Research On Control System Of Mechanical Automatic Transmission For Small Tractor

At present,most domestic tractors use manual transmissions,which require the driver to shift gears manually.Improper shifting operations can easily stall the tractor and even cause damage to the engine and gearbox.In addition,the tractor needs to change the gear frequently when working,which will not only reduce the efficiency of the tractor,but also increase the driver’s fatigue and affect the driving safety.Therefore,it is of great significance to carry out research on automatic transmission for tractors.The Automatic Manual Transmission（AMT）can achieve automatic shifting while retaining the advantages of manual transmission,which is very suitable for small tractors.However,AMT is prone to power interruption,long shifting time,and shifting frustration,which brings discomfort to the driver.This paper will carry out the research on the control system of the tractor AMT actuator,and improve the AMT’s long shift time and shifting setback problems by improving the control accuracy and response time of the actuator.First,research on AMT automatic clutch control system.The internal structure and working principle of the dry clutch are analyzed,and the mathematical model of the automatic clutch system is established according to Newton’s second law and Kirchhoff’s law;the AMT automatic clutch control system is designed based on the backstep control algorithm.The AMT automatic clutch system and controller model are built with Matlab/Simulink to verify the control effect of the designed control system.It can be seen from the simulation results that under the action of this control strategy,the response time of the motor is 0.2s,and the maximum control error does not exceed 9×10^-5rad.Secondly,the control system of the AMT shifting actuator is designed.Because The DC motors of the shifting actuators are of the same model.The difference between the two is only the resistance experienced by the actuators.Therefore,this article mainly carries out the modeling of the shifting actuators.Based on the established mathematical model of the AMT shift actuator,this paper proposes an improved sliding mode active disturbance rejection control strategy（MSMADRC）,which combines the advantages of sliding mode control（SMC）and active disturbance rejection control（ADRC）.What’s more,the jitter problem of SMC is improved.The AMT shift actuator and its controller model are built in the Matlab/Simulink environment for simulation verification.The simulation results show that MSMADRC has better response speed and control accuracy,and has good robustness and anti-interference.Then,the thesis carries out the hardware design of the automatic transmission controller for the small tractor.According to the requirements of the controller,the overall architecture of the controller hardware is designed.Based on the overall architecture of the controller hardware,the minimum system circuit,power supply voltage conversion circuit,signal processing circuit and DC motor drive circuit of the controller are designed.The schematic and PCB circuit board of the controller were designed with the help of Altium Designer.Finally,the AMT shifting experiment was carried out on the AMT experimental bench built.It can be seen from the bench test results that under the action of the MSMADRC,the response time of the DC motor of the shift actuator is 0.8s,and it has high control accuracy,which can meet the requirements of AMT shifting precision control requirements.