GB2464918A

GB2464918A - Automatic gear shift for bicycles

Info

Publication number: GB2464918A
Application number: GB0819393A
Authority: GB
Inventors: Chan Yang Edwin Koh
Original assignee: Individual
Current assignee: Individual
Priority date: 2008-10-23
Filing date: 2008-10-23
Publication date: 2010-05-05
Also published as: GB0819393D0

Abstract

An automatic gearshift mechanism 10 for a bicycle comprises a detector 16 for the road speed, and an actuator 32 for a Bowden cable 36 leading to a gear shift mechanism controlled to adjust the Bowden cable in dependence on the road speed. Such a device could be controlled by centrifugal force, to extend or retract (as required) the cable of a bicycle derailleur to prompt a shift to a higher gear as the bicycle speed increases, and vice versa. Thus, an inertia arm 22 comprises an arm pivotally connected at one end 24 to a shaft 20, having a centre of gravity spaced from the pivotal connection 24, and being biased toward the shaft 20 via slider 32, link arm 28 and biasing compression spring 34, the shaft 20 being driven rotationally at a speed correlated with that of the bicycle. The shaft 20 is be driven by a wheel 12 of the bicycle via a roller 16 located in contact with a tyre of the bicycle. Bracket 14 may have an external stabiliser to prevent rotation of Bowden cable 36.

Description

Automatic gearshift for bicycles

FIELD OF THE INVENTION

The present invention relates to an automatic gearshift for bicycles.

BACKGROUND ART

The bicycle is a well-known and ubiquitous form of personal transportation. For certain types of journey, it offers a range of advantages in terms of the absence of any fuel, insurance or taxation costs, the absence of any carbon or other emissions, and the personal fitness benefits that result. These benefits are however a direct consequence of what is (for some) the main difficulty involved in cycling -that the rider must provide the motive effort.

The main way in which this difficulty has to date been alleviated is by way of allowing the rider to alter the gear ratio between the pedals and the driven wheel. This (evidently) reduces the effort required by allowing the rider to exert themselves at a substantially constant cadence rate regardless of the road speed of the bicycle. Most modern bicycles allow this adjustment by way of a derailleur mechanism in which the driven wheel carries a number of cogs of differing diameters, mounted in a laterally spaced array along the axle. The drive chain from the pedals is passed through a derailleur -essentially a frame carrying two small jockey cogs which define a serpentine path for the chain -which is moveable laterally relative to the axle. This device I9xes the lateral position of the chain, and is controlled by a Bowden cable which can be adjusted by the rider. Thus, the rider can adjust the lateral position of the derailleur and thereby draw the chain onto a selected cog.

A similar arrangement can be provided for the front chain ring, although as the derailleur is then acting on the upper (tensioned) section of the chain, it usually consists of a guide (or cage) for the chain rather than jockey cogs.

The total number of speeds offered by a specific bicycle is thus the product of the number of cogs on the driven wheel (usually up to 9) and the number on the front chainring (typically 2 or 3). Thus, it is common to see 18 or 27 gears (or speeds) on a bicycle, with a typical maximum of 33. This offers the ability to tailor the gear ratio closely to the speed of the bicycle, but does so at the expense of increasing the complexity of the system and hence the degree of control required by the rider. For day-to-day use, as opposed to racing or recreational use, this is unwelcome as the rider has other matters which require their concentration, such as the surrounding traffic.

As an alternative, hub gear systems employ a number of epicyclic gears offering different ratios, housed within the hub of the wheel and selectable via a Bowden cable. This arrangement is more commonly used on utility bicycles, particularly in Continental Europe.

US 200710213150A1 (Jesse Chattin et al.) discloses a device which allows for automated selection of an appropriate gear. It is however a complex device which is integrated into the hub and the derailleur directly. It is therefore not susceptible to easy retrofitting to existing bicycles, nor is it applicable to hub gear systems.

SUMMARY OF THE INVENTION

The present invention therefore provides an automatic gearshift mechanism for a bicycle, comprising a detector for the road speed, and an actuator for a Bowden cable leading to a gear shift mechanism controlled to adjust the Bowden cable in dependence on the road speed.

Such a device could be controlled by centrifugal force, to extend or retract (as required) the cable of a bicycle derailleur to prompt a shift to a higher gear as the bicycle speed increases, and vice versa.

Thus, the detector of the present invention can be an inertia arm, comprising an arm pivotally connected at one end to a shaft, having a centre of gravity spaced from the pivotal connection, and being biased toward the shaft, the shaft being driven rotationally at a speed correlated with that of the bicycle.

The shaft can, for example, be driven by a wheel of the bicycle, such as by a roller located in contact with a tyre of the bicycle. A spring can be provided in order to bias the arm.

The arm can further comprise a link, pivotally connected at one end to the arm at a position on the arm displaced from the connection between the arm and the shaft, and slidably connected at another end to the shaft. The link can be slidably connected to the shaft by way of a connection to a slider mounted slidably to the shaft, and can be biased by a spring acting on the slider. This permits a housing for the Bowden cable to be mounted to the shaft, and an inner wire of the Bowden cable mounted to the slider, to effect the necessary adjustment of the cable.

