| Under the background of national energy conservation,emission reduction and new energy strategy,electric agricultural vehicles will become a major trend of agricultural mechanization development in the future.As one of the main parts of electric agricultural vehicles,electric tractor will usher in the spring of its own development with the gradual maturity of vehicle structure and the continuous improvement of vehicle control theory.Overseas researches on electric tractors are carried out earlier,starting from 1970.At present,certain theoretical system and industrial chain have been formed,and some key technologies have been monopolized.In contrast,domestic research on electric tractors started late and appeared after 2006.In domestic research on electric tractors driving scheme,most of them still stay in the traditional drive axle electric tractors,with little reference to the form of four-wheel independent drive.As for the driving control strategy of electric tractors,the research theory of improving the power performance and steering stability is not yet mature,and there is still a broad space for development.Based on the above analysis,this paper proposes a four-wheel independent drive scheme of wheel-side motor fusion reducer,and analyzes how to reasonably distribute the driving torque under different operating conditions,so that the electric tractor can obtain better dynamic performance and steering stability.In this paper,theoretical analysis,software simulation and bench test are combined to carry out the research.The main work contents and conclusions are as follows:(1)According to the actual performance requirements of the electric tractor,the vehicle driving scheme of four-wheel independent drive of the wheel side motor was determined and the wheel side drive system was designed.The driving system has the function of decelerating and increasing moment,and has good impact resistance and anti-interference,which is very suitable for the complex and harsh working environment of tractors.(2)Planned and designed the test platform and measurement and control scheme for the wheel drive system of electric tractor,and verified the feasibility of the measurement and control scheme through debugging.The control voltage signal between the motor and the powder magnetic brake was calibrated,and the actual relationship between the control voltage signal and the output torque of the motor and the control voltage signal and the output torque of the powder magnetic brake was obtained,which ensured the accuracy of the subsequent test data.The transmission efficiency of the driving system was determined by the drive efficiency test,which laid a foundation for the subsequent research on the control strategy of driving torque distribution.(3)In order to ensure better traction performance under low-speed traction operation,the driving torque distribution control strategy of electric tractor under low-speed traction condition was put forward with the goal of power performance.The e longitudinal dynamics equation with traction resistance was established,and the control strategy of driving torque distribution based on load ratio was proposed,which was compared with the average distribution of torque.The feasibility of the control strategy was verified by the output torque following test of the driving system.The results show that the total driving torque of the tractor driving system is increased by 27.3%.The maximum traction force of the tractor is increased by 20%.(4)With steering stability as the goal,the control strategy of driving torque distribution for electric tractor under medium speed steering condition was proposed.By using layered control,the whole control strategy structure is divided into dynamic model layer,compensating yaw moment formulation layer and driving moment distribution layer,which simplifies the complexity of the control system and improves the control precision.In the compensation yaw moment formulation layer,the particle swarm optimization algorithm was integrated with the traditional PID algorithm to optimize the yaw angular velocity.The feasibility of the proposed control strategy was verified by the yaw compensation moment following experiment.On this basis,the control strategy under continuous steering and constant Angle steering is simulated.The results show that the control strategy can reduce the peak slip rate of the vehicle,restrain the phenomenon of skid instability,and make the yaw velocity reach a stable state quickly,so as to improve the steering stability of the tractor. |
