摘要
液压传动技术广泛应用于工程机械,多路阀是工程机械液压系统的核心控制元件,其性能好坏直接关系到整机的操控和节能性能。传统多路阀每联阀采用单主阀芯结构调节其进口和出口节流面积,而负载口独立控制多路阀的每联阀采用双阀芯结构独立调节其进口和出口节流面积,该结构增加了系统的控制自由度,使工程机械的操控和节能性能进一步提升成为可能。负载口独立方向阀控制系统的执行器速度和压力控制策略、与负载口独立方向阀控制系统在工程机械中的应用,是负载口独立控制技术研究的重点和难点。本学位论文研究负载口独立方向阀控制系统的控制策略和挖掘机负载口独立方向阀控制样机的机液耦合特性,充分利用负载口独立控制技术的优势来提高整机操控和节能性能,具有广泛的工程应用背景和重要的学术研究价值。
本文提出了根据操作者输入控制速度大小来调控负载口独立方向阀两端压差的变压差补偿的速度控制方法,相比传统的机液定压差负载补偿方法,该控制方法在输入控制速度较小时,降低了负载口独立方向阀两端的压差,减少了系统的速度控制增益,提高了系统的稳定和节能性,在输入控制速度较大时,增加了负载口独立方向阀两端的压差,提高了系统增益,改善了系统的快速性,在挖掘机动臂液压缸变速提升典型工况的实验结果表明,该控制方法可节能系统能耗8%以上。建立了负载口独立方向阀控挖掘机系统机液耦合模型和性能测试样机,并设计了控制器,提出了兼顾操控和节能性能的执行器工作模式选择的新方法,在挖掘机动臂下降时,动臂选用高压再生模式,该模式相比低压再生下降模式,提高了系统的阻尼,动臂下降速度控制实验结果表明,可降低速度超调20%以上；在挖掘机动臂和斗杆空载并同时运行时,动臂选用阻抗伸出模式,斗杆选用高压再生模式,相比统一选用阻抗模式,可提高系统的效率7%以上。提出了由平衡阀的延滞时间调节速度控制器闭环增益的变增益速度调控方法,该方法通过估计平衡阀的延滞时间,分段调节执行器速度控制闭环增益,在平衡阀缓慢开启阶段采用小增益速度控制器以减少速度超调,在平衡阀全开阶段采用大增益速度控制器来提高系统动态响应,双执行器同时运行的实验结果表明,采用该方法所获得的速度控制结果相比定增益控制方法减少了执行器速度控制超调40%。本论文的研究成果为应用负载口独立控制技术改善工程机械系统的操控和节能性能提供了理论支撑和工程应用示范。
论文的主要结构如下：
第一章,指出了论文的研究目的和意义,介绍了负载口独立控制技术的研究背景和国内外研究现状,确定了负载口独立方向阀控制系统关键技术的研究内容。
第二章,主要设计了负载口独立方向阀控制系统不同工作模式下执行器压力、速度控制策略,选择适合于负载口独立方向阀控制系统工程应用的控制方法。分别仿真和实验比较了基于计算流量反馈的速度控制器和压力前馈和反馈相结合的压力控制器,基于反馈线性化模型的计算力控制器和自适应鲁棒速度控制器和自适应鲁棒压力控制器三种控制器的控制性能。
第三章,拓展负载口独立方向阀控制系统的应用领域,研究了负载口独立方向阀控制技术与负载敏感技术相结合的控制策略,分析了当前负载敏感技术的控制特点,提出了根据操作者输入速度信号改变控制阀两端压差的变压差补偿的速度控制方法,改善了系统的节能性能；研究了负载口独立控制技术与闭中心负载敏感技术相结合的控制方法,提出了区分轻、重负载执行器模式选择的速度控制方法,并进行了单个执行器工作模式切换的实验研究,该方法为进一步改善系统的节能性能提供了条件。
第四章,研究了多执行器同时运行时的负载口独立比例方向阀控制系统的速度控制特性,建立了双执行器负载口独立方向阀控制系统的同步模型并设计了控制器,对比传统的电液比例控制方向阀控制系统,比较了不同工况下执行器速度控制特性。研究带平衡阀的负载口独立方向阀控多执行器同时运行系统,提出根据平衡阀延滞时间来分段调节速度增益的速度控制方法,改善了带平衡阀支路的速度控制稳定性。
第五章,设计了挖掘机负载口独立方向阀控制系统,建立了基于AMESim的系统机液耦合模型,研究了不同工作模式下,挖掘机动臂和斗杆油缸的速度控制方法,分析获得在动臂油缸处于上升速度控制时,宜采用阻抗伸出模式,而动臂油缸下降速度控制时高压再生下降模式比阻抗下降模式具有更好的速度控制稳定性。对动臂和斗杆油缸进行了同时上升和同时下降速度控制实验,应用第四章设计的负载口独立多执行器控制方法获得了较好的速度控制特性。
第六章,概括了全文的主要研究工作和成果,并展望了今后需要进一步研究的工作和方向。
Hydraulic system is well used in mobile machinery, multi-way directional valve is the key component in hydraulic system of mobile machinery, its properties has high relationship to the operational and energy saving characteristic of mobile machinery. Meter in and meter out orifice of traditional multi-way directional control valve is controlled by a single main spool, but meter in and meter out orifice in independent metering valve is separately controlled by two spools, so control degrees of freedom in independent valve control system is increased, which makes it possible to further improve operational and energy saving characteristic of mobile machinery. Controller design for velocity and pressure control of independent system as well as application of independent valve control system in mobile machinery, which has been considered as a challenge up to now, is responsible to improving system performance. Therefore it is necessary to study control strategies of independent metering valve control system and the mechanical-hydraulic coupling characteristic of mobile machinery, make full use of the increased degree of freedom to enhance operational and energy saving performance of mobile machinery.
