Research On Shift Strategy And Quality Of Hydrodynamic Automatic Transmission For Heavy-duty Vehicle

With the development of economic in our country, a large number ofconstruction projects are increasing rapidly, such as the construction of majorinfrastructures, renovation of the old city, exploitation of large mineral deposits. Thehuge demand of heavy-duty vehicle provides the opportunities to develop theheavy-duty vehicles and also makes this industry more competitive. Nowadays dueto the shortage of core technology and independent intellectual property rights forautomatic transmission, manual transmission plays the major role in the domesticproduction of heavy-duty vehicles. However, the working condition of heavy-dutyvehicle is complicated with frequent shift and large shock, which makes the driverfeel tired commonly. Hence the realization of automatic transmission for heavy-dutyvehicle not only improves the performance of vehicle, which is crucial for vehicles,but also reduces the instensity of labor and accident rate.Nowadays, the core technology of automatic transmission is occupied byEurope, America, Japan and so forth. Our country’s automatic transmissionsequipped in heavy-duty vehicles are mostly dependent on imports or sino-foreignjoint ventures. Shift schedule is one of the core issues of automatic transmission,which directly affects the power, fuel economy, passing ability and environmentaladaptation. Because the foreign shift schedule of automatic transmission isblockaded, we must undertake independent research which is based on the variousrunning factors of vehicle to ascertain the reasonable shift points and lay down the shift strategy to confirm the shift schedule for different requirements of the vehicle.Meanwhile, the shift quality of automatic transmission needs to be ameliorated soon.The foreign researches on the lapping time sequence’s control, reducing shift shockand keeping the steady performance of shift have done for a long time and are inpractical period. Though the controlling of domestic shift quality has been studiedand obtained a certain achievement, there is still a large gap compared with foreign.Therefore, facing the competition of the international market and the demand ofdomestic market, developing the core technology of high-performance automatictransmission for heavy-duty vehicles has become the first priority. It is a criticalmoment for our country to develop the technology of automatic transmission andresearch the shift strategy and quality, which are very meaningful to the developmentof our country’s heavy-duty vehicle industry.In view of the above problems, this paper, supported by the project "Study onautomatic transmission technology of heavy vehicle and special vehicle” ofHangzhou Advance Gearbox Group Co. LTD, combining mechanical transmission,fluid transmission (hydrodynamic transmission and hydraulic transmission) andautomatic control theory and so on, deeply researches the shift strategy and qualityof automatic transmission for heavy-duty vehicle. The main contents and specificconclusions are as follows.1. Research on transmission system and characteristics of the whole vehicleWhen the engine and hydrodynamic torque convert work together, a new powerdevice is constituted, and the vehicle can obtain the fine dynamic performance andfuel economy only through a reasonable matching of engine and hydrodynamictorque convert. The mathematical models of engine and TC are established underunstable condition, hydrodynamic torque convert is designed by CFD and itscharacteristics are calculated, and automatic transmission suitable for heavy-dutyvehicle is designed. The input characteristics, common working points and outputcharacteristics are obtained through the matching of engine and hydrodynamictorque convert. Dynamical equations of the whole vehicle are established, tractionand acceleration characteristics are calculated, which provide a basis for research on dynamic three-parameter shift strategy.2. Estabishment of dynamic three-parameter shift strategy with crankshaftangular accelerationBecause starting and shifting of vehicles are completed under unstablecondition, and automatic shifting has the demands such as stability, small shock, lownoise, accurate and timely, a reasonable choice of shift point is particularly importantin shifting process. The angular acceleration of the engine crankshaft, which reflectsthe changing rate of throttle opening, is proposed in this paper as a control parameter,which reflects the dynamic process of shifting more accurately. The vehicle velocity,throttle opening and crankshaft angular acceleration are regarded as three controlparameters of dynamic shift schedule, which has been proved superior totwo-parameter shift schedule in power and fuel economy by simulation approach.The scheme that a hardware circuit implemented in the transmission control system（TCU） is introduced, in which various control programs are solidified, includingshift control, lockup clutch control, charging and discharging oil control of retarder,shifting quality control etc; The shift schedule applies in application layer softwareof TCU, and implementation paths are given. The results show that angularacceleration of engine crankshaft has a large influence on the selection of shiftingpoints, the proposed dynamic three-parameter shift schedule has an importanttheoretical significance and engineering application value on improving theperformance, dynamic property and fuel economy of automatic transmissionvehicles.3. Study on shift quality controlResearch on shifting quality of AT is significant to improve stability, comfortand safety of running condition; meanwhile, the service life of driveline componentsis prolonged. A mathematical model of electro-hydraulic shift control system isestablished, and the correctness of its shift timing is analyzed and verified bysimulation. For shift quality control methods, both schemes of switchelectromagnetic valve and proportional electromagnetic valve are compared andanalyzed, although the proportional electromagnetic valve can realize more precise control, but it must take into account the actual situation of the project, this paperadopts the smooth combination valve that is scheme of switch electromagnetic valveto control the shift quality, and buffer performance affected by various parameters ofsmooth combination valve and clutch are simulated and analyzed. The resultsindicate that oil pressure controlled by smooth combination valve is smoothly risingand shifting shock is weak, besides, the curves reflecting the influence of variousparameters on the buffering characteristics are acquired by the batch processingfunction, which improves the efficiency of the modeling and simulation.4. Test of electro-hydraulic control systemThe test of automatic shift and shift quality of electro-hydraulic control systemare carried out on the workbench of hydrodynamic automatic transmission. Therationality of dynamic three-parameter shift strategy with crankshaft angularacceleration, the correctness of automatic shift action for electro-hydraulic shiftcontrol system are verified by the test of automatic shift and the transmission controlunit(TCU) can achieve the function of automatic shift. Test and simulation results ofoil pressure are compared and analyzed by the test of shift quality. The test resultsshow that the simulation model of smooth combination valve is correct and effective,and smooth combination valve has a better effect on shift quality.This paper detailedly researches the shift strategy and shifting quality ofhydrodynamic automatic transmission for heavy-duty vehicles, which have not onlyimproved the power, fuel economy and riding comfort of the vehicle, but alsoreduced driver’s labor intensity and accident rates. Moreover, this paper hasimportant theory guiding significance to thorough study electro-hydraulic shiftcontrol technology of automatic transmission, and also provides a better foundationfor the independent research in domestic automatic transmission for heavy-dutyvehicle.