1928-01-01

Ground Gears and Transmission Design 280061

GROUND teeth for transmission gears are advocated because they can be made to the same degree of accuracy as the other fine working-parts of a motor-car.
The designing engineer is held responsible for conditions unfavorable to the adoption of gear grinding by the production department. Mr. Orcutt believes that cluster gears should be avoided because it is impossible to finish them accurately.
Fundamental principles of rigid shafts and correct bearing arrangements are laid down, and the degree of accuracy is specified for the fitting parts. Transmission-case design still needs development and study to avoid resonance.
Designs are recommended that will provide ample center distance to avoid pinions with a small number of teeth. The unmodified involute is recommended as the most satisfactory form of tooth.
Spigot bearings receive special consideration. Two designs of transmission are submitted, in one of which the spigot bearing is eliminated. Simplification is sought by reducing the number of gear sizes used. Four-speed transmissions require gears with only four different numbers of teeth.
Prominent engineers discussed, at the meeting, many of the points in the paper, explaining that their different opinions were caused largely by the difference between conditions in England and in America. Good cut-gears, even cluster gears forged and heat-treated by the best available methods, are said to be as accurate and satisfactory as other parts of the transmission.
American methods of design, based on maximum capacity in pounds-feet per dollar of cost, are described.
Among other points considered are the relative merits of form-grinding and generating-grinding methods; and lubrication, noise and efficiency.

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