In this thesis, a new velocity control method to control the open center load sensing independent metering valve control system has been proposed, pressure difference of velocity control direction valve is regulated according to operator input command velocity, which is not set at a fixed value as in traditional load sensing system. When the command velocity is low, pressure difference is reduced, which reduces the velocity control gain, improve stability and energy saving performance; when the command velocity is high, pressure difference is increased, which increases system velocity control gain and enhances velocity dynamic response, this method was implemented in a variable command velocity lift experiment, obtained results showed that above 8% of energy saving performance was achieved using proposed method. Work modes of excavator actuators have been studied, a work mode selection criterion has been proposed, high pressure regeneration extraction mode is more suitable to control the downward motion of boom than low pressure regeneration extraction mode, experiment showed that high pressure regeneration extraction mode reduced 20% overshoot of velocity; in boom and arm simultaneous motion condition, it suggests that boom uses power extension work mode, arm uses high side regeneration extension work mode, it improved 7% efficient than both using power extension work mode. An independent metering valve control multi-actuator system with a counterbalance has been studied, a variable gain velocity control method has been proposed to improve system stability, experiment showed that the proposed method reduced 40% overshoot of velocity coMPared with using the fixed gain velocity control method. All obtain results provided the theoretical basis and application examples to explore independent metering valve control system.to improve operational and energy saving performance of mobile machinery.
In chapter 1, the aim and significance of the study in the thesis were discussed. The current research progresses on IM technique were reviewed. The main research subjects were presented.
In chapter 2, three different controllers were proposed to control IM valve control system based on the built mathematic model, the performance of those controllers were coMPared through simulation and experiment, Lyapunov based adaptive robust controller obtained highest velocity control accuracy.
In chapter 3, controllers designed for combining IM and LS technique have been developed. A new control method for OCLS-IM system has developed to enhance energy saving performance by varying the pressure differential of IM valve according to the operator input velocity control signal. A CCLS-IM controller which differentiates the level of the external loads to choose work mode for actuators was also developed, it can also improved energy saving performance of the whole system significantly.
In chapter 4, multi-actuators simultaneous motion control method of IM valve control system have been studied. CoMParisons of dynamic response of velocity control between traditional proportion directional valve control two-cylinder system and IM valve control two-cylinder system has been carried out. Obtained simulation results showed velocity response of IM valve control system was faster and more stable. A variable gain velocity control method was proposed to stable IM valve control two-cylinder velocity control system with a counterbalance valve.
In chapter 5, a 2-ton excavator IM valve control system has been built, velocity control performance of different work modes were experimentally tested.It was found, when the boom was in extraction, high side regeneration extraction mode was preferred to be chosen due to its good velocity control performance. OCLS-IM control strategy was also verified in boom lift velocity control mode. Then arm and boom were controlled to lift and lower simultaneously with the IM technique, good velocity control performance was achieved.
In chapter 6, conclusions in this thesis were summarized and future research proposals were suggested.
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