Patent ID: 7036836

Claim:
A structure of an automatic speed change device for bicycle gearbox, comprising: a body consisted of a front plank and a rear plank, wherein the body comprises a hollow column between the front plank and the rear plank; a shaft base, wherein one end of the shaft base is a shaft, wherein the shaft comprises a thread part and a clip element positioned at an extension of the shaft; a connecting element, wherein said connecting element is a framework and the upper and lower portion of said connecting element respectively comprise an aperture; a lock-shaft, wherein one end of said lock-shaft is formed in a thread part and another end of said lock-shaft is formed in a connecting part; a spring disposed on said shaft of said shaft base, wherein said spring is between said clip element of said shaft base and said hollow column of said body; and gears respectively positioned at both sides of said body and one end of said clip element of said shaft base; whereby said automatic speed change device is constructed and assembled onto a bicycle, the above-mentioned design is able to control the speed change and gear shift of a rear wheel speed change device with the treading rate of an user, and thus the user can ride more easily and the gear shift is automatically adjusted by road conditions.