What is the principle of automatic transmission?
3 Answers
Automatic transmissions are divided into the following four types, with their working principles as follows: 1. Hydraulic automatic transmission: Achieves automatic shifting through hydraulic transmission and planetary gear combination. 2. Mechanical continuously variable transmission (CVT): Transmits engine power via a steel belt and the grooves of two pulleys, from the primary pulley to the secondary pulley, and then through the final drive to the driving wheels, achieving power transmission. 3. Electronically controlled mechanical automatic transmission: Expresses driver intentions through the accelerator pedal and selector (including gear range, shift pattern, cruise control, etc.) to the microcontroller. Numerous sensors constantly monitor the vehicle's status, and the computer controls the throttle opening, clutch engagement, and gear shifting according to the optimal program stored within (optimal shift pattern, optimal clutch engagement pattern, and adaptive engine throttle adjustment pattern) to achieve the best match, thereby obtaining excellent driving performance, smooth starting, and rapid shifting capability. 4. Dual-clutch automatic transmission: Arranges the gears on two input shafts connected to two clutches according to odd and even numbers, completing the shifting process through alternating clutch switching, achieving uninterrupted power shifting.
I've been driving for over twenty years and find the principles of automatic transmissions quite fascinating. Simply put, it uses a torque converter to transfer power—the engine drives the pump wheel to rotate hydraulic fluid, which then flows to push the turbine and output to the gearbox. Inside, there are planetary gear sets that automatically combine to produce different gear ratios for shifting. For example, at low speeds, the planetary carrier is fixed, while the sun gear and ring gear work together to output high torque. The hydraulic system adjusts oil pressure based on vehicle speed and throttle position to control gear changes. It drives smoothly and effortlessly, especially in traffic jams where you don't need to press the clutch. However, it's important to change the transmission fluid regularly; otherwise, wear on the torque converter or gears can cause rough shifting. Modern cars also incorporate computer control, making them even smarter and more efficient.
From a technical perspective, automatic transmission operation involves two steps: The torque converter first uses fluid flow to cushion and amplify engine torque, similar to one fan blowing another. Then, the planetary gear set alters gear ratios by combining different gear trains (sun gear, ring gear, planetary carrier), while hydraulic clutches or brake bands automatically shift gears under hydraulic pressure. The computer system monitors speed and throttle inputs to precisely control solenoid valve oil circuits. During driving, acceleration is smooth, but frequent sudden braking should be avoided to protect internal gears and oil circuits.
