Research on shifting quality of electronically controlled mechanical automatic transmission Chen Yongdong, Zhong Shaohua (School of Automotive Engineering, Wuhan University of Technology, Wuhan 430070) proposed some methods to improve the quality of AMT shifting.
Sheng, mainly engaged in automotive CAD / CAE research.
0刖 Electronically controlled mechanical automatic transmission (AMT) has the advantages of high transmission efficiency, compact structure and reliable operation. People have always hoped that the AMT shifting process will be carried out smoothly and without impact. However, the AMT is a non-power shifting gear. During the shifting process, the clutch is disengaged to cut off the power for shifting. There is no superior condition for the hydraulic automatic transmission to mitigate vibration and shock through the torque converter during starting and shifting. Therefore, different degrees of impact will occur during the shifting process. When the impact is severe, the dynamic load of the transmission system will be greatly increased, the shifting smoothness will be reduced, and the passengers will be discomforted.
One of the most important performance characteristics of a car with an automatic transmission is the shift quality. Improving shift quality is a key technology in the development of AMT. Modern automatic transmissions can only be widely adopted after greatly improving the smoothness and service life of the shift. Therefore, it is of great significance to study the AMT shifting process, understand the influence of various factors on the shifting process, and improve the AMT shifting quality.
1 Shifting quality 1.1 Definition The so-called shifting quality refers to the degree to which the vehicle can shift quickly and smoothly under the premise of ensuring the vehicle's power and the life of the powertrain, which is embodied as comfort.
For AMT, durability mainly reflects the life of each component of the powertrain system should meet the requirements of use; power mainly refers to the power interruption time during the shifting process should be as little as possible to reduce unnecessary power waste, improve the vehicle's Power and transportation efficiency; comfort is mainly considered from the occupant's feeling. It requires no shifting shock during the shifting process, no abnormal noise of the engine, no occupant feeling of discomfort, and no feeling of shifting.
1.2 Evaluation indicators People always hope that the shifting process is carried out smoothly and without impact, but since the powertrain is a multi-momentary inertia system and the shifting is not instantaneous, the shifting gear for AMT is shifting. There are always different levels of impact in the process.
The requirements for the shifting process are: the speed of the vehicle changes smoothly, and there is no excessive instantaneous acceleration or deceleration, which makes the passenger feel uncomfortable and reduces the dynamic load in the powertrain components. The quality of its control directly affects the performance of AMT. There are many indicators for shift quality evaluation, which are also very complicated.
From the aspects of simplicity, practicality and effectiveness, the shifting time, the impact degree and the sliding performance can be used to evaluate the shift quality.
1.2.1 Shifting time tk Shifting time refers to the time elapsed from the start of the shifting command from the controller to the new gear, the speed of the clutch main driven disc is completely synchronized and the power is restored, that is, from the clutch to the separation The time elapsed since the clutch is engaged again. It includes the time to separate the clutch, the off-hook time, the selection time, the synchronization, the gearing time, and the time to engage the clutch.
This indicator is a technical and economic indicator of AMT shift quality. Because the AMT shift is a non-power shift, the power interruption caused by the shift time tk causes the vehicle speed to drop, directly affecting the power of the car, and when going uphill or overtaking. Will affect security. Good shift quality requires that the shift time should be as short as possible on the basis of smooth shifting.
1.2.2 Impact degree j The index of the degree of smoothness of the clutch engagement process during shifting is the impact degree, which is the rate of change of the longitudinal acceleration of the vehicle, ie: longitudinal acceleration, v is the running speed of the vehicle, Rt is the rolling radius of the driving wheel, io is The main reduction ratio, ig is the transmission ratio, Tc is the clutch friction torque, and the shift smoothness is measured by the impact.
This parameter can not only truly reflect the true feelings of people's comfort, but also can exclude the road conditions and the operational impact of the driver's non-shifting factors, truly reflecting the changes in the dynamic load of the car's drive train during the shifting process and the car's Movement state. The magnitude of the impact affects occupant ride comfort, driveline dynamics and driveline life. It can be known from equation (1) that to meet the impact index, the key is to control the smooth change of the torque transmitted by the clutch during the sliding phase.
