Power and fuel economy optimizations of gasoline engines using hydraulic variable valve actuation system

Abstract

The hydraulic variable valve actuation (HVVA) system can provide greater freedoms to the engine valve motions than most of the traditional cam-based valve train systems do. By considering the characteristics of the HVVA system, the strategies of putting its outstanding flexibilities into use for further improving the performances of gasoline engines with respect to power and fuel economy are developed in this research. A new GT-suite HVVA engine model is proposed which is able to realize the interdependencies of the HVVA system and the engine. In addition, the model is calibrated by experimental data and the proposed genetic algorithm (GA) optimization schemes are carried out for optimizing the engine outputs at full engine load and fuel economy at partial engine load. A potential average improvement of 10.4% on the engine outputs at full load over the entire operating speed range of the test engine is noticed from implementing the optimized HVVA valve motions. Moreover, the advanced GA algorithm for fuel economy optimization ensures the GA optimizer could maintain its proper functionality while non-linear constraints are taken into considerations. The late exhaust valve closure (LEVC) and early intake valve closure (EIVC) strategies are adopted at the same time for granting the engine an internal exhaust gas recirculation (IEGR) feature and together evolved into the HVVA strategy for fulfilling the partial engine loads without throttling. By conducting the advanced GA optimizations with the proposed HVVA strategy for partial engine load operations, the resulted break specific fuel consumption (BSFC) of the HVVA engine could be brought down by 13.1% on average with a maximum of 15.8% over its working speed range at the exemplary 7Nm load point comparing to those of the original test engine.