Research On The Driving Technology For Motorized Wheels Of Electric Vehicle

Under the stress of environment pollution and the scarcity of oil source, Electric Vehicle (EV) becomes an important consideration in the twenty-first century in order to get the sustainable development of Automobile industry. In our country, the researches and developments of EV will also be very valuable to improve urban environment and relief the stress of Oil source scarcity. Based on theoretical analysis, the options of EV Powertrain Schedule and Powertrain components are discussed in this thesis. As a conclusion, an EV Powertrain Schedule suitable to our country is put forward after considering the state-of-art of the automobile technology and the EV technology development tendency. The control strategy and the working modes of the selected EV Powertrain Schedule are determined, the relative control system is also designed in this thesis. The choosing of the HEV Powertrain Schedule and the designing of the relative control strategy play a basement on the parameters designing and matching of the EV Powertrain. Based on theoretical analysis and relative reference, the parameters designing method of the HEV Powertrain is brought out, at the same time the Parameter matching analysis is given according to the requirement of Power-assisted EV. According to the performance of dynamics , such important parameters as the power and rev of the motor can be calculated by using the knowledge of automobile and motor. Then another important parameter , reduction ratio also can be calculated. We can get the upper limit from two ways , one is the full speed of the vehicle and the highest rev of the motor, the other is the resistance of the vehicle while running with the full speed and the output torque of the motor while rotating with full rev. We also can get the lower limit from the resistance while the vehicle running on the road with the highest grade and the maximal output torque. An optimum reduction ratio will be decided. From the result of the simulation, we know that the reduction ratio is reasonable and in effect. The mathematic models of the vehicle, tyre and motor will be predigested. The mathematic model of vehicle has seven freedoms, displacements of X direction and Y direction, rotate speed of the vehicle, and revs of the four wheels. The mathematic model of the tyre is a semi-empirical model, it is based on the experiences, so it accords with the facts better. In this model the forces of X and Y directions can be calculated from the rate of slippage. The model of the motor is established on the direct current motor, so it is not complex. Thus the frame of the models of simulation has been established. Then the control system will be designed. This control system contains two parts, PI controller and fuzzy controller. The PI controller is used to control the torque when the vehicle starts. After the invariable torque of starting being decided, the PI controller is designed in method of Ziegler-Nichol. The fuzzy controller is designed to control the slip ratio. First the anticipant slip ratio should be decided. The actual slip ratio should be measured, from which the anticipant slip ratio is subtracted. Thus we get the error. The range of the error and the changing rate of it will be decided by calculation. The range of the control voltage is determined according to the motor. The fuzzy controller is designed in the Fuzzy Logic toolbox Simulink of MATLAB. In this toolbox the function of subjection and the rule of ratiocination are easy to be established. After finishing what has been mentioned above, the factors are determined according to the range of the input and output. After simulating the vehicle running on the road with bad adhesion and the road with different adhesions on both sides, we can conclude that model of the vehicle is correct and the controller is feasible. The simulation is realized in Simulink after finishing constructing the models of EV and controller. Any data can be easily obtained. It makes the analysis more convenient. In this article the results of simulation is analyzed from the angles of dynamic performance, handling stability, anti-slip-regulation, and differential performance. From the analyses we know that the mathematic models of EV and controller are proper and applicable. The mathematic models accord with the facts very well. In addition, the result shows that the driving mode that is introduced in this article has much more advantage. Because of this driving mode the driving wheels don't interfere each other when they run at different speeds and thecontroller is easy to establish. To a great extent the performance of an EV depend on the motors and the controllers. This point is the difference from traditional vehicle. The further research work of EV simulation that has been developed in this paper, will promote the process of EV design. On the base of the frame of models, we can continue consummating the models and making them more accurate. At last an exact model of EV will be created. The research work will accelerate the design and development of EV, even the industrialization course of EV in china.