AVL Efficiency Diesel Engine - IC Engine Design
AVL Efficiency Diesel Engine
The Efficiency Engine –
Cost-effective Alternative to Downsizing
AVL has developed the so-called efficiency engine as an alternative to the familiar option of downsizing diesel engines. Because of the engine's moderate power density, its peak pressure requirements are lower in some areas than those of turbocharged gasoline engines. Consequently, its mechanical friction and fuel consumption can be significantly reduced, as the comparison with a conventional and a downsized diesel engine demonstrates.
The lower gas forces allow a reduction of piston pin diameter from 26 to 20 mm. A reduction in wall thickness below the combustion bowl and the elimination of the piston cooling gallery due to the moderate specific power together permit a reduction in piston compression height to only 48% of the cylinder bore without requiring bearing bushes in the piston.
- Piston Rings:
The lower gas forces also allow a reduction in ring widths and tensions to a level more familiar from gasoline engines with corresponding reduction of friction.
- Connecting Rod:
The small end is redesigned to the reduced pin diameter and the shank cross-section adapted to the lower gas load. The big end is also reduced to suit the optimized crankpin diameter. The lower piston height allows an increase in con rod length of 5.25mm which gives and additional friction benefit due to the reduction of side forces at the piston-line interface. Nevertheless the weight of the con rod assembly was reduced by nearly 25%. The application of cost-intensive sputter bearings at the big end could be avoided.
Here the focus is on minimization of diameters of the main and crankpin bearings. In the first step, parameter variation was performed using FEM-Analysis of a single crankweb, based on a metric of bending deflection under gas load. The new layout was compared to a wide range of proven designs based on this metric. The resulting layout was then validated using the full 3D Multi-Body-Simulation and Finite Element capabilities of AVL-Excite, including Elasto-Hydrodynamic simulation of the bearings. It is noted that the crankshaft design is here limited by its stiffness – and hence the edge-loading of the main bearings. Including the proportional reduction of the counterweights, an overall saving in crank train mass of around 10% was achieved.
- Oil pump:
Adaption of oil pump size to reduced flow requirements of optimized crank train.