| The hydro-pneumatic suspension (HPS) technology is a new vehicle suspension technology that combines hydraulic transmission and control technology with suspension technology, which makes HPS have not only performances of traditional passive suspension, but also comprehensive performances of (slow) active suspension. HPS is a key technology to develop special vehicles and engineering vehicles, and it has enormous potential market as well as broad industrial application prospects.The thesis takes the HPS with dual gas-accumulators of a type of automobile as project for research, the systematic research into the HPS system of engineering vehicles involving its dynamics analyzing, modeling and simulating with the application of the vehicle dynamics theory, hydraulic transmission and control theory and computer simulation technology is achieved. Non-linear mathematical model of the HPS with dual gas-accumulators is built up. According as the non-linear mathematical model, the switch controller and fuzzy controller are built for the HPS to control its damping force and elastic force and to make it be an active suspension, and the computer simulation is carried out in Matlab/Simulink. The simulation results provide a theoretical foundation for developing and designing semi-active HPS system and active HPS system.The thesis mainly includes the following contents:(1) The need of studying the active suspension and active HPS isindicated. The development and application of passive suspension,semi-active suspension and active suspension are introduced in detail, and the technical specialties,development history and application status of HPS are introduced as a main content of the thesis.(2) The working priciple of HPS with dual gas-accumulators is educidated, and a physical model and a non-linear mathematical model of HPS with dual gas-accumulators are built up. The physical model is simplified reasonably by taking account of hydraulic oil compressibility, hydraulic hose expansibility and other factors.(3) The thesis deduces the mathematical model presented by a series of equations between damping force and elastic force of HPS from the HPS physical model and mathematical model, which supports that HPS has non-linear damping characteristic and non-linear rigidity characteristic in substance. By means of the computer simulation which take different frequency,different amplitude sine wave as the signal input, the factors which affect damping characteristic and rigidity characteristic are analyzed in detail.(4) The controllers are designed for the HPS. The switch controller is applied to control the damping force by means of controlling the number of damping holes; the fuzzy controller is applied to control the elastic force of the gas-accumulators by means of controlling the initialization pressure of the gas.(5) Referring to the international standards about road classification, a time-domain model of road surface based on power spectrum density (PSD) of road surface is built up. On the basis of the non-linear damping model and non-linear rigidity model of HPS, the thesis sets up the two-freedom non-linear dynamics model (1/4 vehicle dynamics model) for the HPS system excited by the random road surfaces and typical sine wave road suefaces. By the use of the simulation software—Matlab/Simulink, the simulation of the dynamicmodel of HPS system is performed, and the time-domain signals,frequency-domain signals such as accelerations of vehicle body,dynamic displacements of suspension and dynamic loads of wheel are obtained. After the signals are obtained, their root-mean-square (RMS) is gotten. The results gotten from the simulation prove that the controllers are reasonably.(6) The advice for the farther research of HPS is put forward referring to the researchful results of the thesis.In brief, concerning advanced technology and engineering applications of varieties of HPS at home and abroad, taking HPS of a practical engineering vehicle as object for research, the systematic research into it is achieved through Matlab/Simulink, and the controllers are designed for it, and the effect is good.
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