Hybrid Geared Traction Transmissions,
TRANSMISSION RESEARCH INC CLEVELAND OH
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Roller traction drives and geared planetary drives have the common characteristic of multiple drive elements clustered symmetrically around a central member. This form of construction, adopted in order to maximize torque capacity, results in the drive input and output members being coaxial. Geared planetary drives are associated with high torque delivered from a unit of low frontal area, whereas fixed ratio and variable ratio types of traction drives are renowned for their ability to accept high input speeds at moderate torque levels with least noise. A combination of the two-drive systems retain the feature of coaxial construction and results in a geared section which is capable of providing high torque and a traction section which transfers torque from the toothed pinions to the high-speed input member. Direct coupling of the traction planet rollers with the pinions of the geared unit allows generation of a speed ratio much higher than possible from a planetary unit. This present work explores the basic configuration of geared traction drives, outlines geometric and structural factors to be considered in their construction, and describes current work on hybrid helicopter transmissions rated at 500 and 3000 hp.