Design And Research On A Mechanism Of Continuously Variable Valve Lift

In the 21st century, with the rapid development of China’s automobile industry, the car ownership has substantially increased. The proportion of Gasoline and diesel consumption from vehicles has also increased, which casing energy shortages problems become more prominent. In this background, China has successively launched the third and fourth stages of vehicle fuel consumption regulations, which require the vehicle must have a strict fuel consumption of gasoline.Technology of continuously variable valve lift (CVVL) is a new kind of fuel-saving technologies used in vehicle with a gasoline engine, which can reduce the pumping losses of gasoline engine. What’s more, valve lift can be used to control the amount of intake air of a gasoline engine, which in turn control the load and improve the fuel economy of gasoline engine. This paper designed a continuously variable valve lift mechanism, and conducted in-depth discussion of the design and principles of the CVVL mechanism. The main works of this paper are:(1) This paper proposed a continuously variable valve lift mechanism design scheme based on a 2.0T engine valve train, and designed a corresponding cam profile, according to the structural characteristics of the CVVL mechanism, so that the valve train had the same buffer segment in all valve lifts; addition, calculated the middle rocker cam profile of this mechanism, which combined the cam profile and the target curve of the valve lift. The valve lift curve of this mechanism meted to the relevant design requirements, according to the verified of Kinematics.(2) Built a dynamic model of the CVVL mechanism by use of GT-power software, and conducted a dynamic simulation. Results show that:the dynamic characteristics of the valve were good, and the valve did not appear rebound quadrant in the condition of maximum lift and speed; the cam follower did not fly off; but the contact pressure between the cam and the roller of control rocker was a little large and made a detailed analysis of the reasons why stress is large. The CVVL mechanism had better dynamics characteristics by optimized its entire layout.(3) According to the dynamic calculation, made a finite element analysis for the middle rocker and the control rocker of this mechanism. Results showed that:there was a stress concentration on the middle rocker and its structural strength is not enough. Therefore, optimization design had been taken to the middle rocker. Results after optimization showed that:stress concentration significantly reduced and the structural strength were meet to the requirements. The optimization is effective.(4) Conducted a trial sample production of the CVVL mechanism and designed a cylinder head matching with the machine. Did stability test research in the valve train test bench and take measure the valve lifts and the torque of cam shaft. Result of test is good.