（1.College of Mechanical and Vehicle Engineering Research Center for Advanced Powertrain Technology, Hu’nan University,Changsha 410082;2.Hubei Sanjiang Spaceflight Hongyang Machinery Co.,Ltd.,Xiaogan 432000）
Based on the requirements of improving fuel economy, the traditional Ottocycle engine was changed into Atkinsoncycle engine. The design of valve train mechanism was very important for cycle modification. The model of valve train mechanism for gasoline engine was built, the kinematics and dynamics analysis were conducted, the cam profile was optimized and the valve timing was redesigned. By using DVVT of intake and exhaust camshaft, the optimal control design of DVVT for the optimized engine was conducted under different loads and speeds. Finally, the bench test results showed that the modification of engine cycle was successful. The optimal specific fuel consumption of original engine decreased from 250 g/(kW·h) to 232 g/(kW·h) and low fuel consumption area moved to the normal working area of the engine, which verified the accuracy and effectiveness of the design method of valve train.
