Variable Geometry (VG) technology for diesel
The ideal diesel engine turbocharger is light-weighted and compact and provides a wide operational flow range. Obviously, the costs are an important factor as well. Where a 2 stage system provides the widest engine expansion ratio, it is paid off with the costs and the size and weight of the complete system. A regular waste-gate turbocharger is cheap, small in size and light weighted, however the engine expansion ratio is a limiting factor for nowadays diesel engines.
A “variable geometry system” is the perfect solution to meet in the middle.
The VG system consists of a regular turbocharger equipped with a pack of vanes in the turbine throat area that are adjustable using an electric actuator. In the event of low energy at the turbine, the vanes will be closed, resulting in a small throat area. A small turbocharger is then virtually present on the engine. In order to meet the maximum flow required to operate the engine at high rpm, a big virtual big turbocharger is needed as well. This is achieved by opening the vanes, increasing the turbocharger throat area. In between these two maximum positions of the vanes, the turbocharger boost is continuously adjustable. During all engine operating points, the position of the vanes are continuously set on such position to always create the correct turbocharger output.