Earticle

The compressor wheel and shaft assembly significantly influence the structural stability and durability of high-speed rotating turbochargers. In this study, the structural characteristics of the compressor wheel were investigated under a press-fit condition and axial loads of the lock nut under centrifugal load. Finite element analysis was performed based on an axisymmetric compressor wheel model. Stress distribution, contact pressure, and deformation characteristics were analyzed by combinations of boundary conditions, such as press-fit, axial loads, and rotating speeds. As a result, high local stresses were generated at the shaft contact surface and the back wall of the compressor wheel. However, the introduction of press-fitting significantly decreased the overall stress levels at the back wall and contact areas. These findings suggest that press-fitting stabilizes the contact state and improves the structural integrity by inducing stress redistribution.

In this study, the structural analysis for the compressor wheel of a high-speed rotating turbocharger is presented, and the failure phenomenon that occurred during the durability test is analytically reproduced. Next, in order to set the optimization conditions, the stress for design shape, fastening force, and press-fit condition were analyzed. As a result, the maximum stress in the failure areas increases as the fastening force increases. Therefore, in order to improve the durability of the compressor wheel, the axial force is reduced while applying the press-fit between the wheel and the shaft. Meanwhile, when the shape of the back surface of the wheel was changed, the stress was additionally reduced by approximately 8.5%.

The paper presents the optimal design of a oil-free two-stage compressor, which is driven by 75 kW motor at an operating speed of 39,000 rpm, and the pressure ratio of which is up to 4. First, an attempt is made to obtain the optimal design of a bump bearing which supports a compressor rotor. Second, bump bearings and shaft are considered simultaneously, and the weighted sum of rotor weight and frictional torque is minimized. Finally, the optimal geometry of compressor wheel is considered. The mean efficiency and the - minimum efficiency are maximized respectively. The results presented in this paper provide important design information necessary to reduce the energy loss.

Hot-forging Process and die design was made for a large-scale compressor wheel of Ti-6Al-4V alloy with 2-D FE analysis. The design integrated the geometry-controlled approach and dynamic materials modelling(DMM). In order to obtain the processing contour map of Ti-6Al-4V alloy based on DMM, compression tests were carried out in the temperature range of 915$^{\circ}C$ to 1015$^{\circ}C$ and the strain range of 10$\^$-3/s$\^$-1/ to 10s$\^$-1/. In the die design of the compressor wheel using the rigid-plastic FE analysis, forging dimensional accuracy, the capacity of the forging machine and defect-free forging were considered as main design factors. The microstructure of hot forged wheel using the designed die showed a typical alpha-beta structure without forging-defects.