Reglerstrategi för fria ventiler
? Utveckling av en fyrtakts förbränningsmodell för att prediktera optimala ventilinställningar
As emission legislations across the world continuously pushes engine development forward,engineers constantly need to come up with and implement fuel saving technologies. During thelast decade, variable cam phasing has become a popular solution to increase gas exchangeefficiency. This configuration is typically mechanically constrained by camshaft limitations, anda solution to circumvent this problem would be to use a different valve actuation principle.One example of this is to use pressurized air controlled by electrical solenoids. Such a systemhas been developed byCargine Engineering and this provides the starting point for this work. Tobe able to operate the valvetrain on an actual engine, a control system is needed. For thispurpose, the AVL developedRaptor provides a suitable design environment. The Simulinkimplementation is straightforward to alter and customize and based on feedback from positionsensors mounted on each valve, closed loop control on both intake and exhaust valve timings hasbeen implemented. Together with the implementation of a script for predefining a large numberof operating points that the engine test bed can then execute automatically, gathering of largequantities of data has become easy.Based on this data set, an existing combustion model for predicting a full four-stroke cylinderpressure trace has been modified. Focus has been on taking the influence of valve timings andlift heights into account and the result is a model that, for the current data set, predicts IMEPwith a standard deviation of 4.9% for the relative error. The corresponding relative error standarddeviation for PMEP estimation is 8.8%.With this model accuracy, an optimization routine for looping through possible valve settingsoffline has been developed. This routine is able to, based on user defined engine speed and fuelmass (and assuming stoichiometric combustion), provide a level curve corresponding to a map ofoptimal valve settings with respect to minimal fuel consumption. This routine works well forcertain operating points, but shows low prediction accuracy for others. The conclusion is thatmore work needs to be done regarding modelling of the actual combustion event, currentlycharacterized by the Vibe function.