“Failure Analysis of 2 Liter 4 Cylinder Engine Turbochargers,”
This paper presents a study of the failure of several 2 liter four-cylinder engine turbochargers. The failed turbocharger components are presented to show the damaged components. Detailed computer simulations are also presented to explain the nonlinear dynamical behavior of these turbochargers and to explain the causes of failures with these high speed turbochargers.
The standard bearing type employed for the majority of diesel and automotive turbochargers is the floating bronze bushing bearing. This bearing type has been well researched for its dynamical characteristics. This bearing type was first introducedin the 1930’s by GM with the goal of reducing bearing friction losses.
From a linear stability standpoint, the floating bush bearing is inherently unstable at all speeds. The turbocharger first and second critical speed modes may be excited. The excitation of these modes creates distinct audible tones. All of the turbochargers utilizing floating bush bearings operate with subsynchronous whirling over the entire speed range.
The floating bush bearings are able to operate with bounded limit cycle motion due to the nonlinear forces generated by the floating bush inner and out ring pressure profiles.
Failure is essentially caused from the excitation of these unstable subsynchronous modes. It was determined, in particular, that the compressor end bearing was under lubricated and overloaded in all failed turbochargers. Some amounts of compressor inner bearing clearance wear will lead to impeller contact with the volute.