| China is the world’s largest fruit producer.The fruit industry is an important pillar of rural economic development and farmers’prosperity in China.At present,the closed orchard still have a large planting area in China,and the area of the apple closed orchard alone has reached about 1.333×10~6hm~2.Such orchards are confined in space,it is difficult for large and medium-sized operating machinery to enter the operation,and the main operation links of orchard production are still mainly manual operations.In this paper,aiming at the agronomic characteristics of fruit tree planting in the closed orchard in China and the problem of fewer pure electric drive general power machinery in the existing closed orchard,a dual-motor distributed drive small electric crawler tractor suitable for the closed orchard was developed.The details of the study are as follows:(1)Overall scheme design and matching of electric drive system components.According to the agronomic characteristics of the closed orchard,the design requirements of small electric crawler tractors were clarified,and by comparing the three different electric crawler chassis drive schemes of single power source centralized drive,dual power source distribution drive and multi-power source distribution drive,the power transmission mode of the small electric crawler tractor in this paper was determined as dual motor distributed drive,and then the design of the overall scheme and the determination of the main design parameters were completed.Through the calculation and selection of the motor,reducer and power battery pack in the electric drive system,the matching of the core components of the electric drive system is completed.(2)Key component design analysis and virtual prototype model building.The track parameters and wheel set parameters were determined in the crawler traveling system;The structural design of the frame was completed,the finite element simulation model of the frame was established by ANSYS/Workbench software,and the force of the frame under the traction condition was analyzed,and the relevant loads and constraints were applied.The test results showed that the stress and strain of the frame meet the requirements;The modal analysis of the frame was carried out,and the natural frequency and mode shape of the first ten modes of the frame were obtained,and the study showed that the frame would not produce resonance phenomenon according to the frequency comparison.The 3D drawing software Creo was used to build a virtual prototype model of a small electric crawler tractor.(3)Research on speed collaborative control of dual-motor distributed drive system.The mathematical model of permanent magnet synchronous motor under three coordinate systems was established,several common control algorithms of permanent magnet synchronous motor were analyzed,and the model construction and simulation analysis of the vector control system of a single permanent magnet synchronous motor were completed in Matlab/Simulink software,and on this basis,the fuzzy PID control algorithm was introduced to optimize the system.The common synchronous control strategies of dual-motor systems were analyzed,and the modeling and simulation of dual-motor cross-coupling synchronous control system based on fuzzy PID was completed.The simulation results showed that the single-motor vector control system based on fuzzy PID had better dynamic response characteristics than the traditional vector control system,and the dual-motor cross-coupling synchronous control system based on fuzzy PID had better anti-interference performance and synchronization performance than the traditional cross-coupling synchronous control system.(4)Trial production and test of small electric crawler tractor prototype.The processing and assembly of the small electric crawler tractor prototype was completed,and the prototype was tested and analyzed.Through the analysis of the position of the center of gravity of the prototype,the results showed that the electric tractor had good lateral stability and longitudinal stability.Through the climbing performance test of the prototype,the maximum climbing degree of the electric tractor was not less than 25°;Through the steering performance test of the prototype,the minimum in-situ turning radius of the electric tractor was 728mm,and the steering maneuverability was better.Through the obstacle crossing performance test of the prototype,it was obtained that the electric tractor could cross a vertical boss with a height of 20cm and a trench with a width of 40cm,and the obstacle crossing performance was better.Through the straight-line driving performance test of the prototype,the deflection rate of the electric tractor was 1.109%,which was much smaller than the 6%deflection rate in the national standard.The data acquisition and recording system of small electric crawler tractor was built,and the traction power test of the prototype at 1km/h,3km/h,5km/h and 7km/h speed was completed,and the test results showed that the average traction force generated by the electric tractor at the main driving speed when the slip rate did not exceed 15%was above 5320.4N,and the traction power could reach9173.3W,and the traction performance was better.The test results showed that the average trenching depth and trench surface width of the prototype ditching operation were 25.38cm and 40.76cm,respectively,the ditching depth stability was more than 93.2%,the maximum linear deviation of ditching was 13cm,and the average ditching speed was 0.765m/s,and all indicators meet the requirements of orchard ditching operation.During the ditching test,the average output power of the electric tractor power battery pack was 8129W,the average power consumption was 149.02Wh,the maximum fluctuation range of motor output torque was 20～106N·m,and the overload capacity of the whole electromechanical drive system was strong,which can provide sufficient driving force according to the change of soil conditions.Finally,a prototype trenching operation endurance test was conducted,and the test results showed that the entire machine could achieve 3.57 hours of continuous trenching operation when fully charged,and the endurance meets the design requirements. |
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