Torque amplifier

A torque amplifier is a mechanical device that amplifies the torque of a rotating shaft without affecting its rotational speed. It is mechanically related to the capstan seen on ships. Its most widely known use is in the power steering on automobiles. Another use is on the differential analyzer, where it was used to increase the output torque of the otherwise limited ball-and-disk integrator. The term is also applied to some gearboxes used on tractors, although this is unrelated. It differs from a torque converter, in which the rotational speed of the output shaft decreases as the torque increases.

The first electric-powered torque amplifier was invented in 1925 by Henry W. Nieman of the Bethlehem Steel Company of Bethlehem, Pennsylvania. It was intended to allow manual control of heavy equipment; e.g., industrial cranes, artillery, etc. Vannevar Bush used Nieman's torque amplifier as part of his differential analyzer project at M.I.T in the early 1930s.Lord Kelvin had already discussed the possible construction of such calculators as early as the 1880s, but had been stymied by the limited output torque of the ball-and-disk integrators. These integrators used a ball bearing pressed between the surface of a rotating shaft and a disk, transmitting the rotational force of the shaft to the disk. By moving the ball along the shaft, the speed of the disk could be smoothly varied. The torque on the output shaft was limited by the friction between the bearing and the disk, and as these were generally made out of friction-limiting metals such as bronze to allow smooth motion, the output torque was quite low. Some calculating devices could use the output directly, and Kelvin and others built several systems. But in the case of a differential analyzer, the output of one integrator drove the input of the next integrator, or a graphing output. The torque amplifier was the advance that allowed these machines to work.

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