Technical characteristics and development trend of heavy-duty vehicle transmission
Heavy-duty vehicle transmissions are transmissions that are matched with heavy commercial vehicles and large passenger vehicles. Although there is no clear limit on the capacity division of transmissions in the industry, we usually refer to automotive transmissions with a nominal input torque of 900 Nm or more as heavy-duty vehicle transmissions.
1 Structural features of foreign heavy-duty truck transmissions
In foreign countries, transmission specialization manufacturers pay great attention to product serialization, which provides great convenience and flexibility for the main engine factory to select the most satisfactory transmission. For example, Germany ZF (ZF) has seven basic transmissions with center distances of 8.0, 95, 105, 115, 120, 143, and 154mm. The input torque is 130-1900Nm, and the number of gears ranges from 3 to 17. The steered transmission adapts to different matching requirements of the vehicle. Japan's Toyota Motor Corporation Aisin Seiki Co., Ltd. has five basic types of center distances: 72, 78, 88, 98, and 135mm, and 286 kinds of transmissions are available for users to choose. However, many automobile transmission manufacturers in China have not yet formed the transmission serialization products of this enterprise.
The 9S109 synchronizer type 9-speed compound transmission manufactured by ZF of Germany has 5 forward gears in the main transmission and the planetary gear train transmission structure in the auxiliary transmission. When the synchronizer sleeve in the auxiliary transmission is engaged with the fixed outer ring gear, the ring gear of the planetary gear is fixed and cannot be rotated, and the auxiliary transmission is engaged in the low gear. At this time, the main transmission is respectively hung in 5 different gear positions. The combined transmission has 5 larger transmission ratios. When the clutch sleeve is engaged with the high-speed ring gear of the auxiliary transmission, the planetary gear shaft, the output shaft, the planetary gear inner ring gear and the auxiliary transmission input shaft gear are fixed together and rotated synchronously, and the auxiliary transmission is engaged in the high-grade (direct gear), the main The five gear ratios of the transmission are equal to the combined transmission, respectively.
A smaller gear ratio. Since the two gear ratio values ​​are very close, one gear ratio is eliminated to form a 9-speed transmission. The transmission has a maximum input torque of 1250Nm and a total mass of 310kg. It is directly connected to the engine or installed separately, left horizontal or right horizontal. The control system of the transmission is remotely operated or directly operated by the rotating shaft. The double XH type shifts the gears, the auxiliary transmission is automatically shifted by the compressed air, the crawling gear and the reverse gear are shifted by the engaging sleeves, and the other gears are shifted by the synchronizer.
US Eaton Fuller Series Double Auxiliary Transmission Structure Features
The BT-11509C double countershaft double-speed 9-speed combined mechanical transmission produced by Eaton Corporation of the United States has a double intermediate shaft structure for the main and auxiliary transmissions. The main transmission has 5 forward gears. The auxiliary transmission is a two-speed (high-grade and low-range) gear transmission. Since two transmission ratios are very close, one is omitted to form a nine-speed transmission.
The double countershaft double-speed combination transmission has the following advantages:
(1) Since the gears on one shaft and two axles mesh with the corresponding gears on the two intermediate shafts at the same time, the power splitting, theoretically, the torque transmitted on each pair of gears is 1/2, which makes each The torque transmitted to the gear is reduced by 50%, so that the center distance of the transmission, the gear modulus and the width can be reduced, thereby reducing the quality and size of the transmission, especially the length dimension.
(2) Since the two-axis driven gear is in a radial floating state on the shaft, the axial center lines of the two intermediate shafts are evenly distributed on a cylindrical surface centered on the axis of the two-axis theory and having a radius of the center distance, so The radial forces generated by the gears on the shaft and the one-shaft gear meshing with the corresponding gears on the two intermediate shafts are balanced, that is, cancel each other out. The two shafts do not withstand radial forces and only transmit torque, so that the two shafts can be designed to be thinner, the structure can be simpler, and the rear bearings can be selected in smaller sizes, which also helps to reduce the quality and size of the transmission.
(3) Due to the radial floating of the two-axis gear and the articulation of the two axes
As a result of the float, the gears automatically offset a portion of the manufacturing and assembly errors when engaged, and the meshing quality is superior to the single countershaft. The meshing area is easy to meet the design requirements, and the actual use also confirms this. This is advantageous in reducing the meshing noise and improving the durability.
(4) Since the double countershaft double-speed combination transmission can significantly reduce the mass and axial size of the transmission, the maximum transmission power and torque of the transmission can be improved and the range of use can be expanded.
