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.

Intake Manifold Boosting of Turbocharged Spark-Ignited Engines

“…For the following investigations the same downsized and turbocharged SI engine is used as in [9]. The basic parameters of the engine are listed in Table 1.…”

System Design and Analysis of a Directly Air-Assisted Turbocharged SI Engine with Camshaft Driven Valves

“…In the boost mode, the torque can be controlled by the ignition angle [14] by retarding the ignition angle if the amount of air-fuel mixture in the cylinder is too high. In the pump mode, the friction brakes are used to control the torque if the desired deceleration is larger than the power absorption of the pump mode.…”

“…If there is too much air-fuel mixture in the cylinder, the ignition timing is delayed, which reduces the torque. More details on the torque control can be found in [14].…”

“…In [14], the air demand for the entire turbo lag compensation m a,b is presented for various engine speeds and torque requests. The tank pressure was held constant atp t,b .…”

“…The right-hand plots in Figure 2 show the resulting air demand for tank pressures higher thanp t,b . The same control strategy is applied as in [14]. The upper plot shows the air mass used as a function of the tank pressure.…”