液压可变配气系统气门运动规律研究

发布时间：2018-09-18 21:32

【摘要】：配气系统作为发动机的重要组成部分,其性能将直接影响发动机的动力性、经济性及排放水平。可变气门配气技术能够根据发动机的工况变化合理调节配气参数,使发动机提高充气效率,降低换气损失,从而达到提高发动机的动力性、降低燃油消耗及减少废气排放的目的。本文以课题组提出的一种新型液压可变配气系统为研究对象,以最大程度地满足发动机配气需求,且使气门运动具有良好的运动学及动力学特性为目标,以理论研究与试验相结合的方式,对液压可变配气系统的气门运动规律进行研究。重点对液压可变配气系统的调节方法及参数与发动机最优配气参数的适应性、气门运动参数优化等展开研究。主要研究内容包括:对发动机在不同工况下的配气参数需求进行了分析研究。在建立发动机工作过程仿真模型基础上,对发动机配气相位角、升程等配气参数进行了优化,获得了发动机不同工况下最优配气参数的目标值,指出了发动机可变配气参数随发动机工况而变化的趋势和一般规律,为可变配气系统的调节方案制定及参数确定奠定了基础。对可变配气系统气门调节方案进行了研究。研究表明:对于具体的某种可变配气系统,其配气参数的调节受该系统可实现的方法、技术、结构、参数等限制,一般只能在一定程度上满足发动机对配气参数变化的需求。根据发动机最优配气参数随发动机工况而变化的趋势要求,在综合考虑发动机配气需求、系统调节控制、配气凸轮设计和系统结构集成特点等相关限制条件的基础上,拟定了液压可变配气系统的气门调节方案。与目前应用较多的基于凸轮轴相位可变的气门调节方案相比,液压可变配气系统气门调节方案更加符合发动机最优配气参数需求的调节方案。建立了液压可变配气系统数学模型和仿真模型,在充分考虑对系统运动规律影响较大的液压参数、结构参数等因素的基础上,对系统运动规律及参数进行了数值仿真。通过与对应的试验结果进行的对比分析表明:仿真与试验结果吻合度较高,仿真模型、参数设置、输出结果可信度较高,建立的仿真模型能够作为下一步气门运动参数分析和优化的基础。根据发动机最优配气参数对气门调节的要求,以及前期研究试验中存在的问题,对液压可变配气系统气门运动参数进行了优化。研究了针对液压可变配气系统中配气凸轮的优化设计方法,使凸轮既能满足气门调节参数、油液压缩补偿和压力波动控制的要求,又能满足接触应力、润滑特性、机构尺寸等要求;研究了气门弹簧参数对气门调节性能的影响,利用系统仿真优化了气门弹簧参数,有效改善了前期研究中出现的气门动力特性、液压参数特性、气门参数可调节性能等不够合理的问题;研究分析了气门落座速度和落座相位的影响因素,利用系统仿真优化了缓冲机构参数,有效改善了气门落座特性,使气门同时具有较低的落座速度和较小的相位延迟。根据优化结果对配气凸轮、气门弹簧参数和落座缓冲机构参数进行了修改,开展了气门运动规律试验研究和性能评价。结果表明:通过优化配气凸轮型线,降低加速度峰值,有效减小了系统压力波动,使系统适用转速提高至5000r/min以上;气门弹簧参数优化后,改善了系统在较高转速时的气门可调节性能,保证了系统在低于4500r/min转速范围内对气门的有效调节;优化后的缓冲机构在保证较小落座相位延迟的前提下,降低了气门落座速度和反跳高度,达到了气门平稳落座的要求。不同转速时的气门调节试验参数表明:液压可变配气系统可实现的实际配气相位和升程与发动机最优配气参数接近。发动机性能预测结果表明:液压可变配气系统与目前常用的其他可变配气系统比较,以及与原机固定配气系统比较,均具有明显优势。
[Abstract]:As an important part of the engine, the performance of the valve system will directly affect the power performance, economy and emission level of the engine. In order to reduce fuel consumption and exhaust emissions, a new type of hydraulic variable valve system proposed by our research group is studied in this paper. It aims at satisfying the engine valve requirements to the greatest extent and making the valve movement have good kinematics and dynamics characteristics. The hydraulic system is variable by combining theoretical research with experimental research. The valve motion law of the valve system is studied. The adjustment method of the hydraulic variable valve system and the adaptability of the parameters to the optimal valve parameters of the engine and the optimization of valve motion parameters are emphatically studied. On the basis of the engine working process simulation model, the engine valve timing parameters such as valve timing angle, lift and so on are optimized. The target values of the optimal valve timing parameters under different working conditions are obtained. The trend and general law of the engine variable valve timing parameters changing with the engine operating conditions are pointed out. The regulation scheme for the variable valve timing system is formulated. The research shows that for a specific variable valve system, the adjustment of valve parameters is limited by the method, technology, structure and parameters that can be realized by the system, and generally can only meet the requirements of engine valve parameters to a certain extent. According to the changing trend of the engine's optimal valve parameters with the engine operating conditions, the valve regulation scheme of the hydraulic variable valve system is worked out on the basis of considering the engine's valve requirements, system regulation control, valve cam design and system structure integration characteristics. Compared with the valve regulation scheme with variable axle phase, the valve regulation scheme of the hydraulic variable valve system is more in line with the requirements of the optimal valve distribution parameters of the engine. The simulation results show that the simulation results are in good agreement with the experimental results, the simulation model, the parameter settings and the reliability of the output results are high. The simulation model can be used as the basis for the next step of valve motion parameter analysis and optimization. According to the requirement of valve regulation for the optimal valve distribution parameters of the engine and the problems existing in the previous research and test, the valve movement parameters of the hydraulic variable valve distribution system are optimized. The requirements of force fluctuation control can also meet the requirements of contact stress, lubrication characteristics, mechanism size, etc. The influence of valve spring parameters on valve regulating performance is studied, and the valve spring parameters are optimized by system simulation, which effectively improves the valve dynamic characteristics, hydraulic parameters and valve parameters adjustable performance in the previous study. The influence factors of valve settling speed and phase are studied and analyzed, and the parameters of cushioning mechanism are optimized by system simulation, which can effectively improve the valve settling characteristics and make the valve have lower settling speed and less phase delay at the same time. The results show that the system pressure fluctuation is effectively reduced by optimizing valve cam profile, and the suitable speed of the system is increased to more than 5000r/min. After optimizing valve spring parameters, the valve of the system at higher speed is improved. The adjustable performance ensures the valves to be adjusted effectively in the range of less than 4500r/min speed; the optimized buffer mechanism reduces the valve settling speed and rebound height on the premise of ensuring a small settling phase delay, and meets the requirements of valve settling smoothly. The valve adjusting test parameters at different speeds show that the hydraulic pressure is adjustable. The results of engine performance prediction show that the hydraulic variable valve system has obvious advantages over other variable valve systems and the fixed valve system.
【学位授予单位】：贵州大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TH137

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