Modelling and Simulation of Gearset Behavior : Effects of Manufacturing Errors and Electrification

Sammanfattning: Due to electrification, new demands are imposed on gears regarding e.g., quality, noise, lubrication, and gear ratio.Therefore, a better understanding of gearset meshing and operation is needed. Experiments are valuable tools, butalso tend to be cumbersome and time consuming. Moreover, contact pressure cannot be measured satisfactorily.Thus, a simulation tool is needed. In this thesis, an LTCA simulation tool is developed, which simulates meshingof gears with manufacturing errors (ME). Contact is found from common normal directions together with acompliance condition, instead of using a predetermined load distribution. The LTCA accounts for non-Hertzianpressure, contact outside the nominal line of action (LOA), and tip contact. Contact pressure of gearsets withdifferent combinations of ME tolerances is simulated, i.e., relating deviations in geometry caused by manufacturingto performance of the gearset.The transmission of motion should also be smooth. This is quantified by the transmission error (TE). TE issimulated together with contact pressure. Since they tend to counter-vary, optimization is performed. Designcurves are presented to show how to choose tolerances to simultaneously optimize TE and contact pressure.It is concluded that ME adversely impact gearsets. Too tight tolerances, however, increase the risk of unjustifiedscrapping, which increases production time and cost, material waste, and environmental impact. To avoid this, it issuggested to use tip contact threshold torque as a single metric to assess ME, i.e., basing assessment on performanceinstead of only geometry. The feasibility of the method is shown in a case study, where some scrapping is shownto be unjustified.To account for lubrication, a thermal elasto-hydrodynamic lubrication (TEHL) method is developed. It findslubricant pressure and temperature by solving the Reynolds equation and the heat equation, and considers varyingviscosity and density, as well as cavitation. Load distribution found from the LTCA is used as input to includeME. Results show that ME also cause an increase in temperature and a decrease in film thickness.Apart from the single gear pairs, a study of a two-stage gear reduction used in an electric vehicle is presented.Two stages open further possibilities for optimization. This is done by finding the optimum dog leg angle bymeans of the lowest reaction forces, which in turn allows for smaller bearings. The decreased enclosed volume ofthe gearset also results in a lower housing mass. Both propulsion and regenerative braking are accounted for