Study On Modeling Methods And Dynamic Characteristics Of Vehicular Air Damping Air Spring

Air damping air spring(ADAS)adds the throttling element between the main chamber and auxiliary chamber to produce air damping,which is possible to replace traditional hydraulic shock absorber.ADAS is helpful to improve the fatigue life of compenents and vehicle performance and to achieve the lightweight of vehicle.ADAS has the characteristics of variable stiffness and variable damping,which not noly extends the performance of air spring,but also is the hot point of development of vehicle suspension.This research topic originates from prediction models of structural parameters and the nonlinear model of rubber bellows,which improves the modeling method of air spring and solves structural parameters identification and the relatively large calculation error peoblem due to ignore the effect of rubber bellows,which also provides the theoretical support for forward design of air spring.On the basis,the mathematical modeling and dynamic characteristics of ADAS are studied.This study will provide the theoretical and experimental foundation for design and matching of stiffness and damping,parameter optimization and control strategyg of ADAS applied to vehicle.The main research work is as follows,(1)A new refined model of air spring including compressed air model and rubber bellows model is achieved.it is pointed out that the effective area,the change rate of effective area,the effective volume and the change rate of the effective volume are the key parameters.These four structural parameters is important for the mechanical properties of air spring.For two differently typical structure of convoluted air spring and rolling lobe air spring,two theoretical prediction models of structural parameters including design parameters are established using a geometrical and mechanical analysis approach.Two analytical models of structural parameters are validated by experiments.These models completely change the approach of obtaining structural parametes mainly by experiment.On the basis,influence laws of design parameters are further analyzed,which provide importantly theoretical guidance for forward design of air spring.(2)Experimental researches on static and dynamic characteristics of air springs are carried out.The experiments show that the rubber bellows have a great influence on the static and dynamic characteristics of air springs.The nonlinear characteristics of rubber bellows include hysteresis loop characteristic,amplitude dependence and frequency dependence,and so do air springs.Considering the nonlinear characteristics of rubber bellows,the nonlinear model of rubber bellows is composed of friction model and fractional derivative Kelvin-Voigt model for representing amplitude dependence and frequency dependence of rubber bellows.Six-steps indentification method of model parameters of rubber bellows is put forward.The mechanical model of air spring is further improved.Model parameters of double convoluted air spring and rolling lobe air spring are obtained by the proposed identification method.The effectiveness and universality of rubber bellows model are verified by experiments.(3)Comprehesively considering the variation of structural parameters,the nonlinear effect of rubber bellows,pressure change,temperature change and turbulence effect,the nonlinear and linear model of ADAS including key design parameters are established.The model of ADAS is complemented.Based on MTS370,The experimental platform of static and dynamic characteristics of ADAS is set up.The linearized model of ADAS is validated by experiments.Dynamic characteristics are compared for throttling orifice type and throttling pipe type ADAS.A selection suggestion of ADAS is also provided.Characteristic parameters of dynamic characteristics of ADAS are proposed.Equivalent stiffness,equivalent damping coefficient,loss factor and equivalent damping ratio equations are also derived by equivalent complex stiffness method.The dynamic performance parameters of ADAS are directly introduced into vehicle suspension design field.Finally,the influences of turbulence effect and rubber bellows characteristics on the dynamic characteristics of ADAS were analyzed.The influence laws of external excitation and key design parameters on the dynamic characteristics of ADAS are further studied.These lay the foundation for the application,design,matching and parameter optimization of ADAS.(4)A PADAS is integrated into a quarter car model.The influence laws of key design parameters on the ride comfort of a quarter car is analyzed.Meanwhile,the feasibility of replacing traditional hydraulic shock absorber is also investigated.In view of the shortcoming of air damping which cannot suppress the tire resonance,two new methods of adding a small hydraulic shock absorber in parallel with PADAS or double-pipes PADAS of different diameters are proposed.This method completely not only takes advantage of the good vibration reduction of air damping on body resonant area,intermediate frequency area and high frequency area,but also effectively suppress the tire resonance by utilizing a small shock absorber.In particular,the new scheme of the double-pipes PADAS of different diameters in parallel with a small hydraulic shock absorber is presented,which greatly enhances the ability of suppressing the body's resonanse and improves ride comfort.