How is the speed controlled in an automatic transmission?

[LeRylee]

Automatic transmission speed control method: You can lightly lift the throttle pedal at the appropriate time, and the transmission will automatically upshift, keeping the engine at a lower RPM at the same speed. Then, by gently pressing the throttle pedal to continue accelerating, the transmission will not immediately downshift. This is a "preemptive upshift, delayed downshift" function designed by engineers to prevent frequent gear changes. Driving an automatic transmission car does not require manual shifting, as the computer automatically shifts gears based on the depth of the throttle pedal press. In other words, controlling the speed in an automatic transmission car simply requires managing the throttle pedal well. Over time, you will naturally develop a feel for the car.

[AlessandraLynn]

I find driving an automatic transmission car particularly hassle-free, as speed control mainly depends on how deep I press the accelerator. When I lightly press the accelerator, the transmission automatically shifts up from 1st gear gradually, resulting in a smooth increase in speed. If I press the accelerator deeply, it automatically downshifts to accelerate, delivering an immediate push-back sensation. Essentially, there's an intelligent system inside the transmission that monitors vehicle speed, throttle opening, and engine RPM, deciding on its own when to shift gears. For example, when going uphill, the computer detects that the engine is under strain and downshifts to maintain power. Switching to sport mode makes a completely different experience—gears won’t shift up until the RPM hits the redline, making overtaking exceptionally crisp. On long descents, I can also switch to manual mode and engage a lower gear to use engine braking, reducing the need to constantly press the brake pedal.

[SanCassidy]

Driving an automatic transmission is like having a thoughtful assistant managing the speed. The torque converter between the engine and transmission is crucial—it works like two fans blowing at each other, where one turns and the other follows, transmitting power through transmission fluid. The ECU computer calculates data hundreds of times per minute. When you press the accelerator 30%, the computer decides whether to gradually accelerate in 3rd gear at 1,500 RPM or drop to 2nd gear at 3,000 RPM for a burst, based on slope and vehicle weight. In traffic, lightly tapping the accelerator only needs to shift up to 2nd gear, while on the highway, pressing halfway will engage the highest 6th or 8th gear for fuel efficiency.

[Paislee]

Automatic transmission vehicles employ a three-layer control system. When the accelerator pedal is pressed, the sensor first takes readings and transmits the throttle opening to the transmission computer. The computer then evaluates data from wheel speed sensors and gradient sensors to determine: Is the current 3.8th gear paired with 2500 RPM appropriate? If not, it immediately instructs the solenoid valves in the valve body to shift gears. Some high-end models even feature paddle shifters behind the steering wheel, allowing drivers to manually intervene in gear changes with a simple finger flick. Hybrid models are more complex, requiring coordinated power output between the electric motor and combustion engine. During hard braking, the computer automatically downshifts in preparation for reacceleration—all these actions are completed within 0.3 seconds.