Research On Control Technology For Torque Assist Mechanism AMT Based On The Wet Clutch

foreign heavy commercial vehicles has got tremendous development. However, due to thestructure of AMT, it still needs to cut off the power in shift process, which impacts greatlyon the vehicle fuel economy and dynamic performance. On the other hand, since the mainclutch between the engine of the vehicle equipped with AMT and AMT gearbox is a dryclutch, the control effect of clutch engagement stability in starting process is stillunsatisfactory, which thus affects the starting comfort and smooth of heavy commercialvehicles. All these problems have hampered the promotion and application of AMT in thevehicle market.To overcome the shortages of AMT in heavy commercial vehicles, this paper,combining with enterprise cooperation projects, is designed to do the following research oftorque assisted AMT control technology based on wet clutch:(1) On the basis of analyzing abroad research status of torque assisted AMT controltechnology, through comparative analysis and program design of wet clutch torque assistedAMT structure, the study puts forward and develops the wet clutch torque assisted AMTstructure based on wet clutch as the main clutch of heavy commercial vehicles. Theadvantage of the structure is that, by using wet clutches as the main clutch and torqueassisted clutch, not only the power will not be cut off in shift process of torque assistedAMT, but also the vehicle starting stability could be improved.(2) In this paper, the performance characteristics and control requirements of wetclutch torque assisted AMT have been discussed and analyzed in detail. And based on theoverall program design of electronic control system of wet clutch torque assisted AMT inXC2785microcontroller, combining with mastered theory and technology of automotiveautomatic transmission, the electronic control system hardware and software have beendesigned and developed to meet the control requirements of the wet clutch torque assistedAMT structure based on wet clutch as the main clutch of heavy commercial vehicles. As tothe micro-controller module of wet clutch torque assisted AMT, it is comprehensivelyconsidered that the system has special demands on computing speed, real-time, interfacefunction and quantity, automatic transmission has a particular choice of shift timing, and torque assisted clutch requires the coordination of engine control and the real-time ofelectronic control system. As to the control software of the electronic control unit, thesoftware is designed with required functions of the system such as shift control, shift qualitycontrol, launch control and stability control, self-tuning and self-diagnostics and so on.Taking account of the complex scheduling between tasks functions, and complicated andvariable features of communication and vehicle driving conditions, the controller of wetclutch torque assisted AMT is designed as the embedded controller pattern in order tocollect and handle multiple concurrent date parameters and parallel process a variety oftasks. The software design adopts the modular design concept and the scheduling method isdesigned to set different modular priorities based on the requirements of system control.(3) Mathematical model and simulation model established on the basis of wet clutchengagement process have used simulation for analyzing the wet clutch engagement processof the key components of wet clutch torque assisted AMT. From the analysis, it can be seenthat film thickness between the friction plates in the stages of extrusion, compression andrough contact during the wet clutch engagement process, changes with time and torque atdifferent stages. The result research shows that, when the wet clutch starts to extrude, thetorque it transfers increases quickly; when entering the extrusion stage, the transmissiontorque will be superposed by two parts of torque in the clutch engagement process; when inthe rough contact stage, the transmission torque in clutch engagement gradually becomesconstant.(4) In the analysis of the effect that wet clutch engagement characteristics have on thevehicle starting, the paper is designed to do deep research in the engagement process on thewet clutch of the wet clutch torque assisted AMT based on the wet clutch as the main clutch,combining the pressure control strategy, wet clutch pressure parameter self-tuning PIDcontrol strategy and the driver’s intent fuzzy control strategy in the starting process. Theresearch shows that comparing with the variable parameter PID control strategy based onthe look-up table method and the fuzzy PID control strategy based on fuzzy theory, in thispaper, wet clutch pressure parameter self-tuning PID control strategy in the starting processcan realize the real-time and follow-up control of the target pressure. Namely, control theclutch pressure through adjusting duty cycle of the control value and compare with thetarget clutch pressure; meanwhile, realize self-tuning of PID control parameters based onfuzzy controller and the difference of comparison and the PID control parameters Kp, Ki, Kd of rate of change adjusting. Other researches show that, in this paper, the starting fuzzycontrol strategy of wet clutch enhances the robustness and adaptability affected by uncertainfactors such as the driver’s initial intent and vehicle conditions. Specifically, carry out fuzzyidentify on the driver’s starting intentions through the acceleration pedal position operatedby the driver and its’ rate of change, and based on the establishment of rules of driver’sstarting intent and fuzzy control of vehicle conditions, and the corrected parameters ofengine speed, the minimum combination speed and the clutch oil temperature and so on,realize the fuzzy control of wet clutch in starting process.