Impact of Combustion Engine Operating Conditions on Energy Flow in Hybrid Drives in RDC Tests

Energy flow in vehicles with hybrid propulsion systems depends primarily on the drive system design. The full hybrid propulsion system (series-parallel) enables differentiated energy flow management using different drive system operating conditions and energy recovery methods. The article attempts to estimate the energy differences resulting from this type of a system operating in two different modes: mode D - normal driving and mode B - forcing partial use of engine braking. Using these two driving modes in the real drive test, the energy flow characteristics of the vehicle were determined. Different operating conditions of the internal combustion engine and drive system in both modes allowed for the energy consumption during driving tests to be assessed. The components of the energy balance calculation referred to regenerative braking, battery charging and discharging and they were assessed in the RDC (Real Driving Conditions) test using the two selected driving modes (The Authors do not use the term Real Driving Emissions, as exhaust emissions have not been tested here). A detailed analysis of the operating conditions of electric devices was carried out, both for the electric motor and power generator mode (when braking). Based on the conducted analyzes, different energy flow conditions were found in the two analyzed configurations: from using only the hybrid mode with continuous operation of the internal combustion engine (mode B) to the typical hybrid drive using the electric mode - electric motor drive (mode D). Similar final battery charge values were obtained, which indicates different ways of managing energy flow in both driving modes: the biggest differences relate to the method and amount of energy recovered in vehicle braking