【作者】 郝鹏；

【导师】 何清华；

【作者基本信息】 中南大学 ， 机械电子工程， 2008， 博士

【摘要】 随着工程机械品种和数量的不断增多,国内外对工程机械尾气排放、噪声等限制愈加严格;随着人们环保意识的日益增强,使环保节能型产品的研制开发成为工程机械发展的趋势。在能源危机及绿色环保的今天,对液压挖掘机的节能研究已成为一个非常具有发展前景的课题。本文正是在此背景下并借助国家863课题,以提高液压挖掘机的动力性和经济性为研究目的,开展了对液压挖掘机动力系统匹配及节能控制的研究,论文的主要工作如下:论述了液压挖掘机动力系统匹配与控制的研究现状,分析了液压挖掘机的特点及施工工况,给出了发动机—液压泵—负载—操作手之间的相互关系和信息传递方式以及五种动力系统匹配不当造成能量损失的形式及原因。结合现有液压挖掘机的特性及节能控制技术的发展趋势构建了基于车载PLC和PC104总线系统的硬件平台和VxWorks嵌入式软件平台的液压挖掘机动力系统控制方案。建立了发动机有效扭矩、转速与每循环供油量之间的传递函数。提出了液压泵最大排量的1/4以上是其经济工作区,并作为功率控制的依据。分析了LUDV(是德文的缩写对应的英文为Load IndependentFlow Distribution Control System)系统的特性和效率,建立了电液比例系统的数学模型并对其简化,提出了工作装置等效质量和液压缸承受反向负载力的估算公式,并对液压系统参数Kq进行了辨识。建立了铲斗末端的位姿表达式和工作装置转角与驱动液压缸长度的关系式,成功判断出挖掘机的四个工作循环以及液压缸的溢流工况。建立了负载阻力与系统压力之间的关系式,并对铲斗作空载水平直线运行时液压缸的受力进行了仿真分析。对液压挖掘机在空载、固定载荷和实际挖掘三种工况下的压力进行了分析,采用加权平均滤波法对信号进行处理,利用泵出口压力的概率分布并结合工作装置的位姿对负载工况进行辨识。分析了影响发动机油耗的负载特性。用分段函数对理想位移控制曲线进行拟合,采用斜坡函数控制方法对执行器的速度进行控制,提出自动怠速控制应满足的三个指标,采用自适应控制方法对PWM信号占空比的控制范围、最短斜坡时间和自动怠速转速进行优化。根据发动机最常使用的三个转速区间,通过对发动机供油量控制,液压泵的功率控制,负载传感阀的压差控制以及比例减压阀的出口压力控制四种控制方式的协调匹配,提出了变p-Q曲线的功率协调匹配控制方法实现发动机-泵-负载的经济性协调匹配控制。提出了恒功率与变功率协调匹配控制的方法,夹逼发动机的工作区域,实现系统动力性协调匹配控制。分析了在不同安装方式和不同环境下发动机的工作特性,以液压泵的压力,转速差和转速差的变化率作为输入,泵功率控制电流和负载压差控制电流作为输出,采用模糊控制对动力系统的匹配与节能控制方法进行了优化。搭建了液压挖掘机测试平台,用液压泵的输出功率与发动机耗油量的比值作为评价液压挖掘机经济性的指标。对原装系统液压挖掘机和采用节能控制系统的挖掘机在轻载、490kg固定载荷和实际挖掘三种工况下发动机的耗油量和液压泵的出口压力和流量进行测试,试验结果表明,无论是稳定负载,还是波动负载,采用论文所提出的匹配和控制方法,在不同转速和不同工况下都可以提高系统效率,特别是在实际挖掘工况,能节约至少8%的能量,证明了所采用的控制策略的正确性和有效性。而且论文将所研究的算法运用到其它吨位的机型中,也收到良好效果,为研究方法的进一步推广奠定了基础。总之,论文以实现挖掘机动力性和经济性为目的,将发动机—液压泵—负载—操作手作为整体考虑,提出自动怠速控制、变p-Q曲线控制、恒功率与变功率协调匹配控制以及模糊控制等方法,解决了由系统匹配不当造成能量损失的问题,最后将研究的理论结果应用到实际挖掘工况,取得了比较好的节能效果。论文为液压挖掘机动力系统的匹配与节能控制提供了一套完整的理论和方法。更多还原

