Turbochargers are commonly used in reciprocating compressors and internal combustion engines to improve overall efficiency, thereby reducing fuel requirements. In reciprocating compressor applications, turbochargers typically operate in the range of 15,000 rpm to 30,000 rpm. These turbomachines operate at higher rotational speed in automotive applications, often exceeding 100,000 rpm. These high speeds result in bearings that are often highly non-linear, with large limit cycle shaft orbits and high subsynchronous vibration levels. These large orbits also result in much higher power losses than would be observed for the same bearing with low vibration levels. These devices are often used in automotive applications, where there are significant cost pressures, ruling out more expensive bearing options such as tilting pad bearings. There is a need for bearing designs that are effective at stabilizing turbochargers and are also low cost.
In this paper, a theoretical turbocharger for a reciprocating compressor application is considered. The initial design incorporated plain axial groove bearings. Several replacement bearing options were considered, including pressure dam bearings and tilting pad bearings to improve rotor stability. The pressure dam bearing is used to impose a load on the shaft, making it run off center. This feature reduces subsynchronous whirl instability and also reduces power loss. The tilting pad bearing eliminates self-excited forces from the bearings but has increased power loss when compared to fixed-pad bearings. Starved lubrication of the tilting pad bearing reduced the power loss but also reduced the stability margin. The application considered for this paper is a larger turbocharger with a rotational speed of 25,000 rpm, and is unstable with conventional bearings.