The Vibration Of Hydraulic Single Free Piston Engine

The Free Piston Engine (FPE) is a kind of power-plant which realizes the energyconversion through the rectilinear reciprocating piston. FPE has three stages ofdevelopment, which includes the generated stage of concept, the stage of gasifier, and thestage of linear hydraulic pump (or linear generator). The most studied, currently, are theHydraulic Free Piston Engine (HFPE) and the Free Piston Generator (FPG) in domesticand overseas. The single piston style, the double piston style and the opposed piston styleare three kinds of HFPE structurally. The thesis researched the single piston style HFPEwhich inherently has the problem of vibration.According to the structure and function, the HFPE system can be divided into foursubsystems, the combustion system, the hydraulic system, the controlling system and thesupport system. The working process of HFPE can be segmented into four phases, thepreparatory phase, the start-up phase, the stabilization phase and the halt phase. And on thebasis, three ideal model were established, which included the thermodynamic model ofcombustion room, the pressure model of hydraulic and the dynamic model of free piston.The equations of forces effected on free piston and engine body, derived from these models,are the foundation of dynamics simulation.Characteristics of vibration of HFPE system are self-excited, variable stiffness anddamping, and single degree of freedom. Two methods, test and simulation, were used toresearch the vibration in the thesis.Test. The step of test is that designed the scheme of test, installed sensors andinstruments, and collected, disposed and saved data by the vibration noise tester of LMSTest.Lab. Two conclusions can be summarized from figures. Firstly, the vibration isolationcan weaken effectively the amplitude of vibration transmission in the extensive frequencyrange, however can’t change frequency. Secondly, at Bottom Dead Center (BDC), theimpact between the free piston and the engine body, can cause shock excitation on the latter. Therefore, a buffer structure was placed at the BDC, to avoid or weaken the force ofimpact.Simulation. The3D model of engine was created by employing software Creo, andwhich was imported ADAMS software to build the virtual prototype. The result ofsimulation gave the same conclusion of the test.Against the problem of impact, three kinds of buffer structure were designed, whichwere rubber solution, hydraulic solution, and spring solution. The rubber solution waschosen to build rigid-flexible coupling model. The modal neutral file (MNF) of flexiblebody was created by employing software ANSYS. And then the MNF was importedADAMS to make dynamics simulation. The result of simulation showed that bufferstructure can cushion the impact, however enlarge the cycle period of free piston motion.The design scheme of supporting leg and vibration isolation structure shouldaccording to the characteristic of engine vibration, and satisfy the demand of support theweight of engine. And then to build the rigid flexible coupling model, and to simulate. Theresult of simulation show that the vibration isolation structure can weaken the vibrationtransmission and vibration of engine to some extent. However, the vibration model ofpedestal is more complexity than engine body. The kinetic energy of pedestal wasapproximately equally assigned to translational kinetic energy and angular kinetic energy.There are many contents need to deeply research, such as, to build more elaboratesimulation model, to conduct modal analysis of engine body, and to solve the vibrationproblem by using the technology of balance mechanism or active control.