GB2156015A - Vehicle transmission - Google Patents

Abstract

A vehicle transmission, in particular for a bicycle (10), comprises a driving wheel (14) which is supported in bearings (16) slidably mounted in an elongate shell (18). A control (27) operating through a cable (26), a worm (23), wheel (32) and screwed shaft (12) is provided to move the bearings (16) and driving wheel (14) forwardly or rearwardly of the bicycle (10) to tension the drive belt (25). The driving wheel (14) has two coaxial parts (14a, 14b) which are relatively axially movable and spring loaded towards each other. The parts (14a, 14b) form the inclined sides of a peripheral groove (36) in which belt (25) runs at a radius dependent upon the belt tension, thereby providing an infinitely variable gearing within the limits of the dimensions of the driving wheel (14) and driven wheel (15). <IMAGE>

Description

SPECIFICATION Vehicle transmission This invention relates to vehicle transmissions, and in particular to a transmission arrangement for a bicycle.

Bicycles are ridden by a wide range of people in respect of age, size and physical ability, and over a wide range of conditions in respect of gradient, surfaces and wind strength and direction. In consequence it is desirable to have a transmission which incorporates a wide range of gearing if a particular bicycle is to be used either by different people and/or under widely differing circumstances.

However, since most people have a relatively narrow range of optimum pedalling speeds, it is also desirable to have relatively small increments between successive gearing ratios. To have a wide overall range of gear ratios and relatively small increments between successive ratios requires that a large number of individual gear ratios must be provided. This has not been conveniently possible with hub gear systems and in general derailleur gear systems are provided for this purpose. Whilst such derailleur gear systems are satisfactory for racing cyclists and enthusiastic touring cyclists, they are relatively expensive and require too much maintenance for ready acceptance by the casual or purely commuter cyclist.In addition, deraillerur gears are subject to the disadvantage that in use of the largest and smallest rear cogs the chain is considerably misaligned relative to the chainwheel and this leads to inefficiency of the transmisson, rapid wear of the chain and sometimes derailment of the chain. Furthermore, provision of more than six gear ratios involves the use of two operating levers and this is inconvenient.

It is an object of the present invention to provide a vehicle tranmission which is particularly suitable for cycles used by the casual or commuter cyclist, but which is not subject to the abovementioned disadvantages.

The invention provides a vehicle transmission comprising a driving wheel, a driven wheel and an endless belt extending therebetween, said wheels providing a substantially V-shaped peripheral groove to receive said belt therein, wherein at least one of said wheels comprises two coaxial parts, each of which provides a sidewall of said peripheral groove of said one wheel, at least one of said parts being movable axially relative to the other to adjust the radius at which said belt passes around said one wheel. Preferably said parts are resiliently biassed towards each other.

By substantially V-shaped is intended to include trapezoidal cross-sectioned grooves and/or belt having mutually inclined sidewalls. Said belt may also be of substantially Vshaped cross-section.

By means of the invention the precise gear ratio may be selected for any particular person for any particular cycling condition, since the transmission is infinitely variable within the range provided by the dimensions of the wheels and the range of movement of the wheel parts.

Preferably said driving wheel comprises said two parts.

The transmisson may also include belt tensioning means, which may comprise means operable to move one of said driving and driven wheels towards and away from the other. Preferably said belt tensioning means moves said driving wheel towards and away from said driven wheel.

One embodiment of vehicle transmission in accordance will now be described with reference to the accompanying drawings in which: Figure 1 is a diagrammatic exploded view of a bicycle with parts thereof shown to differing scales, Figure 2 is a diagrammatic exploded view to an enlarged scale of part of the bicycle of Fig. 1, Figure 3 is an exploded view of the drive wheel of the bicycle of Figs. 1 and 2, and Figure 4 is a cross-sectional view of the drive wheel assembly.

Referring now to Fig. 1 there is shown a bicycle 10 having a frame 11 in which an elongate bearing shell or "bottom bracket" shell 1 8 is fitted instead of the conventional shell of circular cross-section. Within the bottom bracket shell 18 is slidably mounted a bearing unit 1 6 in which the axle 1 3 is rotatably mounted. The bearing unit 16 can move forwardly or rearwardly of the bicycle 10 and is moved by means of a screwed drive shaft 1 2 passing therethrough. At each end of bearing unit 16 is a nut 28 secured thereto by dowels 30 so as to be non-rotational relative thereto.Rotation of shaft 1 2 is effected by means of a worm 23 cooperating with a wheel 32 secured to shaft 1 2 which is rotatably mounted in shell 1 8 so as not to be movable axially of itself. Worm 23 is rotated by means of a cable drive 26 operated by a "throttle" control 27 secured to the handlebars 31 of the bicycle 10.

Referring to Fig. 2 it may be seen that mounted on the axle 1 3 is a driving wheel 14, and a drive belt 25 passes around the driving wheel 14 and a driven wheel 1 5 secured to the hub 33 of the rear wheel (not shown) of the bicycle 10. The driven wheel 1 5 has a V-shaped peripheral groove 34 and incorporates a free-wheel in conventional manner. Bearing unit 1 6 is maintained in shell 1 8 by means of guide strips 29 removably secured to the shell 1 8.

