Variable Geometry (VG) technology for diesel
The ideal diesel engine turbocharger has a wide map, is light-weighted and is compact. Obviously, the costs are an important factor as well. Where a 2 stage system has the widest map, 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 map size 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.
Mitsubishi turbocharger division continuously improves the quality and performance of VG turbochargers. Engineering challenges are related to decreasing (inside) tolerances, to increase efficiencies and reduce overall weight by amongst others reducing the total amount of subcomponents.
Having all these challenges in mind, Mitsubishi turbocharger division managed to develop a VG turbocharger for a premium OEM which was capable of meeting the highest durability requirements, along with severe performance targets. Furthermore, compared to previous generations of in-house developed VG turbochargers, we managed to reduce the total VG turbocharger weight by 18%.This contributed to achieving very interesting and competitive vehicle CO2 emissions, supporting this OEM in living up to the European emission legislation requirements.