The Valve Train’s Improvement For The Transformation From Otto Cycle To Miller Cycle

As one of the important components of the internal combustion engine, valve train directly affects its performance such as the power, economics, reliability, vibration and noise. As is known, cam is the hard core of the valve train. By redesigning the key parameters of valve train and the cam profile, we can improve the performance of the engine, and even change the engine thermodynamic cycle. On the basis of perfecting the valve train performance, by calculation, analysis and redesign of the Otto cycle gasoline engine valve train, the transformation from Otto cycle to Miller cycle was realized in the paper.The research contents and innovations include as following:The kinematics and dynamics model of the valve train were established. Calculation and analysis of the parameters were carried out. By analyzing the original valve train performance, it was found that the max jerk and the contact force between cam and tappet exceeded the permitted value range. Those leaded to the unnormal vibration and additional wear of the valve train. Optimization was proposed to solve those problems and to meet the engine performance requirements of the transformation from Otto cycle to Miller cycle.Mainly considering fuel economy and the peak pressure, the geometry compression ratio and the valve phases were determined based on GT-power. The two load control strategies of intake valve and throttle, were compared for fuel consumption rate. Considering the pumping loss, requirement of cam characteristics and clearance between the valves and piston, maximum valve lift were optimized, and the cam profiles were redesigned by AVL-EXCITE Timing Drive.By calculating the kinematics and dynamics characteristics of the valve train, it was found that performance of the valve train is improved, the problems of the original engine solved. Finally, the experiments were carried out to check engine performance after the camshafts manufactured. The results show that the fuel economics were improved, performance parameters of the Miller cycle engine meeting expectations, and the camshafts passed the bench endurance test.