Characterization of wear mechanisms in exhaust-exposed, unlubricated tribological systems

Project description

Increased environmental and efficiency requirements are significantly increasing the complexity of today's combustion engines, which are fueled by a wide variety of operating materials. Multi-stage supercharging, exhaust gas recirculation, and aftertreatment result in a high level of control and regulation in the exhaust system, which is why several valve systems and actuators must be used. The unlubricated bearings of these exhaust flaps are subject to significant wear due to high thermal loads and contact with the exhaust gas atmosphere. They are therefore considered critical tribological systems, characterized by a high probability of failure and a short service life.

Until now, tribological characterization of these bearings has mostly been based on complex and costly tests on complete engines. As a result, the targeted, application-specific further development of materials systems has been slowed down, and participating suppliers have been dependent on cooperation and knowledge transfer with engine manufacturers. As an alternative to this lengthy process, Fraunhofer IWM, in collaboration with the Institute for Applied Materials – Reliability and Microstructure (IAM-ZM) at the Karlsruhe Institute of Technology (KIT), has developed and validated a time and cost-efficient qualification methodology specifically for these exhaust-exposed tribosystems, which can replace complex full engine tests.

The qualification strategy consists of two complementary test methods, the suitability of which was verified within the project by comparison with worn components from field tests. A linear reversing sliding test with a line contact geometry was used for quick and easy materials screening. For application-oriented tribological testing, a new test setup was also developed that includes a shaft-bushing contact with application-specific dimensions and can be exposed to a real exhaust gas atmosphere. The final validation and evaluation of the strategy by comparison with worn field components demonstrated the strategy's suitability and the high transferability of the results.

Transfer of project results to the following Fraunhofer IWM R&D services for companies:

• Characterization and qualification of unlubricated tribosystems
• Application-oriented component testing
• Fast and simple materials screening for new materials systems in the exhaust system