Generally, planetary gear type traveling reduction gear is composed of multiple planetary gear stages and has a hollow sun gear in the last stage planetary gear. In designing reduction gear, it is important to evaluate accurately the bending stress at the tooth root of the sun gear as the sun gear is the weakest component in the reduction gear system. Although bending stress can be calculated easily using gear standard codes such as the American Gear Manufacturers Association (AGMA) and International Organization for Standardization (ISO) 6336 for almost all gears, meticulous calculation is needed for the hollow sun gear because of its low backup ratio (rim thickness divided by tooth height) and comparatively large root fillet radius. In this study, a finite element analysis (FEA) is carried out to investigate the effect of rim thickness and root fillet radius on bending stress at the tooth root of the hollow sun gear. In standard codes, bending stress at the tooth root is calculated linearly with a constant slope for the backup ratio below 1.2. However, the effect of the rim thickness on bending stress is more complex in the planetary gear system. Bending stresses calculated by FEA with various backup ratios and root filler radii are compared with the bending stresses calculated by the standard codes.

Dynamic characteristics of a tilting pad bearing strongly depend on the direction of applying load as well as the magnitude. As the bearing load of geared compressor are determined by aerodynamic forces of impellers and mesh forces of helical gears in accordance with operating speed, dynamic coefficient of each bearing also varies with respect to rotor speed. Hence, in order to ensure rotordynamic stability of geared compressor, accurate estimations of bearing loads and corresponding dynamic characteristics of tilting pad bearings in accordance with operating speeds are highly requested. In this study, bearing dynamic test rig was developed based on floating bearing housing design, with speed range from 3000 to 32,000 rpm. In order to precisely estimate lateral critical speeds and the stability of pinion rotor of integrally geared compressor, the experimental investigation has been carried out on five pads tilting-pad journal bearings of 45 mm in diameter. Static eccentricities of the tilting pad bearings were investigated with various load directions and corresponding dynamic characteristics were also obtained. Multifrequency excitations have been used to evaluate the nature of frequency dependency of the bearing dynamic coefficients. Using experimentally identified dynamic coefficients of rocker-back type tilting pad bearing with respect to rotating speed, rotordynamic analysis of gear-driven pinion rotor was carried out and compared with shaft vibration measurement. The predicted rotor behavior showed good agreement with measured one.

In this paper it was attempted to treat the hydrodynamic journal bearing as a time-based nonlinear reaction source in each step of rotor rotation in order to observe the bearing effect more realistically and accurately in stead of the conventional method of simple linearized stiffness and damping. Lubrication analysis based on finite element method is employed to calculate the hydrodynamic reaction of bearing and Newmark's method was used to calculate the rotor dynamics in the time domain. Simulation for an industrial electrical motor showed remarkable results with differences compared to those by the conventional method in the dynamic behavior of the rotor.