WO2013013270A1

WO2013013270A1 - Gearing assembly

Info

Publication number: WO2013013270A1
Application number: PCT/AU2012/000887
Authority: WO
Inventors: Johann Franz KAISER; John Lionel Brauer
Original assignee: Kaiser Johann Franz; John Lionel Brauer
Priority date: 2011-07-28
Filing date: 2012-07-26
Publication date: 2013-01-31

Abstract

A gear assembly is discussed the gearing assembly includes a front face plate (102), drive (plate103) and guide plates (104, 108), sprocket (106) and shifting mechanism (200). The sprocket (106) is constructed from a set of segments (1061, 1062, 1063, 1064, 1065) and (1066) each segment being coupled to the drive plate via drive pins (1071, 1072, 1073, 1074, 1075) and (1076). Each segment includes two pairs of guide pins (1091, 1092) disposed on the front and rear faces of the segments and which engage slots disposed in the guide plates (104, 108). The shifting mechanism includes a gear selection plate (201) a shifting plate (202) and a gear selection mechanism (203). The shifting mechanism (200) is coupled to the drive pins (1071, 1072, 1073, 1074, 1075 and 1076) to permit the movement of the segments (1061, 1062, 1063, 1064, 1065 and 1066) between discrete gear positions.

Description

TITLE

Gearing Assembly

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates in general to a gearing assembly. In particular although not exclusively the present invention relates to a sprocket having multiple gearing ratios.

Discussion of the Background Art

A gear is in essence a rotating machine part having cut teeth, or cogs, which mesh with another toothed part in order to transmit torque. The use of gearing in mechanics allows for changes speed, magnitude, and direction of a power source. One of the most common forms of gearing arrangement is a sprocket which essentially a profiled wheel with teeth that mesh with a chain, track or other perforated or indented drive mechanism. It differs from most other forms of gears in that it does not mesh directly with another gear. Sprockets are utilised in a number of applications to transmit rotary motion between two shafts where gears are unsuitable or to impart linear motion to a track, tape etc. Some of the more common uses of sprockets to transfer rotatory motion is in drive systems for bicycles, motorcycles, some motor vehicles, tracked vehicles etc.

In the case of bicycle, a number of sprockets can be utilised to modify the overall gear ratio of the drive chain by varying the diameter (and therefore, the tooth count) of the sprockets on each side of the chain. This concept is the basis of derailleur gears. A derailleur gearing system provides a variable-ratio transmission system consisting of a chain, multiple sprockets of different sizes, and mechanisms to move the chain from one sprocket to another. Modern derailleur typically include front and rear moveable chain-guide that are operated remotely by a Bowden cable attached to a shift lever mounted on the down tube, handlebar stem, or handlebar of the bicycle. When a rider operates the lever while pedalling, the change in cable tension moves the chain-guide from side to side, "derailing" the chain onto different sprockets. In a 10-speed bicycle, for example two different-sized driving sprockets (high and low range) and five different-sized driven sprockets are utilised allowing up to ten different gear ratios. The resulting lower gear ratios make the bike easier to pedal up hills while the higher gear ratios make the bike faster to pedal on flat roads. In a similar way, manually changing the sprockets on a motorcycle can change the characteristics of acceleration and top speed by modifying the final drive gear ratio.

Originally, bicycle gear controls consisted of simple levers. In order to change gears a user was required to push or pull the lever so that the derailleur would move the chain to a different sprocket on the rear hub. The user would then need to adjust the lever to canter the chain on the sprocket. This type of shifting is generally known as friction shifting.

One of the problems with friction shifting systems is that the rider was expected to judge how far to move the lever for each shift. If the lever was moved the wrong amount, the derailleur might shift the chain too far, or not shift at all. It might also shift to the desired gear, but not line up quite right with the sprocket (i.e. chain positioned in between two sprockets), so the chain would run rough and noisy. The rider was expected to correct this by feel and by ear. This need for constant adjustment in friction gearing systems lead to the introduction of index shifting. With indexed shifting there are a number of stops in the shifter, each stop corresponding to a specific derailleur position. This series of discrete stops provides the rider with a tactile guide as to how far to move the shifter to shift from one gear to the next. This makes it near impossible to miss shift, but at the expense of having more difficult initial adjustment.

While index shifting has improved gear selection on the rear sprocket set the change between high and low range on the front sprocket is done utilising a friction shift derailleur. In most bikes the front derailleur moves between two positions to guide the chain between the two front sprockets. The problem with this arrangement is that there is a slight delay in the shift between ranges which causes a slight chain slip. Minor delays and chain slips may not bother your average recreational cyclist but for your competitive road cyclist the fraction of a second delay could mean the difference between first and second. That is as the shift from high to low range is affected there is an instant where no power transferred from the crank to the chain. In the worst case scenario the slight slippage can lead to de-chaining, i.e. the chain is free to jump off the drive sprocket due to a release of chain tension.

In addition the need to accommodate the lateral movement of the front derailleur limits the number and size of the front sprockets due to the angular displacement of the chain relative to the rear sprockets. This angular displacement of the chain causes wear on the sprocket teeth as well as the links in the chain. Indeed the problem with the angular displacement of the drive chain is not only unique to bicycle gearing systems but is also present in any sprocket based drive system where the gears in the sprocket set are not directly in line. It is this angular displacement of the chain or drive belt which limits the number of sprockets which can be accommodated.

While the above discussion focus primarily on a sprocket drive system for bicycles it will of course be appreciated by those of skill in the art that similar problems associated with power transfer, wear on the drive mechanisms etc in other forms of sprocket driven arrangements and more specifically where gearing ratios are changed by cantering the drive belt/chain or the like across one or more sprockets.

Clearly it would be advantageous to provide a gearing assembly which provides for increased gearing ratios with minimal disruption to power transfer during a drive stroke. It would also be advantages to provide a gearing system which allows for increased gearing ratios and which reduces wear on the drive mechanisms due to misalignment of one or more drive components. SUMMARY OF THE INVENTION

Disclosure of the Invention

Accordingly in one aspect of the present invention there is provided a sprocket including a plurality of segments wherein each segment is movable between a first and second position and wherein the size of the sprocket is varied by sequentially moving each segment between the first and second positions.

