On-Engine Measurement of Automotive Turbocharger Turbine Blade Vibration

Automotive turbochargers are carefully designed to avoid resonance of the turbine blades and backwall, which can result in High Cycle Fatigue failures. Blade Tip Timing is an established technique which utilizes fiber optic probes to measure turbine blade displacements in real time on turbochargers spinning at upwards of 150,000 RPM. Historically, Blade Tip Timing measurements of automotive turbochargers have been made under steady-state conditions using a Hot Gas Stand. In an industry first, General Motors conducted testing of a turbocharger on a running gasoline engine to capture realistic exhaust pressure dynamics. A reference turbocharger was measured on an engine testbed running a production calibration; the same turbocharger was then tested on a Hot Gas Stand to observe how the blade behavior changed. Blade displacements were found to be lower on engine, because the dynamics of engine pulsation reduced the in-phase work available to drive the turbine blades, resulting in lower blade stresses and an improvement in calculated blade fatigue life. Testing also confirmed that key blade resonances had been successfully moved out of the operating space of the engine. Additionally, blade vibration was measured at multiple temperatures on the hot gas stand, and a clear trend was observed between blade temperature and frequency of vibration. The conclusion is that the new turbine design is ready for adoption and poses no concerns for High Cycle Fatigue. While on-engine testing is more challenging to perform, significant advantages are noted; on-engine testing provides a more realistic life estimate for turbine stages than can be obtained using hot gas stand data alone.