Study On The Mechanism Of Free Piston Engined Hydraulic Reciprocating Pump

This doctoral thesis comes from the project "Free piston engined hydraulic reciprocating pump" supported by the National High Technology Research and Development Program ("863" Program), and the project serial number is 2001AA423150, and the project "Study on the Mechanism of Hydraulic Free Piston Internal Combustion Engine" (the project serial number is 50075077) supported by National Natural Science Foundation of China (NSFC).A free piston engined hydraulic reciprocating pump (abbreviated as HFPE), integrates internal combustion engines and a hydraulic pump into one compact unit. In practical view, there is only one linearly moving part, i.e. the piston assembly in the HFPE. Comparing with crankshaft internal combustion engines (CSICE), the piston assembly within HFPE is not restricted by any mechanical linkages, so its compression ration is variable. When the piston assembly moves linearly back and forth between left and right extremes by means of the fuel energy, simultaneously its hydraulic piston directly produce hydraulic energy.Comparing with the single piston or opposed piston HFPE, the dual piston HFPE (abbreviated as DHFPE) has its own special features such as the highest power density, so selected and determined as the research object .In this thesis, theoretical and experimental studies of the dual piston HFPE are comprehensively and systemically dealt with. The main contents of this thesis could fall into eight chapters as the followings.Chapter 1 covers literatures review. In this chapter, as the inheritor of free piston engines (FPE), the historical background of hydraulic free piston engines, which renewedly takes the stage of power machinery, is first discussed in terms of the trends of the energy resource structure and the needs of the human sustainable development. Secondly, the evolution process of FPE is summarized with presenting its four stages. In addition, HFPE's state of the art, structure types and typical representations, characteristics and future application are described as well as the key problems.Chapter 2 analyzes the design idea and the energy balance of the HFPE prototype. In this chapter, all the subsystems of the prototype are introduced first, then about the steady-going HFPE principles of energy flow and conversion such as the input, dissipation, distribution and output energy, are analyzed. As a result, the proportions of the every energy component and the maximum velocity of the free piston as well as the load pressure are computed or estimated. Last but not the least, methods taken to improve fuel-economic of the engine are concluded.Chapter 3 deals with the dynamic characteristics simulation and the performance parameters calculation on the HFPE prototype. The mathematical models of every subsystem included in the HFPE, such as combustion model of its internal combustion engine, force equilibrium equation of the free piston assembly, models of the hydraulic subsystem, as well as the electronic control unit (ECU), are built up. And the algorithm and the software, i.e. Matlab/Simulink, are discussed. Next, the dynamic characteristics of HFPE are studied, based on which HFPE's structure design, parameters optimization, ignition and control system design, are developed. At last, the performance parameters of the prototype such as the indicated and net efficiency are figured out.Chapter 4 is on the theoretical analysis of the starting system in the HFPE studied. To start HFPE perfectly depends on the harmonious action of every part within the prototype, especially the hydraulic accumulator that serves as the system's energy resource and hydraulic oil resource, the 4/3directional valve and the position sensor as well as the ECU. Then mixture organization, the minimal stroke numbers, energy conversion during starting process are discussed and analyzed. Based on the results above, the guide for selecting the starting hydraulic accumulator is provided. At last the mathematical model is obtained, which is nonlinear two-order differentiate equation of the mass-spring system of the starting system. Meanwhile, the physical significance of any items within it is explained in detail.Chapter 5 discusses the ignition and the control subsystems about the HFPE prototype. In this chapter the relationship between the minimum ignition energy and the mixture concentration is first dealt with as well as the principle and the basic...