【作者】 谢宗法；

【导师】 王志明；

【作者基本信息】 山东大学 ， 热能工程， 2011， 博士

【摘要】 全可变气门机构(fully variable valve system,简称FVVS)可实现气门最大升程、气门开启持续角和配气相位三者的连续可变,对发动机的节能减排具有重要意义。FVVS能够采用进气门早关(EIVC)或进气门迟闭(LIVC)的方式控制进入气缸内的工质数量,从而取消节气门,实现对汽油机负荷的调节。由于完全取消了节气门对进气的节流作用,这种无节气门汽油机将大幅度地降低泵气损失,使中小负荷时的燃油耗降低10-15%。此外,全可变气门机构可通过改善充量系数,提高发动机功率；通过发动机内部EGR减少有害气体的排放。全可变气门技术已成为发动机新技术的发展方向之一。全可变气门机构的主要结构形式有机械式、电磁式和电液式。电液全可变气门机构由于流体的可流动性,可灵活控制气门运动规律,其研究已受到人们的重视。具有较大影响的电液全可变气门机构有Lotus的EHFVVT系统和菲亚特的UNIAIR系统。但这些机构尚存在气门落座冲击大、电磁阀响应速度不够高的问题。因而阻碍了电液式全可变气门机构的进一步发展和商品化生产。为了开展对全可变液压气门机构的进一步研究,本文设计开发了一种配气凸轮驱动的全可变液压气门机构,简称SDFVVS系统。该机构通过设置在配气凸轮与进气门之间的液压气门驱动机构驱使进气门开启,用泄油控制机构释放液压系统中的油压使进气门关闭,并采用落座缓冲机构控制气门落座速度。由于采用了泄油控制机构作为液压系统的油控开关,不但降低了制造成本,而且克服了高频电磁阀频响特性低的不足。为全可变液压气门机构的进一步发展奠定了良好的基础。根据液压气门机构的结构特点,建立了SDFVVS系统气门运动规律的计算模型,并对气门运动规律进行了模拟计算。采用位移传感器和压力传感器对SDFVVS系统的气门升程和液压压力进行了试验测量。通过对模拟计算结果和试验结果的对比,证明了模拟计算的正确性。模拟计算结果和试验结果表明：SDFVVS系统可通过改变泄油相位角实现进气门最大升程和进气迟闭角的连续可变,完全达到了其设计目的。控制气门落座速度是全可变液压气门机构的一项技术难题。在SDFVVS系统中,气门落座缓冲机构采用流通面积可变的节流孔控制气门落座速度。通过合理匹配节流孔的节流面积变化率、最小节流面积和最小节流面积对应的气门升程等措施控制气门落座速度。试验结果表明SDFVVS系统实现了气门的平稳落座。试验结果同时证明SDFVVS系统的气门最大升程对气门落座速度的影响较大,而发动机转速对气门落座速度的影响相对较小。提高液压气门机构的最高使用转速,对SDFVVS系统具有重要意义。液压气门机构内的液压压力波动决定了的其最高允许转速。当发动机转速达到或超过该最高允许转速时,液压系统内压力波动将加剧,最低压力波谷值将会达到或低于低压系统的压力值。在此情况下,液压油将不能及时得到排出,气门运动规律已失去有效控制,SDFVVS系统对进气量也失去调节作用。通过研究发现：降低气门机构运动件质量、提高液压气门机构的刚度、减小液压系统内部的节流作用,能够有效降低SDFVVS系统的液压压力波动。试验结果表明：经过改进设计后,SDFVVS系统中的压力波动明显降低,样机的最高允许转速已达到5600r/min。在SDFVVS系统中,配气凸轮是气门运动的动力驱动源,也是气门机构的振动源。因此要改善液压系统内的压力波动,提高SDFVVS系统的最高使用转速,最根本的问题是设计合理的配气凸轮型线。模拟计算结果表明：采用最大加速度点在凸轮工作段始点、最大速度值相对较低的高次多项式配气凸轮,对改善液压系统内的压力波动现象十分有利。SDFVVS系统通过改变泄油相位角可以实现气门最大升程和气门开启持续角的连续可变,从而取消节气门,实现对汽油机负荷的调节。这种无节气门汽油机的进气性能与传统节气门式汽油机有本质的区别。通过建立发动机进气过程一维流动的数学模型,对发动机的进气性能进行数学模拟计算。并采用低压传感器对进气管内的进气压力进行了试验测量。通过对模拟计算结果和试验结果的比较,发现进气压力的实测结果与模拟计算结果吻合良好,验证了进气过程模拟计算的正确性。通过对进气管内实测进气压力的对比发现：在节气门的节流作用下,原机进气压力随充量系数的降低和发动机转速的升高迅速下降,节气门之后的压力与节气门之前的压力之比甚至小于临界值,节气门处的气体流动已达到临界状态。但在无节气门汽油机中,进气量的改变对进气管内的压力几乎没有影响；转速的升高虽然使进气压力有所降低,但变化幅度很小。因此无节气门汽油机显著提高了中小负荷时的进气管压力。进气流动的模拟计算结果表明：与传统节气门式汽油机相比,无节气门汽油机显著降低了中小负荷时的泵气损失,这种较低的泵气损失使气缸内的工质温度有一定程度地降低。为了研究SDFVVS系统对进气量的调节作用,采用进气流量计试验测量了无节气门汽油机的进气量。研究结果表明：SDFVVS系统完全能够采用进气门早关或进气门晚关的方式实现对进气量的调节。当采用进气门早关方式调节进气量时,相同泄油相位角条件下的进气充量随转速的增大而增加；当采用进气门晚关方式调节进气量时,相同泄油相位角条件下的进气充量随转速的增大而减小。SDFVVS系统能够实现在各种转速下的最佳配气定时,与原机相比其各种转速下的充量系数都有一定程度的提高。更多还原

