Gangwar, H., Anderson, R., and Kim, K., "Ultra-Long Life Oil-Free Supercharger for Fuel Cell and Hybrid Vehicle Power Trains," SAE Technical Paper 2013-01-0478, 2013, doi:10.4271/2013-01-0478.
Automotive hybrid electric vehicle applications require 1 million (or more) start-stops. This same level of start-stops is also required for hydrogen PEM fuel cell vehicles. In this investigation, a test regime is developed to stress the failure mode of a set of airfoil journal bearings caused by start-stops, and conceive a proper improvement to meet the requirement. Airfoil bearings have been limited by the number of start-stops due to their inherent wearout of coating(s) at low speed. A complete electronic air cathode compressor (electronic supercharger) assembly is tested, employing a pair of φ25 mm journal airfoil bearings. The foils have 34 μm of surface PTFE coating. After 50,000 start-stops, the coating is worn through. Next an improved system is tested, which has modified coating on the bearing journal surfaces. These bearings are examined roughly every 250,000 start-stops. After 1 million start-stops, the coating has worn 5 μm. The data is further analyzed using statistical reliability techniques. These predict an L₁₀ of 8.7 million start-stops. The cost of modifying the treatment to extend the lifetime to 1 million start-stops is a 1% price change (off a base of $20). This shows the technology is feasible for automotive usage.