NL1037563C2

NL1037563C2 - Measuring device for measuring a pedalling force exerted by a cyclist.

Info

Publication number: NL1037563C2
Application number: NL1037563A
Authority: NL
Inventors: Gijsbertus Cornelis Franciscus Roovers; Bastiaan Andreas D'herripon
Original assignee: Idbike B V
Priority date: 2009-12-16
Filing date: 2009-12-16
Publication date: 2011-06-20
Also published as: WO2011074947A1

Description

TITLE: Measuring device for measuring a pedalling force exerted by a cyclist

FIELD OF THE INVENTION

The present invention relates in general to a device for measuring a pedalling force exerted by a cyclist, and for providing an electrical output signal representing this force.

5 Such device is useful, among other things, in electrically assisted bicycles where an auxiliary propulsion motor is; controlled to provide assistance propulsion power proportional to the human pedalling force, or in exercise equipment such as spinning apparatus or sporting bicycles where it is desired to 10 measure the power exerted by the cyclist.

In the following, the present invention will be specifically explained for the case of a bicycle, which is per definition a vehicle having two wheels mounted behind each other. However, the present invention is generally useful in 15 any pedal-powered apparatus, including mono-cycles, vehicles with three or more wheels, spinning apparatus, as long as such vehicle or apparatus comprises a set of pedals mounted on a common axle (hereinafter indicated as pedal axle) to be rotated by a human user (using his feet or hands). Such 20 apparatus will be indicated by the general phrase "pedal-powered apparatus".

Several measurement systems have already been proposed, and many systems are designed for measuring a deformation in a stationary constructional part of a cycle apparatus. The 25 present invention aims to propose a device suitable for use in the rotating pedal assembly. Even more generally, the present invention may also be useful for measuring torque in any rotating assembly. -

BACKGROUND OF THE INVENTION

1037563 30 2

Figure 1 schematically shows a cross section of a pedal system 10 in, for instance, a bicycle 1. The figure shows a bottom bracket 2 with a bearing 3, in which an axle 11 is mounted for rotation; this axle will be indicated as pedal 5 axle or bottom bracket axle. On either end of the pedal axle 11, pedals 12 are mounted through cranks or pedal arms 13. Since such pedal systems 10 are commonly known, a further more detailed description is not needed. It is noted that the word "pedal" may suggest actuation by a user using his feet, but 10 the present invention applies also in the case of.handbikes where the user rotates the pedals using his hands.

The pedals are used for conveying a driving force to a driving wheel via a transmission member. Such transmission member is in many cases implemented as a chain, and such 15 embodiment is shown in figure 1: the figure shows a chain wheel assembly 20 mounted on the pedal axle 11, while the chain engaging on this chain wheel is indicated at 15. Instead of a chain, the transmission member may for instance be implemented as a belt. Instead of a flexible coupling member 20 arranged in a loop around a portion of the wheel's perimeter, the transmission member may also be implemented as a rotating axle (shaft drive) arranged perpendicular to the pedal axle 11, coupled to the wheel assembly via bevel gearings.

Figure 2 schematically shows the design of a chain wheel 25 assembly 20 in more detail. The chain wheel assembly 20 generally comprises a splined inner ring 21 and an outer ring 22, and a series of radial spokes 24 connecting the outer ring 22 to the inner ring 21. The radial spokes 24 preferably have mutually identical dimensions, although this is not essential. 30 In rotation direction, the inner ring 21 is fixed with respect to the pedal axle 11. In the embodiment shown, this is accomplished by the inner ring 21 being provided with a series of splines at its inner surface, engaging matching splines (not shown) on the pedal axle 11. The outer ring 22 is 35 provided with a series of holes 25, for mounting a chain wheel blade or sprocket blade (not shown) to the outer ring 22. Alternatively, it would be possible that the outer ring 22 itself is implemented as a chain wheel or sprocket, i.e. provided with teeth for engaging the chain 15, but the design 3.

shown has the advantage that chain wheel blades can be exchanged relatively easily. It is noted that the present invention can also be utilized if the outer ring is for coupling with a transmission belt or the like, in which case 5 the sprocket would be replaced by a pulley, or for coupling with a drive shaft, in which case the sprocket would be replaced by a bevel gear. In the following, the combination of inner ring 21, outer ring 22 and spokes 24, which is preferably made as one formpiece, will be indicated as spider 10 28.

