| The fuel injection system of the future diesel engines should have the advantages of low cost,miniaturization,adjustable injection pressure,fast response speed,and randomly controlled injection mass.However,the current mainstream fuel injection system cannot fully meet these requirements,and therefore it is necessary to propose a new one.Multi-sole no id valve control fuel injection system(referred to as multi-valve fuel injection system)is based on the unit pump system and the common rail system,with the advantages of both systems The unit pump system and the common rail system have solid theoretical bases,however the research on the multi-valve fuel injection system is still in the newborn stage,and the system construction and fuel supply characteristics still need to be explored.This thesis focuses on the design of the cam profile and the fuel pressure characteristics of the multi-valve fuel injection system.The combination of test and simulation calculations was used to research the design of the cam profile,the system structure matching,the pressure fluctuation characteristics and the control methods of the multi-valve fuel injection system.First,the parametric design method of the cam of the multi-valve fuel injection system was studied.A double bugle constant speed function cam was proposed as the fuel supply cam for the multi-valve fuel injection system,by analyzing the performance of the multi-valve fuel injection system and comparing the characteristics of different fuel supply cams The characteristics of the working process of the cam were analyzed,and the mathematical model of the cam lift curve was established from the aspects of fuel pressure characteristics of multi-valve system,cam force conditions,processability and full fuel absorption.Then,a method for determining the minimum cam base circle was proposed,taking the maximum contact stress between the roller and cam,the maximum pressure angle,and the minimum radius of curvature of the cam as constraints.The design of the multi-valve fuel supply cam was completed according to the given key parameters and the validation and verification of the double bugle constant speed function cam were carried out through the simulation calculation and tests,which provided the foundation for the research of the multi-valve fuel supply system.Then,the fuel supply characteristics and the fuel pressure characteristics of the multi-valve fuel injection system were studied.The matching methods of the main structural parameters in the multi-valve fuel system were proposed,by studying the influence of the key structural parameters of the system on the fuel supply characteristics.Subsequently,the multi-valve fuel injection system test bench was used to study the fuel pressure fluctuation characteristics of the system and the results showed that there was a significant fluctuation in the fuel pressure at the pump end of the system due to the fuel pressure reflection at the nozzle end.Finally,taking the unit pump system as the research object,the influence law and internal mechanism of the fuel temperature on the system performance were deeply studied It was proposed that the performance characteristics of the unit pump fuel injection system affected by the fuel temperature would change with the change of the rotation speed.Based on the study of the effect of fuel temperature on the performance of the unit pump system,the influence of the fuel temperature on the performance of the multi-valve fuel injection system was analyzed.The results showed that under the same control mode,the injection quality per cycle and the injection pressure of the multi-valve fuel injection system decreased with the increase of the fuel temperature,but the influence of the fuel temperature on the start-up and shut-off processes of the multi-valve fuel injection system was constrained by the control processFinally,the control method of the multi-valve fuel injection system was studied.The correction method of the supply advance angle under different speeds was explored by analyzing the influence of speed on the supply advance angle in the multi-valve fuel injection system.The fuel pressure characteristics of the multi-valve fuel injection system at different speeds were analyzed using the revised injection advance angle and the fuel supply pulse width.The results showed that when the multi-valve fuel injection system was not spraying,the peak fuel pressure was closely related to the actual cam working section and was not sensitive to cam speed.A systematic study of the fuel supply advance angle and injection advance angle in the multi-valve fuel injection system was conducted and the response characteristics of the system were analyzed.Based on which,the method of accurately controlling the injection pressure under arbitrary rotation speed of the multi-valve fuel injection system was proposed,and the control MAP of NOP under different fuel supply duration conditions was given,which provided the foundation for the application of multi-valve fuel injection system in diesel engines.At last,based on the multi-valve system cam designed in this paper,the fuel supply characteristics between the cycles of the multi-valve fuel injection system were compared.It was found that the multi-valve fuel injection system had stable fuel supply characteristics under different control modes.And the goal that one pump feed two cylinders was achieved. |
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