GB2237341A - A variable speed drive mechanism comprising ratio selection by an indexing member - Google Patents

Abstract

A variable speed drive mechanism for bicycles comprising a drivable input member (1), an output member (2) for providing rotational drive to a member, a selectable gear mechanism interconnecting the input and output members (1, 2), the selectable gear mechanism having independently rotatable concentric annular output gears (23-27), each being drivable by at least one of a number of drive gears (16-20) fixed relative to each other, and a selector arrangement for selecting one of the output gears, the selector arrangement including an indexing member (26A) rotatable with the output member (2) in fixed relationship thereto but being movable relative to the output member (2) upon operation of the selector arrangement to effect a change in output gear preferably by engagement of a pawl and ratchet arrangement. The movement of the indexing member is preferably enabled by movement of a pin (50) by electric, hydraulic or mechanical means. There may be an LCD readout of the ratio engaged. There may be three sets of drive gears, each set mounted on its own shaft. <IMAGE>

Description

A VARIABLE SPEED DRIVE MECHANISM This invention relates to a variable speed drive mechanism for, but not limited to, a bicycle.

It is well known in the bicycle industry to use which the drive gears are located in the central hub of the wheel. The output gears are selected by mechanically moving a coupling member along the rotational axis of the hub. However, the number of output gears is generally limited to 3 or 5.

An alternative speed drive mechanism is the Derailleur system which on a typical modern touring bicycle provides 2 front chain sprockets driven by the pedals, 5 rear sprockets located on the axis of but offset from the rear wheel, a rear gear changing arm, a front changing arm, dual cables and control levers, all of which are exposed to the elements.

Nevertheless, such a system does provide a variable drive mechanism covering a range of some 10 gears with similar such systems covering up to 21 gears.

Whilst the Derailleur system provides a greater range of selectable gears, such a system is bulky, takes a long time to change gears, and is unreliable by its physical nature when the chain translates from one sprocket to another.

Therefore, it is desirable to provide a compact hub variable speed drive mechanism in which the abovementioned mentioned disadvantages are overcome.

According to a broad aspect of this invention there is provided a variable speed drive mechanism comprising a drivable input means, output means for providing rotational drive to a member, a selectable gear mechanism interconnecting the input and output means, the selectable gear mechanism having independently rotatable concentric annular output gears each being driveable by at least one of a number of drive gears fixed relative to each other, and selector means for selecting one of the output gears, the selector means including indexing means rotatable with the output means in fixed relationship thereto but being movable relative to the output means upon operation of the selector means to effect a change in output gear.

When provided on a bicycle, the variable speed drive mechanism may be such that the input means is drivable by the chain of the bicycle, and the output means is connectable with a drive wheel of a bicycle.

In one preferred form of a variable speed drive mechanism in accordance with the present invention the indexing means comprises an output tubular member surrounding the outer peripheral surface of the output gears. Conveniently, the output tubular member includes a plurality of aperture patterns spaced about the output tubular member, each aperture pattern being aligned with a respective one of the output gears.

The aperture patterns are preferably angularly displaced one relative to the other about the output tubular member. The output means preferably has a plurality of pawls aligned for engagement with a respective one of the output gears in dependence upon which one of the output gears is selected by aligning a particular aperture pattern in the output tubular member with a particular set of pawls on the output means so that the pawls engage for rotation with the output gears.

The selectable gear mechanism may include at least one input gear. The selectable gear mechanism preferably has two input gears. The two input gears are preferably a pair of annular ring gears mounted concentrically with the output gears and which drive a pair of gears mounted concentrically with and fixed relative to the drive gears for the output gears. The input gears are conveniently circumferentially surrounded by an input tubular member having two aperture patterns one for each gear, said aperture patterns being angularly displaced relative to one another. The input tubular member is conveniently arranged to support a plurality of pawls associated with each input annular gear, the pawls being engageable through a respective aperture pattern to engage an appropriate one of the input gears as selected.

In the preferred embodiments of the variable speed drive mechanism, the output gears are rotatably mounted about a shaft between two spaced members fixed relative to the shaft. Preferably three equicircumferentially spaced sets of drive gears are mounted on respective rotatable axles for each set, said axles being supported between opposed support members and being radially spaced relative to the shaft about which the output gears rotate.

Conveniently, the input and output tubular members are each capable of being rotated by radially extending teeth engagable with their respective gear wheels respectively mounted on the input and output means. Each gear wheel is itself rotatable about a spigot on which is also mounted an indexing wheel so that the wheel will rotate about the fixed axis. An indexing pin is conveniently mounted on one of the support members for engagement with the indexing wheel. Preferably, two indexing pins are provided, one on each side of the spigot, to selectively rotate the indexing wheel in one or the other direction.

Each indexing pin may be pneumatically, electrically or mechanicially operated to engage with the rotating indexing wheel when a gear change is to be made. Only one pin per wheel is operated at any one time to rotate the indexing wheel in a forward or backward direction.

