Optimisation of transient response of a gasoline engine with variable geometry turbine turbocharger

Maintaining transient torque response is challenging on turbocharged engines because of the period of time required to accelerate the turbocharger. Variable Geometry Turbine (VGT) turbochargers offer a route to improve the transient response. In order to explore the transient operation without any limitation imposed by the production control strategy, an on line search was conducted using a series of open loop actuator trajectories applied to a VGT turbocharger installed on a gasoline engine. The trade-off between the responses in different stages in the transient event has been illustrated. The time required to reach 50% of maximum torque rise (T₅₀) was improved by up to 0.54s (35.5%) whilst the turbocharger acceleration was maintained. Fully closing the VGT resulted in high exhaust back pressure and low volumetric efficiency. This suggests that a simple boost pressure feedback control will likely not deliver optimised performance due to the excessive exhaust back pressure, reducing the available brake torque during the early part of the transient. Therefore, a model based control strategy may be required.