Torque Coordinated Control In Engine Starting Process For A Single-Motor Parallel Hybrid Electric Vehicle

The stress of the global energy shortage and environmental pollution,as well as the improvement of environmental awareness,is promoting the automakers to develop and produce new energy vehicles with the enhancement of worldwide consciousness on environment protection.Hybrid electric vehicles(HEVs)are considered to be the feasible plan of energy saving and emission reduction in new energy vehicles.They have the superiority in the combination of oil and electricity with the combination of advantages of pure electric and traditional vehicles,and complementary of disadvantages of each other,which has become a hot topic in the automotive industry.The smoothness of mode switching in HEVs is becoming more and more important in terms of HEVs performance.If the control is improper,the transmission torque will fluctuate and the vehicle riding comfort will be influenced.Therefore,it has great significance to carry out research on mode switching process,especially engine starting process,which is crucial to the independent research and development capability of hybrid electric vehicle.Meanwhile,a good quality of mode switching will contribute to the practicality and industrialization of HEVs.In this paper,the single motor hybrid system is taken as the research object,and the torque coordinated control strategy of the starting engine is developed.The research work is carried out as followings.(1)The structure of single motor parallel HEV is introduced.The model of power transmission system is established according to the characteristics of key components.The whole vehicle model is established,which provides the basis of the control strategy for engine starting process.(2)The switch process from pure electric to driving charge is taken as example in this paper,the engine starting process is divided into three phases.And the dynamic equations of each stage are analyzed,the study finds out that there is a sudden change of torque before and after the clutch synchronization.The expressions of the vehicle jerk are derived from the vehicle dynamic formula in each phase,and the influences of various parameters on the jerk are analyzed.After analysis,the feasible regions of control variables are given,the regions provide the theoretical basis for the control strategy.(3)The control of key components is well studied in this paper.The engine is controlled based on the slope limit of throttle valve,and the engine angular acceleration is used to estimate the engine torque.The cutch is controlled by phases: the clutch sliding speed is reduced rapidly in second phase and the clutch sliding angular acceleration is reduced rapidly in third phase.Therefore,the clutch oil pressure adjustment algorithm during synchronization is put forward.The feasible domain of torque coordination control can be achieved according to theory.Combined with the control methods of each component,the control strategy is developed for each phase in engine starting process.(4)The simulation of the proposed control strategy is carried out and compared with the existing control strategies,which verifies the effectiveness of the proposed control strategy to improve torque fluctuation during inter engine starting process.The influence of different condition-thresholds of clutch oil pressure adjustment algorithm on the vehicle jerk in the engine starting process,switching time and slipping work has been simulated.The condition-thresholds are optimized.The simulation results with the optimized parameters show that the selected parameters have a better effect on the riding comfort and rapidity of the engine.