A friction clutch between the indexing wheel and a gear wheel may be provided to allow for over-running of the indexing wheel to allow the indexing pin to exit in the event that either of the two tubular indexing members is constrained from moving during the indexing phase. Without the clutch, the indexing pin could damage the indexing wheel.

Embodiments of the present invention will now be described solely by way of example and with reference to the accompanying drawings, in which: Fig. 1 is a cross-sectional view of a variable speed drive mechanism according to the present invention; Fig. 2 is a partial cross-sectional view along the line X-X, of Fig. 1; Fig. 3 is a partial cross-sectional view along the line Y-Y, in Fig. 1; Fig. 4 is a partial cross-sectional view illustrating a pawl assembly used in the embodiment described in Fig. 1; Fig. 5(a) is a developed view of the input tubular indexing member shown in Fig. 1 and illustrates the particular slot pattern with 2 slot tracks with slots in each track repeating every 60 degrees around the circumference with laterally adjacent slots being angularly displaced 30 degrees relative to each other;; Fig. 5(b) is a developed view of the output tubular indexing member shown in Fig. 1 and illustrates the particular slot pattern with 5 slot tracks with slots in each track repeating every 120 degrees around the circumference with the slots in any track being angularly displaced 24 degrees relative to the slots in the track applicable to the next engagable gear; Fig. 6(a) is a developed view of an input tubular indexing member with 2 slot tracks with slots in each track repeating every 36 degrees around the circumference with laterally adjacent slots being angularly displaced 18 degrees relative to each other, to show an input slot pattern which can be used with the output slot pattern shown Fig. 6(c); ; Fig. 6(b) is a developed view of an alternative input tubular indexing member with 2 slot tracks with slots in each track repeating every 180 degrees around the circumference with laterally adjacent slots being angularly displaced 90 degrees relative to each other, which can be used with the output slot pattern shown in Fig. 6(c); Fig. 6(c) is a developed view of an output tubular indexing member with 5 slot tracks to show a particular slot pattern with slots in each track repeating every 90 degrees with laterally adjacent slots being angularly displaced 18 degrees relative to each other, which can be used with either of the input slot patterns illlustrated in Figs. 6(a), 6(b);; Fig. 7 is a cross sectional view of a modified variable speed drive according to the present invention providing for input control by the output tubular member and a direct drive by-passing the annular gears; Fig. 7(a) illustrates a developed view of the input tubular indexing member to show the particular input slot pattern used in the embodiment of Fig. 7 namely the input slot pattern on 7(a) with two adjacent sets of slots with slots in each track repearting every 120 degrees on the circumference, each set being angularly displaced 30 degrees relative to the other set; and Fig. 7 (b) illustrates a developed view of the output tubular indexing member to show the particular output slot pattern used in the embodiment of Fig. 7 namely the output slot pattern of Fig. 7(b) with 6 slot tracks around the circumference; the tracks being numbered from the left.

Referring more particularly to Figs. 1 to 4 of the drawings there is shown a variable speed drive mechanism in accordance with the present invention which comprises an input member 1 and an output member 2 each rotatably mounted about a fixed shaft 3 having flatted ends 3a. The input member 1 and output member 2 rotate about bearings 4 and 4a, and 5 and 5a respectively. Bearings 4, 4a are axially located by spacing washers 11, 12, 13. Bearing 5a is axially located by spacers 7a, 7b. End support plates 6, 7 are fixedly mounted on the shaft 3 and serve to support therebetween three equi-circumferentially spaced shafts 8 (shown in Fig. 3), each rotatable in bearings 9, 10 mounted in the fixed end plates 6, 7 and each radially spaced from the longitudinal axis of the fixed shaft 3.It is however to be understood that although three shafts are preferred, the invention is operable with only one shaft and in the decription below only one shaft will be referred to.

A plurality of drive gears 14 to 20 of varying diameters are fixedly mounted on the shaft 8 to rotate together with the associated shaft 3. Each of the shafts 8 has identical gear clusters fixedly mounted thereon and located between the end plates 6, 7 at 120 degrees spacing about the shaft 3. A plurality of annular gear rings 21 to 27 of equal external diameters and varying internal diameters are independently rotatably mounted side by side between the fixed end plates 6, 7 and with their internal teeth engaged with the respective ones of the drive gears 14 to 20. The external teeth on the annular gear rings 21 to 27 are engagable with pawls mounted on the input or output members 1, 2 as will be described below.

The annular gear rings 21 to 27 are surrounded by two cylindrical indexing members 25A, 26A which are each provided with radially inwardly extending toothed flanges 27A, 28, respectively, which intermesh with gear wheels 29, 30 rotatably mounted on inwardly extending spigots 31, 32 on input member 1 and output member 2 respectively. The spigots 31, 32 are radially displaced from the fixed shaft 3. The spigots 31, 32 also rotatably support indexing wheels 35, 36 which are each driveable via a friction coupling or friction clutch arrangement (not shown) by the gear wheels 29, 30 respectively.

