Torque Control of a Small Gasoline Engine with a Variable Nozzle Turbine Turbocharger

The ideal torque curve of automotive engines should be high and flat from low engine speed. To achieve this, we installed a variable nozzle turbine (VNT) turbocharger to a retail natural aspirated (NA) small gasoline engine. In the VNT turbocharger, variable vanes are set around the turbine wheel and form nozzles that changed the flow velocity of the exhaust gas. The vane position was controlled to adjust intake pressure at a target. As a result, the maximum torque improved by 27% and the engine speed at maximum torque was lowered by 1550rpm. A flat torque curve was achieved from 5450rpm to 8000rpm.