WO2003076260A1

WO2003076260A1 - Transmission system having radially adjustable sprockets

Info

Publication number: WO2003076260A1
Application number: PCT/CA2003/000336
Authority: WO
Inventors: Alain Bernard
Original assignee: Alain Bernard
Priority date: 2002-03-12
Filing date: 2003-03-12
Publication date: 2003-09-18
Also published as: AU2003208239A1; GB0205710D0

Abstract

A transmission system including a first sprocket wheel having a set of first sprockets movably attached thereto for translational movement in a radial direction substantially perpendicular to the first wheel axis of rotation. The first sprockets are selectively movable between a first sprocket retracted configuration and a first sprocket expanded configuration wherein the first sprockets are positioned radially outwardly when in the first sprocket expanded configuration comparatively to when the first sprockets are in the first sprocket retracted configuration. A first sprocket moving system is operatively coupled to the first sprockets for selectively moving the first sprockets between the first sprocket retracted and expanded configurations. The transmission system also includes a second sprocket wheel, the second sprocket wheel being rotatable about a second wheel axis; the second sprocket wheel having a set of second sprockets extending therefrom; a transmission chain for mechanically coupling the first sprocket wheel and the second sprocket wheel, the transmission chain having chain links for engaging both the first and second sprockets; either one of the first or second sprocket wheels being attachable to the driving shaft while the other one of the first or second sprocket wheels is attachable to the driven shaft; whereby the first sprockets define a first sprocket diameter, the second sprockets define a second sprocket diameter and the ratio of the first sprocket diameter to the second sprocket diameter defines a gear ratio, the first sprocket moving means allowing for selective adjustment of the gear ratio by selective adjustment of the first sprocket diameter through selective movement of the first sprockets between the first sprocket expanded and retracted configurations.

Description

Patent application of :

Alain Bernard for a:

Transmission System Having Radially Adjustable Sprockets FIELD OF THE INVENTION:

The present invention relates to the general field of vehicle components and is particularly concerned with a transmission system having radially adjustable sprockets.

BACKGROUND OF THE INVENTION:

A large number of vehicles use a transmission system for transmitting a propelling force generated by a motor, muscle action or any other type of power generating means to the driving wheels of the vehicle. In the following text, a transmission system is disclosed as being used in the context of transmitting power to the wheels of a conventional bicycle. It should, however be understood that the present invention could also be applied to other types of vehicles without departing from the scope of the present invention.

Most multiple speed bicycles typically include a bicycle frame having a top tube, a down tube, a seat tube, a pair of seat stays and a pair of chain stays. The top, down and seat tubes generally define a frontwardly positioned triangle of the bicycle frame, with the seat tube, seat stays and chain stays collectively defining a rear triangle of the bicycle frame.

Typically, the back ends of corresponding pairs of the seat and chain stays are attached to respective ones of an opposed pair of drop-outs for accommodating the rear wheel axle of the rear wheel. Also, the bottom ends of the down and seat tubes and the front ends of the chain stays are typically attached to a sleeve which rotatably accommodates a bottom bracket axle. Conventionally, attached to the bottom bracket axle is a pair of pedal cranks, each of which includes a pedal rotatably connected thereto.

Typically, a multiple chain wheels of differing diameters are also attached to the bottom bracket axle although, in some situations, only one chain wheel is attached to the bottom bracket axle. Similarly, a sprocket cluster is typically attached to the rear wheel axle. The sprocket cluster includes multiple sprockets of differing diameters. One of the chain wheels is mechanically coupled to one of the sprockets of the sprocket cluster via a drive-chain.

With most conventional multiple speed bicycles, the drive-chain may be selectively shifted unto any one of the chain wheels via a front derailleur. Most conventional front derailleurs are typically attached to the seat tube. Additionally, the drive-chain may be selectively shifted to any one of the sprockets of the sprocket cluster via a rear derailleur which is typically attached to one of the drop outs.

Hence, for many years, it has been a common practice of bicycle manufacturers to provide, as original equipment, ratio changing power transmissions in the power train between the pedal crank and the traction wheel of the vehicle. The gear ratio of the transmission is typically defined as the ratio of the diameter of the drive sprocket on the pedal crank to the diameter of the driven sprocket on the traction wheel. This gear ratio produces a speed ratio of the same value between the drive and driven sprockets.

Typically, in bicycle parlance, the lowest speed ratio, that is the lower speed range is called first speed or first gear and higher ratios are called second, third and fourth speed and so on. A bicycle provided with a transmission having three different speed ratios is referred to as a three-speed bicycle, one having ten different ratios is referred to as a ten-speed bicycle and so on. Bicycles are commonly provided with three-speeds, ten-speeds, fifteen-speed and twenty-speed transmissions.

With conventional transmission systems, the range of transmission ratios between the bottom bracket assembly rotating speed and the wheel rotating speed extends between two extreme ratios, one of which corresponds to the larger chain wheel and the smaller sprocket and the other corresponds to the smallest chain wheel and the largest sprocket. There exists a certain number of intermediate ratios between these two ratios which depend on the number of sprockets and chain wheels.

During a ratio change, the variation in the transmission ratio does not have the same amplitude, depending upon whether one changes a chain wheel or a sprocket. It is known that for the various chain wheels, the ratio changes obtained by sweeping the entire sprocket cassette, overlaps. Hence, out of the set of possible ratios, which is equal to the number of sprockets multiplied by the number of chain wheels, only a portion, approximately one half, is actually exploited, or actually useful. For example, the same ratio or almost the same ratio can be obtained with two different combinations between the chain wheels and the sprockets.

If a progressive variation in the transmission ratio is desired, a change of chain wheels must be accompanied by a change of one or two, or even three sprockets in the reverse direction to compensate for the jump due to the change of chain wheel. Such a maneuver is relatively slow and causes a break in the pedaling rate. This break is all the more pronounced as the change of chain wheel requires momentarily lightening the force exerted on the pedals to reduce the tension on the tensioned chain strand.

In addition, such a system lacks uniformity in the progression of the ratios. For example, the rate of increase or decrease in the transmission ratio varies in an irregular manner when shifting gears, mainly upon the change of chain wheel. This rate is related to the variation in torque that the cyclist exerts on the pedals. Certain gear shifts yield substantial variation in torque or, conversely, small variations resulting in lack of ease of use by the cyclist.

There also exists problems related to the chain alignment, for example, it is not recommended to associate the small sprocket with the small chain wheel and conversely. An incorrect alignment causes a loss of inefficiency, undesirable friction and noise during a change of sprocket and chain wheels. Certain combinations of sprocket and chain wheels are not used for these reasons.

As mentioned previously, the ratio changing is accomplished by a mechanism called a derailleur which controllably shifts the chain from engagement with one sprocket wheel to another. A manual actuating shifter lever, usually mounted on the front part of the down tube or top tube of the bicycle frame, is connected by a cable to the derailleur.

In the conventional bicycle transmission shifter, the pedal sprocket derailleur includes a laterally moveable chain cage which urges the chain into alignment with the selected one of the sprockets at the pedal crank. The wheel sprocket derailleur comprises a guide sprocket and tensioning sprocket which successively engage the chain in its slack portion (as distinguished from its driving portion) between the pedal sprocket and the wheel sprocket. The sprocket wheels are axially aligned and laterally displaced from each other with progressively larger diameters from the outboard to the inboard sprocket. The derailleur is provided with a cable operated transfer levers, typically a spring loaded bell-crank lever that shifts the guide sprocket laterally so that it can be aligned with any one of the sprocket wheels.

