Design Of Tractor Automatic Shift Modes And Control System

In actual agricultural production, automatic transmission technology is not widely usedon agricultural tractors. In order to improve the work quality and efficiency of tractors,reduce labor intensity, the automatic shift strategy and laws suited for tractors are needed tostudy. It is great significance for promotion of agricultural mechanization and automation toenhance the level of agricultural industrialization in our country.There are many factors affecting the tractor shift, such as people factors, environmentalfactors and working conditions factors. When tractors working in field, the complex soilconditions are obviously different from the travel environment of cars; different job typeshave specific requirements for the tractor speeds, which also determines the tractor engineconditions. All these situations are different from cars’. For these reasons, in accordancewith the engine characteristics and engine energy equation, a new automatic shift strategy isproposed, namely the use of the three parameters: engine speed, fuel rod displacement andthe throttle position, to control the tractor’s automatic transmission, and its essence is tocontrol the gear shift according to the changes of throttle positions and the effective powerof engine. For the various tractor working types, a number of shift modes are designed. Ineach shift mode, the tractor exchanges gear position between the designed two, eliminatingthe trouble of the need for repeated manual gear shifts.In accordance with the way of thinking of the shift strategy and shift patterns, a MCUautomatic transmission control system is designed, including hardware and softwaresystems. The design of hardware system contains sensor selection, A/D converter circuit,display circuit, buttons circuit, solenoid valve drive and isolation circuit, MCU interfacecircuit, serial communication circuit, etc. The software system is designed with MCU Cprogramming language, containing the main program, the subroutine of A/D conversionroutine, display, buttons, solenoid valve control, etc. In the process of design, AltiumDesigner10.0and Keil μVision3is respectively used for the circuit schematic drawingand the compilation of the MCU C language program.Through MCU system co-simulation using Keil μVision3and Proteus, thecorrectness of the circuit diagram and program is preliminary proved.Then,an experimentalcircuit board is produced. Nextly, the C language program files are downloaded into the MCU chip, by using STC_ISP_V480software on computer. Through Debugging Running,the system program and the MCU hardware system are further tested, in order to detectwhether the progrma is corrcet and whether the MCU hardware system can normallyoperate.After repeated modification, debugging, and running, the final experimental resultsshow that the MCU system can normally operate in accordance with the expected shiftmodels and strategies, and also automaticly shift gears abiding by the driver’s intentions andthe changes of external load. Meanwhile, the results show that the hardware circuit and theprogram of the MCU system are correct, and the whloe system is reliable, and the overalldesign scheme is feasible.