Technical characteristics and development trend of heavy vehicle transmission
Heavy-duty vehicle transmission refers to a transmission that is matched with heavy-duty commercial vehicles and large passenger vehicles. Although there is no clear limit on the capacity of transmissions in the industry, we usually refer to automotive transmissions with a nominal input torque of more than 900Nm as heavy-duty automotive transmissions.
1 Structural characteristics of foreign heavy vehicle transmissions
In foreign countries, specialized transmission manufacturers attach great importance to product serialization, which provides great convenience and flexibility for the OEM to choose the most satisfactory transmission. For example, the German ZF (ZF) company has 7 base transmissions with a center distance of 8.0, 95, 105, 115, 120, 143, and 154mm. It can adapt to an input torque of 130-1900Nm, and the number of gears ranges from 3-17. There are various The transmission of the operation mode is suitable for vehicles with different matching requirements. Japan Toyota Motor Corporation Aisin Seiki Co., Ltd. has five basic combinations of center distance 72, 78, 88, 98, 135mm, and 286 transmissions for users to choose. However, many automobile transmission manufacturers in China have not yet formed their own series of transmission products.
The 9S109 synchronizer double-gear 9-speed combination transmission produced by the German ZF company has 5 forward gears for the main transmission and a planetary gear train transmission structure for the auxiliary transmission. When the synchronizer sleeve in the auxiliary transmission is engaged with the fixed external ring gear, the planetary gear ring gear is fixed and cannot rotate, then the auxiliary transmission is engaged in low gear, and the main transmission is respectively engaged in 5 different gears. 5 large transmission ratios of combined transmission. When the coupling sleeve is engaged with the high-grade ring gear of the auxiliary transmission, the planetary gear shaft, the output shaft, the planetary gear ring gear and the auxiliary transmission input shaft gear are fixed together and rotate synchronously, then the auxiliary transmission is engaged in high gear (direct gear), the main The five gear ratios of the transmission are respectively equal to the combined transmission.
A smaller transmission ratio. Since there are two transmission ratios that are very close, one transmission ratio is omitted and a 9-speed transmission is formed. The maximum input torque of the transmission is 1250Nm, and the total mass is 310kg. It is directly connected to the engine or installed independently, left horizontal or right horizontal. The control system of the transmission is remotely or directly operated by the rotating shaft. The double XH type shift arrangement is arranged. The auxiliary transmission is automatically shifted by compressed air. The creep gear and reverse gear are shifted by mesh sleeves. The other gears are shifted by synchronizers.
Structural Features of Fuller Series Double Countershaft Transmission of Eaton Corporation
The BT-11509C dual countershaft double-gear 9-speed combined mechanical transmission produced by Eaton in the United States adopts a dual countershaft structure for both the main and auxiliary transmissions. The main transmission has 5 forward gears. The auxiliary transmission is a 2-speed (high-end and low-speed) gear transmission. Because there are 2 transmission ratios very close, one is omitted and a 9-speed transmission is formed.
Double countershaft double-gear combined transmission has the following advantages:
(1) Since the gears on the first and second shafts mesh with the corresponding gears on the two intermediate shafts at the same time, the power is divided. In theory, the torque transmitted on each pair of gears is 1/2, which makes each The torque transmitted to the gears is reduced by 50%, so that the center distance, gear modulus and width of the transmission can be reduced, thereby reducing the quality and size of the transmission, especially the length.
(2) Because the two-shaft driven gear is in a radial floating state on the shaft, the axis lines of the two intermediate shafts are evenly distributed on the cylindrical surface with the two-axis theoretical axis as the center and the center distance as the radius. The radial forces generated by the gears on the shaft and the gears of one shaft meshing with the corresponding gears on the two intermediate shafts are balanced, that is, they cancel each other out. The two shafts do not bear radial forces and only transmit torque. In this way, the two shafts can be designed thinner and the structure can be simpler. The rear bearing can be selected to a smaller size, which also helps reduce the mass and size of the transmission.
(3) Due to the radial floating of the two-axis gear and the articulated type of the two-axis
As a result of the floating, the gears can automatically offset part of the manufacturing and assembly errors when meshing, and the meshing quality is better than the single countershaft. The meshing area is easy to meet the design requirements, and the actual use has confirmed this. This is beneficial to reduce meshing noise and improve durability.