In yet another aspect of the present invention there is provided a gearing assembly the assembly including:

a drive plate;

a pair of guide plates positioned behind the drive plate;

a sprocket positioned between the guide plates, the sprocket including a plurality of segments each segment being in communication with the drive plate via a drive pin;

a shifting assembly for varying the size of the sprocket by moving each segment between preset positions on the drive plate via selective engagement and disengagement of the drive pins with the drive plate. The drive plate may be in the form of an annular disc having a planarity of apertures disposed therein. The disc preferably has a thickness of approximately 3mm and may be constructed from stainless steel, titanium or other such suitable metal, alloy or composite material. The drive plate may include various apertures laid out at various distances from the centre of the drive plate. The drive plate preferably has a diameter of at least 156mm.

Suitably the drive plate has a first set of apertures adjacent the central aperture of the drive plate for the attachment of a crank. Preferably the central aperture of the drive plate has a diameter of approximately 55mm. The first set of apertures may be positioned on a circle having a diameter of 70mm as measured from the centre of the drive plate. Preferably each aperture within the first set of apertures are spaced from adjacent aperture in the set at an angular distance of 60° as measured form the centre of the drive plate. The preset positions on the drive plate may be formed by a plurality of lateral slots disposed radially on the drive plate. The lateral slots may be arranged in a series of slot sets disposed about the drive plate. Suitably the drive plate includes six sets of radially disposed lateral slots.

Preferably each lateral slot within each slot set corresponds with a specific gear position for the corresponding segment of the sprocket. Suitably the each slot set includes at least three slots corresponds to first, second and third gear positions for the sprocket. The first slot in each slot set may be positioned on the circumference of a circle having a diameter of 77mm as measured from the centre of the drive. The second slot in each slot set may be positioned on the circumference of a circle having a diameter of 101.2mm as measured from the centre of the drive plate 103. The third slot in each slot set may be positioned on the circumference of a circle having a diameter of 125.4mm as measured from the centre of the drive plate. Suitably the slots increase incrementally in length from the first to the third slot.

Suitably positioning the segments of the sprocket in the first, second and third slot positions allows the sprocket diameter to be varied. Preferably the sprocket is equivalent to a 42 tooth sprocket in the first slot position, a 48 tooth sprocket in the second slot position and a 54 tooth sprocket in the third slot position. The slots are preferably disposed within an arc of 20° within the 60° arc between the centres of the apertures with the first set of apertures. The ends of the slots may be rounded such that the centre for each of the arcs forming the ends of the slots lie on the rays forming the 20° arc and the circumference of each circle on which the slot is centred.

Preferably the guide plates are in the form of annular disc and include a second set of apertures adjacent the central aperture of the guide plate. Suitably the guide plates have a diameter of at least 156mm and the second set apertures are disposed on a circle having a diameter of 70mm as measured from the centre of the relevant guide plate. Suitably each aperture in the second set of apertures are spaced from adjacent aperture in the set at an angular distance of 60° as measured form the centre of the relevant guide plate. Each of the guide plates may have a thickness of approximately 3mm and may be constructed from stainless steel, titanium or other such suitable metal, alloy or composite material.

The guide plates may also include a plurality of radially disposed longitudinal slots for accommodating the drive pins. Suitably the central axis of each longitudinal slot is disposed along radii which are disposed at an angular distance of 60° as measured form the centre of the relevant guide plate so as to align with the centre of the longitudinal slots with the lateral slots provided in the drive plate. The guide plates may also include a series of secondary longitudinal slots associated with each of the radially slots, the secondary slots extending substantially parallel along either edge of their respect longitudinal slot. The secondary longitudinal slots may be adapted to receive one or more guide pins disposed on the segments of the sprocket.

In one embodiment of the present invention the longitudinal slots and secondary longitudinal slots of the guide plates may include one or more niches. Suitably the niches are positioned such that they align with the centre of each lateral slot provided in the drive plate.

The gearing assembly may include a spacer positioned between the guide plates and adjacent the segments of the sprocket. The spacer may include a plurality of lugs disposed about a central hub. Each of the lugs may include an aperture which co-operate with the first and second set s of apertures to permit attachment of the crank. Suitably the angular displacement between the centres of the apertures in the spacer is approximately 60° as measured from the centre of the hub. The exterior surface of the spacer between each of the lugs maybe contoured. Preferably the contour is shaped receive the base of the segments of the sprockets. The segment may include a pair of angled lateral sides which angle toward the base of the segment. Suitably the lateral sides are angled toward the base at a pitch of approximately 60° as measured from the sprocket's centre. The base of the segment may include one or more recessed sections. The recessed sections co-operate to match the shape of the outer surface of the central spacer when the segments are brought into engagement with one another.

The base of the segments is preferably provided with a socket for the receipt of the drive pin. The drive pin can be held within the socket via a number of retaining arrangements. A pair of guide pins for engagement with the secondary slots on the guide plates may be disposed on either side of the socket. Suitably the guide pins are positioned at a distance of 16 mm from the centre of the socket. The guide pins may be vertically offset from the socket by 8mm as measured from the socket's centre.

Each segment of the sprocket preferably includes a plurality teeth disposed along its peripheral edge. The tooth profile of the segments may be designed to suit a particular chain type. Most preferably the tooth profile is designed to suit an ANSI R40 chain. In such instances each tooth has 12.7mm pitch.

The shifting mechanism preferably includes a pair of mounting brackets for attaching the shifting mechanism to a support structure. Suitably the shifting mechanism includes a gear selection plate and a shifting plate. Preferably the shifting mechanism includes a gear selector mounted behind the shifting plate. The- gear selector may be in the form of a magnetic selector. The magnetic selector may be a rare earth magnet which is position to pull the drive pin from the drive plate at the commencement an upshift or downshift of the segments between the preset positions.

A range selector may also be coupled to the shifting plate. The range selector may be utilised to slide the shifting plate forward or backward depending on the shifting operation required (i.e. upshift or downshift). Preferably the range selector is designed to move the selection plate at least 21 mm in either direction.

The shifting mechanism may also include a sliding wedge mounted on the shifting plate and in communication with the selection plate. Preferably the wedge is designed to contact the drive pins to force them into engagement drive plate once gear selection is complete. Preferably the wedge is positioned within a pair of grooves disposed in the selection plate. Suitably the grooves in the selection plate are positioned at the ends of one or more tracks provided on the selection plate. The wedge may be mounded on a slide bracket to enable the wedge to maintain alignment with the grooves when the shifting plate is moved forward or backward.

Preferably the selection plate includes at least two guide tracks formed between a plurality of rail members. The rails and tracks may be of a generally arcuate shape. Suitably the radius of curvature of the tracks and rails enables the tracks to be toggled between the one or more gear position by sliding the_^selection plate back and forward.

