外文原文.pdf

Y Zhang Associate Professor e mail anding umich edu X Chen Graduate Student Department of Mechanical Engineering University of Michigan Dearborn Dearborn MI 48128 X Zhang H Jiang W Tobler Scientific Laboratory Ford Motor Company Dearborn MI 48128 Dynamic Modeling and Simulation of a Dual Clutch Automated Lay Shaft Transmission This paper presents a systematic model for the simulation and analysis of a power shift transmission that features a dual clutch design The paper models the kinematics dynam ics and control of the transmission for the analysis of powertrain overall performance and shift transient characteristics The model is implemented in an object oriented soft ware tool Analytical formulations and look up tables are both used for modeling of powertrain components The vehicle system model is established by integrating the vari ous components and subsystem models according to the transmission power fl ow and control logic The input to the simulation model is the vehicle speed time profi le and the output provides the speed follow up engine and clutch operation status for the drive range and shift processes involved As a numerical example the model is used for a vehicle equipped with the power shift transmission to simulate the speed follow up over a specifi ed drive range and the dynamic transients during shifts 2004 American Insti tute of Physics DOI 10 1115 1 1829069 1Introduction Automatic transmissions in most passenger vehicles use plan etary gear trains as the power transmitting units In a planetary train transmission different gear ratios are realized by coupling a planetary member to the input and grounding another to the hous ing alternatively Although the planetary gear train design has been applied in transmissions since the early days of automatic cars it has the intrinsic drawbacks in structure complexity and low effi ciency due to the nature of planetary gearing As fuel economy improvement is becoming ever increasingly important transmissions with lay shaft gearing are gaining popularity in the automotive industry especially so for applications in compact to midsize passenger vehicles This is evidenced by the successful applications of lay shaft transmissions in Saturn and Honda mod els 1 In a lay shaft transmission all gear axes are fi xed with respect to each other There are two technically feasible designs for lay shaft gearing transmissions One uses a torque converter for launch and hydraulically activated clutches for shift while the other uses automated clutch and shift selector for launch and gear change operations The later termed in automotive industry as automated manual transmission AMT is actually a manual transmission with an added on control unit that automates the clutch and shift operations Similar to manual transmissions there is an interruption of torque transmission at a gear change since the engine is cut off by the clutch during shift This torque interrup tion leads to unanticipated passenger feels on vehicle acceleration discontinuity and is highly uncharacteristic of conventional auto matic transmissions A dual clutch transmission design was re cently proposed to overcome this intrinsic drawback 2 In this design the two clutches are engaged alternatively in different speeds and power transmission continues during a shift through the control of clutch slips A shift process involves the engage ment of the oncoming clutch and the release of the offgoing clutch This results in shift characteristics that are typical of clutch to clutch shifts commonly seen in conventional automatic transmissions 3 As in any other control systems the success of control depends on the analytical model that effectively describes the dynamics during system operation Before a prototype is built model simu lation is the only tool for the analysis and evaluation on the per formance of vehicle equipped with a dual clutch lay shaft gearing transmission In recent years the ever increasing demand on ve hicle fuel economy and passenger comfort has led to the develop ment of new types of transmissions and new control technologies for powertrain systems 4 6 Model simulation plays an impor tant role in the validation and calibration of such systems and has therefore attracted the interests from both academic and industrial communities Recent researches in powertrain modeling and simulation areas cover various types of powertrains currently in production or under development including conventional auto matic transmissions 7 8 continuously variable transmissions 9 11 and hybrid drivetrains 12 13 As revealed by the litera ture search the modeling and control of dual clutch AMT systems is still a new area contrary to the technology maturity of other type of transmissions The purpose of this paper is to present a systematic model for the simulation and analysis of vehicle pow ertrains equipped with the dual clutch transmissions The model is implemented using the Modelica Dymola programming language in an object oriented environment Standard component models available in the Modelica Dymola library 14 are directly used for the avoidance of the lengthy derivations of mathematical equa tions governing component characteristics Emphasis is placed on the development of nonlibrary models such as shift controller clutch pressure control etc which are specifi c to the transmission system All subsystem models such as the driver engine gear pairs clutches etc are integrated into an overall vehicle system model based on powertrain structure kinematics and control logic The control system for the dual clutch AMT includes shift schedule control and shift process control The shift schedule con troller triggers an upshift or downshift based on engine throttle and vehicle speed feedback and signals the engaging or releasing of the involved clutches State equations governing the system Contributed by the Design Automation Committee for publication in the JOUR NAL OFMECHANICALDESIGN Manuscript