Multi-variable optimization on variable intake valve closing timing system for engine overall performance

Variable valve timing (VVT) technology has a remarkable impact on engine power output, fuel economy and emission levels. To achieve a tradeoff among its potential benefits on various aspects, a novel multi-objective optimization method is proposed to complement among engine performances over entire speed-load regions. Intake valve closing (IVC) timing has been widely accepted to be the most effective means of VVT technologies. IVC timing is therefore investigated to accomplish engine overall performance optimization. The bench tests have been conducted using an introduced variable working position belt extender system. A 5-valve, double overhead cam (DOHC) spark ignition engine is selected. The sample testing data of engine power and torque outputs, fuel economy and emission levels are collected from engine bench tests, which are then interpolated with regular engine speed operating ranges via smoothing cubic spline fitting. For multiobjective control problem, principal component analysis can be conducted for the multiple-objective analysis by alternating different engine parameters, such as valve timing, sparking timing, A/F ratio, and so on. On account of the extra expense of engine experiments, a simplified optimization approach is then formulated in order to analyze the potential of IVC technology in terms of engine power output and fuel economy under constraints of emission levels at individual high speed, medium speed and low speed regions, etc. Variable IVC timing control has been shown in this research to improve engine performance throughout speed-load regions. Multi-variable optimization is also demonstrated to be feasible and effective for the optimal performance achievement on speed-load regions.