The key to turbocharging is to maximise and control the boost pressure over as wide a field of engine operation as possible. Cummins Turbo Technologies' patented Holset VGT^TM technology gives infinite control of boost pressure.

The Holset VGT uses a turbine stage where the swallowing capacity is automatically varied while the engine is running. This permits turbine power to be set, providing sufficient energy to drive the compressor at the desired boost level wherever the engine is operating. This is achieved by varying the area of a nozzle; a set of guide vanes that control the flow of exhaust gas through the turbine.

Conventional designs pivot the vanes to achieve different nozzle areas. The Holset VGT is extraordinary in that the vanes do not pivot but slide axially; this design ensures a high level of durability and reliability, essential for today's commercial diesel applications.

The sliding nozzle ring alters the aperture through which the exhaust gases flow onto the turbine wheel. This alteration in the geometry of the turbocharger increases the boost as the nozzle is closed down. Reducing the aperture increases exhaust manifold pressure and increases the turbocharger speed. As the nozzle ring opens up, the exhaust pressure reduces and the turbocharger boost decreases. In effect it creates an infinite number of fixed geometry turbochargers.

Pneumatic or Electric Actuation
The Holset VGT is part of a totally integrated fuel and air control system controlled by the engine electronics. Either electric or pneumatic actuation can be used to regulate the turbocharger's nozzle geometry. Pneumatic actuation harnesses air pressure from the vehicle braking system. Alternatively a watercooled and automatically calibrated electric motor actuator makes for a simplified installation whilst maintaining responsiveness and overall turbocharger performance.