| With the energy crisis and environmental pollution problems have become increasingly prominent, countries began to explore different forms of energy saving mode, among of these, to reinforce the efficient use of fuel and reduce emissions and pollution have become more urgent. Research shows that the control of intake phase is important for the combustion process optimization and pollution control of the engine. In particular, the use of variable valve timing and variable valve lift technology has played a significant role in improving the engine intake air to improve the thermal efficiency of the combustion and the control of internal EGR rate of the engine.A variable valve mechanism based on hydraulic control was designed in this study. A four-cylinder diesel engine was simulated using the GT-power software, the engine performance was researched on conditions of different intake advance angle, different intake late closed angle and different valve lift. The simulation results showed that, at different speeds, the optimum valve state required by the engine was different. The simulation results showed the necessity and value of the design mechanism clearly.This electro-hydraulic variable valve timing mechanism has been overall planned and physical designed. Hydraulic simulation software AMEsim was used to simulate this mechanism. Several parameters such as system hydraulic pressure, throttle parameters, spring rate, spring pre-tightening force and outer diameter of the large plunger were mainly simulated. Results showed that: the hydraulic pressure of the system, spring stiffness coefficient and spring pre-tightening force have a great impact on valve lift, and showed some of regularity. The throttle parameters and the outer diameter of the large plunger have a great impact on the valve resitting speed. The designed mechanism in this paper was used on four-valve engine,it has a more complicated structure compared with a two-valve mechanism, but it can guarantee a better air input. Meanwhile, electromagnetic hydraulic valve timing mechanism can achieve independent control of the four-valve, inlet conditions can be optimized to achieve the stratification and activation in cylinder.A electro-hydraulic variable valve timing mechanism test platform was established in this study, and the device was tested on this platform. The kinematic data and control data of the mechanism was collected using data acquisition card. Experimental results showed that the designed mechanism basically achieved the same motion curve with the simulation results, and a good repeatability can be found. The dynamic response of the mechanism was analyzed, results showed that under the same pressure conditions, the dynamic response time of the valve’s opening and closing follows a normal distribution law. The correlation between the desired response time of valve’s opening and closing and the system hydraulic pressure was explored. Statistical results showed that, with the increase of the hydraulic pressure, valve opening delay time gradually increased, the valve closing response time gradually shortened. This study provides possibility for the feed-forward control of valves. At the same time the correspondence between the valve lift and the system hydraulic pressure has been found in this test, the valve lift achieved a change from 5mm to 9mm with the hydraulic pressure changed from 8MPa to 12 MPa, which achieved a variable valve lift. |
PDF Full Text Request