SUMMARY OF THE INVENTION

When the cyclist is exerting pedal force on the pedals, the axle 11 is rotated and the inner ring 21 is driven for 15 rotation, as indicated by a rotation arrow A. On the other hand, the chain 15 exerts a tangential force (typically a horizontal force) on the outer ring 22, as indicated by a longitudinal arrow B. As a result, the spokes 24 undergo some deformation. The deformation in the spokes 24 is proportional 20 to the pedal force exerted. This has already been recognized by prior art, and prior art has already proposed to measure the deformation of the spokes in order to provide a measuring signal proportional to the pedal force. However, the spoke deformation is not symmetrical, i.e. changes from one spoke to 25 the next. This can be understood by realizing that the tangential chain force can be considered as a superposition of a pure linear force acting on the outer ring 22 and being, directed perpendicular to the rotation axis of the pedal axle 11, and a pure torque acting on the outer ring 22. The spoke 30 deformation can be considered as a combination of two deformations, each caused by the respective force components. The pure torque will cause a pure rotation of the outer ring 22 with respect to the inner ring 21, causing all spokes 24 to bend to the same extent. The pure linear force will cause a 35 pure linear displacement of the outer ring 22 with respect to the inner ring 21, causing elongation or shortening of the spokes directed parallel to this displacement and causing bending of the spokes directed perpendicular to this displacement. Even if said forces are constant, each spoke 4 will"rotate over 360° and thus will undergo a cycle of constantly varying deformation. Therefore, a deformation sensor sensing the deformation of any one single spoke will provide an output signal that varies as the spoke concerned 5 travels around the rotation axis of the rotation axle 11.

Since it is desired that a measuring signal is provided that at all times is accurately proportional to the driving force, prior art requires that each spoke is provided with a dedicated deformation sensor, and that a control device 10 performs an averaging operation on the plurality of measuring signals obtained in this way. Further disadvantages of having a plurality of measuring sensors are the increase of costs, and the increased power consumption of these sensors * (typically strain gauges) and hence reduced battery life.

15

The present invention aims to overcome these disadvantages. More particularly, the present invention aims to provide a system capable of operating with one sensor only.

20 To this end, the present invention provides a ring-shaped torque-measuring device, to be mounted coaxially with the spider 28, and comprising an intermediate ring member and an inner ring member within the intermediate ring member. The inner ring member is fixed to the splined inner ring. The 25 intermediate ring member is coupled to the inner ring member by coupling members that are radially stiff. The intermediate ring member is coupled to the outer ring at a plurality of connection points via respective coupling members that are flexible. These coupling members exert individual tangential 30 forces on the intermediate ring member. While the pedals are rotated, the individual tangential force by each respective individual coupling member varies with the rotation angle, but the overall force exerted on the intermediate ring member, i.e. the summation of all individual tangential forces, is 35 substantially constant. Consequently, the tangential displacement of the intermediate ring member with respect to the inner ring member is substantially constant and can be measured with only one sensor. Or, the tangential force exerted by the intermediate ring member on the inner ring 5 member is substantially constant and can be measured with only one sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

5 These and other aspects, features and advantages of the.

present invention will be further explained by the following description of a preferred embodiment according to the present invention with reference to the drawings, in which same reference numerals indicate same or similar parts, and in 10 which: figure 1 schematically shows a cross section of a pedal system in a bicycle; figure 2 schematically illustrates a chain wheel assembly; figure 3 schematically shows a torque measuring device 15 according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Figure 3 schematically shows an embodiment of a torque measuring device 100 according to the present invention. The 20 torque measuring device 100 comprises an intermediate ring member 140 and an inner ring member 120 arranged coaxially with respect to each other. The torque measuring device 100 further comprises an inner coupling system 130 for mechanically coupling the intermediate ring member 140 and the 25 inner ring member 120 to each other. The coupling between the intermediate ring member 140 and the inner ring member 120 should have high radial stiffness. In the embodiment shown, the inner coupling system 130 comprises a plurality of inner coupling members 131, 132, each implemented as radial spokes, 30 each such spoke being solid such as to have relatively high radial stiffness.

The inner ring member 120 is provided with inner attachment members 121 for firmly attaching the inner ring member 120 to the inner ring 21 of the spider 28; in this 35 embodiment, the inner attachment members 121 are implemented as holes in the inner ring member 120, arranged on a common first circle, so that the inner ring member 120 can be fixed to the inner ring 21 by screws. Instead of an inner ring member 120 with a plurality of inner attachement members 121, 6 it is possible that inner coupling members 131, 132 are individually provided with inner attachment members.