BRIEF DETAILS OF THE DRAWINGS

In order that this invention may be more readily understood and put into practical effect, reference will now be made to the accompanying drawings, which illustrate preferred embodiments of the invention, and wherein:

FIG. 1 is an exploded view of a gearing assembly according to one embodiment of the present invention;

FIG. 2 is a schematic diagram depicting one arrangement of a drive plate for use in the gearing assembly of Fig 1 ;

FIG. 3 is a schematic diagram depicting one arrangement of a guide plate for use in the gearing assembly of Fig 1 ;

FIG. 4 is a schematic diagram depicting one arrangement of a spacer for use in the gearing assembly of Fig 1 ; FIG. 5A is a schematic diagram depicting one arrangement of a segment of a sprocket assembly for use in the gearing assembly of Fig 1 ; and

FIGs. 5B and 5C are cross sectional views of the sprocket segment of Fig 5A depicting retaining arrangements for a drive pin in greater detail;

FIG. 6 is a schematic diagram depicting one arrangement of a crank for use in the gearing assembly of Fig 1 ;

FIG. 7 is a schematic diagram depicting one arrangement of a shifting mechanism for use with the gearing assembly of Fig 1 ;

FIG. 8 is a schematic diagram depicting the one possible construction of a gear selection plate for use with the shifting mechanism of Fig 7;

FIG 9 is a schematic diagram depicting the position of the sprocket segments for each gear;

FIG 10A Is a schematic diagram depicting one possible arrangement of a drive pin for use with gearing assembly of Fig 1 ;

FIGs. 10B and 10C depict the engagement and disengagement of the drive pin during a gear shift according to one embodiment of the present invention;

FIG. 11A to 1 1 C are schematic diagrams depicting the various positions of the gear selectors during different stages of downshift;

FIGs. 11 D to 11 F are schematic diagrams depicting the various positions of the gear selectors during different stages of upshift;

FIGs. 12A and 12B depict the movement of the drive pin relative to the change plate during upshift to a higher gear setting;

FIGs. 12C and 12D depict the movement of the drive pin during downshifting operations;

FIGs. 13A to 13C are schematic diagrams depicting the gear configuration of the sprocket in each of the gear positions; and

FIG. 14 is a schematic diagram depicting the construction of a gearing assembly according to a further embodiment of the invention. DESCRIPTION OF EMBODIMENTS OF THE INVENTION

With reference to Fig 1 there is illustrated an exploded view of a gearing assembly 100 according to one embodiment of the present invention. In this particular example the gear assembly is in the form of a front sprocket for a bicycle which is driven by cranks 101₁, 1012. Crank 101 i in this case is attached to the front face plate 102, drive plate103 and guide plates 104, 108.

The sprocket 106 in this instance is positioned about a central spacer 105 and between the guide plates 104, 108. As with the guide plates the central spacer 105 is attached to crank 1011. The sprocket 106 in this example is constructed from a set of segments 106_{1 (} 106₂₎ 106₃, 106_4l 106₅ and 106₆ each segment being coupled to the drive plate via drive pins 107i, 1072, 107₃₎ 107₄, 107₅ and 107₆. In addition to the drive pin each segment 106^ 106₂, IO63, IO64, IO65 and 106₆ includes a two pairs of guide pins 109i, 109₂ disposed on the front and rear faces of the segments and which engage slots disposed in the guide plates 104, 108.

The assembly 100 also includes a shifting mechanism 200 which attaches to the frame of the bicycle about the bottom bracket. The shifting mechanism in this example includes a gear selection plate 201 a shifting plate 202 and a gear selection mechanism 203. The shifting mechanism 200 is coupled to the drive pins 107i, 107₂, 107₃, 107₄, 107₅ and 107₆ to permit the movement of the segments 106i, 106₂₎ 106₃₎ 106₄, 106₅ and 106₆ between a number of discrete gear positions. The selection of the desired gear is discussed in greater detail below.

Fig 2 depicts the drive plate 103 in greater detail as shown the drive plate is in the form of an annular disc having a planarity of apertures disposed therein. The disc in this case has a thickness of approximately 3mm and is preferably constructed from 316 stainless steel or other such suitable material. The drive plate depicted here has a diameter of approximately 56mm with the various apertures laid out at various distances from the centre of the drive plate 103. As shown a first set of apertures 110i , 110₂, 110₃₎ 110₄₎ 110₅ and 110₆ for the attachment of the drive plate to the crank are provided adjacent the central aperture of the drive plate. In this example the central aperture has a diameter of approximately 55mm for accommodating a portion of the central spacer 105. The apertures 110i, 110₂, 1 0₃, 1 0₄, 110₅ and 110₆ being centred on a circle having a diameter of 70mm as measured from the centre of the drive plate. Each aperture 110i, 110₂, 110₃, 110₄, 110₅ and 110₆ being spaced from the adjacent aperture in the set at an angular distance of 60° as measured form the centre of the drive plate 103.

The drive plate 103 also includes a plurality of lateral slots which radiating out from the centre of the drive plate and are disposed between the angular segments formed between apertures 110i, 110_2l HO3, 110 , 110₅ and 110₆ ₍i.e. the slots are positioned within the 60° wedge formed between the centres of the apertures 110₁₍ 110₂, 110₃, 110₄, 110₅ and 110₆₎. The lateral slots being arranged into a series of slot sets. In the depicted example the drive plate includes six sets of radially disposed lateral slots sets (1111.1, 1111.2 III1.3). (III2.1, III2.2 1 12,3), (III3.1, III3.2 1113,3), (1114,1, 1114,2 1114,3). (1115,1, 1115,2 1115,3) and (111β,ι, 116.2 111β,3)· Each lateral slot within each slot set corresponds with a specific gear position for the corresponding segment of the sprocket.

In this case the slots 111i,i, IH2.1, Ί 13,1 , 111 ,1, 111δ,ι and 111e,i correspond to the first gear position for the sprocket 106, the slots being centred on the circumference of a circle having a diameter of 77mm as. measured from the centre of the drive plate 103. Similarly slots 1111,2, 112,2,

1113.2, 1114,2, 1115,2 and 111β,2 correspond to the second gear position for the sprocket 106 and are centred on the circumference of a circle having a diameter of 101.2mm as measured from the centre of the drive plate 103. Finally the third gear position of the sprocket 106 is provided by slots 111_1>3,

1112.3, 1 13,3, 1114,3, 1115,3 and 111₆.3, the slots being centred on the circumference of a circle having a diameter of 125.4mm as measured from the centre of the drive plate 103. As can be seen from Fig 2 the slots are disposed within an arc of 20° within the 60° arc between the centres of apertures1 10i, 110₂, 110₃, 10₄, 110₅ and 1 10₆ . More specifically the ends of the slots are rounded such that the centre for each of the arcs forming the ends of the slots lie on the rays forming the 20° arc and the circumference of each circle on which the slot is centred.

