Industrial Technology Research Institute

Chwan-Cherng Wang

Ching-Huan Tseng

Chung-Biau Tsay

Chung-Ping Chiang

Pai-Hsiang Hsu

Chan-Hua Feng

Chang-Dau Yan

A sprocket trimming method for a multi-stage sprocket assembly is disclosed which includes the steps of: (1) aligning the two sprockets at a gear shift position where a chain is escaping from one sprocket and engaging with another sprocket and is being tilted at a tilting angle; (2) using a computer aided design simulation to simulate how the gear shift operation is taking place and thus identify the portion of the sprocket tooth that will be overlapped and/or interfered with the chain when the chain is moved from an escaping sprocket tooth to an engaging sprocket tooth; and (3) trimming the overlapping and interference portion of the sprocket teeth to a depth according to the following equation: ##EQU1## wherein: D is the depth of the overlapping and interference portion of the sprocket teeth to be trimmed, w is the pitch width of the chain, Lc is the pitch length of the chain, .theta. is the tilting angle of the chain at gear shift position, Ts is the thickness of the sprocket of a smaller diameter, Sg is the distance between the two sprockets. The trimming allows the gear shift operation to be performed without the chain interfering with the sprocket teeth located between the escaping and engaging teeth.

Sprocket trimming method for the multi-stage sprocket assembly

A multiple sprocket assembly for use in a bicycle comprising: (1) at least a large sprocket wheel and a small sprocket wheel, each of the large and small sprocket wheels having a plurality of teeth on an outer edge thereof, and the large sprocket wheel having more teeth than the small sprocket wheel; (2) each of the sprocket wheels being adapted to engage with a chain guided by a derailleur; the chain comprising a plurality of rollers connected in series by link plates. The multiple sprocket assembly is characterized in that the small sprocket wheel has at least two consecutive teeth, each with a portion of its side surface trimmed off, and the large sprocket wheel has at least three consecutive teeth each also with a portion of its side surface trimmed off, so as to avoid interference between the link plates and the large sprocket when the chain is being shifted from the small sprocket to the large sprocket. In a preferred embodiment, at least two of the trimmed portions on the small sprocket are formed on the first distal side surface, and the trimmed portions on the large sprocket contain at least two trimmed portions on the second distal side surface and at least one trimmed portion on the second proximal side surface. The side surfaces of the teeth of the small sprocket are trimmed in such a manner such that the escape roller will not be immediately lifted up, but will be pushed laterally as a result of the trimmed portions of the small sprocket. The side surfaces of the teeth of the large sprocket are trimmed in such a manner such that one of the surfaces contains an axially extending portion, which serves as a fulcrum for the engage roller to be pivotally engaged with the large sprocket.

Two sprocket tooth trimming methods and the structure thereof for the

Growing community of inventors

Taipei, Taiwan

Chwan-Cherng Wang