Although prior art multiple speed bicycles have been in existence from many years, they possess certain deficiencies which detract from their overall utility. Some of these deficiencies are related to the transmission system and particularly the use of conventional derailleur. Although the conventional derailleur leaves much to be desired, it is still the predominant type of bicycle shifting mechanism.

Shifting by the rear derailleur is accomplished by repositioning the selector lever during pedaling to move the guide sprocket, and hence the chain, in either inboard or outboard direction to the adjacent sprocket. This lateral movement of the guide sprocket leads the chain from meshing engagement with one sprocket to a position in which it picks up a tooth of the adjacent sprocket and become meshed therewith. The shifting is controlled by the rider mostly by the feel of the selector lever and the resultant interaction of the chain and sprocket.

Even for a skilled rider on a familiar bicycle with a well adjusted derailleur, shifting sometimes results in a relatively rough transition from one speed to another. The problem is further compounded for a rider of lesser skill, especially with an unfamiliar bicycle and a poorly adjusted derailleur.

Also, the front and rear derailleur of most prior art bicycles are of complex construction and typically include multiple parts or components. As such, the derailleurs are susceptible to mechanical failure or breakage, particularly when the bicycle is used in off-road conditions as generally occurs with multiple speed mountain bikes and the like.

Additionally, because of their relatively complex construction, the front and rear derailleurs are also susceptible to being displaced from their normal orientation and falling out of proper adjustment when exposed to debris, such as dirt or rocks, or when subjected to a sudden impact force that typically occurs when the rider falls. Any such displacement of the front or rear derailleur usually causes the drive chain to be completely disengaged from the chain wheels or the sprockets of the sprocket cluster when shifting between the chain wheels or the sprockets is attempted by the rider. The readjustment of the front and rear derailleur or the repair thereof, in the event of breakage, is usually both expensive and time consuming. Additionally, because of the relatively large number of sprockets typically included in the sprocket cluster of the rear wheel axle, the rear wheel cannot be provided with a wide "stance" that could assist in the handling of the bicycle.

The ability to more readily customize a speed changing mechanism to provide a desired set of specific gear ratios or speeds on a rider-by-rider basis could also be desirable given the wide range of riding experience, physical condition and general athletic ability encountered in the bicycle-riding community. This capability would be likely to be limited in conventional derailleur-based systems, since adjacent gears in the drive gear set and adjacent gears in the driven gear set, generally have to be relative close inside to allow drive chain to be easily moved from one gear to the next.

An additional drawback of current derailleur-based speed changing mechanism relates to the type of shift mechanism employed to affect the selection of the desired speed. In a system employing both front and rear derailleurs, two separate shift levers are used, and frequently are designed and installed on the bicycle such that shifting to a smaller sprocket on both the front and rear derailleur involves moving the shift levers in the same direction. However, moving to a smaller sprocket on the front derailleur has the opposite effect of moving to a smaller sprocket on the rear derailleur. This shift pattern can cause confusion to the rider in determining what shifting action need to the effected in order to bring about the desired speed change.

Inasmuch as the art consist of various types of bicycles, it can be appreciated that there is a continuing need or an interest in providing an improved gear mechanism for vehicles such as bicycles and more particularly for an improved transmission system which could circumvent the hereinabove mentioned disadvantages. SUMMARY OF THE INVENTION:

Advantage of the present invention include that the proposed transmission system, when used in the context of bicycles, provides for a smooth transition from a resting position to high speed without the usual shifting of gears that is encountered on conventional multi-speed bicycles. Also, the proposed transmission mechanism allows for the customization of gear ratios or speeds on a rider-by-rider basis.

Furthermore, the proposed transmission system allows for the shifting of gears through a set of ergonomical steps, with reduced risks of confusing the rider when the latter determines what shifting action needs to be affected in order to bring about the desired speed change.

Also, the proposed transmission system is designed so as to be light weight and relatively compact. Furthermore, it is designed so as to be less susceptible to mechanical failure or breakage even when the bicycle is used in off-road conditions.

Furthermore, the proposed transmission system is designed so as to be adaptable and eventually retro-fittable to most types of conventional bicycles without requiring special tooling or manual dexterity and through a set of easy and ergonomical steps. Also, the proposed transmission system is designed so as to be substantially aerodynamical and may even be positioned within the frame and/or wheel(s) of the vehicle.

Still further, the proposed transmission system is designed so as to be manufacturable through conventional forms of manufacturing and with conventional pieces of equipment so as to produce a transmission system that will be economically feasible, long lasting and relatively trouble free in operation. In accordance with the present invention, there is provided a transmission system for controllably transmitting to a driven shaft the torque emanating from a driving shaft, the transmission system comprising: a first sprocket wheel, the first sprocket wheel being rotatable about a first wheel axis; the first sprocket wheel having a set of first sprockets movably attached thereto for translational movement in a radial direction substantially perpendicular to the first wheel axis, the first sprockets being selectively movable between a first sprocket retracted configuration and a first sprocket expanded configuration wherein the first sprockets are positioned radially outwardly when in the first sprocket expanded configuration comparatively to when the first sprockets are in the first sprocket retracted configuration; a first sprocket moving means operatively coupled to the first sprockets for selectively moving the first sprockets between the first sprocket retracted and expanded configurations; a second sprocket wheel, the second sprocket wheel being rotatable about a second wheel axis; the second sprocket wheel having a set of second sprockets extending therefrom; a transmission chain for mechanically coupling the first sprocket wheel and the second sprocket wheel, the transmission chain having chain links for engaging both the first and second sprockets; either one of the first or second sprocket wheels being attachable to the driving shaft while the other one of the first or second sprocket wheels is attachable to the driven shaft; whereby the first sprockets define a first sprocket diameter, the second sprockets define a second sprocket diameter and the ratio of the first sprocket diameter to the second sprocket diameter defines a gear ratio, the first sprocket moving means allowing for selective adjustment of the gear ratio by selective adjustment of the first sprocket diameter through selective movement of the first sprockets between the first sprocket expanded and retracted configurations.

Conveniently, the transmission system also comprises a movement timing means operatively coupled to the first sprockets for timing the translational movement of the first sprockets in the radial direction with the angular position of the first sprockets relative to the first wheel axis so as to ensure that the translational movement of the first sprockets occurs when the first sprockets are not in direct contact with the transmission chain. Typically, the first sprocket wheel includes a first wheel hub mountable on the first shaft and a set of first wheel arms extending substantially radially and outwardly from the first wheel hub; a carriage component being slidably mounted on at least some of the first wheel arms for slidable movement at least partially therealong; at least one first sprocket being attached to at least some of the carriage components for movement solidarly therewith between the sprocket expanded and retracted configurations.

Conveniently, at least one of the carriage components includes a substantially radially extending sprocket attachment section; at least one of the first sprockets being selectively and releasably attachable at two distinct positions along at least a portion of the sprocket attachment section so as to allow for the customization of the radial positioning of the at least one of the first sprockets relative to a corresponding sprocket attachment section; whereby the customization of the radial positioning of the at least one of the first sprockets relative to the sprocket attachment section allows for the customization of at least part of the first sprocket diameter.

Typically, the first sprocket moving means includes a piston component operatively coupled to at least some of the sprocket attachment sections and a fluid circuitry fluidly coupled to the piston components for selectively moving at least some of the moving sprockets between the expanded and retracted configurations.