This is the ideal transmission for short-wheelbase high-power heavy-duty vehicles and special vehicles. RT-11509C transmission has a maximum input torque of 1500Nm, a maximum input power of 265kW, a total length of 735mm, XXH or single H operation, and can be operated by left or right, with a total mass of 270kg.
2 Structural features of domestic mechanical heavy-duty transmissions
The technology of domestic heavy-duty truck transmission products originates from the United States, Germany, and Japan. The introduction of technology is mostly from the 1980s to the 1990s. As a long-term introduction and digestion process of heavy-duty automotive transmissions in the advanced technology field of automobiles, it has made great progress. Based on the introduction of the original technology, it can develop new products that meet the supporting requirements through the modification, and the annual heavy-duty vehicles. More than a dozen new products are available in the transmission industry. However, from the development of today's heavy-duty vehicle transmissions, the domestic heavy-duty vehicle transmission still takes a general development process in the development of new products, and there is no real core technology product; from the domestic heavy-duty vehicle transmission market capacity, there are three One-third of the products are imported, while more than 80% of the other two-thirds of the products are from foreign technology. The sales of heavy-duty automotive transmissions developed independently in China are small, indicating that the domestic independent development capability of heavy-duty vehicle transmission manufacturers remains It is very weak, and the ability to cope with the new vehicle accessory products is far from enough. China's urban vehicles will focus on the development of the 13.8m passenger car used in the transmission, currently only ZF can supply to domestic enterprises, it is enough to show that the domestic heavy-duty transmission company is still very small, there is still a long way to go in terms of technology.
The domestic heavy-duty vehicle transmission is almost covered by Shaanxi Fast Gear Co., Ltd., Hanjiang Gear Transmission Co., Ltd., Shanxi Datong Gear Group Co., Ltd., and FAW Harbin Transmission Factory. The transmission products produced by these companies are focused on different markets. For example, Shaanxi Fast has a market share of more than 40% in the heavy-duty vehicle market above 8t, and has an absolute advantage in the heavy-duty vehicle market above 15t, with a market share of over 85%. ;ç¶¦æ±Ÿé½¿è½®ä¼ åŠ¨æœ‰é™å…¬å¸ is mainly for 7~12m high-grade large and medium-sized passenger cars of Ankai, Xiwo, Yaxing Benz, Guilin Daewoo and Xiamen Jinlong, as well as heavy-duty trucks and saddle tractors with total mass of 14~50t , dump trucks and various special vehicles, special vehicles; Shanxi Datong Gear Group supporting market is mainly in the 8 ~ 10t class of low-tonnage heavy-duty trucks.
3 Technical characteristics of mechanical heavy-duty transmission
Heavy-duty trucks are loaded with high quality and complex conditions of use. To ensure that heavy-duty vehicles have good power, economy and acceleration, it is necessary to expand the range of the transmission ratio and increase the number of gears. In order to avoid the structure of the transmission being too complicated and to facilitate serial production, a combined mechanical transmission is often used. That is to say, one or two 4-6 transmissions are the main components. By changing the series of gear pairs and configuring different auxiliary transmissions, a series of transmissions with different gear positions and different transmission ratio ranges are obtained. At present, combined mechanical transmissions have become the main type of heavy-duty vehicles. The combined mechanical transmission is generally divided into a double gear (segmented gear) combined mechanical transmission and a half gear (plug-in type) combined mechanical transmission.
3.1 double gear combined mechanical transmission
The double-speed combined mechanical transmission is equipped with a 2-speed (high-grade and low-range) auxiliary transmission in series at the rear of the main transmission to increase the number of gears of the main transmission by one time. The increased gear ratio is equal to the main transmission ratio and The product of the auxiliary transmission ratio, and the number of gear pairs is less than the number of gears, so the size of the casing is shortened, the length of the shaft is shortened, and the rigidity is increased, so that the capacity of the transmission is increased. For example, in the rear end of a 5-speed main transmission, a sub-transmission with high and low 2 speeds is installed in series to form a 10-speed (or 9-speed) double-speed combined mechanical transmission. The technical difficulty in increasing the maximum input torque and the lowest gear ratio of the double-speed combination transmission is that the strength capacity of the auxiliary transmission low gear is insufficient, exceeding the bearing capacity of the gear teeth. The solution is to shunt the load that is carried by one tooth to several teeth. In this way, the input gear torque is constant, and the load of each tooth will be equal to the average value of the number of simultaneous contact teeth.
