Study On Dynamic Characteristics Of Air Springs And Vibration Systems With Air Spring

Compared with coil spring and leaf spring suspensions,air suspension systems equipped with air springs have the advantages of adjustable height,changeable stiffness,low operation noise,and lightweight.These benefits improve vehicle ride comfort,handling stability,and trafficability.However,inherent nonlinear features exist in air springs on materials,contact,and geometry.In addition,the dynamic characteristics of air springs with an auxiliary chamber(ASAC)exhibit strong frequency and amplitude dependence.Therefore,dynamic characteristic modeling for air springs is a challenging problem.This dissertation aims to develop accurate dynamic characteristic models for air springs and optimize the vibration response of air spring systems based on theoretical analysis,simulation,and experimental validations.The main contents of the dissertation are summarized as follows:(1)An experimental setup is developed to study the static and dynamic characteristics of air springs and the vibration response of air spring isolation systems.A test bench with air supply system and vibration excitation system is built.The influences of bellow number and cord angles on the static characteristics of air springs,flow passage sizes on the dynamic characteristics of ASAC,and excitation frequencies and amplitudes on air spring system response are analyzed,respectively.The test results show that the static stiffness of air springs decreases with the increased bellow number but increses with the increased cord angle.The dynamic stiffness of an orifice-type ASAC increases monotonously with the excitation frequency,while a pipe-type one exist a resonance peak.Under step excitation,the transmitted force of an orifice-type ASAC monotonically attenuates while a pipe-type one oscillately attenuated.Besides,the vibration response of the air spring system appears with additional resonance peaks whose magnitude decreases with increasing excitation amplitude.Acceleration transmissibility curves of different amplitudes intersect at amplitude-independent points.(2)A static characteristic model of air springs is developed based on the geometric analysis method.The closed-form expressions for the static stiffness of air springs are derived and some key model parameters such as effective area,volume and their variation rates are obtained by force and geometric analysis.The mathematical model of convoluted air springs(CAS)and rolling lobe air springs(RLAS)are established respectively.Since bellow’s tensile deformation is considered when modeling,the proposed model has a high prediction accuracy for CAS and RLAS.The developed CAS model is proved to have good applicability for CAS with different bellows,while the RLAS model can well represent the RLAS with different cord angles.(3)A frequency-domain and a time-domain dynamic characteristic model of ASAC are developed based on thermodynamic theory.The analytical formula of the complex stiffness of ASAC is derived,considering the frequency and amplitude dependence of the air damping of the flow passage.The mechanism,features,and creation of the resonance peaks exhibited in the dynamic stiffness of pipe-type ASAC are theoretically explained.A parameter identification method is proposed to obtain the frequency-domain model parameters.By using the convolution method,the time-domain transmitted force response under harmonic,step,and random inputs are derived.It is verified that the proposed frequency-domain and the timedomain dynamic characteristic models are accurate and have good applicability for both orificetype and pipe-type ASAC.Based on the time-domain model,the reason for the difference of step force response between the two type ASAC is explained theoretically.(4)Frequency response analysis for a single-degree-of-freedom(1DOF)system with an air spring and a vehicle system with air suspensions are performed,respectively.The dimensionless model of acceleration transmissibility of the 1DOF system is proposed and verified by the test results.The expression of the amplitude-independent point on the acceleration transmissibility curve of the 1DOF system is derived,and a vibration isolation performance design scheme of the system is proposed.Then the ASAC is applied to a vehicle system to analyze its vibration response characteristic.Under the input of the road surface excitation and pulse excitation,the differences in vibration characteristics of the vehicle system with different air spring models are compared and analyzed.