System and Thermal Modeling for a Novel On-Road Hydraulic Hybrid Vehicle by Comparison With Measurements in the Vehicle

Hydraulic hybrid powertrains, which can be applied to many types of vehicles including cars, have several important advantages over electric hybrids, such as lower costs, higher power density, and more regenerative energy available from braking. There have been various investigations for hydraulic hybrid architectures and there always exists room for improvement in terms of performance and efficiency. In order to achieve improved performance and efficiency, a novel hydraulic hybrid transmission architecture has recently been suggested in Maha Fluid Power Research Center, which is implemented in the platform of 1999 Range Rover. Previous studies of the Maha hydraulic hybrid vehicle (HHV) mainly focused on the optimization of system components and controller. In order to further study and optimize hydraulic hybrid architectures, the thermal behavior has to be considered as well. A few existing thermal studies on other hydraulic systems have mostly focused on steady state characteristics due to the difficulty of simulating the unsteady state conditions. In this paper, a novel approach to thermal modeling of HHV for a novel HHV architecture is presented. The results have been validated with the measured data collected while driving the vehicle. The thermal model utilizes the flow rate and pressure obtained from the hydraulic system model and calculates the system temperature at different locations. In order to capture the rapid transition of the hydraulic system in HHV, a novel simulation scheme considering the flow direction for the control volume inputs is applied in the presented study. In addition, the presented model considers compressible flow in order to improve the accuracy of the model.