| Loader is a kind of engineering vehicle,which is widely used in engineering construction.Its transmission system generally includes pure machanical,hydrodynamic mechanical,electrical and hydrostatic technology.Pure mechanical transmission system has high transmission efficiency,but can not achieve continuous stepless speed.Hydrodynamic mechanical transmission system has strong automatic adaptability,but it has the shortcoming of narrow high efficiency region and low transmission efficiency.Hydrostatic transmission system can achieve stepless speed,but it also has the disadvantage of low transmission efficiency.In recent years,by combining the advantages of purely mechanical transmission and hydrostatic transmission,a transmission system with high transmission efficiency and stepless speed change performance is obtained,called hydro-mechanical power split transmission.By changing the volume of the variable displacement pump in the hydraulic circuit,the continuous stepless transmission of the transmission system is realized.Hydro-mechanical power split transmission system has been widely used in agricultural machinery,but the research on construction machinery,especially loader,is relatively less.The study designs and analyzes the hydro-mechanical power split system of loader.For this system,a fuzzy speed ratio control strategy based on driver’s driving intention is proposed,on AMESim software platform,the hydro-mechanical split power transmission system and machine operation simulation based on this control strategy.The simulation accuracy and control strategy of hydro-mechanical power split are verified.The following research contents and conclusions are draw(1)The hydro-mechanical power split transmission system of a 7 ton loader is developed.The input split and output split transmission scheme are analyzed and compared,and the input split transmission scheme is selected for further design.Through the compound of forward planetary gear and reverse planetary gear,the transmission system of hydro-mechanical power split working section except hydraulic working section is developed.Firstly,analyze its characteristics,then select the variable displacement pump and quantitative motor,and finally design and calculate other parameters of the transmission system.The simulation model is established to verify the characteristics of the designed transmission system.The results show that it can realize continuous stepless speed,and the transmission efficiency is higher than that of hydrostatic transmission system and hydrodynamic mechanical transmission system of the same tonnage.(2)A fuzzy speed control based on the driver’s driving intent is proposed.The mathematical model of the engine is created based on the external characteristics and the universal characteristic diagram of the selected engine.According to the analysis,the optimal dynamic target speed control strategy and the optimal economic target speed control strategy are determined.By introducing the driver’s driving intention,the fuzzy amount of the driver’s intention is converted by the fuzzy controller into an exact amount and the control strategy is formulated based on the driver’s driving intention.Adjust the displacement of the variable displacement pump by the signal sent by the controller to complete the adjustment in the working area.If the setting in the workspace no longer meets the demand,turn the workspace to setting.Fuzzy speed ratio of driver’s intention transformation and actual speed ratio of transmission system are adjusted by PID to control the speed of the loader.(3)The simulation model of hydro-mechanical power split transmission system is established.The working conditions and dynamics of the loader are analyzed.The simulation model of the entire machine is built on AMESim software platform.The typical working conditions of the loader of the hydro-mechanical split power transmission system are simulated and analyzed,and the laws of variation of the system parameters of the loader under these working conditions are obtained,including vehicle speed,output speed and torque of the pump and motor,traction,pressure of hydraulic system and power split ratio,etc.Through the analysis of the simulation results,it can be seen that in the whole cycle operation process of the loader,the power split ratio is the largest during the shovel operation.In other stages,the power of hydraulic flow can be limited to less than 50% of the total power,and efficient stepless speed regulation can be realized.The designed hydro-mechanical transmission system and proposed control strategy can meet the loader’s operating requirements under typical working conditions. |
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