Input member 1 has a cylindrical skirt 40 which extends axially to cover annular gear rings 21, 22 and drive gears 14,15 respectively. These two sets of gears are referred to hereinafter as the input gears.

Fixed to the skirt 40 is an annular pawl carrier 41 on which is mounted a plurality of spring loaded pawls 70 biased to extend downwardly to engage the teeth on the external peripheral surfaces of the ring gears. The pawls may be biased by a compression spring in each or by a wire ring acting on a cam surface of each pawl, the wire ring providing a radially outward bias on the rear of the pawls so that the tooth engaging portion of the pawls is biased inwardly. The pawl support 41 is fixed relative to the skirt 40 and both are rotatably mounted on bearings 4, 4a.

Output member 2 is also provided with a cylindrical skirt 43 which covers drive gears 16 to 20 and their corresponding annular gear rings 23 to 27. The outer peripheral surface of the output member 2 is provided with a radially extending flange 44 having a plurality of circumferentially spaced apertures 44A each for receiving a respective one of the spokes of a drive wheel of a bicycle.

In addition the skirt 43 extends axially to cover the skirt 40 of the input member 1. The outer peripheral surface of the skirt 43 is provided with a radially extending flange 44B having a plurality of circumferentially spaced apertures 44C each for receiving a respective one of the spokes of a drive wheel of a bicycle. An annular pawl carrier 45 is located in the skirt 43 in a similar manner to the pawl carrier 41 in the skirt 40 of the input member, and carries a plurality of spring loaded pawls which are arranged to be biased inwardly to engage, when required, the teeth on the external surfaces of the annular gear rings 23 to 27.

The pawl carriers in the input and output members 1, 2 respectively are fixed relative to the skirts 40, 43. The skirt 43 is supported by a flanged disk 43A which is rotatable about the shaft 3 through the bearing 5 mounted on the input member 1 which itself rotates about the shaft 3 through the bearings 4, 4a.

The end plate 7 supports a pneumatically, electrically or mechanically operated spring-loaded pin 50 which is operable, upon an operator wishing to change gear, to extend outwardly from and through the end plate 7 into the path of the indexing wheel 36 so that upon engagement with the indexing wheel 36, the indexing wheel 36 rotates to move the cylindrical indexing member 26A relative to the skirt 43. The pin 50 is located such that during normal pin operation the indexing wheel 36 will be rotated in an anticlockwise direction. A similar such pin (50A shown in Fig. 3) is mounted on the end plate 7 on the other side of the spigot 32 on a different radius from pin 50 so that when operated the pin will engage the indexing wheel 36 and move the indexing wheel 36, in a clock-wise direction. Although not shown, similar indexing pins are located on the end plate 6 for engagement with the indexing wheel 35. In Fig. 1 the internally sprung pin 50 is released by a sprung latch 51 when air pressure inflates a bellows 54 between a plate which is part of the latch 51 and a latch housing 55 mounted on the end plate 7. The air pressure is provided by squeezing another bellows (not shown) attached to an air line 54A.

The circular indexing wheel 36 (shown in Fig. 2) is provided with five radially extending spokes 60 which are angularly spaced at 72 degrees intervals. The spokes 60 stand out from the indexing wheel 36 so that as the output member 2 rotates taking the spigot 32 with it, the pin 50 locates within a space 61 between the spokes 60 and engages the spokes 60 forcing the indexing wheel 36 to rotate until the pin 50 can freely disengage with the spokes 60, thereby causing a 72 degrees rotation of the indexing wheel 36. The rotational movement of the indexing wheel 36 is transmitted through the frictional clutch arrangement to the gear wheel 30 with 24 teeth which engages with the toothed flange 28 with 72 teeth of the cylindrical indexing member 26A to rotate the same through 24 degrees. Therefore, a relative movement of 24 degrees occurs between the skirt 43 and indexing member 26A.Such relative movement is effective to disengage one set of pawls from one of the annular gear rings 23 to 27 and to allow another set of pawls to drop through appropriate apertures in the indexing member 26A to engage another set of the annular gear rings 23 to 27.

A change of gearing is similarly obtained with the input gears by operating an appropriate indexing pin (not shown) to provide a movement of the indexing wheel 35 with four extending spokes spaced at 90 degree intervals, the gear wheel 29 and the input indexing member 25A. In this case the relative movement of the indexing member 25A relative to input member 1 is 30 degrees. Selection of the gears 14, 21 or 15, 22 is effective to change the range of gearing which is selectable amongst the output gears 16 to 20 and 23 to 27, the full range of 5 output gears being selectable for each selected one of the two input gears.

Mounted on the output member 2 are ramps 52, 53 such that when the pin 50 exits the indexing wheel 36, rotational movement of the output member 2 causes the pin 50 to be pushed back into the end plate 7 where it is retained by the sprung latch 51 engaging a circumferential groove in the pin 50. Pin 50A is similarly operated. The ramps 52, 53 slope up to a flat surface and then down again so when moving in either direction they push the pins 50, 50A in.

