Variable Geometry Turbo-Compressor

The turbo "TGV (Variable Geometry Turbo) differs from the conventional turbo for the use of a crown or dish on which are mounted one movable vanes that can be targeted (all together) at an angle determined by a lever mechanism and a push rod A valve vacuum system similar to that used in the Wastegate valve.

For maximum air compression at low rpm shall close the vanes as decreasing the section between them, increases the speed of the exhaust that focus more strongly on the turbine blades (smaller section = higher speed). When the engine rpm increases and increases pressure in the intake manifold, the valve detects it through a tube directly connected to the intake manifold and turn it into a movement that pushes the control system of vanes so that they move for an open position which decreases the speed of the exhaust that focus on the turbine (higher = less speed section).
The fins are mounted on a crown (as shown in the picture below), connected by a shaft which is screwed on the valve shaft vacuum.

The key positions that can take the fins can be described in the text and image as follows:

In the left figure: see how fins adopt a closed position that only leaves room for the passage of exhaust gases. This position is adopted by the turbo when the engine rotates at low rpm and the speed of the exhaust gas is low. With this is done to speed the exhaust gas, while passing through the narrow space left between the fins, which is focusing more strongly on the gas turbine. Also adopts this position when the engine requires the maximum benefits starting from a low speed or relatively low, which causes the engine to accelerate as quickly as required by the driver, for example in a crossing or an abrupt acceleration vehicle.
In figure center: the fin take a more open position which corresponds to an engine operating with an average engine speed and normal speed, in this case the variable geometry turbo would behave like a conventional turbo. Fins take an intermediate position that does not interfere with the passage of exhaust gases which affect and without varying the speed of the turbine.
In the right figure: the vanes adopt a very open due to high speeds at which the engine rotates, the exhaust enters the great speed at the turbo spinning the turbine very quickly. The open position very fins acts as a brake on the exhaust which is limited by the speed of the turbine. In this case, the position of vane performs the function it performed in the valve wastegate turbos conventional means, limits the speed of the turbine when the motor rotates at high speeds and there is a very high pressure in the intake manifold, this explains why the variable geometry turbos have no wastegate valve.

The operation that we saw for the variable geometry turbo is theoretical since the control valve, vacuum in the same way as in conventional modern turbos, is done through an electronic management in charge of regulating the pressure reaches the valve vacuum GV turbos and wastegate valve in the conventional turbos at all engine operating margins and taking into account other factors such as intake air temperature, atmospheric pressure (altitude above sea level) and the requirements of the driver.

The advantages of the turbo-compressor GV are working to achieve a more progressive motor powered on. The difference of the first motors used with conventional turbo-compressor where there was a big jump in power from low revs to high, the behavior ceased to be blunt to get a very progressive power curve with a large amount of air from low speeds and for maintaining a wide area of number of motor revolutions.

The drawback is that this system presents its greater complexity, and therefore the price when compared with a conventional turbo-compressor. As the lubricating system that need to use oils of higher quality and more frequent cuttings.
Until now, the turbo-compressor GV can only be used in diesel engines (except porsche 911 carrera 997 turbo), since the gas temperature of the exhaust gas is too high (200-300 ° C higher) to allow systems like these.