Conveniently, the first sprocket wheel includes a first wheel hub and a set of first wheel arms extending substantially radially and outwardly from the first wheel hub; each of the first wheel arm defining a radially proximal arm proximal end and a radially opposed arm distal end; each of the first wheel arm also defining an arm first lateral surface and an opposed arm second lateral surface; each of the first wheel arm having a substantially radially oriented piston chamber formed therein, the piston chamber defining a radially proximal chamber proximal end and an opposed chamber distal end, the first sprocket moving means including a piston component mounted in the piston chamber for reciprocal movement therein and a piston moving means for reciprocating the piston component within the piston chamber, the piston component defining a radially proximal piston proximal end and an opposed piston distal end; the first sprocket moving means also including a carriage component attached to the piston component for reciprocal movement solidarly therewith; a first sprocket being attached to the carriage component for reciprocal movement between the sprocket expanded and retracted configurations.

Typically, each of the first wheel arms has an arm fluid channel extending from an exterior surface thereof to the piston chamber substantially adjacent the chamber proximal end for allowing fluid flow therethough; the first sprocket moving means also including a pressure creating means for selectively forcing the flow of a fluid under pressure through the arm fluid channel into the piston chamber between the chamber and piston proximal ends so as to fluidly urge the piston component towards the chamber distal end; the first sprocket moving means also including a piston biasing means for biasing the piston component towards the chamber proximal end.

Conveniently, the piston chamber defines a spring receiving section located substantially adjacent the chamber distal end, the piston biasing means including a spring component mounted within the spring receiving section, the spring component defining a radially proximal spring proximal end and an opposed spring distal end, the spring component being configured and sized so as to be resiliently compressed when the piston is moved towards the chamber distal end.

Optionally, the biasing component is provided with a biasing force adjustment means for allowing adjustment of the strength of the biasing force exerted by the spring component when the spring component is being compressed.

Typically, each of the carriage components includes a substantially radially extending sprocket attachment section for allowing attachment thereto of a first sprocket and a substantially perpendicular piston attachment section for allowing attachment thereof to the piston component, the first sprocket being releasably attachable at various radial locations along the sprocket attachment section; each of the first wheel arms having a carriage receiving slot extending at least partially therealong for receiving a portion of the piston attachment section and allowing attachment of the piston attachment section to the piston component; the carriage receiving slot allowing the slidable movement therein of the piston attachment section when the piston component reciprocates within the piston chamber.

In one embodiment of the invention, a set of sprockets is attached to each of the sprocket attachment sections; each set of sprockets extending from a common generally arcuate sprocket base plate, each of the sprocket base plates defining a pair of opposed base lateral peripheral edges and a pair of substantially perpendicular base end edges; the sprocket base plate having a plate attachment flange extending substantially radially therefrom substantially adjacent to one of the base lateral edges; the sprocket base plate also having a stabilizing protrusion extending substantially laterally therefrom from a position located substantially adjacent the opposed base lateral edge; the transmission system being further provided with a sprocket stabilizing component for engaging the stabilizing protrusion so as to stabilize the set of sprockets.

Typically, the sprocket stabilizing component includes a set of substantially radially extending stabilizing arms, the stabilizing arms being positioned, configured and sized so as to be substantially in register with the first wheel arms and in a laterally spaced relationship therewith; each of the stabilizing arms being provided with a stabilizing slot formed therein for receiving a corresponding stabilizing protrusion and allowing slidable movement thereof when the sprocket base plate reciprocates as the first sprockets part of a corresponding set of sprockets move between the sprocket expanded and retracted configurations. Conveniently, each of the arm fluid channels is in fluid communication with a corresponding venting channel leading to a venting aperture.

In one embodiment of the invention, the first wheel arms merge integrally with each other about a proximal segment thereof so as to form a merged portion having a substantially disc-shaped configuration; each of the carriage components being mounted on the arm first lateral surface and each of the arm fluid channels extending from a corresponding piston chamber to a corresponding channel aperture located in the merged portion on the outer surface of the arm second lateral surface; the channel apertures being offset relative to each other both radially and circumferentially; the channel apertures being separated from each other radially by circumferential arm sealing rings defining arm annular segments therebetween; the timing means including a fluid distributing component fluidly coupled to the arm annular segments for selectively and sequentially distributing a pressurized fluid to the channel apertures.

Conveniently, the fluid distributing component has a substantially annular configuration defining an annular lateral distribution surface and a radial distribution peripheral surface; the fluid distribution component having a set of distribution channels extending therethrough from corresponding peripheral distribution apertures formed in the radial distribution peripheral surface to corresponding lateral distribution apertures formed in the annular lateral distribution surface; the lateral distribution apertures being separated radially from each other by circumferential distribution sealing rings defining distribution segments therebetween; the lateral distribution surface being positionable laterally against the arm second lateral surface and rotatable relative to the latter with the distribution sealing rings sealingly contacting the arm sealing rings so as to prevent radial flow of the pressurized fluid between distribution segments and between arm segments; each distribution and corresponding channel apertures being configured, sized and positioned relative to each other so as to allow the flow of the pressurized fluid therebetween only when the first arm wheel is in a rotational position such that the corresponding sprockets associated with corresponding distribution and channel apertures are not in contact with the transmission chain.

Typically, the transmission system further comprises an actuating means for allowing selective movement of the set of sprockets between the retracted and expanded configurations; the actuating means including an actuating manifold defining a set of actuating chambers; each of the actuating chamber being fluidly coupled to a corresponding fluid duct in fluid communication with a corresponding peripheral distribution aperture; each of the actuating chambers having an actuating piston mounted therein for reciprocal movement between a first actuating configuration and a second actuating configuration wherein the actuating piston respectively urges the pressurized fluid outwardly and allows the fluid to penetrate the actuating chamber through the fluid duct; a main trigger plate being mechanically individually coupled to each of the actuating pistons by a plate-to-piston coupling component, each of the plate-to-piston coupling component being resiliently deformable so as to be able to transmit an actuating force exerted on the main trigger plate to a corresponding actuating piston when the latter is movable towards the first actuating configuration and so as to be able to resiliently deform when the actuating force is exerted on the main trigger and the corresponding actuating piston is prevented from moving towards the first actuating configuration.

In accordance with the present invention, there is also provided a transmission system for controllably transmitting to a driven shaft the torque emanating from a driving shaft, the transmission system comprising: a variable diameter sprocket wheel having a plurality of radially displaceable sprockets, the sprocket wheel being rotatable about a rotation axis, actuating means coupled to the sprockets for allowing the selective radial displacement of the sprockets; a movement timing means operatively coupled to the sprockets for timing the radial movement of the sprockets with the angular position of the sprockets relative to the rotation axis so as to ensure that the radial movement of the sprockets is only allowed when the sprockets are in a predetermined angular position range.

Typically, the sprockets are displaceable radially through a predetermined radial displacement range between a first radial position located at a first radial distance from the rotation axis and a second radial position located at a second radial distance from the rotation axis, the transmission system being further provided with a customization means for allowing the customization of the first and second radial positions.

Conveniently, the sprockets extend substantially in a radial direction relative to the rotation axis, the transmission system being further provided with a sprocket stabilizing means for stabilizing the sprockets in an axial direction substantially perpendicular to the radial direction and parallel to the rotation axis. Typically, the stabilizing means also stabilizes the sprockets in a direction parallel to the rotation axis.

