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Publisher Summary This chapter discusses power units and power transmissions. A good design demands that the power source is placed as close as possible to the driven unit. Shafts used in power transmissions will invariably be either solid- or thick-walled tubes. In gearboxes and similar assemblies, the shafts will be comparatively short and the design objective will be for these to be made as stiff as possible. Torsional stresses are unlikely to be of major concern. In many applications, a transmission shaft will be machined, will incorporate many different diameters along its length, and may contain splines or serrations and through-diametric holes. All these features add up to stress discontinuities and therefore adequate attention must be given to avoiding a sudden change of section and to ensuring adequate blending radii. For relatively short straightforward shafts where torque is transferred from one end to the other, the stresses are limited to torsion and bending. An important element in power transmission systems is coupling whereby two relating shafts can be joined together. For large-diameter shafts revolving at low speeds, the simplest device is a solid flanged coupling, but this does not allow for any misalignments in the shafts. Smaller installations would use a coupling that would be appropriate for small shaft offsets and deviations in parallelism. |
