Research On Integrated Powertrain Control Technology Of Pure Electric Vehicle With Two Gears Dual Clutch Transmission

The pure electric vehicle with advantages of low noise, zero emission, and the widelysourced electricity power, is regarded as the tendency of the automobile technology. Itattracts widespread interest, and becomes one of the hot technologies.The dual clutch transmission shifts gears without power interruption by switchbetween two clutches that are established on different shafts. It also has the advantage ofhigh transmission efficiency. Therefore, it is well considered as a type of new promisingtransmission with optimistic application.Based on the technological background mentioned in the former，this researchestablishes the dual clutch transmission on pure electrical vehicle, and study on integratedcontrol technology for powertrain of pure electric vehicle with dual clutch transmission, inorder to improve economic performance and gear-shift quality of electric vehicle. Thisresearch is helpful for the new energy vehicles technology development.This paper takes electric vehicle with two gears dual cluth transmission as study object,to research integrated control technology of powertrain. It discusses mainly about how toconstitute the powertrain control system for electric vehicle, how to establish gear-shiftschedule of integrated powertrain control, and how to optimize the gear-shift processcontrol strategy with integrative control of powertrain. The main research points are asfollows.(1) The powertrain system match solution of the objective pure electric vehicle isdesigned according to the national standards and the design goal of pure electric vehicle ofthe research, as the basis of the research. Comparison and analysis from several aspects isimplemented to determine the key parameters of power battery, electric motor andtransmission parameters. And Matlab/Simulink is used to establish the vehicle simulationmodels including dynamics model of electric vehicle, gear decision model of transmission,power battery model, and the driver model. Simulation tests in ECE, ECE_EUDC, andconstant velocity driving cycles with these models are carried to analyze the match effect.The simulation results verify, that the electric vehicle with the match solution proposed inthis paper can satisfy requirements of national standards and design goal in aspects offollowing the target velocity, acceleration ability, and driving range. The real vehicle tests are also carried to check the match effect. The result indicates that the match solution canmeet the national standards and design requirements in aspects of economic performance,climbing slope, and acceleration ability.(2) For the electric vehicle with dual clutch transmission, the powertrain controlsystem consits of master control logic, DCT control system and electric motor controlsystem. The issue that how to control the DCT and electric motor responding to the controlstrategy accurately and quickly is one of the most important points for integrated conroltechnology of powertrain. In the DCT control system research, mathematic model of drydual clutch transmission transferring torque is established to reflet the relationship betweenthe torque transferred by clutch and displacement of separable bearing in clutch. Theauto-adapted Neural Network Prediction Control method is applied to establish the neuralnetwork prediction controller. Based on the proportional flow valve model that establishedin the paper, this controller is used to control displacement of separable bearing in thehydraulic gear-shift mechanism of dry dual-clutch to follow the target displacemment.Consequently, the torque transferred by transmission is controlled to follow the target torquefrom the master control logic of powertrain control system. In the electric motor controlsystem, the CAN communication controller is designed for electric motor to extend CANcommunication function of the motor driver on pure electric vehicle with dual clutchtransmission. With the controller, the eclectic motor can send CAN instructions respondingto the master control logic of powertrain control system. The research of DCT controlsystem and electric motor control system in the paper construct the executive platform forintegrated powertrain control.(3) Gear-shift schedule is one of the key of the master control logic in the powertraincontrol system on electric vehicle. It dicides when and which gear the transmission shouldshift to. In addition, the gear-shift schedule of integrated powertrain control also determinsthe output torque of electric motor under certain opening degree of acceleration pedal. Thispaper discusses three types of gear-shift schedule for electric vehicle, dynamic gear-shiftschedule, economic gear-shift schedule and general gear-shift schedule in which thedynamic characteristic coefficient is added to access the intention of driver, based on traditional automobile gear-shift shedule. Considering the problem that the generalgear-shift schedule can’t get good effect both in dynamic performance and economicperformance, a new gear-shift schedule based on integrative control of electric motor andDCT is proposed in the paper. In the new gear-shift schedule, the