GB2434565A

GB2434565A - Bicycle drive transmission

Info

Publication number: GB2434565A
Application number: GB0608304A
Authority: GB
Inventors: Alan Burr
Original assignee: Individual
Current assignee: Individual
Priority date: 2006-01-10
Filing date: 2006-04-27
Publication date: 2007-08-01
Also published as: GB0600391D0; GB0608304D0

Abstract

A bicycle has a two-stage drive transmission mounted on a swinging arm 16, e.g. of box section, which pivots about a pedal crank shaft 20 and carries a rear wheel 32 driven by the transmission. The transmission, enclosed by the swinging arm 16, comprises a first chain 24 driven from the shaft 20 via a first set of different diameter chainwheels and a second chain 28 driven from a set of different diameter chainwheels which are driven by the first chain 24.

Description

--

BICYCLE DRIVE

The present invention relates to a drive transmission apparatus suitable for use on pedal driven vehicles, in particular but not exclusively bicycles. The invention also relates to a bicycle fitted with a drive transmission apparatus.

Many different types of drive transmission apparatus or mechanism have been utilised for pedal driven vehicles, especially bicycles. In a typical bicycle drive a pedal driven shaft, rotated by the rider of the bicycle, is drivingly connected by means of a chain or belt loop to the rear wheel of the bicycle. Variable gearing can be provided in a number of different ways with such an arrangement. Typically, where a chain is used, different sized sprockets for the chain are fitted to the driven wheel and, optionally, to the pedal driven shaft. Gear changes are effected by means of the well known derailleur mechanisms which move the chain as desired from one sprocket to another of a different size. Such arrangements have been highly developed and are generally robust and reliable in normal use.

As cycling has evolved, specialised bicycles have been developed, in particular the mountain bike' for riding over rough ground. As mountain bikes have evolved over the years riding has become more extreme, but there are certain parts of the bicycle that have not changed much. The ability to participate with increasingly extreme riding has come about by improvements in suspension for mountain bikes. Having been involved in racing mountain bikes off and on since 1986, the inventor has seen first hand how they have evolved from a modified road bike with fat tyres to the current designs which are the biggest areas of development in cycling today.

Mountain biking is all about the challenge of riding on or over different obstacles be it natural or man made.

Certain areas of mountain bike design have not been fully explored as the design links with the early mountain bikes have not been broken. There have been plenty of interesting designs over the years, but there are certain parts of the bike that are vulnerable to damage especially now that riding is becoming more and more extreme.

The intention of this invention is to address some of the weakness of the designs of mountain bikes to overcome their vulnerability to damage and to fit in with what is now possible due to development of other areas of mountain bike design. The main area for attention are the gearing mechanism, sprocket drive and rear disc brakes. The developments described herein will also find use in other forms of bicycle or pedal driven vehicle.

An alternative drive apparatus with certain advantages has been suggested for use with pedal driven vehicles such as bicycles. European Patent Application EP 1 462 354 (Honda Motor Co Ltd) discloses an improved two stage drive transmission apparatus and its use on a bicycle. In a two stage drive mechanism, the drive from the pedal driven shaft is not directly linked to a driven wheel of the vehicle (by means of a chain or belt for example) Instead, the drive from the pedal driven shaft is transmitted to an intermediate rotating shaft which then in turn transmits the drive via a second chain or belt loop to the driven wheel. Although more complex than a traditional single stage' drive the two stage drive can provide benefits. For example, variable gearing can be provided on the intermediate rotating shaft rather than on the driven wheel. This removes the complexity of multiple gears (and the associated gear changing mechanism) from a vulnerable position on the driven wheel and places it on the intermediate shaft, which can be located towards the centre

S

of the vehicle (bicycle) to which it is fitted.

Furthermore, with a two stage drive the dimensions of the gears (e.g. sprockets) required to provide the desired gear ratios can be reduced, leading to improved ground clearance and reductions in weight.

