Commercial vehicle automatic transmission technology development and program selection

In recent years, China's auto market has grown at a rate of more than 20% every year. China has become the world's largest auto market and the world's most promising and dynamic auto market.
Under the support of the continuous and steady growth of automobile demand, the automobile transmission, which is one of the key automotive assemblies, has also maintained rapid development. In 2009, China's auto transmission market reached 52 billion yuan, and it is growing at a rate of more than 20% per year. It is expected to reach 150 billion yuan in 2015. At present, the sales volume of automatic transmission models in China's sedan market accounts for about 35% of the total sales volume, and the sales of commercial vehicle automatic transmissions are beginning to appear. The market potential of China's auto transmissions is huge.
Since the 1980s, the international commercial vehicle market has entered the era of automatic transmission. Major automobile manufacturers such as Japan, the United States, and Europe have introduced automatic transmissions for commercial vehicles, such as ZF's Astronic transmission, Mercedes-Benz Actor transmission, Volvo's I-Shift transmission, and Eaton's Ultrashift transmission. The application of the commercial vehicle automatic transmission effectively relieves the driver's driving intensity and improves driving safety and comfort. At present, in the domestic commercial vehicle market, companies such as Fast, China National Heavy Duty Truck and FAW have successively launched their own automatic transmission products (mainly AMT), with an annual sales volume exceeding 1,000 units. With the increase in user acceptance of automatic transmissions, China's commercial vehicle automatic transmission market will have a huge room for development.
Technical route of commercial vehicle automatic transmission
At present, the automatic transmissions used in automobiles mainly include electronically controlled mechanical automatic transmission (AMT), hydraulic mechanical automatic transmission (AT), continuously variable automatic transmission (CVT) and dual clutch automatic transmission (DCT).
1. Electronically controlled mechanical automatic transmission AMT
The AMT is based on the original manual transmission (MT) with an electronically controlled hydraulic unit. During operation, the electronic control unit (ECU) controls the hydraulic device to operate the clutch and shift lever of the stepped mechanical transmission to automatically separate and engage the clutch. The transmission gear is switched by the ECU according to the vehicle speed, engine speed and throttle. The opening is automatically controlled to achieve automatic clutching and automatic gear selection of the stepped mechanical transmission.
The utility model has the advantages of high transmission efficiency, good fuel economy, and can be up to 95% or more; the structure is simple, the manufacturing and maintenance cost is low, only 1/3 to 1/4 of the AT; it is suitable for various vehicles, especially for commercial vehicles. The shortcomings are that the shifting stability is not high, the comfort is poor, and the power is interrupted when shifting; the control parameters are too much, and the automatic control is difficult.
Because AMT retains most of the original MT's parts, the production inherits well, the transformation cost is low, and the optimized design of the software can improve the vehicle's performance. Therefore, the world's major auto companies are carrying out this technology. research and develop. China began AMT research in the early 1980s, which is equivalent to the international level in terms of technical theory. However, in terms of industrialization, there is a big gap with foreign countries. In the past two years, domestic AMT has made breakthroughs in industrialization, and France, FAW, and heavy trucks all have corresponding AMTs to market.
2. Hydraulic mechanical automatic transmission AT
AT is currently the most widely used automatic transmission in automobiles, and the variable speed torque is realized by the combination of hydraulic transmission and gear.
The advantages are smooth shifting, no impact and vibration, good ride comfort; no restrictions on transmission power, suitable for all types of vehicles. The shortcomings are low transmission efficiency, large fuel consumption, complex structure, high manufacturing cost, and difficult maintenance and repair technology. AT is geared, shifting shock can still be felt, and the torque range is limited. There is no MT sensitivity to the change in velocity.
At present, AT technology is the most mature and widely used. AT accounts for more than 70% of the global automatic transmission market, mainly in the passenger vehicle field. In China, it is more than 90%, almost all of which are used in passenger cars, and almost all of them are imported or produced by joint ventures. In the field of commercial vehicles, large and medium-sized passenger cars and off-road vehicles have broad application prospects. Among them, Fast has already launched AT products.
3. Stepless automatic transmission CVT
The CVT uses a V-shaped belt and a variable working main and driven wheel to transmit power, enabling an automatic transmission with a continuously changing gear ratio over a wide range. Since the working radius of the driving wheel and the driven wheel can be continuously adjusted, the stepless speed change is realized.
The advantage is that the real stepless speed change is achieved, the ride comfort is good, the acceleration performance is good, the fuel economy is high, the structure is simple, and the number of parts is small. The downside is that the transmission torque is limited and the application range is limited. It is only suitable for vehicles with engine displacement below 3L. The drive belt is easily damaged and has a limited service life.
Currently, more than one million vehicles worldwide are equipped with CVTs each year, most of which are in Japan, accounting for about a quarter of the world market. Japan's JATCO is the world's largest producer of CVT. Bosch is the largest producer of metal strips. At home, Jetco is the leading manufacturer of CVT. Due to the limitation of input torque, the use on commercial vehicles is limited.
4. Double clutch automatic transmission DCT
The DCT is a dual clutch device consisting of two clutches. In essence, DCT is equivalent to combining two (three-speed) MTs into one.
Advantages are shorter shift times, higher shift comfort; more reliable transmission quality, lower maintenance costs; better acceleration performance, lower fuel consumption; unlimited transmission power limitations Used in a variety of models. The shortcoming is that the electronic control system is more complicated, technically difficult, and the production cost is relatively high. At present, only a few companies such as BorgWarner in the United States and Schaeffler in Germany have mastered the core control module of DCT.
Due to the torque capacity of the dual clutch and the limitation of the hollow shaft structure, it has not been applied to commercial vehicles for the time being.
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