TECHNICIAL FIELD

[0001 ] The present invention generally relates to a transmission system, in particular the invention relates to an automatic transmission system. In several embodiments the transmission system incorporates one or more clutches, wherein the one or more clutches are of a fixed width.

BACKGROUND ART

[0002] Transmission systems are used in various vehicles and industrial equipment to provide controlled application of power from an input to an output. These systems typically use a number of gears as well as one or more clutches, to control the application of power from the input to the output.

[0003] Transmission systems are configured to provide a required output(s) of a given input. This may result in controlling the application of power from the input to provide slower output speeds at a high torque, or to provide higher output speeds.

[0004] The purpose of a clutch in a transmission system is to connect and disconnect two rotating shafts, such that when the clutch is engaged, the rotation of an input shaft is transferred to an output shaft, whereupon disengagement of the clutch, rotation of each shaft is independent of each other. Clutches typically work by axial movement of one component relative to another component whereupon the components frictionally engage or interlock to transfer motion therebetween. The space required to allow the axial movement can be problematic to accommodate, particularly in small transmission systems.

[0005] A transmission system typically provides multiple gear ratios, depending on the number of gears, as well as a means to shift between those ratios to provide variations in speed and/or direction.

[0006] Considering a bicycle, its transmission system typically incorporates a centrally located chain ring to which is fixed two crank arms. The chain ring is spaced from a rear sprocket set with a chain/belt spanning therebetween. A rider engages the crank arms to provide the input and rotate the chain ring. As a result of the rider’s input torque is exerted on the chain ring and transferred to the rear sprocket through the chain. This causes the rear sprocket to rotate. The rear sprocket set is secured to the axle of the rear wheel of the bicycle such that rotation of the rear sprocket set translates to rotation of the rear wheel.

[0007] To control the application of force from the rider to the rear wheel the transmission system provides a gearing system. The gearing system enables the rider to shift gears and therefore control the effect the rider’s input has on the rear wheel. This gear system generally comprises a number of co-axially mounted rear sprockets of varying diameter and a number of co-axially mounted chain rings also of different diameter. By shifting gears the rider can cause the chain to move to different combinations of sprockets or chain rings, enabling the rider to choose the gear ratio which best suits the conditions.

[0008] The gearing system typically incorporates a derailleur which is caused to move and guide the chain of the bicycle to a different sprocket in order to provide a different gear ratio. Where the bicycle has multiple rear sprockets as well as multiple chain rings the bicycle will have a derailleur dedicated to each set.

[0009] While the use of derailleurs with respect to bicycles is widespread they are not without their problems. With current bicycle transmission systems, the derailleurs can dislodge the chain during gear changes and can cause difficulties when shifting gears (up or down).

[0010] Furthermore, most combinations of gears result in the chain being positioned in a plane which is at an angle to the plane of the chain ring and/or the plane of the rear socket to which the chain is engaged. This significantly reduces the efficiency of the bicycle transmission system as well as making it impractical for all gear ratios to be utilised. In fact straight line chain setting, which provides the greatest efficiency, is only achievable for a small number of gear settings of the bicycle transmission system.

[0011 ] The typical gearing system on a bicycle requires the operator to manually adjust a lever in order to change the gears. This therefore relies on the rider knowing exactly when the best time to shift gears is. The optimum point to shift gears is a challenge even for seasoned riders let alone those with little or no experience. In most cases, riders find it inconvenient having to continually select gears and/or do not change gears when appropriate resulting in a reduction in speed and efficiency.

[0012] In addition, derailleur transmissions are exposed to the environment, facilitating contamination, which in turn reduces their effective service life and increases maintenance and risk of failure. For optimal operation the derailleurs require frequent adjustment and lubrication to ensure the chain is guided to the correct gear when shifting gears.

[0013] An additional disadvantage of derailleur transmissions is that the process of shifting gears results in a temporary loss of power transmission while the chain relocates. This results in a loss of rider input, particularly when riding uphill, as the resulting loss of momentum requires additional effort to bring the bicycle back to the speed before the gear shift.

[0014] Derailleur transmissions are also sensitive to physical shocks to the bike, lack of mechanical alignment, componentry mismatch, and incorrect operation by the rider. These factors can lead to dislodgment of the chain and a general inefficiency in converting the rider’s energy to motion of the bicycle.

[0015] The above discussion of the background art is intended to facilitate an understanding of the present invention only. While the discussion focusses on transmission systems of bicycles, it would be readily understood that similar problems exist in transmission systems used in other applications.

SUMMARY OF INVENTION

[0016] It is an object of this invention to provide a transmission system which ameliorates, mitigates or overcomes, at least one disadvantage of the prior art, or which will at least provide the public with a practical choice. [0017] The present invention provides a transmission system which controls output from an input based on certain predetermined criteria, the transmission system comprises: a first shaft which provides the input; a second shaft which provides the output; the first shaft being connected to the second shaft; at least one transmission clutch movable between an engaged condition wherein the input from the first shaft causes the second shaft to rotate, and a disengaged condition wherein the first shaft rotates independent to the second shaft, the transmission clutch comprising: a clutch output member fixed to the second shaft, the clutch output member being selectively connected to a clutch input member, wherein the axial distance between the clutch output member and the clutch input member is fixed; a control means to move the transmission clutch from a disengaged condition to an engaged condition, the control means comprises one or more sensors for sensing one or more conditions of the transmission system whereupon the control means sensing that the one or more conditions meet predetermined criteria the control means moves the transmission clutch to an engaged condition.

[0018] Preferably the transmission system automatically controls the output from the input based.