Fig. 4 is a partial cross-sectional view of a portion of the indexing member 26A and the pawl carrier 45 as well as a plurality of pawls 70 which are pivotally mounted in the pawl carrier 45. The pawls 70 are spring-biased and arranged to extend, when required, through apertures 71 in the indexing member 26A. Each aperture 71 is provided with outwardly divergent end surfaces 72, 73 which act as cam surfaces to disengage the pawls 70 from the outermost teeth of the appropriate annular gear ring irrespective of the direction of relative rotation of the indexing member 26A in relation to the pawl carrier 45.The pawls 70 are each provided with a shoulder with an additional cam surface 74 to engage cam surface 73A when the indexing member 26A moves in an anti-clockwise direction in relation to the pawl carrier 45, whilst the cam surface 72 engages the back surface 75 of the pawls 70 when the member 26A is rotated in a clockwise direction in relation to the pawl carrier 45. The pawl carrier 45 is rigidly fixed and an integral part of the output member 2.

In the embodiment described, the aperture patterns shown in Figs. 5(a) and 5(b) in the indexing members 25A, 26A, are arranged so that one ring of apertures around each indexing member 25A, 26A is located immediately adjacent a respective one of the annular gear rings. The aperture patterns are then arranged so that the apertures of one pattern are angularly displaced relative to the apertures of the next adjacent pattern by 30 degrees in the input indexing member 25A and by 24 degrees in the output indexing member 26A, thus ensuring that when when one set of pawls drops through an aperture pattern the adjacent or other sets of pawls are prevented from doing so by the non-apertured portions of the relative indexing members. In the embodiment described only one set of pawls can be engaged on the output side at any one time.Similarly on the input side only one set of pawls can be engaged at any one time.

As shown in Fig, 1, an input drive sprocket la is mounted on a bush ic. The bush lc is mounted on the input member 1 and is secured in position by a wire ring 1d. The input drive sprocket la is secured in position by a wire ring lb. Thus when a cyclist is pedalling, the bicycle chain drives the rear wheel input drive sprocket 1b and hence the input member 1 so that input member 1 rotates about the shaft 3 which is fixed in the rear frame of the bicycle.It is assumed that the pawls surrounding the annular gear ring 21 are arranged with that gear ring 21, whilst amongst the output gears, the pawls adjacent to the annular gear ring 23 are engaged with that gear ring 23 so that there is a continuous drive from the input drive sprocket la to the output flanges 44A and 44B and hence the drive wheel.

When the rider wishes to change gear from annular gear ring 25 to select the annular gear ring 24, the rider presses an up button which pneumatically, electrically or mechanically causes unlatching of the internally-sprung pin 50 which then moves laterally to the left in Fig. 1 projecting beyond the surface of the end plate 7 and into the path of the indexing wheel 36. As the spigot 32 rotates about the fixed shaft 3 the indexing wheel 36 passes the pin 50 each time the bicycle wheel rotates through one revolution. When the pin 50 engages into a slot 61 on the indexing wheel 36, the pin 50 engages an appropriate spoke 60 and rotates the indexing wheel 36 through 72 degrees causing through friction coupling the gear wheel 30 to rotate with it and to subsequently rotate the indexing member 26A through the toothed flange thereof.After the gear change, the pin 50 is re-cocked by being pushed back into the end plate 7 by the ramp 52 in the pin path fixed to the output member 2.

The change of gearing between the annular gear ring 25 and 24 occured because of the relative movement between the pawl carrier 45 and the indexing member 26A. As this relative 24 degrees movement occurred, the pawls which were engaged with the ring 25 were disengaged from the teeth of the gear ring 24 by the sloping surface 72 engaging the back surface of the pawls 75, forcing the pawls to retract within the pawl carrier 45. The indexing member 26A holds the pawls in the retracted position within the pawl carrier 45 but movement of the indexing member 26A relative to the output member then exposes the next not necessarily adjacent set of pawls which to this point have themselves been held in the retracted position within the pawl carrier 45, to the next set of apertures thereby allowing the pawls to be biased into engagement by springs 46 with the outer peripheral teeth of the annular gear ring 24.

The gear change is smooth and quickly achieved having been effected within one rotation of the bicycle wheel. However the gear change will not be possible during drive conditions, i.e. when the rider is pedalling, since under these conditions the pressure of the pawls on the teeth of the annular gear ring 24 will be such as to prevent disengagement and accordingly it is necessary in changing gear for the rider to stop pedalling for an instant. Had the rider wished to change through a range of gears from annular gear ring 25 to annular gear ring 27 then the up-control button on the handlebars can be depressed and held depressed, whereupon the pin 50 will be unlatched pneumatically and each time the spigot 32 rotates about the shaft 3 the pin 50 will engage the spokes 60 of the indexing wheel 36 and rotate the indexing wheel 36 through 72 degrees.Each rotational movement of the indexing wheel 36 will cause a 24 degrees movement of the indexing member 26A relative to the pawl carrier. Each time the relative 24 degrees movement occurs the pawls of one gear ring, say, 23, are disengaged whereupon the slots of the next gear ring to be engaged, say, 24, appear in front of the pawls applicable to 24 which then engage 24. Upon the next revolution of the bicycle wheel the indexing wheel 36 will again be moved through 72 degrees causing a relative movement between the indexing member 26A and the pawl carrier and effecting a change of gear for pawls to engage with teeth on the gear ring 26. The operation is repeated until pawls engage the teeth on gear ring 27.

