Investigations on energy flow in the optimized CVT-hybrid-driveline

Based on the experience of more than ten years research on hybrid driveline technology at Technische Universität München the Optimized CVT-Hybrid-Powertrain was designed and manufactured and is under investigation. The research project is run in close cooperation between university and industry (GM Powertrain Europe, ZF Friedrichshafen AG and ZF Sachs AG). The project is focused on reduction of fuel consumption and emissions at low additional cost for hybridisation. Designed as a parallel hybrid vehicle the driveline combines a small efficient electric motor (synchronous machine, 14 kW) with a series-production Diesel engine (88 kW). Double layer capacitors (ultracaps) are used for electric energy and power storage. The core piece of the driveline is a two-range continuously variable transmission (iVi-transmission) which is based on a chain variator. Without interruption of traction force the ratio range of the chain variator is used twice by a special shifting process of two synchronized clutches. The driveline management is done by an optimized vehicle controller. Vehicle pull-away is typically done by electric driving; according to the drivers power demand the ic-engine is started by fast ratio change of the chain variator at driving speeds between 7 and 20 km/h; an additional starter is not required. The driveline is assembled into an Opel VECTRA Caravan for investigations on practical use and at a test rig for detailed measurements on fuel consumption, energy flow and system behaviour. Based on test rig investigations and simulations the fuel consumption and the energy flow in the Optimized CVT-Hybrid-Driveline are analysed and evaluated; energy losses are detected and further saving potential can be seen.