[0019] The present invention further provides an automatic transmission system comprising: a first shaft which provides an input; a second shaft which provides an output; the first shaft being connected to the second shaft; at least one transmission clutch movable between a disengaged condition and an engaged condition, wherein in the engaged condition the input from the first shaft causes the second shaft to rotate, the transmission clutch maintaining a fixed axial width when moving between the disengaged condition and the engaged condition; a control means to move the transmission clutch from a disengaged condition to an engaged condition, the control means comprises one or more sensors for sensing one or more conditions of the transmission system whereupon the control means sensing that the one or more conditions meet predetermined criteria the control means automatically causes the transmission clutch to move to an engaged condition.

[0020] The second shaft may selectively provide a desired output.

[0021 ] The present invention further provides an automatic transmission system comprising: a first shaft which provides an input; a second shaft which selectively provides a desired output; the first shaft being connected to the second shaft; at least one transmission clutch movable between a disengaged condition and an engaged condition, wherein in the engaged condition the input from the first shaft causes the second shaft to rotate, the transmission clutch maintaining a fixed axial width when moving between the disengaged condition and the engaged condition; a control means to move the transmission clutch from a disengaged condition to an engaged condition, the control means comprises one or more sensors for sensing one or more conditions of the transmission system whereupon the control means sensing that the one or more conditions meet predetermined criteria the control means automatically causes the transmission clutch to move to an engaged condition. [0022] The at least one transmission clutch may be associated with the second shaft. Preferably the at least one transmission clutch is mounted on the second shaft.

[0023] The transmission system may be configured to provide a variety of outputs for a given input. That is to say, the input may result in an output which is faster than the input, equal to the input or slower than the input.

[0024] The transmission system may comprise a gearing system which may be configured to provide the desired output.

[0025] The gearing system may comprise one or more drive wheels fixed to the first shaft. The one or more drive wheels may vary in diameter.

[0026] The gearing system may comprise one or more input wheels fixed to the second shaft. The one or more input wheels may vary in diameter.

[0027] In one variation the gearing system may comprise an intermediate gear apparatus wherein the one or more drive wheels directly mesh with an input of an intermediate gear apparatus, and an output of the intermediate gear apparatus directly meshes with the one or more input wheels. The intermediate gear apparatus may comprise one or more shafts, each shaft having one or more wheels thereon. Alternatively, the intermediate gear apparatus may be in the form of a further transmission system, being the same type or a different type to the transmission system of the present invention.

[0028] Preferably for each drive wheel there is a corresponding input wheel.

[0029] Preferably each of the one or more drive wheels is connected to its corresponding input wheel, such that movement of the one or more drive wheel causes movement of the corresponding input wheel. Preferably each of the one or more drive wheels is connected to its corresponding input wheel to be in constant mesh.

[0030] In one aspect of the invention each of the one or more drive wheels is connected to its corresponding input wheel by a cable, wherein the cable engages the drive wheel and input wheel. The cable may frictionally engage the drive wheel and input wheel. As would be readily understood by the person skilled in the art the cable may be in the form of a belt or other similar flexible elongate element spanning between each drive wheel and its corresponding input wheel, such as a chain or a toothed belt.

[0031 ] In another aspect of the invention each of the one or more drive wheels is in the form of a drive gear, and its corresponding input wheel is in the form of an input gear, wherein the one or more drive gears directly mesh with its corresponding input gear.

[0032] In yet another aspect of the invention each of the one or more drive wheels is in the form of a drive gear, and its corresponding input wheel is in the form of an input gear, wherein the one or more drive gears directly mesh with an input of an intermediate gear apparatus, and an output of the intermediate gear apparatus directly meshes with the input gear which corresponds to the drive gear. The intermediate gear apparatus may comprise one or more shafts, each shaft having one or more gears thereon. Alternatively, the intermediate gear apparatus may be in the form of a further transmission system, being the same type or a different type to the transmission system of the present invention.

[0033] In yet another aspect of the invention each of the one or more drive wheels is in the form of a drive sprocket, and its corresponding input wheel is in the form of an input sprocket, wherein each of the one or more drive sprockets is connected to its corresponding input sprocket by a chain.

[0034] In one arrangement the one or more drive wheels and corresponding input wheels may comprise a first drive sprocket and its corresponding first input sprocket, a second drive sprocket and its corresponding second input sprocket and a third drive sprocket and its corresponding third input sprocket. The transmission system may comprise as many drive sprockets and input sprockets as required based on the application. Such variations are readily conceivable by the person skilled in the art and are within the scope of this specification. [0035] The first drive sprocket, second drive sprocket and third drive sprocket may be fixedly mounted on the first shaft.

[0036] The corresponding first input sprocket, second input sprocket and third input sprocket may be mounted on the second shaft.

[0037] In this arrangement the first input sprocket is associated with a first clutch, the second input sprocket is associated with a second clutch, and the third input sprocket is associated with a third clutch. The first clutch is in the form of a sprag clutch, or similar uni-directional device, or may be as per the transmission clutch herein described. Preferably the second clutch and the third clutch are as per the transmission clutch herein described.

[0038] Each input sprocket may incorporate a bearing to allow the respective input sprocket to rotate independent of the second shaft when the respective clutch is disengaged.

[0039] The first drive sprocket and the first input sprocket may provide a first gear ratio and may be interconnected by a first chain extending therearound. The first gear ratio may provide the lowest gear ratio. The first gear ratio may be the default gear ratio (i.e. default condition) whereupon the rotational force being removed from the first shaft results in the transmission system returning to the arrangement of the first gear ratio.

[0040] The second drive sprocket and the second input sprocket may provide a second gear ratio and may be interconnected by a second chain extending therearound.

[0041 ] The third drive sprocket and the third input sprocket may provide a third gear ratio and may be interconnected by a third chain extending therearound. The transmission system may include additional drive sprockets, input sprockets, chains and clutches to provide further gear ratios.

[0042] The transmission system may comprise a tensioner for maintaining the chains at the required tension. [0043] The transmission system may be housed in a substantially sealed housing wherein the first shaft and the second shaft extend therefrom.

