What are regenerative brakes? Hey Engineering Lovers, you may have heard the term regenerative braking somewhere. I particularly started hearing this term in 2009, in Formula 1 races.
Little by little this technology became popular and nowadays it is equipped in all electric cars and some hybrid cars. But why is this a good thing? If you drive in chaotic city traffic, you know what it would be like walking and braking, and walking and braking.
This is the traffic routine in major cities. In addition to being a huge waste of time, what's less obvious is that it's also a waste of energy. Making a car move requires a large input of energy, and every time you hit the brakes, all the energy you have built up is wasted on the brake pads as heat.
Wouldn't it be nice if you could store that energy somehow and reuse it the next time you start accelerating? Well, that's the basic concept of regenerative brakes, which are widely used in electric trains and the latest electric cars. But why does braking waste energy?
If you ride a bike around town, it's pretty obvious that braking is a huge waste of energy. You have to pedal to move, and it takes a lot of energy from your legs to keep the bike moving, and when you brake, you simply waste all the momentum you gained. So, every time you want to move the bike again, you need to pedal more intensely to get out of inertia.
Now, put your hands anywhere near a bike's brake pads and you'll know exactly where the energy goes. This is because every time you brake and the brake pads press against the wheel, the friction between the materials converts the energy you had when you were moving into heat, which disappears uselessly into the air. Just a warning, be very careful if you try this because the brakes can get very hot to the point where you could burn yourself.
And cars are no different. Car drivers are virtually oblivious to the energy braking wastes because driving requires no real physical effort. Not only that, but the car's brakes are hidden out of sight, inside the wheels, where you can't see the heat energy they're wasting.
But the heat they generate is enormous, and according to one manufacturer, Brembo, the brakes on Formula 1 racing cars, for example, can heat up to 1,000 degrees Celsius. But the whole question is how we could make better brakes. Let's try to imagine designing a better braking system for a bicycle with science in mind.
When we're cycling, our bodies and bikes have kinetic energy, the energy that all moving objects have. When we brake, all this kinetic energy has to be transformed into another type of energy or be wasted as heat. When we start pedaling again, we need more kinetic energy.
An ideal braking system would involve temporarily storing our kinetic energy somewhere, without throwing it away forever. In other words, a way to store energy so that we can recover it again in the future. But how could we do this?
If you are a cyclist, an easy but impractical way would be to carry a giant ramp on your back. Each time you wanted to stop, you could drop the ramp down into the road in front of you so that you would ride your bike up and back up the ramp and stop gradually, some distance away on the ground. As you walked up the ramp, it would be like walking up a hill, where your kinetic energy would quickly be converted into potential energy and you would slow down until you stopped.
When you were ready to start again, you would simply roll to the other side of the ramp and regain most of your original energy, the stored potential energy would be converted back into kinetic energy, just like when you roll down a hill in a bicycle. Of course, you would also need to attach the ramp to your body with a bungee cord so that it automatically snaps back onto your back as you pedal. Okay, this is a little crazy and I went too far, but then, what else could we do?
If your bike has a dynamo, a small electricity generator, to power the lights, you'll know that it's harder to pedal when the dynamo is on than when it's off. This is because part of your pedaling energy is being "stolen" by the dynamo and transformed into electrical energy in the lights. If you are going at high speed and suddenly stop pedaling and turn on the dynamo, it will bring you to a stop more quickly than you normally would for the same reason, as it is robbing you of your kinetic energy.
Now imagine a bicycle with a dynamo 100 times larger and more powerful. In theory, it could stop your bike relatively quickly by converting its kinetic energy into electricity, which you could store in a battery and use again later. And that's the basic idea behind regenerative brakes!
Electric trains, cars and other electric vehicles are powered by electric motors connected to batteries. When you're driving, energy flows from the batteries to the motors, turning the wheels and providing the kinetic energy needed to move. When you hit the brakes, the entire process reverses.
The electronic circuits cut the power to the motors, but their kinetic energy and momentum make the wheels continue to turn the motors. Then the engines work like generators and start producing electricity instead of consuming it. In other words, when you step on the accelerator, you use the battery's energy with the electric motor, and when you brake, the roles are reversed and the motor acts as a generator and starts charging the batteries.
And that's why electric cars have better consumption in the city than on a long-distance trip, because in the city you'll have to accelerate and brake several times, and the braking energy ends up helping to charge the batteries. In practice, regenerative brakes take a while to slow things down, so most vehicles that use them also have regular, friction brakes working alongside them, and that's also a good idea in case the regenerative brakes fail. This is one of the reasons why regenerative brakes don't save 100% of your braking energy.
But does this type of brake work the same for everything? How much energy do regenerative brakes save? Well, this will all depend on the vehicle.
Large, heavy vehicles that move quickly, like electric trains, accumulate a lot of kinetic energy, so they have the best economies. Although they weigh less and go slower, delivery trucks that stop and start frequently can also make big savings. Cars vary in what they can save from about 8 to 15 percent depending on the car and whether it is driving in city traffic or on the open highway.
Electric bicycles are light and go very slowly, so the regenerative brakes can recover little energy from braking. In electric and hybrid cars, regenerative braking charges the main battery, effectively extending the vehicle's range between charges. Electric trains, which are powered by overhead power lines or along the tracks, work a little differently.
Instead of sending braking energy to the batteries, they send it back to the power line. A typical modern electric train can save about 15 to 20 percent of its energy by using regenerative brakes in this way. And even in some vehicles, they use banks of supercapacitors to store energy instead of batteries, which can be used in a sprint or when the vehicle needs to come out of inertia.
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