Other objects and advantages of the present invention will become apparent from a careful reading of the detailed description provided herein, within appropriate refέrence to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the present invention will now be disclosed, by way of example, in reference to the following drawings in which:

Figure 1, in a schematic side elevational view, illustrates a transmission system in accordance with an embodiment of the present invention, the transmission system being mounted on a conventional bicycle; Figure 2, in a partial exploded view with sections taken out, illustrates some of the components of the front derailleur shown in Fig. 1 ;

Figure 3, in a side elevational view, illustrates part of the front derailleur as shown in Figs. 1 and 2;

Figure 4, in a partial transversal cross-sectional view taken along arrows 4-4 of Fig. 3, illustrates some of the components of the front derailleur shown in Figs. 1 through 3;

Figure 5, in a partial transversal cross-sectional view similar to that of Fig. 4, illustrates some of the components of the rear derailleur as shown in Fig. 1 ;

Figure 6, in a close-up partial cross-sectional view, illustrate in greater detail some of the components shown in Fig. 5;

Figure 7, in a side elevational view taken along arrows 7-7- of Fig. 4, illustrates some of the features of a fluid distributing component part of a transmission system in accordance with an embodiment of the present invention;

Figure 8, in a side elevational view taken along arrows 8-8 of Fig. 4, illustrates some of the features of the sprocket wheel shown in Fig. 4;

Figure 9a, in a perspective view, illustrates a set of sprockets attached to the sprocket attachment section part of a transmission system in accordance with an embodiment of the present invention; Figure 9b, in a side elevational view, illustrates the set of sprockets and sprocket attachment section shown in Fig. 9a;

Figure 9c, in a longitudinal cross-sectional view, illustrates some of the features of the set of sprockets and sprocket attachment component shown in Figs. 9a and 9b;

Figure 9d, in a top view taken along arrows 9d-9d of Fig. 5, illustrates some of the features of the set of sprockets and attachment section shown in Figs. 9a through 9c;

Figure 10a, in a side elevational view, illustrates an actuating component part of the transmission system in accordance with an embodiment of the present invention;

Figure 10b, in a cross-sectional view taken along arrows 10b-10b of Fig. 10c, illustrates some of the features of the actuating component shown in Fig. 10a;

Figure 10c, in a top view, illustrates the actuating components shown in Figs. 10a and 10b.

Figure 11a: in a schematic elevational view, illustrates the positioning of piston components, part of a transmission system, in accordance with an embodiment of the present invention, when the piston components are in a fully retracted configuration;

Figure 11b: in a schematic elevational side view, illustrates the movement of a piston, part of a transmission system, in accordance with an embodiment of the present invention, when the piston is in move from a retracted to an extended configuration; Figure 11c: in a schematic side elevational view, illustrates the movement of a second piston, part of a transmission system, in accordance with an embodiment of the present invention, as the second piston is being moved from a retracted to an extended configuration;

Figure 12a: in a schematic side elevational view, illustrates the positioning of pistons, part of a transmission system, in accordance with an embodiment of the present invention, as the pistons are in their fully extended configuration;

Figure 12b: in a side schematic elevational view, illustrates the positioning of a piston, part of a transmission system, in accordance with an embodiment of the present invention, as the piston is being moved from an extended to a retracted position;

Figure 12c: in a schematic side elevational view, illustrates the retraction of a pair of pistons, part of a transmission system, in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to Fig. 1, there is shown a transmission system 10, in accordance with an embodiment of the present invention. The transmission system 10 is shown mounted on a conventional bicycle 12. It should, however, be understood that the transmission system 10 could be used in other contexts such as with other types of vehicles or mechanical devices without departing from the scope of the present invention.

The transmission system 10 is typically used for controllably transmitting to a driven shaft the torque emanating from a driving shaft. When mounted on a conventional bicycle such as the bicycle 12, the transmission system 10 is typically used for controllably transmitting to the rear axle 14 and, hence, to a rear wheel 14 the torque emanating from the bottom bracket axle 16. As is well known in the art, conventional bicycles such as the bicycle 12 typically include a top tube 18, a seat tube 20 and a down tube 22 defining a so-called front triangle. The frame of the bicycle 12 also includes a pair of seat stays 24 (only one of which is shown) and a pair of chain stays 26 (only one of which is shown) defining together with the seat tube 20 a so-called rear triangle.

The back ends of corresponding pairs of the seat and chain stays 24, 26 are attached to respective ones of an opposed pair of drop-outs for accommodating the rear axle 14 of the rear wheel 28. The bottom ends of the down and seat tubes 22, 20 and the front ends of the chain stays 26 are typically attached to a sleeve 30 which rotatably accommodates the bottom bracket axle 16. A pair of pedal cranks 32 (only one of which is shown) is attached adjacent opposite ends of the bottom bracket axle 16. A pedal 34 is rotatably connected to each pedal crank 32.

The conventional bicycle 12 is typically further provided with a seat 36 attached to a seat post 38 telescopically inserted in the seat tube 20. Also, a front wheel 40 is attached to a front wheel axle 42 supported by a forked yoke 44 having a mounting segment rotatably mounted in a handle tube 46 and attached to a handle bar 48.

In the embodiment shown in Fig. 1 , the transmission system 10 includes a first sprocket wheel 50 mounted adjacent the intersection of the seat and down tubes 20, 22 and mechanically coupled to the bottom bracket axle 16 for rotatable movement about a first wheel axis 52 shown in Fig. 4. The transmission system 10 also includes a second sprocket wheel 54 mounted adjacent the intersection of the seat and chain stays 24, 26 for mechanical coupling to the rear axle 14. The second sprocket wheel 54 is mounted so as to be rotatable about a second wheel axis 56 shown in Fig. 5.

Fig, 1 illustrates a situation wherein both the first and second sprocket wheels 50, 54 are provided with radially adjustable sprockets. It should however be understood that only either one of the first or second sprocket wheels 50, 54 can be provided with radially adjustable sprockets without departing from the scope of the present invention.

As illustrated more specifically in Fig. 2 and 4, the first sprocket wheel 50 is provided with a set of first sprockets 58 movably attached thereto for translational movement in a radial direction indicated by arrows A in Fig. 3. The first sprockets 58 are hence movably attached for translational movement in a direction substantially perpendicular to the first wheel axis 52.

The first sprockets 58 are selectively movable between a first sprocket retracted configuration shown in Figs. 1 through 4 and a first sprocket expanded configuration (not shown). When in the first sprocket expanded configuration, the first sprockets 58 are positioned radially outwardly comparatively to when the first sprockets 58 are in the first sprocket retracted configuration. A first sprocket moving means operatively coupled to the first sprockets 58 is provided for selectively moving the first sprockets 58 between the first sprocket retracted and expanded configurations.

A transmission chain 60 or other suitable linking means is used for mechanically coupling the first sprocket wheel 50 and the second sprocket wheel 54. Typically, second sprocket wheel 54 is provided with a set of second sprockets 62 extending therefrom. Typically, the transmission chain 60 is provided with chain links (not shown) for engaging both the first and second sprockets 58, 62.

Typically, the first sprockets 58 define a first sprocket diameter, the second sprockets 62 define a second sprocket diameter and the ratio of the first sprocket diameter to the second sprocket diameter defines a so-called gear ratio. The first sprocket moving means allows for selective adjustment of the gear ratio by selective adjustment of the first sprocket diameter through selective movement of the first sprocket 58 between the first sprocket expanded and retracted configurations. In situations wherein both the first and second sprocket wheels are provided with radially adjustable sprockets, a sprocket moving means allows for selective adjustment of the gear ratio by selective adjustment of either one of or both the first and second sprocket diameter through selective movement of either one of or both the first and second sprockets 58, 62 between the first and second sprocket expanded and retracted configurations.

