| Researches show that the new type of electric tractor is one of the effective ways to solve the problems of energy and environmental protection caused by agriculture machinery. But in our country, there are few researches about the electric tractor. Therefore, carrying on an in-depth study on the design theory and drive characteristics of electric drive system has great significance to the development of agriculture electric tractor.Based on the requirements of the agriculture electric tractors for the electric drive system, and the nowadays study actualities of electric drive system home and abroad, a new type of electric tractor drive system based on series DC motor was deveoped. The finished work and achieved results are generalized as follows:1. Researches of the design theory and calculation method of electric tractor drive system. Based on the working condition of the tractor, a new type of electric tractor drive system which combines a motor and a gear, and the evaluation index and the calculation method for dynamic performance of electric tractor are suggested; taking an electric tractor drive system as design object, the balance graph of drive-resistance force, climbable gradient under different shifts, and continuous working time are calculation analyzed. Researches show that the drive force characteristics of the electric tractor drive system based on series DC motor is close the ideal characteristics, the curves are concave, low speed with constant power, and high speed with constant torque; the electric tractor has large working speed under different shifts, but the extensive coincidence speed shows that the variable ratio of the gear is unreasonable; the maximum climbable gradient of this electric tractor is more than 30%, and does not need frequent shift when working for its extensive climbable gradient; there are many influence factors of continuous working time, which the more obvious factors are working speed and working load, the working time increases with the increase of the working speed and working load.2. Simulation researches on the drive characteristic of the electric tractor. Begin with the traction force analysis of the electric tractor, the drive equilibrium equation, simulation model and control strategy of the drive system were established, and the simulation system of the electric tractor was developed based on the ADVISOR; taking the low speed EUDC cycle and a uniform speed cycle as the drive cycle input, some simulation were carrying on about the traction force and the dynamic characteristics of the drive system. Researches show that the electric drive system work normally because the simulation speed tracking the target speed exactly; the torque is related to the working conditions, it is constant under uniform speed condition and change under accelerating or decelerating condition; the current of the battery is affected by the working load and running speed, and increases with the increase of the working load or running speed; the SOC of the battery indicates the residual capacity, the smaller the SOC, the fewer the residual capacity; the electric tractor based on series DC motor has a strong anti-overload ability, and the maximum sudden load is more than 1.4 times of the rated load under normal working condition; and the electric tractor also has an adaptive load ability, it can still work under lower speed when the working load increasing.3. Researches of the electric drive system test-bed. Analysis was made on the advantages and disadvantages of different test study methods, and the researches on electric tractor drive system was carried on using indoor simulation test-bed; the test-bed of the electric tractor drive system was established with modularization, and a measurement and control system of the test-bed was developed based on LabVIEW; in addition, the static calibration of sensors used in the test was carried on. Research results show that the test-bed with good expansibility can used to finish the performance test not only the whole vehicle but also some components; the test-bed can control the braking torque of the magnetic powder brake by the output voltage of the data acquisition card, and simulates the resistance load of different conditions conveniently.4. Experimental researches on the drive characteristics of the electric tractor drive system. A series of test researches were carried on about the drive characteristics and power characteristics of the drive wheel researches, the voltage and current characteristics of the battery research, the transmission efficiency of the electric drive system research, the motor controller efficiency characteristics research, the maximum speed and maximum climbable gradient researches, etc. Research results show that the drive characteristics are consistent with the theoretical analysis, it is approximate hyperbola and affected by the external characteristics of the DC motor, the torque will increase with the speed decreasing; the battery SOC has no effect on the drive characteristics unless its voltage below the minimum voltage of the motor, but it can affects the continuous working time; the drive torque and transmission efficiency under different shifts have great difference, and the electric tractor has better power performance and fuel economy when working underâ…¤,â…¥shifts; in order to obtain higher transmission efficiency, we should design different gear ratios for different working conditions because the drive characteristics under different shifts is suitable for different working conditions; the voltage and current of the battery are consistent with the theoretical analysis; the efficiency of the motor controller has little effect on the transmission efficiency, because it is more than 90% under normal condition.5. Simulation working researches of the electric tractor. The output characteristics of the drive system under different working conditions were experimentally studied. Research results show that change trends of the battery voltage and current under different working conditions are almost uniform, the voltage decreases more with the working load increasing, and it has small fluctuation with the changing of the working speed; the voltage will increase after finish the working, and the voltage difference between initial voltage and terminal voltage can indicate how much power used; the battery current will be upper and lower with the fluctuation of the speed and load, and increases with the speed and load increasing; the gear is suitable for heavy load condition because the average transmission efficiency under plowing condition is higher than that under transport working condition; the electric tractor can work stably under fluctuation loading 1.57 times of rated load besides the slight fluctuation of the speed.Research on this subject is expected to provide theoretical and technological support for the study and development of electric drive system.
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