Once the appropriate gear has been selected, the rider will release the up-button and the pin 50 will quickly be pushed back by the slope of the ramp 52 flush with the surface of the end plate 7 thereby leaving a constant drive to the output member 2. The ramp 52 has angularly displaced upward and downward slopes which will push in the pin 50 when the ramp 52 is moving either clockwise or anti-clockwise.

Should the rider wish to reverse the change of gear sequence, the rider may simply press the down-button on his or her control thereby to operate the second of the indexing pins 50A so that upon each revolution of the bicycle wheel, the pin strikes the indexing wheel 36 and moves it in the opposite direction to the direction of rotation caused by the pin 50. The reverse movement of the indexing wheel 36 would in effect cause the pawls engaged with the annular gear ring 27 to be disengaged and for the pawls associated with the gear ring 23 to engage therewith and so on until a required gear is selected.Similarly, if the rider wishes to change the range of output gearing, the rider may do so by operating the "range" button on his or her control to effect a change of input gearing from the pawls being engaged with the annular gear ring 21 to the pawls being engaged with the annular gear ring 22 in a similar manner to that previously described with respect to the output gear rings. In this case the indexing wheel 35 is rotated in the appropriate manner sufficiently to change the aperture pattern to the next one required, by means of an indexing pin not shown.

In Figs. 5(a) and 5(b) the cylindrical indexing members 25A and 26A are shown in a developed form to illustrate the particular aperture patterns as shown by the two rows of elongated apertures in the indexing member 25A, and the five rows of apertures in the indexing member 26A. The aperture patterns in the input indexing member 25A are shown to be staggered by an amount which is equivalent to a 30 degree angular rotation of the cylindrical indexing member 25A. The aperture patterns in the output indexing member 26A are similarly staggered but in this instance there are five aperture patterns, one for each of the output gears, and the aperture patterns are successively staggered by 24 degrees, one relative to the next aperture pattern.

An alternative form of input indexing member aperture pattern to that shown in Fig. 6(a) is shown in Fig.

6(b) where in each track the equivalent of five output-size apertures are substantially contiguous with one another to form a long aperture which repeats every 90 degrees about the circumference and the aperture pattern of the adjacent row of apertures is similarly configured but angularly displaced 90 degrees. This aperture pattern will work with the output aperture pattern shown in Fig. 6(c). The apertures are angularly displaced so that only one set of pawls (3 pawls) is engaged on the output side and one set (3 pawls) on the input side at any one time. An 18 degree tubular indexing member movement relative to the output member is required to change a set of apertures on the output side.On the input side an 18 degree angular movement of the input indexing member relative to the input member will result in an aperture change, i.e. from one track to the other, but this 18 degree movement only effects this at the aperture ends on the input side when one set of pawls is picked up and the other engaged, otherwise more angular movement is needed. (The input and output tubular indexing member movements can of course be independent of each other as per the embodiment described in Figs. 1, 5(a) and (5b).) If input and output clockwise controls are interlinked and similarly input and output anticlockwise controls are interlinked,i.e. both pins are released at the same time in each case, both cylindrical indexing members will move at the same time, i.e. within the same one wheel revolution, in the same direction by the indexed amounts. The indexed amount in degrees may differ on each side according to the fixed displacement of the aperture patterns. However the particular advantage to be gained from the input aperture pattern of Fig. 6(b) used with the output aperture pattern of Fig. 6(c) is that a change in range occurs automatically in each direction. The tubular indexing members may or may not rotate at the same speed. It does not matter.

Further, the changeover can be restricted with stops (not shown) to only allow 180 degrees of total movement of the indexing members relative to their respective input or output member 1 or 2. Thus it is possible to go from the bottom of the low range to the top of the low range and then on to and from the bottom of the high range to the top of the high range with the range changeover in the middle being achieved automatically with just one 18 degree movement. Without the stops, pressing the up-control when in the highest gear would result in being put into the lowest gear, and similarly pressing the down control when in the lowest gear would result in being put in the highest gear.

With the five output gear rings 23 to 27 shown in Fig. 1 there are two 1:1 direct gears so that selection of the input slot pattern allows ten output gears but only nine different speeds. If only one set of drive gears were matched there would be only one direct 1:1 gear giving ten selectable gears and ten speeds. If none were matched there would still be ten selectable speeds with the possibility of an eleventh 1:1 direct gear by locking the input and output members together, an option not included in Fig. 1.

In the above mentioned embodiments each indexing wheel 35, 36 can operate only once per bicycle wheel revolution so that only one gear change sequence is possible for each of the cylindrical indexing members 25A, 26A per bicycle wheel revolution. With a bicycle having a 27 inch diameter wheel moving at 10 miles per hour, it takes less than half a second to change gear. Doubling the number of indexing wheels would halve this.

