Sizing Criteria for Traction Drives,
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION CLEVELAND OH LEWIS RESEARCH CENTER
Pagination or Media Count:
The development of reliable, lightweight, high-power traction drives for aerospace and terrestrial applications is rapidly expanding. Adjustable-speed drives have been used in a variety of commercial applications for over 50 years. Recent improvements, in terms of fluids with higher traction, materials with greater fatigue resistance, and design techniques with greater accuracy, have helped to increase their performance and reliability. When designing or selecting a traction drive, one must be concerned with the service life of the unit. Presently, very little fatigue data are available from well-controlled traction contact fatigue tests. However, many investigations have been conducted on rolling-element fatigue for rolling-element bearings. Because of the similarity in the expected failure mode, namely, rolling-element fatigue, the life analysis methods used to establish rolling-element bearing capacity ratings should be applicable to determining the service life and capacity of traction drive contacts. The purpose of this paper is to present a simplified traction drive fatigue analysis, which was derived from the Lundberg-Palmgren theory. A second objective is to use this analysis to investigate the effects of rotational speed, multiplicity of contacts, and variation in the available traction coefficient on traction-drive system life, size, and power capacity. Simplified equations are provided for determining the 90 percent survival life rating of steel traction-drive contacts of arbitrary geometry. References to life-modifying factors for material, lubrication, and traction will be made.