【作者】 郝允志；

【导师】 孙冬野；

【作者基本信息】 重庆大学 ， 车辆工程， 2011， 博士

【摘要】 常规的变速器试验台是以模拟车辆实际运行工况为目标建立的,结构复杂、成本高、功耗大。为克服这些缺点,本文对基于无级变速器(Continuously Variable Transmission, CVT)的空载/轻载型硬件在环试验台的设计理论和试验方法展开研究,主要工作内容如下:①新型硬件在环试验台设计。提出了将真实CVT置于仿真回路中的硬件在环仿真试验台结构,采用小功率电机代替发动机和加载设备,构成小功率电封闭试验台,CVT处于空载/轻载状态运行,在保证试验精度的情况下,大大降低了试验台的成本和功耗。②CVT基本性能试验。1)夹紧力阀特性试验结果表明:稳态系统压力主要取决于工作电压,在主要工作压力范围内呈线性关系;瞬态系统压力具有良好的动态响应性能,能够适应工况的剧烈变化,转速对系统压力的瞬态特性影响较小,只对低速下的压力升高过程有明显影响。2)速比响应特性试验表明,速比响应过程与传递转矩无关,低速时的速比减小过程存在响应延迟,延迟时间随转速的升高而逐渐减小并消失;提出了面向控制的速比变化率测量和计算方法,避免了传统方法依赖于主动轮压力的问题。3)对CVT的功耗和传动效率进行了试验,结果表明:空载转矩损失取决于速比和系统压力,与转速基本无关,当速比小于1时,转矩损失随速比的减小而快速增大,当速比大于1时,转矩损失与速比基本无关;传动效率也基本与转速无关,因此可以通过测量低速下的效率来反映CVT的整体效率特性,从而提出了利用小功率电机测量CVT效率的方法。③控制体系分析与系统建模。1)将CVT控制体系结构分为驾驶员、控制策略、控制算法、执行机构、传动系统五个层次,分别对应于提出需求、设定满足需求的目标、制定实现目标的方法、控制执行机构实现目标、系统响应使需求得到满足。2)在建立传动系统主要部件模型的基础上,采用功率流建模方式构建了传动系统整体模型;更进一步,将仿真模型与试验台相结合构建了CVT硬件在环仿真试验系统。④底层控制算法研究。1)提出了夹紧力半闭环控制算法,由系统压力控制表得到基本控制量,由闭环控制算法计算修正控制量,充分利用对象的已知信息,提高了系统的鲁棒性和动态响应性能。2)提出了基于动态安全系数的夹紧力控制方法,分析目标夹紧力影响因素和发动机转矩波动特性,根据传动系统发生转速突降时的发动机转矩变化趋势和变化范围来设定安全系数,论述了动态安全系数法的计算流程,仿真结果表明:该方法能够保证转矩传递可靠性,明显降低夹紧力。3)在速比控制方面,提出了基于主动耦合干预的无级变速器速比控制方法,利用夹紧力控制与速比控制之间的耦合作用,在保证夹紧力安全的基础上,通过联合调节主、从动轮油缸压力来干预速比控制,扩大速比变化率的可控范围,仿真结果表明:该方法在保证可靠性、经济性和舒适性的前提下,改善速比跟踪性能和提高动力性,增强对驱动轮打滑等恶劣工况的适应性。⑤上层控制策略研究。1)在稳态控制策略方面,针对现有无级变速传动系统效率优化算法的不完整性,以整体效率最优为目标,设计最佳工况点求解算法,制定基于功率需求的传动系统整体优化控制策略,将满足功率需求的最高效率点作为基本控制目标,以实现最佳经济性;当功率需求超出传动系统功率范围时,将当前车速下的最大输出功率点作为控制目标,以实现最佳动力性;求解液力变矩器理想状态切换线,制定实际切换控制线。2)在瞬态控制策略方面,针对无级变速车辆在急加速工况下出现的动力疲软问题,提出了瞬态工况下基于有效功率的通用补偿控制方法,以变速器输入功率作为控制目标,克服了现有控制方法依赖于车辆及路况信息的缺陷,通过分层次量化补偿功率,将控制方法划分为功率维持、零功率、增加后备功率和综合模式等四种控制模式,为灵活设定过渡曲线和优化瞬态工况性能提供量化依据,仿真结果表明:该控制方法能够实现所要求的补偿效果,克服急加速过程中的动力疲软。本文研究成果不仅为CVT性能测试和控制系统的研究试验方法开辟新的途径,也为其他类型的自动变速器和传动机构的研究提供借鉴,甚至可作为一种较为通用的传动系统硬件在环仿真试验方法。更多还原