In the arrangement described above applicable to the embodiment described in Fig. 1 using aperture patterns described in Figs. 5(a), 5(b), the tubular indexing member 26A has 72 teeth on its flanged internal peripheral surface whilst the spigot gear 30 has 24 teeth and rotates through 72 degrees when engaging the pin 50. When this tubular indexing member 26A moves it must move 24 degrees. Thus on the output side, a new set of pawls must fall into their respective apertures. As when pedalling all sets of pawls cannot be disengaged at the same time, i.e.

open apertures will be available for one set of pawls to engage through, there is no scope for forward pedal-spin, i.e. loss of drive. In the embodiment in Fig. 1 assuming no change of input gear, for the same output gear to be selected in the same rotational direction a movement of 120 degrees (that is five movements of 24 degrees) is required.

Gear change control for the gear change mechanism is preferably mounted on the handebars of the bicycle so that the rider can easily operate the gears without undue movement of the hands, whereby during gear changing maximum control is retained over the bicycle. In the particular embodiment described in Figs. 1, 5(a) and 5(b) the controls require three switches, namely one to control the gear change between the two input gear possibilities and the other two to allow forward or reverse ranging across the five output gears. Thus by using the three switches it is possible to change the gearing across the two ranges separately or to leap between the two at any point.Pressing the output side up-control at the top of the high range causes the gearing to engage into direct gear at the bottom of the high range, unless the clockwise rotational movement of the tubular indexing member 26A is prevented by a stop (not shown); similarly pressing the down switch at the bottom of the low range causes the gearing to engage the direct gear at the top of the low range if allowed to; if not, the pin will exit the indexing wheel by rotating it. In this case the indexing wheel will not rotate the friction-coupled spigot gear.

By making use of both input and output gears the following complete range of gears may be provided for: For one revolution of the input gear the output gear revolution is: Toothed Gear expressed Gearing in inches Gear 1 84/33 x 15/66 = 0.578 33.49 Gear 2 84/33 x 18/69 = 0.664 38.40 Gear 3 84/33 x 21/72 = 0.742 42.91 Gear 4 84/33 x 27/78 = 0.880 50.90 Gear 5 84/33 x 33/84 = 1.000 57.84 or 66/15 x 15/66 = 1.000 Gear 6 66/15 x 18/69 = 1.148 66.40 Gear 7 66/15 x 21/72 = 1.283 74.20 Gear 8 66/15 x 27/78 = 1.523 88.09 Gear 9 66/15 x 33/84 = 1.729 100.00 The variable speed change mechanism described above with reference to Figs. 1 to 5(b) can be modified by changing the aperture pattern in the input cylindrical indexing member 25A to that shown in Fig.

6(b) and the output aperture pattern to Fig. 6(c).

(The flanges of the tubular indexing members 25A, 26A, must now have 64 teeth, their respective meshing gears 16 teeth each, and the indexing wheels 5 spokes each.) With this particular arrangement the input gear selection control, the "range" control, can be eliminated by interconnecting the pin release controls so that upon operating the forward output switch, the forward indexing pins, both the input and output indexing systems, operate at the same time the same way, i.e. clockwise or anti-clockwise, and in the reverse direction the reverse switch releases the reverse indexing pins simultaneously.

Consequently, it will be appreciated that as both input and output indexing members 25A, 26A are operated at each gear change, a relative movement will occur between the indexing members and the respective pawl carriers so that as the gear change operation ranges through the five output gears, the five corresponding input apertures of aperture pattern on the input indexing member 25A are selected in turn whilst the pawls corresponding with the second aperture pattern of the input indexing member 25A are held in their retracted position.

With two 1:1 direct gears in the embodiment described 10 gears are provided but only nine speeds are obtainable.

This would be a 9-speed hub with an up/down control with automatic end-of-range range-changing in the middle of the 9 speeds. Thus one would be able to go up or down the whole range (i.e. the range from the bottom of the low range to the top of the high range) consecutively by keeping the button pressed or up or down at any point. Obviously, if the two input gears are not matched with any identical ones on the output side then 10 different gears are possible, not in all cases necessarily with consecutive access.

It is however desirable to have a direct gear bypassing the tooth gear trains altogether, ideally with the input tubular indexing member controlled by the output tubular indexing member.

Fig. 7 shows an embodiment of a 7-speed hub with a modified input tubular indexing member 25B with a tubular skirt which extends over the external surfaces of the annular gear rings 21 and 22. The flange 25C of the input tubular indexing member 25B has the same external diameter as the annular output gear rings 24 to 27 but not necessarily the same teeth on its external peripheral surface. The input member 1 includes a pawl carrier 41A with inwardly biased pawls in respect of the two annular input gear rings 21, 22 which are engagable through apertures in tracks 1 and 2 in the input tubular indexing member 25B as illustrated in Fig. 7(a) and teeth on its external peripheral circumference engagable through apertures in track 6 of the output tubular indexing member 26B by pawls pivotally seated in pawl carrier 41 rigidly fixed in the output member 2. Thus the input member 1 can be coupled to either of the two input annular gear rings 21,22 or direct to the output member 2. When coupled direct to the output member 2 there is a direct 1:1 drive by-passing the gears altogether. All pawls are retracted on the output side.