1.2.3 Sliding and rubbing work of the clutch The sliding friction work Lc of the Lc clutch is an index for evaluating the service life of the clutch during the shifting process. It mainly occurs in the clutch re-engagement phase, which is the magnitude of the sliding friction between the main driven friction discs during the engagement of the clutch. It is defined as: how much mechanical energy is converted into temperature rise and wear; to the torque transmission during clutch engagement Time t1 is the moment when the clutch master driven friction disc enters synchronization from slipping; Tc is the friction torque transmitted between the clutch master driven friction disc; called the clutch active disc angular speed, that is, the engine speed; it is called the clutch driven disc angular speed.
2 shift process analysis AMT system can be based on the driver's intention (throttle opening) and the vehicle's motion state (engine speed, input shaft speed, vehicle speed, gear position, etc.), according to shifting rules, clutch engagement law, by means of The corresponding actuator (selective shift actuator, clutch actuator, throttle actuator) automatically operates the engine, clutch, and transmission. The electronically controlled mechanical automatic shift control system is composed as shown.
The electronically controlled mechanical automatic shift control system AMT shifting process control is complicated. It is necessary to coordinate the control of the engine, clutch and gearbox to achieve smooth shifting, and also consider the slipping of the clutch and the fluctuation of the engine speed. It also has a strict timing relationship. The shifting process is divided into the following five stages: 2.1 Before the shift, the engine is rigidly connected with the drive train at the original speed, the vehicle is in the original gear position, the clutch and the synchronizer are all engaged, and the transmission transmits the torque according to the gear ratio ig1 of the gear. .
2.2 Clutch disengagement, interrupting the power AMT's shifting operation must separate the clutch to interrupt the power transmission between the engine and the drive train, and must control the engine's fuel supply (in the form of throttle control) to avoid a sudden drop in load. The engine speed rises sharply. When shifting gears, first adjust the throttle of the engine to idle speed and then disconnect the clutch. In this way, the torque transmitted by the clutch is reduced to zero, and the vibration of the drive train and the impact of the vehicle are not caused by the sudden interruption of the torque. If the throttle back idling and the disconnection of the clutch are simultaneously performed, the lag reaction of the engine power reduction after the throttle idling will cause the engine speed to rise after the clutch is disengaged, which is not conducive to the synchronization of the main clutch follower after the later gear shifting. The synchronization time is lengthened.
2.3 Selecting the neutral gear After the clutch is disconnected to separate the engine and the drive train, the transmission is removed from the original gear position by controlling the shifting actuator, and the neutral gear corresponding to the new gear position is selected (when the two gears are in the same selection) The gear slot can be selected without a gear. Since the power has been interrupted, it is easy to change the transmission from the original gear to the neutral gear. This increase in the intensity of the first stage caused the passengers to bump forward and back. The time spent on the ialEleeiePublisht device is completely determined by the design parameters of the selected shift actuator.
2.4 When the new gear is engaged in the new gear (the transmission ratio is ig2), there is a difference in the speed between the main driven gears of the transmission. Therefore, it is necessary to control the speed difference to a certain extent before the purpose is to hang into the new gear. However, due to the common use of the synchronizer, the speed difference between the input shaft speed of the transmission and the output shaft speed is synchronized by the synchronizer, which greatly simplifies the complexity of the control process.
During this process, the transmission input shaft speed gradually decreases.
3 Influencing factors of shift quality During the shifting process, the friction torque of the clutch/brake is related to the degree of engagement or separation. A change in the friction torque in the clutch/brake can cause a shift shock of the vehicle. The main factors affecting the shift quality are as follows: 3.1 Timing of the action of the shift actuator In theory, it is required that the separation of one joint element and the joint of the other joint element should occur simultaneously, so that the power can be uninterrupted or impacted. But in fact, the two are not overlapping too much, that is, power interruption. The former will appear / double lock " phenomenon, causing a large dynamic load of the drive train, while causing the friction element to wear heavily due to excessive overlap. The latter will make the engine tend to / fly" and cause a sharp change in torque, making the 3.2 inertia During the energy shifting process, the inertia energy causes the drive train to impact. During the shifting process, the vehicle speed remains basically the same. Due to the change of the speed ratio, the engine speed changes rapidly, and all the rotating parts from the engine to the transmission are There will be a large amount of inertial energy released, which will be converted into a huge torque disturbance to the vehicle, causing a huge shift shock.
3.3 Actuator friction torque The friction torque of the friction element changes dramatically during the shifting process. During the engagement of the clutch or brake, due to the sudden change of the friction coefficient and the fluctuation of the system oil pressure, a large impact will be caused in the transmission system.
