What are the structures of automobile automatic transmission?
I. Introduction
Automobile automatic transmission refers to automatically changing the transmission ratio, adjusting or changing the power output performance of the engine, transmitting power economically and conveniently, and better adapting to the needs of external loads and road conditions. Automatic transmission has developed rapidly since 1939, when General Motors first used automatic transmission in automobiles. Especially after the application of electronic technology and microprocessor in gear shifting, the long-sought automatic transmission technology has entered a brand-new period of rapid development. Since 198 1, some automobile companies in the United States and Japan have successively developed various microcomputer-controlled automatic transmission systems, such as electronically controlled hydraulic torque-changing automatic transmission and electronically controlled multi-stage gear transmission. The electronically controlled transmission (ECT) produced by Toyota Company of Japan was first applied to the luxury Crown car. The advantages of this microcomputer-controlled four-speed transmission are: it can ensure the best shift law, good shift accuracy, good fuel economy and satisfactory power performance, and reduce pollution; Flexible shifting, smooth shifting process, no impact and vibration, good shifting quality, comfortable driving and accurate and timely shifting action; The control system works stably and reliably, and can work normally under high and low temperature, large bumps, impact vibration, strong magnetic field and electronic interference; Drivers can intervene in automatic gear shifting to adapt to complex traffic conditions and terrain conditions; The control system has self-correcting gear shifting and high-sensitivity self-diagnosis function; The operation is simple, and the safety and reliability of vehicles can be greatly improved in traffic jams. Due to the above reasons, automatic transmissions have been widely used in cars, buses, large buses, off-road vehicles and heavy tractors, and the loading rate has increased rapidly, especially in cars produced in the United States, Japan, Germany and other countries, the proportion of electronically controlled transmissions is getting higher and higher. Of course, the electronically controlled automatic transmission also has some shortcomings, such as complex structure, high precision requirements for parts, great manufacturing difficulty, high cost, complicated corresponding maintenance technology and lower transmission efficiency than manual transmission.
At present, the main feature of the development of electronically controlled automatic transmission is to realize multi-parameter and multi-rule control of one machine, and on this basis, the microcomputer controlling the transmission and the microcomputer controlling the engine are integrated to realize its comprehensive control. One machine, one control, multi-parameter diversification, that is, the control parameters include not only signals such as engine speed, vehicle speed and throttle opening, but also signals reflecting the working environment of the engine and transmission and the driving environment of the vehicle, which can fully reflect the actual working conditions of the engine and transmission. Multi-laws refer to storing multiple shift laws in the control microcomputer at the same time, such as the best economic shift law and the best dynamic shift law. The driver can call the corresponding laws as needed to achieve the best shift control. The so-called comprehensive control is to delay the ignition time of the engine while the microcomputer of the engine and transmission processes the signals, so that the output torque of the engine is slightly reduced, the impact phenomenon in the transmission process is greatly reduced, and the transmission performance is obviously improved. The block diagram of integrated control is shown in figure 1- 1.
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Figure 1- 1 integrated control block diagram
1- engine; 2- automatic transmission; 3- Engine control signal; 4- variable speed control signal; 5- Microcomputer for engine control 6- Engine control signal; 7- Engine speed state control signal; 8- Microcomputer for variable speed control; 9- Engine and variable speed control unit ECU；; 10- throttle position sensor; 1 1- speed sensor (in the transmission); 12- speed sensor (in speedometer); 13- water temperature switch; 14- shift mode selector switch; 15- neutral start switch; 16- stop light switch; 17- variable speed control switch
Secondly, in order to improve the transmission efficiency and fuel economy, the electronically controlled automatic transmission generally adopts the locking hydraulic torque converter. In a front-engine front-wheel drive vehicle (FF), in order to reduce the weight and shorten the power transmission route, an automatic transmission and a drive axle are usually combined to form an automatic drive axle. In order to broaden the speed range and narrow the transmission ratio range, automatic transmission is developing to multi-speed, and four-speed transmission has generally become the standard structure of cars, and five-speed automatic transmission has already been put on the market. In order to facilitate the use and maintenance, the diagnostic function of the control system is constantly enhanced. In addition, the world's major automobile companies are very active in the research of CVT, and it is estimated that electronically controlled CVT will be used in modern automobiles in a short time.
