1. Field of Use
This invention relates generally to power transmission systems such as are used for controlling the swing mechanism in mobile cranes, or the like. In particular, it relates to power transmission systems comprising a torque converter driven by a prime mover through a modulatable torque converter clutch, and a transmission driven by the torque converter and comprising a pair of alternately operable modulatable transmission clutches.
2. Description of Prior Art
In some apparatus, such as cranes and power shovels, it is common to employ a prime mover, such as an internal combustion engine, to drive a torque converter to raise or lower the crane or shovel boom. However, the use of an engine-driven torque converter transmission system to swing the upper section of a machine on which a boom is mounted is known but not widespread. For example, in some prior art systems, a single prime mover is employed to drive two separate torque converters, one for effecting hoisting and boom control functions, and the other for effecting operation of the swing mechanism by means of a pair of "dry" type friction clutches. In such systems, the dry-type clutches in the swing mechanism are subject to wear, but wear can be reduced by modulating the speed of the torque converter which furnishes power for the swing clutches. Furthermore, modulation of the torque converter for the swing clutches reduces shaking and vibration which can become severe and dangerous, particularly when relatively long booms are swung. U.S. Pat. Nos. 3,376,981 and 3,221,896, disclose examples of prior art type transmission systems of present interest.