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Great article from Clean Technica on the ID.4's regen braking.


A few days ago, Volkswagen let us know how the braking system operates on its upcoming ID.4 crossover. Unlike many EVs, the company optimizes for coasting instead of regenerative braking. When used properly by the driver, this maximizes range. Of course, the system also allows the driver to choose more regenerative braking if they want it.

“It’s a difficult question: what should happen when drivers of electric vehicles take their foot off the right-hand pedal to initiate a thrust phase?,” the company said in its press release. “Should the electric drive motor act as an generator, converting kinetic energy into electrical energy or should it run without generating electrical energy, so that the vehicle’s momentum is used for coasting?”

On social media, this question gets a lot of debate among EV owners.

What Is Regenerative Braking?
On the surface, regenerative braking (often called “regen” by EV drivers) sounds like it would be the most efficient way to drive, because you use the electric motor or motors as a generator, and the generator’s drag slows the car down. Your vehicle weighs thousands of pounds, and when it’s moving, that’s a lot of kinetic energy. It took a lot of energy from your EV’s battery pack to get the vehicle moving, and putting some of that energy back in the battery makes a lot of sense.

ICE cars can’t do anything like that. When you press the normal friction brakes, that kinetic energy gets converted into heat, and that heat dissipates into the air. It’s gone, forever, and can’t be used again. Even EVs can waste energy like this, because they have both regenerative braking and normal brakes like a gas car.

Another Option: Coasting
That’s why some readers will think VW is wrong to default to not using regen, but to see why they’re right, you have to consider another option for stopping your car: coasting.

Ask any hypermiler, and they’ll tell you the same thing. The trick to maximizing range or MPG is to plan ahead and let the car coast to a stop as much as possible. Instead of using brakes, you let off the accelerator pedal and let the car slow down on its own. It can take a long ways to do that, so it’s not always a good option, but it really uses the least energy when all is said and done.

It all comes down to conversion losses. Every time you convert energy to another type of energy, some gets wasted in the process. When you take the chemical energy in your battery and convert it into electrical energy, some of that energy gets lost as heat. Hopefully your EV has liquid cooling to get rid of that heat. After that, the motor converts electricity into mechanical energy, and a little more energy gets lost to heat. Then, your car uses the drivetrain, wheels, and tires to convert that mechanical energy into kinetic energy (your car moving). Once again, some of that energy gets lost to heat. It all adds up.

Regenerative braking does all this in reverse. The car’s kinetic energy becomes mechanical energy, turning the motor/generator. The motor/generator turns the mechanical energy into electricity. The electricity then goes back into your battery pack. At each of those steps, some energy gets lost to heat.

In the end, only about 60% of the energy that left the battery pack actually survives the round trip.

Coasting works because your car is always fighting resistance to keep moving. Your car has to push itself through the air. There’s rolling resistance between the tires and the road. The wheel bearings are also constantly trying to slow the car down a bit. All that adds up, and will slowly bring your car to a stop if you quit adding energy from the motor. It turns out that this is the most efficient way to bring the car to a stop (when possible) because you let off on the accelerator pedal sooner. Instead of wasting energy to keep going and then using brakes, you keep the energy in your battery pack more.

By skipping the conversion losses, you maximize your range.

Volkswagen Gives You Options in the ID.4

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Volkswagen knows that you can’t always coast up to a stop, so the car does give you options. In “D” mode, releasing the accelerator lets the vehicle mostly coast. If something makes you have to stop quicker, you’ll still get regenerative braking when you press the brake pedal, and extra braking will come from the normal disc brakes when you press the pedal harder. Whenever possible, you can coast to max out your range.

Drivers also have the option of using “B” mode, and that mode gives heavier regen. If you want some limited “one pedal driving” around town, or you want to be able to go down a steep hill without wearing out your brakes, B mode gives you that option.

This Will Backfire With Many Drivers, Though
The one problem with Volkswagen’s approach is that it requires drivers to know what they’re doing to drive efficiently.

If you are an efficient driver who doesn’t have your car at the brake shop very often, Volkswagen’s approach will work well for you. You’re already coasting a lot more than other drivers, and that will work well for you in the “D” mode on the ID.4. You’ll keep doing what works, and the car is ready to accommodate that.

If you’re the kind of person who spends a lot of time with your foot on the skinny pedal and then waits until the last minute to stop, you’ll see no benefit, or might even get worse range than you’d get with heavier regen. You’re going to waste a lot of energy keeping full speed for too long, and then when you nail that brake pedal, regen will not be enough, and you’ll waste the energy again using friction/disc brakes. If that’s you, definitely put your car in “B” mode all the time to take advantage of more regen.

Ideally, though, it’s best to learn to take full advantage of your EV, whether it’s a VW or not. The trick is to do as much coasting as you can safely do. Plan ahead, and let the skinny pedal off earlier when you know you’re going to have to stop at a red light. If you can’t coast, take advantage of regen using soft braking or the car’s “B” or “L” mode.

VW knows that some drivers will need a little coaching, and the company has set up its infotainment system to give drivers little tips. Hopefully most inefficient drivers will get the hint and change their ways a bit.
 
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