Bicycle transmission with torque biasing means

Abstract

The present invention relates to a bicycle gearbox (2000, 3000) comprising a continuously variable transmission (2300) comprising an input pulley (1310), an output pulley (1330) and a V-belt (1320) connecting the input pulley (1310) and the output pulley (1330), the continuously variable transmission (2300) further comprising an input pulley axis (1314), on which the input pulley (1310) is mounted, the input pulley (1310) comprising a fixed sheave (1312) and a sliding sheave (1313), the sliding sheave (1313) being configured to slide on the input pulley axis (1314), and torque biasing means (2315, 3315A, 3315B), configured to bias the sliding sheave (1313) towards the fixed sheave (1312), when torque is applied from the input pulley axis (1314) to the input pulley (1310).

Description

[0001] Bicycle transmission with torque biasing means

[0002] The present invention relates to a gearbox layout that is compact, light and able to provide a functional continuously variable transmission for a bicycle, while ensuring good and efficient operation.

[0003] State of the art

[0004] Gearboxes based on continuously variable transmissions for bicycles are known, for instance from document WO2017103110A1 , which are based on two pulleys and a V-belt.

[0005] Those known designs face several difficulties.

[0006] When a continuously variable transmissions changes gear there is often a certain amount of hysteresis between the gear changes. In other words, when the continuously variable transmissions changes up a gear at a certain speed, it will not change down a gear at the same speed, but at a lower speed.

[0007] In some practical implementations, It has been found that a continuously variable transmission for a bicycle, designed to maintain an rotational speed of 70 RPM on its input will, for instance, upshift at approximately 80 RPM and downshift at approximately 60 RPM. This is problematic in bicycle application which intends to maintain a constant pedal cadence.

[0008] Moreover, for bicycle applications, it has been found that higher torque is generally generated at lower RPMs so that it is important to avoid the belt slipping between the pulleys in those regimes.

[0009] Summary of invention

[0010] The invention is defined by claim 1 and has been developed to overcome at least one of the issues identified above. The dependent claims comprise further features defining further advantageous embodiments.

[0011] In general, it has been found that the addition of a so-called torque slot, which can generally be understood as being a mean for increasing grip on a belt on the input pulley as a function of the torque being applied, can cure one or both of the issues identified above.

[0012] In particular, by increasing the grip on the belt, the gear change on the upshift can be forced to happen at a lower speed than without it, and in particular at an RPM value designed to match the downshift speed, so as to reduce the hysteresis discussed above. Moreover, the increased belt clamping force from the torque slot can also reduce the belt slip between the pulleys, as the higher torque will also result in a higher grip on the belt. Those two improvements provide advantages in terms of use for the cyclist, which feels a more natural transmission and has less losses in efficiency from the pedals to the rear wheel. Additionally, is has been found that by using specific dimensions and characteristics of the V-belt, further advantages can be obtained.

[0013] An embodiment specifically relate to a bicycle gearbox comprising a continuously variable transmission comprising an input pulley, an output pulley and a V-belt connecting the input pulley and the output pulley, the continuously variable transmission further comprising an input pulley axis, on which the input pulley is mounted, the input pulley comprising a fixed sheave and a sliding sheave, the sliding sheave being configured to slide on the input pulley axis, and torque biasing means, configured to bias the sliding sheave towards the fixed sheave, when torque is applied from the input pulley axis to the input pulley.

[0014] In some embodiments, the torque biasing means can comprise a collar fixedly connected to the sliding sheave, a slot being implemented in the collar, and a pin fixedly connected to the input pulley axis, the pin and the slot can be configured such that the pin can slide in the slot, and the pin can be configured to transfer torque from the input pulley axis to the collar.

[0015] In some embodiments, the torque biasing means can comprise a collar fixedly connected to the sliding sheave, a slot being implemented in the input pulley axis, and a pin fixedly connected to the collar, the pin and the slot can be configured such that the pin can slide in the slot, and the pin can be configured to transfer torque from the input pulley axis to the collar.

[0016] In some embodiments, the input pulley axis extend along an input pulley elongation axis, the slot extends along a slot elongation axis, an angle can be defined between the input pulley elongation axis and the slot elongation axis, the angle can be larger than 1 degree, preferably larger than 3 degrees, even more preferably larger than 5 degrees, and / or the angle can be smaller than 25 degrees, preferably smaller than 20 degrees, even more preferably smaller than 15 degrees.

[0017] In some embodiments, the angle can be configured to reduce a difference in rotational speed between upshifting and downshifting of the continuously variable transmission.

