Design And Experimental Research Of The Electric Tractor Electric Hitch System

Hitch system is an important component of electric tractors,which was used to raise and maintain the tools in different required positions.And the performance of the hitch system will directly affect the power economy and quality of the tractor.With the development of technology,the drawbacks of hydraulic systems are gradually emerging,such as low efficiency,high manufacture and operation costs.Moreover,the traditional hitch systems are not suitable for the electric tractor.The electric hitch system is driven by the motor,which has the advantages such as simple structure,low energy consumption,sensitive reaction,and the lower complexity of power transmission.Therefore,the research on electric hitch systems will improve the level of agricultural operations in China and promote the development of agricultural electric vehicles.Based on the research of tractor hitch systems at home and abroad,this study has taken a type of domestic 25.7 kW tractor hitch mechanism as the object and conducted in-depth research on tractor electric hitch systems according to the agricultural wheeled tractor rear-mounted three-point hitch system standard.1.Research on the overall design scheme of electric hitch system.According to the design standard of tractor hitch system,the paper had proposed an overall design scheme of electric hitch system,including the power drive mechanism,power actuator and tillage adjustment control system.The electric actuator is used as the power drive mechanism,the operation panel is used as the traditional operation handle,and the single-chip microcomputer is used as the control core of the hitch system.The traditional three-point suspension was selected as the power actuator.Compared with the traditional hitch system,the hitch system was superior to the traditional hitch system in terms of structure and performance.2.Establishment and analysis of mathematical models of electric hitch system.The paper had established a mathematical model of the tractor electric hitch system.Taking the tractor as the research object,the motion coordinate system of the hitch system was established based on the rear axle of the tractor,and the kinematics and mechanical model of the electric hitch system were also established.According to the kinematics analysis of the electric hitch system,the theoretical calculation formula of the lifting stroke and the lifting ratio were obtained and it provided a theoretical basis for the selection of the angle sensor.According to the mechanical analysis of the tractor suspension mechanism and the hanging agricultural implement,the paper provided a theoretical basis for the selection of the force sensor.Combining kinematics and mechanical model analysis,it provided the theoretical basis for the selection of electric actuator.Based on the mathematical model of the tractor suspension mechanism and national standards,the design parameters of the electric hitch system were initially selected.3.Dynamic simulation and parameter optimization of electric hitch system.The paper had established a simulation model of electric hitch system in the Adams/view software.In order to reduce the loading of the electric actuator,the length of the lift arm,the length of the lift rod,the position of the hinge point of the pull rod,the position of the hinge point of the lift rod and the pull rod,the position of the hinge point of the electric push rod and the lift arm were selected as the variables.The single factor and multi-factor combination methods were used to analyse the driving of electric actuator and obtained the force map.The simulation results show that after the optimization,the maximum driving force of linear actuator decreases by 36%,the average driving force decreases by 51%.4.Tillage adjustment control system of electric hitch system.The comprehensive controller of force and position was designed,including the hardware and software design.Based on the functional requirements of the force and position adjusting control system,the STC15W4K32S4 microcontroller was selected as the main control chip,and using the angle sensor,force sensor,the control chip and the control panel to complete the controller hardware circuit design,including the power supply circuit,etc.The software program was written in C language,including the main program of the controller,AD conversion subroutine,ascending descending subroutine,and force and position comprehensive adjustment subroutine.5.Experimental study on electric hitch system.the tractor was used as the carrier to complete the prototype assembly of the electric hitch system,the indoor bench test and field tillage test of the electric hitch system were carried out respectively.The results showed that: the operation time is less than or equal to 3 s,the lifting stroke is more than 420 mm,and the maximum lifting force is more than 580 kg,which satisfies the design requirements and verifies the correctness of the simulation analysis.According to the design principle of Box-Behnken test design,the three-factor and three-level test methods were designed to carry out field tillage experiment.The results showed that the maximum variation coefficient of tillage depth was 7.5%,the minimum value was 2.6%,and all were less than 10%,meet the agronomic requirements,the uniformity of the ploughing depth was good,and the response time of the ploughing depth adjustment system was short.