An investigation of the mechanics of tapered roller bearings

Abstract

This investigation is concerned with the performance of tapered roller bearings under a pure thrust load. The design and development of a suitable test rig is described in some detail and the results of friction torque and film thickness measurements are compared with values predicted using recent elasto-hydrodynamic theory. It is shown that the reaction torque on the outer race may be ascribed to two principal sources. Firstly, to viscous rolling friction depending upon the product of speed and viscosity, and secondly to metallic hysteresis depending upon the load. If the maldistribution of load due to small dimensional differences in the rollers, is taken into consideration close agreement is obtained between the experimental and theoretical values of friction torque for a wide range of loads and speeds. At higher loads a third source becomes significant due to sliding between the ends of rollers and the lip of the inner race. A further important effect of the uneven loading of rollers is its influence on the life of a bearing. It is suggested that improved roller matching would result in an increase in bearing life. Measurements of race and cage speeds, taken throughout the investigation failed to detect any cage slip. Electrical resistance measurements made across the races confirm the presence of a lubricant film of a thickness which is consistent with theory. A visual display of the voltage drop indicated that the degree of asperity contact dependedupon the surface finish and the thickness of the oil film. An analysis of the dynamics of the tapered roller bearingshowed that although the geometry leads to a gyroscopic couple acting on the rollers, its magnitude is small and of little practical importance.