[0018] In some embodiments, the input pulley can further comprise an input pulley spring and the collar can be at least partially overlapping with the input pulley spring, in a direction along the input pulley elongation axis.

[0019] In some embodiments, a majority of an extension of the collar, in the direction along the input pulley elongation axis, can be overlapping with the input pulley spring.

[0020] In some embodiments, the collar can be at least partially overlapping with the sliding sheave, in a direction along the input pulley elongation axis. In some embodiments, a majority of an extension of the collar, in the direction along the input pulley elongation axis, can be overlapping with the sliding sheave.

[0021] In some embodiments, the V-belt can have a cut angle lower than 25 degrees.

[0022] In some embodiments, the V-belt can have a Young's modulus higher than 700 MPa, preferably higher than 800 MPa, and even more preferably higher than 850 MPa.

[0023] A further embodiment can relate to a bicycle frame comprising a seat tube, a down tube and chain stays, and the bicycle gearbox of any of the previous claims, wherein the bicycle gearbox can be solidly connected to at least the seat tube and to the down tube.

[0024] A further embodiment can relate to a bicycle comprising the bicycle gearbox according to any of the previous embodiments, or the bicycle frame according to the previous embodiment

[0025] Brief description of drawings

[0026] Figure 1A schematically illustrates a bicycle frame BF comprising a bicycle gearbox 1000;

[0027] Figure 1 B schematically illustrates a top schematic view of a bicycle gearbox 1000, with a top housing portion removed;

[0028] Figure 2 schematically illustrates a top schematic view of a bicycle gearbox 2000 including a schematic view of torque biasing means 2315;

[0029] Figure 3 schematically illustrates a top schematic view of a bicycle gearbox 3000 including a possible implementation of input pulley spring 3311 and / or of torque biasing means 3315A;

[0030] Figures 3A and 3B schematically illustrate a top schematic view possible implementations of torque biasing means 3315A and 3315B.

[0031] Detailed description of embodiments

[0032] Figure 1A schematically illustrates a bicycle frame BF comprising a bicycle gearbox 1000. A top schematic view of the gearbox 1000, with a top housing portion removed, is shown in figure 1 B.

[0033] As can be seen, the bicycle gearbox 1000 has a housing 1100 which has a substantially elongated shape, along a main elongation axis EA. That is, the housing 1100 has its longest dimension along a main elongation axis EA of the housing 1100. It will be clear that the main elongation axis EA can be placed in any direction with respect to the bicycle frame BF. The housing 1100 is made of generally resilient material, preferably of metal and even more preferably of aluminum, and is configured to be connected to a frame tube of a bicycle, which can be any of a seat tube ST, a down tube DT and chain stays CS, or other non-standard frame construction. The connection between the housing 1100 and the frame can be of any known type, preferably however the housing 1100 is welded to one or more, preferably two or more, even more preferably three of the frame’s tubes.

[0034] Preferably, as it is the case for the down tube DT in figure 1 , the housing 1100 is configured to be connected to a given frame tube such that the frame tube is positioned parallel to the main elongation axis EA. This is particularly advantageous, since it allows the housing 1100 to be used as a structural element, replacing at least part of the respective frame tube. In this manner, the housing replaces some otherwise present material, thus reducing weight of the bicycle.

[0035] As visible in figure 1A, the housing 1100 comprises two crankshaft openings 1110, of which only the left one is visible, but it will be understood that the right one is symmetrically placed, configured to allow a crankshaft 1600 to pass through the housing 1100.

[0036] The gearbox 1000 further comprises a continuously variable transmission 1300, itself comprising an input pulley 1310, an output pulley 1330 and a V-belt 1320 connecting the input pulley 1310 and the output pulley 1330.

[0037] A chain sprocket 1500, visible in figure 1 B and not illustrated in figure 1A for clarity of illustration, is configured to connect to a chain connecting to the rear wheel, in a manner per se known.

[0038] The elements above are generally sufficient for implementing the continuously variable transmission 1300, so that it will be understood that not each and every element illustrated in figure 1 B has to be implemented together with them.

[0039] Generally the operation of the gearbox 1000 is that power is transmitted from the crankshaft 1600 to the input pulley 1310, trough optional input gears 1200 which will be described later, from the input pulley 1310 to the output pulley 1330 through the V-belt 1320, and from the output pulley 1330 to the chain sprocket 1500 through optional output gears 1400, which will also be described later. The presence of the optional input and output gears enables the continuously variable transmission 1300 to operate at a rotational speed which is different from the rotational speed of the crankshaft 1600 and / or of the chain sprocket 1500. This is particularly advantageous since it has been found by the inventor that, specifically for bicycle application, the continuously variable transmission 1300 operates better at rotational speeds which are higher than those normally applied to the crankshaft 1600 and / or of the chain sprocket 1500.

