In-cylinder boosting of turbocharged spark-ignited engines. Part 2: Control and experimental verification

Abstract

Downsizing and turbocharging is a common approach to improve the fuel economy of spark-ignited combustion engines. However, the inherent turbo lag results in a loss of driveability. In-cylinder boosting is an effective way to eliminate this problem. In the first part of this two-part study, a deactivatable camshaft-driven valve controlling the air mass flow from a pressurised air-tank directly into the cylinder was proposed as the main actuator of such a system, where also a model-based design procedure was demonstrated. In this paper, the torque control during the turbo lag compensation is discussed. The control is complicated by the limited variability of the mechanical valve-train. This limited variability gives rise to a trade-off between fuel and pressurised air consumption. However, the proposed control strategy minimising the consumption of pressurised air (thereby minimising the space required for the pressurised air tank), causes only a small penalty in fuel consumption. This air-mass-based control strategy actuating the throttle, ignition timing and boost mode timing is analysed in simulation and then verified experimentally in various operating conditions.