It will be appreciated by those of skill in the art that diameters the circles on which each slot is position have been chosen to ensure that the gearing ratios provided by the sprocket 106 fall within the current rule governing gear assemblies set down by the International Cycling Union (UCI). Other diameters may be utilised depending on the application in which the gearing assembly is utilised. It will also be appreciated by those of skill in the art that the arcuate spacing of the various apertures have been selected to ensure proper alignment of sprocket segments when the sprocket is positioned in first gear.

Fig 3 depicts one possible arrangement of the guide plates 104, 108 according to the present invention. As with the drive plate 103 each of the guide plates 104, 108 is approximately 3mm thick and is constructed from 316 stainless steel or other such suitable material. As shown the guide plates 104, 108 each include a second set of apertures 112i, 112₂, 1 12_3l 112 , 1 12₅ and 112₆ provided adjacent the central aperture of the guide plate for securing the plates 104, 108 to the crank 1011. Again the apertures 1 12^ , 1 12₂₎ 112₃, 1 12₄, 112₅ and 112₆ being centred on a circle having a diameter of 70mm as measured from the centre of the drive plate. Each aperture 1 12i, 112₂, 1 12a, 1 12₄, 112₅ and 1 12e being spaced from the adjacent aperture in the set at an angular distance of 60° as measured form the centre of the relevant guide plate 104, 108. That is the second set of apertures 112_{1 t} 1 12₂₎ 112₃, 112₄, 112₅ and 112₆ align with their counterpart on the opposing guide plate in addition the second set of apertures 1 2_{1 t} 112₂, 1 12₃, 1 12 , 112₅ and 112₆ align with the first set of apertures 1 10i, 1 10₂, 110₃, 110 , H O5 and 110β to permit the attachment of the crank 101 i. The guide plates 104, 108 also include a plurality of radially disposed longitudinal slots 1 13i, 1 13₂₎ 113₃, 1 13₄, 1 13₅ and 1 13₆ for accommodating a portion of the drive pins 107i, 107₂, 107₃, 107₄, 107₅ and 107₆. As shown the central axis of each slots 113/, 1 13₂, 113₃, 1 13₄, 1 13₅ and 1 13₆ is disposed along radii spaced apart at an angular distance of 60° as measured form the centre of the relevant guide plate 104, 108. That is the slots are positioned at an angle of 30° is provided between the cental axis of the slots 1 13-t, 1 13₂₎ 1 13₃, 1 134, 113_δ and 1 136 and the centre of adjacent apertures 1 12i, 1 12₂, 1 123, 1 12₄, 1 12₅ and 112β (i.e. slots are disposed about the centre of the segment formed between adjacent apertures 1 12i, 1 12₂, 112₃, 1 12₄, 1 12₅ and 112₆). Positioning the slots 1 13i, 1 13₂, 1 13₃, 1 13₄, 113₅ and 1 13₆ in this manner ensures that they align with the centre of the slots provided in the drive plate 103. To ensure the proper alignment of the drive pins 107i, 107₂, 107₃, 107₄, 107₅ and 107₆ within slots 113i, 113₂, 1 13₃, 1 13₄, 113₅ and 1 13₆ a pair of slots 1 14i, 1 142 for the receipt of the guide pins disposed on the segments of the sprocket are provided along side each slot 113i, 113₂, 113₃, 1 13₄, 1 13s and 1 13β· The slots 114i, 1 14₂ extend substantially parallel with the edges of their respect slot 113i , 113₂, 1 13₃, 113₄, 1 13₅ and 1 13₆.

One arrangement of the central spacer 105 according to the present invention is depicted in Fig 4. As shown the central spacer 105 includes a plurality of lugs 1 15i , 1 5₂, 115₃, 1 15₄, 15₅ and 115₆ disposed about a central hub 116. each of the lugs includes an aperture 117i , 17₂, 117₃, 117₄, 117s and 1 17β to permit attachment of the spacer 105 to crank 101 _n. Again as in the cases of the drive 103 and guide plates 104, 108 the angular displacement between the centres of the apertures 1 17i, 1 17₂, 117₃, 1 17₄, 1 17₅ and 117e is 60° as measured from the centre of the hub 1 16. The apertures 1 17i, 1 7₂, 1 17₃, 117₄, 117₅ and 117¾ co-operate with the apertures 110i , 1 10₂, 110₃, 1 10₄, 110₅ and 1 10₆ and 112i, 112₂, 112₃, 112₄, 112₅ and 112₆ in the drive and guide plates to facilitate attachment of the crank 101_L In this particular example the exterior surface of the spacer between each of the lugs 115i, 152, 53, 115₄, 1 15₅ and 115₆ is contoured. The contour in this instance is shaped to fit the base of the segments 106i , IO62, I O63, 06₄, IO6₅ and 1066 when position in first gear. The spacer effectively act as a stop to minimise the potential jamming from misalignment of the segments 106i, 106₂, 106₃₎ IO6₄, 106₅ and 106₆ when they are brought into close relation.

Fig 5A shows the construction of one of the segments 106i, IO62, IO63, IO64, IO6₅ and 106β of the sprocket 106 according to one embodiment of the present invention. For clarity description the following discussion will focus on the construction of the first segment IO61, however it will be appreciated by those of skill in the art that all remaining segments have the same construction. As shown the peripheral edge of the sprocket segment IO6₁ includes plurality teeth 1 18. The tooth profile in this case is designed to suit an ANSI R40 chain and have a 12.7mm pitch. It will of course be appreciated by those of skill in the art that other tooth profiles ca be utilised depending on the type of power transfer mechanism chosen.

The segment's IO6₁ lateral sides 119i, 119₂ are angled toward the base 1 19 of the segment at 60° pitch as measured from the sprocket 106 centre. The base of the sprocket segment includes recessed sections 120i, 120₂. When the segments are brought into close relation when the sprocket is positioned in first gear the recesses 120i, 120₂ in each segment co-operate to match the shape of the outer surface of the central spacer 105 as can be seen from Fig 1.

A socket 121 is provided in the base of the segment IO6₁ for the receipt of the drive pin 107i. The drive pin can be held within the socket in a number of ways, a more detailed view of two different retaining arrangements are shown in Fig 5B and 5C discussed in greater detail below. Guide pins 109i, 1092 in this example are disposed on either side of the socket 121. As shown the guide pins are positioned at a distance of 16 mm from the centre of the socket 121 i.e. there is 32mm between the centre of each guide pin. In addition the guide pins are vertically offset from the socket by 8mm as measured from the socket's 121 centre.

