Abstract
Future emission legislation will require simultaneous reduction of toxic exhaust emissions and fuel consumption. Based on in-depth analysis of various CO2 -reduction technologies, downsizing of diesel drive trains proves to be most effective to meet future legislative limits. Another key technology is an advanced power net for electrical assisted cruising. However, both measures will require new drive train concepts. Shifted engine operation to higher loads improves efficiency but is more critical to NOx and particulate trade-offs due to increased fuel amounts and deteriorated EGR conditions. To cope with customer driveability demands advanced charging technologies and electrical motor assistance shall be utilised.
A drive train concept with a 1.2L 3-cylinder engine will be presented which has been optimised for mid-class passenger cars in view of the above challenges. Assisted by a 8 kW electric motor the engine is intended to replace current 1.9-2.0 L engines. A new mixture formation/combustion concept is applied using piezo-actuated CR fuel injection system of the 3rd generation in combination with an extreme variation of swirl charge motion concept. A high efficient EGR cooling system has been developed using heat pipe technology in order to increase EGR rates and operation range. This concept offers new degrees of freedom for charge and fuel preparation and enables usage of a hybrid combustion system - in situ homogeneous charge with compression ignition at part load, classical stratified at full load. In view of minimised mechanical friction losses 2-valve configuration is used.
The powerful electric motor enables the whole range of mild hybrid potentials, idle shut off, regenerative braking, electrically assisted acceleration and cruising (e-boost and e-drive). In combination with intelligent thermal and energy management strategies (electrically driven coolant pump and 14/42 V power net) it has shown significant improvements in driving cycle fuel consumption in the range of 7-10 percent additional to gains due to engine downszing. The drive train concept presented demonstrates that CO2 -emissions of 90-120 g/km can be achieved for vehicles in the 1300-1400 kg ITW-class and engine out emissions will simultaneously be cut down to approx. 40% of the Euro4 limits.