Active Control of Hydrodynamic Gas Film Bearings with Piezo-Actuator

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Hydrodynamic gas film bearings are used for supporting high-speed rotating machinery such as gas expander, turbo-pomp, high-speed motor and so on. Especially, stepped gas bearings are widely used for such machinery because of their simple structure, high load carrying capacity and high stability. However, conventional type of stepped gas film bearing has disadvantage of low damping capacity for sudden changes of applied load, for example, impulsive load.The aime of this resarch is to develop a new type of hydrodynamic stepped thrust gas film bearings by use of the piezo-type actuators to control activily the step height. The experimental apparatus was designed, in which the range of rotational speed is from 0rpm to 30000rpm and the shaft is rotated with built-in-type high speed motor. The number of pads is six, the pad extent angle is 55deg., the outer diameter of pad is 30mm, the range of applied load is from 1.5kg to 2.62kg, respectively. These variables were determined by the hydrodynamic lubrication theory including the inertia effects at the step. At the present step, the rotating part of apparatus has been completed, and the stator including bearing surface is now under manufacturing. Using such type of bearing, the damping capacity of gas film can be controled actively with varying the step hight through piezo-actuator.On the other hand, the static and dynamic characteristics of stepped thrust gas bearings are theoretically examined for a wide range of operating conditons. From the numerical results, the combined effects of fluid film inertia at the step and compressibility of gas film on the bearing characteristics were clarified.