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Prediction of heat generation in high speed bearings

Friction in a rolling bearing represents a wasteful power dissipation manifested in the form of heat generation. Heat generation inside a bearing arises from a number of distinct mechanisms which are influenced by many parameters. Several geometrically distinct features which each contributes to the overall energy dissipated are:
rolling element raceway interaction;
rolling element cage pocket interaction;
cage ring pilot surface interaction;
cage churning and windage drag. In order to estimate the heat dissipated in each contact, surface velocities and friction forces are required. Furthermore, the internal kinematics depending on the amount of lubricant present in the bearings is studied coupled with the energy balance. The force and moment equilibrium equations for each bearing element which describe the bearing balance, provide a realistic description of the rolling bearing performance. Existing hydrodynamic and elastohydrodynamic models are used to determine the normal and traction forces corresponding to the geometrical interactions between the different elements of a bearing. Cage churning and windage is one of the most difficult mechanism to analyse in a general way since it involves the turbulence due to rotation of a complex form in a biphase fluid; lubricant and air. An experimental programme was carried to obtain direct measurements of churning losses and to observe how these losses are influenced by parameter variations. The programme of tests was established to represent the engines running conditions. The influence of the various parameters classified from highest to lowest effect is:
speed;
oil flow;
oil temperature;
applied loads.
This project has resulted in the creation of 2 analytical tools (QUASAR for roller bearings and 3554 MK4 for ball bearings able to predict friction power loss occuring in high speed bearings. Their effectiveness has been demonstrated by correlations with the results of rig tests.

Reported by

Turbomeca
64511 Bordes
France
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