【作者】 任好玲；

【导师】 杨华勇； 谢海波；

【作者基本信息】 浙江大学 ， 机械电子工程， 2013， 博士

【摘要】 液压自由活塞发动机是一种新兴的动力装置,与传统的内燃机驱动液压泵结构相比,它的结构简单,零件数目少,具有较大的功率／重量比；活塞运动时无侧向力,减小了活塞的磨损,降低了维修成本,延长了活塞使用寿命；没有外部机构限制活塞的直线运动,活塞的止点位置是“自由”的,具有可变的压缩比,能够适应为缓解能源紧张而研制的多种替代燃料,燃料的适应范围广；且液压系统具有很好的能量回收功能,因此液压自由活塞发动机尤其适应于需要频繁起动的城市公交系统以及进行抓举的起重机等工程机械。液压自由活塞发动机涉及到内燃机技术、液压技术、传感与检测技术、控制技术等多学科领域,对其展开研究可以拓展新技术,推动相关学科的发展,具有广泛的工程应用前景和重要的学术研究价值。本学位论文提出一种两缸四冲程单活塞式液压自由活塞发动机新结构,该结构具有独立的排气、吸气冲程,使发动机的换气过程更加充分,改善了自由活塞发动机的燃油经济性和排放性能,仿真结果表明,该结构的换气效率比二冲程自由活塞发动机的换气率提高了15%。自由活塞组件是两缸四冲程液压自由活塞发动机的唯一运动部件,建立了其在燃烧腔高温气体、液压腔液压力、摩擦力等作用下的非线性振动方程,分析了活塞振动过程中,燃料燃烧释放能量与液压能之间的能量转化,揭示了活塞组件在压缩和膨胀冲程中振动存在差异性的根本原因是所受作用力不同。由于活塞组件在两个冲程中的振动特性存在差异,两个冲程的振动时间也不同。调节各工作参数保证发动机的膨胀与压缩时间之比约为0.65。为保证两个冲程中的平均输出流量相等以降低发动机的流量脉动率,设计发动机在膨胀与压缩冲程中泵腔的容积变化之比为0.65。仿真结果表明四冲程液压自由活塞发动机在两个冲程中输出的平均流量基本相等,一个工作循环内的流量脉动率约为1.7；对应于没有液压泵输出流量脉动控制的液压自由活塞发动机,其输出流量脉动率约为2.1。本文的研究结果对深入研究液压自由活塞发动机提供了理论分析和设计参考。本学位论文的基本结构如下：第一章,介绍了自由活塞发动机的特点、关键技术问题和发展历程,重点介绍了单活塞式液压自由活塞发动机的研究现状,论述了本学位论文的研究目的和意义,确定了本学位论文研究的主要内容。第二章,介绍了单活塞式液压自由活塞发动机的三种基本结构,综合比较了三种结构下系统所需要的压缩能、输出液压力的脉动、燃油消耗量、机体振动和效率等,确立本学位论文研究的主要对象。第三章,介绍了两缸四冲程单活塞式液压自由活塞发动机的基本结构和工作原理,建立活塞组件的振动非线性方程,讨论活塞组件在不同条件下的振动特性,研究了两个冲程中活塞振动特性存在差异的本质及影响因素；讨论了活塞组件振动特性差异性对单活塞式液压自由活塞发动机性能的影响。第四章,利用伺服电机代替曲轴机构来驱动内燃机的配气机构和喷油系统,并重新设计了凸轮轴；对液压自由活塞发动机压缩腔的缓冲特性和压缩特性进行了设计和计算；并对发动机的整体结构进行设计以期最大限度地减小一个工作循环内的流量脉动、增加发动机的稳定性。第五章,基于理论和设计计算,对发动机整体性能进行仿真,分析了活塞组件的运动特性、各液压腔和燃烧腔的压力特性、内燃机的温度特性、燃油喷射和放热特性、进气和排气特性等；分析了发动机一个工作循环内的能量分配情况,为更好地提高发动机的效率,优化发动机设计提供依据。第六章,对发动机的压缩、泵油、‘‘缺火’’复位、缓冲及伺服电机驱动的配气和喷油等子系统进行测试,验证各子系统的预定功能；研究压缩腔的建压时间即活塞启动延迟时间对系统运行频率和输出功率的影响,分析影响建压时间的因素并提出优化措施。第七章,总结了本学位论文的主要研究和成果,指出本学位论文研究的创新点,并对今后的研究工作进行了展望。更多还原