[0040] As indicated, in some embodiments the gearbox 1000 can comprise input gears 1200, which are generally configured to connect the crankshaft 1600 to the input pulley 1310. In particular, the input gears 1200 are configured to increase a rotational speed of the crankshaft 1600 and provide the increased rotational speed to the input pulley 1310. The input gears 1200 are only schematically illustrated in figure 1 B it will however be clear to those skilled in the art that they can be implemented in any known manners, for instance by planetary gears, by cog wheels, etc.

[0041] The output gears 1400 are similarly generally configured to connect the output pulley 1330 to the chain sprocket 1500, and more in particular so as to reduce a rotational speed of the output pulley 1330 and provide the reduced rotational speed to the chain sprocket 1500. The same considerations made for the specific implementation of the input gears 1200 also applies to the output gears 1400. In preferred embodiments, the output gears 1400 is implemented as a planetary gearset, with the axle of the sun gear being in line with the axle of the crankshaft 1600.

[0042] Preferably, the input gears 1200 and the output gears 1300 are placed on two opposite sides of the continuously variable transmission 1300. This has been found to allow for an efficient configuration of the gearbox 1000.

[0043] As illustrated in figure 1 B, the output pulley 1330 are coaxial with the crankshaft 1600. It will be clear to those skilled in the art that this can be implemented in several manners. For instance, the pulley 1330 can be mounted on bearings mounted on the crankshaft 1600. Alternatively, or in addition, the crankshaft 1600 can be inserted in one or more cylindrical sleeve, coaxial with the crankshaft 1600, and the pulley 1330 can be mounted on bearings mounted on the one or more sleeve.

[0044] This construction, which differs from the known prior art, is particularly advantageous because it enables a granter gear range for the input gears 1200 and / or for the output gears 1400, compared to the prior art. Moreover, this configuration is more compact in the width, along the Z direction, of the pedal crank, which is a key factor for many bikes to reduce the Q factor, or the width of the pedals. In particular, a narrower Q factor is better for rider efficiency and reduced impact on the legs.

[0045] More specifically in preferred implementations in which the input gears 1200 as implemented as a two-stage spur gear arrangement, a higher gear range can be obtained than with a single planetary gearbox, and with a thinner dimension. While a dual stage planetary gearbox could be used as well, for the input gears 1200, this would likely result in a wider implementation. As it will be clear to those skilled in the art, a two-stage spur arrangement can be implemented by two pairs of cogwheels, where the output of one pair drives the input of the other pair.

[0046] In preferred embodiment, the implementation described above allows the input gears 1200 to increase the rotational speed of the input pulley 1310 with respect to the speed of the crankshaft 1600 by an increasing factor, which is at least 10, preferably at least 20, even more preferably at least 25. It has been found that this amount of increase leads the continuously variable transmission 1300 to operate in a range which, for average crankshaft speeds, leads to an ideal size and function of the continuously variable transmission 1300. While the above limitation applies to a minimum value of the increasing factor, in some embodiments the increasing factor can also be limited in its upper value. Thus, in some optional embodiments, the increasing factor can be less than 50, preferably less than 40, even more preferably less than 35.

[0047] Similarly, in preferred embodiments the output gears 1400 are configured to reduce the rotational speed of the output pulley 1330 by a reducing factor, which can be at least 0.01 , preferably at least 0.05, even more preferably at least 0.1. In some optional embodiments the reducing factor can be less than 0.3, preferably less than 0.2, even more preferably less than 0.15.

[0048] It will be understood by those skilled in the art that the increasing factor can be defined as rotational speed of input pulley 1310 increasing factor = - - - - — - - — — - - rotational speed of crankshaft 1600 and the reducing factor can be defined as chain sprocket 1500 reducing factor = - - - - — - - - - rotational speed of output pulley 1330

[0049] Moreover, it has been found through extensive tests and experimentation, that a gear range between 1.5 and 10, preferably between 1.8 and 4 is ideal for the continuously variable transmission 1300. In other embodiments, it has been found that a gear range is preferably higher than 1.5, even more preferably higher than 1.8 and / or preferably lower than 10, even more preferably lower than 4. The gear range can be defined as rotational speed output pulley in high gear rotational speed output pulley in low gear

[0050] Similarly, It has been found that it is particularly advantageous to configure the input gears 1200 and the continuously variable transmission 1300 so that the input pulley 1310, when the gearbox 1000 is in use, has an input rotational speed of at least 500 RPM, preferably at least 1000 RPM, even more preferably at least 1500 RPM, and / or less than 3500 RPM, preferably less than 3000 RPM, even more preferably less than 2500 RPM.

