Many existing literatures mostly talk about the control problem of automatic transmission is the key to restrict the development of China's automatic transmission independent brand. It is true that the localization of automatic transmission cannot be separated from advanced electronic controllers, actuators and algorithms, but the control strategy The formulation is based on the detailed mastery of the working characteristics of the control object. Without knowing the characteristics of the object, control cannot be discussed. From the perspective of each specific key technology, according to China's national conditions, some technologies can carry out independent research and development by strengthening scientific research and development, and boldly rely on innovation to open up new horizons. Not all technologies must follow the "introduction-digestion-absorption" The route should be believed that we have this ability and strength. We should not rely on, imitate and copy the foreign technology, so that the localization of the entire automatic transmission industry in our country is in a very passive state. This paper analyzes several key technologies that restrict the development of automatic transmissions in China from the technical roots, and puts forward corresponding suggestions.
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At present, automatic transmissions used in automobiles are roughly classified into four types: Automatic Transmission (AT), Automated Mechanical Transmission (AMT), and Automatic Continuous Transmission. (Continuously Variable Transmission, CVT) and Dual Clutch Transmission (DCT).
AT is a hydraulic automatic transmission composed of a torque converter, a planetary gear mechanism and an electro-hydraulic control system. Although the automatic transmission currently used is usually called AT, it has actually developed rapidly with the development of microelectronics. It has become an Electronic Controlled Automatic Transmission (ECT), and the past hydraulic control AT has been eliminated. AMT is an electronically controlled mechanical automatic consisting of a common manual shifting transmission, shift controller, electronic control unit (ECU), clutch control mechanism, gear selection and shift control mechanism, engine throttle control mechanism, sensor and power supply system. The transmission, which is based on the traditional fixed-shaft transmission and dry-type clutch, applies electronic technology and automatic shifting theory. With the electronic control unit as the core, the clutch is separated and engaged by the actuator, the gear position is changed and the throttle is adjusted. To realize the automatic operation of the car starting and shifting. The CVT has four main product types: a continuously variable transmission engaged with a manual transmission, a continuously variable transmission composed of an electromagnetic clutch, a two-state continuously variable transmission combined with a torque converter, and a stepless combination with a wet clutch. transmission. The DCT can be considered as a dual set of AMT, and each set of AMT is responsible for the parity gear.
At present, there are several difficulties that restrict the development of self-owned brand automatic transmissions. It is hoped that these issues will attract the attention of relevant government departments, industry organizations and scientific research institutions.
1. Mastering and controlling the dynamic characteristics of the wet clutch engagement process
The clutch is still an indispensable unit throughout the shifting process, and control of the clutch has been one of the key technologies for the development and design of automatic transmission products. The wet clutch used in the hydraulic automatic transmission is the main friction component. In all working conditions including shifting and blocking, precise control of the wet clutch friction plate is required. The core of the key technology is the wet clutch. Mastering the dynamic joint characteristics of the main and passive friction plates. The clutches on the dual clutch automatic transmission are both wet and dry. The control problem of the dual clutch automatic transmission is mainly the overlap control of the two clutches and the starting control of the vehicle, and the core content of the key technology is also wet. Mastering the dynamic engagement characteristics of the main and passive friction plates of the clutch. For a stepless automatic transmission without a torque converter, it is necessary to add a wet clutch for the step. The control of the wet clutch is one of the core technologies of the CVT.
In the automatic transmission, the clutch generates a large amount of heat during the shifting process. If the heat is not dissipated in time, the frictional surface of the clutch will generate local high temperature and cause the warping deformation or even sintering of the friction plates. The material of the clutch friction plate, the wear resistance, the friction coefficient and the groove design of the friction surface are key technical problems that need to be solved urgently. In addition, the quality of the shifting of the vehicle will directly affect the comfort of the vehicle and the strength of the system, which will easily cause a large transient longitudinal impact of the transmission system. The main component involved in the shifting process is the wet clutch. It is a key component in improving the performance of a vehicle's NVH.
Mastering the dynamic engagement characteristics of the wet clutch is a prerequisite for precise control of the wet clutch. Research on the dynamic engagement characteristics of wet clutches is one of the important common technologies for the development of automatic transmissions.
The wet clutch is a typical nonlinear system. The difficulty in establishing the mathematical model of the joining process is that it involves not only liquid-viscous transmission but also thermal bombing. The ability to transmit torque and power is the result of many complex factors. At present, there is no satisfactory mathematical model in foreign countries, which is a hot topic of research. Domestic research on the characteristics of wet clutch engagement process is far from enough.