The torque measuring device 100 further comprises a plurality of outer attachment members 110 for firm attachment 5 to the outer ring 22 of the spider 28; in this embodiment, outer attachment members 110 are implemented as circular screw eyes, arranged on a common second circle coaxial with the first common circle and having a radius larger than the first common circle, so that each outer attachment member 110 can be 10 fixed to the outer ring 22 by screws. It is noted that instead of circular, rings, the outer attachment members 110 may have another contour provided with a hole for„accomodating an attachment screw.

The torque measuring device 100 further comprises an 15 outer coupling system 150 for mechanically coupling the outer attachment members 110 to the intermediate ring member 140. In the embodiment shown, the outer coupling system 150 comprises a plurality of coiter coupling members 151, each individual outer coupling member 151 extending between a corresponding 20 outer attachment member 110 and a point of the intermediate ring member 140. Several designs are possible for the outer coupling members 151, as will be described later. In any case,, it is preferred that the outer coupling members 151 mutually have the same design. For sake of convenience, and as shown in 25 figure 3, it is preferred that the intermediate ring member 140, the outer attachment members 110 and the outer coupling members 151 form an integral whole, but it is even possible that the outer coupling members 151 are implemented as separate springs to be hooked in the outer ring 22 on the one 30 hand and in the intermediate ring member 140 on the other hand.

It is noted that, here, the outer attachment members 110 are radially aligned with the inner attachment members 121.

For sake of convenience, attachment points 26 for the 35 outer attachment members 110 are shown in the outer ring 22 of figure 2. The figure shows a preferred arrangement, where the number of attachment points 26 (and hence the number of attachment members 110) is equal to the number of holes 25 and 7 wherein the attachment points 26 are always arranged equidistantly between two neighbouring holes 25.

With respect to the design of the coupling members, the 5 following is noted.

It is preferred that all outer coupling members 151 are mutually equal, or at least have mutually identical stiffness properties, and are distributed evenly around the intermediate ring member 140. However, it is possible to use outer coupling 10 members of different types, in which case the members of each type are evenly distributed in order to achieve a preferred symmetry.

Likewise, it is preferred that all inner coupling members 131, 132 are mutually equal, or at least have mutually 15 identical stiffness properties, and are distributed evenly around the intermediate ring member 140. In the embodiment shown, there are two different types of inner coupling members 131, 132, wherein the members 131 of first type are distributed evenly and wherein the members 132 of second type 20 are distributed evenly.

In the embodiment shown, the coupling members 131, 132, 151 are implemented as solid members. This has the important advantage that the torque measuring device 100 can be manufactured as a whole out of one plate-shaped body, 25 including the coupling members. The material of this plateshaped body may be metal, for instance aluminium or steel or aluminium-on-steel. The material of this plate-shaped body may also be a glass fibre composite material. In a particularly useful embodiment, the material of this plate-shaped body was 30 made from glass fibre composite material laminated with a copper layer, specifically intended as printed circuit board (PCB), which has the advantage that an electronic circuit for processing measuring signals can be built on this plate, close to the sensor.

35 Each inner coupling member 131, 132 is implemented as a radial bar having its one end connected to the inner ring member 120 and having its opposite end connected to the intermediate ring member 140: this will provide radial stiffness. Coupling members 131 of first type are connected at 8 opposite ends to the inner and intermediate rings via relatively thin body parts, which can flex relatively easily, so that such coupling members 131 can bend relatively easily in the tangential direction. Coupling members 132 of second 5 type are connected to the inner ring member 120 via a similar relatively thin body part, but have larger tangential dimension (width) and are connected to the intermediate ring member 140 over substantially their entire width.

Each outer coupling member 151 in the exemplary '10 embodiment shown is implemented in an L-shaped contour, having a substantially radial foot part 152 and a substantially tangential leg part 153 connected together. The free end of the foot part 152 is connected to the intermediate ring member 140. The free end of the leg part 153 is connected to a 15 corresponding outer attachment member 110. Such design will make it relatively easy to design the radial stiffness and the tangential stifness of the outer coupling members 151 more or less independently from each other, by selecting suitable length and thickness for the foot part 152 and the leg part 20 153, as should be clear to a person skilled in the art.

