Analysis Of DCT Shift Strategy On Gear Rattle

In recent years,the proportion of passenger cars equipped with automatic transmission is gradually increasing,among which DCT transmission is a popular new type of transmission,which is more and more favored by major automobile companies.Along with it,DCT transmission is easy to produce rattle noise.The rattle noise of transmission is a kind of main noise in automobile transmission system,which has the phenomenon of noise level jumping and wide band,and easily causes the driver and passengers to be irritable.It has become one of the important problems affecting the quality of the whole vehicle.Domestic research on gear rattle of manual transmission has been more comprehensive,but the research on gear rattle of DCT shift strategy is not deep enough.Therefore,it is of great significance to study the influence of DCT shift strategy on gear rattling.This paper takes a passenger car equipped with a 7-speed DCT transmission as the research object,analyzes the mechanism of gear rattling of DCT transmission,and analyzes the shifting process and dynamic model of DCT transmission.Based on AMESIM software,the whole vehicle system simulation model is established.By formulating different shift strategies,the influence of shift control strategy on gear rattle is studied,and the shift quality is improved by optimizing shift overlap time.This paper mainly includes the following aspectsThe rattling mechanism of DCT transmission is expounded theoretically,and the external and internal excitation causing the knocking are analyzed.Through the establishment of DCT dynamic model,the dynamic analysis of transmission shifting process is carried out.The whole vehicle system simulation model including DCT transmission is established based on AMESIM software.According to the working parameters and structural parameters of the engine,the model of engine torque output is established.Considering the number of friction plates,inner and outer diameter,dynamic and static friction coefficient,the clutch simulation model is established.According to the structural parameters of the gear shaft,the rotational inertia,stiffness and damping dynamic parameters of the gear shaft,the simulation model of DCT transmission is established.At the same time,the differential simulation model and the body simulation model of the transmission system are established.It provides a simulation platform for studying the influence of shifting strategy on gear ratting.According to the vehicle test,the angular velocity data of input shaft in transmission1-4 gears are collected,and the second-order component of angular acceleration is extracted as the benchmark to check the simulation accuracy of transmission system model.By comparing the results of vehicle test and simulation,the simulation model of transmission system is verified effectively.The shift strategy is formulated,including clutch engagement pressure,engine speed and shift time.By using the control variable method,the forces of gears under different shifting strategies are simulated and analyzed,and the influence of different shifting strategies on gear knocking is analyzed.The results show that the shorter the shift time,the higher the clutch engagement pressure and the unreasonable speed matching between the engine and the transmission will aggravate the transmission loose gear knocking.The shifting strategy is optimized by considering the two evaluation indexes of impact and sliding work.