Holset Variable Geometry Turbochargers

The key to turbocharging is to maximize and control the boost pressure over as wide a field of engine operation as possible. Holset patented VGT™ 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 the 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. In addition, the vanes are fixed in an optimum position that creates the most favorable angle of incidence of the exhaust gas onto the turbine wheel blades thus raising average turbine efficiency throughout its operating range.

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 can decrease; or simply maintain ideal boost levels as the aperature increases to raise the turbine's exhaust swallowing capacity to compensate for increasing engine r.p.m. (See Image of Process Here) In effect it creates an infinite number of fixed geometry turbochargers.

Benefits of Holset VGT

• Good transient response
• Improved fuel economy
• Increased useful engine operating speed range
• Enhanced compression brake capability
• Proven durable design
• Reduced engine swept volume and package size for a given rating
• Helps control Exhaust Gas Recirculation (EGR) to meet emissions regulations

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 water cooled and automatically calibrated electric motor actuator makes for a simplified installation while maintaining responsiveness and overall turbocharger performance.

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  The Turbo

  The purpose of a turbocharger is to compress the air flowing into the diesel engine, this lets the engine squeeze more air into a cylinder and more air means that more fuel can be added. The engine burns air and fuel to create mechanical power, the more air and fuel it can burn the more powerful it is.

  In simple terms, a turbocharger comprises a turbine and a compressor connected by a common shaft supported on a bearing system. The turbocharger converts waste energy from an engine’s exhaust gases into compressed air, which it pushes into the engine. This allows the engine to burn more fuel producing more power and improve the overall efficiency of the combustion process.

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