Research On 48V Mild Hybrid Vehicle Control Strategy And Economic Dynamic Matching

China’s fourth-stage fuel consumption regulations require that by 2020,the average fuel consumption of passenger cars produced in that year should reach 5.0L/100 km.The strict fuel consumption policy has prompted automobile manufacturers to vigorously develop new energy and other new technologies that can effectively reduce vehicle fuel consumption.The hybrid vehicle integrates a battery-motor system on the basis of the traditional fuel vehicle,which can effectively improve the engine operating points and reduce the fuel consumption of the whole vehicle.Among them,the 48V mild hybrid system with energy saving and low cost increase has attracted more and more attention.In this paper,a 48V mild hybrid vehicle is taken as the research object and the following contents are mainly done:1.The research background and significance of 48V mild hybrid system are introduced,and the research status of 48V mild hybrid system at home and abroad are summarized.2.The power drivetrain system structure of 48V mild hybrid sample vehicle is analyzed.The control strategy of engine start/stop,braking energy recovery,torque assist and intelligent charging of the sample vehicle are analyzed.The ideas of strategy analysis test and the signals needed to be collected in the test are given.3.The NEDC cycle and constant-velocity test data of the sample vehicle are analyzed,and the whole vehicle model is built by AVL Cruise software.4.Based on the control rules of logic threshold,the control strategy models of the sample vehicle are built under the environment of Matlab/Simulink software and integrated into Cruise software for joint simulation.The maximum difference between the simulation results and the measured fuel consumption results is not more than 1.2%.The simulation results show that the fuel consumption benefit of 48V mild hybrid system of the sample vehicle under NEDC cycle is 12.4%.Among them,the fuel consumption benefit of engine start/stop control strategy is 5.08%,and the fuel consumption benefit of braking energy recovery and torque assist control strategy is 7.29%.5.The 48V BSG belt speed ratio was innovatively matched and optimized with gearbox and final drive speed ratios.After selecting the evaluation indexes and unifying the dimension,the vehicle performance evaluation equation is established,and the joint simulation model with Cruise is built in the Isight software.The Pointer mixed optimization algorithm in Isight is used to simulate and optimize the speed ratios.The results indicated that under the condition of meeting the dynamic performance,the fuel consumption level of the original48V system has been improved under various working conditions after speed ratios optimization,in which the comprehensive fuel consumption of NEDC has been reduced by2.4% and the SOC difference at the end of NEDC before and after optimization is 2.66%,and the fuel consumption result is credible.