| Fully variable valve system (FWS) can realize the continuous variability of the maximum valve lift, the valve opening duration and the valve timing. So there is an important significance to energy conservation and emission reduction of the engine. FWS can control the number of the working medium in the cylinder by the way of EIVC or LIVC. So the throttle valve is cancelled and the the load of SI engine is controlled by FWS. Owing to the totally elimination of the throttling action to the air inflow, this kind of unthrottled SI engine can greatly decrease the pumping loss, which makes the fuel consumption reduce10%to15%under small and medium-sized load. In addition, FWS can increase the engine power by improving the volumetric efficiency and decrease the emission of the harmful gas by the internal EGR of the engine.In order to carry out the further research of FWS, a kind of FVVS driven by valve-train cam is designed and developed. The intake valve is opened by the hydraulic valve actuator which is set between the camshaft and the intake valve, and it is closed by the reliever which could relieve the oil pressure of the hydraulic system in FVVS. The valve-seating velocity is controlled by the valve-seating buffer mechanism. Due to using the reliever as the switch controlled oil pressure in the hydraulic system, it not only reduces the cost of manufacture, but also overcomes the shortage that the frequency response characteristic of the solenoid valve is low, and it lays a good foundation of the further development of FVVS.In this paper, study on finite element simulation of fully variable valve system is introduced. The main work of this paper includes the following three aspects.Firstly, based on the structure characteristics of the fully variable valve system, the finite element model of the FVVS is established by the ADINA software. Then completed the parameter settings of this model, including boundary conditions, material, element, and so on. And based on relevant theory, the simplification of the key components in the FWS has been completed. Secondly, the simulation results of the maximum valve lift, the valve opening duration and the pressure fluctuations in the FVVS are got through the model mentioned above. Then these simulation results are analyzed. By the comparison of the results between the simulation and the measurement, the validity of the simulation is proved. The results of the simulation and the measurement show that FVVS can realize the continuous variable valve lift and EIVC by changing the time of relieving oil pressure, and the design goal is totally achieved.Lastly, through the analysis of the pressure fluctuation in the FVVS, some suggestions are offered to improve the maximum permissible speed of this system. The maximum permissible speed of the hydraulic valve train is determined by the pressure fluctuation of hydraulic system. When the maximum permissible speed reaches or exceeds, the pressure fluctuation of hydraulic system will be intensified and minimum value of pressure decrease to below the pressure in low-pressure system. In the case, the hydraulic liquid can’t drain in time, the characteristics of valve movement will be out of control, and the intake air volume can’t be regulated by FVVS. The pressure fluctuation of fully variable valve train can be improved by decreasing the mass of move parts in valve train, increasing the stiffness of valve train, reducing the choking effect in the hydraulic system. |
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