Typically, the transmission system 10 also includes a movement timing means operatively coupled to the first and/or second sprockets 58, 62 for timing the translational movement thereof in the radial direction with the angular position thereof relative respectively to the first and/or second wheel axes 52, 56. The movement timing means is adapted to insure that the translational movement of the first and/or second sprockets 58, 62 occurs when the first and/or second sprockets 58, 62 are not in direct contact with the transmission chain 60.

As illustrated more specifically in Fig. 4, the first sprocket wheel 50 includes a first wheel hub 64 and a set of first wheel arms 66 (only one of which is shown in Fig. 4) extending substantially radially and outwardly from the first wheel hub 64. Each first wheel arm 66 defines a radially proximal arm proximal end 68 and a radially opposed arm distal end 70. Each first wheel arm 66 also defines an arm first lateral surface 72 and an opposed arm second lateral surface 74.

Referring now specifically to Fig. 6, there is shown in greater details some of the components of the second sprocket wheel 54. It should be understood that the first and second sprocket wheels 50, 54 are substantially similar and, hence, similar reference numerals will be used to denote similar components. Each second wheel arm 66 has a substantially radially oriented piston chambers 76 formed therein. The piston chamber 76 defines a radially proximal chamber proximal end 78 and an opposed chamber distal end 80.

The first or second sprocket moving means includes a piston component 82 mounted in the piston chamber 76 for reciprocal movement therein and a piston moving means for reciprocating the piston component 82 within the piston chamber 76. The first or second sprocket moving means also includes a carriage component 84 attached to the piston component 82 for reciprocal movement therewith. At least one and preferably a plurality of first or second sprockets 58 or 62 are attached to the carriage component 84 for reciprocal movement between the sprocket expanded and retracted configurations.

The piston component 82 defines a radially proximal piston proximal end 86 and an opposed piston distal end 88. Each first or second wheel arm 66 has a corresponding arm fluid channel 90 extending from an exterior surface thereof to the piston chamber 76 substantially adjacent the chamber proximal end 78 for allowing fluid flow therethrough. The first or second sprocket moving means also includes a pressure creating means for selectively forcing the flow of a fluid under pressure through the arm fluid channel 90 into the piston chamber 76 between the chamber and piston proximal ends 78, 86 so as to fluidly urge the piston component 82 towards the chamber distal end 80.

The first or second sprocket moving means also includes a piston biasing means for biasing the piston component 82 towards the chamber proximal end 78. Typically, the piston chamber 76 defines a spring receiving section 92 located substantially adjacent the chamber distal end 80. The piston biasing means typically includes a spring component 94 mounted within the spring receiving section 92.

The spring component 94 defines a radially proximal spring proximal end 96 and an opposed spring distal end 98. The spring component 94 is configured and sized so as to be resiliently compressed when the piston component 82 is moved towards the chamber distal end 80.

Typically, the biasing component is provided with a biasing force adjustment means for allowing adjustment of the strength of the biasing force exerted thereby. When a spring component 94 is used, the biasing force adjustment means allows adjustment of the biasing force exerted by the spring component 94 when the latter is being compressed.

Typically, the spring component 94 is a helicoϊdal-type spring and the biasing force adjustment means includes a spring force adjustment screw 100 threadably mounted adjacent the piston chamber distal end 80 for contacting the spring distal end 98. Rotation of the spring force adjustment screw 100 causes axial movement of the latter which, in turn, changes the compression state of the spring component 94.

Typically, piston sealing rings 102 are mounted between the piston component 82 and a peripheral wall of the piston chamber 76 adjacent the piston proximal and distal ends 86, 88. Also, typically, a piston abutment rod 104 extends generally radially from the piston proximal end 86 for maintaining the piston proximal end 86 in a spaced relationship relative an adjacent end wall of the piston chamber 76 so as to provide clearance for the arm fluid channel 90 when the first or second sprockets 58, 62 are in the sprocket retracted configuration.

As illustrated more specifically in Figs. 9a through 9d, each carriage component 84 typically includes a substantially radially extending sprocket attachment section 106 for allowing attachment thereto of a set of first or second sprockets 58, 62. Each carriage component 84 also includes a piston attachment section 108 extending substantially perpendicularly from the sprocket attachment section 106 for allowing attachment thereof to the piston component 82. Typically, the sprocket attachment section 106 has the configuration of a generally flat plate while the piston attachment section 108 has the general configuration of an eyelet.

Typically, the first or second sprockets 58, 62 are grouped in sets of at least two and typically five sprockets. Each set of sprockets 58, 62 extends from a common and generally arcuate sprocket base plate 110. Each of the sprocket base plates 110 defines a pair of opposed base lateral peripheral edges 112 and a pair of substantially perpendicular base end edges 114. The sprocket base plate 110 has a plate attachment flange 116 extending substantially radially therefrom substantially adjacent to one of the base lateral edges 112.

Preferably, the first or second sprockets 58, 62, are releasably attachable at various radial locations along the sprocket attachment section 106. Typically, the plate attachment flange 116 is provided with at least one and preferably two flange attachment apertures 118 extending therethrough. Also, typically, the sprocket attachment section 106 is preferably provided with a set of attachment section apertures 120 extending therethrough at various radial positions.

Attachment components such as a conventional screw of the like are typically used for releasably attaching the plate attachment flange 116 to the sprocket attachment section 106 using the flange and sprocket attachment sections apertures 118, 120. The possibility of attaching the first or second sprockets 58, 62 at various radial locations along the sprocket attachment section 106 allows for customization of the first and/or second sprocket diameters and, hence, of the gear ratio.

Each first or second wheel arms 66 has a carriage receiving slot 122 extending at least partially therealong for receiving a portion of the piston attachment section 108 and allowing attachment of the piston attachment section 108 to the piston component 82. The carriage receiving slot 122 is adapted to allow the slidable movement therein of the piston attachment section 108 when the piston component 82 reciprocates within the piston chamber 76.

As illustrated in Fig. 6, the piston attachment section 108 is typically attached to the piston component 82 using a conventional fastening means such as a screw 124. Also, typically, the piston attachment section 108 is attached to the piston component 82 between the piston distal end 88 and the spring component proximal end 96.

The transmission system 10 is preferably further provided with a sprocket stabilizing means for stabilizing the first or second sprockets 58, 62 against unwanted movement resulting from the forces exerted thereon by the linking chain 60 during use. As shown more specifically in Figs. 9a through 9d, the sprocket base plate 110 is typically further provided with a stabilizing protrusion 126 extending substantially laterally therefrom from a position located substantially opposite the plate attachment flange 116.

As shown more specifically in Figs. 2 and 6, the transmission system 10 is typically further provided with a sprocket stabilizing component 128 for engaging and stabilizing the stabilizing protrusion 126 and, hence, stabilizing the first or second sprockets 58, 62. The stabilizing component 128 is provided with means for ensuring its rotation solidarly with the first or second sprocket wheel 50, 54.

Typically, the sprocket stabilizing component 128 includes a set of substantially radially extending stabilizing arms 130. The stabilizing arms 130 are positioned, configured and sized so as to be substantially in register with the first or second wheel arms 66 and in a laterally spaced relationship therewith.

Each of the stabilizing arms 130 is provided with a corresponding stabilizing slot 132 formed therein for receiving a corresponding stabilizing protrusion 126 and allowing slidable movement thereof when the sprocket base plate 110 reciprocates as the first or second sprockets 58, 62 part of a corresponding set of sprockets moves between the sprocket extended and retracted configurations.

