Analysis On Dynamic Characteristics Of Interconnected Air Suspension And Its Effects On Full Vehicle Vibration Performance

With the increasing requirements on vehicle ride comfort, the application of air suspension on vehicles is widely used. As the development of vehicle technology, the interconnected air suspension which is developed on the base of ordinary air suspension is introduced to the vehicles, where the independent air springs are connected by pneumatic pipes controlled by electromagnetic valves. The gas in the air springs can be exchanged according to different driving conditions to realize variable stiffness characteristics. Combined with the adjustable damping of shock absorber, the air suspension performance can be further improved. The thesis focuses on the dynamic characteristics of air suspension and its effects on full vehicle vibration performance.The thesis was carried out from the research of part to the vehicle, which included three different parts: modeling and simulation of the interconnected air spring, vibration characteristics and dynamic stiffness of the interconnected air spring system, modeling of the interconnected air suspension system and its effects on vibration performance of full vehicle.As the interconnected air springs are the core components of the interconnected air suspension, the mathematical models of interconnected air springs modules and pneumatic pipe modules were established respectively based on the theory of engineering thermodynamics and fluid mechanics. The corresponding simulation models were established under the Matlab/Simulink environment. Based on the two degrees of freedom vibration system, the free vibration and forced vibration responses of the system were analyzed. The results showed that the interconnected state, pipe diameter and phase angle had a significant influence on the characteristics of vertical and angular vibration responses.Based on the mathematical models of interconnected air spring modules, the theoretical calculation model of nonlinear dynamic stiffness of interconnected air springs was derived, which revealed the influence of variable parameters on the dynamic stiffness of interconnected air springs and the coupling relationship between the variables. The mathematical model of each module of the interconnected air spring system was linearized by tangent method and the linear dynamic stiffness model of interconnected air springs under the small amplitude condition was derived, which eliminated the nonlinear variables in the dynamic stiffness model and reduced the complexity of the nonlinear model calculations.Based on the former research on the system characteristics of interconnected air springs, the full vehicle model with interconnected air suspension which integrated non-interconnection, lateral interconnection, longitudinal interconnection and four-corner interconnection was established based on the vehicle dynamics theory and was analyzed by simulation. The effects of four interconnected modes on the vertical, pitch and roll inherent frequency was analyzed. The time-domain model of random roads and twist roads were used as the road inputs. The responses of body acceleration, suspension working space, wheel dynamic load and torsion load under four interconnected modes were studied. The results showed that interconnected air suspension could reduce the natural frequency of body angular vibration, improve the ride comfort on uneven roads and reduce the torsion load of vehicle body.The full vehicle test bench of interconnected air suspension was built. The step excitation, sinusoidal excitation and strengthened pavement excitation were applied as the road inputs. The influences of pipe diameter, shock absorber damping and initial height of air spring on frequency responses of left front body acceleration were studied. The effects of non-interconnected, lateral interconnection, longitudinal interconnection and four-corner interconnection on the frequency responses of vertical, lateral and longitudinal acceleration of vehicle body were analyzed contrastively. The results showed that the interconnected air suspension could improve the vehicle vibration performance in a wide frequency range, absorb the impact of pavement and improve the vehicle ride comfort on uneven road.