[0044] The second shaft may provide an output sprocket for driving an output, such as the rear wheel of a bicycle. The output sprocket may be external of the housing.

[0045] The transmission clutch comprises a clutch output member which is selectively connected to a clutch input member, wherein the axial distance between the clutch output member and the clutch input member is fixed.

[0046] The clutch output member and the clutch input member may be fixed relative to each other when selectively connected.

[0047] The clutch output member and clutch input member may be coaxially mounted on the second shaft, such that the clutch output member and the clutch input member rotate independent of each other when the transmission clutch is in the disengaged condition, and are rotatably fixed relative to each other when the transmission clutch is in the engaged condition.

[0048] The clutch output member may be fixed to the second shaft.

[0049] The clutch input member may be in the form of the input wheel, wherein the input wheel may be adapted to be connected directly or indirectly to the first shaft, as noted above.

[0050] The transmission clutch may also comprise an engagement means which is adapted to move from a first position to a second position. The engagement means may comprise at least one engaging portion which selectively fixes the clutch output member relative to the input wheel, preferably in at least one rotational direction.

[0051 ] In one aspect of the invention the at least one engaging portion engages with the clutch output member to fix the clutch output member relative to the input wheel. [0052] In another aspect of the invention the at least one engaging portion engages with the input wheel to fix the clutch output member relative to the input wheel.

[0053] The at least one engaging portion may be movable between a retracted position wherein the clutch output member and input wheel are independent of each other, and an extended position wherein the clutch output member and input wheel are fixed relative to each other. With this arrangement the clutch output member and the input wheel are positively engaged when the at least one engaging portion is in the extended position.

[0054] The at least one engaging portion may be biased to a retracted position.

[0055] The input wheel may comprise a receiving portion for receiving the engaging portion.

[0056] Each of the at least one engaging portion may be in the form of a projection which moves between the retracted position and the extended position.

[0057] Each of the at least one engaging portions may be in the form of a pawl pivotally mounted on the clutch output member such that the pawl may pivot between the retracted position and the extended position. There may be one or a multiple of pawls.

[0058] The receiving portion of the input wheel may be in the form of one or more recesses, each recess being adapted to receive an end of the pawl as the pawl moves to the extended position.

[0059] There may be two pawls which are spaced from each other. Preferably the two pawls are spaced to be angularly equidistant from each other. The input wheel may have at least two recesses spaced angularly equidistant from each other. As would be apparent to a person skilled in the art there may be more than two pawls and more than two recesses. The scope of this specification covers such variations. [0060] Each recess may be configured to retain the pawl therein to fix the clutch output member to the input wheel.

[0061 ] The recess may be configured to retain the pawl therein to fix the clutch output member to the input wheel when the rotational speed of the clutch output member is equal to the rotational speed of the input wheel.

[0062] The recess may be configured to release the pawl when the rotational speed of the input wheel is greater than the rotational speed of the clutch output member, allowing the clutch output member and input wheel to rotate independently of each other.

[0063] Each pawl may be biased to the retracted position when released from the recess. Biasing of the pawl may be caused by springs, magnets or other means as would be readily apparent to a person skilled in the art.

[0064] The transmission system may further comprises an activation means for activating the transmission clutch .

[0065] Preferably when the engagement means is in the first position the transmission clutch is in the disengaged condition, whereupon activation of the activation means the engagement means moves to the second position to fix the clutch output member relative to the input wheel such that the transmission clutch is in the engaged condition.

[0066] The activation means may comprise a governor member which is operably connected to the engagement means to move the engagement means between the retracted position and extended position.

[0067] The governor member may be coaxially mounted on the second shaft with the clutch output member and the input wheel.

[0068] The governor member may be pivotally connected to each pawl.

[0069] The governor member may be linked with the clutch output member such that it is movable between a first angular position, wherein each pawl is in the retracted position, and a second angular position, wherein each pawl is in the extended position.

[0070] Each pawl may have an arm extending therefrom, wherein an end of that arm is secured to the governor member. Each arm may be retained relative to a slot formed in the governor member. Each arm may provide a peg which is received in the respective slot.

[0071 ] In one aspect of the invention the activation means is electronically activated. The activation means may act in a radial orientation relative to the clutch. The activation means may comprise a rotary voice coil which upon activation causes the governor member to move from the first angular position to the second angular position. In other variations of the invention, as would be understood by the person skilled in the art, and which fall within the scope of the present invention, the activation means may comprise other actuators which act in a radial manner and which may be electronic and/or mechanical in nature.

[0072] In another aspect of the invention the activation means is mechanically activated. The clutch output member and governor member may be biased by a biasing means, such as a spring extending between the governor member and the clutch output member. Until the force of the biasing means is overcome the governor member remains in its first angular position and the pawls are held in the retracted position.

[0073] The activation means may alternatively comprise a plurality of masses secured to the input wheel. At a predetermined speed the centripetal force generated by the masses counteracts the force of the biasing means to cause the governor member to move to the second angular position causing the pawls to move to the extend position, whereupon engagement of each pawl with its respective recess in the input wheel fixes the input wheel relative to the clutch output member .

[0074] The control means may activate the activation means. [0075] The conditions of the transmission system monitored by the control means may include one or more of the following: linear velocity of the clutch, angular position of the clutch, angular velocity of the clutch output member, angular velocity of the input wheel. The control means may activate the activation means when the one or more conditions being monitored reach predetermined values.

[0076] In an alternative arrangement the control means may cause activation of the activation means through a contact coupling such as a slip ring to selectively cause the transmission clutch to move between the disengaged condition and the engaged condition.

