Japanese boost in turbo design
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• The first truck diesel engine to be fitted as standard with a variable geometry turbocharger will be a Japanese one. At the Tokyo Motor Show this week Garrett Automotive confirmed that its new VNT (variable nozzle turbine) turbocharger is about to be fitted to an 11-litre engine made by one of the four leading Japanese truck manufacturers — Hino, lsuzu, Mitsubishi and Nissan diesel.
The VNT is Garrett's solution to the relative inefficiency of a conventional turbocharger at low engine speeds, and to the problem of "turbo lag". While the vanes on the rotor of a conventional turbocharger are fixed, and rotor speed is thus solely dependent on the speed of exhaust gas flow, on the VNT the vanes, which are made of stainless steel, can swivel and are controlled electronically by the engine's boost pressure control system. Specific fuel consumption, torque, and exhaust emission can thus be better controlled over a wide engine speed range, claims Garrett.