Variable geometry turbocharger
Encyclopedia : V : VA : VAR : Variable geometry turbocharger
Variable geometry turbocharger (VGT) improves upon turbocharger design by being able to change the orientation of the vanes of the turbine, thus changing the surface they present to the exhaust gases. With this technology, it becomes possible to present a greater turbine surface at low engine rotations (therefore minimizing turbo lag) and a smaller one, nearly zero, at high engine rotation (therefore removing the need for a waste gate). The same kind of control is used on power plant turbines.
These VGT turbochargers have a minimal amount of lag, have a low boost threshold and are very efficient at higher engine speeds. In many setups these turbos don't even need a wastegate. The vanes are controlled by a membrane identical to the one on a wastegate but the level of control required is a bit different. The first production car to use these turbos was the limited-production 1989 Shelby CSX-VNT, equipped with a 2.2L petrol engine. The Shelby CSX-VNT utilised a turbo from Garrett, called the VNT-25 because it uses the same compressor and shaft as the more common Garrett T-25. This type of turbine is called a Variable Nozzle Turbine (VNT). Turbocharger manufacturer Aerocharger uses the term 'Variable Area Turbine Nozzle' (VATN) to describe this type of turbine nozzle. Other common terms include Variable Turbine Geometry (VTG), Variable Geometry Turbo (VGT) and Variable Vane Turbine (VVT).
The 2006 Porsche 911 Turbo has a twin turbocharged 3.6-litre flat six, and the turbos used are BorgWarner's Variable Geometry Turbos (VGTs). This is significant because although VGTs have been used on advanced turbo diesel engines for a few years and on the Shelby CSX-VNT, this is the first time the technology has been implemented on a high production petrol car (only 500 Shelby CSX-VNTs were ever produced). This is because in petrol cars exhaust temperatures are much higher (than in diesel cars), and this normally has adverse effects on the delicate, moveable vanes of the turbo, BorgWarner engineers however have managed to combat this problem with the new 911 Turbo.
From Wikipedia, the Free Encyclopedia. Original article here. Support Wikipedia by contributing or donating.
All text is available under the terms of the GNU Free Documentation License See Wikipedia Copyrights for details.