[0077] In an alternative arrangement the control means may cause activation of the activation means through a contactless coupling. The contactless coupling may comprise a non-rotating member capable of generating a power field, and a rotating member in close proximity to the rotating member. The rotating member may be in communication with each transmission clutch. The non-rotating member may receive signals to selectively energise the rotating member and activate the relevant transmission clutch. In an alternative arrangement, the control means comprises a switch which may be manually operable to activate the activation means. The switch may be in place of the one or more sensors.

[0078] The present invention further provides a transmission system comprising one or more transmission clutches as herein before described.

[0079] The present invention further provides an automatic transmission system comprising at least one transmission clutch which is moveable between an engaged condition and a disengaged condition, the clutch comprising a clutch output member which is selectively connected to an input wheel , wherein the axial distance between the clutch output member and the input wheel is fixed; an engagement means which is adapted to move from a first position to a second position to fix the clutch output member to the input wheel; and an activation means; wherein the transmission clutch is in the disengaged condition when the engagement means is in the first position, whereupon activation of the activation means the engagement means moves to the second position to fix the clutch output member relative to the input wheel whereby the transmission clutch is in an engaged position.

[0080] The present invention further provides an automatic transmission system comprising at least one transmission clutch which is of fixed width and is moveable between an engaged condition and a disengaged condition, the transmission clutch comprising an clutch output member ; an input wheel which is selectively fixed to the clutch output member ; an engagement means which is adapted to move from a first position to a second position to fix the clutch output member to the input wheel; and an activation means; wherein the transmission clutch is in the disengaged condition when the engagement means is in the first position, whereupon activation of the activation means the engagement means moves to the second position to fix the clutch output member relative to the input wheel whereby the transmission clutch is in an engaged position.

[0081 ] The present invention further provides an automatic transmission system comprising at least one transmission clutch, the clutch comprising: a first member adapted to be fixed relative to an input; a second member adapted to be selectively fixed to the first member, the second member providing an output; an engagement means to engage the first member relative to the second member; an activation means to activate the engagement means between an engaged position, wherein the clutch is in an engaged condition and a disengaged position wherein the clutch is in a disengaged condition; whereupon activation of the engagement means the transmission clutch is in the engaged condition such that the first member is fixed to the second member to transfer the input to the output, whereupon the engagement means moving to the first condition the transmission clutch is in the disengaged condition such that the first member is independent of the second member, the width of the transmission clutch remaining constant as it moves between its engaged condition and disengaged condition.

[0082] The present invention further provides an automatic transmission system comprising at least one transmission clutch, the clutch comprising: a clutch output member which is selectively connected to an input wheel, the axial distance between the clutch output member and the input wheel being fixed; an engagement means which is adapted to move from a first position to a second position; and an activation means; wherein when the engagement means is in the first position the transmission clutch is in a disengaged condition, whereupon activation of the activation means the engagement means moves to the second position to rotationally fix the clutch output member to the input wheel such that the transmission clutch is in an engaged condition. [0083] The present invention further provides an automatic bicycle transmission system comprising one or more transmission clutches as herein before described, wherein the clutch output member is fixed relative to an output sprocket, the output sprocket being connected to the rear sprocket of a rear wheel of the bicycle by a chain.

BRIEF DESCRIPTION OF THE DRAWINGS

[0084] Further features of the present invention are more fully described in the following description of several non-limiting embodiments thereof. This description is included solely for the purposes of exemplifying the present invention. It should not be understood as a restriction on the broad summary, disclosure or description of the invention as set out above. The description will be made with reference to the accompanying drawings in which:

Figure 1 shows a bicycle incorporating a transmission system

according to a first embodiment of the present invention;

Figure 2 is a perspective view of the transmission system shown in figure 1 ;

Figure 3 is a perspective view of the transmission system shown in figure 1 without a housing;

Figure 4 is a schematic of the transmission system according to the first embodiment as applied to a bicycle;

Figure 5 is an exploded view of the transmission system according to the first embodiment;

Figure 6 is an exploded view of a transmission clutch, two of which are included in the transmission system of the first embodiment;

Figure 7 is a front assembled view of the transmission clutch of figure 6 in a disengaged condition;

Figure 8 is a front assembled view of the transmission clutch of figure 6 in an engaged condition; Figure 9 is a view similar to figure 8 but with a magnet and faceplate removed;

Figure 10 is a detailed view of a pawl in a position which corresponds to when the transmission clutch is in an engaged condition;

Figure 1 1 is a schematic of a control system of the transmission system of the first embodiment;

Figure 12 is a cross sectional view of the transmission system when configured to be in a first gear ratio;

Figure 13 is a representative side view of the a portion of transmission system of the first embodiment when configured to be in the first gear ratio, as represented in Figure 12;

Figure 14 is a cross sectional view of the transmission system when configured to be in a second gear ratio;

Figure 15 is a representative side view of a portion of the transmission system of the first embodiment when configured to be in the second gear ratio, as represented in Figure 14;

Figure 16 is a cross sectional view of the transmission system when configured to be in a third gear ratio;

Figure 17 is a representative side view of a portion of the transmission system of the first embodiment when configured to be in the third gear ratio, as represented in Figure 16;

Figure 18 is a perspective view of the transmission system according to a second embodiment;

Figure 19 is an exploded view of the transmission system shown in figure 18;

Figure 20 is a front view of the transmission system shown in figure 18; Figure 21 is an exploded view of a transmission clutch, two of which are included in the transmission system of the second embodiment;

Figure 22 is a front assembled view of the clutch of figure 21 in a disengaged condition;

Figure 23 is a front assembled view of the clutch of figure 21 in an engaged condition;

Figure 24 is a representative side view of a portion of the transmission system of the second embodiment when configured to be in the first gear ratio;

Figure 25 is a representative side view of a portion of the transmission system of the second embodiment when configured to be in the second gear ratio;

Figure 26 is a representative side view of a portion of the transmission system of the second embodiment when configured to be in the third gear ratio;

Figure 27 is side view of an alternate transmission clutch which may be used in the transmission system of the first embodiment.