Fig 5B is an enlarged view of section A of the base of socket 121 and depicts one possible retaining arrangement for the drive pin 107i according to one embodiment of the present invention. As shown the retaining arrangement in this instance includes a steel ball 122 which protrudes into the cavity within the socket 121 the ball is held in place by a urethane insert 123 and grub screw 124. Fig 5C depicts an alternate arrangement of the retaining arrangement for the drive pin for section A of the socket 121. In the case of Fig 5C a locking screw 125 is inserted into the base of the socket such that a portion of the screw protrudes into the cavity of the socket 121. As shown the end of screw 125 is rounded off. In both of the retaining arrangements of Figs 5B and 5C the section which engages the drive pin 107i has a spherical surface. This shape enables the drive pin 107i to be moved between the drive and shift positions with reduced friction. The operation of the drive pin and the retaining arrangements are discussed in greater detail with respect to Figs 10A to 10C. Typically most bicycle cranks are attached to the sprocket via what is commonly called the spider which includes a set of 4 or 5 lugs through which a set of retaining bolts are inserted. However, as the sprocket 106 in this instance is composed of 6 segments the crank 1011 need to be modified. Fig 6 is a schematic diagram depicting the construction of the crank 1011 according to one embodiment of the present invention. As shown the crank includes a crank arm 126 and spider 127 which in this instance includes 6 lugs 128i, 1282, 128₃, 128₄₎ 128₅ and 128₆ arranged in a star configuration. The star configuration matching the configuration of the central spacer. The lugs 128!, 128₂, 128₃, 128₄, 128₅ and 128₆ include apertures lugs 129i, 129₂, 129₃, 129₄, 129₅ and 129β which co-operate with the apertures in the drive plate, guide plates and spacer to provide a passageway for the insertion of the retaining bolts to secure the crank 1011 to the gear assembly. The construction of the shifting mechanism 200 according to one embodiment of the present invention is shown in Fig 7. As shown the shifting mechanism includes a pair of mounting brackets 207i, 207₂ for attaching the shifting mechanism 200 to the bottom bracket of the bicycle. As noted above the ' shifting mechanism 200 also includes a gear selection plate 201 and a shifting plate 202. Mounted behind the shifting plate 202 is the gear selector 203 which in this a particular example includes a magnetic selector 204 which is coupled to a standard cable shifting mechanism via rod 205. Also coupled to the shifting plate 202 is range selector 206, the range selector 206 is utilised to slide the shifting plate 202 forward or backward depending on the selection operation required. For example when upshifting is required then the selector 206 draws the shifting plate forward 21mm aligning the gear selection plate 201 with the relevant slots on the drive plate for the selected gear change operation. When downshifting is required the selector 206 draws the shifting plate 202 backward 21 mm aligning the gear selection plate 201 with the relevant slots on the drive plate for the selected gear change operation. The selector 206 in this instance is coupled to a standard cable shifting mechanism via pin 206i.

As can be seen from Fig 7 the selection plate 201 includes two grooves 212i, 2122 which accommodate portions of wedge 208. The wedge 208 is also mounted on a slide bracket 209. As the selection plate 202 is moved forward and backward the potions of the wedge 208 move along grooves 212i, 212_∑ causing the wedge to move laterally on the slide bracket 209 thereby maintaining the wedge's position within the grooves 212i, 212₂.

Fig 8 depicts the construction of the selection plate 201 in greater detail. As shown the shifting plate 201 includes two guide tracks 210i , 2102 formed between rails 211 i, 211₂, 21 ₃. The rails 211 i, 2112, and 2113 in this case are of a generally arcuate shape, which also imparts a curvature to the guide tracks 210 _t 2102. The radius of curvature of the track 210_{1 (} 210₂ enables the tracks to be toggled between the 3^rd and 2^nd gear change position and the 2^nd and first gear change position by simply sliding the selection plate 201 back and forward. As shown grooves 212i, 212_∑ which accommodate portions of the wedge 208 are positioned at the upper ends of the tracks 210i, 2102.

Fig 9 depicts the movement of the segments IO6₁, I O6₂, IO6₃, IO6₄, IO65 and 106β during a gear shift operation with respect to the position of the gear selection plate 201. As shown the selection plate 201 is position on the rear half of the sprocket 106 i.e. the section of the sprocket which is not actively engaged with the chain. As such the selection of the gear is performed in the region of the sprocket 106 where no pressure is exerted on the segment IO6₁. Once the drive pin 107iis disengaged it is guided into one of the gear selection tracks disposed on selection plate 201 by the magnetic selector 203. Once the desired gear is selected the drive pin is re-engaged via the wedge 208 prior to the teeth of the segment 1061 engaging the chain. As can be seen from Fig 9 the segment IO6₁ can be positioned in three discrete locations thereby altering the overall diameter of the sprocket 106. In the depicted example the moment of the segment IO6₁ from first to third gear varies the diameter of the sprocket 106 between 84mm to 109mm. In this particular case when the segments are in first gear the effective diameter of the sprocket 106 is 84.98mm, while positioning the segments in second gear expands the diameter of the sprocket to 97.09mm. In third gear the sprockets diameter is expanded to 109.21 mm. This variation in diameter of the sprocket provides a variation in the gearing ratio. Figs 10A depicts the construction of the drive pin, while Figs 10B and 10C show its operation during gear shift. The drive pin '\ 07-_\ as shown in fig 10A is a cylindrical member 130 having a pair of notches 130ι, 130_∑ disposed therein. The notches 130i, 1302 engage with the spherical surface of the retaining arrangement to lock the drive pin in the shift or drive positions as shown in Figs 10B and 10C.

Fig 10B depicts the moment of the drive pin 107i during the first portion of a gear. As illustrated the magnetic shifter 203 draws the drive pin 107τ back toward the selection plate 201. This disengages the drive pin 107i form the slot which it is currently positioned in within the drive plate 103. Drawing the pin 107i back in this manner causes the interlocking arrangement which in this example is composed of a spring loaded ball bearing 131 arrangement held in position by a set screw 132 to engage notch 130_∑ thereby locking the drive pin in the shift position.

