| Although the suspensions with air springs as their elastic elements have many advantages, the performance of suspension would be further improved if an auxiliary chamber is appended to air spring. Not only for the road vehicles, but for the off-road vehicles such as agriculture vehicles, construction vehicles, forestry vehicles, the application of air suspension to them would help to improve their adapting ability to running road condition and working environment.Based on 1T15M-2 type diaphragm air spring produced by Firestone company, the air spring with auxiliary chamber system was established through a tube and a orifice. According to related studies at home and abroad in present, the dynamic characteristics of air spring with auxiliary chamber system was systematically researched using the methods of theoretical analysis combining with experiments, and influential factors and influential laws on the system's dynamic characteristics have been analyzed in detailed, and design schemes of air suspension with auxiliary chamber system were presented. The completed work and achieved results are generalized as follows:1. The non-linear dynamics theoretical model of air spring with auxiliary chamber was established based on rigid dynamics, thermodynamics and fluid dynamics. Simulation model of system was established under Matlab/Simulink environment. Displacement step respond characteristics and amplitude frequency characteristics of the system were simulating analyzed. The results showed that, natural frequency of the system would be reduced under the function of auxiliary chamber, and vibration of the system would be greatly attenuated by properly adjusting the open size of orifice.2. Relation between static stiffness of air spring and air spring deformation and relation between effective area of air spring and air spring deformation were established according to the static characteristics experiments. The dynamic stiffness theoretical model of system was established, and the experimental system for dynamic stiffness of system was established. The dynamic stiffness theoretical model was verified to be correct by experiments, and the influential factors on dynamic stiffness were analyzed. The results showed that, dynamic stiffness of system increases with the increasing of air spring pressure, vibration frequency and vibration amplitude, and dynamic stiffness of system drops from the maximum to minimum with the increasing of orifice diameter. Increasing volume of auxiliary chamber is help to decrease dynamic stiffness of system, but when the volume of auxiliary is more 2-3 times than that of air spring, changing volume of auxiliary chamber has little affect on dynamic stiffness. The results of dynamic stiffness theoretical model and the results of experiments are close on the whole, which proved that dynamic stiffness theoretical model are correct.3. In order to simply the model and help to analyze and control suspension, the mathematical model of air spring with auxiliary chamber system was linearized with small deviation linear method under the condition of little amplitude. The linear dynamic stiffness model of system and linear kinematics difference equation were obtained, and transfer function of sprung mass displacement was reduced from linear difference equation.4. Effective stiffness calculating model, effective damp ratio calculating model and natural frequency calculating model of air spring with auxiliary chamber system were established based on complex stiffness. Test system for mechanical parameters of effective model was established, and the influential laws of orifice open, auxiliary chamber volume, sprung mass on the mechanical parameters of effective model, at the same time the effective mechanical parameters calculating models were verified by test. The study results showed that, when the volume of auxiliary chamber was 2 times that of air spring, with the increasing of orifice open, effective stiffness of system could be decreased by 60%, and natural frequency could be decrease by 0.45Hz, and effective damp ratio was increased first, then decreased. By increasing volume of auxiliary chamber can decrease effective stiffness and natural frequency, but when the volume of auxiliary chamber was more than 2-3 times that of air spring, increasing volume of auxiliary chamber has little effect on effective stiffness and natural frequency of system. When orifice open widely, by increasing the volume of auxiliary chamber only increased damp ratio of system a little, while orifice open at the condition of maximum damp, by increasing volume of auxiliary chamber could obviously increased effective damp ratio of system. Keeping the static operational high of air spring unchanged, effective stiffness would increase with the increasing of sprung mass, but the change of sprung mass has little effect on effective damp ratio and natural frequency of system. Comparing calculation results of model with test results showed that the calculation model of effective stiffness, effective damp ration and natural frequency keep a high accuracy within a certain limit range. 5. Experimental system for vibration response characteristic of air spring with auxiliary chamber was established, Effect of orifice diameter, volume of auxiliary chamber and excitation frequency on displacement transmissibility, maximum dynamic load and response acceleration was studied by experiments. Experiments showed that, during the course of increasing orifice open from close to wide, the change laws of displacement transmissibility, maximum dynamic load and response acceleration of system were about the same, they all fell rapidly at first, they fell to the minimum value when orifice diameter increase to about 6mm, and then they all increased slowly with the continue increase of orifice diameter. Change of auxiliary chamber volume also has obvious effect on displacement transmissibility, maximum dynamic load and response acceleration of system. By increasing volume of auxiliary chamber could depress the tree indexes mentioned above, but when the volume of auxiliary chamber was more than 2 times that of air spring, increase of auxiliary chamber has little effect on the tree indexes.6. Design schemes of passive air suspension with auxiliary chamber and semi-active air suspension with auxiliary were presented and analyzed. A quarter-vehicle vibration model with adjustable stiffness and adjustable damp suspension was established, and the simulation model for vehicle ride was established under Matlab/Simulink environment based on the vibration model. Ride performance indexes of passive air suspension and semi-active suspension with adjustable stiffness and adjustable damp were compared and analyzed through simulation of vehicle running on different pavements with different velocity. The results showed that, acceleration root mean square vehicle body with semi-active suspension increased more than 30% on the most pavements. But the dynamic load of tire has little improvement under the precondition of effectively decreasing acceleration of vehicle body.Through the research in this project, the dynamics theory system of air spring with auxiliary chamber will be further improved, which will provide a theoretical basis and technical support for design and control of air suspension with auxiliary chamber. And this research is of important theoretical significance and practical value to promote the application of air spring with auxiliary chamber system to vehicle and to improve the performance of vehicle suspension system.
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