| The transmission mode of the loader drive system generally includes two types,hydrodynamic transmission and hydrostatic transmission.The hydrodynamic transmission system has automatic adaptability,but there are problems such as narrow efficiency range and low transmission efficiency.The hydrostatic transmission system utilizes the characteristics of volumetric speed regulation,and can adjust the movement speed of the actuator by changing the displacement of the variable hydraulic pump and the variable motor in the circuit,so that the engineering vehicle can complete the automatic shifting.The hydraulic oil output from the variable displacement pump in the volumetric speed control circuit is directly input to the variable motor without overflow and throttling loss,and the system pressure of the circuit is determined by the load on the motor.It has higher efficiency and more flexible structure arrangement than hydraulic transmission.In this paper,a single pump-double motor hydrostatic transmission system for loaders is analyzed,and a static fluid system variable regulation law is proposed for the system.The simulation of the hydrostatic transmission system based on the variable regulation law is carried out in the AMESim environment.Comparative analysis is carried out with the test results.The main research contents and conclusions are as follows.(1)A 4 ton loader single pump-dual motor hydrostatic transmission system is analyzed to replace the traditional hydrodynamic transmission.Through the analysis of the hydraulic system and the traction characteristics of the whole vehicle,it is concluded that the transmission can well meet the vehicle requirements of a 4 ton loader.Comparing the static matching analysis of a 4 ton conventional hydrodynamic loader,it is found that the hydrostatic loader is significantly superior to the hydrodynamic loader in terms of power and economy.It is more efficient than the traditional single pump-single motor hydrostatic transmission system.The larger shifting range can make full use of the small motor,small torque,high speed and large motor,high torque and low speed.(2)A variable regulation law based on single pump-double motor hydrostatic transmission system is proposed.The variable adjustment law is divided into one-speed start adjustment and second-speed start adjustment.When material shoveling is required,the load is large,and the loader starts in one gear.At this time,the two motors work at a small displacement at the same time.The reaction is more sensitive.When the load increases,the displacement of the two motors increases at the same time,which can quickly meet the load demand and ensure the shovel loading efficiency of the loader.When the loader needs the empty car transfer operation,it starts in the second gear and the speed is stable.When the small motor works alone,the load increases in the early stage,the large motor does not react,and the small motor increases the displacement separately to meet the traction requirement.When the system pressure increases to the maximum,the large motor output shaft clutch is engaged.And the large motor displacement begin to increase,keeping the system pressure stable.(3)The AMESim simulation model of the hydrostatic transmission system is established.In the AMESim environment,the corresponding physical model is built for the hydrostatic system circuit of a 4 ton loader.On the basis of the simulation model,the two typical working conditions of the loader are simulated,that is,the driving condition and the V-type shovel condition.Under these two conditions,the variable regulation of the proposed single pump-double motor hydrostatic transmission system is used to analyze the important parameters such as system pressure,traction,pump displacement and motor displacement in the time domain.(4)A dynamic characteristic test of a 4 ton hydrostatic loader is carried out.The dynamic traction characteristics of the hydrostatic loader are tested.Loaded by the loader,the traction force of the loader and the main parameters of the hydraulic system are collected,and the simulation results of the hydrostatic transmission system are compared with the whole machine test.It is found that the measurement results of the traction force,system pressure and pump and motor displacement of the loader are basically consistent with the simulation results,which verifies the correctness of the simulation and variable regulation of the hydrostatic transmission system. |
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