What is the working principle of engine braking?
2 Answers
The working principle of engine braking is as follows: 1. The higher the gear, the smaller the gear ratio: Due to the presence of the transmission, different gears have different "gear ratios," and the higher the gear, the smaller the gear ratio. For example: During normal driving, when in first, second, or third gear, the engine turns 100 times while the wheels turn 5, 10, and 20 times respectively. Since the wheel circumference is constant, the higher the gear, the longer the distance covered per unit of time, meaning the faster the speed. 2. The lower the gear, the more noticeable the drag effect: Engine braking utilizes the drag effect of the engine to slow down the vehicle. The lower the gear, the more noticeable the drag effect and the stronger the braking performance. When driving on long downhill roads, shifting into a lower gear and using the engine's drag effect can reduce the burden on the brakes and the frequency of braking, preventing brake overheating and subsequent thermal fade. When driving on snowy or muddy roads, using engine drag braking can help prevent skidding.
I often deliver goods on mountain roads, and when encountering steep slopes, I use engine braking to control the speed, which is both safe and saves brake pads. The principle is quite straightforward: when you release the accelerator pedal, the engine's throttle closes, creating a vacuum inside. Compressing the air requires energy, which generates a drag force that slows down the wheels. Especially with a manual transmission, I'm used to downshifting to third or second gear. When the RPM rises, the drag becomes more noticeable, acting like a gentle brake without worrying about overheating the brake pads. This effect is even stronger in diesel vehicles due to their higher compression ratio, providing more stable deceleration. Over time, this not only saves fuel but also reduces brake wear, making it an essential technique for mountain driving.
