Researches On Dynamic Characteristics Of Hybrid Electric Tractor

In recent years, the pressure of agricultural vehicles on the environment and resources is increasing year by year, so carrying out the research and development of new energy-conservation tractors has become the imminent important subject. However, in our country, there are few researches about the hybrid electric tractor. Therefore, carrying on an in-depth study on power coupler, design theory of drive system, hybrid electric drive characteristics and energy consumption of hybrid electric tractor have great significance to the development of hybrid electric tractor.Based on the requirements of the work and transmission characteristics for the hybrid electric drive system, and the nowadays study actualities of hybrid electric drive system home and abroad, designed and manufactured a power coupler for parallel hybrid electric tractor. Then a new type of hybrid electric tractor drive system based on a single-cylinder diesel engine and series DC motor was developed. The finished work and achieved results are generalized as follows:1. Design and simulation of the power coupler. Through the analysis of principles and characteristics of various types of power couplers and in combination with the requirements the work and transmission characteristics of tractors, deigned the transmission ratio, characteristic parameters and matching number of gear teeth of the power coupler, then a differential planetary gear transmission power coupler for parallel hybrid electric tractor was developed. On the basis of the establishment of the simulation model of the power coupler in SimulationX, three operation modes that the engine working only, motor working only and hybrid mode working were researched. Results show that, in each mode, the speed and torque relationships of sun gear, ring gear and planet carrier were in consistent with the speed and torque relationships of general differential planetary gear transmission; in the instant of start and stop, and in the process of acceleration and deceleration, the loss of internal torque and power of differential planetary gear transmission were produced; the torque direction of sun gear and ring gear was consistent with the rotation direction of engine or motor when which played a major role, while planet carrier torque was in the opposite direction with the rotation direction of engine or motor when which played a major role.2. Researches of the design theory and calculation method of hybrid electric tractor drive system. Based on the working condition of the tractor, a new type of electric tractor drive system was designed, which contained a single-cylinder diesel engine and series DC motor as input power, and the power coupler cooperated with the gearbox to control speed, then suggested the evaluation indicator and calculation model of dynamic and economic performance and the parameter design methods of each component of drive train of hybrid electric tractor, established the theory model of each component of drive train, and proposed the match principle of engine and motor power. Taking a hybrid electric tractor as design object, the driving force, climbing property and speed matching range of engine and motor on different load of engine and different shift, the total transmission efficiency of engine and motor in the same or reverse rotation and equivalent energy were calculation analyzed. Results show that the driving force and climbing property is proportional to the load of engine and is inversely proportional to the shift of gearbox, while speed matching range of engine and motor decreases when the load of engine increases, but has nothing to do with the shift changes. The total transmission efficiency on engine and motor in the same rotation is greater than on engine and motor in the reverse rotation, when engine and motor are the same speed. And the total transmission efficiency increases when the speed of engine or motor increases on engine and motor in the same of inverse rotation. When the level of shifts is lower, the power matching range of engine and motor is greater, and equivalent energy consumption is lower on the same speed of engine and motor. On certain shift, equivalent energy consumption increases when the speed of engine and motor increases. The equivalent energy consumption of hybrid electric tractor is less than the fuel tractor on the same power, and the highest energy conservation is up to24%.3. Simulation research on dynamic characteristics of hybrid electric tractor. The model establishment and parameters set of each component of hybrid electric have been processed in SimulationX, then developed the simulation system of hybrid electric tractor. Simulation analysis of dynamic characteristics of hybrid electric tractor in three operation modes-engine working only, motor working only and hybrid mode and in two different working conditions including no-load transport and sowing shows that, when the shift and external load is constant, the speed range and the maximum driving speed are the biggest in hybrid mode, second biggest in engine working only mode, the lowest speed range and minimum driving speed in motor working only mode. With the increase of the shift, the driving speed increases in three modes. The torque of engine, motor and some power coupling devices including sun gear, ring gear and planet carrier increases with the increase of the shift and external load. Torque is constant on the constant driving speed condition and will wave on acceleration or deceleration conditions. Driving wheel torque increases only with the external load increases, and has nothing with the shift. When the shift and external load is constant, the fuel consumption per hour of engine increases with the increase of engine speed; the battery output power and motor input voltage increases