Abstract
An electrically assisted turbocharger (EAT) is a technology that integrates a high-speed motor into the shaft of a traditional turbocharger. This integration is designed to enhance the transient response performance of the traditional turbocharger, further improving its operational efficiency and exhaust gas utilization. However, the motor integration brings complexity to the turbocharger structure and a new challenge to the stability of the turbocharger rotor-bearing system. In this paper, a five-node, 24 degrees-of-freedom rotor-bearing nonlinear dynamic model for the EAT is established by simplifying the model of the EAT using the lumped parameter method, and by using the Capone's model as well as the theory of the short-bearing approximation to obtain the nonlinear oil film force of the floating ring bearing (FRB). This study delves into the nonlinear dynamics of EATs supported by FRBs, focusing on oil whirl, oil whip, and total instability caused by oil instability. The effects of inner and outer oil film clearances in FRBs, motor rotor mass, motor placement, and oil film viscosity on the synchronous vibration, sub-synchronous vibration, and total instability are analyzed. The research results indicate that when the outer oil film clearance is larger than the inner oil film clearance, the system stability improves as Cout/Cin approaches 1. Increasing the motor rotor mass, placing the motor rotor farther from the bearing, and decreasing the oil film viscosity all lead to a decrease in system stability. The research reveals the complex dynamic behavior of EATs, providing a theoretical foundation for the future design of rotor-bearing systems in EATs.
