Study On Double Clutch Transmission

In the automotive industry automatic transmissions were for a long timeconsidered as a luxurious alternative to a manual gearbox, offering automatedgear shifting and thus sparing the driver from having to engage the gear himself.However as fuel economy of cars became one of the key aims of carmanufacturers, the advantage of an automated gear schedule became moreimportant. By shifting the task of selecting an appropriate gear for optimal engineoperation from the driver to the gearbox it was possible to let the engine operatein points of low fuel consumption. Among the further advantages of automatictransmissions was the improved driving comfort. However the conventionalautomatic transmission utilizing a hydraulic torque converter and planetary gearsets, despite all the improvements over the years, still suffers from inferiormechanical efficiency compared to the manual transmission. Thus one of the aimsof automotive industry during the last years had been to improve the mechanicalefficiency of automatic transmissions whilst retaining the comfort of automatedgear shifting together with powershifts of good shift quality. Two main conceptshave evolved among fixed gear ratio transmissions during recent years. The firstconcept, the automated manual transmission, offers a robotized actuation of mainclutch and synchronizers. This layout was introduced in small cars, sports cars andheavy-duty vehicles with some success. These gearboxes showed improvedmechanical efficiency over the conventional automatic transmission however stillsuffered from the disadvantage of not offering true powershifts withoutinterruption in traction at the wheels. The second concept, the double clutchtransmission, however seems more promising and combines the advantages ofhigh mechanical efficiency and powershifts without interruption in the traction.The principle of a double clutch transmission is depicted in chapter 1 and worksas following: There are two gearboxes (gearbox 1 for the odd and gearbox 2 forthe even gear numbers) that are both built up like conventional manualtransmissions comprising of helical gears and synchronizers to engage theselected gears. Both gearboxes are connected to the output shaft via a gear stageand can be coupled to the main input shaft of the transmission and therefore to theengine by either of the two clutches. By changing from one gearbox to the other(i.e. by disengaging the offgoing clutch and engaging the oncoming clutch) agearshift can be accomplished. This results in shift characteristics that are typicalof clutch to clutch shifts commonly seen in conventional automatic transmissions.This thesis analyzes the principle, the architecture, the shifting characters and theclutch pressure control system of the DCT. Furthermore, the concrete plan and thecontrol strategy is introduced in this thesis. The thesis is composed of fivechapters.In the first chapter, this thesis introduce the development process of automatictransmission in the first instance. Then I analyze the advantages and applicationprospect of DCT and propose the object, significance and content of the paper.In the second chapter I analyze the system structure of double clutch transmission.First I analyze the structure characteristic of single middle shaft DCT and discussthe power flow and shift process in the case of shift from first speed to secondspeed. Then I introduce the system structure and the basis control method of DCT.In addition, based on the characteristic analysis of the dry clutch and wet clutch, Idecided to use wet clutch as work component of the Cherry Car DCT. To obtainthe design foundation, I compared the traditional clutch slave-slice twistingdamper with the dual-mass-flying wheel damper, introduced the workcharacteristics of the dual-mass-flying wheel damper.At last, I analyze the threecomponents of DCT hydraulic system and the working principle of each part.The third chapter is the research of shift process of DCT. I analyze the reason ofshift shock and factors that influence the shift quality and propose that shift timeand jerk are the two appraisal criteria of shift quality. Then I set up the dynamicsmodel and math model of powertrain system, analyze the direction and value ofclutch torque in the engagement and disengagement states and the shift process.Also, I set up the engine model and introduce three popular methods of torquecontrol. Based on comprehending the mechanism of DCT in depth, a dynamicmodel of the powertrain with DCT has been established with Matlab-Simulink inthis paper. The main contents include: dynamics analysis of powertrain with DCT,analysis of clutch friction characteristic, the principle for judging the clutch workstate such as slipping and sticking, simulation controller design of clutch andengine. Then a satisfied result is shown.The fourth chapter is the research of clutch hydraulic system. In the first instance Ianalyze the components of clutch hydraulic system and the control methods of...