Research On Torque Distribution Strategy Of Four-wheel Independent Drive Electric Tractor

As a large agricultural country,agricultural machinery occupies a large proportion in the industrial field,and with the development of agricultural mechanization,new energy and intelligent agricultural machinery will gradually replace the traditional internal combustion engine.Electric tractors have been studied abroad since the 1970s,there is a certain level of technology at present.In the domestic,the study of electric tractors is very scarce,due to lack of support of key technologies,there has not been a certain industrial chain.Most of the current electric tractor drive structure is the traditional drive axle type,there is little research on hub direct drive.This paper proposes an independent driving scheme of wheel hub motor.Analysis of how to coordinate torque distribution under different operating conditions to achieve better performance of electric tractors.In this paper,mainly through theoretical analysis,software simulation and the way of platform verification to study,the main work and conclusions are summarized in the following sections.(1)The drive scheme of electric tractor is designed and the system parameter is matched.The calculation and matching of related parameters of electric tractor are carried out based on the same power diesel tractor.There are main machine parameters,motor parameters and battery parameters.The design of the whole machine parameters is the same as the distance between the center of mass and the front and rear axle,so as to ensure that the front and rear driving wheels have a certain load to play a good driving performance.The motor parameters are matched according to the total power,the design is the front wheel 5 kW,the rear wheel 10 kW,and the working voltage is 200 V.The power battery needs to ensure that the four motors can work simultaneously,the discharge voltage is 211 V and the capacity is 160 A·h.(2)Four-wheel independent drive electric tractor test bench is constructed.Through the 3d software Pro e and 2d software CAD,the whole planning and design of the test bed was carried out,based on Labview software,the measurement and control system is integrated,install and debug mechanical parts and measurement the control system.In order to ensure the accuracy of the test data,the sensor is calibrated,there are torque sensors,speed sensors,voltage sensors and current sensors.The external characteristic test of hub motor is analyzed,the maximum output torque of 5 kW motor is about 90 N·m,and the maximum speed is about 850 r/min,the maximum output torque of 10 kW motor is about 110 N·m,and the maximum speed is about 1000 r/min.(3)The torque distribution strategy of four wheel independent drive electric tractor in the working condition of the plough is studied.Due to good traction performance is required during the traction performance,the torque distribution is based on dynamic performance.A torque distribution strategy based on load ratio is proposed,based on the analysis of the balance between the front and rear driving wheels and the ground contact point and the torque balance,the relationship between the load ratio and the drag resistance of the torque is obtained,and compared with torque constant distribution.Through the bench test analysis,in the case of constant torque distribution,when the coupling traction resistance moment reaches 80 N·m,the front drive wheel reaches the adhesion limit,but the rear drive wheel has a lot of adhesion properties that are not fully utilized.Under the distribution strategy based on load ratio,when the coupling traction resistance moment reaches 110 N·m,the front and rear wheels reach the adhesion limit of the ground simultaneously,the actual effective driving force generated can be 2000 N more than the constant equal distribution,the effectiveness of the proposed strategy is verified.(4)The torque distribution strategy of four-wheel independent drive electric tractor in the working condition of road transportation is studied.The electric tractor has relatively stable demand for various performance during road transportation,the pursuit is longer work time and mileage,so the goal of torque distribution is economy.The optimal torque distribution strategy based on drive motor efficiency is adopted.The torque-speed-efficiency Map of the front and rear wheel drive motor is measured through the test,an optimal torque distribution function based on drive motor efficiency is established,and compared with torque constant distribution.Based on PI,the speed closed-loop loading control is adopted,the drive motor can achieve the target distribution torque while maintaining the stability of the rotational speed,and analysis the driving efficiency.The results show that,based on the optimal torque distribution strategy,the efficiency value can be increased by up to 8%,the effectiveness of the proposed strategy is verified.