Research On Hydraulic Hybrid System Design And Control Strategy Of Loader

In order to improve the fuel economy during the cycle operation of the loader,a pressure-coupled hydraulic hybrid power system and its control strategy is proposed in this thesis.The control strategy includes energy management strategy and dynamic coordination control.The energy management strategy realizes the reasonable distribution of engine power and accumulator power to optimizes the working range of the engine,so that the installed power and the fuel consumption of engine can be reduced.The dynamic coordinated control is used to reduce system impact during mode switching,to ensure accurate torque distribution and to improve engine transient fuel efficiency.Based on the National Natural Science Foundation of China(No.51875239),the oil hybrid power system and its control strategy of loaders have been researched in this thesis.The main contents of this thesis are as follows:(1)Based on the hydraulic system of loader,a set of pressure-coupled oil-liquid hybrid power system is designed.In this system,the accumulator is connect to the hydraulic system as an auxiliary power source and the decoupling between the output power of the engine and the demand power of the hydraulic system is realized.The two-way pressure compensation valve is used to compensate the pressure difference between the load demand pressure and the accumulator pressure,so as to avoid the action speed of each hydraulic cylinder affected by the pressure state of the accumulator.When the load demand pressure is low and the demand flow is large,the connection between the accumulator and the main oil circuit can be disconnected by controlling the solenoid switch valve to reduce the throttling loss of the system.(2)The optimal energy allocation rules is researched based on dynamic programming algorithm.The dynamic programming model of pressure-coupled hydraulic hybrid power system is established with the minimum cumulative fuel consumption as the optimization goal.Based on the known load data,the optimalenergy distribution trajectory is recursively deduced by traversing the accessible state set and the allowable control set at each moment.The relationship between the working mode of the system and the load characteristics is analyzed to guide the formulation of the energy management strategy.(3)Considering the throttling loss of hydraulic system and the fuel efficiency of engine,the energy management strategy is worked out.According to the load characteristics of each operation section in the cycle condition,the working conditions are divided into three conditions.The switching logic of the system mode and the energy distribution rules of each mode are formulated to ensure that the engine works in the economic zone as far as possible.Besides,the throttling loss can be reduced by taking the expected pressure of the accumulator as the control target and disconnecting the solenoid switch valve at the right time.(4)The coordinated control strategy between variable pump and electromagnetic switch valve is formulated to ensure the total flow of variable pump and accumulator change smoothly during mode switching.The dynamic coordinated control method of variable pump and engine based on closed loop feedback of engine speed is presented.With the dynamic coordinated control method,the torque of engine can be accurately distributed between walking system and hydraulic system according to the decision of energy management.(5)Co-simulation analysis.The co-simulation model based on AMEsim and Simulink is built to analyze the control strategy,working principle and Energy efficient of the system.In this thesis,a pressure-coupled oil-liquid hybrid power system is proposed for loaders,and its energy management and dynamic coordinated control strategy are researched.The results of this thesis can provide reference for the related research of loader hybrid power system.