Research On Design And Control Of Tractor Electric Power Steering System

As a necessary power device in agriculture,tractors have played a quite important role in the development of China's agricultural modernization.The tractor's steering system is still dominated by conventional hydraulic and electronically controlled hydraulic steering systems at present.However defects remain unsolved such as mechanical steering problems,leakage of hydraulic oil,and inconvenience in installation,maintenance,and inspections.Based on the tractor's own structure and driving characteristics,and combined with the existing electric power steering system on the vehicle,this article aims to design an electric power steering system suitable for the tractor(hereinafter referred to as the tractor EPS system).The driving safety,handling stability and energy saving and environmental protection of the tractor have been improved,which not only promotes the economic benefits,but also expands the research and development space and reduces the development cost.At the same time,it also provides the basis for the follow-up research on tractor EPS systems and the development of pure electric tractors.The specific research content of this article is as follows:First,the overall structure of the tractor EPS system is designed.Based on the existing small and medium-sized tractors,the main components of the tractor's EPS system,such as the mechanical steering gear,the booster motor,the deceleration mechanism,and the sensors are analyzed,designed,selected,modeled and reasonably assembled.With the design of the overall shell structure,a certain degree of beauty and practicality is achieved.Secondly,a comprehensive analysis of the three power-assisted characteristic curves is performed.In terms of design,adjustment,and use,it is considered that the straight-line power assistance characteristics are selected and related parameters are determined,and the follow-up power steering assistance is realized.The fuzzy PID control strategy suitable for this system is selected,and the relevant design is developed around the fuzzy PID controller.The EPS system of the tractor not only has the precision of the traditional PID control,but also has the timeliness of fuzzy control,thus optimizing the control effect of the system.Then,the controller of the tractor EPS system is designed.The hardware circuit uses STM32F407VGT6 as the main control chip,and completes the design of the main control circuit,assisted motor drive and sensor signal acquisition;the software part gives the flow chart of three subroutines respectively of the main program of the system and the A/D acquisition,digital filtering and fuzzy PID control.Finally,the simulation and analysis of the tractor EPS system and three control modes are completed.Based on the simplified EPS model of the tractor,the simulation models of the steering wheel and the upper steering shaft,the assist motor and the deceleration mechanism,the lower steering shaft,the mechanical steering gear,the controller and the tractor EPS system are established through Matlab/Simulink.Therefore the correctness of the designed tractor EPS system is testified.In addition,the three control modes of tractor's assisting compensation,steering return and damping are designed-The Simulink modeling simulation analysis is used to verify the rationality and effectiveness of the design.