Page 275 - Steam Turbines Design, Applications, and Rerating

254 Chapter Thirteen

Figure 13.11 Hydroviscous drive. (Philadelphia Gear Corporation, King of Prussia, Pa.)

drives. Figure 13.11 shows a typical hydroviscous drive marketed by the
Philadelphia Gear Corporation under the trade name Synchrotorque.
The Synchrotorque variable-speed drive operates on the principle of
shearing an oil film to transmit torque. This hydroviscous (hydrody-
namic shearing) effect transmits torque in proportion to a variable
clamping force. For unrestrained loads, the higher the clamping force,
the faster the output speed. The input drive plate functions as the
driver. The output friction disk is faced with a suitably grooved
resilient material. The material couple between input drive plates and
output friction disks allows virtually infinite speed control right up to
100 percent of input speed. This simple phenomenon (based on estab-
lished hydrodynamic bearing principles) is the basis of controlled
torque transmission in hydroviscous drives.
More specifically, the input member accelerates the oil particles tan-
gentially, and a hydrodynamic film is established through the action of
the friction disk oil grooving. The oil particles also are acted upon by
centrifugal force, which accelerates them outwardly. This natural
pumping action ensures a uniform oil film across disk faces for con-