| The land area of China is about 9.6 million square kilometers of which the hilly and mountainous areas are approximately 6.66 million square kilometers,accounting for 69.4%of the country’s land area.Due to the influence of topographical factors,the level of agricultural mechanization in the region is low,and the supply of mountain tractors that can meet the requirements of hilly mountain operations is seriously inadequate.Therefore,the mountain tractor was used as the the research object of this study.A hydrostatic drive system which is suitable for mountain crawler tractors was designed.The main research contents and conclusions of this study are as follows:(1)Scheme determination and parameter matching of the mountain crawler tractor drive system.The hydrostatic drive was finally determined to be used in the study after comparing four driving modes which contain mechanical drive,hydraulic drive,electric drive and hydrostatic drive.According to the operation requirements of the mountain crawler tractor,after the dynamics and kinematics of the tractor was analyzed,the parameters of the key components of the three-cylinder diesel engine,hydrostatic drive unit(HST),drive rear axle and other key components of drive system were matched.The main performances were all checked containing traction performance,system pressure and operating speed etc.(2)Simulation analysis of tractor drive system based on AMESim.According to the transmission principles of the hydrostatic drive system and the relevant parameters of mountain crawler tractor,the simulation model of the drive system was established using AMESim software,and the system parameters were set.The start acceleration,deceleration braking and load shock conditions of the drive system were emulated.The simulation results showed that the driving speed could be changed with the change of HST variable pump displacement.The maximum driving speeds of the three gears were 4.28km/h,6.07km/h and 8.28km/h respectively.Under the influence of the step load,the pressure of the system fluctuated greatly,but still could reach stability in 2s.Simulation showed that the components are well matched to meet the performance requirements of the tractor,which could be the technical support for the actual test of the system.(3)The design of test platform of the drive system and the experiments of dynamic performance of the drive system.According to the test requirements of the drive system,the overall scheme of the drive system test bench was determined,and the design of the loading system,hydraulic control system and throttle adjustment mechanism was done.The UG software was used to realize three-dimensional modeling and virtual assembly of the test bench components,which was the basis of the test bench’s design.The hardware part of the test system’s test bench was designed and manufactured with the acquisition system and control system integrated.The drive system’s test bench was constructed finally.The traction performance,acceleration performance and load shock characteristics of the drive system were tested separately.The test results showed that when the engine was at1700r/min,the stable driving torque of I gear was 1180.0N·m,and the stable driving torque of II gear was 1063.6N·m,which is greater than the theoretical maximum operating torque of 983.7 N·m,indicating the drive system could satisfy the job requirements of larger loads.(4)Optimal economic control of mountain crawler tractors with consideration of HST efficiency.According to the relationship between the various components of the tractor drive system,the efficiency of the drive system was analyzed,and the main factors affecting the fuel economy of the system were load torque,engine speed and HST variable pump swashplate angle.After the fuel test of engine-HST system under different speed ratio loads was implemented,the prediction model of the specific fuel consumption and output power of the system was established.The prediction model was analyzed by the response surface method,and the optimal fuel economy control strategy of the system under different load torque and output power was proposed in the study.By comparison,the optimized control strategy was more effective than the traditional engine speed control strategy,indicating the proposed control strategy was effective. |
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