Research On Starting Control Of Dct Vehicle Considering Dynamic Engagement Characteristics Of Wet Clutch

Dual Clutch Transmission（DCT）is currently receiving widespread attention in the automotive automatic transmission field.Compared with Continuous Variable Transmission（CVT）and Automatic Transmission（AT）,DCT has the advantages of simple structure,no power interruption,high transmission efficiency,good fuel economy and low manufacturing cost.Wet clutch as a key component of wet DCT,its dynamic engagement characteristics and wet DCT vehicle starting control are the research hotspots of domestic and foreign scholars.At present,in the study of the dynamic engagement characteristics of wet clutch,the friction coefficient usually adopts a fixed value or only considers the change with relative speed,and the combined effects of friction pairs surface temperature,relative speed,roughness and load on the friction coefficient are not fully considered.Secondly,the wet clutch torque model established in the research of wet DCT vehicle starting control are mostly static torque model based on the classic Coulomb friction model,and the wet clutch dynamic torque model is not introduced from the perspective of the wet clutch friction transmission mechanism,and most of them focus on the study of starting control strategy,but there are few studies on how to improve the execution accuracy of starting control strategy.Therefore,it is of great academic and applied value to study DCT vehicle starting control with consideration of dynamic engagement characteristics of wet clutch.This paper selected a certain 7-speed wet DCT vehicle as the research object,and launched in-depth theoretical research on the dynamic engagement characteristics of wet clutch and the starting control of wet DCT vehicle.The specific research work is as follows:（1）Considering the combined effects of the friction pairs surface temperature,relative speed,roughness and load on the friction coefficient,based on hydrodynamic lubrication theory,rough surface elastic contact theory,heat transfer theory and adsorption heat theory,lubricating oil film pressure model,micro convex body contact force model,friction plate temperature field model and friction coefficient model during the wet clutch engagement process were established respectively,and combined with the established bearing capacity model,torque model,balance equation of bearing capacity and torque duing the wet clutch engagement process,lubricating oil film thickness,lubricating oil film pressure,micro convex body contact force,friction pairs relative angular velocity,viscous torque,rough friction torque and total torque during the wet clutch engagement process were solved.Discussed respectively the effects of engagement pressure,friction pairs surface roughness,friction lining permeability and friction pairs equivalent elastic modulus on lubricating oil film thickness,friction pairs relative angular velocity and torque during the wet clutch engagement process.（2）Based on the engine steady state torque test data,an interpolation fitting method was used to establish the engine steady state torque model and amended it to obtain the engine dynamic torque model.At the same time,the torque characteristics diagram of the engine under steady state condition was plotted.Based on the theoretical analysis in chapter 2,the dynamic torque model of wet clutch was established.Based on the dynamic analysis of the wet DCT vehicle using the clutch C1 starting process,the wet DCT vehicle single clutch starting dynamic equation was established,and the dynamic equation of the vehicle in first gear was obtained according to the relationship between the engine angular velocity and the clutch C1 driven disc angular velocity after the driving and driven discs of the clutch C1 were synchronized.By analyzing the working principle and composition of the wet DCT hydraulic control system,the proportional pressure solenoid valve and the hydraulic actuator model were established.（3）By analyzing the starting process of wet DCT vehicle,the starting process was divided into four stages,and the starting control target was determined according to the characteristics of each stage.The main evaluation indexes of starting quality:vehicle jerk,clutch sliding friction work and their calculation formulas were described.The formulation method of starting control strategy were studied.Firstly,a starting intention identifier was designed to reflect the driver’s starting intention.Then the target angular velocity of the engine was determined based on the principle of engine constant speed control.Secondly,the second stage target jerk and the friction pairs relative angular velocity threshold of t₁ time and the target angular velocity of the engine etc were used to calculate the target angular velocity of the clutch C1 driven disc,which effectively controlled the peak value of the target jerk during the starting process,so that the starting smoothness of the vehicle was improved.Finally,the simulation analysis was carried out based on the formulated wet DCT vehicle starting control strategy.（4）Wet DCT vehicle starting tracking control scheme was designed,and throttle opening and solenoid valve input current were selected as controlled variable.Based on PID control theory,adaptive control theory and sliding mode control theory,the engine angular velocity tracking controller and clutch pressure-angular velocity double closed-loop tracking controller were designed.The designed controllers were integrated with the relevant models established in chapter 2,3 and 4,and the simulation verification of the control effect was carried out.