空气悬架系统以其可变高度、轻量化、偏频较固定、可显著提升车辆操纵稳定性和平顺性等优势，现已成为车辆领域的研究热点。但目前由于其多物理场耦合所致的非线性和滞回特性导致其缺乏定量解耦的物理模型、结构设计和材料选择的一般方法、和对系统非线性传递特性的量化阐述。其关键原因就是对空气弹簧的机理建模不够深入，对空气悬架的动态特性认识不足，进而在空气悬架系统的设计和动力学匹配阶段需付出大量试错成本。本文从热力学、橡胶非线性力学和系统传递特性出发，开展了以下创新性的工作。1）建立了空气弹簧统一动力学模型，能适用于单腔室和双腔室空气弹簧的变质量充放气过程和定质量工作过程。该模型综合考虑了各腔室刚度、热交换及连接孔处产生的等效阻尼特性，具有明确的物理意义及精确的数学表达，可以精确解耦地反映空气弹簧动刚度频率相关性。基于非线性理论，针对空气弹簧二次非线性特性提出了主共振及谐波共振情形下共振峰及其对应频率的解析表达式。2）提出了空气弹簧由橡胶气囊Payne效应导致的动刚度振幅相关性理论，总结了空气弹簧总刚度的一般解耦表达式。基于橡胶材料黏弹性理论指出了橡胶材料的Payne效应是空气弹簧动刚度振幅相关性的直接诱因；根据最小余能原理阐明气囊厚度和垂耳半径是导致附加刚度的主要因素；结合空气弹簧有效面积和有效体积识别方法，指明了空气弹簧在不同工况下的动态特性变化规律。3）揭示了空气悬架非线性传递特性随激励频率和振幅变化的机理。通过构建精确的非线性空气悬架四分之一车辆模型，首次定量揭示了空气悬架传递特性的频率和振幅相关现象。结合所搭建的高精度、多功能台架验证了不同腔室和模式的空气悬架系统的低通滤波特性，明确了不同设计参数及载荷情形下空气悬架系统的幅相特性变化规律。4）搭建了考虑空气弹簧非线性动刚度特性的七自由度整车模型，结合惯性测量单元软测量技术验证了带空气悬架整车在不同速度、路面和减振器阻尼情形下的动态特性。基于驾乘体验主观评价结果，总结分析了装配有不同空气悬架整车动态特性的对比结果及其机理解释。本文所提出的低动静比低阻尼空气弹簧技术可为空气弹簧动态特性的精确预测和指导正向设计及动力学匹配提供完整有效的理论体系，该理论可直接用于空气弹簧设计或初期试制，从而加快我国自主研发国际一流空气弹簧的进程。
The air suspension system has become a research hotspot in vehicles because of its variable height, lightweight, relatively fixed natural frequency, and can significantly improve vehicle control stability and ride comfort. However, due to the nonlinear and hysteretic characteristics caused by its multi-physics field coupling, it lacks a quantitative decoupled physical model, a general method for structural design and material selection, and a quantitative elaboration of system nonlinear transfer characteristics. The key reason for this is the inadequate in-depth modeling of the air spring mechanism and the insufficient understanding of the dynamic characteristics of the air suspension, which results in a significant trial-and-error cost in the design and dynamic matching stage of the air suspension system. This paper carries out the following work from the perspective of thermodynamics, rubber nonlinear mechanics and system transfer characteristics.1) The unified dynamic model of the air spring is established, which can be applied to the variable mass inflation/deflation process and the constant mass working process of the single- and dual-chamber air springs. This model comprehensively considers each chamber‘s stiffness, the equivalent damping characteristics generated by heat exchange and the connecting orifice. It has a clear physical meaning and precise mathematical expression, and can accurately decouple and reflect the frequency dependence of air spring dynamic stiffness. Based on nonlinear theory, an analysis is conducted on the quadratic nonlinear characteristics of air springs, and analytical expressions for resonance peaks and their corresponding frequencies are proposed for the cases of primary and harmonic resonance.2) The theory of the amplitude correlation of the air spring dynamic stiffness caused by the Payne effect of the rubber diaphragm is proposed, and the general decoupled expression of the total stiffness of the air spring is summarized. Based on the viscoelastic theory, it is pointed out that the Payne effect of rubber materials is the direct cause of the amplitude-dependence of air spring dynamic stiffness. According to the principle of minimum complementary energy, it is explained that the thickness of the rubber diaphragm and the lobe radius are the main factors causing additional stiffness. Combined with the proposed identification methods of the effective area and effective volume of the air spring, the changing regulations of the dynamic characteristics of the air spring under different working conditions are pointed out.3) The mechanism of the air suspension‘s nonlinear frequency- and amplitude-dependent transfer characteristics has been revealed. By constructing an accurate nonlinear quarter-car air suspension model, the frequency- and amplitude-dependent phenomena of air suspension transfer characteristics are quantitatively demonstrated for the first time. Combined with the built high-precision and multi-functional bench, the low-pass filter characteristics of the air suspension system with different chambers and modes are verified. The amplitude-phase characteristics of air suspension systems under different design parameters and load conditions are clearly identified.4) The seven-degree-of-freedom vehicle model considering the nonlinear dynamic stiffness characteristics of the air spring is constructed, and the dynamic characteristics of the vehicle with air suspension under different speeds, road surfaces and shock absorber damping conditions are verified by combining the soft measurement technology of the inertial measurement unit. Based on the subjective evaluation results of driving experience, the comparative results and mechanism explanations of the dynamic characteristics of vehicles equipped with different air suspensions are summarized and analyzed.The low dynamic-and-static-ratio and low-damping air spring technology proposed in this paper can provide a complete and effective theoretical system for accurately predicting and guiding the forward design and dynamic matching of air spring dynamic characteristics. This theory can be directly used in air spring design or initial trial production, thus accelerating the process of independent research and development of world-class air springs in China.