[0051] Similarly, It has been found that it is particularly advantageous to configure the output gears 1400 and the continuously variable transmission 1300 so that the output pulley 1330, when the gearbox 1000 is in use, has an output rotational speed of at least 500 RPM, preferably at least 700 RPM, and / or less than 4500 RPM, preferably less than 4000 RPM. Alternatively, or addition, it has been found particularly advantageous for the output rotational speed to have a range of at least 1000 RPM, preferably at least 2000 RPM, even more preferably at least 2500 RPM.

[0052] All the numerical values above are not intended to limit the invention. However, they have been found as being a particularly effective configuration which results in a smaller size for the gearbox 1000 and yet in an effective operation of it.

[0053] As previously described in preferred embodiments and as visible for instance in figure 1 B, the output gears 1400 can be implemented by an epicyclic gear system, or a planetary gear, comprising a sun gear and a plurality of planet gears and a ring gear. Preferably, the sun gear can be coaxial with the crankshaft 1600. For the mounting of the epicyclic gear system on the crankshaft 1600 without the epicyclic gear system rotating together with the crankshaft 1600, the same considerations made above for the output pulley 1330 apply. In particular, the epicyclic gear system can be separated from the crankshaft 1600 by one or more bearings and / or sleeves, as appropriate. The input of the output gears 1400 can be the output pulley 1330.

[0054] In further preferred embodiments, the chain sprocket 1500 can be coaxial with the crankshaft 1600. Similarly, also the output of the output gears 1400 can be coaxial with the crankshaft 1600, and can be connected to the chain sprocket 1500. The same considerations made above for the coaxial mounting on the crankshaft also applies to the output of the output gears 1400 and / or to the chain sprocket 1500.

[0055] This has been found to be particularly advantageous because it allows a coaxial output from the output pulley 1330, which can itself be coaxial with the crankshaft, so that a chain or belt can be located on the same axis as on a typical bike which renders the gearbox 1000 compatible with existing bicycle frame layouts.

[0056] As described above, in preferred embodiment, the input gears can be implemented with a non- planetary gearset, and preferably with a two-stage spur mechanism.

[0057] Figure 2 schematically illustrates a top schematic view of a bicycle gearbox 2000 including a schematic view of torque biasing means 2315.

[0058] In particular, as visible, the bicycle gearbox 2000 comprises a continuously variable transmission 2300, of which only the input part is represented, comprising an input pulley 1310, an output pulley 1330, visible for instance in figure 1 B, and a V-belt 1320 connecting the input pulley 1310 and the output pulley 1330.

[0059] The continuously variable transmission 2300 further comprises an input pulley axis 1314, on which the input pulley 1310 is mounted. In particular, the input pulley 1310 comprises a fixed sheave 1312 and a sliding sheave 1313. The fixed sheave 1312 is configured to rotate fixedly with the input pulley axis 1314, both in terms of rotational speed and in terms of movement along the input pulley axis 1314. That is, the fixed sheave 1312 is fixedly connected to the input pulley axis 1314.

[0060] On the other hand, the sliding sheave 1313 is configured to slide on the input pulley axis 1314, along the axial direction, indicated by direction Z in the drawings. Moreover, while the average rotational velocity of the sliding sheave 1313 s the same as that of the input pulley axis 1314, those two rotational velocities might differ at specific time points due to the action of the torque biasing means 2315, as will become clearer to those skilled in the art based on the following description, since the torque biasing means 2315 allows for a limited play, in the rotational movement of the sliding sheave 1313 around the input pulley axis 1314. In preferred embodiments, this play is less than 30 degrees, even more preferably less than 20 degrees.

[0061] As schematically illustrated, the continuously variable transmission 2300 of figure 2 differs from continuously variable transmission 1300 of figure 1 B in that it further comprises torque biasing means 2315. In figure 2 those are only schematically illustrated, and it will be clear to those skilled in the art, that any mechanical means, which can be configured to bias the sliding sheave 1313 towards the fixed sheave 1312, when torque is applied from the input pulley axis 1314 to the input pulley 1310, can be implemented as torque biasing means 2315.

