Static And Dynamic Characteristics Of Cab Air Suspension Of Commercial Vehicle

With the rapid development of high-grade highway and the increase of traffic of our country, and with people's demand of ridding comfort extending from car to commercial vehicle, the demand of performance of commercial vehicle is getting higher and higher. In the traditional design, the cab of truck was located on the frame directly. Therefore, the libration of the frame was transmitted to the cab directly, and the ridding comfort was bad. To increase the ridding comfort of the cab of commercial vehicle, especially of heavy truck, companies and factories started to induct technique of isolation of vibration. Whit the springing up of air spring, its application extended from coach to truck. Nowadays, application of air spring on commercial vehicle is highly developed. Ministry of communications of PRC has stipulated that from 1st January of 2007, suspension of the first grade of large coach and the second grade of middle coach should be air spring suspension. The use of air suspension on commercial vehicle instead of leaf spring suspension, coil spring suspension is the inevitable trend as well as the objective requirement.Integrated the development project of commercial vehicle cab's air mount, this paper took the diaphragm spring of front mount of commercial vehicle'cab as study object. By means of non-linear finite element theory, non-linear dynamics, the characteristic of air spring was theoretically analyzed, tested and simulated.This paper represented the structure and characteristic of air spring and air suspension, introduced the development status and the research status. Base on that, the consequence of further study was brought on the desk.The basic theory of finite element was introduced, its application and development was represented. And then the material nonlinearity, geometry nonlinearity, contact nonlinearity and the air-structure coupling characteristic of air spring were analyzed, the necessary of induction of finite element method is represented, and finite element analyzing software ABAQUS used in this study was briefly instructed.The main contents and studying achievements were as follows:1. Base on the theory of engineering thermodynamics, the dynamical model of air spring was set up,and the mathematical expressions of stiffness and frequency were deduced, the characteristic was theoretically studied, the main parameters that have effects on the characteristic, such as variable index of the air, initial inflation pressure of rubber balloon, initial volume of rubber balloon, the changing rate of effective bearing area, and their trend of contribution, were analyzed. A kind of theoretical basis was provided.The results of theoretical study showed that the dynamical model of air spring could be simplified as a structure of two springs. Air spring has obviously variable non-linear stiffness characteristic, and its stiffness and frequency were related to the initial inflation pressure or rubber balloon, initial volume of rubber balloon and the changing rate of effective bearing area.2. The theory and method of test of air spring's characteristic were introduced. The curves of static characteristic and dynamic characteristic were achieved. Through these curves, the effect to static bearing ability, static stiffness of initial inflation pressure, the effect to dynamic stiffness of initial inflation pressure, frequency and amplitude of the excitation were analyzed.The testing results told that the static bearing ability and static stiffness changes when the load changed, and the static load—displacement curve is as the shape of reversed"S". The curve is subdued near the standard height and sheer at the extruding side and compressing side. In other words, the static stiffness is small near the standard height and large at the extruding side and compressing side. The static bearing ability and static stiffness of air spring increase as the initial inflation pressure increases. As initial inflation pressure or frequency of the excitation increases, or as amplitude of the excitation decreases, the dynamic stiffness of air spring increases. The initial inflation pressure has more contribution to the changing of dynamic stiffness, while the amplitude of the excitation has less. The frequency of the excitation has more contribution to the changing of dynamic stiffness in the range of low frequency and has less in the range of high frequency. The testing results were the same as the result of theoretical analysis, so it proved the result theoretical analysis right.3. The characteristics of air spring were studied with finite element analysis.Firstly, the method of setting up the finite element model of air spring was represented. The whole process of setting up the model was introduced, including selecting the types of elements, defining the parameters of materials, setting up the 3-D model, defining the contact conditions and boundary conditions, determining the step of analyzing.And then the static and dynamic characteristics were analyzed by finite element method, and the results were compared with the testing results to prove the finite element model right. After that, the air spring was further finite element analyzed, such as analyzing the stress and strain of the rubber balloon in the inflating status, max-extruding status and max-compressing status.Lastly, the sensitivity of designing parameters of air spring were analyzed by finite element model, such as the effect to the static bearing ability and dynamic stiffness of initial inflation pressure, angle of curtain-line, spacing of curtain-line in the plain, cross-sectional area of curtain-line and number of layers of curtain-line. The results showed that the static bearing ability and dynamic stiffness of air spring increase as the initial inflation pressure or cross-sectional area of curtain-line or number of layers of curtain-line increases, and as the angle of curtain-line or spacing of curtain-line decreases. The initial inflation pressure, angle and number of layers have more contribution, while the spacing and cross-sectional area have less. All these results can provide a basis of designing and optimizing of air spring.