Introduction to the working principle of CVT (Continuously Variable Transmission)

Introduction to the working principle of CVT (Continuously Variable Transmission)

　　CVT is also called continuously variable transmission. It is a kind of automobile transmission. The main difference from stepped transmission is that its speed ratio is not an intermittent point, but a series of continuous values, thus achieving good economy and power. And driving smoothness, and reduce emissions and costs.
The automobiles currently sold in my country are equipped with various transmissions, including manual transmission (MT), automatic transmission (AT) (including DSG) and continuously variable transmission (CVT).A brief introduction is given below.
1. MT
The manual transmission (MT: Manual Transmission) uses a gear set. Since the number of teeth in each gear set is fixed, the speed ratio of each gear is a fixed value (that is, the so-called "stage").For example, the first gear ratio is 3.455, the second gear is 2.056, and the fifth gear is 0.85. These numbers are multiplied by the final gear ratio to get the total transmission ratio of the vehicle's power transmission system. The 5-speed transmission has 5 values ​​(that is, 5 Stage), so it is a stepped transmission.
Manual transmission is a common transmission. Compared with AT and CVT, its structure is simple. It is mainly composed of input shaft, output shaft and intermediate shaft, shaft bearings, various gears, synchronizers, and shift operating mechanism.The manual transmission has a relatively low failure rate and low operating cost.
2. AT
Automatic transmission (AT: Automatic Transmission) can automatically upshift and downshift. The computer mainly controls the upshift and downshift according to the vehicle speed and load (accelerator pedal stroke), and also refers to various signals such as transmission oil temperature and shift mode. The similarity between AT and MT is that they are both stepped transmissions, but AT has a continuous speed ratio change in each gear, and can automatically increase or decrease the gear according to the speed of the car, which can eliminate the hand The shifting feeling of "stuck" when blocking the car.
(1) AT structure:
Compared with the manual wave, the hydraulic automatic wave (AT) is very different in structure and use.The manual wave is mainly composed of gears and shafts, which generate variable speed and torque through different gear combinations; while AT is composed of a hydraulic torque converter, planetary gears and a hydraulic control system, the variable speed is achieved by means of hydraulic transmission and gear combination. Moment.Among them, the hydraulic torque converter is a characteristic component of AT. It is composed of pump wheels, turbines, guide wheels and other components, which directly input engine power to transmit torque and clutch.
(2) Advantages and disadvantages of AT:
The AT does not need a clutch to shift gears, the gears are less variable and the connection is stable, so the operation is easy, which brings convenience to the driver and comfort to the rider.
But there are many shortcomings. One is that it is slow to respond to speed changes and is not sensitive to manual waves. Therefore, many car users like to drive manual wave cars. The other is that fuel consumption is not economical, and the transmission efficiency is low. The torque range is limited. In recent years, electronic control technology has been introduced. This problem has been improved; the third is that the mechanism is complex and repairs are difficult.The hydraulic oil circulating at high speed in the torque converter will generate high temperature, so use the specified high temperature hydraulic oil.In addition, if the car cannot be started due to lack of battery power, it cannot be started by cart or trailer.If hauling a faulty vehicle, pay attention to keeping the driving wheel off the ground to protect the automatic gear from damage.
(3) AMT