Design And Test Of Power And Longitudinal Adjustment Mechanism Of Center Of Gravity Of Electric Tractor

The traditional oil-fueled tractors are highly dependent on fossil energy,and the gradual increase of energy use aggravates the energy crisis and environmental pollution such as haze.Moreover,when oil-powered tractors operate in closed spaces such as greenhouses,exhaust gas and noise will bring some negative effects on the health of operators.However,electric tractors have the advantages of no pollution,low noise and suitable for operation in greenhouses.The improper adjustment of the center of gravity of the tractor in ploughing operation and uphill is easy to make the stability of the plough running worse,the sliding rate of the driving wheel increases,the traction efficiency decreases,the stability of the uphill decreases,etc.The longitudinal adjustment mechanism of the tractor center of gravity can automatically adjust the center of gravity of the tractor to improve the traction efficiency and stability of the tractor.Therefore,it is of great significance to electrify the tractor and design a mechanism that can automatically adjust the center of gravity.This paper aimed to the problems of the traditional oil-powered tractors need to use non-renewable energy,pollute the environment,need to manually adjust the balance weight,time-consuming and labors,and often occur improper center of gravity adjustment problems,put forward a gravity adjustable electric tractor scheme.The main research contents and conclusions are as follows:(1)The overall scheme of a longitudinal adjustment mechanism for power and center of gravity of electric tractor.Determining the function and performance requirements of electric tractor;The overall scheme of the electric tractor was designed.According to the advantages of the permanent magnet synchronous motor such as high energy density,strong overload capacity and good control,and the advantages of the lithium iron phosphate power battery with low cost and high safety,the power scheme of the electric tractor was determined.According to the characteristics of the longitudinal adjustment of the center of gravity and the chassis structure,the scheme of the longitudinal adjustment mechanism of the center of gravity with the slide-screw mechanism driven by the stepping motor as the main component was determined.The working principle of electric tractor and longitudinal adjustment mechanism of center of gravity were expounded.(2)Design of the longitudinal adjustment mechanism for power and center of gravity of electric tractor.The longitudinal adjustment mechanism of tractor power and center of gravity,such as driving motor and power battery,was designed and calculated.The minimum power of the driving motor is calculated as 9.8 KW and the rated speed is no less than 3312 r/min according to the two typical working conditions of the electric tractor ploughing and the highest speed.The number of units needed for the power battery was calculated as no less than45 strings according to the continuous working time of the electric tractor under the rated power and the peak power of the driving motor.According to the electric tractor in the climbing slope of 30% when the analysis of the slide and lead screw force,the center of gravity longitudinal adjustment mechanism of the slide and lead screw design,according to the center of gravity adjustment process of the power battery movement speed and acceleration of the stepper motor selection calculation,completed the center of gravity longitudinal adjustment mechanism design.(3)Design of control system for longitudinal adjustment mechanism of power and center of gravity of electric tractor.The vector control method was used to control the permanent magnet synchronous motor,which has the characteristics of high control precision and fast response.Matching the upper computer software to the controller,the information of driving motor speed,temperature and output power can be displayed in real time.The power battery management system was designed to make it have functions of thermal management,energy management,safety management and balance management,and equipped with a BMS meter,which can display the voltage,SOC,temperature and alarm information of the power battery,to improve the safety of electric tractor.The longitudinal adjustment control system of the center of gravity was designed.STM32F103ZET6 was used as the control chip,and the strain type embedded pull bar is designed to measure the force.The system can realize the automatic longitudinal adjustment of the center of gravity.Development of data acquisition and storage of the upper computer software,Bluetooth transmission,the upper computer software acquisition and storage of data functions.The vehicle control system was integrated so that the driving motor and power battery can work together,and the center of gravity of the electric tractor can be adjusted longitudinally according to different working conditions.(4)Prototype trial production and test.The electric tractor prototype was trial-produced,and the parameters of the electric towing center of gravity were tested.The longitudinal center of gravity of the electric tractor chassis is 0.425 m from the rear axle,and the height of the whole machine center of gravity is 0.481 m.The performance test of the electric tractor showed that the maximum driving speed is 21.6 km/h.The maximum traction force is 4020 N;The tractional resistance which can be overcome by ploughing is about 3557 N.All meet the functional and performance requirements.The experiment results show that the average traction efficiency and the average load of the front wheel are 64.5% and 2045.0 N respectively with the center of gravity adjustment function,which are 8.4% and 19.6% higher than that without the center of gravity adjustment function.When the center of gravity is adjusted uphill,it can be automatically adjusted according to different slopes,and the analysis shows that the tractor’s rolling Angle is increased by 5.8% through longitudinal adjustment of the center of gravity.