Dynamic behaviors of a high-speed turbocharger rotor on elliptical floating-ring bearings

Floating-ring bearings are commonly used in automotive turbocharger applications due to their low cost and their suitability under extreme rotation speeds. This type of bearings, however, can become a source of noise due to oil whirl-induced sub-synchronous vibrations. The scope of this paper is to examine whether the concept of a floating-ring bearing with an elliptical clearance might be a solution to suppress sub-synchronous vibrations. A very time-efficient approximate solution for the Reynolds equation to the geometry of elliptical bearings is presented. The nonlinear dynamic behaviors of a turbocharger rotor supported by two concepts of elliptical floating-ring bearings are systematically investigated using run-up simulations. For the first concept of elliptical floating-ring bearings i.e. the outer bearing of the floating-ring bearing changed in the form of elliptical pattern (see Figure 1(b) in the article), some studies have pointed out that its steady-state and dynamic performances are superior to plain cylindrical floating-ring bearings but, the nonlinear run-up simulation results shown that this type of elliptical floating-ring bearings is not conducive to reduce the self-excited vibration levels. However, for the second type of elliptical floating-ring bearings i.e. both the inner and outer films of the floating-ring bearing changed in the form of elliptical pattern (see Figure 1(c) in the article), it is shown that the sub-synchronous vibrations have been considerably suppressed. Hence, the second noncircular floating-ring bearing design is an attractive measure to suppress self-excited vibrations. Figure 1. Geometries of plain cylindrical and elliptical FRBs: (a) a plain cylindrical FRB; (b) the first concept of elliptical FRB; (c) the second concept of elliptical FRB. The oil film thicknesses are exaggerated for illustration.