The characteristics of the wet clutch engagement process involve many fields such as nonlinear dynamics, viscous fluid mechanics, computational science, tribology, etc. At present, compared with the foreign situation, the research and development of wet clutch is too little and insufficient attention. Constant financial resources are needed to encourage more researchers from different disciplines to study the dynamic characteristics of wet clutches.
2. AMT control system and actuator
In order to achieve electronically controlled shifting, AMT has higher requirements on the selection of shifting actuators, clutch actuators and transmissions. However, China's current processing technology is relatively low, and even if mass production is realized, its reliability is still unknown.
3. Mastery of the basic theory of metal belt transmission in CVT
The most important theory of the metal belt transmission in CVT is the research and control of the clamping force of the metal belt. The clamping force of the metal belt directly affects the transmission efficiency of the CVT. When the clamping force is too small, the metal belt slips on the wheel. This will reduce transmission efficiency, accelerate the wear of metal strips and wheels, and shorten their service life. When the clamping force is too large, sliding between the metal belt and the wheel will cause unnecessary loss, which will also reduce the transmission efficiency. If the clamping force is too large, the tension of the metal strip will be too large, shortening the service life of the belt. The clamping force needs to be controlled within a small range of the target value according to the running condition of the car, and is one of the key technologies of the CVT transmission system.
4. The manufacture of metal strips in CVT is one of the key technologies
Initially, the CVT used a belt of rubber material for the continuously variable transmission. It has been changed to a steel ring made of many thin steel sheets, so that it can be engaged with the grooves of the two cone wheels at different radii to change the speed ratio. This is the VDT (Von Doorne's Transmission), which was officially sold as a commercial vehicle in 1982. At present, only Bosch and other individual component giants have production capacity, and domestic enterprises are unlikely to achieve industrialization in a short period of time. Steel belts can only rely on foreign procurement. In order to improve the transmission capacity of the belt, the bandwidth of the wet metal belt has been increased to 30mm (the old type is 24mm), the width of the 9-layer steel ring is expanded by 25%, and the stage high oil pressure system is adopted. In addition, Daihatsu Co., Ltd. used a dry belt on newly developed cars, using materials such as resin and aluminum alloy. From the development of the material and manufacturing of the transmission belt, it can be seen that the transmission belt material is an important innovation point of CVT technology breakthrough. For the temporary technical backwardness of China, we can jump out of the existing foreign patent technology thinking framework and invest more scientific research power to do more. Innovative R&D work, bypassing existing patented technologies and developing its own products.
5. The design of CVT electro-hydraulic control system is difficult
The electro-hydraulic control system is the most important part of the continuously variable transmission, including the TCU, the hydraulic control unit and the actuator. The key technologies are: hydraulic control system design and test methods; proportional solenoid valve test and development technology; speed ratio control technology and product consistency and reliability technology. There is an urgent need for the system's hydraulic control system analysis methods and design theory to form the ability to develop hydraulic control systems independently.
6. Hydraulic valve body assembly and electronic control unit are the key to developing DCT
The DCT power transmission and shifting process is realized by the electronic control unit issuing a control signal to control the hydraulic execution of the original, and its control system is essentially an electro-hydraulic control system. The analysis and design of the hydraulic system oil circuit and the working state of each hydraulic valve and the manufacture of hydraulic modules are the key to developing the DCT control system. The DCT hydraulic control unit mainly consists of a quantitative pump, an oil filter, a main pressure slide valve, a safety valve, a safety slide valve, a gear position switch valve, and a multi-way modulation valve. The hydraulic control system consists of a clutch pressure control section, a synchronizer pressure control section, and a lubrication and cooling control section. At present, the design and manufacturing technology of key components such as valve body and solenoid valve cannot be broken, which has restricted the further development of DCT in China.
7. Summary
As the core technology of automatic transmission, the world's major manufacturers pay great attention to the protection of intellectual property rights. Taking the electro-hydraulic control system of CVT as an example, different electro-hydraulic control systems are basically the same in function, but the implementation is quite different. Even if there are certain similarities in the implementation, there will be significant differences in the structural design. From the history of the evolution of technology, we can see that many core technologies that restrict the industrialization of China's automatic transmissions still have the potential for innovation. We should invest more financial, human, and material resources, strengthen the alliance of production, education, and research, and strengthen the simultaneous development of automatic transmissions by related enterprises. Cooperate to form a public technology research and development platform for automatic transmissions, pay attention to independent innovation, and form independent development capabilities for China's national conditions, instead of blindly joining foreign-funded enterprises or imitating foreign products. Transforming our country from a manufacturing power to a manufacturing power.
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