VARIABLENOZZLE TURBOS

Two types of tech are employed to control the boost-pressure output of a turbo. The rst is the wastegate that dumps exhaust-gas energy straight to the exhaust pipe, bypassing the turbo’s turbine. The other method uses a variable-nozzle turbo (VNT) to alter the turbine-vane angle via an electric motor to decrease or increase the power to the compressor side of the turbo. The VNT’S advantage is that it is more ef cient than a wastegate system and enhances the turbo’s performance over a wider speed range of the engine.

While VNT technology is nothing new in turbo- diesel engines, the problem with petrol engines is that high exhaust-gas temperatures at full load (around 1 000 °C) require special materials in the moving-vane mechanism, limiting VNT to highend applications.

That is, until Honeywell developed a VNT turbo in the new 1,5-litre VW Group turbopetrol. In combination with the Miller cycle that alters valve timing to increase ef ciency, this engine achieves a CO2 gure of 108 g/km in a vehicle weighing 1 250 kg. Honeywell won a PACE award for managing to bring VNT tech to mass production.