AU2011101669A4 - Dual Range Drivetrain for Extended Drivetrain Cycles - Google Patents

Abstract

DUAL RANGE DRIVETRAIN FOR EXTENDED DRIVETRAIN CYCLES A dual range drivetrain for extended drivetrain cycles comprised of a primary drive coupled to an intermediate, secondary, geared drive which is coupled to a tertiary, geared drive on the rear axle or wheel of the cycle. The chainring of the primary drive is linked by chain to a high range gear assembly of the secondary drive which is linked by chain to a low range gear assembly of the tertiary drive. This configuration provides a wider range and a greater number of gears that can be selected by the operation of indexed gear levers positioned on a steering mechanism and connected by cable to derailleur. A smooth transition through the gears, from the lowest to the highest and back to the lowest is intrinsic. Double shuffling in order to engage the next higher or lower gear when changing chainrings is eliminated ensuring that the cycle is in the right gear at the right time. eCn 'UM 0*L 4)l

Description

AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION INNOVATION PATENT DUAL RANGE DRIVETRAIN FOR EXTENDED DRIVETRAIN CYCLES The following statement is a full description of this invention, including a procedure of operation.

I DUAL RANGE DRIVETRAIN FOR EXTENDED DRIVETRAIN CYCLES FIELD OF THE INVENTION The present invention relates to extended drivetrain cycles which have 5 longer drivetrains than those of standard road or off road cycles; such as: recumbents, rickshaws, tandems and disability cycles (particular reference to the group of extended drivetrain cycles known as recumbent cycles is used herein for illustrative purposes). 10 BACKGROUND OF THE INVENTION Prior art extended drivetrains usually have the following components: a pedal assembly containing two or three chainrings, a long chain, one or more jockey wheels and a cluster or cassette of sprockets attached 15 to a drive wheel at the rear. Although jockey wheels play a major role in the control of the long chain they play no part in gearing which is achieved using a combination of chainrings and sprockets selected by gear levers attached by cable to derailleur. 20 The limitations of a cycle with a prior art extended drivetrain are a relatively small number and range of gears and the need to change sprockets in order to select the next lower or higher gear when changing chainrings, called "double shuffling". This double shuffle is sometimes difficult to execute and always requires skill. 25 2 OBJECT OF THE INVENTION It is therefore an object of the present invention to provide a drivetrain for extended drivetrain cycles which provides a greater number and a 5 wider range of gears than prior art extended drivetrains and a gear change mechanism and procedure that does not involve double shuffling. STATEMENT OF THE INVENTION 10 The present invention, a dual range drivetrain for extended drivetrain cycles, is comprised of a primary drive (PD) coupled to an intermediate, secondary, geared drive (SD) which is coupled to a tertiary, geared drive on the rear axle or wheel of a cycle. 15 The chainring of the primary drive is linked by chain to a high range cluster or cassette of the secondary drive which is linked by chain to a low range cluster or cassette of the tertiary drive (TD). 20 Additionally, an optional auxiliary power source can be linked by chain to an auxiliary chainring fitted to the primary drive. BRIEF DESCRIPTION OF THE DRAWINGS 25 An embodiment of the invention is now described by way of example only with reference to the accompanying drawings in which: Fig 1 is an elevation of a long wheel base recumbent cycle with an optional power source 3 Fig 2 is an elevation of a short wheel base recumbent cycle with an optional power source Fig 3 is a schematic illustrating a SD cluster Fig 4 is schematic illustrating a TD cluster 5 Fig 5 is an example table of available gear ratios and Figs 6a and 6b are tables of gear ratios demonstrating the need for double shuffling associated with prior art extended drivetrains. DETAILED DESCRIPTION OF THE INVENTION 10 Fig 1 shows a long wheel base recumbent cycle 1 with optional auxiliary power source 3, PD 4, SD 5 and TD 6. Chain 2c links the optional power source 3 with PD 4, chain 2a links the latter with SD 5 and chain 2b links the latter with TD 6. 15 Fig 2 shows a short wheel base recumbent cycle 1 with the same drive and chain components but with the optional power source 3 and PD 4 located in front of the headstock rather than behind as in Fig 1. 20 The optional power source 3 (powered by electric, solar or internal combustion engine) is not part of the present invention. PD 4 consists of a pedal assembly (not shown) and a single chainring connected to SD 5 by chain 2a which may be guided by jockey wheels 25 or chain tube. SD 5 consists of a high range cluster or cassette shown schematically in Fig3, matching derailleur (not shown) and an indexed gear lever (not shown) positioned on the steering mechanism and connected by cable (not shown) to the derailleur.