Referring now to Figs. 3 and 4 there is shown the two parts 1 4a, 1 4b of the driving wheel 14. One part 14a, to which a pedal crank 36 is attached, is secured to axle 1 3 in conventional manner, for example by means of cotter pins 35. Part 14a includes a central boss 1 7 on the periphery of which are splines 24 and part 1 4b has a central recess 1 9 and grooves 20 to receive the central boss 1 7 and splines 24 respectively of part 14a. By this means rotation of part 1 4b relative to part 1 4a is prevented but part 1 4b can move towards and away from part 14a.Three bolts 22 on which strong compression springs 21 are located, only one being shown in Figs. 3 and 4 for clarity, secure parts 1 4a and 1 4b to each other and the springs 21 bias part 14b towards part 14a. Parts 1 4a and 1 4b together define a wheel 14 having a peripheral, generally V-shaped groove 37 of adjustable width.

Radial ribs 38 are formed on parts 14a, 1 4b to assist in gripping of the belt 25.

In use of the bicycle 10 there will occur occasions on which the rider wishes to alter the gearing ratio. Movement of the "throttle" control 27 causes the bearing unit 1 6 to move forwardly or rearwardly as desired within the bottom bracket shell 1 8 and this will increase or decrease respectively the tension in the belt 25. An increase in tension will cause the belt 25 to move to a smaller radius around wheel 14, overcoming the compressive force of springs 21 and causing separation of the parts 1 4a, 1 4b until a new equilibrium position is reached. A decrease in tension will allow the springs 21 to force part 1 4b towards part 1 4a and the belt 25 move to a larger radius around wheel 14.In the former case a lower gear ratio will result and in the latter case a higher gear ratio will result. With the transmission of the present invention the gear ratio is infinitely variable within the limits dictated by the dimensions of the wheels 14,15 and the movement of part 1 4b relative to part 14a. The arrangement is simple, cheap to manufacture and requires little maintenance.

Although the transmission is illustrated and described in relation to a bicycle, it may have application for other vehicles and/or machines requiring a simple, maintenance free transmission with infinitely variable gearing.

Alternative embodiments of transmission in accordance with the invention will be readily apparent to persons skilled in the art. For example the wheel 14 may be mounted in a conventional bottom bracket shell 1 8 instead of the elongate one shown, and the rear wheel of the bicycle moved relative to the frame 11. The "throttle" control may be mounted on the frame 11 instead of the handlebars 31 and the wheel 14 may be secured on axle 1 3 on splines or a tapered square axle end instead of using cotter pins 35. The worm 23, wheel 32 and shaft 1 2 may be replaced by a linkage mechanism operable to move bearing unit 1 6 relative to the shell 18. In addition, the belt 25 and peripheral groove in the driven wheel 1 5 may be of circular cross-section if desired.

Claims (15)

1. A vehicle transmission comprising a driving wheel, a driven wheel and an endless belt extending therebetween, said wheels each providing a radially inwardly tapering peripheral groove to receive said belt therein, wherein at least one of said wheels comprises two coaxially disposed parts, each of which provides a sidewall of said peripheral groove of said one wheel, at least one of said parts being movable axially relative to the other part to adjust the radius at which said belt passes around said one wheel.

2. A vehicle transmission according to claim 1 wherein said belt has a pair of mutually inclined sidewalls.

3. A vehicle transmission according to claim 2 wherein said belt is of V-shaped crosssection.

4. A vehicle transmission according to any one of claims 1 to 3 wherein said other part is secured to a spindle having splines thereon cooperating with splines on said one part.

5. A vehicle transmission according to claim 4 wherein said parts are resiliently biassed towards each other.

6. A vehicle transmission according to claim 5 comprising bolts securing said two parts to each other, on which bolts are springs operable to bias said two parts towards each other.

7. A vehicle transmission according to any one of claims 1 to 6 wherein said sidewalls of said groove have radially extending ribs thereon.

8. A vehicle transmission according to any one of claims 1 to 7 comprising belt tensioning means.

9. A vehicle transmission according to claim 8 wherein said belt tensioning means comprises means operable to move one of said wheels towards and away from the other.

10. A vehicle transmission according to claim 9 wherein said belt tensioning means is operable to move said driving wheel towards or away from said driving wheel.

11. A vehicle transmission according to any one of claims 1 to 10 wherein said one wheel comprising said two parts is said driving wheel.

1 2. A bicycle having a vehicle transmission means according to any one of claims 1 to 11.

13. A bicycle according to claim 12 having belt tensioning means operable to move said driving wheel towards or away from said driven wheel, wherein said driving wheel is supported by bearings mounted in an elongate shell.

14. A bicycle according to claim 1 3 comprising a screwed shaft extending through said shell and operable on rotation thereof to move said bearings and said driving wheel forwardly or rearwardly of said bicycle.

15. A bicycle according to claim 14 comprising a worm cooperable with a wheel secured to said shaft to drive said shaft in rotation.

1 6. A bicycle according to claim 1 5 comprising a cable attached to said worm, and control means secured to a part of said bicycle, movement of said control means effecting movement of said cable, said worm and wheel, said shaft and hence said bearings within said shell.

1 7. A vehicle transmission substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

1 8. A bicycle substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.