TOOTHED and friction-gearing are said by the author to be the two distinct classes of power transmission between two shafts, and the silent chain he describes is in the toothed-gearing class according to his statement, since it has a fixed speed-ratio and causes a bearing pressure that varies almost directly with the power transmitted. It is argued that, because of its elasticity and the peculiar method of contact with the teeth of the sprocket, the silent chain constitutes a medium that absorbs shocks and variations in angular velocity, and has a bearing action similar to that of a belt.
The improved silent chain is made of stamped, arch-shaped link-plates assembled in alternate succession and joined by pins that act as bearings. The spacing of the pins forms the “pitch” of the chain. When assembled, the chain can be considered a flexible gear or rack. The projecting teeth of the link-plates engage the sprocket-wheels over a considerable arc of the periphery of each and reduce the pressure per tooth, thus minimizing tooth-wear.
Illustrations and descriptions of the rocker-joint, the pin-type joint and the constant-pressure-angle chain are presented and, in addition, a typical layout employing the triangular and other types of drive. In conclusion, it is said that all engineering requires compromises in the design of parts and that this is true also regarding silent-chain drives. The object of their use is silence and satisfactory length of life, both of which are controlled mainly by design; hence, great care should govern the design. The successful drives are those that have been developed after careful consideration of the advantages to be gained and the pitfalls to be avoided.