Second, the composition of electronic automatic transmission
Electronically controlled automatic transmission usually consists of five parts: hydraulic torque converter, planetary gear transmission system, shift actuator, hydraulic automatic control system and electronic control system. Figure 2- 1 is the structural diagram of a typical four-speed automatic transmission.
1. Hydraulic torque converter
Hydraulic torque converter is an indispensable core component of electronically controlled automatic transmission, which can continuously and automatically transfer the torque from the input shaft to the output shaft. It is a typical hydraulic transmission device. At present, the single-stage integrated hydraulic torque converter (Figure 2-2) composed of pump impeller, turbine and guide wheel is widely used in automobiles, which has the advantages of simple structure, reliable operation and good performance. Hydraulic torque converter is actually a kind of hydraulic automatic transmission which can automatically and continuously change the torque. In addition to the above three main components, some torque converters also have lockup clutches. The lock-up clutch is located at the front end of the turbine and is a fully automatic clutch directly controlled by hydraulic pressure. Its operation is controlled by the computer control system, that is, the computer control system controls the electromagnetic valve according to the signals input by the engine speed sensor and the vehicle speed sensor, and the electromagnetic valve locks or separates the locking clutch by controlling the flow direction of the working fluid (ATF) in the oil path leading to the torque converter.
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Figure 2-2 Composition of Hydraulic Torque Converter
The torque converter is filled with automatic transmission oil, which is provided by the oil supply pump. The oil supply pump also provides constant pressure and quantitative working fluid for each system of the automatic transmission, completing tasks such as torque transmission, control, lubrication and cooling. The oil supply pump is usually driven by the claw of the wheel sleeve of the torque converter pump.
Hydraulic torque converter has the ability of automatic adaptation and torque change, and its main feature is that the torque change ratio K(K= turbine output torque/pump wheel input torque) changes with the relative speed of turbine and pump wheel (pump wheel speed is equal to engine speed), that is, it changes automatically and steplessly with the speed ratio i(i= turbine speed/pump wheel speed). When the vehicle speed is low, the hydraulic torque converter can output larger torque, and when the vehicle speed is high, the high efficiency of the hydraulic coupling can be used, so it combines the dual advantages of hydraulic components and is called the comprehensive hydraulic torque converter, which is just suitable for the characteristics of vehicle driving resistance change.
2. Gear speed change system
Although the hydraulic torque converter can transmit and increase the engine torque, the torque ratio is not large and the speed range is not wide, which is far from meeting the needs of automobiles. Therefore, an auxiliary speed change device-gear speed change system, mostly planetary gear speed change system or parallel shaft (fixed shaft) gear speed change system, is installed behind the hydraulic torque converter to further increase the torque, expand its speed change range and improve the adaptability of the automobile. Planetary gear transmission system is a kind of constant meshing transmission, and its transmission ratio can be easily realized by the separation and combination of clutch or brake, which is especially beneficial to power shift or automatic shift. The planetary gear transmission system of electronically controlled automatic transmission is generally composed of two rows of stars or three rows of stars, and three degrees of freedom transmission is widely used. Figure 2-3 is a schematic diagram of a double-row planetary gear transmission, which has two single-row planetary gears on the same shaft. The two rows of planetary gears are connected through a hollow sun gear, and the sun gear meshes with the planetary gears of the two planetary gears. This double-row planetary gear transmission has a forward gear and a reverse gear, and is usually installed on a FR car driven by a front engine.
