| In modern society, the automobile is becoming an important part of people’s life. The automobile brings a series of questions such as the environmental pollution and energy crisis while offers comfort and convenience to people. These questions put forward higher request to the automobile, especially the engine, as the core of the engine. The fixed valve timing which is used by the valve train of traditional engines cannot take into account inlet performance both in the high-speed and low speed condition. The throttling action increases the pumping loss during the gas exchange process, which leads to the deterioration of the fuel economy and the emission, so it makes a great difference to research the fully variable valve train, of which the maximum valve lift, the opening angle and the valve timing are continuously variable.A kind of fully variable hydraulic valve system or SDFVVS for short is introduced in this paper. The throttle is removed in this system and the valve is driven by a mechanical-hydraulic system, thus realizing the continuous variability of the maximum valve lift and the opening angle. A K157FMI engine was taken as a prototype in this paper, and the research about the valve movement characteristics was done from both kinematics and dynamics aspects. The main contents are as follow:First of all, the basic structure and the transmission chain of SDFVVS were analyzed and the structure was divided into high-pressure and low-pressure section or control and drive section. The working process, including the valve-opening, valve-seating and tappet back stages, was also respectively stated. In addition, the main control units were introduced and designed to lay the foundation for the follow-up work.Then it was introduced that the kinematics analysis and design of SDFVVS. The movement characteristics of the hydraulic tappet and the valve cam were stated and the basic guideline and requirement of the cam profile design were analyzed considering the practical situation of SDFVVS. The cam profile was divided into buffer section and working section. The proper type of the buffer section was selected and the equation of it was designed. Then the equation of working section was calculated by the way of computer programming and the accuracy of the result was also verified. The result showed that the valve of SDFVVS can be opened and closed at the ideal moment to realize the ideal valve movement characteristics by a rational design of the cam profile.In the last place, it was introduced that the dynamical simulated analysis of SDFVVS. The dynamical model of SDFVVS was built at the basis of the one-mass dynamic model of the valve train, and the calculation method was also stated. The finite element model of dynamical simulated analysis was built by the software ADINA and the results in variable engine speed and oil drainage angle were obtained. The correctness of the model was checked by comparing with the experimental results and the reasons of the error were also analyzed. The result showed further that SDFVVS can control the valve directly and change the maximum valve lift and the opening angle in a large range, which makes the valve movement characteristics change by the engine speed and oil drainage angle and realizes continuously variability of the maximum valve lift, the opening angle and the valve timing. |