[0085] In the drawings like structures are referred to by like numerals throughout the several views. The drawings shown are not necessarily to scale, with emphasis instead generally being placed upon illustrating the principles of the present invention.

DESCRIPTION OF EMBODIMENTS

[0086] The transmission system of the present invention is advantageous in its construction and configuration when compared to prior art transmission systems. In particular the present transmission system, as described in the below embodiment, operates automatically based on the conditions experienced by the transmission system. For instance the transmission system automatically moves to a higher gear ratio at a predetermined rotational velocity. The automatic nature of the transmission system allows the transmission system to control the output such that the transmission system is able to operate at its most efficient configuration based on the conditions.

[0087] Another advantage of the transmission system is that the components are axially fixed relative to each other. As a result the axial width of the transmission system can be narrower than those transmission systems which rely on axial movement of their components in order to control the output, allowing the transmission system to be utilised in applications where space is limited/critical. This is partly achieved by incorporating one or more transmission clutches which do not rely on axial movement to move from a disengaged condition to an engaged condition. Instead of requiring axial movement, components of the clutch positively engage each other through radial movement of an engagement means.

[0088] The automatic nature of the transmission system removes the need for an operator to control the transmission system, enabling optimum efficiency to be achieved according to the required application.

[0089] Referring to figures 1 to 17, the invention according to a first embodiment is in the form of a transmission system 13. In this application the transmission system 13 is deployed on a bicycle 15.

[0090] While an example application is in relation to a bicycle, the present invention is not limited to such an application as there are many more applications in other types of driven equipment. These include applications which have a gear train, such as in vehicles, motorcycles, and industrial equipment. Other applications as would be understood by the person skilled in the art are considered to be within the scope of this specification. The transmissions system can readily be applied to electric and non-electric applications.

[0091 ] Referring to figures 1 to 4, the transmission system 13 comprises a first shaft 17, which supports a chain ring and crank arms 19 of the bicycle, and a second shaft 21 to which is fixed an output sprocket 23. The transmission system 13 is encased in a housing 110 to protect the components of the transmission system. As best shown in figure 2 the first shaft 17 and the second shaft 21 extend beyond the housing, the output sprocket 23 being located on the portion of the second shaft 21 extending outwardly from the housing 110. The housing 1 10 protects the transmission system to significantly reduce the maintenance requirements and extend the service life of the transmission system.

[0092] The bicycle comprises a chain 25 which extends from the output sprocket 23 to a rear sprocket 27, which is fixed to the rear wheel. Whereupon a rider pedaling provides a rotational input to the first shaft 17, which, via the transmission system 13, rotates the output sprocket 23, causing the chain 25 to rotate the rear sprocket 27 and the rear wheel. As will be described below, the transmission system 13 is configured to provide different gear ratios to control the transfer of power from the input (rider) to the output (rear wheel).

[0093] As represented in figure 4, the first shaft 17 supports a plurality of drive wheels being a first drive sprocket 1 12, a second drive sprocket 1 14 and a third drive sprocket 1 16. Each of the drive sockets are fixed to the first shaft 17 such that rotation of the first shaft will cause each drive socket to rotate.

[0094] The second shaft 21 supports a plurality of input wheels being a first input sprocket 1 18, a second input sprocket 120 and a third input sprocket 122. Each of the input sprockets incorporate a bearing 33 such that when mounted on the second shaft 21 each input sprocket may be capable of rotating independent to each other as well as the second shaft 21.

[0095] Each drive sprocket 112, 1 14, 116 has a corresponding input sprocket 1 18, 120, 122 to which it is connected to provide different gear ratios. In particular: the first drive sprocket 1 12 and the first input sprocket 1 18 are interconnected by a first chain 124 to provide a first gear ratio; the second drive sprocket 1 14 and the second input sprocket 120 are interconnected by a second chain 126 to provide a second gear ratio; and the third drive sprocket 1 16 and the third input sprocket 122 are interconnected by a third chain 128 to provide a third gear ratio. With this arrangement the first shaft 17 and second shaft 21 are connected in constant mesh.

[0096] The first gear ratio provides the lowest gear ratio, while the third gear ratio provides the highest gear ratio.

[0097] The transmission system 13 incorporates a tensioner 129 to maintain the chains at a set tension.

[0098] The transmission system 13 also comprises a first clutch 130 in the form of a sprag clutch. The first clutch 130 operatively engages the first input sprocket 1 18 such that the first input sprocket 1 18 is limited to rotate in one direction. At rotational speeds between zero and a first speed the first clutch 130 ensures that rider input through the first shaft 17 translates to rotation of the second shaft 21 , which turns the output sprocket 23 to rotate the rear sprocket 27 and the rear wheel.

[0099] The transmission system 13 also comprises a second clutch 132 which is associated with the second input sprocket 120. At rotational speeds between the first speed and a second speed the second clutch 132 transmits the rider input through the first shaft 17 to the second shaft 21 to cause rotation thereof. This turns the output sprocket 23 to rotate the rear sprocket 27 and rear wheel.

[00100] The transmission system 13 also comprises a third clutch 134 which is associated with the third input sprocket 122. At rotational speeds above the second speed the third clutch 132 transmits the rider input through the first shaft 17 to the second shaft 21 to cause rotation thereof. This turns the output sprocket 23 to rotate the rear sprocket 27 and rear wheel.

[00101 ] In this embodiment the second clutch 132 and the third clutch 134 are similar to each other in relation to configuration and operation. Hereafter each of the second clutch 132 and the third clutch 134 will be referred to/described in terms of the transmission clutch 1 1. [00102] Each transmission clutch 11 is movable between a disengaged condition and an engaged condition, wherein in the engaged condition rotation of the first shaft 17 causes the second shaft 21 to rotate, the transmission clutch maintaining a fixed axial width when moving between the disengaged condition and the engaged condition;

[00103] Referring to figures 6 to 10 the transmission clutch 11 comprises an clutch output member 29, which is fixed to the second shaft 21 , and a clutch input member 31 which is mounted on the second shaft 21.

