| With the intensification of global energy tension and environmental pollution,electric vehicles characterized by "zero emissions","high performance" and "low noise" have developed rapidly and become the top priority of the development of the automotive industry in various countries.At present,the drive configuration of pure electric vehicles can be divided into centralized drive and distributed drive according to the location of the drive motor.The former has low technical difficulty and is convenient for commercial application;Although the latter is technically difficult,it has higher maneuverability and economic potential than centralized drives,so it has become a frontier topic in the development of electric vehicles.Distributed drive electric vehicles have the characteristics of independent and controllable torque of each wheel and high degree of system integration,which has great potential in giving full play to chassis technology innovation and improving vehicle driving performance.On the other hand,the use of two-speed transmission drive system has gradually become one of the development trends of electric vehicle transmission system.Compared with the fixed speed ratio reducer,the two-speed transmission can realize transmission with variable gear ratio,taking into account the power and economic needs of the whole vehicle,so it has obvious advantages in reducing the cost of the motor and improving the performance of the whole vehicle.At present,the research on the application of two-speed transmission mainly focuses on centralized drive electric vehicles,with the intention of further playing the performance advantages of distributed drive vehicles,this paper proposes a new two-speed transmission system for distributed hub drive electric vehicles.However,the traditional two-speed transmission has a certain period of power interruption during the gear change process,which will cause the longitudinal speed increase and deceleration impact of the whole vehicle and reduce the driver’s riding comfort,so it has become one of the essential factors limiting the further commercial application of the two-speed transmission.For the two-speed transmission system of the hub motor proposed in this paper,the power discontinuity will further complicate the synchronous shifting problem.Therefore,it is necessary to study the power continuity of this two-speed transmission,and realize the smooth and continuous power output of the twospeed transmission through structural design and shift control.Therefore,based on the proposed hub motor two-speed transmission system,this paper achieving the following research:First of all,the structure and working principle of the hub motor two-speed transmission system are analyzed,the configuration is composed of a hub motor,two wet multi-plate friction clutches,a one-way clutch and planetary gear system,through the rational use of the selflocking and disengagement of the one-way clutch,only need to control the switch of the friction clutch to achieve the switching of the first,second and reverse gears of this two-speed transmission.Subsequently,based on the dynamic parameters of the focused vehicle,the parameters of the two-speed transmission system of the hub motor were matched.Next,the simulation verification of the vehicle dynamics and economy is carried out in the CRUISE software to show that the performance of the vehicle meets the requirements and the results of parameter matching are reasonable.Then,in order to analyze the gear shift process in depth,a two-speed transmission model and a complete vehicle model were built.By reasonably simplifying the two-speed transmission as the research object,the kinematics law of the Lagrange equation method is derived.Then,the vehicle seven-degree-of-freedom model is established,including the body model,tire model and longitudinal driver model,and the modeling correctness of the built model and the mature commercial software Car Sim are compared and verified,which lays the platform foundation for the following simulation analysis.Next,on the basis of the above configuration,this paper formulates the upper shift control strategies of two-parameter dynamic gear shift and two-parameter economical gear shift.Then,the indicators for evaluating the quality of its shifting were analyzed and selected,and the analysis of non-power interruption gear shifting and left-right coordinated gear shifting was carried out based on the specific shift control process.For the non-power interruption gear shift,the analysis of the upshift process without power interruption is carried out,and the theoretical torque trajectory diagram of each component of the upshift process and the downshift process is drawn,in order to provide a theoretical analysis basis for formulating the shift control strategy.Aiming at the problem of the influence of non-coordinated gear shifting on the driving stability of the whole vehicle on the left and right sides,the communication delay of a certain actuator on one side and the speed of the left and right motor are not synchronized in the process of shifting the gear,and the horizontal and longitudinal movement of the whole vehicle under two working conditions are analyzed,and it is concluded that the left and right coordinated shifting factors need to be considered when formulating the shift control strategy.Finally,the non-dynamic interruption shift control strategy based on feed-forward plus feedback and the left-right cooperative shift control strategy based on logic threshold are formulated respectively,and the simulation verification of the non-dynamic interruption shift control strategy and the left and right collaborative shift control strategy are carried out through the Simulink model.The simulation results show that the control strategy formulated in this paper can effectively avoid the power interruption during the shift of the two-speed transmission,achieve stable power output,and significantly reduce the sudden changes in the horizontal and longitudinal acceleration of the whole vehicle caused by the left and right uncoordinated shifting. |
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