[0062] Here, the torque which causes the bias of the sliding sheave 1313 towards the fixed sheave 1312 is a torque applied in a direction corresponding to the rotation of the sliding sheave 1313 under normal operation of the continuously variable transmission 2300. That is, in the direction of rotation of the continuously variable transmission 2300 when a user is cycling forward and putting pressure on the pedals.

[0063] Thanks to the bias under pressure, the gripping action on the V-belt 1320 between the sliding sheave 1313 towards the fixed sheave 1312, which is normally regulated by the input pulley spring 1311 , also biasing the sliding sheave 1313 towards the fixed sheave 1312, can be increased as a function of the applied torque.

[0064] In preferred embodiments, the torque biasing means 2315 can be configured so that the increase in bias of the sliding sheave 1313 towards the fixed sheave 1312 is a function of the torque applied, where the function is positive and monotonically increasing.

[0065] As indicated above, the skilled person is aware that several possible mechanical implementations can achieve the functional definitions provided above. In general, any mechanical and / or electromechanical device acting on the sliding sheave as a function of the torque inputted by the input pulley axis 1314 can be implemented.

[0066] In the following, some specific examples will be discussed with reference to figures 3, 3A and 3B, so as to illustrate specific possible implementations of the concept of the invention. It will however be clear to those skilled in the art that the invention is not necessarily limited to those implementations.

[0067] Figure 3 illustrates a possible specific implementation in which the input pulley spring 3311 is a helicoidal spring, acting between a rest plate, not numbered, fixedly connected on the input pulley axis 1314 and the sliding sheave 1313, so as to generally bias the sliding sheave 1313 towards the fixed sheave 1312.

[0068] Also represented in figure 3 is a possible specific implementation of torque biasing means 2315, in form of torque biasing means 3315A. As the input pulley spring 3311 covers the torque biasing means 3315A, those are illustrated, in enlarged view for more clarity, in figure 3A.

[0069] The torque biasing means 3315A will now be described. It will however be clear that the invention is not limited thereto and that, for instance as an alternative, torque biasing means 3315B such as illustrated in figure 3B can be implemented instead.

[0070] As visible in figure 3A, the torque biasing means 3315A comprises a collar 3316 fixedly connected to the sliding sheave 1313, a slot 3317 being implemented in the collar 3316, and a pin 3318 fixedly connected to the input pulley axis 1314.

[0071] The pin 3318 and the slot 3317 are configured such that the pin 3318 can slide in the slot 3317. As visible, the slot 3317 has a generally elongated shape, which defines the possible travel of the pin 3318. The dimension substantially perpendicular to the main elongation direction is at least larger than the size of the pin 3318, so as to allow the pin 3318 to slide through the slot 3317. In preferred embodiments, this dimension of the slot 3317 is at most twice, preferably less, of the size of the pin 3318, so as to avoid too much play in the operation of the bicycle gearbox.

[0072] The pin 3318 is configured to transfer torque from the input pulley axis 1314 to the collar 3316. This can be done by the pin 3318 pushing on the sides of the slot 3317, as will be clear to those skilled in the art.

[0073] It will be clear that further components might be implemented, which are not illustrated. For instance, the pin 3318 might be configured to as to allow rotation on the walls of the slot 3317, as an alternative, or addition, to a sliding movement. Alternatively, or in addition, the walls of the slot 3317 might have further layers for reducing wear from the movement of the pin 3318.

[0074] The operation of the biasing means 3315A will be evident to those skilled in the art. By increasing the torque on the input pulley axis 1314, the force with which the pin 3318 acts on the walls of the slot 3317 changes, which causes the pin 3318 to slide through the length of the slot, as soon as the slot is not aligned with the input pulley axis 1314. It will be therefore sufficient for the input pulley axis 1314 and the slot 3317 to be at an angle higher than zero degrees for enabling this operation. More details on possible values for this angle will be described later in the description.

[0075] As already indicated, figure 3B discloses a possible alternative to torque biasing means 3315A in form of torque biasing means 3315B. As visible, torque biasing means 3315B comprises a collar 3316 fixedly connected to the sliding sheave 1313, a slot 3317 being implemented in the input pulley axis 1314, and a pin 3318 fixedly connected to the collar 3316. As in the case of torque biasing means 3315A, the pin 3318 and the slot 3317 can be configured such that the pin 3318 can slide in the slot 3317, and the pin 3318 is configured to transfer torque from the input pulley axis 1314 to the collar 3316.