(4) Since the double countershaft double-gear combined transmission can significantly reduce the mass and axial size of the transmission, the use of this advantage can increase the maximum transmission power and torque of the transmission and expand the range of use.
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 from the left or the right, with a total mass of 270kg.
2 Structural characteristics of domestic mechanical heavy vehicle transmissions
The technology of domestic heavy-duty vehicle transmission products mostly comes from the United States, Germany, and Japan. The imported technologies are mostly foreign products from the 1980s to the 1990s. As a long-term domestic introduction and digestion process of heavy-duty automobile transmissions in the field of advanced automotive technology, there has been considerable progress. Based on the introduction of original technologies, we can develop new products that meet the supporting requirements by retrofitting. More than a dozen new products can be introduced to the market in the transmission industry. However, judging from the development of today's heavy-duty vehicle transmissions, domestic heavy-duty vehicle transmissions still follow a general development process in the development of new products, and there is no real core technology product; from the perspective of the domestic heavy-duty vehicle transmission market capacity, there are three One-third of the products come from imports, and more than 80% of the other two-thirds of the products are derived from foreign technology. The sales volume of domestically developed heavy-duty automobile transmission products is very small, indicating that the independent development capabilities of domestic heavy-duty automobile transmission manufacturers are still It is very weak, and the ability to deal with supporting products of new models of the whole vehicle is far from enough. China's urban vehicles will focus on the development of the 13.8m passenger car transmission. At present, only ZF can supply domestic companies, which is enough to show that the domestic heavy-duty transmission companies are still very small, and still have a long way to go in terms of technology.
Domestic heavy-duty automobile transmissions are almost taken over by Shaanxi Fast Gear Co., Ltd., Qijiang Gear Transmission Co., Ltd., Shanxi Datong Gear Group Co., Ltd., and FAW Harbin Transmission Plant. The transmission products produced by these companies have different focuses on the market. For example, Shaanxi Fast has a market share of more than 40% in heavy vehicles above 8t, and has an absolute advantage in the heavy vehicle market above 15t, with more than 85% market share. ; Qijiang Gear Transmission Co., Ltd. is mainly for the 7-12m high-end large and medium-sized passenger cars of Ankai, Xiwo, Yaxing Benz, Guilin Daewoo and Xiamen Jinlong, as well as heavy trucks and saddle tractors with a total mass of 14-50t , Dump trucks and all kinds of special vehicles and special vehicles; Shanxi Datong Gear Group's supporting market is mainly 8 to 10t low-ton heavy-duty trucks.
3 Technical characteristics of mechanical heavy vehicle transmission
Heavy trucks have a large loading quality and complicated use conditions. To ensure that the heavy-duty vehicle has 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 convenient for serial production, the combined mechanical transmission is mostly used. That is, one or two types of 4 to 6 speed transmissions are the main body. By replacing the series of gear pairs and configuring different auxiliary transmissions, a set of transmission series with different gear positions and different transmission ratio ranges is obtained. At present, the combined mechanical transmission has become the main type adopted by heavy vehicles. Combined mechanical transmissions are generally divided into double-speed (segmented gear) combined mechanical transmissions and half-speed (inserted gears) combined mechanical transmissions.
3.1 Double gear combined mechanical transmission
The double-shift combined mechanical transmission is to install a 2-speed (high-end and low-speed) auxiliary transmission in series at the rear of the main transmission, which doubles the number of gears of the main transmission. The value of the increased gear ratio is equal to the main transmission gear ratio and The product of the transmission ratio of the auxiliary transmission, and the number of gear pairs is less than the number of gears, so the size of the box is shortened, the length of the shaft is shortened, and the rigidity is increased, so the capacity of the transmission is increased. For example, at the rear end of a 5-speed main transmission, a secondary 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-gear combined transmission is that the strength and capacity of the low gear of the auxiliary transmission is insufficient, exceeding the load capacity of the gear teeth. The solution is to shunt the load carried by one gear tooth to several gear teeth. In this way, the input gear torque remains unchanged, and the load of each gear tooth will be equal to the average value of the number of teeth in contact at the same time.