In practice, the inner ring 21 of the spider 28 will show hardly or no deformation; in any case, such deformation may be neglected. Therefore, in the following, the operation of the 25 torque measuring device 100 will be described as seen in a coordinate system rotating with the inner attachment member 121, which means that the inner ring 21 with the inner attachment member 121 are considered to be stationary.

When a cyclist is cycling, the outer ring 22 will undergo 30 non-homogenous deformation and relative displacement with respect to the inner ring 21, as explained in the above. The inner attachment members 121 of the inner ring member 120 are fixedly attached to the inner ring 21 and the outer attachment members 110 are fixedly attached to the outer ring 22, so the 35 outer attachment members 110 are displaced with respect to the inner ring member 120. This relative displacement has a radial component and a tangential component; these components vary during rotation because of the varying chain force. Thus, during rotation of the pedals, each outer attachment member 9 110 will describe a cyclic path with respect to the inner ring member 120, such path having a radial amplitude and a tangential amplitude. Assuming the outer attachment member 110 are mutually identical, the respective paths are mutually 5 identical yet they differ in phase.

In radial direction, the path amplitude is relatively small. Further, in radial direction, the stiffness of the outer coupling members 151 is very low as compared to the relatively high radial stiffness of the inner coupling members 10 131, 132, while also the intermediate ring member 140 has a radial dimension such as to be sufficiently stiff. Therefore, in radial direction, the intermediate ring member 140 may be considered to be stationary.

In tangential direction, the stiffness of the individual 15 outer coupling members 151 will be indicated as cTi, i being an index distinguishing the individual coupling members 151. The momentary tangential displacement of the outer attachment members 110 with respect to the inner ring 21 will be indicated as dTi- Thus, when considering the intermediate ring 20 member 140 to be stationary, each individual outer coupling member 151 exert^ locally on the intermediate ring member 140 a tangential force fTj according to the formula fTi = cTi-dTi.

The intermediate ring member 140 is thus submitted to an overall tangential force FT that can be written as the 25 summation of all individual forces according to the formula

Ft = SfTi. While the individual tangential forces fTi exerted by the individual outer coupling members 151 may mutually differ from each other, and will periodically vary with the rotation of the pedals, the overall tangential force FT will be 30 substantially constant and will in any case be the same again after rotation of the spider 28 over 360°/N, N being the number of outer coupling members 151. It can be said that the intermediate ring member 140 functions to average out the individual force contributions.

35 As an overall result, the intermediate ring member 140 is rotated with respect to the inner ring member 120 over a substantially constant angle of rotation proportional to the chain force (which is proportional to the torque exerted by the cyclist), whereas in radial direction the intermediate 10 ring member 140 is held substantially stationary with respect to the inner ring member 120. Thus, the design of the torque measuring device 100 is effectively averaging the deformations of the radial spokes 24 of the chain wheel assembly 20.

5 Since the overall tangential force FT will be substantially constant and hence the rotation of the intermediate ring member 140 with respect to the inner ring member 120 will be substantially constant, i.e. does not ^-depend on the rotational position of the system, it is 10 possible to use a single sensor mounted at one single, suitably selected measuring location, between the intermediate ring member 140 and the inner ring member 120. The design of such sensor and the design of the system can be adapted to each other, as will be explained in the following.

15 While the overall tangential force FT exerted on the intermediate ring member 140 is substantially constant, the amount of tangential displacement of the intermediate ring member 140 as a whole (measured in mm or in degrees) with respect to the inner ring member 120 depends on the tangential 20 stiffness KT of the coupling between the intermediate ring member 140 and the inner ring member 120. This tangential stiffness can be written as KT = SkTi + kTS, wherein kTS indicates the tangential stiffness of the sensor, and wherein kTi indicates the individual tangential stiffness of an 25 individual inner coupling member 131, 132. Three specific embodiments will be described in more detail below.

In one embodiment, it is possible to use a force sensor, for instance implemented as a separate tension element (for instance a tangential tension bar) connected between the 30 intermediate ring member 140 and the inner ring member 120, and equipped with a strain gauge for meauring tension in this element. In such case, kTS and hence kT is very high, so that the intermediate ring member 140 can be considered as being stationary in tangential direction. The tangential stiffnesses 35 kti of the individual inner coupling members 131, 132 are preferably relatively low as compared to the outer coupling members 151 and can be neglected with respect to kTS. The tangential displacement of the outer attachment members 110 is entirely with respect to the intermediate ring member 140, and 11 the tangential stiffnesses cTi of the individual outer coupling members 151 should be selected to be high enough to induce sufficient force on the tension element while also being low enough to accommodate said displacements without leading to 5 too high forces on the intermediate ring member 140. Further, the elasticity and flexibility of the individual outer coupling members 151 should be sufficient to accommodate said displacements.

