Determination of ball bearing impedances under steady-state operating conditions using a further developed rolling contact model with full lubrication

• Applicants: Professor Dr. Stefan Götz; Professor Dr.-Ing. Bernd Sauer
• Subject Area: Engineering Design, Machine Elements, Product Development
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 470273159

As a result of the increasing use of frequency converters to control variable speed drive systems, electric motors and generators, the number of damages caused by parasitic bearing currents (corrugation, cratering, lubricant oxidation) in rolling bearings is increasing. To predict or prevent possible bearing damage, electrical drive systems can be modelled with equivalent circuit diagrams, considering the relevant main components of the motor as capacitive and resistive equivalent variables. In this consideration, the rolling bearing also acts as a capacitor. Its electrical behaviour depends significantly on the lubrication and friction conditions. Currently, the description of the interaction between the tribological system and the resulting defined electrical behaviour is a challenging task, which is realized by electromechanical models of the rolling contact with the help of electrical capacitances using correction factors and correction functions. For this purpose, experimental and simulative investigations will be carried out within the scope of the project in order to improve the electrical modelling of the rolling bearing and thus enable the possibility of more accurate modelling of the drive system.The subject area will be investigated within the work program in two groups (modelling and experiment) and in two levels each (single contact and rolling bearing level). Modelling is performed by means of coupled mechanical and electrical simulation of the rolling contact and detailed consideration of the boundary influences (or the inlet and outlet area of the contact). Experimental results using impedance and charge curve measurements are used for validation. In parallel, limitations and applicability of the developed and existing electrical contact models (and correction functions) will be determined using the electrical field investigations. The aim of the project is to develop an improved rolling bearing impedance model for (initially) purely axially loaded ball bearings under full lubrication conditions. The validated impedance model is to serve as the basis for deriving a physically based electrical rolling bearing model for combined axial/radial loaded rolling bearings with point contact. The investigations focus on the exact description of the operating condition through the computational and experimental determination of the electrical contact capacitance in the rolling bearing. Investigations of the mixed friction condition and electrical aging processes or damage mechanisms are not the subject of the project.

• DFG Programme: Research Grants