2006: VTG charger for petrol engines
In 2006, the 911 Turbo surprised the motoring world by featuring variable turbine geometry, a world first for a turbocharged petrol engine. Variable turbine geometry uses guide blades to simulate the cross-section of a turbocharger always optimised in size. At low engine speeds, the blades angle to form small air-flow openings. The exhaust gas flowing through a smaller cross-section is accelerated accordingly, hitting the turbine wheel with a high level of energy and therefore acting as a small turbocharger. This blade angle is maintained until the system has built up the required boost pressure.
With the flow of exhaust gas continuing to increase as a function of higher engine speed, the VTG guide blades open up and regulate the boost pressure accordingly. The electronic management and the electrically driven control mechanism – the control of which are integrated into the engine’s Motronic management system – are set up to give the blades an adjustment period from “open” to “closed” of approximately 100 milliseconds. Furthermore, the variable turbine geometry of the turbocharger is able to handle even the maximum conceivable flow of exhaust gas. This eliminates the need for a bypass valve.
The principle of variable turbine geometry (VTG) has been applied to diesel engines on a large scale for nearly ten years. However, the systems used on diesel engines could not be transferred readily to petrol engines, mostly for thermal reasons. For example, exhaust gas temperatures at the point leading into the turbine on a diesel engine are between 700 and 800°C. The exhaust gas on Porsche’s turbocharged power units, on the other hand, has a temperature of 1000°C. This creates a significantly higher load and extra strain on the adjustable guide blades, demanding the utmost of the materials and construction method applied. Only the development of materials that are extremely resistant to high temperatures allowed the production of VTG turbochargers with the long-term performance and life expectancy required. Porsche’s engineers also developed a two-stage oil cooling system including a follow-up pump, as well as a water cooling system for the bearing housing, to help reduce the high temperatures.