There are two power split methods for the auxiliary transmission of the double-gear combined transmission: one is the transmission method using the planetary gear system. This structure is very compact, small in size and large in torque capacity, and it is still widely used until now; another power split The method is to use double countershaft transmission structure. The biggest technical difficulty of the double countershaft transmission is to ensure that the main transmission gear can simultaneously contact the gear teeth of the engaged double countershaft gear. The solution is to use the floating main transmission gear to eliminate the manufacturing error of the tooth shaft alignment and ensure that The gear teeth are in contact at the same time to achieve the purpose of power distribution. The shift synchronizer adapted to this also has a certain amount of float.
3.2 Half-speed combined mechanical transmission
The gear ratio of the auxiliary transmission is evenly inserted between the gear ratios of the main transmission with a large gear ratio interval, which doubles the number of gears of the transmission. The half-speed auxiliary transmission is connected in series at the front of the main transmission. It has only a pair of gear pairs and a shift synchronizer. The early half-speed auxiliary transmission consisted of a single box. In recent years, it has been developed to place the half-speed gear pair directly into the main transmission, which not only shortens the transmission length but also simplifies the half-speed structure. The half-speed auxiliary transmission is composed of a pair of constant-mesh gear pairs similar to a shaft. The ring gear is freely rotated on the power input shaft. When the ring gear on the power input shaft is combined with the main transmission shaft, the transmission ratios of each gear are controlled by the main transmission. One shaft gear pair. When the ring gear is connected with the engagement teeth on the power input shaft, the constant meshing gear is connected with the intermediate shaft on the main transmission, so the main shaft of the main transmission also rotates, and the gear ratios composed of these are evenly inserted into the gears of the main transmission Between transmission ratios. The model ZFAK / 6-80 ten GV80 half-gear combined mechanical transmission is composed of a 6-speed AS6-80 main transmission and a series of half-gear auxiliary transmissions. The maximum input torque is 750Nm, the transmission ratio range is 0.83 ～ 9.0, and the reverse transmission ratio is 7.05 / 8.46. This 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 Company is equipped with a pair of half-gear gear pairs and other mechanisms at the front end of the 4-speed main transmission, and then a planetary gear transmission auxiliary transmission is connected in series at the rear end. The second shaft of the main transmission has been extended into the power input shaft hole of the half gear pair, and the first shaft of the main transmission is free to rotate on the intermediate shaft. The maximum input torque of the transmission is 1600Nm, the transmission ratio range is 1.00 ～ 13.63 or 0.85-11.46, the reverse transmission ratio is 9.41 / 11.06 or 8.64 / 10.15, the length is about 950mm, and the total mass is about 300kg.
Half-gear combined transmissions are widely used abroad, especially in European medium- and heavy-duty vehicles. This type of transmission is widely used, of which long-distance vehicles (including coaches) are used more. Various vehicles with car engine power ranging from 85 to 200kW use half-speed auxiliary transmissions to increase gears, because the length of the half-speed combined transmission is shorter than that of the double-speed combined transmission, and its simple structure, low cost, easy maintenance and maintenance Favored by users. Foreign medium and heavy-duty vehicles with engine power of 200kW) basically use half-speed combination transmissions, and those with engine power above 200kW mostly use double-speed (or double-speed plus half-speed) combined transmissions.
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 to improve the starting acceleration performance of the vehicle, thereby improving the overall running speed of the entire vehicle, especially the city bus. At the same time, due to the effect of the torque converter, the automatic transmission can increase the torque during the starting stage of the vehicle, which is conducive to the full use of engine power.
Automatic transmissions have been widely used in foreign urban buses. Its penetration rate in the United States is basically 100%, and that in Western Europe is 95%. However, only a few cities in Shenzhen and Shanghai are using it in China. Representing the international advanced technology level are ZF, Voith and Allison. Learning from the experience and advanced technology of foreign transmission development can play a multiplier role. The structural principles and technical characteristics of the two transmissions are introduced below.