Although the known two stage drive devices such as that of EP 1 462 354 provide advantages and improvements over single stage drive arrangements, there is still a need to provide a further improved drive transmission apparatus, especially for use with pedal driven vehicles that have suspension systems for the driven wheel(s). As the suspension system of a driven bicycle wheel operates, there is a tendency for a chain drive to be subject to stretching or chain growth', caused by changes in the relative distances between the axle and the other shaft about which the chain runs. This can result in reduced chain life, even where compensating mechanisms are provided to allow for chain growth.

It is an object of the present invention to provide a drive transmission apparatus that avoids or at least minimises one or more some of the aforementioned disadvantages.

Accordingly the present invention provides a drive transmission apparatus for a pedal driven vehicle, the apparatus comprising a two stage drive mechanism mounted on or in a swinging arm, wherein said swinging arm has a first end pivotally connected to a frame of the pedal driven vehicle and a second end connected to a driven wheel of the pedal driven vehicle.

Preferably, the first end of the swinging arm pivots, in use, about a pedal driven rotating shaft of the drive transmission apparatus said shaft being rotatably mounted to said frame.

Providing a two stage drive mechanism that is mounted on or in a swinging arm has a number of benefits. All of the benefits described above relating to a two stage drive are maintained. For example, the ability to use smaller gear wheels or sprockets and the ability to locate any gear and gear change mechanism towards the centre of the pedal driven vehicle. At the same time, as the two stage drive mechanism is mounted on or in a swinging arm, when the suspension of a pedal driven vehicle, to which it is fitted, operates and the swinging arm pivots there is no change in the distances between the pedal driven shaft, the intermediate shaft and the centre of the driven wheel. In particular this means that there is no chain growth' caused by a changing distance between the intermediate shaft and the centre of the driven wheel. Therefore the final chain or belt drive is not subject to potentially damaging shock forces as the suspension operates and does not have to have a compensating mechanism to allow for chain growth, preventing breakage.

Furthermore the two stage drive mechanism, when mounted on or in a swinging arm, can more easily be protected from damage and wear during use, as described hereinafter with reference to specific embodiments of the apparatus of the invention.

The drive transmission apparatus may be fitted to any form of pedal driven vehicle, for example bicycles, tricycles or quadricycles. It may be fitted to provide either front wheel drive or rear wheel drive to the pedal driven vehicle. The preferred use is to provide rear wheel drive to a bicycle. The most preferred use is to provide rear wheel drive to a mountain bike.

Thus according to another aspect, the present invention provides a bicycle comprising the drive transmission apparatus of the invention.

It will be understood by the reader that the two stage drive mechanism in a drive transmission apparatus of the invention will be a mechanism in which the drive from a pedal driven shaft is transmitted first to an intermediate rotating shaft and then to a driven wheel of the vehicle, for example a bicycle. The two stage drive mechanism is mounted on or in a swinging arm i.e. the two stage drive mechanism is attached directly to the swinging arm or is mounted on it by means of brackets or linkages which attach to the swinging arm.

The two stage drive mechanism may take any suitable form to provide the required delivery of energy from the pedal driven shaft via the intermediate shaft to a driven wheel.

Preferably belts or chains are used to transmit the drive from the pedal driven shaft to the intermediate shaft and also from the intermediate shaft to the driven wheel. In this case sprockets or drive wheels are fitted to the shafts and wheel for mounting the chains or belts. The relative sizes of the drive wheels or sprockets determine the gearing applied through the drive transmission apparatus to the driven wheel.

Alternatively, the drive between the pedal driven shaft and the intermediate shaft may be by means of intermeshing gear wheels, mounted on the shafts. If required to provide the desired gearing from the drive, intermeshing gears may be provided on a further rotating shaft or shafts placed between the pedal driven shaft and the intermediate shaft i.e. drive is by a gearbox arrangement for the first stage of the two stage drive.

Preferably the intermediate shaft is located above the line between the pedal driven shaft and the centre of the driven wheel. This provides good ground clearance for a vehicle fitted with the apparatus of the invention. Typically the intermediate shaft is also located closer to the pedal driven shaft than to the wheel to provide the benefit of a compact arrangement with weight concentrated towards the centre of the vehicle.

The two stage drive mechanism may be single speed'.

