Influence of hydraulic losses on the friction of roller bearings

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Frictional torque is a significant parameter to describe the efficiency of a roller bearing. It is a result of internal friction which influences the heat generation in the bearing and also determines its losses. The total losses of a bearing can be divided into different parts. The main part is mechanical friction which results from contact forces between rolling elements and the runway as well as rolling elements and the cage. The second part of total friction is caused by displacement of lubricant and churning, called hydraulic losses. To determine these losses bearing manufacturers provide empirical equations considering the influence of lubricant by various factors. Some of these influencing factors are assigned by approximation. In a project financed by DFG the applicants carried out basic research on vertical bearing arrangement to investigate hydraulic losses. Thus studies take into account rotationally symmetrical operating conditions with view to load and lubricant distribution in the bearing and provide important insights regarding the factors and the occurring effects. These studies provide conditions for the investigation of hydraulic losses of horizontally bearing arrangement with oil bath lubrication and non-uniform distribution of the lubricant, which are planned as part of this follow-up project. The aim of the follow-up project is the development of technical -mathematical calculation models which enable to calculate the total friction torque, taking into account hydraulic losses at rotationally asymmetrical operating conditions. These calculation models are created and validated by using a specific combination of experimental tests as well as MBS and CFD simulations considering oil bath lubricated bearing arrangements. For the expert the project results delivers the opportunity for analytical or numerical calculations to take the fluid flow related losses of every bearing part surface into account, which is not possible with the state of the art equations.