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Variable-geometry turbocharger
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Variable-geometry turbocharger
Variable-geometry turbochargers (VGTs), occasionally known as variable-nozzle turbochargers (VNTs), are a type of turbochargers, usually designed to allow the effective aspect ratio (A/R ratio) of the turbocharger to be altered as conditions change. This is done with the use of adjustable vanes located inside the turbine housing between the inlet and turbine, these vanes affect flow of gases towards the turbine. The benefit of the VGT is that the optimum aspect ratio at low engine speeds is very different from that at high engine speeds.
If the aspect ratio is too large, the turbo will fail to create boost at low speeds; if the aspect ratio is too small, the turbo will choke the engine at high speeds, leading to high exhaust manifold pressures, high pumping losses, and ultimately lower power output. By altering the geometry of the turbine housing as the engine accelerates, the turbo's aspect ratio can be maintained at its optimum. Because of this, VGTs have a minimal amount of lag, a low boost threshold, and high efficiency at higher engine speeds.
The rotating-vane VGT was first developed under Garrett and patented in 1953.
Nissan was one of the first to use an early variable-area turbocharger system on the VG20ET "Jet Turbo". Their 1985 Cedric/Gloria announcement described a production passenger-car engine with a "variable nozzle turbo", and Nissan's related patent described a "variable capacity turbine" using a pivotal tongue or throttling member to vary the turbine throat area. This differed mechanically, but produced similar results as Honda's 1988 C20AT "Wing Turbo", which used fixed and movable guide wings around the turbine, with the movable wings varied according to operating conditions to control exhaust velocity and boost pressure.
The limited-production 1989 Shelby CSX-VNT, with only 500 examples produced, was equipped with a 2.2-litre Chrysler K engine with a Garrett turbo called the VNT-25 (because it used the same compressor and shaft as the fixed-geometry Garrett T-25).
In 1991, Fiat incorporated a VGT into the Croma's direct-injected turbo diesel.
The Peugeot 405 T16, launched in 1992, used a Garrett VAT25 variable-geometry turbocharger on its 2.0-litre 16-valve engine.
The 2007 Porsche 911 Turbo had twin variable-geometry turbochargers on its 3.6-litre horizontally opposed six-cylinder gasoline engine.
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Variable-geometry turbocharger
Variable-geometry turbochargers (VGTs), occasionally known as variable-nozzle turbochargers (VNTs), are a type of turbochargers, usually designed to allow the effective aspect ratio (A/R ratio) of the turbocharger to be altered as conditions change. This is done with the use of adjustable vanes located inside the turbine housing between the inlet and turbine, these vanes affect flow of gases towards the turbine. The benefit of the VGT is that the optimum aspect ratio at low engine speeds is very different from that at high engine speeds.
If the aspect ratio is too large, the turbo will fail to create boost at low speeds; if the aspect ratio is too small, the turbo will choke the engine at high speeds, leading to high exhaust manifold pressures, high pumping losses, and ultimately lower power output. By altering the geometry of the turbine housing as the engine accelerates, the turbo's aspect ratio can be maintained at its optimum. Because of this, VGTs have a minimal amount of lag, a low boost threshold, and high efficiency at higher engine speeds.
The rotating-vane VGT was first developed under Garrett and patented in 1953.
Nissan was one of the first to use an early variable-area turbocharger system on the VG20ET "Jet Turbo". Their 1985 Cedric/Gloria announcement described a production passenger-car engine with a "variable nozzle turbo", and Nissan's related patent described a "variable capacity turbine" using a pivotal tongue or throttling member to vary the turbine throat area. This differed mechanically, but produced similar results as Honda's 1988 C20AT "Wing Turbo", which used fixed and movable guide wings around the turbine, with the movable wings varied according to operating conditions to control exhaust velocity and boost pressure.
The limited-production 1989 Shelby CSX-VNT, with only 500 examples produced, was equipped with a 2.2-litre Chrysler K engine with a Garrett turbo called the VNT-25 (because it used the same compressor and shaft as the fixed-geometry Garrett T-25).
In 1991, Fiat incorporated a VGT into the Croma's direct-injected turbo diesel.
The Peugeot 405 T16, launched in 1992, used a Garrett VAT25 variable-geometry turbocharger on its 2.0-litre 16-valve engine.
The 2007 Porsche 911 Turbo had twin variable-geometry turbochargers on its 3.6-litre horizontally opposed six-cylinder gasoline engine.
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