With reference to Fig. 7(b), in tracks 1, 4, 5, 6, the apertures in each track repeat every 120 degrees around the circumference. In tracks 2, 3 the centreline spacing of the apertures is 45 degrees then 75 degrees, repeating about the circumference. Each aperture pattern in tracks 1, 2, 3, is angularly displaced 15 degrees in the same direction to the next adjacent aperture pattern as shown. The aperture pattern in track 4 is angularly displaced 15 degrees forward of the aperture pattern in track 3. The aperture pattern in track 4 is also angularly displaced 45 degrees forward of the apertures in tracks 5, 6. The apertures in track 6 repeat every 120 degrees about the circumference and have centrelines adjacent to the apertures in track 5.Thus each pattern of apertures used by the drive pawls in a track is angularly displaced 15 degrees relative to the pattern applicable to the next consecutive gear.

A 15 degree movement of the output indexing member 26B relative to the output member 2 can be obtained using a six spoke indexing wheel 36A coupled through a friction clutch to a small gear wheel 30A with 16 teeth meshing with the internal flange 51A of the output tubular indexing member which has 64 teeth.

When the indexing wheel 30A engages a pin 50B it must rotate 60 degrees to free itself. A similar pin (not shown) creates the same movement in the other direction.

With reference to Fig. 7(a) concerning the aperture pattern in the input tubular indexing member 25B the "range change" pawl slots in adjacent tracks are angularly displaced 30 degrees relative to each other.

Two 15 degree angular movements are required to change over the aperture pattern in the input tubular indexing member 25B. During the changeover phase, one 15 degree movement of the output indexing member 26B retracts the pawls then in use by the input member 1 and allows the set corresponding to track 6 of the output indexing member 26B to directly couple with the input member, which has teeth on its external peripheral surface engagable for direct drive. During this phase, through apertures in track 5 of the output member pawls engage the teeth in the external flange 25C of the input tubular indexing member 25B and rotate it relative to the input member 1 scooping up the input member pawls and retracting them.Thus in direct drive the input member 1, input tubular indexing member 25B, output tubular indexing member 26B, and output member 2 all rotate locked together quite independently of the gear core. A further 15 degree movement takes the system out of direct gear and into the next consecutive gear with a changeover of input slot pattern having occurred controlled by the output indexing member.

Fig. 7 shows an embodiment of the gear change mechanism using the aperture patterns shown in Figs.

7(a) and 7(b) for a 7 speed gear change mechanism with a direct gear by-passing the gear core and low and high gears of - 42%, - 26%, - 12% ,and, + 28%, + 52% and + 73%, respectively. The input annulus gear/internal gear ratios are 84/33 and 66/15. The output gear internal gear/annulus gear ratios are 33/84, 27/78, 21/72 and 15/66.

The variable speed drive mechanism of the present invention is particularly suitable for a 10 gear hub providing for 9 speeds as described. However, a 10 gear 10 speed hub can be provided by substituting a 90 tooth annular gear ring and corresponding 39 tooth internal spur gear for the 84/33 combination previously described.

A ratchet-operated indexer may be provided for the input and output indexing members 25A, 26A respectively so that when the bicycle is stationary gear changing can be achieved by operating the ratchet-operated indexer to rotate the respective input and output indexing members 25A, 26A.

The handlebar controls described above operating indexing pins pneumatically may be modified so the indexing pins are controlled electrically or mechanically. Preferably a liquid crystal display readout unit will indicate the gear number engaged.

The liquid crystal display readout unit conveniently plugs into the side of the handlebar control and can be removed to prevent theft.

Conveniently, the pawls-and-indexing system utilised in the present invention is also applicable to epicyclic hubs. In a 3 speed version of an epicyclic hub the input selections are: (a) annulus (cage is output for low gear), (b) cage Cannulus is output for high gear), (c) both for direct gear (with the sun gear able to rotate clockwise-only on the axle).

Locking the input and output parts together and bypassing the gear core is also an option.

The variable speed drive mechanism of the present invention is particularly advantageous in that there are no epicyclic gear trains with their inherent inefficiency. A much wider overall gear spread and a plurality of gears is provided with no lateral movement of any parts other than indexing pins. The gears are always in constant mesh and there is no possibility of pedalling out of gear, that is forward pedal spinning when trying to change gear or afterwards. There are no cables or toggles to pull around 90 degree bends and no adjustment is required.

The gear selection is achievable with ease and confidence. There is also scope for non-consecutive gear selection, i.e. rapidly skipping unwanted intermediate gears. Moreover drive mechanisms can be made with no duplicated or overlapping gears.

