What is the working principle of an electric assist bicycle (E-bike)?

Hey, that's a great question, and one many people are curious about. I'll try to explain it in plain language.

You can think of an electric assist bicycle (E-bike) as a regular bicycle that's been "on steroids." Its core purpose isn't to make you lazy, but to make your rides easier, allow you to go further, and be more enjoyable. You still have to pedal yourself, but it feels like someone is constantly giving you a push from behind.

This "mysterious power" primarily comes from a few key components:

1. Motor: This is the "engine," the source of power. It's usually installed in one of two places: either in the hub of the wheel (called a "hub motor") or at the bottom bracket where you pedal (called a "mid-drive motor"). As soon as you start pedaling, it activates, helping to turn the wheels or augmenting your pedaling power. Mid-drive motors offer a more natural feel, making it seem like your own leg strength has increased.

2. Battery: This is the "fuel tank," supplying power to the motor. It's typically a large unit fixed to the bike frame, often removable so you can take it home to charge, just like charging a phone. The larger the battery capacity, the further you can "assist" your ride.

3. Sensor: This is the most crucial "brain," determining when and how much power the motor provides to assist you. There are two main types:

   • Speed/Cadence Sensor: This is more basic. It only detects "if you are pedaling." As long as your feet are moving, it provides a fixed amount of assistance from the motor. Whether you pedal fast or slow, the power it gives is roughly the same (though you can manually adjust the assist level, like modes 1/2/3). It feels like an on/off switch: pedal, and you get power; stop, and it stops.
   • Torque Sensor: This is more advanced and offers the best experience. It can sense "how much effort you're putting into pedaling." For example, if you're pedaling hard uphill, it immediately tells the motor to provide significant assistance; if you're pedaling lightly on flat ground, it only gives a little boost. This feels very natural, as if your own strength is amplified many times over, creating a fantastic sense of unity between rider and bike.

So, the overall riding experience is like this:

You get on the bike, turn on the power (usually via a small display on the handlebars), and select your desired assist level (e.g., "Eco Mode" or "Sport Mode"). Then you start pedaling just like you would on a regular bicycle.

The sensor immediately detects your movement and tells the motor, "Hey buddy, time to get to work!"

The motor instantly kicks in, giving you a smooth push. In an instant, you'll feel incredibly light on your feet. Uphills and headwinds that used to be strenuous now feel as easy as riding on flat ground.

To summarize:

It's not a motorcycle; you don't twist a throttle (though a very few models might have a similar function). You're still exercising, and your heart rate will still increase, but you won't get as breathless and exhausted as you would on a regular bike. It filters out the most strenuous parts of cycling, leaving only the enjoyment. That's why many people say that after buying an e-bike, their frequency and distance of riding have significantly increased.