Analysis of Energy Flow in the Hybrid Power-Split (PS) System of SUV Vehicle in Real Driving Conditions (RDC)

Hybrid powertrains are replacing conventional combustion drives at an accelerating rate, while offering a reduction in fuel consumption and toxic exhaust emissions. The large share of hybrid solutions in engine vehicles has been observed for the compact class and in SUVs. The Authors of this study proposed an energy flow assessment in the hybrid powertrain system of an SUV in various driving conditions: urban, extra-urban and motorway. The tests were performed in accordance with the stipulations of the RDC test conditions and its requirements. The tests were carried out on a Toyota RAV4 HEV equipped with a 2.5 dm³ engine in a hybrid drive system along with Li-Ion batteries, which had an energy capacity of 1.11 kWh (4.3 Ah). The research was carried out on an urban route in Poznan as well as in its vicinity using three drive modes of the drive system: Eco, Normal and Sport. Based on the results of energy flow tests, it was found that, regardless of the initial state of charge (SOC) of battery, the vehicle would reach constant SOC values in the second phase of the test - in the extra-urban driving phase. Such conditions stabilize after about 30 km of urban driving. The differences in the range of these SOC values were around 10%. Due to the conditions of motorway driving, the SOC changes were very small and amounted to about 3-5% while covering about 20 km (in this driving mode). The tests confirmed the slight influence that the driving mode (eco, normal, sport) had on the final measured charge values: for discharge, charging or regeneration. The share of time operating in electric mode for individual test phases was also determined, and it was approximately 65-68%, 25-30% and 5-8% in the urban, extra-urban and motorway phases, respectively.