There are two types of auxiliary transmission power splitting methods for double-speed combined transmissions: one is the planetary gear train transmission method, which is very compact, small in size and large in torque capacity, and is still widely used until now; another power shunt The method is to use a double countershaft transmission structure. The biggest technical difficulty of the double countershaft transmission is to ensure the simultaneous contact between the main transmission gear and the teeth of the engaged double countershaft gear. The solution is to eliminate the manufacturing error of the cog alignment by using the floating main transmission gear. The teeth are in contact at the same time to achieve the purpose of power splitting. The shift synchronizer that is compatible with this also has a certain amount of floating.
3.2 Half-speed combined mechanical transmission
The auxiliary transmission ratio is evenly inserted between the gear ratios of the main transmission with a large transmission ratio interval, thereby increasing the number of gears of the transmission by one time. The half-speed auxiliary transmission is connected in series at the front of the main transmission, which has only a pair of gear pairs and a shift synchronizer. The early half-speed splitter consisted of a single box that has evolved in recent years to place the half gear pair directly into the main transmission, both reducing the length of the transmission and simplifying the half-gear structure. The half-speed auxiliary transmission is composed of a pair of similar-axis permanent meshing gear pairs. The ring gear sleeve is freely rotatable on the power input shaft. When the ring gear on the power input shaft is combined with the main transmission shaft, the gear ratios are all by the main transmission. A shaft gear pair is composed. When the ring gear is connected with the engaging teeth on the power input shaft, the constant meshing gear is connected with the intermediate shaft on the main transmission, so that the intermediate transmission intermediate shaft also rotates, and the gear ratios thus formed are evenly inserted into the main transmission gears. Between the gear ratios. The model is a ZFAK/6-80 GV80 half-speed combined mechanical transmission consisting of a 6-speed AS6-80 main transmission in series with a half-speed auxiliary transmission. The maximum input torque is 750Nm, the transmission ratio range is 0.83~9.0, and the reverse gear ratio is 7.05/8.46. This type of transmission has been widely used in Europe, such as Mann, Iveco, Steyr, Volvo and so on. The ECOSPLIT-16S 16-speed combined mechanical transmission developed by ZF has a pair of half-gear gear pairs at the front end of the 4-speed main transmission, and a planetary gear transmission auxiliary transmission in the rear end. The two shafts of the main transmission extend into the power input shaft hole of the half gear pair, and the main transmission shaft is free to rotate on the intermediate shaft. The transmission has a maximum input torque of 1600Nm, a transmission ratio range of 1.00 to 13.63 or 0.85 to 11.46, a reverse gear ratio of 9.41/11.06 or 8.64/10.15, a length of approximately 950 mm and a total mass of approximately 300 kg.
Half-speed combination transmissions are widely used abroad, especially in medium-sized and medium-duty vehicles in Europe, where long-distance buses (including buses) are used more. The engine power of the car is increased from 85 to 200 kW for various vehicles. The length of the half-speed combination transmission is smaller than that of the double-speed combination transmission, and its structure is simple, the cost is low, and the maintenance is easy. Users favor. The medium and heavy-duty automobile engines under the power of 200kWl) basically use a half-speed combination transmission, and the engine power is more than 200kW, and the double-speed (or double-speed plus half-speed) combined transmission is used.
4 Application and development trend of automatic transmission
The automatic transmission can meet the requirements of frequent starting and frequent acceleration of the vehicle, and can continuously accelerate to the highest speed, improve the starting acceleration performance of the vehicle, thereby improving the overall running speed of the whole vehicle, especially the city bus. At the same time, due to the function of the torque converter, the automatic transmission can increase the torque during the starting phase of the vehicle, which is beneficial to the full utilization of the engine power.
Automatic transmissions have been widely used in foreign city buses. Its penetration rate in the United States is basically 100%, and that in Western Europe is 95%. In China, only a few cities in Shenzhen and Shanghai are in use. The ZF, Voith and Allison automatic transmissions represent the international advanced technology. Learning from the experience and advanced technology of foreign transmission development can play a multiplier role. The structural principles and technical features of the two types of transmissions are described below.
4.1 Hydraulic Automatic Transmission (AT)
Compared with manual transmissions, hydraulic automatic transmissions are quite different in construction and use from manual transmissions. The manual transmission is mainly composed of gears and shafts, which generate variable speed torque through different gear combinations. The AT is composed of a hydraulic torque converter, planetary gears and hydraulic control system. The hydraulic transmission and gear combination are used to achieve the variable speed. Moment. Among them, the hydraulic torque converter is the most characteristic component of AT. The pump wheel and the turbine of the torque converter are like two fans placed oppositely. The wind blown by one fan will drive the blades of the other fan to rotate, and the wind becomes the medium for kinetic energy transmission. The liquid is used instead of the air to be the medium for transmitting energy. The pump wheel drives the turbine to rotate through the liquid, and then a guide wheel is added between the pump wheel and the turbine. The reaction speed is used to achieve the speed difference between the pump wheel and the turbine. Change the moment. Since the range of the automatic torque converter of the hydraulic torque converter is not large enough, several rows of planetary gears are connected in series behind the turbine to improve the efficiency, and the hydraulic control system automatically manipulates the planetary gears according to the change of the engine operation, thereby realizing the automatic shifting torque.
