Samuel, K., Brigham, D., and Jennings, M., "Development and Validation of A High Fidelity Distributed Loss Powersplit Transaxle Model," SAE Technical Paper 2015-01-1153, 2015, doi:10.4271/2015-01-1153.
The powersplit transaxle is a key subsystem of Ford Motor Company's hybrid electric vehicle line up. The powersplit transaxle consists of a planetary gear, four reduction gears and various types of bearings. During vehicle operation, the transaxle is continuously lubricated by a lube oil pump. All these components consume power to operate and they contribute to the total transaxle losses which ultimately influences energy usage and fuel economy.In order to enable further model-based development and optimization of the transaxle design relative to vehicle energy usage, it is essential to establish a physics-based transaxle model with losses distributed across components, including gears, bearings etc. In this work, such a model has been developed. The model accounts for individual bearing losses (speed, torque and temperature dependency), gear mesh losses, lube pump loss and oil churning loss. The losses are implemented as physics based equations as opposed to 2D or 3D table data, to enable smooth acausal simulation. Required bearing loss data are initially obtained from bearing suppliers.To aid the model development process, transaxle spin loss and torque loss tests were conducted. The test data was used to calculate unknown component loss information. The developed model was calibrated to match the transaxle test data. The model was also validated through comparison of dynamometer test data with vehicle level fuel economy simulations of the standard EPA City, Highway, US06 and FTP20 drive cycles and detailed energy analysis.