[00104] The clutch input member 31 is forms part of its respective input sprocket 120, 122. In this regard the clutch input member 31 is able to rotate with its respective input sprocket 120, 122 so as to be capable of rotating independent of the second shaft 21 when mounted thereon. The clutch input member 31 also comprises four recesses 35 spaced around the periphery of the clutch input member 29 such that an opening of each recess 35 opens inwardly away from the periphery of the clutch input member 31 , for reasons which will be described below.

[00105] The transmission clutch 1 1 also comprises an engagement means which moves between a first position whereby the clutch output member 29 and clutch input member 31 are free to rotate independent of each other, and a second position whereby the clutch output member 29 and clutch input member 31 are fixed relative to each other. In this embodiment, when the clutch output member 29 and clutch input member 31 are fixed relative to each other they are only able to rotate in one direction. The engagement means provides engaging portions, which in this embodiment are in the form of two pawls 37.

[00106] Each pawl 37 is pivotally mounted on the clutch output member 29 to move from a retracted position (as shown in figure 7) to an extended position (as shown in figure 8). Each pawl 37 has an end 39 distal from where the pawl is mounted which is adapted to be received in the recess 35 of the clutch input member 31 when in the extended position. Each pawl also provides an arm 41 which extends away from the pawl at a position along its length, for reasons which will be described below.

[00107] The transmission clutch 11 also comprises an activation means, which in this embodiment is electronic in nature. The activation means comprises a governor member 43 which is co-axially mounted with respect to the clutch input member 31 and clutch output member 29. The governor member 43 is limited to angular movement between a first angular position (as shown in figure 7) and a second angular position (as shown in figure 8).

[00108] The governor member 43 provides two slots 51 which, in the present embodiment, extend radially outward from the center of the second shaft 21. Once assembled each slot 51 receives a peg (not shown) extending from an underside of the arm 41 of each pawl 37. Each slot 51 restricts movement of the peg along the slot to govern the movement of each pawl 37.

[00109] The activation means also comprises a rotary voice coil 45 which directly acts to cause angular movement of the governor member 43.

[00110] The voice coil 45 comprises two magnets 47 secured to the clutch output member 29 in a spaced apart relation. The voice coil 45 also comprises a copper coil 49 which is fixed to the governor member 43 and is received between the magnets 47 when the transmission clutch 1 1 is assembled.

[0011 1 ] The transmission system 13 also comprises a control means 53, to activate the activation means. The control means 53 is adapted to react to certain conditions experienced by the bicycle 15 and/or the transmission system 13 to selectively activate the activation means.

[00112] As shown in figure 1 1 the control means 53 comprises a plurality of sensors which, in the present embodiment include two speed sensors 55, an inclinometer 57, a power supply 59 and a microprocessor 61. The microprocessor 61 can be programmed such that upon the sensors detecting a predetermined condition the microprocessor 61 activates the activation means by pulsing the relevant voice coil 45. [00113] Figure 1 1 shows two voice coils 45, one forming part of the second clutch 132, the other forming part of the third clutch 134.

[00114] The operation of the transmission system 13 will now be described in relation to its application to the bicycle 15.

Bicycle is travelling at a speed slower than a first speed.

[00115] With reference to figure 12, and as noted by arrows“A”, when the bicycle is at rest, or at a speed less than a first speed, the first clutch 130 is engaged while the second clutch 132 and the third clutch 134 are in their disengaged condition.

[00116] The first clutch 130 translates any movement from the rider through the first drive sprocket 1 12 on the first shaft 17, to the first input sprocket 1 18 via the first chain 124 to rotate the second shaft 21 , and simultaneously rotate the output sprocket 23. When the first input sprocket 1 18 and the second shaft 21 rotate together at the same velocity, the input from the rider is transmitted to the first input sprocket 118 to rotate the second shaft 21 and therefore rotate the output sprocket 23 which rotates the rear sprocket 27 and the rear wheel.

[00117] When the first input sprocket 118 rotates at a slower speed than the second shaft 21 , the first clutch 130 and first input sprocket 1 18 are in a freewheeling/over-run condition whereby the input from the rider is not transmitted through the first input sprocket to the second shaft 21.

Bicycle is travelling at a speed between the first speed and a second speed.

[00118] When the bicycle is travelling at a speed between the first speed and the second speed, the first clutch 130 and first input sprocket 118 are in the freewheeling/over-run condition, the second clutch 132 is caused to move to its engaged condition, while the third clutch 134 remains in its disengaged condition. This is represented in figure 14 as noted by arrows“B”.

[00119] When the bicycle 15 exceeds the first speed the speed sensors 55 of the control means 53 cause the microprocessor 61 to activate the activation means by pulsing the voice coil 45 associated with the second clutch 132. This causes the second clutch 132 to move to the engaged condition whereby movement from the rider is transmitted through the second drive sprocket 1 14 on the first shaft 17, to the second input sprocket 120 via the second chain 126 to cause rotation of the second shaft 21 , and simultaneously rotate the output sprocket 23.

[00120] Considering the operation of the second clutch 132 with reference to figures 7 to 10, pulsing the voice coil 45 causes angular movement of the governor member 43. As the governor member 43 rotates the arm 41 is forced to move along the slot 51 to move the pawls 37 from their retracted condition to their extended condition. The clutch output member 29 will continue to rotate relative to the clutch input member 31 until the end 39 of each pawl aligns with one of the recesses 35 in the clutch input member 31. When the end of the pawl extends sufficiently the end of the pawl will be received in the recess 35 to positively engage the clutch input member 31 to fix the clutch input member 31 relative to the clutch output member 29. The clutch input member 31 and the clutch output member 29 will remain positively engaged with each other while rotation of the clutch output member 29 and the clutch input member 31 is at the same velocity.

