Automatic transmission (AT)
Manual transmissions require high skilled operating skills for drivers, while automatic transmissions do not require too high operational skills.
Nowadays, many automatic transmissions installed by automatic gear cars are controlled by hydraulic pressure. This kind of transmission is mainly composed of hydraulic torque converter and planet gear transmission.
The transmission is controlled by electronic control system (ECU) and hydraulic pressure, so that it can automatically complete the transmission.
The hydraulic torque converter acts as a clutch in the manual transmission, as well as as a torque converter, which can transfer the power of the engine to the planet gear transmission.
The structure of automatic transmission
Hydraulic torque converter
The hydraulic torque converter is composed of input pump wheel, output turbine and guide wheel. It transmits the power of the engine to the planet gear transmission through hydraulic oil.
When the pump wheel rotates, the hydraulic oil is fed into the turbine to make the vortex. The wheel rotates.
Even if you step on the brake pedal, the hydraulic oil between the pump wheel and the turbine will continue to flow and produce friction, so the engine will continue to run, and release the brake pedal.
even if you do not step on the throttle pedal, the vehicle can move forward slowly (creep phenomenon).
In addition, due to the speed difference between the input and output ends, the torque will increase, which is why the torque obtained by the car at start-up is greater than the output torque of the engine.
The hydraulic oil circulates between the pump wheel and the turbine, thus increasing the torque. There is a hydraulic oil that can flow freely between the input and the output.
so the hydraulic torque converter can form an automatic clutch state.
Some automatic transmissions are provided that when the speed increases to the same speed as the speed of the turbine and the pump wheel, the two are automatically connected to automatically transmit the torque of the engine.
Planet gear transmission
Fine variable speed can not be realized in hydraulic torque converter, but can be realized in planet gear transmission. A unit in a planet gear transmission consists of a central solar gear.
an outer gear ring, a planet gear between the sun gear and the tooth ring, and a planet rack.The planet gear transmission changes the input force and output force by fixing different components.
so as to complete the variable speed or reverse operation. The planet gear transmission is controlled by oil pressure, so the oil pressure control mechanism is also installed in the automatic transmission.
Characteristics of planet gear transmissions:
Change the transmission ratio to meet the needs of traction force under different driving conditions
Transfer large torque
Configure the input shaft and the output shaft on the coaxial shaft
The disadvantage of distributing load on each planet gear and reducing wear and tooth rupture is that the structure is complex and the gear ratio calculation is complex.
Continuously variable transmission (CVT)
Manual transmission and automatic transmission can be variable step by step through gear, while continuously variable transmission can be carried out by belt wheel and transmission belt.
The continuously variable transmission adopts transmission belt and belt wheel with variable slot width to transfer power.
When the slot width of the pulley is changed, the radius of rotation of the transmission belt on the driving wheel and the follower wheel is changed, and the variable speed can be completed.
CVT has high transmission efficiency and can make full use of the power of the engine, so it can not only maintain greater power, but also save fuel and reduce consumption.
In addition, it can also continuously control the operation and speed ratio of the engine, so that the vehicle can run smoothly and smoothly.
In recent years, cars usually use step-by-step and stepless transmissions in conjunction with each other, which can compensate for the torque lost in the process of transmission to the transmission belt and chain, and at the same time.
it can compensate the torque at the beginning of the vehicle.
In the past, people focused on price and weight when designing cars; now, people pay more attention to the energy saving and driving comfort of cars.
The structure of metal belt CVT: by changing the slot width between the two pulleys, the driving wheel and the follower wheel are changed. Upload the radius of rotation of the moving belt to achieve the purpose of stepless speed change.
Double clutch automatic transmission (DCT)
The structure of the double clutch automatic transmission and the manual transmission have clutch and gear.
The difference is that there are two automatic clutches in the double clutch automatic transmission, the main shaft is divided into odd gear input shaft and even gear input shaft two systems, by automatically changing the clutch in advance to set the next gear position.
the speed change can be completed more quickly. The gear in the double clutch automatic transmission completes the meshing by mechanical way, which improves the transmission efficiency of the transmission and reduces the fuel consumption at the same time.
Double clutch automatic transmission not only has the same sense of direct acceleration as manual transmission, but also can save fuel and reduce consumption, so in recent years, more and more cars are loaded with dual clutch automatic transmission.
Semi- -automatic transmission can also automate clutch control, but the transmission has only one clutch, so there will be a moment of loss of torque in the process of transmission.
The double clutch automatic transmission has two clutches and two spindles, so the two manual transmissions are combined in-up.
In the figure, the colored lines represent the input shaft and the output shaft, the blue lines represent the clutch, position and shaft corresponding to the odd gear, and the pink line represents the clutch.
position and shaft corresponding to the even gear. For example, when hanging in gear 3, the blue line in the clutch is joined with the color line on the input side, and the pink line is separated from the color line.
and the fourth block is ready to be connected to the clutch; then the color line is separated from the blue line, joined with the pink line, and hung in the fourth block.