[0076] It will be clear to those skilled in the art that, for both the torque biasing means 3315A and 3315B, while only one slot and one pin have been illustrated and described, the invention is not limited thereto and a plurality of similar slots and pins can be implemented instead, to divide the transfer of torque between them.

[0077] As anticipated above, the operation of the torque biasing means 3315A and 3315B depends on the slot 3317 being at least partially not aligned with the input pulley axis 1314.

[0078] In more specific embodiments, as schematically illustrated in figure 3A, the input pulley axis 1314 extends along an input pulley elongation axis A’ and the slot 3317 extends along a slot elongation axis A”. In case of a non-straight shape for the slot 3317, which can be implemented, the slot elongation axis A” can be considered to be the linear interpolation of the shape of the slot 3317.

[0079] An angle is defined between the input pulley elongation axis A’ and the slot elongation axis A”, as visible. As the crossing of the two lines define, in fact, two angles, the angle under consideration in this description is the smaller of the two.

[0080] In preferred embodiments, the angle is larger than 1 degree, preferably larger than 3 degrees, even more preferably larger than 5 degrees. Alternatively, or in addition, in preferred embodiments the angle is smaller than 25 degrees, preferably smaller than 20 degrees, even more preferably smaller than 15 degrees.

[0081] Those values have been found to be particularly advantageous. In particular, it has been found that if the angle is higher than the values above, then the impact of the torque biasing means on gear change becomes too high, and this might lead to the upshifting happening at lower RPMs than downshifting, which again leads to the hysteresis indicated above, in the opposite direction as without the presence of any torque biasing means.

[0082] Moreover, using an angle higher than the value above has been shown to lead to a decrease in the effective force of the spring applied to the clamping of the V-belt. This decrease in V-belt clamping results in the V-belt slipping at lower RPMs. where the input torque by the cyclist is generally the highest.

[0083] Thus, in some embodiments, the angle is configured to reduce a difference in rotational speed between upshifting and downshifting of the continuously variable transmission 2300. It will be clear to those skilled in the art that this can be obtained with reasonable experimentation and simulation, by fixing other parameters of the continuously variable transmission 2300 and then testing various values of the angle and measuring or simulating the impact.

[0084] The configurations above can all be implemented independently on the specific location of the torque biasing means 2215, 3315A and 3315B, as long as the torque biasing means can act on the sliding sheave 1313. Thus, even though a specific location of the torque biasing means is visible in figures 3A and 3B the present invention is not limited thereto.

[0085] Nevertheless, the implementation showed in figures 3A and 3B is particularly advantageous. In this implementation, the input pulley 1310 comprises an input pulley spring 3311 and the collar 3316 is at least partially overlapping with the input pulley spring 3311 , in a direction along the input pulley elongation axis A’. Preferably, a majority of an extension of the collar 3316, in the direction along the input pulley elongation axis A’, is overlapping with the input pulley spring 1311 , 3311.

[0086] Thanks to this configuration, the width of the transmission in the Z direction can be advantageously limited, since the biasing means 2215, 3315A and 3315B does not contribute to taking space which is not already taken by the spring.

[0087] Alternatively, or in addition, instead of the biasing means 2215, 3315A and 3315B being located next to the sliding sheave 1313 in some embodiments the collar 3316 can be at least partially overlapping with the sliding sheave 1313, in a direction along the input pulley elongation axis A’. Preferably, a majority of an extension of the collar 3316, in the direction along the input pulley elongation axis A’, namely the X direction in the figures, can be overlapping with the sliding sheave 1313.

[0088] Also in this configuration, the width of the transmission in the Z direction can be advantageously limited, and the use of material can also be advantageously reduced.

[0089] It will be clear that the two configurations described above can be combined, for instance by having at least part of spring 3311 also entering into the sliding sheave 1313, in the Z direction.

[0090] The various embodiments discussed above enable to the invention to, among other advantages, reduce slipping of the V-belt 1320 on the input pulley 1310. In addition to those approaches, in some embodiment a further reduction in slippage can be obtained by implementing the V-belt 1320 with a cut angle lower than 25 degrees, and / or preferably higher than 18 degrees. Here the cut angle is the angle defined by the two sides of the V-belt 1320 defining its V shape, that is the two sides engaging respectively with the sliding sheave 1313 and the fixed sheave 1312.