【Abstract】 The target of normal transmission test bench is to simulate vehicle’s running condition precisely. This kind test bench is characterised by complex, expensive and energy-intensity. To overcome these disadvangages, study on design theory and experiment method of light duty hardware in the loop(HIL) CVT test bench was carried on. The main work as follows:①Novel HIL test bench construction. A new kind HIL structure was presented by involving a real CVT in simulation loop. Compared to normal test bench, engine and load equipment were replaed by double relative small motors, and electric-close-loop bench was established. Accuracy was ensured and while construction cost and power dissipation was reduced dramatically.②CVT main performance test. 1) Experiments on clamping-force static and dynamic performance were carried on. According to the results, system pressure static value was mainly determined by the applied voltage, and has a good linear character in main working range. System pressure has a good dynamic performance which could adapt the transient change of working condition. 2) ratio-shift-rate performance was tested. According to the results, ratio-shift-rate has no relationship with the torque transmitted and the rotate speed except in low speed. A method calculating ratio-shift-rate was presented with on need sampling primary pressure value. 3) Dissipation and efficiency was measured. According to the results, dissipation and efficiency have no relationship with speed, and were mainly determined by ratio and primary torque. When the ratio is less than 1, the torque loss increased rapidly with the decline of ratio. When the ratio is large than 1, the torque loss has no obvious relation with ratio. As a result, it is possible to measure efficency with small poer motor instead larger motor or engine.③Study on control hierarchy and system modeling. 1) CVT control system was devided into driver, control strategy, control algorithm, acturator and transmission system, which correspond to proposing demand, setting target, making solution method, achieve the target, and satisfying the demand. 2) Based on main components models, transmission system model were established. Further more, integrating simulation model and test bench, CVT HIL system was set up.④Study on low hierarchy control algorithm. 1) Clamping-force semi-close loop control algorithm was presented. Control value consisted of basic value and correction value. Basic control value was available by lookuping pressure static character table. Correction value was calculated by close loop control algorithm. Controlled object information was taken full adavantage. Dynamic performance and roubustness were improved. 2) Traditional constant safety factor method and novel slip-control method are extreme different methods of clamping force control strategy. To integrate advantages of both methods, clamping force control strategy base on dynamic safety factor was presented. Study of theoretical clamping force relevant parameters and engine torque wave characteristics was carried on. Safety factor was determined according to engine torque variation trend and range. Target pressure calculating process was described. Simulation and experiment results showed that by adopting dynamic safety factor, transmission reliability was ensured and the performances of clamping-force and fuel efficiency were improved. 3) To enlarge valid ratio shift range of continuously variable transmission, active coupling control strategy was proposed. Utilizing the coupling effect between clamping force and speed ratio, the shift speed is improved by conditioning the pressure of both primary and second pulleys’hydraulic cylinders. System pressure safety must be ensured to satisfy the clamping force which could meet the requirement of torque transmission. As a result, real ratio tracks the target more rapidly and shift speed range is enlarged. Studies on active coupling control strategy was carried on, which included shift speed, clamping force related transmission reliability, fuel economic, dynamic performance, hard condition adaptability, and shift speed related comfortableness. Simulation results showed that by adopting active coupling control strategy, reliability, economic, and comfortableness were ensured while ratio tracking performance and power performance were improved.⑤Study on high hierarchy control strategy. 1) At the aim of highest efficiency of CVT, an optimization algorithm was designed by considering the efficiency of engine and the main dissipation component. Duel-state hydraulic torque converter (TC) was also included in the algorithm. Control strategy based on power demand was designed in order to realize higher efficiency of whole system. The highest efficiency operating condition which satisfies the power demand is set to be the control objective. As a result, the best economical efficiency is available. While the power demand exceeds the maximum output power under the current vehicle speed, the maximum output power condition is set to be the control objective. As a result, the best dynamic performance is available. TC ideal control line was calculated based on which practice operating line was designed. 2) To improve the drivability of CVT vehicle under hard acceleration condition, a compensation control strategy based on effective power was proposed. Different from normal control methods which are dependent on vehicle and road environment information, the novel strategy set CVT input power as the control objective directly. Power compensation mode was ranked to four classes: holding power, zero power, increasing reserve power, and synthesis control. So, quantification criterions for setting transition curve and optimizing transient condition performance are available. Simulations and experiments results showed that power compensation control strategy could eliminate the harmful effect of power decreasing caused by engine-flywheel inertia and too fast ratio shift-rate and drivability was improved under transient condition.The achievement in this paper not only presented a novel solution for CVT performance test and control system study, but also provided a referrence method for other kinds automatic transmissions and gear boxes. Further more, a relative universal HIL simulation method for transmission system was available.更多还原