Typically, the stabilizing arms 130 extend from a substantially centrally disposed stabilizing plate 134 to a peripheral stabilizing rim 136. Also, as shown more specifically in Fig. 9c, each stabilizing protrusion 126 typically has a generally L-shaped configuration defining a protrusion radial segment 138 extending substantially radially and a protrusion lateral segment 140 extending generally laterally.

As illustrated more specifically in Fig. 6, each stabilizing slot 132 has a corresponding radial receiving portion 142 for receiving a corresponding protrusion radial segment 138 and a lateral receiving portion 144 for receiving a corresponding protrusion lateral segment 140. The combination of the stabilizing protrusion 126 and stabilizing slot 132 hence abuttingly stabilize the first or second sprocket teeth 58, 62 in both a lateral and tangential direction.

As shown more specifically in Figs. 2 and 4, the stabilizing plate 134 used with the first sprockets 58 typically has a pedal crank 32 attached thereto using suitable attachment means such as a crank arm attachment bolt. As illustrated more specifically in Fig. 8, each fluid arm channel 90 is preferably in fluid communication with a corresponding venting channel 146. Each venting channel 146 is, in turn, in fluid communication with a venting aperture 148. Optionally, each venting aperture 148 may be provided with a venting valve 150 fluidly coupled thereto.

As illustrated more specifically in Figs. 2 and 8, the first or second wheel arms 66 typically extend from the first or second wheel hub 64 to a peripheral wheel rim 152. Similarly, the venting channels 146 typically extend from the arm fluid channels 90 to the wheel rim 152. The fluid channels 146 further typically extend from the arm fluid channels 90 to their corresponding venting apertures 148 substantially at an angle relative to an adjacent and corresponding piston channel 76.

As shown more specifically in Figs. 3 and 8, the first or second wheel arms 66 typically merge integrally with each other about a generally proximal segment thereof so as to form a merged portion 154 having a substantially disc-shaped configuration. As shown in Figs. 4 through 6, each carriage component 84 is mounted on arm first lateral surface 72 while each arm fluid channel 90 extends from a corresponding piston chamber 76 to a corresponding channel aperture 156 located in the merged portion 154 on the outer surface of the arm second lateral surface. Typically, the channel apertures 156 are located intermediate the arm fluid channel 90 and the venting aperture 148 along the venting channel 146.

The channel apertures 156 are typically offset relative to each other both radially and circumferentially. The channel apertures 156 are separated from each other radially by circumferential arm sealing rings 158. The circumferential arm sealing rings 158 define arm annular segments 160 therebetween.

The timing means include a fluid distributing component 162 fluidly coupled to the arm annular segments 160 for respectively and sequentially distributing a pressurized fluid to the channel apertures 156. As illustrated more specifically in Figs. 2 and 7, the fluid distributing component 162 typically has a substantially annular configuration defining an annular lateral distribution surface 164 and a radial distribution peripheral surface 166.

The fluid distribution component 162 has a set of distribution channels 168 extending therethrough from corresponding peripheral distribution apertures 170 formed in the radial distribution peripheral surface 166 to corresponding lateral distribution apertures 172 formed in the annular lateral distribution surface 164. Each lateral distribution aperture 172 typically has the form of an arc segment having a predetermined size.

Typically, the size of the distribution apertures 172 increases with the radial distance. Each distribution aperture typically defines a first longitudinal edge thereof generally in register and aligned radially with other first longitudinal edges and an opposed second longitudinal edge thereof generally circumferentially offset relative to other second longitudinal edges. The lateral distribution apertures 172 are separated radially from each other by circumferential distribution sealing rings 174 defining distribution segments 176 therebetween.

The lateral distribution surface 164 is positionable laterally against the arm second lateral surface 74 and rotatable relative to the latter with the distribution sealing rings 174 sealingly contacting the arm sealing rings 158 so as to prevent radial flow of the pressurized fluid between distribution segments 176 and between arm segments 160.

The distribution and corresponding channel apertures 172, 156 paired together at a given radial distance are configured, sized and positioned relative to each other so as to allow the flow of the pressurized fluid therebetween only when the first or second arm wheel 50, 54 are in a rotational position such that the corresponding sprockets 58, 62 associated with corresponding distribution and channel apertures 172, 156 are not in contact with the transmission chain 60. In other words, the distribution and corresponding channel apertures 172, 156 are positioned, configured and sized so as to only allow movement of the first or second sprockets 58, 62 when the latter are disengaged from the transmission chain 60 hence reducing the risks of jamming or kinking.

The actuating means includes an actuating manifold 178 defining a set of actuating chambers 180. Each actuating chamber 180 is fluidly coupled through a corresponding outlet nozzle 185 to a corresponding fluid duct 186. Each fluid duct 186 is, in turn, fluidly coupled to a corresponding peripheral distribution aperture 170. Typically, the fluid ducts are grouped and protectively covered by a duct sleeve 187.

The actuating chambers 180 are separated peripherally from each other by actuating chamber walls 183. In situations wherein both the front and rear sprocket wheels 50, 54 have corresponding radially movable front and rear sprockets 58, 62, the manifold 178 includes a separation wall 184 for separating the manifold 178 into a pair of manifold sub-sections 182 each containing actuating chambers 180 fluidly coupled respectively to the front and rear sprocket wheels 50, 54.

A piston component 188 is slidably mounted within each actuating chamber 180 for reciprocating movement therein as indicated by arrows 196. Typically, each actuating piston 188 is provided with an actuating piston sealing ring 198 for providing a sealing contact with the adjacent actuating chamber peripheral walls 183. Each actuating piston 188 is mounted within a corresponding actuating chamber 180 for reciprocal movement between a first actuating configuration shown in Fig. 10b and a second actuating configuration (not shown) wherein the actuating piston 188 is located substantially adjacent the discharge nozzle 185.

The actuating chambers 180 are filled with the fluid when the actuating pistons 188 are in their first actuating configuration. As the actuating pistons 188 translate towards the second actuating configuration, the fluid within the corresponding actuating chamber 180 is urged outwardly by the actuating piston 188 from the corresponding actuating chamber 180 through the discharge nozzle 185.

The actuating means further includes a main trigger plate 200 mechanically coupled to a trigger lever 202 typically positioned adjacent the bicycle handle bar 48 such as shown in Fig. 1. The main trigger plate 200 is typically mechanically coupled to the trigger lever 202 through the use of an actuating cable 204 redirected by suitable pulley assemblies 206. Typically, the pulley assemblies 206 extend outwardly from the outer surface of the actuating manifold 178. It should, however, be understood that the main trigger plate 200 could be coupled to the trigger lever 202 through other suitable coupling means without departing from the scope of the present invention. The main trigger plate 200 is mounted within a trigger chamber 208 for reciprocal movement therein between a first trigger position wherein the main trigger plate 200 is substantially spaced from the adjacent actuating chamber 180 and a trigger second position wherein the main trigger plate 200 is in a substantially proximal relationship relative to the adjacent actuating chambers 180.

The actuating means typically further includes a plate-to-piston coupling component positioned between the main trigger plate 200 and each individual actuating piston 188 for individually mechanically coupling the main trigger plate 200 to each individual actuating piston 188. The plate-to-piston coupling components also allow the main trigger plate 200 to move towards the trigger second configuration when the movement of individual actuating pistons 188 towards the second actuating configuration is hindered.

