Investigation of the Hybrid Operating Modes Regarding Efficiency, Emissions and Comfort for the Parallel-Series Hybrid Powertrain Concept DE-REX

The “Two-Drive-Transmission with Range-Extender” (called DE-REX) is an innovative hybrid powertrain concept using two electric motors and an internal combustion engine. The two electric motors are permanent magnet synchronous motors with a maximum power of 48 kW each. As combustion engine a 3 cylinder, turbocharged engine with a power of 65 kW is used. The aggregates are coupled to a transmission whose layout is characterized by consisting of two parallel 2-speed sub-transmissions. This layout offers a high flexibility and enables both parallel and series hybrid driving. The hybrid control unit (HCU) has to select the optimal driving mode and power distribution between the aggregates in regard to in some extend competing objectives like efficiency, emissions or driving comfort. In particular, the operation of the internal combustion engine with only two gear ratios is challenging. In the course of the publically funded DE-REX project, the DE-REX powertrain concept was designed, manufactured and set up at an X-in-the-loop test rig. In this paper, the operating point decision is investigated in selected driving situations focusing at the conflict of objectives between the efficiency, the emissions of the combustion engine and the driving comfort. Therefore different hybrid control strategies are introduced on the basis of measurements at the powertrain test rig. Each strategy was designed to aim for one of the objectives gaining advantage out of the high flexibility of DE-REX. The availability of three propelling machines, gear selection and different hybrid modes opens up a wide field of driving power supply possibilities. The different strategy approaches show how an innovative powertrain design can improve system characteristics of modern hybrid vehicles.