General modelling method of power losses in transmission with parameter identification

There is rarely a general or standard method to calculate the overall efficiency of a complete vehicle gearbox. This paper aims to develop such method which can possibly be applied to different types of transmissions in a flexible way and provide a platform to compare several different products from different OEMs or suppliers in parallel.

A number of standards and publications concerning the calculation of power losses specifically for one transmission component such as gears, roller bearings or specific phenomenon like oil churning are available in the literature. Different models from these sources are compared, selected and combined to obtain the resulting efficiency map of a complete gearbox system.

This paper presents the calculation of such a combined efficiency map of a transmission for an electric vehicle through either the standard models (ISO14179) for industry transmissions or this new joint overall model. The comparisons of available experimental data and calculations show that the result of the joint overall model has a better proximity to the test results. Nevertheless, the uncertainties in the input parameters of the model strongly affect the calculated power loss and the resulting efficiency of the gearbox. Parameter studies are conducted to determine the most influential parameters in the joint overall model. Several selected parameters are identified through experimental overall efficiency maps by classic parameter identification method and algorithm. On the one hand, a much better proximity is achieved. On the other hand, the identified parameters indicate the optimization potential of the component losses for benchmarking of transmissions.