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Figure 2-3 Schematic diagram of three-speed planetary gear transmission
C 1- front clutch; C2- rear clutch; B3 B2 b 1- brake; F 1, F2- one-way clutch
If an overspeed planetary row is added to the above three-speed automatic transmission, a four-speed automatic transmission can be formed, and the transmission ratio can be made smaller than 1 by overspeed. In FR vehicles, the overspeed planetary gear train is installed between the hydraulic torque converter and the three-speed planetary gear transmission, and in FF vehicles with front engines, the overspeed planetary gear train is installed behind the three-speed planetary gear transmission. The overspeed planetary row is mainly composed of a planetary row, which is used to clamp the overspeed brake Bo of sun gear and the overspeed clutch C connecting the sun gear and the planetary carrier. And the power is input by the gear ring in the overspeed planetary row and transmitted to the overspeed planetary carrier. Figure 2-4 is the principle of a four-speed planetary gear transmission.
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Figure 2-4 Transmission Principle of Four-speed Planetary Gear Transmission
C0- overspeed clutch; B0- overspeed brake; F0- overspeed one-way clutch
3. Shift actuator
The shift actuator of planetary gear transmission includes shift clutch, shift brake and one-way clutch.
Shift clutch is a kind of wet multi-disc clutch, which is controlled by hydraulic pressure and usually consists of several staggered master-slave clutch plates.
Shift braking is to fix an element (sun gear, planet carrier or ring gear) in planetary gear transmission so that it can't rotate, form a new power transmission route, change to a new gear and obtain a new transmission ratio. It is hydraulically operated like a shift clutch. There are usually two kinds of shift brakes: one is a wet multi-disc brake, which has the same structure as the above-mentioned wet multi-disc clutch, but the difference is that the clutch connects two rotating parts and transmits power, one of which is connected with the rotating parts, and the other is a fixed transmission housing, which is used to stop the rotating parts and make them unable to drive. Another type of shift brake is a band brake.
The function of one-way clutch in planetary gear transmission is to ensure smooth shift without impact. It has the same structure as the one-way clutch in hydraulic torque converter, and consists of inner and outer rings and a wedge between them.
4. Hydraulic automatic control system
Hydraulic automatic control system usually consists of oil supply, manual gear selection, parameter adjustment, shift timing control and shift quality control. The oil supply part includes oil supply pump, oil filter, main oil circuit pressure regulating valve, second pressure regulating valve, oil cooler, etc. The oil supply pump and the main oil circuit pressure regulating valve are the power sources of the hydraulic automatic control system, and the second pressure regulating valve is also called the torque converter compensation pressure regulating valve.
Manual gear selection part includes manual control valve and manual control valve turntable. The manual control valve is controlled by the gear lever, and its function is to realize the conversion of the control oil path by the movement of the slide valve, that is, the hydraulic oil is converted to the oil path of "P", "R", "N", "D", "2" or "L" according to the gear set by the gear lever.
The parameter adjustment part mainly includes two aspects: first, the throttle pressure regulating valve (throttle for short) is used to generate the accelerator pedal control hydraulic pressure according to the throttle opening, and this control hydraulic pressure is added to one end of three shift valves (transmission valves): 1-2, 2-3 and 3-4, and when the throttle opening becomes larger, the accelerator pedal control hydraulic pressure will increase; The second is the speed regulating and pressure regulating valve (also called governor), which is used to generate the hydraulic pressure controlled by the vehicle speed according to the vehicle speed and add this speed regulating hydraulic pressure to the other end of each shift valve. When the vehicle speed increases, the speed control hydraulic pressure increases. The shift valve changes gear according to the above two parameters. In the electronically controlled automatic transmission, the throttle opening and the vehicle speed are collected by the throttle position sensor and the vehicle speed sensor, respectively, and sent to the computer, and the computer controls the shift valve to automatically shift gears through the solenoid valve.
The shift timing control part is mainly the shift valve. In the electronically controlled automatic transmission, the shift valve works according to the shift point and shift signal determined by the electronic controller and automatically shifts gears.
The function of shift quality control mechanism is to control the shift process, make the shift more stable, soft and impact-free, and prevent the generation of large dynamic load. Generally, there are energy storage shock absorbers, buffer valves, timing valves and executive control valves. Is added to the hydraulic passage.