In another embodiment, the sensor can be implemented as a 10 strain gauge 160 mounted on an inner coupling member 132, as schematically illustrated, to measure deformation of such inner coupling member.

In a third embodiment, it is possible to use a displacement sensor, for instance implemented as a Hall 15 sensor, to measure directly the displacement of the intermediate ring member 140 with respect to the inner ring member 120. Since strain gauges and Hall sensors are commonly known, a further explanation is omitted here. In this case, the tangential stiffness of the outer coupling members 151 is 20 designed to be higher than the tangential stiffness of the inner coupling members 131, 132, such as to result in sufficient displacement of the intermediate ring member 140.

In an extreme case, the displacement of the intermediate ring member 140 with respect to the inner ring 21 is equal to the 25 average of the individual tangential displacements dTi of the outer attachment members 110 with respect to the inner ring 21, and the inner coupling members 131, 132 should be flexible enough to accommodate this displacement. Preferably, deformation of the inner coupling members 131, 132 should stay 30 within the elastic region, more preferably the linear elastic region; the same applies to the outer coupling members 151.

Thus, there is some design freedom with respect to the precise stiffnesses of the outer coupling members 151 and the 35 inner coupling members 110. The ratio between these stiffnesses will have influence on the precise angle of rotation of the intermediate ring member 140 with respect to the inner ring member 120. In case a strain gauge is used, such rotation angle can be relatively small. In case a Hall

. —J

12 sensor is used, the rotation angle is preferably somewhat hihger such as to correspond, at maximum torque, to a tangential displacement in the order of about 0.05 to 0.3 mm, at the position of the Hall sensor and depending on the 5 sensitivity of the Hall sensor.

Figure 3 also schematically shows a signal processing device 170, for instance implemented as a microprocessor, also mounted on the intermediate ring member 140 and receiving a 10 signal from the sensor 160,,. The processing device 17 0 is designed for wirelessly transmitting an output signal to a display 180 or control unit (not shown) mounted stationary to the bicycle frame. The display signal may include the pedal torque. It is also possible to display the pedal frequency 15 and/or the pedal power, for which it would be necessary to have a signal indicating the pedal revolution speed or pedal revolution time. These parameters can easily be obtained using for instance a reed relais, or a mercury switch, or a hall sensor, or an acceleration sensor. Alternatively, it would be 20 possible for the signal processing device 170 to calculate the pedal revolution time from a periodical change in the torque signal, which is caused by the natural periodic varying force of the cyclist on the pedals, which is related to the position of the pedals. By multiplying torque and revolution speed, the 25 signal processing device 170 may calculate the power exerted by the cyclist. The signal processing device 170 may communicate this power via a wireless transmission signal: in the case of control of electric bicycle propulsion or in the case of scientific power analysis, this power may be the 30 momentaneous power, but in the case of a power measurement system on a spinning bike or racing bicycle, the signal may communicate an average power.

It should be clear to a person skilled in the art that ' 35 the present invention is not limited to the exemplary émbodiments discussed above, but that several variations and modifications are possible within the protective scope of the invention as defined in the appending claims.

13.

Features described in relation to a particular embodiment can also be applied to other embodiments described. Features of different embodiments may be combined to achieve another embodiment. Features not explicitly indicated as being 5 essential may be omitted. Where the text mentions that two parts are coupled together, this may involve a direct coupling but also an indirect coupling, i.e. for instance via a third part or without contact.

The reference numerals used in the claims only serve as 10 clarification when understanding the claims with a view to the exemplary embodiments described, and should not be interpreted in any way limiting.

1037563

Claims

A torque measuring device (100) for measuring the relative torque between two annular members (21), (22) arranged coaxially with respect to each other and connected to each other by spokes (24), which measuring device 5 comprises: inner ring member (120) provided with a series of first attachment members (121) for attachment to the interior of said annular members (21); a series of second fasteners (110) for fastening 10 to the outer of said annular members (22); an intermediate ring member (140) disposed between said inner ring member (120) and said second fastening members (110); a plurality of first coupling members (131), (132) for mechanically coupling the inner ring member (120) to said intermediate ring member (140); a plurality of second coupling members (151) for mechanically coupling the second mounting member (110) to said intermediate ring member (140); Wherein the first coupling members (131), (132) have a high radial stiffness compared to the second coupling members (151).

