The present invention concerns electric assist devices for bicycles and bicycles equipped with such devices.
In this field, a certain number of devices available on the market are known.
Some of these devices use an electric machine placed in the hub of one of the wheels of the bicycle. This electric machine drives the wheel directly or via a reducer system. This type of device has the disadvantage of a high mass, this mass being moreover located at the level of the wheel, which means that the cyclist is very sensitive to it. Moreover, if the wheel must be removed, for example to change the tyre or to repair a puncture, removing the wheel is complicated by the presence of electrical connections that are necessary for powering the electric machine and specific fixings of the hub that are necessary to transfer the drive torque.
Other devices use a motor-gearbox driving the pedals of the bicycle and therefore using the existing transmission of the bicycle. This type of device has the disadvantage of deeply impacting the architecture of the bicycle so that in particular the frames of the bicycles must be specifically designed to accommodate these devices.
The document DE-20314210-U1 describes a principle of driving a bicycle by an electric motor in which a drive pinion meshes with teeth fastened to the front rim of the bicycle, said teeth being internal teeth, i.e. the teeth point toward the wheel axis. A disadvantage of this system is that the teeth on the rim are liable to retain stones.
An object of the invention is therefore to propose an electric assist device for a bicycle as well as a bicycle equipped with said device that eliminate some or all of these problems.
To this end the invention proposes an electrical assist device for a bicycle, said device comprising:
- an electric machine comprising a rotor,
- a drive pinion driven by the rotor of the electric machine,
- fixing means for fixing the electric machine to the bicycle in the vicinity of a tyre of a wheel of said bicycle,
- a source of electrical energy for powering the electric machine,
- means for controlling the electric machine,
said device being characterized in that the drive pinion includes teeth intended to mesh tangentially with complementary teeth fastened to said tyre, the teeth of the drive pinion being helicoidal teeth.
This type of transmission using pinions and teeth is referred to as “positive” transmission in contrast to friction transmission systems such as roller systems. A positive transmission is not dependent on the coefficient of friction and therefore relatively insensitive to inclement weather or to wear of the components used.
The electric machine is preferably a permanent magnet brushless three-phase synchronous motor. The rotor is preferably an external rotor.
The teeth of the drive pinion are preferably asymmetrical teeth comprising driving faces and non-driving faces, the aperture angle of the driving faces being smaller than the aperture angle of the non-driving faces.
The drive pinion is preferably driven by the electric machine via a freewheel mechanism so that the tyre does not drive the electric machine when the bicycle is moving forward.
Said device more preferably further comprises a display and control unit connected to the control means of the electric machine and adapted to constitute an interface between the cyclist and the control means.
Said device more preferably further comprises a pedalling sensor connected to the control means of the electric machine.
The fixing means more preferably comprise an oscillating arm articulated to a support, the support being intended to be fastened to the bicycle and the oscillating arm carrying the electric machine so that the drive force transmitted to the tyre by the drive pinion generates an additional radial pressure in the gears.
Elastic means more preferably prestress the orientation of the oscillating arm so that, in the absence of drive force, the drive pinion presses radially against the tyre with a non-zero bearing force.
The fixing means more preferably define at least two positions of the electric machine relative to the tyre, said at least two positions comprising a working position in which the drive pinion meshes with the teeth of the tyre and a folded position in which the drive pinion is held away from the tyre.
The invention also concerns an electric assist kit for a bicycle comprising the electric assist device as described above, said electric assist kit further comprising a tyre, said tyre being a pneumatic tyre including said complementary teeth.
Said complementary teeth are preferably placed on a flank of the pneumatic tyre.
Said complementary teeth are more preferably asymmetric teeth comprising driving faces and non-driving faces, the aperture angle of the driving faces being smaller than the aperture angle of the non-driving faces.
The pitch of the complementary teeth is more preferably between 1.8 mm and 5.5 mm and preferably between 1.8 mm and 2.5 mm.
The invention also concerns a bicycle with electric assistance comprising an electric assist kit as described above.
The electric assist kit is preferably installed on the rear wheel of the bicycle.
Other features and advantages of the invention will become apparent thanks to the description of preferred embodiments. The figures respectively represent:
FIG. 1: diagrammatic side view of an electrically assisted bicycle in accordance with a first embodiment of the invention.
FIG. 2: more detailed diagrammatic view of a second embodiment of an electrically assisted bicycle in accordance with the invention.
FIG. 3: diagrammatic sectional view showing the cooperation of the electric machine with the tyre of an electrically assisted bicycle in accordance with the invention.
FIG. 4: detail sectional view of the meshing of the drive pinion with the teeth of the tyre in accordance with a preferred embodiment of the invention.
FIG. 5: diagrammatic sectional detail view of the teeth of the drive pinion from FIG. 4.
