Improved capacitance calculation of thrust bearings by combining EHL- and electric field-simulation
Value for the audience
The presented simulation model allows to determine the influence of the running conditions on the capacitance of a complete thrust bearing with higher accuracy compared to commonly used correction factors.
The capacitance of a thrust bearing is determined numerically by using a combined simulation model. The geometry of the deformed roller contact is calculated by performing an EHL-simulation. The simulation area contains the Hertzian contact area as well as the inlet and the outlet area of the roller contact. The lubricant properties density, viscosity and permittivity are calculated in dependency of the pressure and the lubricants inlet temperature. The Reynolds-equation is solved iteratively using the FBNS-algorithm that calculates the gap height, the pressure and the cavitation degree for every finite volume. Using theses values, the capacitance of each finite volume and eventually of the whole contact area is calculated.
The capacitance of the bearing components outside the contact zone is calculated by a FE-simulation using commercially available software ANSYS Maxwell. In this simulation, a segment of the thrust bearing is modelled, containing one rolling element and the associated parts of the bearing rings, the shaft, the mount of the standing ring and the lubricant. The distance between the rolling element and the bearing rings is adjusted using gap height values from the EHL-simulation. By performing an electric field calculation, the capacitance between the bearing components can be calculated. By combining EHL contact simulation with FE field simulation, scaling problems due to the different dimensions of the microscopic contact geometry and the macroscopic bearing component geometry can be handled.
With help of the combined model, the capacitance of a complete thrust bearing can be calculated without the need for correction factors. The results show good agreement with experimentally determined values and can help to improve the determination of the electrical properties of bearings in dependence on the operating conditions.