Preferably variable gearing is provided. Variable gearing may be provided by any suitable means. For example where intermeshing gear wheels provide drive between the pedal driven shaft and the intermediate shaft, different sized gearwheels may be moved in and out of engagement by a suitable gear change mechanism.

Preferably a derailleur type gear system is employed, with a number of differently sized sprockets or drive wheels mounted on one or more of the shafts or a driven wheel of the drive mechanism. A gear change mechanism is provided to move a drive chain or belt from one sprocket or drive wheel to another. Advantageously, where a derailleur type gear system is employed, the gear sprockets or drive wheels are mounted on the intermediate shaft and/or the pedal driven shaft. This concentrates the mass of the gear mechanism in the middle of the vehicle. Additionally, this also has the benefit that the gear change mechanism does not have to operate at the driven wheel, which is remote from the centre of the vehicle and more susceptible to damage. A centrally located gearing and gear change mechanism can therefore be expected to have an increased life and require less maintenance.

The gear change mechanism employed may be operated by a conventional cable mechanism or by using a hydraulic, pneumatic, electromagnetic or servo-assisted mechanism.

Desirably, where a derailleur gear system is employed operating on a chain or belt connecting the pedal driven shaft and the intermediate shaft, the sprockets or drive wheels mounted on at least one of these shafts can be displaced along the shaft during gear changing. This allows the chain or belt to remain in parallel with a plane perpendicular to the rotating shafts. For example a system as described in EP 1462354 may be employed.

The transmission apparatus of the invention may further comprise a freewheel mechanism as part of the two stage drive. This allows a rider of a pedal driven vehicle to stop pedalling as desired allowing the vehicle to coast.

The freewheel mechanism may be located on any one of the pedal driven shafts, the intermediate shaft or the rear wheel. The freewheel mechanism may, for example, be a conventional ratchet and pawl freewheel as fitted to most bicycles. Alternatively a clutch mechanism may be employed. For example an electric or a magnetic clutch mechanism. Preferably a clutch mechanism, where fitted, will be automatic in operation.

Preferably the two stage drive mechanism is enclosed.

Enclosing the two stage drive mechanism protects it from collision damage in use and also protects it from increased wear caused by dust, grit or other particles which tend to adhere to lubricated components such as chains or be forced 1..

between moving parts, for example, a chain and sprocket, in use.

As the two stage drive mechanism is mounted on or in the swinging arm, enclosing it can readily be achieved. The swinging arm itself may enclose the two stage drive. For example, the swinging arm may take the form of a box structure with the two stage drive mechanism enclosed therein. Alternatively the apparatus of the invention may comprise covers, attachable to the swinging arm or the two stage drive which enclose the two stage drive mechanism.

Enclosing the drive mechanism increases the life of the drive components and reduces the required maintenance.

Preferably, where the swinging arm encloses the two stage drive mechanism, the swinging arm can be opened to allow access for repair or maintenance. Alternatively, access ports, with moveable covers, may be provided at suitable locations on the swinging arm.

Desirably, the swinging arm is reinforced along its lower edges or faces. This provides additional protection from collision with the ground or rocks as the pedal driven vehicle traverses rough ground. For example, the reinforcing may be provided by the provision of a skid plate or skid plates fitted to the bottom of the swinging arm. Alternatively the material of construction of the swinging arm may be thicker along its lower edge or faces.

Advantageously the swinging arm or its associated reinforcement may also protect other components of the pedal driven vehicle. For example, where the apparatus of the invention is fitted to a bicycle, so as to transmit drive to the rear wheel thereof, the swinging arm and its associated reinforcing may be formed and arranged to protect a disc brake, fitted to the rear wheel.

Further preferred features and advantages of the present invention will appear from the following detailed description of some embodiments illustrated with reference to the accompanying drawings in which: Fig. 1 shows a drive transmission apparatus of the invention fitted to a bicycle of the invention; Fig. 2 shows schematically the first stage of a drive transmission apparatus of the invention comprising derailleur gears, in plan view; Fig. 3 shows the gear system of Fig. 2 in a schematic elevation view.

