TABLE OF CONTENTS Long drive shafts are used on cooling towers, some diesel engine-driven equipment, and wherever the shaft ends are spaced far apart. Figure 11.1 shows a typical application. Driveshafts are also used on vehicles with front-engine, rear-wheel drive. On vehicles, the driveshaft is used to span the distance from the transmission to the differential with rotating power. There is large relative motion between the differential and transmission because the transmission is rubber-mounted and the differential is spring-mounted. Two couplings or universal joints allow this large, dynamic, angular motion. This testifies that a driveshaft with two universal joints does not need to be precisely aligned at all. In industrial applications, the universal joint is rarely used because of speed variations and other limitations. Other couplings are smoother and can transmit more horsepower at higher speeds.
The driveshaft, however, is still a necessity where long distances need to be crossed. This configuration is also common on large machines, such as turbines and diesel-driven pumps, where the dimensions and spacings are proportionately larger, requiring either a long shaft extension or a connecting driveshaft with two couplings. The driveshaft is preferred for maintenance convenience, making either machine easier to remove. A long shaft extending outward from inside a machine to several feet externally would be difficult to manufacture, would create large bending stresses at the bearing, and would...