4 The high range cluster or cassette has the following components: sprocket 8' acting as a chainring, called the drive sprocket, separated by spacer 9' from other sprockets 1' to 7', called the high range gear assembly (HRGA). Drive sprocket 8' is continuously connected to TD 6 5 by chain 2b which may be guided by jockey wheels or chain tube. The sprockets of the high range gear assembly are numbered from the largest 1' to the smallest 7'. Sprocket 4' closest to the middle of the assembly is in line with its respective primary drive 4 chainring. SD 5 10 is positioned approximately half way between PD 4 and TD 6. TD 6 consists of the following components: a low range cluster or cassette (LRGA) shown schematically in Fig 4, matching derailleur (not shown), indexed gear lever (not shown) positioned on the steering 15 mechanism and connected by cable (not shown) to the derailleur. The sprockets of the LRGA are numbered from the largest 1" to the smallest 7". Sprocket 4" closest to the middle of the assembly is in line with the drive sprocket of SD 5. 20 The table of Fig 5 gives a gear set example produced by the following drivetrain components: a single 34T primary drive chainring, a 30T secondary drive sprocket, a seven sprocket (15-30) cassette HRGA, a seven sprocket (15-30) cassette LRGA and a 26 inch rear wheel. The total number of gears in the set is 49 and the number of unique gears 25 in the set is 23. Changing gear to successively higher gears gives 13 gears with the following numeric ratios: 29, 33, 37, 42, 47, 52, 59 (low range) and 65, 74, 84, 93, 104, 118 (high range). The gain between any two numeric ratios is constant at 14%.

5 Figs 6a and 6b are tables of gear ratios which demonstrate the limitations of an extended drivetrain cycle with a prior art extended drivetrain, namely a relatively small number and range of gears and the need for double shuffling, Both tables are based on the same size 5 drive wheel used in Fig 5 and in order to achieve a wide range of gear ratios use the smallest and largest standard chainrings (33 and 54 teeth respectively). Fig 6a uses the same set of sprockets as used in Fig 5. The range of 10 gear ratios (29 - 94) is less than for the dual range drivetrain (29 118). 1. Changing Up. A chainring sprocket combination of 33 and 15 respectively gives a gear ratio of 57. To select the next highest gear (gear ratio 67) would require a change of chainrings from 15 33 to 54; however, this would initially give a gear ratio of 94 (too high). In order to achieve the desired gear ratio of 67 a change of sprockets from 15 to 21 is also required (drop back three); double shuffling. 2. Changing Down. A chainring sprocket combination of 54 and 30 20 respectively gives a gear ratio of 47. To select the next lowest gear (gear ratio 41) would require a change of chainrings from 54 to 33; however, this would initially give a gear ratio of 29 (too low). In order to achieve the desired gear ratio of 41 a change of sprockets from 30 to 21 is also required (move up 25 three); double shuffling. Fig 6b uses a different set of sprockets to the set used in Fig 5. The range of gear ratios (27 - 117) is the same as for the dual range drivetrain (29 - 118).

6 1. Changing Up. A chainring sprocket combination of 33 and 12 respectively gives a gear ratio of 72. To select the next highest gear (gear ratio 83) would require a change of chainrings from 33 to 54; however, this would initially give a gear ratio of 117 5 (too high). In order to achieve the desired gear ratio of 83 a change of sprockets from 12 to 15 is also required (drop back three); double shuffling. 2. Changing Down. A chainring sprocket combination of 54 and 32 respectively gives a gear ratio of 44. To select the next lowest 10 gear (gear ratio 41) would require a change of chainrings from 54 to 33; however, this would initially give a gear ratio of 27 (too low). In order to achieve the desired gear ratio of 41 a change of sprockets from 32 to 21 is also required (move up two); double shuffling. 15 It is clear from the above that the dual range drivetrain of the subject invention eliminates the need of prior extended drivetrains to double shuffle in order to engage the next higher or lower gear when changing chainrings. This overcomes the problem of being in the 20 wrong gear at the wrong time when riding. A PROCEDURE OF OPERATION Changing gear initially to successively higher gears on the dual range 25 drivetrain is achieved by shifting from a lower to a higher gear on TD 6 using the TD indexed gear lever and then by shifting from a lower to a higher gear on the SD 5 using the SD indexed gear lever. Changing gear to successively lower gears is achieved by shifting from a higher to a lower gear on SD 5 using the SD indexed gear lever and then by 7 shifting from a higher to a lower gear on TD 6 using the TD indexed gear lever. A single gear change in any range will always be to the next lowest or 5 highest gear and the gain between any two numeric ratios is constant for any given set of gears. This allows for a smooth transition through the gears, from the lowest to the highest and back to the lowest. It also provides an array of easy to select paths between the lowest and highest gears, and subsets of gears while riding thus allowing the rider 10 to tailor a gear set to environmental conditions. An optional auxiliary power source can be connected to the drivetrain by chain 2c to an auxiliary chainring fitted to primary drive 4. 15 VARIATIONS It will be realized that the foregoing has been given by way of illustrative example only and that all other modifications and variations as would be apparent to persons skilled in the art are deemed to fall 20 within the broad scope and ambit of the invention as herein set forth. Throughout the description and claims of this specification the words "comprise" and variations of that word such as "comprises" and "comprising" are not intended to exclude other additives, components, integers or steps. 25

Claims (5)

1. A dual range drivetrain for extended drivetrain cycles comprising a PD coupled to an intermediate, secondary, geared drive which 5 is coupled to a tertiary, geared drive on the rear axle or wheel of the cycle.

2. The drivetrain of claim 1 in which a chainring of the PD is linked by chain to a HRGA of the SD which is linked by chain to a LRGA 10 of the TD.

3. The drivetrain of claim I operated by indexed gear levers positioned on the steering mechanism and connected by cable to derailleur. 15

4. The drivetrain of claim 1 may have an optional auxiliary power source linked by chain to the primary drive.

5. A dual range drivetrain for extended drivetrain cycles 20 substantially as herein described by Figures 1 to 5 of the accompanying diagrams. Paul Prior (Applicant) Date