The magnet shifter 203 then guides the pin 107i into the appropriate track on selection plate 201. Once in the drive pin 107i is positioned in the track the thickness of the selection plate 201 and shifting plate 202 combined weakens the magnetic selector's 203 hold on the drive pin 107-|. This allows the drive pin 107 to move along the selected track within the selection plate 201 enabling the segment to move inwardly or outwardly depending on whether a downshift or upshift is selected via the position of shifting plate 202. In either case the drive pin is free to move up or down within the slot 113i in guide plates 104, 108 to align the socket 121 with the appropriate slot 111i,i, 111 i, 2. 1111,3 of the drive plate 103.

As the drive pin 107i nears the end of the selected track it engages with the tail of wedge 208 protruding from the shifting plate 202 as shown in Fig 10C. The engagement of the drive pin 107i with the wedge 208 forces it forward to engage the relevant slot 111 i,2, H I 1.3 of the drive plate 103. This causes the ball bearing of the retaining arrangement down on the spring allowing the drive pin to move forward. As notch 130i aligns with the retaining arrangement the pressure on the spring is released allowing the ball bearing to engage notch 130i locking the drive pin 107i in the drive position (i.e. end of drive pin engaged with the relevant slot in drive plate 103).

Figs 11A to 11C depict the movements of the magnetic shifter 203 for downshifting between gears. As shown in Fig 11 A the shifting plate 202 is the forward position with the magnetic shifter 203 positioned at its furthest point from the lower bracket of the bicycle i.e. the segment IO61 is in the third gear position third or outer most slot 1111,3 on the drive plate. The selection plate 201 is positioned in the downshift position. As the gear segments pass over the magnet position the drive pin is disengaged from the drive plate and enters the outer most track of the selector plate 201. The track guides the pin down toward the position second slot 1 11 i, 2 of the drive plate 103. As the drive pine near the end of the track in the selection plate 201 it engages the wedge 208 forcing the drive pin into engagement with the middle slot 1111,2 of the drive plate 103 (i.e. the second gear position).

If further down shifting is required, that is a gear change from second to first gear is required, the magnet is then moved from the third gear position to the second gear position as shown in Fig 11 B. Once the magnet is in the second gear position it again disengages the drive pin from the drive plate 103 and guides it into the inner most track of the selection plate 201. The drive pin 107i is then guided toward the inner most slot 1111, 1 provided in the drive plate 03 placing the segment in the first gear position. As the selection plate 103 is maintained in the down position the magnetic shifter 203 is maintained at the second gear position. By maintaining the magnetic shifter's 203 position no a gear change will be effected as drive pin will be channelled into the lowermost track and is continuously re-engaged in the first gear slot of the drive plate 103. Moreover the continual disengagement of the drive pin in this manner has no bearing on power transfer as such action take place in the section of the sprocket 106 where there is no load on the segment I O61 from the chain. When upshift is required the magnetic shifter 203 is moved to the first gear position as shown in Fig 11 C as the selection and shifting plates are moved into position to commence the upshift as shown in Figs 11 D to 11 E .

The upshfiting operation is reverse operation to that of the downshift discussed above and is shown in Fig 11 D to 11 F. To facilitate the upshift the shifting plate 202 is placed in the back position i.e. the plate is slid backward 21 mm from the downshift position via the use of range selector 206.

The selector plate 201 is then placed in the up position. As the magnetic selector is already in the first gear position it is able to disengage the drive pin 107i from slot 111i, 1 and guide it into the inner most track of the selection plate 201. The drive pin is then guided toward the middle slot 1 1 11, ₂ of the drive plate i.e. the second gear position. The dive pin 107i is then re-engaged with the drive plate via contact with the wedge 208. If only an upshift to second gear is required then the magnetic shifter can remain in the first gear position preventing further engagement of the drive pin 107i with the tracks of the selection plate 103. If however further upshifting is required the magnetic shifter 203 is moved to the second gear position as shown in Fig 1 1 E. Once the magnet is in the second gear position it again disengages the drive pin from the drive plate 103 and guides it into the outer most track of the selection plate 201 . The drive pin 107i is then guided toward the outer most slots 111_{1t 3} provided in the drive plate 103 placing the segment in the third gear position. The magnetic shifter's 203 position is then maintained to ensure that no further gear change will be effected. When downshift is required the magnetic shifter 203 is moved to the third gear position as shown in Fig 1 F as the selection and shifting plates are moved into position to commence the downshift as discussed in relation to Figs 1 1A to 11C. Figs 12A to 12D depict the movement of the selection plate 201 and the drive pin 107i with respect to the drive plate 103. Figs 12A and 12B show the position of the selection panel 201 and the drive pin 107i during upshifting. In Fig 12A the selection plate is in the up position, that is the end distal to the magnetic shifter Is positioned such that the outer track 210i is aligned between the second and third gear position on the drive plate 103 and the lower most track 2102 aligns between the first and second gear positions on the drive plate 103. As shown the magnetic shifter 203 is in the second gear position 1111,2 when an upshift is selected the magnet is moved to the first gear position 1 111,1 to disengage the drive pin 107i from slot 1 1 i,i and guide it into the inner most 210₂ track of the selection plate 201. The drive pin is then guided toward the middle slot 1 1 11 , 2 of the drive plate i.e. the second gear position. The dive pin 107i is then re-engaged with the drive plate via contact with the wedge 208 through groove 212₂. Fig 12B depicts the shift from second to third gear. As shown the magnetic shifter 203 is moved to the second gear position 11 11 , 2· Once the magnet is in the second gear position 1 1 11, 2 it again disengages the drive pin 107i from the drive plate 103 and guides it into the outer most track 2 0i of the selection plate 201. The drive pin 107ί is then guided toward the outer most slot 1 1 11 , 3 provided in the drive plate 103 placing the segment in the third gear position. The dive pin 107i is then re-engaged with the drive plate via contact with the wedge 208 through groove 212^ The position of the selection panel 201 and the drive pin 107i during downshifting is shown in Figs 12C and 12D. In the both cases the selection plate is slide back such that the end distal to the magnetic shifter is positioned align track 210i between the third and second gear positions and track 210₂ between the second and first gear positions. Fig 12C shows the shift between third and second gear. Again the magnetic shifter 203 starts in the second gear position 1 1 i_, 2 and on selection of a downshift the selected the magnet is moved third gear position 1 1 1_{1t 3} to disengage the drive pin 107i from slot 1 1 11. 3 and guide it into the outer most track 210i. The drive pin 107i is then guided toward the second gear slot 1 11 i, 2 in the drive plate 103, before making contact with the wedge 208 which forces the dive pin 107i into engagement with the second gear slot 1 1 11 , 2 in the drive plate 103.