with the increase of motor speed and the motor input current remains almost unchanged;1h equivalent energy consumption increases with the increase of the engine and motor speed. With the increase of the shift and external load, the fuel consumption per hour of engine, the battery output power, the motor input voltage and current and1h equivalent energy consumption all increase. On the engine working only mode, the total transmission efficiency increases with the increase of the shift and external load. On the motor working only mode, the total transmission efficiency and motor efficiency increase with the increase of the speed of the motor, the shift and external load. On hybrid mode, the total transmission efficiency increases with the increase of the engine speed, motor speed, the shift and external load; and the motor efficiency increases with the increase of motor speed, the shift and external load. On certain shift, when driving speed is in the range of motor working only mode, the equivalent energy consumption of motor working only mode is the minimum; when driving speed is in the range of engine working only mode, the equivalent energy consumption of hybrid mode is lower. When the external load is constant, the driving speed and the corresponding equivalent energy consumption increase with the increase of the shift in all modes. At the constant shift and the same driving speed, the equivalent energy consumption increases with the increase of external load. In various engine speed and motor speed, the equivalent energy consumption will be different in the same driving speed in hybrid mode. That is to say, the hybrid electric tractor has the greater range of power selecting on some working condition in hybrid mode.4. Construction of the test platform and development of measuring and controlling system for hybrid electric tractor. Constructed the test platform for hybrid electric tractor, based on the modularization notion, developed measuring and controlling system in LabVIEW, and calibrated all sensors used for test platform.5. Experiment on dynamic characteristics of hybrid electric tractor. The experiments include these characteristics-the driving speed of hybrid electric tractor, power match of engine and motor, output power of driving wheel, output torque of engine, motor and driving wheel, the output properties of the battery and the motor, traction efficiency, total transmission efficiency, equivalent energy consumption and so on. Results show that on certain shift and the same speed of engine and motor, the driving speed remains almost unchanged with the change of load torque. But with the increase of the load torque, the highest motor speed and the speed matching range of engine and motor are reduced, so that the corresponding driving speed range is reduced. On certain shift, the power of engine, motor and drive wheel are direct proportion to the load torque, and the efficient power of engine and the motor increase with the increase of the load torque. When the shift and load torque are constant, the trend of the changing of engine power with the speed changing of engine was similar with the load characteristic of engine, and the engine power slightly decreases with the increase of the motor speed; the motor power increases with the increase of the motor rotation speed; the driving wheel power increases with the increase of the speed of motor and engine, and is more sensitive with the changing of motor speed. When the motor speed is lower, the engine power is greater than the motor power; when the motor speed increases, the motor power will be greater than the engine. As the engine speed and load torque increase, the range in which the motor power is greater than the engine power decreases gradually. On certain shift, the engine torque slightly decreases as the motor speed increases, and increases first and then decreases with the increase of engine speed; the motor torque remains almost unchanged as the increase of the speed of motor and engine. When the load torque is constant, the motor torque is almost twice of the engine torque, and the greater the torque loads, the more obvious it is. On constant load torque, the battery voltage decreases with the increase of motor voltage, and the battery current increases with the increase of motor voltage. The battery voltage decreases with the increase of load torque on constant motor voltage; the greater the load torque, the greater the battery voltage drop with the increase of the motor voltage; the battery current increases with the increase of load torque, and the control range of motor voltage decreases with the increase of load torque; the motor current increases with the increase of load torque. When the shift is constant, the traction efficiency, total transmission efficiency and equivalent energy consumption increase with the increase of load torque. When the shift and load torque are constant, the traction efficiency, total transmission efficiency and equivalent energy consumption increase with the increase of the motor and engine speed. Hybrid electric tractor needs to select the best operating point according to the traction efficiency, total transmission efficiency and equivalent energy consumption. When the load torque is780N-m, which simulates the sowing operation condition, the equivalent energy consumption error is less than3%compared with simulation results, that is to say, the simulation results are reliable.The research on this project is expected to provide theoretical basis and technical support for the development of other types of coupler, the power match research of other types of engine and motor and development of control system of hybrid electric tractor, and is of important theoretical significance and practical value to promote the development of energy conservation and emission reduction tractor.