The variable speed drive mechanism is mounted on the fixed shaft 3 and with the simplicity of construction a quick-release axle is possible.

The hub utilising the variable speed drive mechanism of the present invention is particularly advantageous over Derailleur systems in that the gearing is totally enclosed from the weather, water, mud, dust and grit, provides a much faster gear change as well as the possibility of optional static gear changing, will operate with an in-line belt or chain drive for maximum transmission efficiency, and no cables are required. The belt or chain part can also be totally enclosed. In addition the 3:1 gear spread, which can be even higher, covers a typical touring gear range (33 - 100 "gear inches") found on touring bicycles, which in a Derailleur system would normally have two front chain sprockets and five or six rear change sprockets linked by a dirty oily chain. The hub is a very compact system giving both very low and very high gear ratios, impossible with conventional epicyclic hubs, and requiring only one front drive sprocket. Furthermore the hub is particularly suitable for bicycles with small rear wheels as much smaller rear drive sprockets can be fitted. (A Derailleur would necessitate a very long rear arm to gather up the chain in high gear.) Moreover, the hub is self-adjusting with slot dimensions suitably toleranced to ensure this. It cannot be incorrectly fitted and is not prone to damage should the bicycle fall over. In addition, the hub can be equipped to give a liquid crystal display read-out not only for speed, mileage, etc. but gear number as well. As indicated above, the flexible drive mechanism of the invention may drive vehicles and devices other than bicycles so that, for example, the flexible drive mechanism may be used on tricycles and fishing reels.

It is to be appreciated that the embodiments of the invention described above with reference to the accompanying drawings have been given by way of example only. Thus, for example, a bevel gear arrangement or an epicyclic gear arrangement can be used to alter the speed of an annular input gear.

Claims (18)

1. A variable speed drive mechanism comprising a drivable input means, output means for providing rotational drive to a member, a selectable gear mechanism interconnecting the input and output means, the selectable gear mechanism having independently rotatable concentric annular output gears each being drivable by at least one of a number of drive gears fixed relative to each other, and selector means for selecting one of the output gears, the selector means including indexing means rotatable with the output means in fixed relationship thereto but being movable relative to the output means upon operation of the selector means to effect a change in output gear.

2. A variable speed drive mechanism according to claim 1 in which the indexing means comprises an output tubular member surrounding the outer peripheral surface of the output gears.

3. A variable speed drive mechanism according to claim 2 in which the output tubular member includes a plurality of aperture patterns spaced about the output tubular member, each aperture pattern being aligned with a respective one of the output gears.

4. A variable speed drive mechanism according to claim 3 in which the aperture patterns are angularly displaced one to the other about the output tubular member.

5. A variable speed drive mechanism according to claim 3 or claim 4 in which the output means has a plurality of pawls aligned for engagement with a respective one of the output gears in dependence upon which one of the output gears is selected by aligning a particular aperture pattern in the output tubular member with a particular set of pawls on the output means so that the pawls engage for rotation with the output gears.

6. A variable speed drive mechanism according to one of the preceding claims and in which the selectable gear mechanism includes at least one input gear.

7. A variable speed drive mechanism according to claim 6 in which there are two of the input gears.

8. A variable speed drive mechanism according to claim 7 in which the two input gears are a pair of annular ring gears mounted concentrically with the output gears and which drive a pair of gears mounted concentrically with and fixed relative to the drive gears for the output gears.

9. A variable speed drive mechanism according to claim 8 in which the input gears are circumferentially surrounded by an input tubular member having two aperture patterns one for each gear, said aperture patterns being angularly displaced relative to one another.

10. A variable speed drive mechanism according to claim 9 in which the input tubular member is arranged to support a plurality of pawls associated with each input annular gear, the pawls being engagable through a respective aperture pattern to engage an appropriate one of the input gears as selected.

11. A variable speed drive mechanism according to any of the preceding claims in which the output gears are rotationally mounted about a shaft between two spaced members fixed relative to the shaft.

12. A variable speed drive mechanism according to claim 11 in which there are three equicircumferentially spaced sets of drive gears mounted on respective rotatable axles for each set, said axles being supported between opposed support members and being radially spaced relative to the shaft about which the output gears rotate.

13. A variable speed drive mechanism according to claims 2 and 9 in which the input and output tubular members are each capable of being rotated by radially extending teeth engagable with their respective gear wheels respectively mounted on their input and output means.

14. A variable speed drive mechanism according to claim 13 in which each gear wheel is itself rotatable about a spigot on which is also mounted an indexing wheel so that the wheel will rotate about the fixed axis.

15. A variable speed drive mechanism according to claims 12 and 14 in which an indexing pin is mounted on one of the support members for engagement with the indexing wheel.

16. A variable speed drive mechanism according to claim 15 in which two of the indexing pins are provided, one on each side of the spigot, to selectively rotate the indexing wheel in one or the other direction.

17. A variable speed drive mechanism substantially herein described with reference to the accompanying drawings.

18. A bicycle when provided with a variable speed drive mechanism as claimed in any of the preceding claims.