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Investigation to Dynamic and Control of Vehicle Dry Dual Clutches during Engagement

Author: WuMingXiang
Tutor: ZhangJianWu; LuTongLi
School: Shanghai Jiaotong University
Course: Vehicle Engineering
Keywords: Dry dual-clutch transmission Dual clutch engagement in launch Dualclutch overlap in shift Optimal control Feedbacklinearize PID close-loop control
CLC: U463.211
Type: PhD thesis
Year: 2013
Downloads: 363
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Abstract

Mechanical Transmission (MT) and Automatic Transmission (AT) possess intrinsicmerits in fuel economy and ride comfort respectively whilst Continuous VariableTransmission (CVT) possesses comprehensive advantage in both fields. However, asmaximum transferrable torque of CVT is comparatively limited due to low bearingcapacity of driving belt, and constitution complication induced fundamental defects of ATin manufacturing economy is relatively obvious, the electronic controlled MT technology,namely Automatic Mechanical Transmission (AMT) which combines merits of simplestructure and good fuel efficiency of MT and those of driving comfort of AT is proposedand engineered. Although quick and precise control of single clutch engagement improvesdriving comfort in launch phase, the power transmission interruption due to cutting off ofengine power from other driveline components by single clutch in shift makes its shiftcomfort worse than that of AT. Thanks to the invention of dual clutch transmission (DCT)or direct shift gearbox (DSG) in which continuous transmission of engine power to tiresduring shift is realized through proper operations of oncoming clutch engagement andoffgoing clutch release, such defect is remedied intrinsically in theory.After discussing structure design idea and corresponding engineering method of thedry dual clutch transmission (DDCT), the present research investigates dynamic behaviorsof the dual clutch operations and effectiveness of proposed engine and dual clutchmatching control method in depth. Then, through comprehensive utilization of thedalembert’s modeling principle and experiment based study method, the dynamic model ofthe whole DDCT system covering engine, dry dual clutch, mechatronic actuators of drydual clutch, gearbox, output shaft and wheels is constructed. Further, mathematicmodelings for the torque transmissibility of the cushion spring-pressure plate-diaphragmspring assembly and the dynamic behaviors of the mechatronic actuators are investigatedwith emphasis. Finally, experiment verifications of the load-deflection characteristics ofcushion springs, pressure transmissibility of the cushion spring-pressure plate-diaphragm spring assembly and that of the cushion spring-pressure plate-diaphragm spring-fork leverand roller composed actuator-ball screw composed output shaft of the motor assembly arecarried out. All the above investigations into dynamic modeling techniques provideessential theory premise for the research of dynamics and control of engine and dual clutchmaneuvers in launch and shift operations.Ride comfort and friction loss of friction discs are two main traditional evaluationindices of shift quality. Although some articles elaborate integrated optimal controlmethods for engine and dual clutch torque matching in dual clutch engagement processes,which assert that their main control objectives are integrated optimal matching of ridecomfort and friction loss of friction discs, one common problem existing in theseresearches is quadratic approximation of real friction loss of friction discs. Even thoughRiccati equations in these researches are numerically solved offline based on the optimalcontrol theory for linear systems, corresponding solutions of engine and dual clutchtorques resolved as linear time varying combinations of measurable state variablesobviously restrict their engineering applications in instant shift operations of real vehicles.In view of above imperfections, the present research proposes inclusion of objectiveformulations of friction work and shock intensity which should be regarded reflectingreality with very high fidelity into the proposed objective function. Meanwhile, onefeasible way of engine maneuver in correspondence to dual clutch operations is formulatedin terms of square of engine torque and also included in the objective function. Further,feasibility of solving the proposed optimal control problem is discussed strictly on thebasis of the extremum value theorem, and the conclusion that friction loss of dual clutchfriction discs and the vehicle jerk are still two contradictory indices ought to be primarilyconsidered in the evaluation shift qualities torque phase of shift operations is derived onthe condition that the initial and final angular velocities of engine and clutches are keptunchanged in torque phases. Finally, analytical solutions of optimal engine and dual clutchfriction torques presented as linear combinations of angular velocities of the clutch drivingand driven plates as well as the angular acceleration of the driven plate are derived for theease of engineering applications.To realize the ideal launch and shift qualities achieved from the above integratedoptimal control strategy, the affine nonlinear dynamic models covering the whole DDCTsystem is constructed, wherein nonlinear engine torque characteristic, sliding friction coefficient, pressure transmissibility of the cushion spring-pressure plate-diaphragmspring-fork lever and roller composed actuator-ball screw composed output shaft of themotor assembly are regarded the origin of the phenomena of nonlinearities. Definition andcalculation of the relative degrees of the constructed affine nonlinear dynamic models,presentation of the normalized form of the topologically equivalent linear time-invariantsystems, analysis and construction of the diffeomorphism mapping between the originalaffine nonlinear dynamic models and the topologically equivalent linear time-invariantsystems, investigation into PID control method for the topologically equivalent lineartime-invariant systems, solution of the inverse of the diffeomorphism mapping and itsapplication into deriving accurate control inputs to the original affine nonlinear dynamicmodels, which are all accomplished based on the feedback linearization control theory, areimplemented successfully. Controllers of the throttle open and the dual clutch actuators aredesigned on the basis of the mature control theory for the linear dynamic system.In order to verify the practicability of the above control strategy in real engineeringapplications, a bench test and a real vehicle test should be conducted. Therefore, a dry dualclutch assembly, double engaging bearings, twin-input shafts DCT gearbox andmechatronic actuators of the dual clutch and the shifting mechanisms are developed.Meanwhile, the software and hardware equipments for the electronic control system of theDDCT are developed. The test bench and the Chery A520sample car are developed byjoint effort of corresponding manufacturers and research institutes. Functional verificationtest for the DDCT prototype are carried out on the test bench, which proves its mechanicalstructure design ensure smooth operations of dual clutch and shifting mechanisms. Thesubsequent real vehicle tests in typical driving conditions demonstrate stablility andsmoothness in launch and uninterrupted power transmission oriented shift operations,which proves that the developed DDCT prototype work normally and effectively.

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