[0091] In scooter applications, this angle is usually set at values larger than 25 degrees. This is because the larger the belt cut angle, the more force is diverted to increase the belt tension, which is also critical in a single spring CVT. In the invention, it has been found that a cut angle lower than 25 degrees, preferably lower than 23.5 degrees and even more preferably of 22 degrees, provides various advantages.

[0092] In particular, the horizontal movement of the pulleys can be reduced making the transmission thinner in the Z direction. Moreover, as the cut angle is lower than usual, more clamping force acts on the friction of the belt, and less is diverted to creating the belt tension. Since the invention can be preferably implemented with an architecture employing two springs, namely spring 1311 and another spring, not visible in the drawings, biasing the two output pulleys towards each other, less tension is required in the belt to create friction on an unloaded pulley.

[0093] Additionally, it has been found that using a V-belt which is generally harder than those used in the prior art can lead to additional advantages. In particular, currently used V-belts are soft enough to ensure no slip conditions. This, however, means they have overall a higher drag on the system, reducing efficiency.

[0094] As the avoidance of slip can be obtained in other manners in the invention, the V-belt can be manufactured to be harder than common practice, also increasing efficiency and longevity of the transmission.

[0095] In particular, It has been found that a Young's modulus higher than 700 MPa, preferably higher than 800 MPa, and even more preferably higher than 850 MPa, can be particularly advantageous

[0096] Alternatively, or in addition, it has been found that one more relevant parameter can be the compression strength of the V-belt when clamped by the pulleys. This value is not linear in elastomers, but it can be approximated by a linear interpolation over the compression range of the V-belt during the use of the gearbox. The value of the Young’s modulus for the linear interpolation is preferably higher than 5 MPa, more preferably higher than 10 MPa, even more preferably higher than 20 MPa, and / or preferably lower than 200 Mpa, preferably lower than 150 Mpa, even more preferably lower than 100 Mpa.

[0097] If necessary for the computation of the Young’s modulus for the linear interpolation, an exemplary use of the gearbox for computing the compression range of the V-belt can be based on the assumption of a cyclist producing an average of 200 Watts, preferably with a constant force applied to the pedals, and a speed profile for a bicycle mounting the gearbox varying between 0 and 30 km / h.

[0098] If necessary for the computation of the Young’s modulus for the linear interpolation, the specific shape of the speed profile can be chosen at random to simulate various realistic cycling conditions, or it can be chosen to be a period of 10 minutes with the following speed profile

[0099] 00:00 to 01 :00: increasing linearly from 0 km / h to 20 km / h,

[0100] 01 :00 to 02:00: increasing linearly from 20 km / h to 30 km / h,

[0101] 02:00 to 03:00: decreasing linearly from 30 km / h to 10 km / h,

[0102] 03:00 to 04:00: increasing linearly from 10 km / h to 25 km / h,

[0103] 04:00 to 05:00: decreasing linearly from 25 km / h to 5 km / h,

[0104] 05:00 to 06:00: increasing linearly from 5 km / h to 20 km / h,

[0105] 06:00 to 07:00: increasing linearly from 20 km / h to 25 km / h,

[0106] 07:00 to 08:00: decreasing linearly from 25 km / h to 5 km / h, 08:00 to 09:00: increasing linearly from 5 km / h to 35 km / h, 09:00 to 10:00: decreasing linearly from 35 km / h to 0 km / h.

[0107] If necessary for the computation of the Young’s modulus for the linear interpolation, the input gears 1200 can be configured to increase the rotational speed of the input pulley 1310 with respect to the speed of the crankshaft 1600 by an increasing factor of 30, the output gears 1400 can be configured to reduce the rotational speed of the output pulley 1330 by a reducing factor or 0.1 and the continuously variable transmission can be configured to have a gear range between 1.8 and 4.

[0108] Embodiments of the invention can also relate to a bicycle comprising any of the bicycle gearboxes or the bicycle frame BF described above.

