Study On Design Method And Control Method Of An Electromechanical Actuator Of Continuously Variable Transmission

The speed ratio of a continuously variable transmission(CVT)can be changed stepless in a certain range by its actuator,and the vehicle engine can operate in its ideal point for improving the vehicle dynamic and economy performance.At present,Most of the CVT actuator is electro-hydraulic system.However,the electro-hydraulic actuator consumed a large amount of power and result in decreasing the CVT transmission efficiency,this is because it need operate under high pressure and large displacement to assure the control of CVT speed ratio and driven pulley clamping force.The electro-mechanical actuator cousume less energy than electro-hydraulic actuator.Then the electro-mechanical actuator is proposed to replace the electro-hydraulic actuator in CVT.Therefore,the study on the electro-mechanical CVT is meaningful.This paper mainly focuses on the CVT electro-mechanical actuator with two direct current motors.Then the study on the actuator design,optimization and control method of the electro-mechanical CVT was carried out.The specific research content is as following:(1)Firstly the electro-mechanical CVT with two actuator motors,the electro-hydraulic CVT and the electro-mechanical CVT with single actuator motor are compared with each other from the construe and operating principle.It is found that these three kinds of CVT are all based on the metal pushing v-belt CVT while with different actuator.Then the transmission mechanism of the metal pushing v-belt is analyzed from the perspective of kinematics and dynamics.Finally,to illustrate the transmission efficiency advantage of the electro-mechanical CVT with two actuator motors,a simplified CVT transmission efficiency model was developed,and the energy loss and transmission efficiency was compared under driving cycles of ECE and EUDC.It is found that the energy consumed by the electro-mechanical actuator is much less than that consumed by the electro-hydraulic actuator.However,the overall transmission efficiency of the electro-mechanical CVT with single actuator motor is not ideal,this is because its driven pulley clamping is not adjustable.And the transmission efficiency of the electro-mechanical CVT with two actuator motors is highest among those three kinds of CVT.Therefore,it is meaningful to study on the electro-mechanical CVT actuator.(2)The electro-mechanical CVT actuator was designed and optimized in this study.Firstly,the characteristics of the actuator components were described including motors,gear pairs,screw-nut pairs and Belleville springs.Then,the electro-mechanical actuator was designed to meet the function of transmitting torque and reducing energy consumed by actuator with certain engine and metal pushing v-belt CVT.And the effectiveness of the designed actuator was validated with simulation.However,the driven pulley clamping force adjustable range of this designed actuator is limited resulting from that this design method do not take the driving condition into consideration.Finally,the electro-mechanical actuator is optimized.The statistic analysis of the required driven pulley clamping force under different driving cycles was made,and the ideal clamping force which is provided by Belleville springs is adjusted.Based on this adjust,the electro-mechanical actuator with two motors was optimized using genetic algorithm.The function and performance of the optimized actuator was simulated,and the results show that the driven pulley clamping adjustable range is enlarged obviously,and the greatest increase up to 83%.(3)The models of the speed ratio control actuator and the driven pulley clamping force control actuator of the electro-mechanical CVT were developed respectively.And the simulation model of the electro-mechanical CVT with two actuator motors was constructed using MALAB/Simulink.The speed ratio response and the driven pulley clamping force response were simulated and analyzed.The results show that speed ratio and the driven pulley clamping force are controlled well,and the input voltage and output torque of actuator motors changed rapidly while the output speed and load torque changed smoothly.The influence factors of the speed ratio and the driven pulley clamping response were analyzed.It is found that the speed ratio response rate is related to the changing direction of the speed ratio,and the response speed changes with the variation of driven pulley clamping force.In addition,the initial speed ratio has little effect on the speed ratio response,and the dynamic response of the driven pulley clamping force is influenced by the initial speed ratio and the driving pulley clamping force.(4)The control method of the electro-mechanical CVT was studied according to its characteristics and the requirements of a vehicle.For the speed ratio control,the improved PID control algorithm,integral separation and differential forward,was used.For the driven pulley clamping force control,it was used that the active disturbance rejection control(ADRC)technique which is comprised of transient process,tracking differentiator,nonlinear state error feedback controller and extended state observer.The effectiveness of these control algorithm was validated with simulation.The speed ratio control is coupled to the driven pulley clamping force control.Based on this coupling characteristic,a speed ratio control strategy was proposed to decrease its response time.Simulation with this strategy was carried out and the results show that the response speed is increased by 14% when the ratio is increased.In addition,the continuous ratio control strategy in the electro-mechanical CVT will result in the ratio fluctuation when the vehicle speed or the throttle opening swings in a minor range.This is bad for the CVT and the vehicle.In order to solve the problem,discrete ratio control strategy was proposed.And simulation analysis was carried out to illustrate the ratio control strategy.The results show that the ratio fluctuation is removed and there is no adverse effect on the vehicle performance.(5)The test bench of electro-mechanical CVT with single motor was developed based on MATLAB/Simulink and DSPACE.The transmission efficiency experiment was conducted with the test bench,and its value was compared with an electro-hydraulic CVT transmission efficiency which is measured through HIL test bench.In this way,the efficiency superiority of the electro-mechanical with two motors is illustrated indirectly.The speed ratio response characteristic was experimented with the test bench,and the effectiveness of the improved PID algorithm and ADRC technical was validated.In addition,it also shows that the electro-mechanical CVT with two direct current motors is realizable with good performace indirectly.