Simulation and Measurement of an Electric Driven Turbocharger Test Rig with Full Floating Ring Bearing

Abstract

The rotating shafts of automotive turbochargers are commonly supported in floating ring bearings with two fluid films in serial connection. They are – due to the high rotational shaft speed – often designed as full-floating ring bearings with a free rotating ring between shaft and housing. The ring is driven by the shear stresses on the inner and outer surface of the fluid films, which depend on the rotational speed gradient in the fluid and the pressure distribution in the fluid films. If this frequency meets a natural frequency of the system the oil-whirl locks in an oil-whip and causes a circular motion of the shaft in the bearing with very high amplitudes. Finding an optimal bearing design as a result of these nonlinear relations is a sophisticated task. Several parameters of the floating rings could be tuned to avoid such oil-whip effects. Hence, a holistic simulation approach is used to calculate the run-up of an investigated turbocharger by using the simulation software EMD, which contains solution methods for the nonlinear fluid film equations in order to solve them in every time step. However, the simulation has to be validated against measurements. For this sake, the ring speed is measured using a miniature eddy current sensor during an electric driven run-up on a test rig, yielding an integral quantity containing all relevant effects.