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Tapered roller bearings have proven successful in a number of high-volume automatic transaxle designs. Typically, tapered roller bearings are required to carry high loads generated by helical and hypoid gears. To meet the demands of a successful design, a number of factors must be considered in the selection and application of tapered roller bearings. This paper presents a discussion of these factors as well as results from Chrysler's transaxle testing. Selection of tapered roller bearings is based on the transmission duty cycle developed using load and speed histograms, gear data, size constraints, and life requirements. A bearing life analysis considering the total transaxle system is conducted using a sophisticated computer program. Various system effects are analyzed including the load/speed cycle, housing and shaft rigidity, lubrication, bearing setting, thermal effects, and bearing internal design.

Automotive transmissions and transaxles use aluminum housings for weight reduction and tapered roller bearings for increased reliability. The initial bearing setting is obtained by using selective shims to account for tolerance variations of the transmission or transaxle components. Aluminum transmission and transaxle housings have a coefficient of thermal expansion approximately twice that of steel shafts and bearings. This difference results in a change to the initial bearing setting, as temperatures vary. For a direct bearing mounting arrangement (cup adjusted), the bearing setting becomes looser as the operating temperature increases, and tighter as the temperature decreases. Improved operating bearing setting is achieved through the use of a thermal compensating bearing.

This paper explains and quantifies the torque sources within a tapered roller bearing with emphasis on the torque performance of the rib-roller contact. The two major sources of torque, raceway contacts and rib-roller end contacts, are discussed and some general comments offered regarding the operating conditions for which each source is predominant. A description is given of the geometry of the cone rib-roller end contact. The sliding that occurs within the contact ellipse is used to develop the discussion of the torque due to the rib-roller end contact. Some specific examples are used to demonstrate the amount of torque contributed by each of the major sources.