Fig. 1 shows a bicycle 1 which has a drive transmission apparatus 2 of the invention fitted. The bicycle 1 has a main (fixed) frame 4 to which is fitted a front fork 6, handlebars 8, and a seat 10. A spring and damper arrangement 12 is mounted on the main frame 4 and connects via a swing link arrangement 14 to the drive transmission apparatus 2.

The drive transmission apparatus 2 has a swinging arm 16 which is of a box section and encloses and mounts a two stage drive mechanism 18. The two stage drive mechanism 18 has a rotating shaft 20 driven by pedals 22 which is linked by a first drive chain 24 to an intermediate rotating shaft 26. A second drive chain 28 connects the intermediate shaft 26 to the a sprocket 30 of the rear wheel 32 of the bicycle 1. An optional chain tensioner 34 is adjustable to tension the second drive chain 28 and act as a chain guide.

A skid plate 36 is fitted along the bottom edge of the swinging arm 16 and extends 38 under a bottom part of the main frame 4 and also under the disc 40 of a disc brake fitted to the rear wheel 32.

The pedal driven shaft 20 and the intermediate shaft 26 have a number of gear sprockets around which the first drive chain 24 operates (see Fig. 2) with the drive chain movable from one sprocket to another by a derailleur gear change mechanism (not shown) In use the drive transmission apparatus transmits drive from the pedal driven shaft 20 to the centre 30 of the rear wheel 32 via the drive chains 24, 28 and the intermediate shaft 26.

As the two stage drive mechanism is fully enclosed within the swinging arm 16 it is protected from damage and wear caused by exposure to dirt, grit etc. When the bicycle 1 travels over rough ground, the suspension for the rear wheel 32 operates as follows. The swinging arm 16 pivots around the pedal driven shaft 20 in bearings (not shown) allowing the rear wheel to move up and down as indicated by the curved arrow A. This movement is moderated by the operation of the spring and damper arrangement 12 which connects to the swinging arm 16 by means of the swing link arrangement 14. As the suspension operates the relative positions of the pedal driven shaft 20, the intermediate shaft 26 and the centre of the rear wheel (axle) 30 remain unchanged and so there is no chain growth' effect on either of the drive chains 24, 28.

The skid plate 36 protects the swinging arm 16, the enclosed two stage drive mechanism 18 and the disc 40 of the disc brake from collision damage with rocks, logs or other obstacles in use.

Fig. 2 shows in a schematic cut-away plan view the first stage of the two stage drive mechanism of the drive transmission apparatus 2 of Fig. 1. The box section part of the swinging arm 16 which encloses the two stage drive is not shown in this view for clarity.

The pedal driven rotating shaft 20 is mounted in bearings 42 on a part of the main frame 4 of the bicycle. Three different sized gear sprockets 44 are mounted on the pedal driven shaft 20. The swinging arm 16 (only a part shown) pivots about bearings 46 on the pedal driven shaft 20. The intermediate shaft 26 rotates on bearings 47 mounted on the swinging arm 16. It has five gear sprockets 40 for use in connecting to the pedal driven shaft 20 via the first drive chain 24. A further sprocket 50 connects the intermediate shaft 26 via a second drive chain (not shown) to the bicycle wheel (not shown) . A freewheel mechanism 52 is mounted on the intermediate shaft 26.

In use, gear changes are effected by moving the first drive chain 24 from one sprocket to another of either the pedal driven shaft or the intermediate shaft. A standard derailleur gear change mechanism can be employed for movement of the chain, at least at one of the shafts.

(not shown, see Fig. 3) Fig. 3 shows the first stage of the two stage drive shown in Fig. 2, in elevation. The first drive chain 24 follows a path round the sprockets of the pedal driven shaft 20 and the intermediate shaft as shown. A chain tensioner mechanism 54 has two wheels 56, 58 around which the drive chain 24 also passes, to maintain tension irrespective of the size of sprockets being employed. It also acts as a derailleur gear change mechanism to move the chain 24 from sprocket to sprocket as required.