[00121 ] As the clutch input member 31 forms part of the second input sprocket 120, when the second clutch 132 is in its engaged condition wherein the input member 31 is in positive engagement with the clutch output member 29, rotation of the second input sprocket 120 is transmitted to the clutch output member 29. As the clutch output member 29 is fixed to the second shaft any movement of the clutch output member 29 causes the second shaft 21 to rotate.

[00122] The pawls 37 will remain in their extended position to positively engage the clutch input member 31 , fixing the clutch output member 29 relative to the clutch input member 31 until either the clutch input member 31 is caused to rotate faster than the clutch output member (over run/freewheeling) such as will occur when the bicycle travels faster than the second speed, or the force is removed from the clutch output member 29 (e.g. the rider stops pedalling). When either of these events takes place the force maintaining the pawls in the recesses 35 is removed and the pawls 37 are able to return to their retracted position, allowing the clutch input member 31 to rotate independent of the clutch output member 29. When this occurs the clutch is in its disengaged condition.

[00123] When the bicycle 15 exceeds the first speed the second clutch 132 is in the engaged condition, and movement from the rider is transmitted through the second drive sprocket 1 14 on the first shaft 17 to the second input sprocket 120 via the second chain 126 to rotate the second shaft 21 , and simultaneously rotate the output sprocket 23. When the second input sprocket 120 and the second shaft 21 rotate together at the same velocity, the input from the rider is transmitted to the second input sprocket 120 to rotate the second shaft 21 and therefore rotate the output sprocket 23 which rotates the rear sprocket 27 of the rear wheel.

[00124] When the bicycle travels at a speed faster than the second velocity the second input sprocket 120 (which incorporates the clutch input member 31 ), rotates at a slower speed than the second shaft 21 (to which the clutch output member 29 is fixed). When this occurs the pawls 35 are caused to disengage from their recesses 35, allowing the clutch input member 31 , and therefore the second input sprocket 120, to rotate independent of the clutch output member 29 and therefore independent of the second shaft. In this configuration the first clutch 130, the first input sprocket 1 18 and the second input sprocket 120 and are in a freewheeling/over-run condition whereby the input from the rider is not transmitted through the second input sprocket or the second input sprocket to the second shaft 21. In this configuration the second clutch 132 is in its disengaged condition.

Bicycle is travelling at a speed faster than the second speed.

[00125] When the bicycle is travelling at a speed faster than the second speed, the first clutch 130, the first input sprocket 1 18 and the second input sprocket 120 are in the over-run/freewheeling condition, while the second clutch 132 is in its disengaged condition. When the speed of the bicycle exceeds the second speed the third clutch 134 is caused to move to its engaged condition. This is represented in figure 16 as noted by arrows“C”.

[00126] When the bicycle 15 exceeds the second speed the speed sensors 55 of the control means 53 cause the microprocessor 61 to activate the activation means by pulsing the voice coil 45 associated with the third clutch 134. This causes the third clutch 134 to move to the engaged condition whereby movement from the rider is transmitted through the third drive sprocket 1 16 on the first shaft 17, to the third input sprocket 122 via the third chain 128 to cause rotation of the second shaft 21 , and simultaneously rotate the output sprocket 23.

[00127] The operation of the third clutch 134 is identical to that of the second clutch 132 as described above.

[00128] When the bicycle 15 exceeds the second speed the third clutch 134 is in the engaged condition whereupon input from the rider is transmitted through the third drive sprocket 116 on the first shaft 17 to the third input sprocket 122 via the third chain 128 to rotate the second shaft 21 , and simultaneously rotate the output sprocket 23. When the third input sprocket 122 and the second shaft 21 rotate together at the same velocity, the input from the rider is transmitted to the third input sprocket 122 to rotate the second shaft 21 and therefore rotate the output sprocket 23 which rotates the rear sprocket 27 of the rear wheel.

Bicycle is travelling at a speed faster than the third speed.

[00129] When the bicycle travels at a speed faster than a third speed, the rear wheel speed exceeds the input speed (i.e. rider cadence). When this happens the third input sprocket 122 (which incorporates the clutch input member 31 ), rotates at a slower speed than the second shaft 21 (to which the clutch output member 29 is fixed). When this occurs the pawls 35 are caused to disengage from their recesses 35, allowing the clutch input member 31 , and therefore the third input sprocket 122, to rotate independent of the clutch output member 29 and therefore independent of the second shaft 21. In this configuration the first clutch 130, the first input sprocket 1 18, the second input sprocket 120 and the third input sprocket 122 are in a free-wheeling/over-run condition whereby the input from the rider is not transmitted through the first input sprocket 118, the second input sprocket 120, or the third input sprocket 122 to the second shaft 21. In this configuration the second clutch 132 and the third clutch 134 are in the disengaged condition. When this happens the transmission system 13 has effectively reset to a default condition as neither the second clutch 132 nor the third clutch 134 are engaged. When the transmission system is in the default condition the transmission system is at its lowest gear ratio.

[00130] The transmission system 13 immediately responds to changes in conditions, whether this is a result of an increase in speed or the input force (pedalling) ceases. These changes result in the transmission system 13 presenting a different gear ratio to control the output. Due to the configuration and operation of the transmission system 13 changes in gear ratios are rapid wherein the transition is less than 100 milli-seconds. Furthermore, as the transmission system 13 provides a constant mesh arrangement there is no delay in gear changes otherwise caused by the chain moving between sprockets.

