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基于动态规划及BP神经网络的重型拖拉机自动换挡策略优化

Optimization of the automatic shifting strategy for heavy tractors based on dynamic programming and BP neural network

  • 摘要: 重型拖拉机全动力换挡变速箱在田间复杂作业环境中换挡频繁、可靠性差;在道路运输工况中,高挡位利用率低,燃油经济性差。为解决上述问题,该研究提出一种基于动态规划(dynamic programming, DP)算法与反向传播神经网络(back propagation neural network, BP)协同优化的自动换挡控制策略。首先构建以油门开度、车速及田间作业滑转率为参数的换挡规则;采用DP算法,以燃油经济性和换挡次数为优化目标,分别求解田间犁耕作业和道路运输工况下的最优换挡序列;由于DP算法挡位寻优实时性差,利用优化所得的换挡参数与最佳挡位数据训练BP神经网络模型,实现基于神经网络的实时挡位控制。基于AMEsim和Simulink仿真平台构建重型拖拉机传动系统模型及挡位控制模型,进行系统仿真验证。结果表明:相较于基于规则的换挡策略,DP离线求解的犁耕工况换挡次数减少105次,油耗降低5.48%;道路运输工况换挡减少5次,油耗降低15.80%。在犁耕测试工况下,所提出的BP换挡策略油耗仅比全局最优DP高0.7%;道路运输工况下,BP策略实时控制油耗比全局最优DP高4.4%,换挡次数仅增加4次,换挡结果与离线最优解差距较小,验证了该策略的合理性与可行性。本文建立的动态规划DP与神经网络BP的协同优化框架,解决了传统策略局部最优与实时性难以兼顾的矛盾,可为农业装备智能化提供可实施的技术方案。

     

    Abstract: Full-power shift gearbox has been one of the key configurations to improve the operation efficiency of heavy tractors. However, the conventional shift strategy cannot fully meet the requirements of the global optimization under multiple-gear overlap. In heavy tractors, the frequent shifting and high fuel consumption can be caused by the overlap of adjacent gear speeds, seriously restricting the intelligent equipment in modern agriculture. It is often required for the global collaborative optimization of optimal working conditions in real time. In this study, a compound shift strategy was proposed to integrate the dynamic programming (DP) with the global optimization and back propagation neural network (BPNN) for real-time prediction. The shift control was divided into a field mode (throttle, speed, and slip rate) and a road mode (throttle and speed), according to the operational classification. A DP bi-level optimization was constructed to incorporate a penalty function of the shift frequency. Fuel economy was prioritized as the core target. Offline optimization was also performed on the real-vehicle plow load spectrum and road transportation from the suburban cycle driving profiles. A double-hidden-layer BPNN controller for the gear prediction was trained using the DP offline optimization dataset. A series of tests was conducted to validate the optimization via an AMESim-MATLAB/Simulink co-simulation platform. Results demonstrated that the shift strategy fully met the power demands of the working conditions under the DP offline solution. In plowing, the shift frequency and fuel consumption decreased by 50.24% and 5.48%, respectively. In road transportation, the shift frequency and fuel consumption decreased by 13.89% and 15.80%, respectively. Both DP global optimization and BPNN real-time control effectively tracked the vehicle speed to meet the demand of the power after plowing simulation. Furthermore, the BPNN was maintained on the minimum gear at the low speed, indicating the more frequent shifting. The higher gears of the DP were utilized for the significant fuel savings during high-speed segments. While the BPNN instantaneously maintained the higher gears at the low speed, this resulted in slightly higher fuel consumption. Both DP and BPNN were also accurately track the speed under road transportation. The available 24 gears were more fully utilized in the DP with fewer shifts during high-speed sections. Although the driving resistance was relatively low, the engine was placed outside the most economical zone, in order to secure the more efficient points of the DP. The high-gear configuration was optimized in the multiple high-speed segments. The DP achieved significantly lower fuel consumption than the BPNN. Collectively, the gear selection and shift smoothness of the DP were optimized to attain the lower fuel consumption using global information. While the DP real-time strategy shared much higher-speed gear utilization and fuel economy, compared with the BPNN. There were only a few differences in the fuel consumption under working conditions. There was some increase in the shift frequency for the BPNN. The BPNN strategy was verified to meet the real-time requirements with acceptable fuel economy. The global gear optimization was also integrated with the real-time adaptive decision-making. Conventional multi-condition strategies on manual calibration were reduced by the adaptive fuzzy control. The finding can also provide a valuable technical pathway for the intelligent control of the mechanical transmission in modern agriculture.

     

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