The Research Of Lubricant Performance In Magnetic-fluid Bearings

Traction motors on trains are of high speed, are subject to high dynamic load, and run in tough environments, which present demanding requirements on the bearings. Statistics shows that the damage of bearings is the major type of incipient failures for motors. Hence, it is a focus for railway engineers to improve the dynamic load capacity and reliability of bearings under high speed conditions. Utilizing the fact that the viscosity of magnetic fluids changes with magnetic fields, it is possible to effectively improve the dynamic load capacity of bearings, and ameliorate the performance of lubricant in bearings. As a result, recently, magnetic-fluid bearings have gained the attention and interest of a lot of scholars. This paper studies the key problems in regard to lubricant performance in magnetic-fluid bearings, analyzes the magnetic field, temperature field, fluid field as well as the effects of bearing parameters on the lubricant performance and load capacities, and establishes a physics and mathematics model of the lubricant performance of magnetic-fluid bearings.We derived and established a mathematical model of magnetic-fluid bearings based on ferromagnetic fluid dynamics, theory of lubrication in sliding bearings, which involve the film thickness equation, viscosity equation, load capacity equation, Reynolds equation, and other basic equations. Later, considering the effects of external magnetic fields, the equation for the viscosity of magnetic fluids was modified to obtain the relations between viscosity and temperature, viscosity and pressure, as well as other relations when subject to external magnetic fields. We designed the external field for magnetic-fluid bearings, calculated the magnetic distribution in bearings, and verified that the external field could guarantee the minimal magnetic field intensity to provide required viscosity. On the basis, we utilized the finite difference method and an analytical method which is based on the pressure function of infinite-wide bearings respectively to solve for the pressure distribution in the lubricant film in magnetic-fluid bearings. We obtained the pressure distribution in lubricant films, capacity loads, angles of shafts, as well as other steady-state variables. Finally, according to the principle of fluid-structure interaction, we analyzed the temperature field and fluid field in the lubricant region in magnetic-fluid bearings, introduced the cavitation model, and analyzed the temperature distribution and lubricant film pressure distribution in bearings under different eccentricity. The work would provide the theory basis for subsequent magnetic-fluid bearing design and optimization.