【Abstract】 Hydraulic Free Piston Engine (HFPE) is an emerging power source for hydraulic systems, which has a much simpler structure, smaller number of components and larger power to weight ratio compared to the traditional hydraulic pump driven by the crankshaft engine. Due to the linear movement of free piston assembly (FPA), HFPE reduces the FPA wear and the maintenance costs with longer lifetime cycle. Without the restriction of any mechanism, the dead centers of FPA are free. Therefore, HFPE has a variable compression ratio which allows multi-fuel applications. Since hydraulic system has good adaptability to recover energy, it is possible that HFPE could fit into the urban buses and cranes to recover energy, such as the bus frequently starts/stops or the crane lifts/drops loads. HFPE is associated with the combination of the internal combustion engine, hydraulics, sensor, condition monitoring and control technologies. The development of HFPE could bring new technologies and promote the development of the related disciplines.A new structure design of the four-stroke HFPE has been proposed, which enables separate exhaust stroke and intake stroke to work more effectively, hence the fuel usage and particle emission can be reduced. The gas exchange efficiency with the four-stroke structure of HFPE can be improved by15%compared to the two-stroke structure according to simulation study. FPA is the only moving part of the four-stroke HFPE, its nonlinear vibration equation has been established with the force of the hot gas in the combustion chamber, fluid forces both in the pump chambers and compression chamber together with the friction forces. The energy conversion between the energy released from the injected fuel and the hydraulic energy has been analyzed during FPA vibration. The vibration characteristics of FPA are dissimilar between the compression and expansion strokes because the forces acting on FPA are different in the two strokes. As a result, the vibration time of the two strokes are different. The vibration time ratio of the expansion and compression strokes has been adjusted to0.65through regulating the operation parameters. The volume change ratio of the pump chambers in the expansion and compression has been set to0.65to make the average output flow rate equal and to reduce the flow pulsation accordingly. The average flow rate of the expansion stroke are almost equal to that of the compression stroke and the flow pulsation ratio is around1.7calculated in simulation. As a comparison to HFPE without control of the flow pulsation ratio, the ratio was around2.1as shown in the literature. The study in this thesis can be used as a reference for theoretical analysis and design consideration of HFPE.In chapter1, an overview of the features, key technologies and the research state of art on the free piston engine, especially about the single-piston HFPE (SHFPE), are presented. The objectives of thesis study are addressed. The main contents are outlined.In chapter2, the three basic structures of SHFPE are introduced. The structure with two pump chambers is chosen to be the study objective by comparing the compression energy, the pressure pulsation, fuel consumption, engine body vibration and efficiency of SHFPE.In chapter3, the basic structure and operation process of SHFPE are presented. The vibration equation of FPA is established. Vibration characteristics of FPA under different conditions are discussed. Then the influence of the different characteristics of FPA vibration on the performance of SHFPE is presented.In chapter4, the servo motor is used to substitute the crankshaft to drive the valve mechanism and the injection system. And the camshaft is redesigned to suit the operation of SHFPE. The cushion and the compression characteristics of the compression chamber are designed and calculated. The reduction of the flow pulsation and the stability of FPA movement are assured through the overall design of SHFPE.In chapter5, the performance of SHFPE is simulated based on the design parameters and theoretical analysis. The kinematics characteristics, pressure characteristics of hydraulic chambers and combustion chambers are analyzed. The energy distribution within HFPE in one working cycle is discussed. The simulation results can be used as a reference to improve the engine efficiency and to optimize the SHFPE design.In chapter6, the subsystems of the compression, pump and reseting after misfire have been tested and the results have shown that the desired performance of the subsystems can be achieved. The pressure build-up time of the compression chamber has significant influence on the frequency of SHFPE. In addition, the influence factors on the pressure build-up time are analyzed and the optimization methods are proposed.In chapter7, conclusions are summarized and future research outlooks are suggested.更多还原