Turbo Tech

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Variable turbines

How VNT™ works

A Garrett® VNT® turbocharger works by adjusting the gas throat section at the inlet of the turbine wheel in order to optimize turbine power with the required flow velocity.

At low engine speed and small gas flow, the turbocharger reduces the throat section, increasing turbine power and boost pressure. At full engine speed and high gas flow, the VNT™ turbocharger increases the throat section, avoiding turbocharger overspeed and maintaining the booster pressure required by the engine. The throat section modulation can be controlled directly by the compressor pressure through the use of a pressure actuator, or by the engine management system using a vacuum actuator. To modify the throat section, VNT™ Multivane™ models use a mobile multivane system composed of a number of vanes which rotate relative to the turbine wheel axis.

The benefits of VNT™ technology are:
  • Higher power
  • Higher torque
  • Improved transient response
  • Lower fuel consumption
  • Lower emissions
  • Improved braking power

How VGT™ works

A Holset VGT™ turbo is an effective, though complex, method of turbocharging using a turbine stage where the swallowing capacity is automatically varied while the engine is running. This permits turbine power to be set to provide just 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 through the turbine. The Holset VGT™ is unique in that the vanes do not pivot but slide axially. This approach ensures a high level of durability and reliability, essential for commercial diesel applications.

VGT™ turbocharging yields several benefits in engine matching:
  • Good transient response.
  • Good fuel economy.
  • Increased useful engine operating speed range.
  • Enhanced compression brake capability.
  • Reduced engine swept volume and package size for a given rating.
  • High pressure ratio compressors.

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