【Abstract】 Fully variable valve system (FVVS) 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. FVVS 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 FVVS. 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 reduce 10-15% under small and medium-sized load. In addition, FVVS 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. FVVS has been one of the development directions of the new technology of the engine.The main formation types of FVVS are mechanical type, electromagnetic type and electro-hydraulic type. The electro-hydraulic type of FVVS has been taken into account because of the mobility of the liquid and the dirigibility of the valve movement rules. The electro-hydraulic types of FVVS which have a major influence are the EHFVVT system of Lotus and the UNIAIR system of Fiat. However, these systems also have the problems that the valve is seated strongly and the response speed of the solenoid valve is not so fast, which hinder the further development and the commodity production of the electro-hydraulic type of FVVS.In order to carry out the further research of FVVS, a kind of FVVS driven by valve-train cam is designed and developed. It is called SDFVVS for short in this paper. 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 SDFVVS. 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.According to the structural features of SDFVVS, the simulation model of the valve movement rules is established. The valve movement rules of SDFVVS are simulated. The valve lift and the hydraulic pressure of the SDFVVS are measured by using the displacement sensor and the pressure sensor. 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 SDFVVS can realize the continuous variable valve lift and EIVC by changing the time of relieving oil pressure, and the design goal is totally achieved.It is a difficult problem of FVVS that controlling the valve-seating velocity. In SDFVVS, valve-seating velocity is controlled by a variable throttle hole whose flow area is changed with valve lift. The effect of the shape, the minimal flow area and the flow area changing rate of throttle hole on valve-seating velocity is studied. Analysys on valve-seating velocity under different conditions shows that the effect of maximum valve lift on valve-seating velocity is significant, while the effect of engine speed is relatively small. Testing results also show that by reasonably matching the structural parameters, SDFVVS can give steadily seating.Improving the maximum speed of hydraulic valve train has the important meaning to the hydraulic valve actuation 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 not drain in time, the characteristics of valve movement will be out of control, and the intake air volume can not be regulated by SDFVVS. 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. Experimental results show that the pressure fluctuation of SDFVVS decreased in the newly designed valve-train, and SDFVVS can operate steadily and reliable up to 5600r/min.The valve-train cam which drives the movement of valve is the vibration source in SDFVVS. To improve the hydraulic pressure fluctuation and increase the maximum speed of the SDFVVS, the fundamental problem is to rationally design the valve-train cam profile. The simulation results show that the hydraulic pressure fluctuation can be decreased by using a polynomial cam that has the maximum acceleration at the beginning point and the maximum velocity which is relatively lower.The SDFVVS can realize variable maximum valve lift and the early intake valve closing by changing the time of relieving oil pressure, so that the SDFVVS can cancel the throttle valve and realize the load adjustment of SI engine. There is essential difference between unthrottled SI engine and TC engine. In order to simulate the intake performance, the one-dimension nonsteady air-flow model is established. The intake pressure in the intake pipe is measured by using intake air pressure sensor. Through comparing the simulation calculation results and the measured results, it is found that the simulation results are accurate to the measured results.Comparing the intake pressure measured in the intake pipe, it is shows that the intake pressure of the original engine is reducing quickly with the decrease of the intake air volume and the rise of the engine speed because of the throttle effect. The ratio of the pressure after the throttle valve to the pressure before the throttle valve is even less than the critical point. The gas flow in the throttle valve can be reached critical velocity. But in the unthrottled SI engine, the changes of the intake air volume even have no effect on the intake pressure. The intake pressure can be reduced by the rise of engine speed, but the reduced pressure range is small. So the intake pressure at the medium or small load in unthrottled SI engine is larger obviously than in TC engine. The results of the simulation for the intake flow show that unthrottled SI engine reduce the pumping loss at the medium or small load obviously, and which make the temperature of the working medium in the cylinder lower to some extent.In order to research the regulating action of the SDFVVS for the intake air inflow, the intake air volume of the unthrottled SI engine is measured by using an intake flow-meter. The research results show that the intake air inflow can be controlled by the meanings of early intake valve closing or late intake valve closing in SDFVVS. When using the meaning of early intake valve closing, the intake air volume rises with the rise of the engine speed in the same time of relieving oil pressure; for the meaning of late intake valve closing, the intake air volume reduces with the rise of the engine speed in the same time of relieving oil pressure. The SDFVVS can get the best valve timing in all speed range of engine. The volumetric efficiency of SDFVVS is bigger than that of the original engine in all speed range.更多还原