4.1 Hydraulic automatic transmission (referred to as AT)
Compared with the manual transmission, the hydraulic automatic transmission is very different in structure and use from the manual transmission. The manual transmission is mainly composed of gears and shafts, and the variable speed torque is generated through different gear combinations; while the AT is composed of a hydraulic torque converter, planetary gears, and a hydraulic control system. The variable speed is achieved through the combination of hydraulic transmission and gears. Moment. Among them, the hydraulic torque converter is the most characteristic part of AT. The pump wheel and turbine of the hydraulic torque converter are like two fans placed oppositely. The wind blown by one fan will cause the blades of the other fan to rotate, and the wind becomes the medium for kinetic energy transmission. Using liquid instead of air as the medium to transfer energy, the pump wheel will drive the turbine to rotate through the liquid, and then add a guide wheel between the pump wheel and the turbine, and realize the speed difference between the pump wheel and the turbine through the reaction force. Moment changed. Since the torque conversion range of the automatic torque converter is not large enough, several rows of planetary gears are connected in series behind the turbine to improve efficiency. The hydraulic control system will automatically control the planetary gears according to the changes in engine operation, thereby achieving automatic transmission torque conversion.
The Voith automatic transmission is dedicated to city buses and is a fully automatic hydraulic mechanical transmission whose torque converter is used 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 ordinary gear transmission mechanism.
(2) AT does not need clutch to change gears, the gears change little, the connection is stable, so the operation is easy, which brings convenience to the driver and comfort to the passengers. The disadvantage is that the mechanism is complex, and it is more difficult to manufacture and repair. Currently used in cars, the future is becoming less promising.
4.2 Electronically controlled mechanical automatic transmission (AMT for short)
Electronically controlled mechanical automatic transmission is based on the traditional fixed-shaft transmission and dry clutch, applying electronic technology, fuzzy control theory and transmission theory, taking the electronic control unit ECU as the core, and controlling the clutch separation and In combination with the gear selection and shifting operations, the electronic control unit ECU is used to realize the automatic operation of starting and shifting of the vehicle through the adjustment of the engine throttle.
The basic principle of AMT control: according to the driver's intention (accelerator pedal, brake pedal, etc.) and the state of the vehicle (engine speed, output shaft speed, vehicle speed, gear, etc.), according to certain rules (shift law, clutch engagement Laws, etc.), with the help of corresponding actuators (fuel supply actuators, shift selection actuators, clutch disengagement and engagement actuators), the vehicle's drivetrain (engine, clutch, transmission) is jointly operated to achieve Automatic operation of shifting.
The main features of the electronically controlled mechanical automatic transmission are as follows:
(1) Convenient and flexible, can reduce the labor intensity of the driver and improve driving safety This is one of the most important features after shifting from manual gearshift to automatic gearshift.
(2) Economical and fuel-efficient, extending the service life of vehicles. Compared with AT, the efficiency of AMT is almost the same as that of mechanical transmission, which saves energy and improves the degree of environmental pollution than other automatic transmissions currently used in automobiles.
(3) The structure is simple, easy to install, and easy to maintain. Its main disadvantages are twofold. One is that the car is not continuously variable, it is stepped, and there is an interruption of power when changing gears; the second is that there must be a professional debugger when loading and commissioning.
4.3 Development Trend of Automatic Transmission in my country
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 technology is electronic technology, electro-hydraulic control and sensing technology. The current basic industry in China is difficult to meet the high technology and high investment requirements of AT. In addition, the engine displacement matching these products is very different, and it is difficult to serialize the production of AT. For CVT, it is necessary to develop its key component-hydraulic torque converter, which has excellent performance and can also form a new hydraulic mechanical transmission with AMT, which is the "soul" of automatic transmission. China's current national conditions should be based on AMT. It is cost-effective and the price is 1/4 to 1/3 of AT. It is still competitive after the world's death; good inheritance of production, less investment in transformation funds; flexible production volume, small Compared with various models, the hardware development and software development are structurally and theoretically similar, and the results can be extended to various types of cars.
5 Conclusion
With the development and growth of the domestic automotive market, the transmission product spectrum is gradually refined, and the product is more and more targeted. Therefore, while ensuring the production and improvement of the existing transmission, we must fully recognize the good cooperative development opportunities after entering the WTO To learn from each other ’s strengths, while at the same time recognizing the tremendous pressure from suppliers, buyers, substitutes and product competitors. It is necessary to keep up with the development trend of the heavy-duty commercial vehicle industry towards high-end, high-tech content and intelligence, and to closely follow the development direction of low-floor passenger cars, green environmental protection and large-scale urban public transportation. Development and production have independent intellectual property rights and are suitable for The transmission for heavy vehicles in China.
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