Fig 12D depicts the shift from second to first gear, to commence the shift the magnetic shifter 203 is moved to the second gear position 11 11, 2- Once the magnet is in the second gear position 1111, 2 it again disengages the drive pin 107Ί from the drive plate 103 and guides it into the inner most track 210₂ of the selection plate. The drive pin 07 is then guided down the track 210₂ to the first slot 1 1 1 i, 1 where it is re-engaged with the drive plate 103 by wedge 208 securing the segment 1061 in the first gear position.

The configuration of the sprocket in each of the gear positions is shown in Figs 13A to 13C. Fig 13A shows the sprocket in the first gear position, as can be seen the sprocket segments I O61, IO62, I O63, 106₄, 106₅ and 106₆ are in an abutting relation. The sprocket in this case is has 42 teeth which are designed to suit an ANSI R40 chain. The teeth being positioned adjacent the circumference of the sprocket assembly. In this position the force exerted on the drive chain at 160rpm is approximately 1404.8N with the force on each of the guide pins being approximately 397.9N while force on the drive pins is 1047.1 N. It will of course be appreciated by those of skill in the art that only three segments of the sprocket are loaded during each drive stroke consequently only 6 guide pins and 3 drive pins are loaded at any one time.

When the sprocket is positioned in first gear and coupled to a rear sprocket having 15 teeth the gearing ratio provided is approximately 2.8:1. Assuming a pedalling rate of 100 rpm the approximate road speed of the driven wheel would be in the order of 560m per minute.

In the second gear position as shown in Fig 13B the segments 106i, IO6₂, IO63, IO6₄, IO6₅ and 106₆ are moved radially and outwardly form the centre of the sprocket assembly i.e. teeth moved a predetermined distance from the circumference of the sprocket assembly. The movement of the segments IO61, 106₂₎ 106₃₎ IO6₄, IO65 and 106₆ introduces a number of discontinuities in the sprocket 106. However these discontinuities do not alter the operation of the system as the chain is continuously engaged by the teeth maintaining a constant tension. The increase in diameter of the sprocket in this case makes it equivalent to utilising a sprocket having 48 teeth. In this position the force exerted on the drive chain at 160rpm is approximately 1229.5N with the force on each of the guide pins being approximately 205.1 N while force on the drive pins is 787.9N. Again as only three segments of the sprocket are loaded during each drive stroke consequently only 6 guide pins and 3 drive pins are loaded at any one time.

Again assuming that the sprocket is coupled to a rear sprocket having 15 teeth the gearing ratio provided when the sprocket is placed into the second gear position is approximately 3.2:1. Assuming a pedalling rate of 100 rpm the approximate road speed of the driven wheel would be in the order of 896m per minute. Fig 13C depicts the sprocket in the third gear position, here the segments 106-1 , 106₂₎ IO63, IO64, IO65 and 106₆ have again be moved radially outwardly a predetermined distance. This movement further increase the size of the discontinuities within the sprocket as well as its diameter. The increase in size of the sprocket in third gear makes it equivalent to a sprocket having 54 teeth. Again the discontinuities do not effect the operation of the system as constant tension is maintained on the chain. In this position the force exerted on the drive chain at 160rpm is approximately 1093 N with the force on each of the guide pins being approximately 248.7N while force on the drive pins is 636.6N. Again as only three segments of the sprocket are loaded during each drive stroke consequently only 6 guide pins and 3 drive pins are loaded at any one time.

Assuming once more that the sprocket is coupled to a rear sprocket having 15 teeth the gearing ratio provided when the sprocket is placed into the third gear position is approximately 3.6:1. Assuming a pedalling rate of 100 rpm the approximate road speed of the driven wheel would be in the order of 1008m per minute. As can be seen from the above discussion as the sprocket is expanded from first to third gear position the forces acting on the drive components and the chain decrease.

For the purpose of clarity of description the above examples have been discussed with reference to the movements of a single segment IO61 and its corresponding components in the assembly. It will of course be appreciated by those of skill in the art that the remaining segments are operated in an identical manner to facilitate gear change. Fig 14 depicts an alternate construction of the gearing assembly of the present invention. The difference in this instance is construction of the guide plates 104, 108, the remaining components are of the same constructions to that discussed in relation to the above examples. In this case the construction of guide plate 108 is shown. As can be seen in this particular example the guide plate 108 includes a plurality of radially disposed slots 113i , 113₂, 113₃, 113 , 113₅ and 113₆ for accommodating the drive pins 107i, 107₂, 107₃, 107₄, 107₅ and 107₆. However in this instance the slots 1 13i , 1 13₂, 113₃₎ 113₄, 113₅ and 113₆ are not smooth like that of the previous example but include a series of niches 118i, H8₂, H8₃ which correspond with the first, second and third gear slots in the drive plate 103. Similarly slots 114i, 114₂ which extend substantially parallel with the edges of their respect slot 113i, 113_∑, 113₃, 134, 113δ and 113₆ include a series of niches 140ι, 140₂, 140₃ corresponding to the position of the guide pins in the first second and third gear positions.

It is to be understood that the above embodiments have been provided only by way of exemplification of this invention, and that further modifications and improvements thereto, as would be apparent to persons skilled in the relevant art, are deemed to fall within the broad scope and ambit of the present invention described herein.

Claims

1. A gearing assembly the assembly including:

a drive plate;

a pair of guide plates positioned behind the drive plate;

a shifting assembly for varying the size of the sprocket by moving each segment between pre-set positions on the drive plate via selective engagement and disengagement of the drive pins with the drive plate.

2. The gearing assembly of claim 1 wherein the drive plate and guide plates are in the form of an annular disc.

3. The gearing assembly of claim 2 wherein the drive plate has a first set of apertures adjacent the annular disc's central aperture for the attachment of a crank.

4. The gearing assembly of any one of claims 1 to 3 wherein the drive plate includes a plurality of lateral slots radially disposed about the drive plate and wherein the slots are arranged in sets.

5. The gearing assembly of claim 4 wherein the drive plate includes six sets of radially disposed slots.

6. The gearing assembly of claim 5 wherein each slot set includes at least three lateral slots disposed at different radii on the drive plate.

7. The gearing assembly of claim 6 wherein each lateral slot within each slot set corresponds with a pre-set position for a corresponding segment of the sprocket.

8. The gearing assembly of claim 6 or 7 wherein the first lateral slot within each slot set is positioned on a circle having a diameter of 77mm, the second lateral slot within each slot set is positioned on a circle having a diameter 101.2mm and the third lateral slot within each slot set is positioned on a circle having a diameter 125.4mm as measured from the centre of the drive plate.