received November 20 2004 revised May 14 2004 Associate Editor A A Shabana 302 Vol 127 MARCH 2005Copyright 2005 by ASMETransactions of the ASME Downloaded From http mechanicaldesign asmedigitalcollection asme org on 03 17 2015 Terms of Use http asme org terms dynamics caused by a gear change are automatically modifi ed and reorganized by the Modelica Dymola implemented system model according to the new power fl ow and gear mesh path In this paper the pressure profi les for clutch torque control during a shift are modeled as look up tables which can be modifi ed interac tively so as to achieve shift quality improvement The integrated dual clutch AMT vehicle model enables the simulation of vehicle performance over specifi ed drive ranges and the transmission shift processes occurring in a drive range Based on model simulation shift quality metrics such as shift time torque variations can be quantitatively analyzed and improved by adjusting clutch pressure control profi les interactively The simu lation results in the example included in this paper demonstrate the effectiveness of the model as an analytical tool for the devel opment of dual clutch AMT systems 2Dual Clutch AMT Structure and Kinematics The structural layout of the dual clutch AMT can be seen in Fig 1 The transmission has six forward speeds and one reverse There are two hydraulically activated clutches CL1 and CL2 which are engaged alternatively Clutch CL1 is engaged in the fi rst third fi fth and reverse speeds and CL2 in second fourth and sixth A hollow shaft layout is used to provide a compact design for this multiple speed gearbox The hollow shaft and the solid shaft through it are the inputs for odd and even speeds respec tively Reverse gear is achieved by an idler on one of the two counter shafts The fi nal drive has two pinions one transmits torque for fi rst second third and fourth gears and the other for fi fth sixth and reverse gears There are four synchronizers in the transmission shown as switches in Fig 1 The shift selector associated with each syn chronizer assembly is activated by hydraulic piston or step motor Gears for two adjacent speeds can be engaged at the same time since only one of the two clutches is engaged The clutch that is not engaged free wheels with all gears in the mesh path that is not currently transmitting torque For quick upshift responses the next higher gear is engaged before the actual upshift occurs The shift process therefore only involves the engaging of oncoming clutch and the releasing of the offgoing clutch The synchroniza tion of gears has no effect on shift quality since it does not occur during the shift Because of this feature the shift characteristics of the dual clutch AMT is the same in nature as the clutch to clutch shift commonly applied in conventional automatic transmissions 3Dynamic Model Structure The schematic of the dynamic model for the dual clutch AMT is shown in Fig 1 The engine mount input and output shafts are modeled as spring dampers whose stiffness and damping coeffi cients are denoted by km ki ko and cm ci co respectively The shaft assemblies are modeled as lumped masses The mass moments of inertia of the engine output shaft the input shaft and the output shaft are denoted by Ie Ii and Io Similarly Is Ih Ic1 and Ic2denote the mass moments of inertia of the assemblies of the solid shaft the hollow shaft and the two counter shafts respectively For simplicity gear backlash is neglected in the model and powertrain effi ciency is assumed to be a constant As mentioned previously synchronizer assemblies are modeled as switches for the power fl ow paths in different speeds since shift quality is independent of the synchronization of gears Standard Modelica Dymola library models are used for common power trains components such as shafts clutches gears spring dampers etc Key powertrain models such as engine clutch and vehicle are described in the following Engine The engine transients are not considered in the model for simplicity Engine map data are used to calculate the steady state output torque which is formulated as a bivariable third order polynomial function of the throttle angle TAand the engine speed veby the following equation Te5f TA ve 5 aij TA ive j i50 1 2 3 j50 1 2 3 1 where aij i50 1 2 3 j50 1 2 3 are constants determined by the interpolation of the engine map data The engine torque modeled by the above equation is shown in Fig 2 with engine speed rang ing from 0 to 6000 rpm and the throttle angle from 0 to 90 deg Clutch The clutch model in the integrated powertrain system not only formulates the clutch torque but also determines the sys tem confi guration and the change of dynamic status A clutch has three operation states and the torque transmitted in each state is described by the following equation Tc5H Cm Dv Pslipping Tclosed 0open 2 where C is a constant associated with clutch design parameters m is the friction coeffi cient that is a function of clutch slippage Dv and P is the hydraulic pressure in the clutch piston which must be controlled in order to complete a gear change with shift smooth ness T is the torque as determined by system dynamics when the clutch is fully closed In this paper clutch actuation control during shift process is realized by a normalized pressure profi le as de scribed in Sec 4 The clutch model is also used for the synchro nizer assembly where the normalized pressure signal is either 1 or 0 to switch on or off a gear Vehicle Equation of Motion For powertrain performance and shifting dynamics simulation only the longitudinal vehicle dynamics is incorporated into the vehicle system model The torque Ttireon the driving wheel generates the traction force Ftrto Fig 1Model structure for the dual clutch AMT system Fig 2Engine torque output Journal of Mechanical DesignMARCH 2005 Vol 127 303 Downloaded From http mechanicaldesign asmedigitalcollection asme org on 03 17 2015 Terms of Use http asme org terms overcome the road load and to