[0109] List of reference numerals

[0110] 1000: bicycle gearbox

[0111] 1100: housing

[0112] 1110: crankshaft opening

[0113] 1200: input gears

[0114] 1300: continuously variable transmission

[0115] 1310: input pulley

[0116] 1311: input pulley spring

[0117] 1320: V-belt

[0118] 1330: output pulley

[0119] 1340: centrifugal actuator

[0120] 1400: output gears

[0121] 1500: chain sprocket

[0122] 1600: crankshaft

[0123] BF: bicycle frame

[0124] DT : down tube

[0125] HT: head tube

[0126] ST: seat tube

[0127] TT: top tube

[0128] SS: seat stays

[0129] CS: chain stays

[0130] EA: elongation axis

[0131] 2000: bicycle gearbox

[0132] 1312: fixed sheave

[0133] 1313: sliding sheave

[0134] 1314: input pulley axis

[0135] 2315: torque biasing means

[0136] 3000: bicycle gearbox

[0137] 3311 : input pulley spring

[0138] 3315A, 3315B: torque biasing means

[0139] 3316: collar

[0140] 3317: slot

[0141] 3318: pin A’: input pulley elongation axis

[0142] A”: slot elongation axis

Claims

Claims1 . A bicycle gearbox (2000, 3000) comprising a continuously variable transmission (2300) comprising an input pulley (1310), an output pulley (1330) and a V-belt (1320) connecting the input pulley (1310) and the output pulley (1330), the continuously variable transmission (2300) further comprising an input pulley axis (1314), on which the input pulley (1310) is mounted, the input pulley (1310) comprising a fixed sheave (1312) and a sliding sheave (1313), the sliding sheave (1313) being configured to slide on the input pulley axis (1314), characterized by torque biasing means (2315, 3315A, 3315B), configured to bias the sliding sheave (1313) towards the fixed sheave (1312), when torque is applied from the input pulley axis (1314) to the input pulley (1310).

2. The bicycle gearbox (3000) of claim 1 , wherein the torque biasing means (3315A) comprises a collar (3316) fixedly connected to the sliding sheave (1313), a slot (3317) being implemented in the collar (3316), and a pin (3318) fixedly connected to the input pulley axis (1314), the pin (3318) and the slot (3317) are configured such that the pin (3318) can slide in the slot (3317), and the pin (3318) is configured to transfer torque from the input pulley axis (1314) to the collar (3316).

3. The bicycle gearbox (3000) of claim 1 , wherein the torque biasing means (3315B) comprises a collar (3316) fixedly connected to the sliding sheave (1313), a slot (3317) being implemented in the input pulley axis (1314), and a pin (3318) fixedly connected to the collar (3316), the pin (3318) and the slot (3317) are configured such that the pin (3318) can slide in the slot (3317), and the pin (3318) is configured to transfer torque from the input pulley axis (1314) to the collar (3316).

4. The bicycle gearbox (3000) of claim 2 or 3, wherein the input pulley axis (1314) extends along an input pulley elongation axis (A’), the slot (3317) extends along a slot elongation axis (A”), an angle is defined between the input pulley elongation axis (A’) and the slot elongation axis (A”), the angle is larger than 1 degree, preferably larger than 3 degrees, even more preferably larger than 5 degrees, and / or the angle is smaller than 25 degrees, preferably smaller than 20 degrees, even more preferably smaller than 15 degrees.

5. The bicycle gearbox (3000) of claim 4, wherein the angle is configured to reduce a difference in rotational speed between upshifting and downshifting of the continuously variable transmission (2300).

6. The bicycle gearbox (3000) of any of claims 2 to 5, wherein the input pulley (1310) further comprises an input pulley spring (1311 , 3311) and the collar (3316) is at least partially overlapping with the input pulley spring (1311 , 3311), in a direction along the input pulley elongation axis (A’).

7. The bicycle gearbox (3000) of claim 6, wherein a majority of an extension of the collar (3316), in the direction along the input pulley elongation axis (A’), is overlapping with the input pulley spring (1311 , 3311).

8. The bicycle gearbox (3000) of any of claims 2 to 5, wherein the collar (3316) is at least partially overlapping with the sliding sheave (1313), in a direction along the input pulley elongation axis (A’).

9. The bicycle gearbox (3000) of claim 8, whereina majority of an extension of the collar (3316), in the direction along the input pulley elongation axis (A’), is overlapping with the sliding sheave (1313).

10. The bicycle gearbox (2000, 3000) of any previous claim wherein the V-belt (1320) has a cut angle lower than 25 degrees.11 . The bicycle gearbox (2000, 3000) of any previous claim wherein the V-belt (1320) has a Young's modulus higher than 700 MPa, preferably higher than 800 MPa, and even more preferably higher than 850 MPa.

12. A bicycle frame (BF) comprising a seat tube (ST), a down tube (DT) and chain stays (CS), and the bicycle gearbox (2000, 3000) of any of the previous claims, wherein the bicycle gearbox (2000, 3000) is solidly connected to at least the seat tube (ST) and to the down tube (DT).

13. A bicycle comprising the bicycle gearbox (2000, 3000) according to any of claims 1-11 , or the bicycle frame (BF) according to claim 12.

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