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May 23, 2011

Garrett VNT™ DualBoost™ Technology

Staying at the forefront of the rapidly moving turbocharger business requires constant investment and development. With strong market influences on vehicle design, such as downsizing, reduced exhaust emissions and improved fuel economy and reliability, new ideas and designs are constantly being explored by Garrett.

Of course, everyone also expects their new vehicle to have more power and torque than their old one…but at the same time they want to enjoy the benefits of better fuel efficiency. Thanks to turbo technologies developed by Garrett, it’s possible to have it all!

Here is one of the latest ideas recently launched by Garrett that is helping the auto industry to meet and surpass customers’ expectations:

VNT™ DualBoost™ – which recently won the prestigious PACE auto award – has been launched in the US on the 2011 model year Ford Powerstroke 6.7L V8 diesel engine used in the F-Series Super Duty.

Although this is a design bristling with innovations, what makes this turbo really stand duty-out is its compressor technology, which is helping to deliver near two-stage performance in a single unit.

The benefits of having two compressor wheels feeding an engine are well known and two stage turbo installations are becoming more and more commonplace. However, packaging (the space available to fit them) is often restricted, so what Garrett engineers have succeeded in doing with DualBoost is to combine the airflow from two compressor wheels within a single turbo!

In fact, the “two” compressor wheels are actually a single piece, with mirror image blades, running within a complex looking compressor housing (made up from three separate components) with two separate compressor inlets and a single, common outlet. Both inlet sections of the compressor housings also incorporate ported shrouds which broaden the operating flow range of the compressor.

From a VNT™ perspective, DualBoost combines the vane cartridge concept used on our latest 3rd Generation VNT™ turbos, which separates the turbine housing from the vane assembly for improved reliability and performance, with the variable vane assembly of the AVNT™ (Advanced VNT), which has proved such a reliable performer with our US customers. In addition, the turbine housing incorporates a single wastegate valve to enable the use of an even smaller turbine for improved response at low engine speed while further widening flow capability.

The control for the variable vanes is also different to that used on passenger car turbos, as it is electro-hydraulic. The actuator is a powerful hydraulic unit, integrated into the center housing casting, which uses engine oil acting on a power piston to move the vanes through an internal rack and pinion gear. The flow of oil to the actuator is controlled by a variable solenoid valve, which receives its demand signals directly from the vehicle ECU via a single electrical connector.

The high powered actuator is needed on this application because the engine runs with very high levels of EGR (Exhaust Gas Recirculation) in order to comply with the latest US emissions regulations. The variable vanes can be moved towards the closed position on demand, which increases the back pressure in the exhaust manifold and literally “drives” the inert exhaust gas back towards the lower pressure in the air inlet manifold to help reduce regulated emissions. This is only possible using a VNT™ with a high powered actuator.

The torque from the turbine wheel is transmitted to the compressor with minimal power losses, due to the use of an advanced angular contact ball bearing system. This uses light weight, low inertia and highly durable ceramic balls at both ends of the cartridge, performing the combined functions of a journal bearing and thrust bearing system in a single compact assembly. The ball bearing systems have derived from many years of experience gained in our highly successful race/rally/performance turbo range; proven repeatedly in numerous World Rally and Le Mans series wins!

Unusually, the turbo in this application sits on its own integral pedestal in the middle of the Vee, on top of the engine. The pedestal and turbo also include quick connectors for oil and coolant, ensuring that installation and servicing can be completed easily and quickly.

Finally, to ensure that the oil, air and exhaust gas stay where they should be,  piston rings are used at both the turbine and compressor ends, with the latter being pressurized by air. This is fed directly from the compressor’s diffuser section, to ensure efficient sealing under all running conditions.

So to summarize, the new VNT™ DualBoost™ turbo combines some of Garrett Motion finest ideas in a single package….the world’s most advanced turbo.

For further information, click here.

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