Recent Advances in Impedance Modelling of Rolling Element Bearings

Steffen Puchtler

Value for the audience

The audience will be informed about recent advances in ball bearing impedance modelling, supplemented with a profound experimental design over a wide parameter range. Advanced bearing impedance models can also be of benefit for assessing the bearing voltage ratio in electric machine in order to estimate the risk of harmful bearing currents in electric machines.


Digitization in industrial applications drives the demand for cost effective, retro-fitable and design space neutral sensor concepts. Measuring load of rotating shafts, utilizing rolling element bearings as sensors is a promising solution: The Hertz’ian area of the raceway-rolling element contact as well as the lubrication film thickness depend on the applied load. Thus, the electric impedance of the bearing changes, which can be measured in-situ. Therefore, a precise modelling of the impedance is key to enable the sensory utilization of arbitrary bearings in their surroundings.

In this presentation, a comprehensive experimental study is shown. Radial deep groove ball bearings of different sizes, different radial clearances and different cage materials are investigated. The full factorial design allows an study on influences of rotational speed, axial and radial load, as well as oil temperature on the electric impedance measured at three different frequencies. Alongside the experimental results, a physics-based modelling approach omitting any correction factors is presented. Recent advancements include optimized semi-analytical calculation methods of the contact capacitance, improved calculation of position and impedance of unloaded rolling elements as well as approach of accounting for the cage influence on the bearing’s impedance. The model and the experiments are in good accordance for a wide range of operating parameters within hydrodynamic lubrication.


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