Research On Automatic Shift Strategy Of Hydraulic Transmission For Wheel Loader

Construction machinery is gradually favored by users and supported by enterprises because automatic transmission reduces the difficulty of operation,reduces workload and saves fuel consumption,so the research on automatic shifting strategy is of great significance.However,the adaptability of the domestic construction machinery vehicle control algorithm is not high,and the oil pressure is easily affected by changes in environmental factors when the clutch is engaged.Therefore,the traditional automatic shifting strategy is difficult to meet the shifting quality requirements such as smooth operation and good shifting quality.The research object of this thesis is the hydraulic gearbox applied to the wheel loader,and a set of automatic shifting control strategy with strong adaptability and high stability is planned to be developed.The main research work is as follows:First,take the hydraulic automatic transmission as the research object,and carry out the relevant mathematical modeling for the various components of the automatic transmission system.The characteristics of the electro-hydraulic shift mechanism were studied,the effect of temperature change on the clutch engagement pressure during the oil filling process was analyzed,and a data calibration experimental platform was built to study the oil pressure change,which laid a foundation for the subsequent clutch engagement control strategy.Second,taking the automatic shift rule of the loader as the research object,the matching of the engine and the torque converter is analyzed,and the remedial measures after the mismatch are supplemented.The gear shifting requirements of the wheel loader are analyzed,and the dynamic shifting rules to deal with heavy loads and the economical shifting rules to save engine fuel are formulated.Thirdly,taking the clutch engagement state as the research object,analyzing the clutch compression during the engagement process,a MPC-based clutch engagement grading control strategy is proposed.According to the torque transmitted in the slipping stage,an MPC controller is designed to find the effective slipping point,and by analyzing multiple states during the oil filling process of the proportional solenoid valve,the clutch engagement is controlled in stages.Fourth,in terms of software simulation,Matlab/Simulink is used to build models of engines,gearboxes,clutches,etc.,and a working environment is constructed to simulate input and external loads to capture simulation output data.In addition,it is verified by simulation data that the MPC control strategy has better automatic shift smoothness than the original PID control strategy.In the bench experiment,the AWG series gearbox was selected and a real hardware platform was built.By monitoring the gear shift index parameters,it was obtained that the torque mutation after the optimization was reduced by 42.8% and 38.5% at the starting and shifting,respectively.The automatic shift control strategy proposed in this thesis is compared from the simulation level and the bench experiment level to verify its effectiveness.