【作者】 苏建业；

【导师】 周云山；

【作者基本信息】 湖南大学 ， 车辆工程， 2008， 硕士

【摘要】 作为在上世纪九十年代发展起来的第二代CVT,双状态CVT充分利用了液力变矩器对外载荷的自动适应性能和过载保护性能,明显改善了CVT车辆的起步性能、低速行驶性能和加速性能。而且,由于其增矩变速功能,进一步拓宽了整个变速器的速比变化范围,使得发动机按最佳经济性工作线运行更加可行,提高了燃油经济性。因此,双状态CVT已成为当今世界汽车无级变速传动的主流方向。本文以课题组自行研制的新型双状态CVT为研究对象,在前人工作的基础上,进一步明确了该系统的基本结构组成、工作原理以及传动特性,并将电液控制系统分为六大部分,详细讨论了各个子系统的功能,分析了液压系统的工作原理及设计思想。其中,重点研究了夹紧力电液系统和速比电液系统的动态特性。应用功率键合图理论,首先建立了夹紧力控制系统的键合图模型,推导了非线性状态方程,对其动态特性进行仿真研究,找出了影响系统动态特性的关键因素。然后,建立了速比控制阀的键合图模型,导出了其非线性状态方程并对其动态特性进行分析,得出了速比控制阀关键参数的变化对其动态特性的影响规律,在此基础上,建立了速比控制系统的数学模型,通过仿真研究分析其动态特性。这些工作为双状态CVT用控制阀的优化设计及电液系统的动态特性分析提供了理论依据。本文将上述建立的速比控制系统非线性状态方程,经过合理的线性化处理,得出面向控制器设计的速比控制系统传递函数模型。重点探索讨论了DMC-PID串级控制在CVT速比控制中的应用,并进行了与传统PID控制的对比仿真研究。仿真结果表明,DMC-PID串级控制使系统具备较好的鲁棒性和良好的跟踪性,可明显改善系统的动静态性能。另外,以本速比控制系统为研究对象,通过仿真研究,总结了DMC控制参数的选取规律。本文最后部分进行了比例溢流阀、比例减压阀的压力阶跃响应试验和PID控制下的阶越性速比跟踪试验。试验结果验证了所建数学模型是正确的、合理的、有较高的精度,可以用来分析和预测CVT用液压阀的动态特性以及对速比控制策略和算法的仿真研究。更多还原

【Abstract】 As the second generation Continuously Variable Transmission (CVT) developed since 1990s, dual state CVT makes full use of self-adaptive performance to load and over-load protection capacity of hydraulic torque converter, which improves starting performance, acceleration performance and low speed traveling performance apparently. Moreover, due to good properties of hydraulic torque converter such as automatic torque increase, speed variation, the continuously variable speed ratio variation range is extended, which ensures that the engine work on the more optimal fuel economy operation line so it can improve the vehicle fuel economy. Therefore, dual state CVT has been described as the main developmental direction of CVT in the future.This paper selects a new dual state CVT as the research object, which is developed by our group. Based on the previous efforts, the basic structure, working principle and transmission characteristic of the system are further confirmed. What’s more, the electro-hydraulic control system is divided into six parts, the function of each subsystem is discussed, and the working principle and design idea of hydraulic control system are also analyzed. Thereinto, the dynamic characteristics of speed ratio and clamping force control subsystems are investigated mainly. First, the bondgraph model of clamping force control subsystem is established through bond graph modelling technique. The nonlinear state equations of the system are derived from the model and its dynamics are investigated. The simulation study identifies that some critical structure parameters have significant impacting on the transient respond of the system. Then, bondgraph modelling technique is used to investigate the dynamics of speed ratio control valve. Using valve nonlinear state equations derived from bondgraph model, the effect of some key structure and operating parameters on the dynamic characteristic of the valve is discussed. Finally, the dynamic performance of speed ratio control system is investigated according to the nonlinear mathematic model. Therefore, the theoretical foundation for design of the control valve in dual state CVT and analysis of CVT hydraulic systems is built by the research work above.On the basis of the nonlinear state equations of speed ratio control system, the transfer function for the system facing with practical controller design is gained. A DMC-PID cascade prediction control algorithm is designed for CVT speed ratio control. It is shown from simulation that the control algorithm accomplishes the better robustness and tracking performance than general PID. Besides, based on the speed ratio control system, the selection of control parameters in DMC is summarized through simulation study. The experiments of pressure response for proportional relief valve and proportional pressure reducing valve are completed, furthermore, the test of speed ratio step response with PID control when speed ratio occurs step changing is also accomplished. The results prove that the good correctness and precision of mathematic model, which can be used to analyze and predict the dynamic characteristics of valve for dual state CVT, and is feasible to verify the effectiveness of speed ratio control algorithm through simulation study.更多还原