831304 Advances in Traction Drive Technology S. H. Loewenthal and D. A. Rohn National Aeronautics and Space Administration Lewis Research Center Cleveland, OH N. E. Anderson Propulsion Laboratory AVRADCOM Research and Technology Laboratory Lewis Research Center Cleveland, OH International Off-Highway Meeting & Exposition Milwaukee, Wisconsin September 12-15, 1983 Downloaded from SAE International by University of British Columbia, Sunday, August 19, 2018Copyright 1983 Society of Automotive Engineers, Inc. Downloaded from SAE International by University of British Columbia, Sunday, August 19, 2018ABSTRACT Traction drives are among the simplest of all speed changing mechanisms. Although they have been in industrial use for more than 50 years, their operating characteristics and performance capabilities are not widely known. This paper briefly traces their technical evo­ lution from early uses as main transmissions in automobiles at the turn of the century to modern, high-powered traction drives capable of transmitting hundreds of horsepower. Recent advances in technology are described which enable today's traction drive to be a serious candidate for off-highway vehicles and heli­ copter applications. Improvements in mate­ rials, traction fluids, design techniques, power loss and life prediction methods will be highlighted. Performance characteristics of the Nasvytis fixed-ratio drive are given. Promising future drive applications, such as helicopter main transmissions and servo-control positioning mechanisms are also addressed. FRICTION WHEELS OF UNEQUAL DIAMETER were one of the earliest speed changing mechanisms. It is speculated that their use even predates that of gearing "toothed" wheels, whose beginnings date back to the time of Archimedes, circa 250 B.C. (1). Even today, friction drives may be found in eauipment where a simple and economical solution to speed regulation is required. Phonograph drives, self-propelled lawnmovers, or even the amusement park ride driven by a rubber tire are a few of the more common examples. In these examples, simple dry con- *Numbers in parentheses designate refer­ ences at end of paper. tact is involved and the transmitted power levels are low. However, this same principle can be harnessed in the construction of an oil- lubricated, all steel component transmission which can carryhundreds of horsepower using today's technology. In fact, oil-lubricated traction drives have been in industrial service as speed regulators for more than 50 years. Despite this, the concept of transmitting power via traction is not widely known or understood. Although traction drives have been avail­ able for some time (2-6) it is perhaps since the mid 1960's or so that they have been con­ sidered serious competitors to conventional mechanical power transmissions. The earlier drives, particularly those targeted for automo­ tive applications, had their share of dura­ bility problems above nominal power levels. As a consequence, relatively few succeeded in the market place. The underlying reason for this was that certain critical pieces of tech­ nology were generally lacking. Designs were based on mostly trial and error. No uniform failure theories were available to establish service life or reliability ratings. The drive materials of the day were crude by today's standards. In short, traction drives were in their technical infancy. Prompted by the research for more effi­ cient automotive transmissions and bolstered by advancements made in rolling-element bearing technology, interest in traction drives has been renewed. Today's analytical tools, mate­ rials, and traction fluids are far superior to those available prior to the 1970s. This has led to the re-emergence of traction drives and the technology related to their design. It is the intent of this review to discuss the basic principles of these traction drives and to trace the evolution of