First, the basic composition of the automatic transmission
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There are many types of automatic transmissions, and the external shape and internal structure are different, but their composition is basically the same, which is composed of a torque converter and a gear type automatic transmission. Common components are hydraulic torque converters, planetary gear mechanisms, clutches, brakes, oil pumps, filters, pipes, control valve bodies, speed regulators, etc., according to the function of these components, they can be divided into hydraulic The wind turbine, the transmission gear mechanism, the fuel supply system, the automatic shift control system and the shifting control mechanism are five parts.
1. Hydraulic torque converter
The torque converter is located at the forefront of the automatic transmission and is mounted on the flywheel of the engine, which acts like a clutch in a car with a manual transmission. It utilizes the change of kinetic energy during the circulation of oil to transfer the power of the engine to the input shaft of the automatic transmission, and can automatically and steplessly change the transmission ratio and torque ratio within a certain range according to the change of the driving resistance of the vehicle. The deceleration and twisting function.
2. Transmission gear mechanism
The transmission gear mechanism in the automatic transmission is of the type of a common gear type and a planetary gear type. With a conventional gear type transmission, the larger transmission is smaller due to the larger size, and only a few models are used. At present, the gear transmissions in most automatic transmissions of passenger cars are planetary gear type.
The transmission gear mechanism mainly includes a planetary gear mechanism and a shifting actuator.
The planetary gear mechanism is one of the important components of the automatic transmission. It is mainly composed of components such as the sun gear (also called the center wheel), the ring gear, the carrier and the planetary gear. The planetary gear mechanism is a mechanism for realizing the shifting, and the change of the speed ratio is achieved by using different components as the active member and restricting the movement of the different components. During the change of the speed ratio, there is still motion in the entire planetary gear set, and the power transmission is not interrupted, thus realizing power shifting.
The shift actuator is mainly used to change the active components in the planetary gears or to limit the movement of a certain component, to change the direction and speed ratio of the power transmission, and is mainly composed of a multi-plate clutch, a brake and a one-way overrunning clutch. The function of the clutch is to transmit power to an element of the planetary gear mechanism to make it an active part. The function of the brake is to hold a component of the planetary gear mechanism so that it does not move. The one-way overrunning clutch is also one of the shifting components of the planetary gear transmission. Its function is basically the same as that of the multi-plate clutch and brake. It is also used to fix or connect some sun gears, planet carriers, ring gears, etc. in several planetary rows. The basic components allow the planetary gears to form gears with different gear ratios.
3. Oil supply system
The oil supply system of the automatic transmission is mainly composed of an oil pump, a fuel tank, a filter, a pressure regulating valve and a pipe. The oil pump is one of the most important assemblies of an automatic transmission. It is usually mounted behind the torque converter and driven by the sleeve at the rear end of the torque converter housing. When the engine is running, the oil pump is running regardless of whether the car is running or not, and provides hydraulic oil of a certain hydraulic pressure for the torque converter, the shifting actuator, and the automatic shift control system of the automatic transmission. The adjustment of the oil pressure is achieved by a pressure regulating valve.
4, automatic shift control system
The automatic shift control system can automatically turn on or off the oil supply passages of some shifting clutches and brakes according to the set shift schedule according to the load of the engine (throttle opening) and the running speed of the vehicle. The clutch is coupled or disengaged, the brake is braked or released to change the transmission of the gear transmission, thereby achieving automatic shifting.
The automatic shift control system of the automatic transmission has two types of hydraulic control and electrohydraulic (electronic) control.
The hydraulic control system is composed of a valve body and various control valves and oil passages. The valve and the oil passage are arranged in one plate, which is called a valve body assembly. Different types of automatic transmission valve body assemblies are installed at different positions, some are on the upper part, some are on the side, and the vertical automatic transmission is generally installed on the lower part.
In the hydraulic control system, the addition of a solenoid valve that controls certain hydraulic circuits becomes a shift control system for electrical control. If these solenoid valves are controlled by an electronic computer, they become an electronically controlled shifting system.
5, shift control mechanism
The shift operating mechanism of the automatic transmission includes an operating mechanism that manually selects the valve, an operating mechanism of the throttle valve, and the like. The driver changes the position of the manual valve in the valve plate through the joystick of the automatic transmission. The control system uses the hydraulic automatic control principle or the electronic automatic control principle according to the position of the manual valve and the throttle opening degree, the vehicle speed, the state of the control switch and the like. The work of the shifting actuator in the gear transmission is controlled according to a certain rule to realize automatic shifting.
Second, the working process of the automatic transmission
The reason why the automatic transmission can realize automatic shifting is because the position of the driver stepping on the throttle or the vacuum degree of the engine intake manifold and the driving speed of the vehicle can command the automatic shifting system to work, and the control valves in the automatic shifting system Different working states will control the separation and combination of the clutch in the transmission gear mechanism and the braking and release of the brake, and change the power transmission path of the transmission gear mechanism to realize the transformation of the transmission gear.
The conventional hydraulic automatic transmission automatically shifts gears according to changes in the traveling speed of the car and the throttle opening. The shift control mode is to mechanically convert the vehicle speed and the throttle opening signal into control oil pressure, and add the oil pressure to both ends of the shift valve to control the position of the shift valve, thereby changing the shift execution. The oil path of the components (clutch and brake). In this way, the working hydraulic oil enters the corresponding actuator, the clutch is engaged or disengaged, the brake is braked or released, and the upshift or downshift of the planetary transmission is controlled to achieve automatic shifting.
The electronically controlled hydraulic automatic transmission is formed by adding an electronic control system based on the hydraulic automatic transmission. It monitors the running state of the car and engine through sensors and switches, accepts the driver's instructions, and converts the obtained information into an electric signal input to the shift valve of the electric hydraulic control device, causing it to open or close to the shifting gear. The oil path of the clutch and brake controls the shifting time and the shift of the gear to achieve automatic shifting.
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