Approximately Analytical Study On Semi-active Control System

As the car has been used more and more widely, the car industry has a rapid development in the world. The automobile suspension system is the important device in car to reduce body vibration and ensure the safety. Developing the safe, comfort, high-efficiency, energy-saving, clean and intelligent vehicle suspension to satisfy people is not only the development direction of automobile field, but a great challenge to automobile industry. Semi-active suspension has better control performance than passive suspension and simpler structure than active suspension, so that semi-active suspension is a hot spot in the field of vehicle dynamics in recent years.Semi-active suspension in automobile is the main line of this thesis. First of all, the average method has been discussed and extended in Chapter2. The average method is one of the approximately analytical methods to analyze the suspension system usually. Comparison between the improved average method and traditional average method shows that the improved one can get the same results as the traditional one, and has simpler solving process than the traditional one. Then the improved average method is used to get the approximate analytical solutions for the main resonance, superharmonic resonance and subharmonic resonance of three kinds of polynomial type nonlinear system. The results of some typical examples prove the correctness of the theoretical derivation results. The analytical analysis of some other engineering examples can also refer to the above conclusions.In Chapter3the research is focused on dynamical analysis of a single degree-of-freedom semi-active suspension system with time delay. The control method is called as the finite relative displacement control. With the use of the average method the approximate analytical solution is obtained, and the system stability condition is established for the semi-active suspension system and passive suspension system based on Lyapunov theory. Through MATLAB numerical simulation and analytical research, not only proved the superiority of semi-active suspension and the accuracy of approximate analytical solution, but explained the high frequency chattering phenomenon in semi-active control. Finally, the effects of some key system parameters, including control clearance, delay quantity and minimum damping, have been analyzed.At last, a three degree-of-freedom of semi-active combined control system, including vibration absorption and vibration isolation, is presented and studied in Chapter4. With the use of the average method, the approximate analytical solution of the combined control system is analyzed. As a compsrison, the2-DOF semi-active vibration isdolation system and the2-DOF semi-active vibration absorption system are also studied. Through the MATLAB numerical simulation and analytical research, not only proved that the three kinds of system have the accurate analytical solution, but also proved that combined control system has better control performance compared to the2-DOF vibration absorption system and vibration isolation system, which demonstrated the validity of the combined control system.Finally, the summarization is done in Chapter5, and some possibly developing directions in this field are pointed out.