2. Torque measuring device according to claim 1, wherein the inner ring member (120) is located within said intermediate ring member (140) and is coaxial thereto, while the first fixing members (121) are preferably located on a first common circle; wherein the second fasteners (110) are located outside said intermediate ring member (140), preferably on a second common circle coaxial with said first common circle.

3. Coupling measuring device as claimed in any of the foregoing claims, wherein the first coupling members (131), (132) are directed substantially radially. 1 0 3 7 5 63

A torque measuring device according to any of the preceding claims, wherein the second coupling members (151) comprise a substantially tangentially directed leg part (153). 5

5. Coupling measuring device according to any of the preceding claims, as a whole made of PCB.

6. Coupling measuring device as claimed in any of the foregoing claims, provided with a displacement sensor for measuring a tangential displacement of the intermediate ring member (140) relative to the inner ring member (120), which sensor comprises, for example, a strain gauge and / or a hall sensor.

7. Torque measuring device according to any of the preceding claims, provided with a force sensor for measuring a tangential force of the intermediate ring member (140) exerted on the inner ring member (120), which sensor 20 comprises, for example, a tensioning element provided with a strain gauge.

8. Coupling measuring device as claimed in any of the foregoing claims, wherein the first coupling members (131), (132) have a low tangential stiffness compared to the second coupling members (151), wherein the tangential stiffness of the second coupling members (151) is preferably about 2 to 10 times as high as the tangential stiffness of the first coupling members (131), (132). 30

The torque measuring device of claim 6 or 7, further comprising a signal processing device (170) that receives an output signal from the sensor.

The torque measuring device according to claim 9, further comprising a revolution sensor, for example a reed switch, an acceleration sensor, a mercury switch, a light switch, which revolution sensor provides a revolution signal to the signal processing device.

A torque measuring device according to claim 9, wherein the signal processing device (170) is designed to wirelessly send an output signal to a display (180), said output signal preferably comprising a torque output signal and / or a revolution speed signal and / or a power signal ; and wherein preferably the signal processing device (170) is capable of calculating the power exerted by the cyclist by multiplying torque and speed of rotation with each other.

12. Transmission wheel (20), comprising: a spider (28), which spider comprises: an inner ring (21) for mounting on a shaft (11); an outer ring (22) disposed coaxially with respect to the inner ring (21); a series of spokes (24) connecting the inner ring (21) to the outer ring (22), which spokes are preferably 20 radial spokes; and a torque measuring device (100) according to any of the preceding claims, which has its first mounting members (121) attached to the inner ring (21) of the spider and which has its second mounting members (110) attached to the outer ring (22) of the spider.

13. Transmission wheel (20) according to claim 12, wherein the inner ring (21), the outer ring (22) and the spokes (24) are made as one integral molding, preferably from aluminum or steel.

A transmission wheel according to any of claims 12-13, wherein the tangential stiffness of the spokes (24) is higher than the tangential stiffness of the coupling members 35 (131), (132); (151) of the torque measuring device.

A transmission wheel according to any of claims 12-14, wherein the outer ring (22) comprises: a) a series of teeth for engaging a transmission chain, the series of teeth being either formed as one integral mold with the outer ring (22) or be part of a separate sprocket that is attached to the outer ring (22); b) a pulley for engagement with a transmission belt, the pulley being formed as one integral mold with the outer ring (22) or part of a separate wheel blade attached to the outer ring (22); or c) a tapered gear for engaging a tapered gear of a transmission shaft, the tapered gear being formed as one integral mold with the outer ring (22) or part of a separate member attached to the outer ring (22).

A pedal system (10), comprising: a pedal shaft (11); Two pedal arms (13) mounted at respective ends of the pedal shaft (11) with respective pedals (12); and a transmission wheel (20) according to any of claims 12-15 which has its outer ring (21) coupled to the pedal shaft (11). 25

A pedal-driven device comprising a pedal system (11) according to claim 16.

A bicycle (1) comprising: a crankshaft bearing (2) and a pedal system (10) according to claim 16, wherein the pedal system (10) has its pedal shaft (11) mounted for rotation in the crankshaft bearing (2). ^ 3 75 6 3