The impact of drive mode of a hybrid drive system on the energy flow indicators in the RDE test

Abstract

The drive to reduce fuel consumption of vehicles equipped with internal combustion engines leads to an increasing share of hybrid drives used in various means of transport. Such hybrid vehicles, thanks to the use of diesel-electric drive systems, allow for a fuel consumption reduction, and thus to reduce the carbon dioxide emissions. This fuel consumption reduction results from a specifically selected energy flow strategy in hybrid systems. This strategy was the focus of the research performed in order to identify the energy flow conditions in a hybrid drive system in driving conditions corresponding to the RDE test. A Lexus LS 500h vehicle was tested in two drive modes, while determining the related energy flow conditions, including the operating conditions of: electric motors, internal combustion engine and battery. Energy balance was determined taking into account the high voltage battery discharge and charging energy as well as the energy recovered during regenerative braking. It was found that in the RDE test conditions the vehicle is in electric mode for over 30% of the distance and 35% of the drive time, with the energy balance of the vehicle being positive (SOCend > SOCstart). Additionally, it was pointed out that the time spent in the electric mode when driving in urban conditions is about 50% and decreases to about 15% for highway conditions.