9. The gearing assembly of claim 8 wherein the sprocket is equivalent to a 42 tooth sprocket when each of the segments are positioned at the first lateral slot position.

10. The gearing assembly of claim 8 wherein the sprocket is equivalent to a 48 tooth sprocket when each of the segments are positioned at the second lateral slot position.

1 1. The gearing assembly of claim 8 wherein the sprocket is equivalent to a 54 tooth sprocket when each of the segments are positioned at the third lateral slot position.

12. The gearing assembly of any one of claims 4 to 1 1 wherein the angular distance between the centres of adjacent slot sets is 60° as measured form the centre of the drive plate.

13. The gearing assembly of any one of the preceding claims wherein guide plates are in the form of annular discs.

14. The gearing assembly of claim 13 wherein each drive plate includes a second set of apertures adjacent annular disc's central aperture and wherein the second set of apertures co-operate with the first set of apertures to facilitate attachment of the crank.

15. The gearing assembly of claims 13 or 14 wherein each of the guide plates includes a plurality of includes a plurality of radially disposed longitudinal slots for accommodating the drive pins.

16. The gearing assembly of claim 15 wherein each longitudinal slot is centre on radii at an angular distance of 60° as measured from the centre guide plate.

17. The gearing assembly of claim 16 wherein the drive plate includes a plurality of secondary longitudinal slots arranged in pairs and associated with each radially disposed longitudinal slot.

18. The gearing assembly of claim 17 wherein and each secondary slot pair extend substantially parallel along either edge of their respective longitudinal slot.

19. The gearing assembly of the of claim 17 or 18 wherein the secondary slots are adapted to receive one or more guide pins disposed on the segments of the sprocket.

20. The gearing assembly of any one of the preceding claims further including a spacer positioned between the guide plates and adjacent the segments of the sprocket.

21. The gearing assembly of claim 20 wherein the spacer includes a plurality of lugs disposed about a central hub, each lug having an aperture therein and wherein the apertures in the lugs co-operated with the first and second apertures in the drive and guide plates to permit attachment of the crank.

22. The gearing assembly of claim 20 or 21 wherein the spacer is contoured to fit each segment's base when the segments are positioned at the first lateral slot position.

23. The gearing assembly of any one of the preceding claims wherein each segment includes a pair of angled lateral sides.

24. The gearing assembly of claim 23 wherein the lateral sides are angled toward the base of the segment at 60° as measured from the sprocket's centre.

25. The gearing assembly of claim 24 wherein the base of each segment includes one or more recessed sections and wherein the recessed sections co-operate to match the shape of the spacer when the segments are in the first lateral slot position.

26. The gearing assembly of claim 25 wherein the base of each segment includes a socket for the receipt of a drive pin.

27. The gearing assembly of claim 26 wherein each segment includes each segment includes a pair of guide pins disposed adjacent and on opposing sides of the socket.

28. The gearing assembly of any one of the preceding claims wherein each segment includes a plurality teeth disposed along its peripheral edge.

29. The gearing assembly of claim 28 wherein the teeth are shaped to fit a particular drive mechanism.

30. The gearing assembly of claim 30 wherein the drive mechanism is a chain drive.

31. The gearing assembly of claim 30 wherein the chain drive includes an ANSI R40 chain.

32. The gearing assembly of any one of the preceding claims wherein the shifting mechanism includes a gear selection plate and a shifting plate.

33. The gearing assembly of claim 32 wherein the shifting mechanism includes a gear selector mounted behind the shifting plate.

34. The gearing assembly wherein the gear selector is in the form of a magnetic selector coupled to a cable shifting arrangement.

35. The gearing assembly of any one of claims 32 to 35 wherein the shifting mechanism includes a range selector coupled to the shifting plate.

36. The gearing assembly of claim 35 wherein the range selector slides the shifting plate forward or backward to facilitate an upshift or downshift of the segments between the pre-set positions.

37. The gearing assembly of any one of claims 32 to 36 wherein selection plate includes at least two guide tracks formed between a plurality of rail members.

38. The gearing assembly of claim 37 wherein the tracks accepted a portion of the drive pin during the commencement of an upshift or downshift of the segments between the pre-set positions.

39. The gearing assembly of claim 38 wherein the shifting mechanism includes a sliding wedge mounted on the shifting plate and in communication with the selection plate.

40. The gearing assembly of claim 39 wherein the wedge contacts the drive pins to force them into engagement with drive plate on completion of an upshift or downshift of the segments between the pre-set positions.

41. The gearing assembly of claim 40 wherein the wedge is positioned within a pair of grooves disposed in one end of the selection plate.

42. The gearing assembly of any one of the preceding claims wherein the drive plate and guide plates have a thickness of 3mm and a diameter of at least 156mm.

43. A sprocket including a plurality of segments wherein each segment is movable between a first and second position and wherein the size of the sprocket is varied by sequentially moving each segment between the first and second positions.

44. The sprocket of claim 43 wherein each segment includes a pair of angled lateral sides.

45. The sprocket of claim 44 wherein the lateral sides are angled toward the base of the segment at 60° as measured from the sprocket's centre.

46. The sprocket of claim 45 wherein the base of each segment includes one or more recessed sections and wherein the recessed sections co-operate to match the shape of the spacer when the segments are in the first lateral slot position.

47. The sprocket of claim 46 wherein the base of each segment includes a socket for the receipt of a drive pin.

48. The sprocket of claim 47 wherein each segment includes each segment includes a pair of guide pins disposed adjacent and on opposing sides of the socket.

49. The sprocket of any one of claims 43 to 48wherein each segment includes a plurality teeth disposed along its peripheral edge.

50. The sprocket of claim 49 wherein the teeth are shaped to fit a particular drive mechanism.

51. The sprocket of claim 50 wherein the drive mechanism is a chain drive.

52. The sprocket of claim 51 wherein the chain drive includes an ANSI R40 chain.

53. The sprocket of any one of claims 43 to 52 wherein each segment is movable between a number of a pre-set position between the first and second position.

54. The sprocket of claim 53 wherein each of the present positions corresponds to a different gearing ratio.

55. The sprocket of claim 43 to 52 wherein the sprocket segments are movable between the first, second and at least one intermediate position.

56. The sprocket of claim 55 wherein the sprocket is equivalent to a 42 tooth sprocket when each of the segments are positioned at the first position.

57. The sprocket of claim 55 wherein the sprocket is equivalent to a 48 tooth sprocket when each of the segments are positioned at the intermediate position.

58. The sprocket of claim 55 wherein the sprocket is equivalent to a 54 tooth sprocket when each of the segments are positioned at the second position.