FIG. 6: diagrammatic sectional detail view of teeth of a preferred embodiment of a tyre in accordance with the invention.
FIG. 7: side view of a drive pinion with helicoidal teeth in accordance with a preferred embodiment of the device of the invention.
FIG. 8: sectional perspective view of a pneumatic tyre equipping a bicycle in accordance with the invention.
FIG. 9: diagrammatic perspective view of a detail of a preferred embodiment of the electric assist device in accordance with the invention.
FIG. 10: diagrammatic perspective view of the FIG. 9 embodiment from a different point of view.
The figures represent different general and detailed views of preferred embodiments of an electric assist device and an electrically assisted bicycle in accordance with the invention. In the various figures, identical or similar elements bear identical references. The references are not systematically repeated in each figure in order to simplify the understanding of the drawings.
In FIG. 1 are seen the principal elements of an electrically assisted bicycle in accordance with the invention. An electric machine 2 is fixed to the frame 11 of the bicycle 1 in the vicinity of a tyre 5, here in the vicinity of the tyre of the rear wheel 61. A source of electrical energy, here a battery 7, powers the electric machine via control means 8. The drive pinion 3 meshes tangentially with teeth 51 of the tyre 5 and can therefore transmit to it a drive force that assists the cyclist.
FIG. 2 represents another embodiment in which the electric assist device is intended to cooperate with the tyre of the front wheel 62 of the bicycle. There are seen better in this figure the fixing means 4 of the electric machine 2. The fixing means preferably comprise an oscillating arm 41 articulated to a fixed support 42 about an axis 43 substantially parallel to the shaft of the electric machine. The support 42 is fastened to the bicycle, here to the front fork 12 of the bicycle. The drive pinion 3 meshes with the teeth 51 fastened to the flank of the tyre 5. The fixing means are preferably configured as here so that the transmission of a drive force by the drive pinion generates an additional dynamic force pressing the pinion onto the tyre and therefore an additional radial pressure in the gears. This effect is obtained, for example, if the pivot axis 43 is as here located away from the meshing plane, toward the outside of the tyre in this configuration.
Elastic means (not visible in the figures) preferably prestress the orientation of the oscillating arm so that in the absence of drive force the drive pinion 3 bears radially against the tyre with a non-zero bearing force. The elastic means may for example consist of a torsion spring acting about the rotation axis 43 of the oscillating arm or a simple tension or compression spring acting directly between the oscillating arm 41 and the support 42.
A preferred embodiment of the cooperation between the electric machine 2 and the tyre 5 has been represented in FIG. 3 as seen in the plane of the wheel. The teeth 31 of the drive pinion 3 are seen to mesh tangentially with the complementary teeth 51 of the tyre. The electric machine is inclined at an angle a relative to the plane 611 of the wheel 61. In accordance with the invention, the angle α may vary but is preferably between −10° and +30°. In this example α has a value of approximately 25° and the teeth 51 are fastened to a flank 52 of the tyre and situated radially below the equator 54. The tyre may be a pneumatic or non-pneumatic tyre, or even a solid tyre.
The electric machine preferably drives the drive pinion directly, that is to say with no intermediate reduction means, the pinion being carried by the shaft of the electric machine. In accordance with a preferred embodiment of the invention, a freewheel mechanism is nevertheless disposed between the shaft and the pinion so that the tyre does not drive the electric machine when the bicycle is moving forward. Assuming that the device were not to comprise a freewheel, recovery of electrical energy may be effected when the cyclist brakes.
As represented in all the figures, the electric machine 2 is preferably placed radially outside the drive pinion 3 relative to the axis of the wheel of the bicycle, that is to say above the drive pinion 3 in this configuration.
FIG. 4 shows in detail the meshing of the drive pinion 3 with the tyre. The pinion transmits a drive force FM to the tyre. There is seen here a preferred embodiment in which the teeth 32 of the pinion are asymmetrical and configured so that the aperture angle of their driving faces 33 is smaller than the aperture angle of their non-driving faces 34. The shape of the complementary teeth 51 fastened to the tyre is naturally adapted accordingly. This arrangement makes it possible to improve significantly the efficiency of meshing and to increase the maximum value of the drive force FM that can be transmitted. Also represented is the force F with which the pinion bears on the tyre. This force is transmitted by the fixing means of the electric machine and has the effect of maintaining meshing even in the event of deformation of the various elements of the device. If F0 denotes the bearing force of the pinion in the absence of drive force and FD denotes the additional dynamic force generated by the effect of the drive force, it may be stated that F=F0+FD.
