Also found in: Dictionary, Thesaurus, Wikipedia.
a device in which mechanical energy and motion at specified forces (torques) and speeds (rpm) are transmitted and converted by means of a fluid. Hydraulic transmissions are used in ships, diesel locomotives, motor vehicles, aircraft, lathes, machine tools, road-building machinery drives, compressors, ventilators, pumps, and so on. They are classified according to the principle of operation into two basic groups, the positive displacement type and the hydrodynamic type. They are also divided into those that convert or transmit mechanical power (hydraulic power transmissions) and those that convert motion for automatic control purposes.
Hydraulic transmissions may be combined with gearing so that the motion will be transmitted from the driving shaft via the hydraulic transmission, the gearing, or both simultaneously. Devices operating on this principle, known as hy-dromechanical transmissions, transmit larger amounts of power and have a greater control range than is possible with the usual hydraulic transmission.
Hydraulic transmissions are versatile, durable, and easily controlled, and they protect mechanisms from overloading. For these reasons they are widely used in modern machines.