characterized in that the connection mechanism comprises a freewheel and a clutch (7) of centrifugal clutch type which switches from the closed position to the open position when the speed of rotation of the motor (3) is less than a given speed V1.

12. Device according to the preceding claim, characterized in that the clutch mechanism comprises a plurality of segments, each equipped with friction pads that can come into contact with a friction cylinder (771) and in that in open position, the friction pads (76) are not in contact with the friction cylinder (771), while in closed position, the segments (74), subject to the centrifugal force, exert an effort on the friction cylinder such that segments (74) and friction cylinder (771) are secured in rotation and that the motor (3) can transmit a non-zero torque to the drive shaft.

13. Device according to one of the preceding claims in combination with claim 3 , characterized in that the clutch mechanism (7) is placed between the motor (3) and the reducing gear (5).

14. Electrical assistance method for a bicycle equipped with a device according to one of Claims 1 to 12, and comprising a microcontroller which controls the rotation of the motor (3) in a first direction, called positive direction, when an assistance is desired by the user, said positive direction being such that it generates the forward motion of the bicycle; characterized in that, when the speed of rotation of the cranks (16) is zero or when the latter revolve in the direction opposite to the forward motion of the bicycle, the microcontroller controls the rotation of the motor (3) in the direction opposite to the first direction, during a short time period.

15. Electrical assistance method for a bicycle equipped with a device according to claim 13, wherein the reducing gear (5) has a reduction ratio R, characterized in that when the speed of rotation of the motor (3) is less than V1, the clutch mechanism is in open position, said speed V1 being such that V1 / R < 25 rpm.