[00131 ] As noted above the control means 53 moves the second clutch 126 and the third clutch 134 from a disengaged condition to an engaged condition based on conditions experienced by the transmission system 13/bicycle 15. In the present application to a bicycle these conditions would typically include speed of the bicycle (using speed sensors 55), in particular the rear wheel, and the angle at which the bicycle is travelling (using inclinometer 57). The microprocessor 61 of the control means 53 is programmed such that when certain speeds combined with certain angles are identified the control means automatically activates the activation means to cause the second clutch 132 or the third clutch 134 to move to their engaged condition.

[00132] A transmission system 213 according to a second embodiment of the invention is illustrated in figures 18 to 26. For convenience features of the transmission system 213 that are similar or correspond to features of the transmission system 13 of the first embodiment have been referenced with the same reference numerals. The transmission system 213 is very similar to that of the first embodiment with variations in configuration, including a variation in each transmission clutch 21 1 , and the inclusion of a wireless coupling 217.

[00133] Considering the clutch 21 1 in this embodiment, the input member 31 differs from that of the clutch 1 1 of the first embodiment in that it comprises ten recesses 235 rather than four, as best shown in figures 21 to 23. These recesses 235 are spaced equidistance around the periphery of the input member 29. An opening of each recess 235 opens inwardly away from the periphery of the input member 31 and has a closed end with an apex 269. Each pawl 235 has an end 239 which is complementary in shape to the recess 235 such that there is positive engagement of the pawl end 239 and recess 235 so that the likelihood of the pawl 37 unintentionally disengaging the input member 29, or slipping from one recess 235 to an adjacent recess 235 is minimised. As would be apparent to a person skilled in the art, the clutch may incorporate any number of recesses.

[00134] The configuration of the clutch 21 1 of the second embodiment allows for a more accurate and faster clutch response due to the increase in the number of recesses 235.

[00135] The transmission system of the second embodiment also includes a contactless coupling 271. The contactless coupling 271 enables non-contact power transfer and communication and overcomes wear issues as are inherent in other power transfer devices such as slip rings. The contactless coupling 271 comprises a non-rotating printed circuit board (PCB) 273 and a coaxially located, rotating printed circuit board (PCB) 275. The non rotating PCB 273 generates an electro-magnetic field which couples into the rotating PCB 275. The electro-magnetic field conveys both power and data to the rotating PCB 275 enabling the selective activation of the rotary voice coils 45. [00136] The rotating PCB 275 draws power from the electromagnetic field that is generated, therefore not needing to be powered by a separate battery, which would otherwise take up space.

[00137] In operation, a control means 251 sends a signal to the non rotating PCB 273 where it is amplified. The resultant power field energises the rotating PCB 275, which then establishes a DC voltage. The control means 51 then sends an activation signal to the PCB which is specific to one of the rotary coil 45 in the transmissions clutches. Depending on when the conditions of the transmission system change the activation signal stops, the powering field collapses, and the specific rotary coil 45 de-energise.

[00138] Figure 27 shows an alternative from of a transmission clutch 311 which may be used in the transmission system 13. For convenience features of the transmission clutch 311 that are similar or correspond to features of the transmission clutch 1 1 , as described above have been referenced with the same reference numerals.

[00139] In this alternative the activation means is mechanically activated. The clutch output member 29 and a governor member 343 are biased by a biasing means, in the form of a spring 363 extending between a spring post 265 on the governor member 343 and a spring post 265 on the clutch output member 29. Until the force of the spring 363 is overcome the governor member 343 remains in its first angular position and the pawls 37 are held in their retracted position, the clutch is disengaged.

[00140] The activation means also comprises a plurality of masses 367 secured to the clutch input member 31. At a predetermined speed (based on mass and spring rate) the centripetal force generated by the masses counteracts the force of the spring to cause the governor member 343 to move to the second angular position causing the pawls to move to the extended position, whereupon engagement of each pawl with its respective recess in the clutch input member 31 fixes the clutch input member 31 relative to the clutch output member 29, the clutch is now engaged. [00141 ] The present invention allows for very rapid response and can be manually or automatically activated between engaged and disengaged conditions. The transmission is in constant mesh allowing efficiency to be optimised through aligned chains and, when applied to a bicycle, eliminates the need for a derailleur.

[00142] The transmission can be set to an infinite number of gear shifting profiles and enables non-sequential gear shifting options.

[00143] By having the transmission contained in a housing the

opportunity for the ingress of contaminants or operator interference is inhibited, significantly reducing the maintenance requirement.

[00144] Modifications and variations such as would be apparent to the skilled addressee are considered to fall within the scope of the present invention. The present invention is not to be limited in scope by any of the specific embodiments described herein. These embodiments are intended for the purpose of exemplification only. Functionally equivalent products, formulations and methods are clearly within the scope of the invention as described herein. For example, the transmission system 13 may include additional drive sprockets, input sprockets, shafts, chains and clutches to provide further gear ratios. Also, where there are restrictions in terms of the axial space available, several transmissions system 13 may be stacked relative to each other to provide additional gear ratios.

[00145] Reference to positional descriptions, such as lower and upper, are to be taken in context of the embodiments depicted in the figures, and are not to be taken as limiting the invention to the literal interpretation of the term but rather as would be understood by the skilled addressee.

[00146] The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms“a”,“an” and“the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprise”, “comprises,” “comprising,” “including,” and “having,” or variations thereof are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

[00147] When an element or layer is referred to as being“on”,“engaged to”,“connected to” or“coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being“directly on,”“directly engaged to”,“directly connected to” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term“and/or” includes any and all combinations of one or more of the associated listed items.

[00148] Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as“first,”“second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments.

Spatially relative terms, such as“inner,”“outer,”“beneath”,“below”,“lower ”, “above”,“upper” and the like, may be used herein for ease of description to describe one element or feature’s relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented“above” the other elements or features. Thus, the example term“below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.