Measurement of Dynamic Characteristics of a Herringbone-grooved Hydrodynamic Journal Bearing used in a Notebook Cooling Fan

Lubricant of hydrodynamic journal bearing substitutes the steel ball of ball bearing to support the shaft under rotating. The lubricant-film force, which is often defined by a set of linear stiffness and damping coefficients, plays a critical role in a hydrodynamic journal bearing. This study presents an experimental method to determine the stiffness and damping coefficients of herringbone grooved hydrodynamic journal bearing used in a cooling fan. In this work, we will discuss the static loading effects and rotating speed effects on the stiffness and damping coefficients. The experimental rotating shaft used in this study is perpendicular to horizon. To simulate the traditional rotating shaft parallel to horizon, which needs to sustain the gravity of its weight and generates an eccentricity, we use an electromagnet to produce a static magnetic force attracting the rotor and generate the static eccentricity of the rotor. The experiments indicate that the using of the electromagnetic loading increases the stiffness and damping effects of hydrodynamic bearing. However, with the growth of the static loading, the values of the dynamic coefficients become more unstable. It means the nonlinear forces of the lubricant film become stronger under the larger loading and eccentricity. From the rotating speed effects on the stiffness and damping coefficients, with the growth of the rotating speed, the stiffness coefficients become larger. However, comparing to the static loading effects, the static loading effects can affect the stiffness and damping coefficients of lubricant film of a hydrodynamic bearing more greatly.