Study On Automatic Shift Strategy And Control Method Of Hybrid Construction Vehicle

Construction vehicles are important equipment, which play an important role in nationaleconomic construction. Studies have shown that the hybrid power technology caneffectively improve engine fuel economy and system energy efficiency, improve emissionand reduce fuel consumption. Automatic transmission technology can realize automaticshift control in construction vehicles, which effectively reduces the pilot operation intensityand improves the operation quality and efficiency. In recent years, for further energy-savingand emission reduction, improving vehicle dynamic performance and driving comfort at thesame time, a variety of vehicles have adopted hybrid technology combined with automatictransmission technology. Automatic transmission technology with hybrid technology hasbecame a hotspot. The construction vehicles do works while driving, due to the complexityof operating environment, the operating load fluctuates frequently and violently.Due to thedifferences in load condition, work mode, control system, related technologies inautomobile industry cannot be directly applied to construction vehicle. The study ofautomatic transmission technology for hybrid construction vehicle (HCV) is still in theexploratory stage at present.This research was supported by the Specialized Research Fund for the Doctoral Programof Higher Education of China (SRFDP)"Research on Severe Hybrid Vehicle AutomaticTransmission Technology"(Grant No.20120061110023). The parallel HCV was as researchobject, to improve fuel economy and energy efficiency, improve power performance, reducework intensity, improve operation quality and efficiency, improve shift quality, combinedwith the working characteristics, system structure, parameters optimization matching andenergy management control strategy, the automatic shift strategy and control method werein-depth studied. The main research works of this paper include the following aspects:1) System parameters matching method was researched according to the structure of HCV.Math models of main components of hybrid system and vehicle dynamic model wereanalyzed and established, the combination of theoretical and empirical formulas was used todescribe their characteristic. From overall optimum to local optimum, the main components’parameters were matched to match load conditions, improve energy efficiency, and reduceinstalled cost and power. Improved particle swarm optimization was used in optimizingparameters matching to improve parameters matching effect. Taking5tons loader as object,parameters matching method achieved good results. 2) Energy management control strategy for HCV was studied. Identification method ofHCV’s working conditions was proposed according to the system needed torque. Torquedistribution control strategy based on fuzzy logic was proposed, which could control theengine work around optimal efficiency torque curve, and ensure balanced charging anddischarging of energy storage elements. Based on fuzzy logic, a driver’s intention coefficientwas defined to identify the driver’s intention, and the engine target speed was controlledbased on the coefficient. Instantaneous optimization was proposed to improveenergy-saving, an optimization model was established for the target of overall optimalefficiency. Experimental results show that the torque distribution control could ensure theengine work in the vicinity of the optimal efficiency torque curve. The hybrid systemreduced4.94%fuel consumption compared to traditional construction vehicle.Instantaneous optimization could further improve fuel economy, which reduced10.08%fuelconsumption.3) Automatic shift schedules and control methods applicable for HCV were researched."Engine speed, vehicle speed and power distribution coefficient" were used as the shiftcontrol parameters. Dynamic shift schedule with the optimal vehicle acceleration as target,economical shift schedule with travel system optimal efficiency as target, and compositiveshift schedule combining the two schedules through the driver’s intention coefficient wereproposed. Intelligent shift control theory for HCV was researched, and intelligent shiftcontrol strategy and method based on BP neural networks were proposed.Levenberg-Marquardt algorithm was used to overcome the disadvantages of BP neuralnetworks: slow convergence and local minimum. Experimental results show under thedynamic, economical, compositive and intelligent shift schedule, it shifted accurately andproperly, achieved shift target under different schedules. The average efficiency of hydraulictorque converter were up to70.8%,73.6%,73.6%and73.2%respectively, which improvedsystem efficiency and energy utilization and with good economic and dynamicperformance.4) The first HCV automatic shift test bench of China was established. For bench test,energy management control system based on CAN bus network and automatic shift controlsystem were designed and developed. The proposed energy management control strategyand automatic shift theory were verified through bench test.Theoretical and experimental researches show that HCV with automatic shift technologyturn out to be more efficient, with more utilization of energy and less shift shock, whichimproves shift quality and is more economic and dynamic. Automatic shift technology for HCV has preferable applicability and practical value.