Designed for city buses, the Voith automatic transmission is a fully automatic hydraulic mechanical transmission with a torque converter for acceleration and deceleration. Since the input power is divided into two by a differential gear device, its efficiency is higher than that of a general hydraulic transmission.
The main advantages of the hydraulic automatic transmission are as follows:
(1) In the mechanical transmission device, the planetary transmission mechanism has the advantages of compact structure, small mass, small volume, large transmission ratio and high efficiency compared with the conventional gear transmission mechanism.
(2) The AT does not use the clutch to shift gears, the gear position changes little, and the connection is stable, so the operation is easy, which brings convenience to the driver and brings comfort to the passenger. The disadvantage is that the organization is complex, and manufacturing and repair are difficult. Currently used in cars, the future is becoming less and less optimistic.
4.2 Electronically controlled mechanical automatic transmission (referred to as AMT)
The electronically controlled mechanical automatic transmission is based on the traditional fixed-shaft transmission and dry-type clutch. It uses electronic technology, fuzzy control theory and shifting theory. The electronic control unit ECU is the core, and the clutch is controlled by the hydraulic control system. Combined with the selection and shifting operations, the electronic control unit ECU realizes the automatic operation of the vehicle starting and shifting by adjusting the throttle of the engine.
The basic principle of AMT control: according to the driver's meaning (the accelerator pedal, brake pedal, etc.) and the state of the vehicle (engine speed, output shaft speed, vehicle speed, gear position, etc.), according to certain rules (shifting rules, clutch engagement) Regularly, by means of the corresponding actuators (oil supply actuator, shift selection actuator, clutch disengagement and engagement actuator), the vehicle's powertrain (engine, clutch, transmission) is jointly operated to achieve the start, Automatic manipulation of shifts.
The main features of the electronically controlled mechanical automatic transmission are as follows:
(1) Convenient and flexible, it can reduce the labor intensity of drivers and improve driving safety. This is one of the most important features after switching from manual gearshifting to automatic gearshifting.
(2) Economy and fuel economy, extending the service life of vehicles. Compared with the AT, the AMT efficiency is almost the same as that of the mechanical transmission, which is more energy efficient than other automatic transmissions currently used in automobiles, and can improve the degree of environmental pollution.
(3) The structure is simple, easy to install, and convenient for maintenance. Its main shortcomings are two points. First, the car is not steplessly variable, it is classy, ​​there is power interruption during shifting; the second is to have a professional commissioner during loading and commissioning.
4.3 Development trend of automatic transmissions in China
The automatic transmission mainly includes a hydraulic automatic transmission (AT), an electronically controlled mechanical automatic transmission (AMT), and a continuously variable automatic transmission (CVT). The key technologies are electronic technology, electro-hydraulic control and sensing technology. China's current basic industry is difficult to meet AT's high-tech, high-investment requirements, and the engine displacement that matches these products is large, and it is difficult to serialize production AT. For CVT, it is necessary to develop its key component, the hydraulic torque converter, which has excellent performance and can also form a new hydraulic mechanical transmission with AMT, which is the "soul" of the automatic transmission. China's current national conditions should be based on AMT, it is cost-effective, the price is 1/4 to 1/3 of AT, it is still competitive after the World Life; good production inheritance, less investment capital; flexible production volume, small Batch, small gains, large quantities, big gains; compared to various models, its hardware development and software development are structurally and theoretically connected, and the results can be extended to all types of cars.
5 Conclusion
With the development of the domestic automobile market, the transmission product spectrum is gradually refined, and the product is becoming more and more targeted. Therefore, while ensuring the production and improvement of the existing transmission, it is necessary to fully realize the good cooperation and development opportunities after joining the WTO. We must learn from each other's strengths and at the same time recognize the tremendous pressure from suppliers, buyers, substitutes and product competitors. It is necessary to keep up with the trend of high-end, high-tech and intelligent development of the heavy-duty commercial vehicle industry. It is necessary to keep up with the development direction of low-floor, green and environmentally-friendly passenger cars, large-scale urban public transportation, and develop and produce independent intellectual property rights. China's national conditions for heavy-duty vehicle transmissions.
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