The automatic transmission can automatically change the transmission ratio according to the engine load and the vehicle speed, so that the vehicle can obtain good power and fuel economy, and reduce engine emission pollution. The automatic transmission is easy to handle, and when the vehicle is crowded, the safety and reliability of the vehicle can be greatly improved.
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The electronically controlled automatic transmission usually consists of a hydraulic torque converter, a planetary gear shifting system, a shifting actuator, a hydraulic operating system, and an electronic control system.
How does the torque converter work?
At present, a single-stage two-phase three-element lock-type integrated hydraulic torque converter composed of a pump wheel, a turbine and a guide wheel is widely used in a car. The pump wheel and turbine are both basin-shaped. The pump wheel is integrated with the torque converter casing and is an active component; the turbine is suspended in the torque converter and connected to the output shaft through a spline, which is a driven component; the guide wheel is suspended between the pump wheel and the turbine through the one-way The clutch and the guide bushing are fixed to the transmission housing.
After the engine is started, the crankshaft drives the pump wheel to rotate, and the centrifugal force generated by the rotation causes the working fluid between the pump wheel blades to be thrown out along the blade from the inner edge to the outer edge; this part of the working fluid has both the circumferential direction of the rotation with the pump wheel. The split speed has an axial split speed that rushes toward the turbine. These working fluids impact the turbine blades and push the turbine to rotate in the same direction as the pump wheel.
The velocity v from the turbine flowing out of the working fluid can be seen as a combination of the partial velocity ω of the working liquid phase flowing out of the turbine blade surface and the rotational velocity u along with the turbine. When the turbine speed is relatively small, the working fluid flowing out of the turbine is backward, and the working fluid impacts the front of the guide vane. Since the guide wheel is not allowed to rotate backward by the one-way clutch, the guide vane guides the backward flowing working fluid to push the pump wheel blade forward, thereby promoting the rotation of the pump wheel, thereby increasing the torque acting on the turbine.
As the turbine speed increases, the partial velocity u also becomes larger. When the combined velocity v of ω and u starts to refer to the back surface of the guide vane, the torque converter reaches the critical point. As the turbine speed increases further, the working fluid will impact the back of the stator blades. Because the one-way clutch allows the guide wheel to rotate forward together with the pump wheel, the guide wheel is free to rotate in the direction of rotation of the pump wheel under the driving of the working fluid, and the working fluid smoothly returns to the pump wheel. When the working fluid flowing out of the turbine coincides with the direction of the exit of the guide vane, the torque converter does not produce a twisting effect (the working condition of the torque converter is called the hydraulic coupling condition).
The torque converter transmits torque by the working fluid, which is lower than the transmission efficiency of the mechanical transmission. The lock-up clutch is arranged in the torque converter, and the pump wheel and the turbine can be locked together under high-speed working conditions to realize direct power transmission and improve the transmission efficiency of the torque converter.
How planetary gears work
Although the torque converter can transmit and increase the engine torque, but the torque ratio is not large, the shift range is not wide, and it is far from meeting the needs of the vehicle. In order to further increase the torque, expand its shift range, and improve the adaptability of the car, an auxiliary transmission, a stepped gear transmission, is installed behind the torque converter. Most of the gears are geared with planetary gears.
The planetary gear transmission is composed of a planetary gear mechanism and actuators such as a clutch, a brake and a one-way clutch. 3. Planetary gear mechanisms usually consist of multiple planetary rows. The number of planet rows is related to the number of gears.
The shifting actuators of the star gear transmission include a shifting clutch, a shifting brake, and a one-way clutch.
The shifting clutch is a wet multi-plate clutch. When the hydraulic pressure causes the piston to press the driving piece and the driven piece, the clutch is engaged; when the working fluid is discharged from the piston cylinder, the return spring retracts the piston to separate the clutch.
Shift brakes are generally available in two forms: one is a wet multi-plate brake that is constructed in much the same way as a wet multi-plate clutch, except that the brake is used to connect the rotating member to the transmission housing so that the rotating member cannot rotate.
Another form of shift brake is an external beam brake.
The one-way clutch of the planetary transmission has the same structure as the one-way clutch in the torque converter.
Control of hydraulic mechanical transmission automatic transmission
The hydraulic automatic control system usually consists of oil supply, manual gear selection, parameter adjustment, shift timing control, shifting sp. The oil supply section adjusts the oil pressure of the oil pump to the specified according to the change of the throttle opening and the selector lever position. The value forms a stable working hydraulic pressure.
In the hydraulically controlled hydraulic automatic transmission, the parameter adjustment part mainly includes a throttle pressure regulating valve (referred to as a throttle valve) and a quick control pressure regulating valve (also called a governor). The throttle pressure regulating valve allows the output hydraulic pressure to reflect the throttle opening; the quick-control pressure regulating valve allows the output hydraulic pressure to reflect the speed of the vehicle.
The shift timing control portion is for switching an oil passage leading to each shift actuator (clutch and brake), thereby implementing shift control.
The lock signal valve is controlled by the solenoid valve to properly engage and disengage the lockup clutch in the torque converter.
The shift quality control section is used to make the shifting process smoother and softer.
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