The plate-to-piston coupling component includes a movement absorbing component such as a spring 192 positioned between the main actuating plate 200 and each individual actuating piston 188. In situations wherein the absorbing spring 192 is a helicoϊdal type spring, abutment components 194 are positioned between the absorbing spring 192 and main trigger plate 200.

Each of the plate-to-piston coupling component 192 is adapted to resiliently deform so as to be able to transmit an actuating force exerted on the main trigger plate 200 to a corresponding actuating piston 188 when the latter is movable towards the first actuating configuration and so as to be able to resiliently deform when the actuating force is exerted on the main trigger plate 200 and the corresponding actuating piston 188 is prevented from moving towards the first actuating configuration.

As mentioned previously, the transmission system 10 is preferably provided with a timing means for timing the displacement of the piston components 82 so that radial movement of the sprockets 62 is effectuated when the latter are not engaged with the driving chain 60.

When the actuating lever 102 pulls on the actuating cable 204 the main trigger plate 200 is moved towards the trigger second configuration, hence increasing the pressure of the fluid in the actuating chambers 76. As the first sprocket wheel 50 rotates relative to the distributing component 162, the lateral distribution apertures 172 will sequentially come in register with corresponding channel apertures 156. When a pair of the lateral distribution aperture 172 and channel apertures 156 are in register, the fluid under pressure in the corresponding actuating chamber 76 is allowed to flow into the corresponding piston chamber 76 for radially outwardly displacing the corresponding sprockets 62.

The pairs of the lateral distribution apertures 172 and channel apertures 156 are circumferentially positioned so that they come in register with each other when the corresponding sprockets 62 are disengaged from the driving chain 60. The sprockets 62 remaining engaged with the driving chain 60 are temporarily prevented from moving radially despite the pressure build-up in their corresponding actuating chambers 180 by the offset between the corresponding lateral distribution apertures 172 and channel apertures 156 preventing the flow of fluid into the corresponding piston chambers 76.

Conversely, when the actuating lever 102 releases the actuating cable 204 the main trigger plate 200 is moved towards the trigger first configuration the pressure of the fluid in the actuating chambers 76 is decreased. As the first sprocket wheel 50 rotates relative to the distributing component 162, the lateral distribution apertures 172 will sequentially come in register with corresponding channel apertures 156. When a pair of the lateral distribution aperture 172 and channel apertures 156 are in register, the fluid under pressure is allowed to flow into the corresponding actuating chamber 180 decreasing the pressure in the corresponding piston chamber 76 allowing the spring component 94 to radially displacing the corresponding sprockets 62 inwardly.

The sprockets 62 remaining engaged with the driving chain 60 are temporarily prevented from moving radially inwardly despite the decrease in pressure in their corresponding actuating chambers 180 by the offset between the corresponding lateral distribution apertures 172 and channel apertures 156 preventing the flow of fluid out of the corresponding piston chambers 76.

FIG. 11a schematically illustrates the first sprocket wheels 50 with all of its piston components 82 and, hence, all of its sprockets 62 in a fully retracted configuration.

In FIG. 11b, one of the piston components, namely the piston component identified by the reference numeral 82', is moved towards its extended configuration. Movement of the piston component 82' is effectuated when the corresponding sprockets 62 disengage a lower segment 60' of the driving chain 60.

In FIG. 11c, the sprockets associated with the piston component 82' engage an upper segment 60" of the driving chain 60 at a longer radial distance relative to the first wheel axis 52 while a second piston component indicated by reference numeral 82" initiates its movement towards its extended configuration as it disengages the lower segment 60' of the driving chain.

Conversely, in Fig.12a, all of the piston components 82 are in their fully extended configuration. In Fig 12b, as the sprockets 62 associated with a piston component identified by the reference numeral 82' disengages the lower segment 60' of the driving chain 60 it is retracted towards its retracted configuration.

In Fig 12c, third and second piston components identified by reference numerals 82", 82'" are retracted towards their retracted configuration while the sprockets 62 associated with the piston component 82' is engaged with an upper segment 60" of the driving chain 60 at a smaller radial distance relative to the first wheel axis 52 than the sprockets associated with the remaining piston components 82.

Claims

The embodiments of the invention in which an exclusive privilege or property is claimed are defined as follows:

1. A transmission system for controllably transmitting to a driven shaft the torque emanating from a driving shaft, said transmission system comprising:

- a first sprocket wheel, said first sprocket wheel being rotatable about a first wheel axis; said first sprocket wheel having a set of first sprockets movably attached thereto for translational movement in a radial direction substantially perpendicular to said first wheel axis, said first sprockets being selectively movable between a first sprocket retracted configuration and a first sprocket expanded configuration wherein said first sprockets are positioned radially outwardly when in said first sprocket expanded configuration comparatively to when said first sprockets are in said first sprocket retracted configuration;

- a first sprocket moving means operatively coupled to said first sprockets for selectively moving said first sprockets between said first sprocket retracted and expanded configurations;

- a second sprocket wheel, said second sprocket wheel being rotatable about a second wheel axis; said second sprocket wheel having a set of second sprockets extending therefrom;

- a transmission chain for mechanically coupling said first sprocket wheel and said second sprocket wheel, said transmission chain having chain links for engaging both said first and second sprockets;

- either one of said first or second sprocket wheels being attachable to said driving shaft while the other one of said first or second sprocket wheels is attachable to said driven shaft; - whereby said first sprockets define a first sprocket diameter, said second sprockets define a second sprocket diameter and the ratio of said first sprocket diameter to said second sprocket diameter defines a gear ratio, said first sprocket moving means allowing for selective adjustment of said gear ratio by selective adjustment of said first sprocket diameter through selective movement of said first sprockets between said first sprocket expanded and retracted configurations.

2. A transmission system as recited in claim 1 further comprising a movement timing means operatively coupled to said first sprockets for timing the translational movement of said first sprockets in said radial direction with the angular position of said first sprockets relative to said first wheel axis so as to ensure that said translational movement of said first sprockets occurs when said first sprockets are not in direct contact with said transmission chain.

3. A transmission system as recited in claim 1 wherein said first sprocket wheel includes a first wheel hub mountable on said first shaft and a set of first wheel arms extending substantially radially and outwardly from said first wheel hub; a carriage component being slidably mounted on at least some of said first wheel arms for slidable movement at least partially therealong; at least one first sprocket being attached to at least some of said carriage components for movement solidarly therewith between said sprocket expanded and retracted configurations.

4. A transmission system as recited in claim 3 wherein at least one of said carriage components includes a substantially radially extending sprocket attachment section; at least one of said first sprockets being selectively and releasably attachable at two distinct positions along at least a portion of said sprocket attachment section so as to allow for the customization of the radial positioning of said at least one of said first sprockets relative to a corresponding sprocket attachment section; whereby the customization of the radial positioning of said at least one of said first sprockets relative to said sprocket attachment section allows for the customization of at least part of the first sprocket diameter.

5. A transmission system as recited in claim 4 wherein said first sprocket moving means includes a piston component operatively coupled to at least some of said sprocket attachment sections and a fluid circuitry fluidly coupled to said piston components for selectively moving at least some of said moving sprockets between said expanded and retracted configurations.

