Bicycle gear shifting method and apparatus

#1. Field of the Invention

#The present invention relates in general to derailleur type bicycle shifting systems, and more particularly to such a system wherein front and rear derailleur mechanisms are precisely controlled by respective rotatable handgrip shift actuators.

#2. Description of the Prior Art

#These and other objects of the invention will become more apparent in reference to the following description and the accompany drawings, wherein:

#FIG. 1 is an elevational view of a bicycle embodying the present invention;

#FIG. 2 is a plan view partially broken away along the line 2--2 in FIG. 1;

#FIGS. 1 and 2 illustrate a 12-speed bicycle, generally designated 10, in which a 6-sprocket rear derailleur mechanism is actuated by a rear handgrip shift actuator according to the invention, and a 2-chain wheel front derailleur mechanism is actuated by a front handgrip shift actuator according to the invention. It is to be understood, however, that the principles of the present invention are equally applicable to any multi-speed bicycle embodying derailleur-type shifting, including three, five, six, seven, ten, twelve, fourteen, and eighteen-speed bicycles, and the like. Bicycle 10 has a primary frame which is generally triangle-shaped, including a head tube 14, a generally horizontal top tube 16 connected at its front end to head tube 14, a main down tube 18 extending downwardly and rearwardly from head tube 14, and a seat tube 20 connected to the rear end of top tube 16 and extending downwardly and forwardly therefrom. Main down tube 18 and seat tube 20 are joined at their lower ends to bottom bracket 22, shown in phantom, within which the pedal crank is horizontally journalled.

#A front fork 24 defines the axis 26 of front wheel 27. A steering tube (not shown) at the upper end of front fork 24 extends upwardly into head tube 14, and is wedge-clamped to a handlebar stem generally designated 28 which extends down into the steering tube within head tube 14. Handlebar stem 28 includes a handle bar clamp 30 at its upper end for gripping handlebar 32. The handlebar 32 which is illustrated in FIGS. 1 and 2 is of the traditional drop bar type, although it is to be understood that the invention is equally applicable to any type of bicycle handlebar.

#A down fork 34 consisting of left and right seat stays extends downwardly and rearwardly from the upper portion of seat tube 20, and a bottom fork 36 consisting of left and right chain stays extends rearwardly from bottom bracket 22. The left sides of down fork 34 and bottom fork 36 are connected at their rear ends, and similarly the right sides of down fork 34 and bottom fork 36 are connected at their rear ends, and these rear end connections support rear wheel dropouts which define the axis 38 of rear wheel 40.