Claims

CLAIMS

1. A drive transmission apparatus for a pedal driven vehicle, the apparatus comprising a two stage drive mechanism mounted on or in a swinging arm, wherein said swinging arm has a first end pivotally connected to a frame of the pedal driven vehicle and a second end connected to a driven wheel of the pedal driven vehicle.

2. A drive transmission apparatus according to claim 1 wherein the first end of the swinging arm pivots, in use, about a pedal driven rotating shaft of the drive transmission apparatus, said shaft being rotatably mounted to said frame.

3. A drive transmission apparatus according to claim 1 or claim 2 having a two stage drive mechanism wherein drive is transmitted by belts or chains from the pedal driven shaft to the intermediate shaft and also from the intermediate shaft to the driven wheel.

4. A drive transmission apparatus according to claim 1 or claim 2 having a two stage drive mechanism wherein drive is transmitted from the pedal driven shaft to the intermediate shaft by means of intermeshing gear wheels.

5. A drive transmission apparatus according to any preceding claim wherein the intermediate shaft of the two stage drive mechanism is located above the line between the pedal driven shaft and the centre of the driven wheel.

6. A drive transmission apparatus according to any preceding claims wherein the intermediate shaft of the two-stage drive mechanism is located closer to the pedal driven shaft than to the driven wheel.

7. A drive transmission apparatus according to any preceding claim wherein the two stage drive mechanism is single speed.

8. A drive transmission apparatus according to any one of claims 1 to 6 wherein the two stage drive mechanism has variable gearing.

9. A drive transmission apparatus according to claim 8 wherein the variable gearing is provided by different sized gear wheels, which intermesh in use to provide drive between the pedal driven shaft and the intermediate shaft of the two stage drive mechanism, and are moved in and out of engagement by a gear change mechanism.

10. A drive transmission apparatus according to claim 8 wherein variable gearing is provided by a derailleur gear system.

11. A drive transmission apparatus according to claim 10 wherein gear sprockets or drive wheels are mounted on the intermediate shaft and/or the pedal driven shaft of the two-stage drive mechanism.

12. A drive transmission apparatus according to claim 10 or claim 11 wherein gear sprockets or drive wheels can be displaced along a shaft during gear changing.

13. A drive transmission apparatus according to any one of claims 8 to 12 wherein the gear changing mechanism for the variable gearing is selected from the group consisting of cable, hydraulic, pneumatic, electromagnetic and servor-assisted mechanisms.

14. A drive transmission apparatus according to any preceding claim wherein the two stage drive mechanism comprises a freewheel mechanism.

15. A drive transmission apparatus according to claim 14 wherein the freewheel mechanism is a clutch mechanism.

16. A drive transmission apparatus according to claim 15 wherein the clutch mechanism is an automatic clutch mechanism.

17. A drive transmission apparatus according to any preceding claim wherein the two stage drive mechanism is enclosed.

18. A drive transmission apparatus according to claim 17 wherein the swinging arm encloses the two stage drive mechanism.

19. A drive transmission apparatus according to claim 18 wherein the swinging arm can be opened.

20. A drive transmission apparatus according to claim 18 wherein the swinging arm has access ports with moveable covers.

21. A drive transmission apparatus according to claim 17 wherein the two stage drive mechanism is enclosed by covers.

22. A drive transmission apparatus according to any preceding claim wherein the swinging arm is reinforced along its lower edges or faces.

23. A drive transmission apparatus according to claim 22 wherein reinforcement is provided by means of a skid plate.

24. A drive transmission apparatus according to claim 22 wherein reinforcement is provided by a thickening of the swinging arm material of construction.

25. A drive transmission apparatus according to any preceding claim wherein the swinging arm or its associated reinforcement is formed and arranged to protect other components of the pedal driven vehicle.

26. A bicycle comprising a drive transmission apparatus according to claim 1.

27. A bicycle according to claim 26 wherein the drive transmission apparatus provides drive to the rear wheel.

28. A bicycle according to claim 26 or claim 27 wherein the bicycle is a mountain bike.

29. A drive transmission apparatus substantially as described hereinbefore and with reference to the accompanying drawings.

30. A bicycle substantially as described hereinbefore and with reference to Figure 1 of the accompanying drawings.