The straight line D1 is the straight line perpendicular to the tangent to the teeth at the point of contact at the mid-height of the teeth (see also FIG. 6). The half-lines D2 and D3 diverge from D1 at an angle γ. The sector A corresponds to the surface between the straight line D1 and the half-line D2. The sector B corresponds to the surface between the straight line D1 and the half-line D3. The angle γ preferably does not exceed 60°. One way of ensuring that the drive force generates an additional dynamic bearing force is to verify that the position of the intersection of the axis 43 with the median plane of the pinion complies with one of the following conditions:
- If the axis 43 is to the front of the pinion relative to the direction of forward movement of the bicycle (situation represented in FIG. 1), the intersection must be situated in the sector A represented in FIG. 4.
- If the axis 43 is to the rear of the pinion relative to the direction of forward movement of the bicycle (situation represented in FIG. 2), the intersection must be situated in the sector B represented in FIG. 4.
The teeth 31 of the pinion 3 have been represented to a larger scale in FIG. 5 in order to show better the preferred asymmetrical embodiment described with reference to FIG. 4. It is seen that the aperture angle A1 of the driving faces 33 is substantially smaller than the aperture angle A2 of the non-driving faces 34.
The teeth 51 of the tyre have been represented to a larger scale in FIG. 6 in order to show better a preferred embodiment. According to the same logic as for the drive pinion, the teeth 511 of the tyre have driving faces 512 and non-driving faces 513. It is seen that the aperture angle B1 of the driving faces 512 is substantially smaller than the aperture angle B2 of the non-driving faces 513. The teeth have a pitch P and a height H. The pitch of the teeth is preferably between 1.8 mm and 5.5 mm and more preferably between 1.8 mm and 2.5 mm in order to minimize the noise emitted by the gears. The straight line D1 referred to above with reference to FIG. 4 has also been represented in this figure.
FIGS. 5 and 6 show teeth having rectilinear faces. In the case of curved faces, the angles described above must be measured considering the tangent at the point corresponding to the tooth half-height (see the mean radius Rm in FIG. 5 and the half-height H/2 in FIG. 6).
The drive pinion 3 and an essential feature of the invention in which the teeth are helicoidal teeth have been represented to a larger scale in FIG. 7. The axis of the teeth 32 is inclined at angle β relative to the axis 35 of the pinion and therefore relative to the shaft of the electric machine. The angle β shown here is approximately 15°, but it may for example be between 4° and 40° and preferably between 15° and 30° in order to minimize noise without excessively degrading the maximum value of the drive force FM that can be transmitted. The inclination of the teeth of the tyre must naturally be adapted accordingly. This arrangement makes it possible in particular to limit the noise emitted by the gears. The drive pinion 3 is preferably made of metal, for example steel. Where appropriate, the freewheel referred to above may be integrated into the interior of the pinion.
In FIG. 8 there is seen a preferred embodiment of the tyre 5. Here it is a pneumatic tyre comprising in the manner known in itself flanks 52, a tread 53 and beads 54 for attaching it to a bicycle rim that is not shown. It is also seen that the teeth 51 fastened to the flank are inclined relative to the radial direction of the tyre at an angle corresponding to the helix angle β for the drive pinion described with reference to FIG. 7.
The teeth of the tyre preferably consist of rubber with a Shore A hardness preferably between 55 and 85 and more preferably between 75 and 85 to favour the maximum value of the drive force FM that can be transmitted. The teeth are preferably moulded at the same time as the pneumatic tyre but may also be attached to a conventional tyre moulded beforehand.
A textile reinforcement may be associated with the surface of the teeth in order to limit wear by abrasion and tooth noise. It is advantageously to use polyamide type textile reinforcement fabric, woven so as to be extendable when moulding the teeth.
As already represented in FIG. 3, the teeth 51 are preferably placed radially below the equator 54 of the tyre 5. Alternatively, the teeth may be placed at the shoulder of the tyre, that is to say in the vicinity of the tread 53, or even at the centre of the tread 53, in a horizontal position.
In FIGS. 1 to 4, the device is represented in the working position. In FIGS. 9 and 10 there has been represented an embodiment of the invention in which the electric machine can be held in a folded position, that is to say away from the tyre, by an electric actuator 44. In this example, the actuator includes a cam 45 coming to bear against the oscillating arm 41. Rotation of the cam causes the drive pinion to be moved away from the tyre and therefore disengagement of the device. The actuator may be a servomotor or an electromagnet, for example.
The folded position enables totally silent functioning of the bicycle in non-assisted mode.
The actuator may be controlled automatically as a function of various parameters such as the speed of the bicycle, the pedalling, the state of charge of the battery. The actuator may equally be controlled by the cyclist, for example by means of the display and control unit.
Of course the pinion may equally be manually disengaged directly at the level of the oscillating arm or by means of a cable connected to a control accessible to the cyclist.
The presence of a freewheel mechanism in the device of the invention in combination with such disengagement means further makes it possible to bring about meshing smoothly even when the bicycle is moving.
Patent Application
20150314829