【Abstract】 With the increase of variety and quantity of construction machinery, limit to the emission-quality and noise level becomes more strictly. With the enhancement of people environmental protection awareness, study on the environment-friendly product is the trend for the research and development of construction machinery. In days of energy crisis and environment-friendly, energy saving of excavator is of higher development potential project. Under this background and combining the national "863" project, aiming at research on powerful and economical excavator, the thesis makes research on power match and energy saving control of excavator’s driving system. The main research work as follows:The development of research on energy saving control of excavator’s driving system at home and abroad is surveyed. Characteristic and working condition of excavator are analyzed. Relationship and information delivery method among engine, pump, load and operator are given. The form and reason of energy lose arousing by improper match of driving system are given. Based on hardware environment of PLC and PC104 and software environment of VxWorks embedded system, the general control scheme of excavator is put out according to the characteristic of excavator and trend of energy saving control technique.The transfer function among engine effective torque, speed and cycle fuel feeding are established. Greater than 1/4 of the maximum displacement is the economic zero of pump. The following power control method is based on this. The characteristic and efficiency of LUDV (Load Independent Flow Distribution Control System) system is analyzed. And then the flow equations are developed. Starting with the basic equations of hydraulic systems and according to experiment and practice, a simplified model of electro hydraulic system is obtained. The estimation methods and formulas for equivalent mass, bearing force of hydraulic cylinder and flow gain coefficient Kq are given.Expression of bucket tip posture and the relationship between the manipulator rotation angle and cylinder distant are put out. the four excavating duty cycle and relief conditon of cylinder are sucessfully distinguish. Expression between load force and system pressure is established. The simulation of bearing force of hydraulic cylinder when the bucket moves at the level lines under free load is given. Under free load, fixed load and actual working condition, the pump pressure is test. Weighted average filtering method is used to process the pressure signal. The load condition is distinguished based on the pressue probability distribution and the posture of manipulator. Section function is adopted to fitting the perfect displacement control curve. The ramping function is used to control the actuator speed. Three criterion to judge the idle control performance is put out. Adaptive control is used to optimize the domain of PWM duty ratio, the minimum ramping time and idle speed.According to the normally used working zero of engine, the engine fuel supply control, pump power control, difference pressure of load sense valve control and output pressure of proportional relied valve control are coordinated. The method of adjusting P-Q curve is put out to realize economic matching among engine, pump and load. The method of combining constant power control with variable power control is put out to realize powerful matching control.The characteristic of engine working at different mounting way and different environment is analyzed. Selecting pump pressure, speed difference and its variance ratio as input, and current of pump power control and pressure difference control as output, fuzzy control is adopted to improve the power matching and energy saving control method.Testing platform is established. Using ratio between output power of pump and fuel consumption to appraise the economic performance of excavator. Under free load, 490kg fixed load and actual working condition, pressure and flow of pump and fuel consumption of engine is test. From the result, no matter on the constant load or variable load, it got good results at different speed and different working condition, especially at the actual working condition, it got at least 8% energy saving using the power matching control method. It proved that the power matching control method is correct and availability. Moreover, the paper put this method into use in the other kind of machine; it also got good result, which established expansive base for the further usage.Generally, the paper aims at powerful and economic control. Taking engine, pump, load and operator into consideration, put out idle control, adjust p-Q curve control, constant power control, variable power control and fuzzy control, solves the energy losing problem. Finally, put the theory into practice use and get good results. The paper provides systematic and intact power matching and energy saving control method for the excavator driving system.更多还原