Design and experimental investigation of a herringbone grooved gas bearing supported turbocharger

The design of an oil free turbocharger supported on herringbone grooved gas bearing was formulated as a multi-objective problem, which was solved by coupling a reduced order parametric model for gas bearing supported rotors with an evolutionary algorithm. The resulting Pareto curve offers the best possible tradeoff between the two competing objectives of maximizing the rotordynamic stability and minimizing the power losses. After manufacturing, the turbocharger was successfully operated up to 170 krpm, beyond a hybrid mode composed of a rigid body cylindrical and a flexural mode. Supercritical operation above a flexural bending mode on rigid gas lubricated bearings was possible due to the smart selection of the location of two balancing planes, to avoid the excitation of the flexural mode. A coast down test suggests minimum friction torque and therefore lift-off at 3 krpm. Bearing power loss tests performed at 40 ℃ and 100 ℃ showed that the herringbone grooved gas bearing supported oil-free turbocharger yields only 50% to 70% of the traditional semi-floating oil bearing supported turbochargers, which is a distinct advantage in terms of efficiency and cut in emissions. The theoretical and experimental results presented in this paper clearly demonstrate the rotordynamic feasibility of oil-free turbochargers supported on herringbone grooved gas bearings.