(5) In the analysis of shift characteristics of automated mechanical transmission, thispaper further studies the control strategy of the wet clutch torque assisted AMT based on thewet clutch as the main clutch at different shift stages, the shift control strategy of differentauxiliary transmission gear ratio of constant mesh based on the wet clutch torque, and shiftcontrol strategy of wet clutch torque assisted AMT based on the analysis of dynamics ofvehicle transmission system. The study shows that when formulating control strategy of wetclutch torque assisted AMT in the shift process, people have to take account of the torqueassisting effects of torque assisted wet clutch in two conditions of abstract file and hangingfile in the AMT shift process, and the torque changes of engine, transmission,synchronization and auxiliary clutch torque at two stages of abstract the gear and gear. Then,through the combination control and separation control of torque assisted wet clutch in theshift process, realize the shift with power non-interruption. That is, leave the vehicle in gearcontrol based on the vehicle speed and the throttle opening degree of the shit schedulingparameter, and control torque assisted wet clutch into binding state. In this process, enginetorque transfers torque with torque assisted wet clutch through the gearbox gears. Duringthis process, the torque that the gearbox gear transfers decreases constantly, accordingly thetorque that the torque assisted wet clutch transfers increases, and when finishing the abstractfile, the transmission is in neutral state and the engine torque is totally delivered by theauxiliary clutch to output shaft. In the hanging file process, the control system is doing theneutral control, torque assisted wet clutch is entering separation state, and at the same time,the system control the gears binding of the target gears in transmission by adjusting theengine output speed and the synchronous speed at both sides of the synchronization. In thisprocess, the torque that the transmission gears transfer increases gradually, the torque of thetorque assisted wet clutch decreases because of separate transferring and after finishing shifting, the engine torque is completely transferred by the transmission gear. In the processof abstract file and hanging file, the coordinated control strategy of the engine and theauxiliary clutch is determined by the gear ratio applied in the torque assisted mechanismengaged gear. On the other side, based on the kinetic analysis of vehicle drive system oftorque assisted wet clutch AMT and the kinetic featured shift control strategy underdifferent freedom degrees of torque assisted wet clutch AMT, the result shows, in order tohook block under the non-producing torque vibration condition, namely, to develop thestability in hook block process, the torque assisted wet clutch should be controlled in totalcombination state and in the maximum torque delivery status so that when the main clutchis in the engagement state, it can be shifted to next gear without obvious vibration. To keepthe continuity of neutral power, the engine speed should be controlled and adjusted and alsothe combination pressure of the auxiliary clutch, to make the auxiliary clutch deliver thetorque to the second shaft smoothly and realize the continuity of neutral power. The controlstrategy of shifting from neutral to next gear is on the basis of coordination control betweenthe auxiliary clutch and engine, that is the synchronous process to accelerate or slow downthe spindle speed to get desired downshift or upshift in order to make the spindle rotationspeed adapted to engage the next gear.(6) Based on the developed electronic control system，this paper studies the pressurecontrol of wet clutch by bench test and analyzes the effects that different control strategieshave on combination characteristics and torque transmission characteristics of wet clutch.The result of the test shows the differences of the peak value and duration of input andoutput speed and transmission torque at the stages of extrusion, compression and roughcontact during the wet clutch engagement process, is controlled by the wet clutch control oilpressure obtained from the duty cycle of different given control signal, while the value andamount of the oil needed to control should depend on the different driving conditions ofvehicle (such as starting, shifting g, accelerating, decelerating and braking conditions) andthe appropriate control strategies.This paper, applying the theory of automotive automatic transmission and electroniccontrol technology, studies the control technology of wet clutch torque assisted AMT basedon wet clutch as the main clutch of heavy commercial vehicles, it has theoretical andpractical significance on the technical development of commercial vehicle AMT and the torque assisted wet clutch AMT, and has a certain reference value to the development of theproducts for torque assisted wet clutch AMT of commercial vehicles.