Due to the above factors, a certain degree of impact is inevitably occurred during the shifting process, which is manifested as a disturbance of the output shaft torque of the torque converter.
Correct analysis of the cause of the impact during the shifting process is the basis for improving the quality of the shift.
4 Ways to improve shift quality The improvement of shift quality is a systematic project that requires coordination between the engine, clutch and transmission. Improving the shifting smoothness of the transmission, from the cause of the impact, there are roughly three ways: 4.1 quality control from the actuator to use the buffer control to ensure the smooth joint of the actuator.
The alternating process of controlling the friction elements is controlled periodically.
Controls the maximum oil pressure value and oil filling time of the joint element. The maximum oil pressure value and oil filling time of the engaging element follow the following rules: increase the maximum oil pressure value of the engaging element, the vehicle dynamics slightly increases, the maximum acceleration value generated by the vehicle during shifting increases, and the impact increases, due to The shifting slip time is reduced, the maximum instantaneous slip power of the engaging element is increased and the slipping work is reduced. Increasing the oil filling time of the engaging element, increasing the time for the vehicle to reach a stable vehicle speed, reducing the power of the vehicle, reducing the maximum acceleration value generated during shifting, reducing the impact, but increasing the shifting time, increasing the sliding of the engaging element Gong.
The free wheel replaces the friction element. The sensitive response to the torque direction can be used to limit the generation of negative torque in the opposite direction, and the positive torque is automatically and timely, which ensures that the shifting moment will not cause power interruption or "double lock". The phenomenon of "stop", the torque disturbance is minimized, the shifting speed and the smoothness are more ideal than the hydraulic synchronization measures, but in order to ensure the smooth connection of the friction elements, there is still a need for buffering measures on the oil filling path. But whether it is an upshift or a downshift, only the type of low gear engagement element can be a freewheel, while the type of high grade engagement element cannot be a freewheel.
The hydraulic cylinder is used in a phased manner, and the execution force is applied by a small hydraulic pressure, and then the execution force is increased by the action of the large piston, or the hydraulic torque converter with the double lock is used to unlock the hydraulic condition during the shifting, which is effective. Improve the quality of the shifting process. Modern torque converter blocking control technology is an effective way to improve transmission efficiency. Since the lock-up clutch is engaged, the direct-drive torque converter loses the function of /soft connection, and the vibration and noise caused by the engine cannot be effectively isolated, resulting in a decrease in the smoothness of the transmission system. For this reason, the torque converter is blocked. Clutch slip control. By controlling the slip of the lock-up clutch, the torque converter can both mitigate the impact of the transmission system and improve the fuel economy of the vehicle.
4.2 Control from power source According to the previous analysis, during the shifting process, the impact mainly occurs in the inertia phase. During the shifting transition process, the engine is feedback-controlled by reducing the throttle, ignition lag or stopping the supply of oil to some cylinders. The torque is adaptively reduced, so that the input torque and the output torque of the automatic transmission can be controlled, and the input torque and the output torque can be controlled at an optimum value to achieve smooth shifting.
4.3 Control by electronic shift control system Due to the control performance limitation of the hydraulic system itself, complex shifting conditions cannot be accurately reflected, that is, different engine speeds, external resistance and throttle opening changes, different gear shifts, each The difference in the condition of the shifting clutch and so on. These factors make the hydraulic control system unable to achieve the desired shifting rules and control of shift quality. The electronic shift control system can reflect the influence of various factors on the shifting process through microcomputer control, and achieve precise shift control. The electronically controlled transmission combines only one engaging element while shifting, and simultaneously disengages one engaging element to achieve shifting. Reasonably designing the shifting overlap of the two engaging elements can effectively improve the shifting performance of the automatic transmission. .
5 Conclusion The study of shift quality is an important topic in the research of automatic transmission. The research on AMT at home and abroad has been heating up year by year. The market potential of AMT is very large, but AMT can only form a competitive position in the market if it improves the quality of shifting. Therefore, research on the quality of AMT shift is the primary task for the market. Good shift quality is the most direct embodiment of modern car automatic transmission control level. In order to achieve the best shifting effect of electronically controlled mechanical automatic transmission, it is necessary to conduct more in-depth research on various factors affecting shift quality. In the transmission transmission structure and control system design, full consideration is given to properly handle the comprehensive effects between many factors in order to obtain good design results.
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