signal of accelerationpedal opening do not control output torque of electric motor directly any more. It isconverted into the signal of driving torque requirement of the vehicle by a functionestablished in the paper, which expresses the relationship between opening degree ofacceleration pedal and driving torque. With the requirement of driving torque as input, theschedule determin the match of output torque of electric motor and the gear of transmission,to keep the electric motor working in the best effiency area under the premise of meetingdriving torque requirement. Simulation comparision of the general gear-shift schedule withthe new gear-shift schedule of integrated powertrain control in ECE driving cycle isimplemented. The simulation result indicates efficiency of electric motor with the newgear-shift schedule is higher than that of the general schedule by8.4%. It verifies the newgear-shift schedule of integrated powertrain control can improve economic performance ofelectric vehicle.(4) After the gear-shift schedule of integrated powertain control system is established,shifting gear smoothly and quikly is another important issue for integrative control ofpowertrain. For the electric vehicle with dual clutch transmission, there are two key issuesmust be solved in the process of gear-shift. One is how to control output torque of theclutches and electric motor to follow the target torque steady. This issue has been solved inresearch point (2) as the former mentioned. Another issue is how to plan the target torque ofthe clutches and that of electric motor to get best gear-shift quality. Therefore, this paperimplements further study on the gear-shift process control strategy with integrative controlof powertrain, for electric vehicle with DCT. On basis of analysis of traditional evaluationindex for gear-shift quality, the integrative evaluation index, that expressed by weightedsum of jerk and slipping work, and takes dynamics characteristic parameters as inputvariables, is proposed in the paper. Combining dynamics analysis of up-shift and down-shiftprocess, dynamics models that reflect the relationship of the dynamics characteristicparameters of clutches and electric motor in different gear-shift situations are established.Based on the integrative evaluation index of gear-shift process and the dynamics models,the gear-shift process control strategy with integrative powertrain control is proposed in the paper. In order to apply Particle Swarm Optimization algorithm to optimize the controlstrategy, Fourier basis vector decomposition method is used to convert the trajectoryoptimizing issue into parameters optimizing issue, and the penalty function is applied todeal with the constraints. Then Particle Swarm Optimization algorithm is used to calculatethe optimal trajectory of the electric motor output torque and the torque transferred by thetwo clutches during gear-shift. This optimal trajectory assures the electric motor and theDCT coorperate with each other to get optimal general gear-shift quality.(5) In order to check the effect of the gear-shift process control strategy withintegrative powertrain control, up-shift and down-shift with positive torque tests are carriedon an electric vehicle equipped with the match solution proposed in the paper. And the testresults are compared with that of traditional gear-shif control stategy. The results indicatethat the electric vehicle under the control strategy with integrative powertrain control canshift gear with small jerk, good comfort, short gear-shift time, and reasonable slipping work.It verifies the gear-shift process contol strategy proposed in the paper can improve qualityof gear-shift.The innovative results of this research are as follows.(a) In the DCT control system, the control of separable bearing displacement in clutchbased on Neural Network Prediction Control (NNPC) method is proposed. The tests resultsverify that displacement of separable bearing in dry dual-clutch with this control methodcan follow the target displacement.(b) Gear-shift schedule of integrated powertrain control for electric vehicle with twogears DCT, which can improve economic performance of the vehicle besides meetingdynamic performance requirement, is established in the research. The simulation resultsindicate that efficiency of electric motor with the new gear-shift schedule is higher than thatof the general schedule by8.4%.(c) For electric vehicle with two gears DCT, the gear-shift process control strategy withintegrative powertrain control based on Particle Swarm Optimization algorithm is proposedin the paper. It offers a new approach for the gear-shift process control of DCT. And it alsooffers a new method for define the target torque of electric motor and dual clutch in processof gear-shift. The real vehicle test verifies that the new gear-shift process control strategycan improve quality of gear-shift.(d) In optimization of gear-shift process control strategy with integrative powertrain control, Fourier basis vector decomposition method is used to convert the trajectoryoptimizing issue into parameters optimizing issue. This method assures the issue ofoptimizing gear-shift process control strategy adapt to Particle Swarm Optimizationalgorithm.