This invention relates generally to automatic transmissions fitted to human-powered vehicles, and more particularly pertains to an electromechanical automatic gear-changing system which can be retrofitted to various multi-speed bicycles for automatically derailing the endless chain from one of a plurality of rear transmission sprockets to another transmission sprocket.
Bicycling has become a popular hobby in recent years in part because of its simplicity and healthiness. Whether done on city streets, country roads, cross country, or on bicycle paths and trails, bicycling is a pleasant, invigorating hobby and form of exercise for individuals or groups, young or old, couples or families.
Multi-speed bicycles have a manually operable and adjustable variable speed transmission, and such bicycles also generally include: a plurality of laterally-spaced, axially-aligned, rear transmission sprockets; a plurality of laterally-spaced front chain wheels; an endless chain drivingly in mesh with the transmission sprockets and chain wheels; shifting levers mechanically connected to a front gear shifting assembly and the front chain wheels; and shifting levers mechanically connected to a rear derailleur shifting assembly which physically interacts with the chain for shifting the transmission by derailing the chain from one to another rear transmission sprocket.
Inexperienced as well as experienced bicyclists frequently encounter problems with transmission gear shifting. The bicyclist often relies on trial-and-error and an intuitive feel for such changing conditions as terrain and speed in a constant, and often unsuccessful, attempt to match the most efficient transmission gear to the desired speed. On long, level stretches, this problem is minimized, but bicycling is done on varied terrain including hills and valleys, abrupt dips, sharp turns, narrow berms, hidden driveways, and woodland trails.
In addition, the derailleur shifting assembly (rear and/or front) may not properly derail the chain from one rear transmission sprocket to another sprocket due to the abruptness of the shift or defects in the handlebar-mounted gear-shifting levers and/or the rear transmission assembly. If the endless chain does not step up or down smoothly and quickly on the various sprockets and chain wheels during shifting, damage to the chain, the sprockets, and chain wheels can result and possible injury to the rider could occur due to the abruptness of chain shifting or lack thereof.
In an effort to improve the reliability of transmission gear shifting, and in order to make such gear shifting easier, a number of electrical, electromechanical, hydraulic, and pneumatic automatic gear-shifting devices have been invented. Two such devices are the Clem electronically-controlled bicycle transmission (U.S. Pat. No. 4,605,240) and the Matsumoto et al. electrically operated transmission gear system for bicycles (U.S. Pat. No. 4,490,127).
For shifting a conventional derailleur on a multi-speed bicycle, the Clem patent employs a digitally-controlled linear motor/actuator electrically connected to a microcomputer. Micro-switches mounted about a screw shaft of the linear actuator provide feedback information to the microcomputer for transmission control function and also to signal the position of the derailleur to the microcomputer. The Matsumoto et al. patent utilizes an electrically operated gear-shifting mechanism which includes a reversible motor, a takeup reel actuable by the motor, a wire joined to the takeup reel and the guide for displacing the latter in response to rotation of the takeup reel to shift the endless chain into driving mesh with one or another of the rear transmission gears.
However, despite the above-mentioned inventions, there remains a need for an automatic gear-shifting mechanism or apparatus which can be retrofitted to various multi-speed bicycles quickly and securely, performs reliably under adverse conditions, includes elements or component parts (sensors and circuit elements) that can withstand rugged treatment and still perform accurately, and yet includes the ability to adapt to different speed parameters, various riding terrains, and different rider modes, such as leisure riding and cross country bicycling. Moreover, there remains a need for a gear-shifting mechanism that can accommodate a range of multi-speed bicycles without altering the existing chain and gear assembly.