Operating condition-dependent model for describing the electrical impedance of rolling bearings for sensory utilization

• Applicant: Professor Dr.-Ing. Eckhard A. Kirchner
• Subject Area: Engineering Design, Machine Elements, Product Development
• Term: from 2021 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 467849890

The state of research shows that relevant influencing factors of the electrical capacitance of a rolling bearing, which depends on the operating condition, are neglected. The rolling contacts outside the load zone have an influence on the impedance of the rolling bearing and contribute to an improvement of the model correlation between load and impedance. To describe the impedance of unloaded rolling elements, the model of a generally curved capacitor with operating condition-dependent geometry corresponding to the point contact between ball and inner or outer ring is used. The objectives motivate the following working hypotheses:WH I. The separating lubricating films of unloaded rolling elements affect the electrical capacitance of rolling bearings; lubricating film thickness on unloaded rolling elements, bearing clearance, and the density of rolling elements must enter into the capacitance.WH II. The boundary factors can be replaced by an operating parameter-dependent physically motivated model to describe the measured impedances of rolling bearings with point contact without empirical factors.In the project applied for, the difference between measurement and calculation is to be reduced to a level sufficient for a sensory concept by considering the unloaded rolling elements in the impedance model at arbitrary load angles for rolling bearings with point contact. This results in the following project objectives:1. description of the load-dependent position and kinematics of the rolling elements outside the load zone for calculation of the capacity of the unloaded rolling contact.2. mapping of the complete impedance contribution of all rolling contacts.3. validation of the extensions in tests on different rolling bearings with point contact in the relevant operating range.Investigations also in mixed friction are necessary to understand the electrical behavior of rolling bearings. The limitation to small measuring voltages is necessary to avoid unwanted current passage and damage to rolling bearings or lubricant. However, the focus is on the hydrodynamic operation of rolling bearings, and the influence of size is investigated randomly on a second size.Changes in the lubricant due to contamination or aging are excluded, as is damage to the rolling bearing. The lubricant is filtered and replaced regularly. The rolling bearings are examined in short-term tests, and a few preliminary tests are also carried out to determine a calculated upper limit for the accumulated damage up to which the rolling bearings can be examined without alteration. In the project, single-row rolling bearings with point contact are considered, primarily stationary at EHD conditions but also in mixed friction. Due to the very short-time events during the overrolling of a rolling contact, the findings from the investigation can also be transferred to rolling bearings with variable-speed loading.

• DFG Programme: Research Grants