This allows the device to operate together with conventional derailleurs instead of replacing them, bringing various advantages such as easier design of the device, a greater prospect for retrofitting to existing bicycles, and compatibility with a wider range of equipment.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the present invention will now be described by way of example, with reference to the accompanying figures in which; Figure 1 shows a perspective view of the device according to the present invention; Figure 2 shows a view of device from above; Figure 3 shows a view of the inertia arm; Figure 4 shows a view of the slider from above; and Figure 5 shows a view of the slider from beneath.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Referring to figure 1, the automatic gearshift mechanism 10 of the present invention is mounted over a rear wheel 12 at the end of a bracket 14 which is secured to a suitable part of the bicycle, such as the seat, seat post, frame or the mudguard (if rigid enough). A roller 16 is rotateably mounted at one end on a axle 18, and is positioned by the bracket 14 and the axle 18 over and in contact with the wheel 12 so that the roller rotates together with the bicycle wheel when the bicycle is in motion.

A shaft 20 projects from the other end of the roller 16 and is securely attached to the roller 16 so that it rotates therewith. An inertia arm 22 is hinged to the shaft 20 at one end via pivot 24, and carries a weight 26 proximate its other end. A link arm 28 extends from a pivotal attachment 30 part-way along the inertia arm 22 back to a slider 32 mounted on the shaft 20. A compression spring 34 is fitted in the shaft 20 and urges the slider 32 away from the inertia arm 22, thereby drawing the link arm 28 and hence the inertia arm 22 closer to the shaft 20.

Finally, the free end of the Bowden cable 36 leading to the derailleur is mounted to the end of the shaft 20 so that its outer housing is fixed (rotateably) to the shaft 20 and the inner wire 44 is mounted to the slider 32, passing within the shaft 20 and spring 34.

The result of this is that as the bicycle speed increases, the rotation speed of the roller 16, shaft 20 and inertia arm 22 increases. This causes a greater centrifugal force to be exerted by the inertia arm 22 and weight 26, drawing the inertia arm 22 outwards against the spring 34. This pulls the slider 32 towards the pivot 24, thereby adjusting the Bowden cable 36. Further increases in the rotational speed of the wheel 12 will cause a corresponding further increase in the centrifugal force, and thus an increase in the outwards deflection of the inertia arm 22. Therefore, the higher the bicycle speed, the greater the outwards deflection of the inertia arm 22, and the greater adjustment of the Bowden cable 36. The extension of the Bowden cable 36 will in turn cause the derailleur to shift to a higher gear.

A corresponding process will operate, in reverse, as the bicycle slows.

Figure 2 shows the roller 16 and shaft 20 in greater detail, with the inertia arm 22 removed for clarity. It can be seen that the shaft consists of a U-shaped member with the free ends attached to an end face of the roller 16 via flanges 38, 40. This then defines an end face 42 at the base of the U, to which the outer sheath of the Bowden cable 36 can be attached. It also defines an open interior in which the spring 34, the Bowden wire 44, and the slider 32 can be accommodated.

Figure 3 shows the inertia arm 22. Constructed inexpensively from sheet metal or a simple U-section profile, one end of the U-section is rebated to leave two parallel forks 46, 48 that can attach to the pivot point 24.

Figures 4 and 5 show the slider 32 from above and from below, respectively. A hook 50 on the upper face allows for attachment of the link arm 28. Ridges 52, 54 allow the slider to locate in corresponding grooves or slots in the shaft 20. An internal wall 56 allows the wire 44 of the Bowden cable 36 to be attached.

The device is shown in the form of a design that is entirely external, for reasons of clarity. A compact device, for example, could be housed within the roller 16.

Other variations will be apparent to the skilled reader. An example is an external stabiliser leading from the bracket 14 or another suitable location for stabilising and preventing rotation of the Bowden cable 36.

In a further variant of the invention, a entirely electromechanical device would employ a speed sensor such as is currently employed for cycle computers linked to a servo device adapted to adjust the Bowden cable. This could be powered by a battery or by a generator mounted to the wheels. Such a generator might be able to double as a speed sensor by detecting the amplitude or frequency of the electrical power that it produced.

It will of course be understood that many other variations may be made to the above-described embodiment without departing from the scope of the present invention. -7-.

Claims

CLAIMS1. An automatic gearshift mechanism for a bicycle, comprising a detector for the road speed, and an actuator for a Bowden cable leading to a gear shift mechanism controlled to adjust the Bowden cable in dependence on the road speed.
2. An automatic gearshift mechanism according to claim 1 in which the detector is an inertia arm, comprising an arm pivotally connected at one end to a shaft, having a centre of gravity spaced from the pivotal connection, and being biased toward the shaft, the shaft being driven rotationally at a speed correlated with that of the bicycle.
3. An automatic gearshift mechanism according to claim 2 in which the shaft is driven by a wheel of the bicycle.
4. An automatic gearshift mechanism according to claim 3 in which the shaft is driven by a rol'er located in contact with a tyre of the bicycle.
5. An automatic gearshift mechanism according to any one of claims 2 to 4 in which a spring is provided to bias the arm.
6. An automatic gearshift mechanism according to any one of claims 2 to 5 in which the arm further comprises a link, pivotally connected at one end to the arm at a position on the arm displaced from the connection between the arm and the shaft, and slidably connected at another end to the shaft.
7. An automatic gearshift mechanism according to claim 6 in which the link is slidably connected to the shaft by way of a connection to a slider mounted slidably to the shaft.
8. An automatic gearshift mechanism according to claim 7 in which the arm is biased by a spring acting on the slider.
9. An automatic gearshift mechanism according to claim 7 or claim 8 in which a housing of the Bowden cable is mounted to the shaft and an inner wire of the Bowden cable is mounted to the slider.
10. An automatic gearshift mechanism substantially as herein described with reference to and/or as illustrated in the accompanying figures.