6. A transmission system as recited in claim 1 wherein said first sprocket wheel includes a first wheel hub and a set of first wheel arms extending substantially radially and outwardly from said first wheel hub; each of said first wheel arm defining a radially proximal arm proximal end and a radially opposed arm distal end; each of said first wheel arm also defining an arm first lateral surface and an opposed arm second lateral surface; each of said first wheel arm having a substantially radially oriented piston chamber formed therein, said piston chamber defining a radially proximal chamber proximal end and an opposed chamber distal end, said first sprocket moving means including a piston component mounted in said piston chamber for reciprocal movement therein and a piston moving means for reciprocating said piston component within said piston chamber, said piston component defining a radially proximal piston proximal end and an opposed piston distal end; said first sprocket moving means also including a carriage component attached to said piston component for reciprocal movement solidarly therewith; a first sprocket being attached to said carriage component for reciprocal movement between said sprocket expanded and retracted configurations.

7. A transmission system as recited in claim 6 wherein each of said first wheel arms has an arm fluid channel extending from an exterior surface thereof to said piston chamber substantially adjacent said chamber proximal end for allowing fluid flow therethough; said first sprocket moving means also including a pressure creating means for selectively forcing the flow of a fluid under pressure through said arm fluid channel into said piston chamber between said chamber and piston proximal ends so as to fluidly urge said piston component towards said chamber distal end; said first sprocket moving means also including a piston biasing means for biasing said piston component towards said chamber proximal end.

8. A transmission system as recited in claim 7 wherein said piston chamber defines a spring receiving section located substantially adjacent said chamber distal end, said piston biasing means including a spring component mounted within said spring receiving section, said spring component defining a radially proximal spring proximal end and an opposed spring distal end, said spring component being configured and sized so as to be resiliently compressed when said piston is moved towards said chamber distal end.

9. A transmission system as recited in claim 8 wherein said biasing component is provided with a biasing force adjustment means for allowing adjustment of the strength of the biasing force exerted by said spring component when said spring component is being compressed.

10. A transmission system as recited in claim 9 wherein each of said carriage components includes a substantially radially extending sprocket attachment section for allowing attachment thereto of a first sprocket and a substantially perpendicular piston attachment section for allowing attachment thereof to said piston component, said first sprocket being releasably attachable at various radial locations along said sprocket attachment section; each of said first wheel arms having a carriage receiving slot extending at least partially therealong for receiving a portion of said piston attachment section and allowing attachment of said piston attachment section to said piston component; said carriage receiving slot allowing the slidable movement therein of said piston attachment section when said piston component reciprocates within said piston chamber.

11. A transmission system as recited in claim 10 wherein a set of sprockets is attached to each of said sprocket attachment sections; each set of sprockets extending from a common generally arcuate sprocket base plate, each of said sprocket base plates defining a pair of opposed base lateral peripheral edges and a pair of substantially perpendicular base end edges; said sprocket base plate having a plate attachment flange extending substantially radially therefrom substantially adjacent to one of said base lateral edges; said sprocket base plate also having a stabilizing protrusion extending substantially laterally therefrom from a position located substantially adjacent the opposed base lateral edge; said transmission system being further provided with a sprocket stabilizing component for engaging said stabilizing protrusion so as to stabilize said set of sprockets.

12. A transmission system as recited in claim 11 wherein said sprocket stabilizing component includes a set of substantially radially extending stabilizing arms, said stabilizing arms being positioned, configured and sized so as to be substantially in register with said first wheel arms and in a laterally spaced relationship therewith; each of said stabilizing arms being provided with a stabilizing slot formed therein for receiving a corresponding stabilizing protrusion and allowing slidable movement thereof when said sprocket base plate reciprocates as said first sprockets part of a corresponding set of sprockets move between said sprocket expanded and retracted configurations.

13. A transmission system as recited in claim 12 wherein each of said arm fluid channels is in fluid communication with a corresponding venting channel leading to a venting aperture.

14. A transmission system as recited in claim 12 wherein said first wheel arms merge integrally with each other about a proximal segment thereof so as to form a merged portion having a substantially disc-shaped configuration; each of said carriage components being mounted on said arm first lateral surface and each of said arm fluid channels extending from a corresponding piston chamber to a corresponding channel aperture located in the merged portion on the outer surface of said arm second lateral surface; said channel apertures being offset relative to each other both radially and circumferentially; said channel apertures being separated from each other radially by circumferential arm sealing rings defining arm annular segments therebetween; said timing means including a fluid distributing component fluidly coupled to said arm annular segments for selectively and sequentially distributing a pressurized fluid to said channel apertures.

15. A transmission system as recited in claim 14 wherein said fluid distributing component has a substantially annular configuration defining an annular lateral distribution surface and a radial distribution peripheral surface; said fluid distribution component having a set of distribution channels extending therethrough from corresponding peripheral distribution apertures formed in said radial distribution peripheral surface to corresponding lateral distribution apertures formed in said annular lateral distribution surface; said lateral distribution apertures being separated radially from each other by circumferential distribution sealing rings defining distribution segments therebetween; said lateral distribution surface being positionable laterally against said arm second lateral surface and rotatable relative to the latter with said distribution sealing rings sealingly contacting said arm sealing rings so as to prevent radial flow of said pressurized fluid between distribution segments and between arm segments; each distribution and corresponding channel apertures being configured, sized and positioned relative to each other so as to allow the flow of said pressurized fluid therebetween only when said first arm wheel is in a rotational position such that the corresponding sprockets associated with corresponding distribution and channel apertures are not in contact with said transmission chain.

16. A transmission system as recited in claim 15 further comprising an actuating means for allowing selective movement of said set of sprockets between said retracted and expanded configurations; said actuating means including an actuating manifold defining a set of actuating chambers; each of said actuating chamber being fluidly coupled to a corresponding fluid duct in fluid communication with a corresponding peripheral distribution aperture; each of said actuating chambers having an actuating piston mounted therein for reciprocal movement between a first actuating configuration and a second actuating configuration wherein said actuating piston respectively urges said pressurized fluid outwardly and allows said fluid to penetrate said actuating chamber through said fluid duct; a main trigger plate being mechanically individually coupled to each of said actuating pistons by a plate-to-piston coupling component, each of said plate-to-piston coupling component being resiliently deformable so as to be able to transmit an actuating force exerted on said main trigger plate to a corresponding actuating piston when the latter is movable towards said first actuating configuration and so as to be able to resiliently deform when said actuating force is exerted on said main trigger plate and said corresponding actuating piston is prevented from moving towards said first actuating configuration.

17. A transmission system for controllably transmitting to a driven shaft the torque emanating from a driving shaft, said transmission system comprising: - a variable diameter sprocket wheel having a plurality of radially displaceable sprockets, said sprocket wheel being rotatable about a rotation axis, - actuating means coupled to said sprockets for allowing the selective radial displacement of said sprockets;

- a movement timing means operatively coupled to said sprockets for timing the radial movement of said sprockets with the angular position of said sprockets relative to said rotation axis so as to ensure that the radial movement of said sprockets is only allowed when said sprockets are in a predetermined angular position range.

18. A transmission system as recited in claim 17 wherein said sprockets are displaceable radially through a predetermined radial displacement range between a first radial position located at a first radial distance from said rotation axis and a second radial position located at a second radial distance from said rotation axis, said transmission system being further provided with a customization means for allowing the customization of said first and second radial positions.

19. A transmission system as recited in claim 17 wherein said sprockets extend substantially in a radial direction relative to said rotation axis, said transmission system being further provided with a sprocket stabilizing means for stabilizing said sprockets in an axial direction substantially perpendicular to said radial direction and parallel to said rotation axis.

20. A transmission system as recited in claim 19 wherein said stabilizing means also stabilizes said sprockets in a direction parallel to said rotation axis.