Minimally Invasive Contact Temperature Measurement in Lubricated Rolling-Sliding Contacts using Thermoelectric Thin-Film Sensors

• Applicants: Dr.-Ing. Thomas Lohner; Dr. Tarek Lutz
• Subject Area: Engineering Design, Machine Elements, Product Development
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 544948187

The contact temperature is an important state variable of lubricated rolling-sliding contacts in machine elements such as gears or roller bearings, since the lubricant properties are highly temperature-dependent having an impact on the power loss. Due to the measuring principle, current thermoresistive, thermoelectric and optical measuring methods for lubricated rolling-sliding contacts with rolling elements made of steel are not minimally invasive and therefore do not provide direct validation data for dependency simulations between contact and sensor data. The overarching goal of the joint project between FZG and NMI is the design of thermoelectric thin-film sensors for minimally invasive measurement of the contact temperature in lubricated rolling-sliding contacts with rolling elements made of steel. Such contacts are mostly found in gearings and roller bearings of transmission systems. The targeted use of the thermoelectric effect circumvents the restrictions of previous measurement methods, which result from the necessary electrical insulation from the substrate material or the optical transparency of a rolling element. Electrical insulation through the lubricant film in the rolling-sliding contact is also not necessary, so that, for example, electrically conductive transmission fluids with a functional portion of water can also be examined. To achieve the project goal, the focus is on the design of minimally invasive thermoelectric thin-film sensors made of constantan on sensor disks made of case-hardened steel typical of gearings. As part of a total of eight work packages, a requirements analysis is carried out initially, taking into account the geometric and process-related boundary conditions. Subsequently, minimally invasive thermoelectric thin-film sensors are designed with iterative adaptation of the sensor architecture and the measurement chain taking into account the electrical properties of the manufactured thermoelectric thin-film sensors. After a static functional verification and achievement of the first milestone, the transfer and the functional verification for rotating rolling elements are carried out on a twin-disk tribometer. The second milestone is reached by successfully demonstrating the function of thermoelectric thin-film sensors in the highly-stressed rolling-sliding contact with rolling elements made of steel. The measurement results obtained are analyzed by means of numerical calculation of the contact temperature and thermoresistive reference thin-film sensor measurements. The conclusion is a synthesis of all findings for transfer to machine elements. By means of minimally invasive thermoelectric contact temperature measurement, the significance and possibilities of current thin-film sensors are expanded. With positive project results for highly-stressed rolling-sliding contacts under fluid-film lubrication, a transfer of the findings to spur gears with mixed lubrication is planned.

• DFG Programme: Research Grants
• Co-Investigators: Professor Dr. Jannik Meyer; Professor Dr.-Ing. Karsten Stahl