move the vehicle According to Newton s Second Law the longitudinal vehicle dynamics is de scribed by the following equation Mv veh5Ftr2Btvveh2bdragvveh 2 2Mg sin aroad 2Fbrake 3 Ftr5Ttire rtire where M is the vehicle mass vvehis the vehicle speed Ftris the traction force Bt is a constant refl ecting tire damping and miscel laneous frictional losses bdrag is the air drag coeffi cient aroadis the road slope angle rtireis the tire radius Fbrakeis the brake force that is described in the following section 4System Control and Modeling The control system of the dual clutch AMT powertrain consists several subsystems namely shift schedule clutch pressure pro fi le synchronizer switch controller and driver Models for these subsystems have been developed and integrated into the vehicle powertrain model as described in the following Shift Schedule Controller The transmission control system controls the shift schedule based on current vehicle speed and throttle angle As shown in Fig 3 a buffer zone is designed be tween two adjacent shift curves to avoid shift hunting the curve at the right represents the threshold for upshifts and that on the left for downshifts The current gear status is maintained within the area between the two curves Based on current vehicle speed V and engine throttle angle TA the controller makes the decision for upshift downshift or gear position holding The block diagram for shift scheduling and for the actuation of the clutches and synchro nizers are shown in Fig 4 As shown in this fi gure the block for shift schedule control decides whether or not the current gear is to be changed or maintained based on the throttle position TA and vehicle speed V The gear position indicator block checks the status of the dual clutches based on the clutch slip signals DvCL and determines whether a shift is in process or completed The control signals for the two clutches CL1 and CL2 are then de termined based on the previous and next gear positions GP and PGP the relative angular velocities of the clutches DvCL and the relative angular velocities of the involved synchronizers DvSYN The control logic for the shift schedule is implemented by the following steps At every simulation time step the threshold shift speeds on the six shift curves which are predesigned for the six speed dual clutch transmission are calculated according to the current throttle angle These speeds are then compared with the current vehicle speed The next gear status is determined based on the comparison mentioned above and the gear status at the current time step For example at a certain throttle angle value if the current gear is the fi rst gear and the current vehicle speed is on the right side of the upshift curve VS12 then a 1 to 2 upshift should take place If the current gear is the second gear and current vehicle speed is on the left side of the downshift curve VS21 then a 2 to 1 downshift should take place If the current vehicle speed is between the upshift curve VS12 and the downshift curve VS21 then the gear status is maintained If a shift is oncoming the next gear position indicator GP is different from the current indicator PGP and remains so until the completion of the shift During the shift process the angular ve locity differences on the two ends of the clutches and the synchro nizers are fedback to the shift controller so as to monitor the status of the shift process Control signals are sent to the clutches and synchronizers according to the gear position indicators and the Fig 3Transmission shift curves Fig 4Shift control block diagram 304 Vol 127 MARCH 2005Transactions of the ASME Downloaded From http mechanicaldesign asmedigitalcollection asme org on 03 17 2015 Terms of Use http asme org terms feedback on the angular velocities These signals trigger the clutch action and the synchronizer switching during powertrain opera tions The logic statements used in the modeling of the shift controller are written using Modelica Dymola programming language and are imbedded in the shift controller model Look up tables are used in the control model for the shift curves Clutch Control The shift process control for the dual clutches is implemented by controlling the hydraulic pressure ap plied to the clutch piston For the dual clutch AMT the shift process is similar to a clutch to clutch shift in a conventional au tomatic transmission 3 During the shift process the hydraulic pressure in the oncoming clutch is gradually increased to the maximum value according to a calibrated pressure profi le while the pressure in the offgoing clutch is gradually decreased to zero Since the pressure signal plays a very important role in shift smoothness it is essential to create a component model to formu late the pressure control signals for the clutches As shown in Fig 4 the shift schedule controller sends out one of the four trigger signals 1 2 3 4 for clutch control These four signals are respectively engaging 1 holding 2 releasing 3 and open 4 Upon receiving the trigger signal the two clutches will be actuated and controlled according to one of the pressure profi les as shown in Fig 5 The clutch control model developed in Modelica Dymola environment works in the following logic Upon receiving a shift signal from the shift schedule control ler the current time is recorded as the starting point for the shift and will be used as the reference for clutch pressure profi le inter polation During the shift process the angular velocity differences as sociated with the dual clutches are fedback to the clutch controller at each simulation step so as to monitor the shift process The pressure values interpolated from the pressure profi le are sent to the dual clutches modeled using standard Modelica Dymola library as a normal force command signal It should be pointed out that the clutch control model uses pressure profi les that are modifi ed interactively based on model simulation Hard ware calibrations have not been conducted for the pressur